Hardware-Electronic product solution company-Electronic and electrical product development-Bluetooth design-S

Hardware

07-01

2023

PCB board anti-ESD design

Anti-ESD design method of PCB board in electronic equipmentIn the design process of electronic products, designers usually start to consider the problem of anti-static discharge (ESD) when the product enters the production process. In order to make electronic equipment pass the anti-static discharge test without destroying the original design, the final solution usually uses expensive components, manual assembly during the manufacturing process, and even a redesign of the PCB board. progress is bound to be affected. Therefore, in the process of designing the PCB board of electronic products, it is necessary to consider the problem of optimizing ESD protection.1. The impact of ESD on electronic equipmentAnti-electrostatic discharge (ESD) design rules must be followed in the design of electronic products, because most electronic devices are in an environment full of ESD for 99% of their lifespan, especially in the current portable products. Low-power logic chips, most of them are designed and manufactured based on CMOS technology, due to the metal oxide semiconductor (MOS) dielectric breakdown and bipolar reverse junction current limitation, these IC chips are very sensitive to ESD. Additionally, most I/O ports (especially USB ports) are hot-swappable systems that are highly susceptible to ESD from the user or from air discharge. ESD can come from the human body, furniture, or even inside the device itself. Although it is rare for electronic equipment to be completely damaged by ESD, ESD interference is very common. ESD interference may cause device lockup, reset, data loss or reduced reliability, and may even cause data bit ghosting, product damage, and even damage to electronic equipment. "Hard fault" or component failure. The result may be: in the cold and dry winter, electronic equipment often fails, but it is normal when repaired, which will inevitably affect the confidence of users in electronic equipment and its manufacturers. It can be seen that it is very necessary to consider ESD protection during the design of electronic products, especially the design of its PCB board.2. The mechanism of ESD generationWhat is ESD? How does ESD enter electronic equipment? ESD has the potential to occur when a charged conductor is in close proximity to another conductor. First, a strong electric field will be established between the two conductors, resulting in field-induced breakdown. An arc occurs when the voltage between two conductors exceeds the breakdown voltage of the air and insulating medium between them. In the time from 0.7ns to 10ns, the arc current will reach dozens of amperes, and sometimes even exceed 100A. The arc will continue until the two conductors touch short or the current is too low to sustain the arc. The generation of ESD depends on the initial voltage, resistance, inductance and parasitic capacitance of the object, for example: the human body, charged devices and machines may generate arcs, hands or metal objects may generate spike arcs, furniture may generate the same polarity or polarity changes Multiple arcs. ESD can enter electronic equipment through the following five coupling paths:(1) The initial electric field can capacitively couple to the network with a large surface area, and generate a high voltage of up to 4000V/m at a distance of 100mm from the ESD arc.(2) The charge/current injected by the arc can cause the following damage and failure: ① Penetrate the thin insulating layer inside the component and damage the gate of MOSFET and CMOS components (common). ②Flip-flop lockup in CMOS devices (common). ③Short-circuit reverse-biased PN junction (common). ④ Short circuit forward biased PN junction (rare). ⑤ Melt the welding wire or aluminum wire inside the active device (rare).(3) The current will cause voltage pulses (V=L×dI/dt) to be generated on the conductors. These conductors may be power supply, ground or signal lines. These voltage pulses will enter every component connected to these networks (common).(4) The arc will generate a strong magnetic field with a frequency range of 1 MHz to 500 MHz, and inductively couple to each adjacent wiring loop, generating a current up to 1 5A/m at a distance of 1 00 mm from the ESD arc.(5) The electromagnetic field radiated by the arc will be coupled to long signal lines, which act as receiving antennas (rare). It can be seen that the ESD frequency range is wide, and it is possible to find the weak point of the device through various coupling paths.In order to prevent ESD interference and damage, the anti-ESD ability of the equipment should be comprehensively considered from the following three aspects:Selection of components: such as considering the ESD capacity of the chip, using a transient voltage suppressor (TVS) diode array, etc.; PCB layout design: such as increasing the grounding area as much as possible, shortening the PCB trace, etc.;Mechanical design: For example, shielding measures such as plastic chassis and air space are used to effectively solve ESD problems.Among them, PCB layout design is one of the most critical elements to optimize ESD protection. Reasonable PCB design can reduce unnecessary costs caused by fault inspection and rework.3. Anti-ESD design method of PCB boardBy analyzing the mechanism of ESD and its hazards, designers can consider optimizing the PCB design scheme for ESD protection from the following aspects:3.1 Reduce circuit loop areaCurrent is induced into closed circuit loops that also have varying magnetic flux. The area of the loop is proportional to the magnitude of the current. The larger the area of the loop, the greater the magnetic flux contained, and thus the greater the current induced in the circuit. Therefore, it is necessary to reduce the loop area as much as possible during design.Figure 1 shows one of the most common circuit loops, formed by power and ground. Where possible, a multilayer PCB design with power and ground planes can be used. The multi-layer circuit board not only minimizes the loop area between the power supply and the ground, but also the ground plane and the power plane, as well as the closely arranged signal line-ground spacing can reduce the common impedance (common impedance) and inductive coupling, and also reduce the The high-frequency EM I electromagnetic field generated by the ESD pulse is reduced.If the use of multi-layer circuit boards is limited by conditions, then the grid structure shown in Figure 2 must be used for power lines and ground lines. The grid size of this grid structure is less than or equal to 60mm, and if possible, the grid size is preferably less than 1 3 mm (0. 5in.). Between vertical and horizontal lines or filled areas, connect as many as possible. Also, keeping the power and ground traces as close as possible can also reduce the loop area.Another way to reduce loop area and induced current is to reduce parallel paths between interconnecting devices.3.2 Shorten the length of the circuit connectionA long signal line can be used as an antenna for receiving ESD pulse energy. In the design, try to use a signal line less than 30cm to reduce the efficiency of the signal line as an antenna for receiving ESD electromagnetic fields. And try to put the interconnected devices in adjacent positions, so that the length of the interconnected printed lines is as short as possible.When it is necessary to use a signal connection line longer than 30cm, a protection line can be used, as shown in Figure 5. The ground layer should be placed near the signal line, and the distance between the signal line and the ground line layer (or protection line) should be less than 1 3 mm (0. 5in.).Another way is to cross the signal line or power line longer than 30cm and its grounding line. The crossed lines must be arranged at regular intervals from top to bottom or from left to right.3.3 Protect all external connections with TVS diodesAdding a TVS device on the power line can help solve the problem of ESD from the power port connected to the power supply. TVS connected to Vcc and ground can prevent ESD interference from the power supply, but the parasitic inductance in the protection circuit should be considered.During an ESD event, the parasitic inductance in the TVS diode path can generate severe voltage overshoot. Although a TVS diode is used, the total voltage that the protection circuit can withstand is the sum of the clamp voltage of the TVS diode and the voltage generated by the parasitic inductance: V T=V C+VL, due to the induced voltage VL=L×dI/dt at both ends of the inductive load , the excessively high overshoot voltage may still exceed the damage voltage threshold of the protected IC. An ESD transient induced current can reach its peak value in less than 1 ns (according to the IEC 61 000-4-2 standard), for example: the lead inductance is 20nH per inch, and the line length is a quarter of an inch. The impulse voltage will be a pulse of 50V/1 0A. Therefore, the shunt path should be designed as short as possible in order to reduce the effect of parasitic inductance. Ground loops must be considered when designing all inductive paths, namely: the path between the TVS and the signal line to be protected, and the path from the connector to the TVS device. In order to reduce the parasitic inductance of the ground plane, the distance between the ground of the TVS diode and the ground point of the protected circuit should be as short as possible.3.4 Reduce ground charge injectionSensitive circuits may be damaged during direct discharge of ESD to the ground plane. Therefore, one or more high-frequency bypass capacitors must be used along with the TVS diodes to protect the power supply from ESD disturbances, as shown in Figure 7. These capacitors are connected between power and ground for vulnerable components. The bypass capacitor can reduce the injection of ground charge, so that the voltage difference between the power supply and the ground port is clamped. The TVS shunts the sense current and maintains the potential difference of the TVS clamping voltage. In addition, TVS and capacitors should be placed as close as possible to the protected IC. In order to reduce the effect of parasitic inductance, ensure that the path from TVS to ground and the length of capacitor pins are the shortest. The connector must be mounted to the copper-platinum plane on the PCB. Ideally, the copper-platinum layer must be isolated from the ground plane of the PCB and connected to the pad by a short wire.
07-29

2021

PCB substrate material requirements

In recent years, the focus of the PCB market has shifted from computers to communications, including base stations, servers, and mobile terminals. Mobile communications devices represented by smartphones have driven PCBs to develop higher density, thinner, and higher functions. Printed circuit technology is inseparable from substrate materials, which also involves the technical requirements of PCB substrates. The content related to substrate materials is now compiled into a special article for reference by the industry.1. The demand for high density and thin line of PCB board1.1 Demand for copper foil in printed circuit boardsAll PCBs are developing towards high-density and thin lines, especially HDI boards. Ten years ago, IPC defined the line width/space (L/S) for HDI boards as 0.1mm/0.1mm and below. Now the industry basically achieves that the conventional L/S is 60μm, and the advanced L/S is 60μm. 40 μm. Japan's 2013 version of the installation technology roadmap data shows that the conventional L/S of HDI boards in 2014 is 50 μm, the advanced L/S is 35 μm, and the trial L/S is 20 μm.PCB circuit pattern formation, the traditional chemical etching process (subtractive method) after photoimaging on the copper foil substrate, the limit of the fine circuit made by the subtractive method is at least about 30 μm, and a thin copper foil (9~12 μm) substrate is required . Due to the high price of thin copper foil CCL and the many lamination defects of thin copper foil, many factories produce 18μm copper foil and then use etching to thin the copper layer during production. This method has many processes, difficult thickness control, and high cost. It is better to use thin copper foil. In addition, when the L/S of the PCB line is less than 20 μm, the general thin copper foil is also not competent, and an ultra-thin copper foil (3~5 μm) substrate and an ultra-thin copper foil attached to the carrier are required.The current fine lines require not only thinner copper foil, but also low surface roughness of copper foil. Usually, in order to improve the bonding force between the copper foil and the base material and ensure the peel strength of the conductor, the copper foil layer is roughened, and the roughness of the conventional copper foil is greater than 5 μm. The rough peaks of the copper foil embedded in the substrate improve the peeling resistance, but in order to control the precision of the wires during the etching of the circuit, it is easy to have the convex peaks embedded in the substrate, resulting in a short circuit between the lines or a decrease in insulation. Lines are particularly serious. Copper foils with low roughness (less than 3 μm) and even lower roughness (1.5 μm) are therefore required. However, the roughness of the copper foil is reduced and the peel strength of the conductor is still maintained. It is necessary to do special treatment on the surface of the copper foil and the surface of the substrate resin. "Molecular bonding technology" is to chemically treat the surface of the resin substrate to form a functional group that can be closely combined with the copper layer.1.2 Requirements for laminated insulating dielectric sheets for printed circuit boardsThe HDI board technology is characterized by the Building Up Process, and the commonly used resin-coated copper foil (RCC), or the lamination of semi-cured epoxy glass cloth and copper foil, is difficult to achieve fine lines. Now it tends to adopt the semi-additive method (SAP) or the modified semi-processing method (MSAP), that is, the insulating dielectric film is laminated, and then the copper conductor layer is formed by electroless copper plating. Because the copper layer is extremely thin, it is easy to form fine lines.One of the technical focuses of the semi-additive method is the laminated dielectric material. In order to meet the requirements of high-density thin lines, the laminated material has requirements for dielectric properties, insulation, heat resistance, and bonding force, as well as the adaptability to the HDI board process. At present, the HDI laminated dielectric materials in the world are mainly ABF/GX series products of Ajinomoto Company in Japan. Epoxy resin is used with different curing agents to add inorganic powder to improve material rigidity and reduce CTE. Glass fiber cloth is also used to enhance rigidity. . There are also similar thin-film laminate materials from Japan's Sekisui Chemical Company, and Taiwan Industrial Technology Research Institute has also developed such materials. ABF materials are also constantly improving and developing. The new generation of laminated materials especially requires low surface roughness, low thermal expansion rate, low dielectric loss, and thin rigid reinforcement.In global semiconductor packaging, IC packaging substrates are replaced by organic substrates and ceramic substrates. The pitch of flip-chip (FC) packaging substrates is getting smaller and smaller. Now the typical line width/line spacing is 15 μm, and it will be finer in the future. The performance of multi-layer substrates mainly requires low dielectric properties, low thermal expansion coefficient and high heat resistance, and the pursuit of low-cost substrates on the basis of meeting performance goals. At present, the mass production of fine lines basically adopts the MSPA process of insulating dielectric lamination combined with thinned copper foil. Use the SAP method to manufacture circuit patterns with L/S less than 10μm.When the PCB is denser and thinner, the HDI board technology develops from core board build-up to coreless board any layer interconnection build-up (Any layer). Board area and thickness can be reduced by about 25%. These must use thinner dielectric layers that maintain good electrical properties.2. High-frequency and high-speed requirements for printed circuit boardsElectronic communication technology is from wired to wireless, from low frequency and low speed to high frequency and high speed. The current mobile phone performance has entered 5G, that is, it has faster transmission speed and larger transmission capacity. The advent of the global cloud computing era has doubled data traffic, and high-frequency and high-speed communication equipment is an inevitable trend. In order to meet the needs of high-frequency and high-speed transmission, in addition to reducing signal interference and loss in circuit design, maintaining signal integrity, and maintaining PCB manufacturing in compliance with design requirements, it is important to have a high-performance substrate.Design engineers address PCBs to increase speed and signal integrity, mainly for electrical signal loss properties. The key factors for substrate selection are dielectric constant (Dk) and dielectric loss (Df). When Dk is lower than 4 and Df is below 0.010, it is a medium Dk/Df laminate. When Dk is below 3.7 and Df is below 0.005, it is low Dk/ Df grade laminates, now there are a variety of base materials to enter the market to choose from.At present, the most commonly used high-frequency circuit board substrates are mainly three types of materials: fluorine-based resins, polyphenylene ether (PPO or PPE) resins, and modified epoxy resins. Fluorine-based dielectric substrates, such as polytetrafluoroethylene (PTFE), have the lowest dielectric properties and are usually used above 5GHz. In addition, there are modified epoxy FR-4 or PPO substrates, which can be used for products between 1GHz and 10GHz. Of these three types of high-frequency substrate materials, epoxy resin is the cheapest, while fluorine-based resin is the most expensive; from the perspective of dielectric constant, dielectric loss, water absorption and frequency characteristics, fluorine-based resin is the best, and epoxy resin is poor. . When the frequency of product application is higher than 10GHz, only fluororesin printed boards are suitable. However, the disadvantages of PTFE are poor rigidity and high thermal expansion coefficient in addition to high cost.For polytetrafluoroethylene (PTFE), in order to improve performance, it is reinforced with a large amount of inorganic (such as silicon dioxide SiO2) filler material or glass cloth to increase the rigidity of the substrate and reduce its thermal expansion. In addition, due to the molecular inertness of PTFE resin itself, it is not easy to bond with copper foil, so special surface treatment is required for the bonded surface with copper foil. The treatment method is chemical etching or plasma etching on the surface of PTFE, increasing the surface roughness or adding an adhesive film layer between the copper foil and the PTFE resin to improve the bonding force, but it may have a negative effect on the dielectric performance. However, the entire fluorine-based high-frequency circuit substrate needs further development.A unique insulating resin synthesized from modified epoxy resin or polyphenylene ether (PPE) and trimellitic anhydride (TMA), diphenylmethane diisocyanate (MDI) and bismaleimide (BMI), similar to glass cloth FR-4 copper clad laminates are widely used at this stage, because they have excellent heat resistance, dielectric properties, mechanical strength, compat and processability of conventional PCBs, and are more popular than PTFE substrates.The glass cloth drags Dk back in the substrate, the Dk of E glass cloth is 6.6 (1MHz), the epoxy resin Dk 3.6 (1MHz), and the Dk of FR-4 is 4.2~4.8. The Dk 4.4 of the new NE glass cloth is about Dk 4.0 of the FR-4. Using new NE glass cloth is an effective way to reduce Dk.For example, the Megtron 6 high-frequency substrate launched by Panasonic uses polyphenylene ether (PPO) as the main resin, Dk=3.4, Df=0.0015 (1GHz). Japan's Lichang Industry also uses polyphenylene ether as the substrate of the main resin. The CS-3376CN new substrate introduced has a Dk=3.1, which is similar to the PTFE substrate. Mitsubishi Gas's new BT resin substrate adjusts the ratio of BT and epoxy resin, and the dielectric properties of its original BT substrate are nearly 60% lower. Isola's Tachyon-100G base material has the same electrical properties as PTFE, and has the same PCB processing conditions as FR-4, Dk 3.0 and Df 0.002 at 40GHz, reaching the transmission of 100 Gigabit Ethernet (100GbE) need.In addition to the special requirements for the performance of insulating materials such as the above-mentioned resins for high-frequency copper clad laminates, the surface roughness (profile) of the conductor copper is also an important factor affecting signal transmission loss, which is affected by the skin effect (Skin Effect). The skin effect is the electromagnetic induction generated in the wire when the high-frequency signal is transmitted, and the inductance is larger at the center of the wire cross section, so that the current or signal tends to concentrate on the surface of the wire. The roughness of the conductor surface affects the loss of the transmission signal, and the loss of the smooth surface is small.At the same frequency, the greater the copper surface roughness, the greater the signal loss, so we try to control the roughness of the surface copper thickness as much as possible in actual production. The smaller the roughness without affecting the bonding force, the better. Especially for signals in the range above 10 GHz. At 10 GHz, the copper foil roughness needs to be less than 1 μm, and it is better to use ultra-flat copper foil (surface roughness 0.04 μm). Copper foil surface roughness also needs to be combined with suitable oxidation treatment and bonding resin system. In the near future, there will be a resin-coated copper foil with almost no profile, which can have higher peel strength without affecting dielectric loss.3. High heat resistance and heat dissipation requirements of printed circuit boardsWith the miniaturization, high function and high heat generation of electronic equipment, the thermal management requirements of electronic equipment are increasing. One of the solutions chosen is to develop thermally conductive printed circuit boards. The primary condition for heat-resistant and heat-dissipating PCBs is the heat resistance and heat dissipation of the substrate. At present, the heat resistance and heat dissipation of the substrate have been improved to a certain extent through resin improvement and filler addition, but the improvement of thermal conductivity is very limited. Typically, metal substrates (IMS) or metal core printed circuit boards are used to dissipate heat from heating components, reducing volume and cost compared to traditional radiators and fan cooling.Aluminum is a very attractive material because of its abundant resources, low cost, good thermal conductivity and strength, and environmental friendliness. At present, most of the metal substrates or metal cores are metal aluminum. The advantages of aluminum-based circuit boards include simplicity and economy, reliable electronic connections, high thermal conductivity and strength, no soldering and lead-free environmental protection, etc. It can be designed and applied from consumer products to automobiles, military products and aerospace. There is no doubt about the thermal conductivity and heat resistance of the metal substrate, the key lies in the performance of the insulating adhesive between the metal plate and the circuit layer.At present, the driving force of thermal management is focused on LEDs. Nearly 80% of the input power of LEDs is converted into heat. Therefore, the thermal management of LEDs is highly valued, and the focus is on the heat dissipation of LED substrates. The composition of high heat-resistant and environmentally friendly heat-dissipating insulating layer materials lays the foundation for entering the high-brightness LED lighting market.4. Flexibility of PCB board and printed electronics and other requirements4.1 Requirements for flexible boardsThe miniaturization and thinning of electronic equipment will inevitably use a large number of flexible printed circuit boards (FPCB) and rigid-flexible printed circuit boards (R-FPCB). The global FPCB market is currently estimated at about $13 billion and is expected to grow at a higher annual rate than rigid PCBs.With the expansion of the application area, there will be many new performance requirements in addition to the increase in the number. There are different types of polyimide film, such as colorless and transparent, white, black and yellow, with high heat resistance and low CTE performance, suitable for different occasions. There is also a market for polyester film substrates with good cost-effectiveness. New performance challenges include high elasticity, dimensional stability, film surface quality, as well as photoelectric coupling and environmental resistance of the film, etc., to meet the changing requirements of end users.FPCB, like rigid HDI boards, must meet the requirements of high-speed and high-frequency signal transmission. The dielectric constant and dielectric loss of flexible substrates must also be paid attention to. Teflon and advanced polyimide substrates can be used to form flexible substrates. circuit. Adding inorganic powder and carbon fiber filler to polyimide resin produces a flexible thermally conductive substrate with a three-layer structure. The selected inorganic fillers include aluminum nitride (AlN), aluminum oxide (Al2 O 3 ) and hexagonal boron nitride (HBN). The substrate has a thermal conductivity of 1.51W/mK and can withstand a 2.5kV withstand voltage and 180-degree bending test.FPCB application markets such as smartphones, wearable devices, medical equipment, robots, etc. put forward new requirements for FPCB performance structure and develop new FPCB products. For example, the ultra-thin flexible multilayer board, the four-layer FPCB is thinned from the conventional 0.4mm to about 0.2mm; the high-speed transmission flexible board adopts low Dk and low Df polyimide substrates to meet the transmission speed requirement of 5Gbps; The power flexible board adopts a thick conductor of more than 100 μm to meet the needs of high-power and high-current circuits; the high-heat dissipation metal-based flexible board is an R-FPCB that partially uses a metal board substrate; the tactile-sensitive flexible board is composed of a pressure sensor The film and electrodes are sandwiched between two polyimide films to form a flexible tactile sensor; stretchable flexible board or rigid-flexible board, the flexible base material is elastomer, and the shape of the metal wire pattern is improved to become stretchable . These special FPCBs of course require unconventional substrates.4.2 Printed Electronics RequirementsPrinted electronics has been booming in recent years, and it is predicted that by the mid-2020s, printed electronics will have a market exceeding US$300 billion. The application of printed electronic technology to the printed circuit industry is a part of printed circuit technology, which has become a consensus in the industry. Printed electronics technology is closest to FPCB, and now PCB manufacturers have invested in printed electronics. They start with flexible boards and replace printed circuit boards (PCBs) with printed electronic circuits (PEC). At present, there are many substrates and ink materials, and once there are breakthroughs in performance and cost, they will be widely used. PCB manufacturers should not miss the opportunity.The current focus of printed electronics is the low-cost manufacture of radio frequency identification (RFID) tags, which can be printed on rolls. Potential are the areas of printed displays, lighting and organic photovoltaics. The wearable technology market is currently emerging as a lucrative market. Wearable technology Various products such as smart clothing and smart sports glasses, activity monitors, sleep sensors, smart watches, augmented reality headphones, navigation compasses, etc. Flexible electronic circuits are indispensable for wearable technology devices, which will drive the development of flexible printed electronic circuits.An important aspect of printed electronics is materials, including substrates and functional inks. In addition to the application of the existing FPCB, flexible substrates are also developed for higher-performance substrates. Currently, there are high-dielectric substrate materials composed of ceramics and polymer resins, as well as high-temperature substrates, low-temperature substrates, and colorless transparent substrates. , yellow base material, etc.4.3 Embedded component board requirementsEmbedded component printed circuit board (EDPCB) is a product that realizes high-density electronic interconnection, and embedded component technology has great potential in PCB. Embedded component technologies include molding component embedding method and printed component embedding method, and printed components are divided into thick film components and thin film components. The production of thin-film components requires special substrates. For example, the lower layer of copper-clad laminates contains nickel-phosphorus alloy foils for the production of thin-film resistors; double-sided copper-clad laminates are sandwiched between high-dielectric constant substrates for the production of planar capacitors, forming printed passive components. board. There is also the development of polymer composite materials filled with ceramic powder, which have high dielectric constant, low dielectric loss at high frequencies, and thin dielectric layer thickness, which can be used to make PCB inner layer RF capacitors. Embedded components are extended to the category of flexible printed boards, and polyimide copper clad laminates are also considered to make polyimide copper clad laminates for thin film components.4.4 Other special requirements of PCB boardNow there is the development of laser direct structuring (LDS: Laser Direct Structuring) technology, which can be used to manufacture model interconnection devices integrated with electronic circuits and components. The LDS process uses thermoplastics and metal oxide materials, which are formed by laser molding and circuit metallization. 3D printing technology is trying to be used in PCB manufacturing. Circuit graphics are not limited to two-dimensional planes and become three-dimensional components. This technology also requires thermoplastic polymer materials.Emerging medical electronic devices have begun to appear, some of which are implanted in the body, such as blood glucose sensing, diagnosis and treatment catheters, and cochlear implants. The PCB substrate used is a biologically inert substrate (PI or LCP). The conductors chosen are stable pure precious metals (gold, platinum).SummarizeThe above PCB technology development hotspots are summarized by reading relevant information on the recent printed circuit industry. The understanding is inevitably biased or incomplete, and it is for reference only. The Internet of Things, smart home, and smart city are proposed to be new growth points for the electronic information industry. Many new electronic devices will be equipped, and there will be many new requirements for PCBs and their substrates. Early preparations and timely additions are required. .The above is the development of printed circuit technology and the requirements for substrates introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.
07-28

2021

Integrated Circuit Technology Development

Integrated circuits are also called integrated circuits, which are miniature electronic devices. This miniature structure is completed by a certain process and has the required circuit functions. It contains a series of components such as diodes, capacitors, resistors and inductors. , these components are interconnected and fabricated in a small dielectric substrate that is housed in a tube. In this way, the volume of the circuit is greatly reduced, and the number of welding points is also reduced, so that the reliability of the electronic components is greatly improved.In recent years, high and new technologies such as information technology and software technology have developed rapidly, which is closely related to the development and application of integrated circuit technology. Integrated circuit technology is not only the cornerstone of the development of information technology, but also the main development direction of computer network technology. It is considered to be one of the greatest engineering technologies of the 20th century. my country is in a critical period of economic transformation. The development of integrated circuit technology is related to the transformation and upgrading of traditional industries and the development of the country's economy and society. It is the top priority of modern industry and technological development. Based on this, this paper briefly studies the basic indicators and development trends of integrated circuit technology.Semiconductor integrated circuits have many advantages, such as low power consumption, high integration, relatively small size, and large industrial scale. It is precisely because of these advantages that communication components based on semiconductor integrated circuits are widely used , For example, the manufacture of a series of terminal equipment such as mobile phones, landline phones, notebook computers, and digital codecs is inseparable from the use of semiconductor integrated circuits. The following will focus on the application of semiconductor integrated circuits in communication systems.1. Indicators of integrated circuit technology levelThe so-called integrated circuit, as the name implies, is to use semiconductor technology to integrate the components required for circuits such as diodes, transistors, resistors, capacitors, and inductance elements on one or several small semiconductor chips or dielectric substrates, and form a complete Finally, the fabricated circuit is packaged in the tube shell, and the microstructure with circuit function thus formed is an integrated circuit. Integrated circuits are an important basic industry for national economic development, and their technological level determines the industrial level of integrated circuits to a certain extent. The following is a brief introduction to several main indicators for measuring the technological level of integrated circuits.(1) Integration: The integration of an integrated circuit refers to the number of transistors contained on an IC chip. In the case of the same chip area, the higher the integration, the more the number of integrated components, and the greater the circuit function. The more powerful the chip is, the performance such as chip speed, reliability, and power consumption has been significantly improved. At the same time, the cost of the chip has been greatly reduced, and the weight and volume of the chip have also been reduced. It can be seen that the degree of integration is an important indicator to measure the advancement of IC technology.(2) Feature size: For electronic components, the feature size refers to the smallest size in a semiconductor device. By reducing the feature size, the integration level of the IC chip can be effectively improved and its performance can be optimized. The development of lithography technology is the premise of reducing the feature size of integrated circuits. In recent years, lithography technology has been improving day by day, and the feature size of integrated circuits has become smaller and smaller. At present, the integration of 0.18μm, 0.15μm, and 0.13μm levels Circuits have been mass-produced, and in the market, 65nm and 90nm integrated chips have mature products.(3) Wafer diameter: In order to improve the integration of integrated circuits, it is often necessary to increase the chip area appropriately, but it should be noted that the increase in the chip area will lead to a decrease in the number of chips contained in each wafer, thus Reduce production efficiency, resulting in increased costs. Increasing the wafer diameter can effectively solve this problem. At present, the mainstream wafer sizes of integrated circuits are 8 inches and 12 inches, and the research and development and application of wafer sizes of 14 inches and above are also the general trend.(4) Packaging: IC packaging first adopted the socket packaging method. In order to meet the needs of high-density assembly of electronic equipment, surface mount packaging technology has gradually replaced the traditional socket packaging method. In some electronic devices, surface packaging can effectively save space, optimize performance, and reduce packaging costs. Compared with the traditional socket packaging method, the cost of the circuit board under the surface package has been reduced by as much as 60%. In addition, the development of system-in-package technology has been relatively rapid in recent years. System-in-package technology is conducive to optimizing system performance, shortening the development cycle, and playing a positive role in improving packaging efficiency and reducing costs. Especially in Bluetooth modules, memory cards, power amplifiers and other low-cost, small-area, short-cycle, portable electronic products, the application advantages of system packaging technology are very obvious.2.The development trend of integrated circuit technology1. The size of integrated circuits is gradually reducedFrom a vertical point of view, with the development of various new technologies, the integration level of integrated circuit chips has increased year by year, basically increasing by 4 times every three years, while the processing feature size has continued to shrink. This is the famous Moore's Law, established by Intel Corporation Dr. Moore, one of the founders, proposed. In recent years, the competition in the integrated circuit chip market has become increasingly fierce. Actively improving product performance and cost performance is the key to long-term development, and it is also the driving force for the development of IC technology. Reducing the feature size is conducive to improving the integration level, thereby improving product performance and cost performance. As far as the current situation is concerned, circuits with feature sizes below 22nm have been produced, and integrated circuits are gradually approaching the physical limit. It should be noted that due to the limitation of process technology and economic endurance, the scale limit needs to be defined. Although there is no clear conclusion yet, the development of miniaturization is still the main trend, and the feature size of integrated circuits is still developing according to Moore's Law . Especially with the improvement of IC design and process technology, the scale of IC is expanding, and the complexity is getting higher and higher. In a chip, the number of integrated transistors is increasing, and integrated circuit technology has gradually developed from the 3G era to the 3T era. The storage capacity is further increased. And the speed of integrated circuits is getting faster and faster, and the data transmission speed has developed from Gbps to Tbps. In the past 50 years, IC technology has developed rapidly, IC technology design rules have become smaller and smaller, and transistor prices have gradually decreased, which is also the development trend of integrated circuits.2. System integrated chipSystem integrated chip is also called SOC, which can combine various functions such as microprocessor, analog IP core, digital IP core and off-chip memory control structure, so as to improve the stability of circuit system design, and also benefit Reduce power consumption, thereby effectively solving the problems of high energy consumption and poor stability of traditional integrated circuits. In the process of future development, it will inevitably lead to a technological revolution in the electronic information industry with chips as the core.3. Emergence of new materials and new technologies for integrated circuitsOf all the materials for integrated circuits, germanium was the first to be used, followed by silicon. For special integrated circuits such as optoelectronic devices, some compound semiconductor materials, such as cadmium sulfide and gallium arsenide, are generally used. Compared with other materials, silicon materials have great advantages in terms of electrical and physical properties and cost, which also makes it the mainstream material for current integrated circuits. Silicon single crystal materials are also in continuous development, and the diameter of silicon wafers is gradually increasing, and has reached the level of 16 and 18 inches at present.4. Application of integrated circuits in new fieldsToday's era is the information age, and integrated circuits have also ushered in a new peak of development in the information age, especially with the maturity of various key technologies of integrated circuits, their applications in various fields are becoming more and more extensive. In smart phones The application and development in various new fields such as mobile phones, smart cars, and linkage security are also worth looking forward to. With the continuous development of smart phones, the new mobile phone chip design technology is getting more and more attention. The key lies in adaptive computing. Using adaptive computing technology can effectively refresh the real circuit of the chip. Compared with the current fixed chip It is said that a single chip can realize the functions of several chips, and at the same time, it is beneficial to improve the speed of the chip and reduce the cost and power consumption. In addition, in the fields of vision repair, train station security system, face recognition, automobile intelligence, etc., the application of integrated circuit technology is becoming more and more extensive, and has gradually penetrated into all aspects of people's lives.3. Application of integrated circuits in communication systemsIn today's information age, people's lives are affected by information technology in all aspects, and all walks of life are affected by it. As the foundation of information technology, microelectronics technology has a great impact on the development of information technology. The core and key of microelectronics technology is the integrated circuit, which is also the foundation and foundation of the development of the entire information society, so it is necessary to study and explore the integrated circuit in depth. The communication network is changing from the previous large volume to small volume, low speed to high speed, and high energy consumption to low energy consumption. This transformation requires the network capacity and speed to be guaranteed. The research on this transformation has become one of the hot spots in the communication field at this stage.1. Application of integrated circuits in wired communication systemsDense wave multiplexing technology and erbium-doped fiber amplifier appeared in the late twentieth century, which made optical fiber communication show a strong advantage and became the first choice in wired communication network. The transmission capacity, transmission distance and transmission speed are greatly enhanced. Since then, the era of early copper wire communication has slowly ended. Today in the 21st century, optical fiber communication continues to develop, and a series of technologies such as microelectronics, optoelectronics, and optoelectronics have emerged. Nowadays, one optical fiber can complete the transmission of hundreds of wavelengths, and the transmission distance can reach more than 1000Km.One of the most critical components in optical communication is the laser source. The life of semiconductor lasers has been very low before. Since the 1970s, the problem of the life of semiconductor lasers has been solved, and long-life semiconductor lasers have been successfully developed. This It laid the foundation for the realization of optical communication. This kind of laser has many advantages, such as: small size and high working reliability, which makes this kind of laser an ideal light source in optical fiber communication. The core device in the composition of semiconductor lasers is an integrated circuit, and the basis of an integrated circuit is a silicon-based compound semiconductor. Nowadays, the realization of DFB laser is precisely by means of optoelectronic monolithic integration technology, and this kind of laser is widely used in the field of optical communication.Optical amplifiers and optical detectors are important components in optical fiber communication, and the composition of their core components is completed by optoelectronic integration technology. This technology can greatly improve the performance of all aspects of the device, and concentrate the devices on the same chip, so that the volume and power consumption can be optimized. The realization of the optical multiplexer or demultiplexer in the DWDM system is also completed by integrated circuit technology, and is currently being explored in the direction of all-optical processing and high-speed transmission. Integrated optics is produced under the background of the wide application of integrated circuits, and now it has continuously developed into a new optical discipline.2. Application of integrated circuits in wireless communication systemsNowadays, my country's information society is developing at a speed that we can't imagine. Wireless communication has many advantages, such as: strong timeliness, flexibility and convenience, etc. The potential of this communication technology is very broad. The second-generation mobile communication system is what we often call 2G. This system was commercialized in the 1980s. Since then, in just over 30 years, wireless local area network, Bluetooth and Global System for Mobile Communications, as well as 3G Even 4G has swept the world and spread to the homes of ordinary people. Various wireless terminals and mobile phones have gradually entered into every aspect of people's lives. For example, hotel reservations, movie ticket reservations, train and air ticket reservations, and travel ticket reservations can be completed through mobile phones. At the same time, the development of wireless communication equipment is becoming more and more miniaturized, with higher capacity and lower power consumption. The realization of miniaturization depends on the integration of electronic components. At present, the core chip size of mobile terminals has been reduced to less than 30 square centimeters. The realization of this transformation is absolutely inseparable from the development of integrated circuit technology. Therefore, it is very necessary to study and explore integrated circuits.Both the baseband unit and the radio frequency unit are key components of a wireless communication terminal, and both components are composed of integrated circuits. Complementary metal oxide semiconductor integrated circuit is called CMOS for short. The composition of the baseband unit is completed by this integrated circuit, and the composition of the radio frequency unit is completed by semiconductor devices. Integrated circuit technology is being widely used in signal processing units and switching equipment of wireless communication base stations, which enables the development and realization of efficient signal exchange processes. It can be seen that with the help of the development of integrated circuits, wireless communication has rapidly realized the characteristics of fast and small, providing users with satisfactory services, enriching and satisfying, and facilitating all aspects of people's lives.4.The application prospects of integrated circuitsThe communication field and integrated circuit technology are like the relationship between fish and water. The communication field has made great progress since the integrated circuit technology has made great progress. Similarly, the continuous emergence of new technologies in the communication industry has also made the integrated circuit technology like a fish in water. developed rapidly. Nowadays, communication is changing to optical communication, and the size of communication components is also getting smaller and smaller, and it is leaping towards the nanometer level. In the future, optical integration will replace electrical integration, and it is believed that there will be a qualitative leap in the field of communication in the near future.1. Application prospect in optical fiber communication systemThe development and research of integrated circuits in optical fiber communication systems will focus on new high-speed all-optical devices. This all-optical device should have the characteristics of being able to realize all-optical signal processing and easy integration, which is the basis for the completion and realization of all-optical communication. Nowadays, there are still some problems to be solved in the optical communication system, and the speed of the optical communication network needs to be improved. It is believed that in the future, with the continuous development of science and technology, the application and innovation of new high-speed plenoptic devices will be realized.2. Application prospects in wireless communication systemsThe terminal chip of wireless equipment plays a huge role in wireless communication. This kind of chip has been developing in the direction of miniaturization, but the future research hotspots are not limited to this, and should be researched in a diversified direction, that is, more An integrated circuit module with business, multi-function, and multiple working modes. In addition, there are some technologies that require continuous in-depth research and innovation, such as smart antenna technology, information transmission between wireless communication terminals, and software radio technology. These technologies will add luster to the development of communication integrated circuit technology.SummarizeTo sum up, looking at the development history of emerging technologies and industries of electronic information in the world in recent years, we can find that integrated circuits are the core and development foundation of contemporary electronic information technology, which is related to the development of the national economy and society, and is a typical foundation Sexual, strategic and leading industries. This paper briefly introduces the concept of integrated circuits, sorts out and summarizes the technological level indicators of integrated circuits, and finally looks forward to its future development trend, aiming to further promote the development of integrated circuit technology.The market economic potential and development prospects of silicon integrated circuits are still very broad, and at least there will be a long time to follow Moore's law to develop steadily. At present, there is also a deeper research on microelectronics technology, which has gradually developed from the nanometer era to the deep nanometer era. In the communication industry and field, there is still a lot of room for improvement in integrated circuit technology, and there are still some difficulties and problems that need to be studied and solved. Nevertheless, integrated circuits will play a more important role with the improvement of material manufacturing level and the continuous development of science and technology. It is believed that the development of integrated circuits will bring better promotion to the progress of social economy and the communication industry and field . The overall benefit of communication engineering is affected by the level of communication engineering technology. Therefore, in the future, we need to keep up with the pace of the times and increase the research and exploration of communication integrated circuits, so as to improve the construction level of communication engineering, and then promote the whole industry. The development and progress of human society.The above is the research on the development trend of integrated circuit technology introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad, including MCU, voice IC, Bluetooth IC and modules, wifi modules. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS solutions, the development of Bluetooth audio, the development of children's toys, and the development of electronic education products.
07-27

2021

BGA chip PCB design

PCB Design of 0.5mm Pitch BGA ChipWith the rapid development of microelectronic technology and technology, high-density ball grid array (BGA) devices have the advantages of small package size, large number of pins per unit area, strong impact resistance of solder balls, good signal integrity and heat dissipation performance, and smaller Therefore, it has been more and more widely used in communication networks, consumer terminals, military electronics, programmable logic devices and other fields. Today, the number of pins of BGA devices visible on the market can reach up to more than 2,000, and the pin pitch can be as small as 0.3mm. The higher pin count and smaller pin pitch make hardware designers face great challenges, and must adopt More advanced PCB technology to meet design requirements, and the most effective way to increase PCB density is to reduce the number of through holes, and accurately set blind holes and buried holes to achieve. This paper takes a project using the EPLD chip of Lattice Company as an example, focusing on the consideration of high-speed signal reflow, stack design, processing technology, etc., and carries out the specific PCB design of the 0.5mm pitch BGA package, which better realizes the single board work performance.1. 0.5mm pitch BGAThe single board design scheme of a certain project adopts the programmable logic device (EPLD) chip of Lattice Company. The number of pins of this BGA device is 256, the size is 10mm×10mm, and the pad spacing is 0.5mm.As shown in the figure: the pad diameter is 0.3mm, the center point distance between two adjacent pads is 0.5mm, the edge distance is 0.2mm (7.87mil), and the center point distance between two adjacent diagonal pads is 0.47mm. Obviously, the thinner the copper wire between the pads, the smaller the distance between the copper wire and the pad, the more difficult the processing technology, the higher the cost of the PCB, and the worse the reliability. At present, the mature process level of mainstream printed board manufacturers is that the width of the copper wire is 0.1mm (4mil), and the distance between the copper wire and the pad is 0.1mm (4mil). To draw a copper wire, the distance required is at least 0.3mm (12mil). Obviously, it is not feasible to directly draw a copper wire between two pads. In addition, the minimum metallized through hole size of domestic mainstream printed board manufacturers is 0.2mm in inner diameter and 0.4mm in outer diameter, which is larger than the 0.4mm distance between two adjacent diagonal pads in Figure 1, so the conventional lead from the pad The punching method is also not feasible.2. BGA chip PCB design schemeIn view of the fact that it is difficult to draw lines directly between the two pads of the 0.5mm BGA chip or the pads are fanned out directly, and because the PCB processing cost has risen sharply after the blind hole technology is adopted, it is decided to use the hole in the board and the special rule area of the BGA. Blind hole technology, that is, directly punch a blind hole on the 0.5mm BGA chip pad to the next second layer, and then continue wiring from the second layer pad.Using laser drilling technology to make blind holes is mature and reliable, and is widely used in the production of 0.15mm micro-vias. However, the depth of blind holes made by laser drilling is limited, and generally cannot exceed 0.075m. Therefore, in this design, 1~2 layers of blind holes Holes, the thickness of the medium between the top layer and the second layer is less than 0.075m, sequential lamination process method.The production of blind vias requires high soldering consistency and reliability. In order to prevent poor solderability caused by copper oxidation, the pads of all devices must be treated with protective coating or electroplating. At present, a low-cost application technology to enhance the success rate of welding is the "OSP (Organic Solderability Preseraties, Organic Solderability Preseraties) + Immersion Gold" solution. OSP is to use chemical methods to form an organic film on the clean bare copper surface. The organic film has good oxidation resistance, thermal shock resistance and moisture resistance, and prevents the metal copper surface from being oxidized in a normal environment; but in the subsequent welding high temperature environment , this organic film must be easy to be quickly removed by flux, so that the newly exposed clean metal copper surface will immediately combine with molten solder to form a firm solder joint in a very short time. Immersion gold is to electroplate a layer of nickel gold on the PCB pad. Since nickel gold has a stronger ability to absorb solder than copper, it can significantly enhance solderability.The sequential lamination method has certain process limitations, and it cannot be interconnected arbitrarily, so when designing a high-density PCB, use as few blind holes as possible, and the blind hole interconnection used should not exceed half of the total number of layers, which can reduce lamination. frequency and processing difficulty. In order to reduce the number of blind holes, the outermost pin pads of the 0.5mm BGA chip in the design are first drawn through through holes, and the inner sub-pins are wired through blind holes.3. Practical application of BGA chip PCBIn fact, the return path of the high-speed signal must be along the path with the least impedance. The return path with the least impedance is generally located on the ground plane closest to the lower part of the signal conductor. The smaller the total loop area, the smaller the external electromagnetic interference and the less susceptible it is to outside interference. Because blind holes need to be made on the pads of 0.5mm BGA chips, local area wiring grooves are formed on the second layer ground plane of the PCB, which will definitely destroy the integrity of the ground plane. For any signal vertically passing through the slots in this area in space, its return path will have to bypass this area, thereby greatly increasing the return area. In order to reduce the impact of slotting in this area, PCB layout and wiring must be fully considered. Try not to place the BGA chip near the center of the board to avoid serious impact on other signal wiring with the slotted ground plane. The single-board PCB design thickness is 1mm, and the number of layers is 6 layers.The 0.5mm BGA chip is placed on the top layer TOP, the second layer is the ground plane, and the dielectric thickness between the top layer and the ground plane is set at 0.071mm (2.8mil) (less than 75m). Since the design scheme needs to penetrate the blind hole to the second layer, and then continue to open the hole on the second layer to switch to other signal layer wiring, so only a small area in the second layer needs to be slotted. In order to reduce the difficulty of wiring, the width of the copper wire in the 0.5mm BGA area on the second layer is 4mil, and the via type is designed with a via hole with an inner diameter of 0.2mm and an outer diameter of 0.4mm. According to the calculation of the impedance design formula, when the width of the copper wire is 0.1mm (4mil), the thickness of the copper on the plane layer can only be 18m.SummarizeFor 0.5mm BGA chips, after using the single-board local blind hole technology in PCB design, the processing cost will not increase much. From the production situation of 10 R&D prototypes using this EPLD device, there is no single board failure caused by poor lead-free soldering of the chip at a high temperature. The control signals from the pins of the chip have also passed strict timing function tests, and the consistency and stability of the board are also very good, with no warping or pad breakage occurring.Since the "hole in the board" and blind hole technology will definitely increase the additional PCB production cost and design difficulty, so in the stage of system solution design and chip selection, it is necessary to pay close attention to the package size of the chip. In the schematic diagram and PCB design stage, it is necessary to use the I/O pin functions of the BGA chip reasonably, so that each signal is distributed as evenly as possible in the entire BGA chip area. Chips are laid out according to the principle of proximity to avoid excessively long traces, so as to reduce the difficulty of PCB design. At the same time, in order to ensure the best soldering effect of the 0.5mm BGA chip, soldering must be started within 24 hours after the bare PCB is unsealed, otherwise the bare PCB will be re-packed in a vacuum-sealed package.The above is the PCB design technology of 0.5mm pitch BGA chip introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.
07-26

2021

Synchronous Switching Noise Analysis

Analysis of Synchronous Switching Noise Problems in PCB DesignAs a large number of highly integrated high-speed digital chips are used on communication equipment circuit boards, the problem of simultaneous switching noise (Simultaneous Switching Noise, SSN) has become a bottleneck restricting high-speed PCB design. SSN means that when multiple logic circuits or I/O pins on the device are in the switching state at the same time, an instantaneously changing current is generated, and when there is an inductance on the return path, an AC voltage drop is formed, thereby causing noise. If the fluctuation of the ground plane is caused, causing the chip ground and the system ground to be inconsistent, this phenomenon is called ground bounce. Similarly, if there is a difference between chip power and system power, it is called power bounce.1. Causes and hazards of synchronous switching noise (SSN)According to the theory of power integrity, one of the main causes of SSN is the impedance of the power distribution system. Specifically, there is a distance from the output end of the power supply to the input end of the chip, and there is impedance on this path. From the point of view of the centralized model, it is equivalent to connecting concentratedly distributed resistance and inductance elements in series. When a certain number of output drive circuits are turned on at the same time, a large current will instantly rush into these inductive elements. The current will generate an induced electromotive force on the inductive element, causing the net supply voltage at the input terminal of the chip power supply to be insufficient or too high. Similarly, according to the theory of signal integrity, another important cause of SSN is the mutual inductance coupling, especially the mutual inductance coupling generated around the edge of the chip package and PCB. The solder balls on the chip BGA package and the vias on the PCB belong to a tightly coupled multi-conductor structure, and each I/O solder ball and its corresponding PCB via are formed by the nearest ground solder ball and ground via. A closed loop, when the state of multiple I/O ports changes at the same time, there will be transient I/O current flowing through these signal loops, and this transient I/O current will generate a changing magnetic field, thus Invasion of adjacent signal loops causes induced voltage noise.The hazard of SSN is very great, it will increase power supply noise, affect signal quality and timing, and lead to missampling of digital circuits. In addition, the problems caused by SSN are generally hidden and only occur when multiple logic units of the device are switched on and off at the same time. It is difficult to find out with normal business testing methods and is easy to miss, which brings huge risks to the reliable operation of the equipment.Based on the mechanism of synchronous switching noise, this paper designs a reliability test method that exposes the SSN problem, and uses this method to find a specific Serdes link abnormal problem. The defects in the PCB design were eliminated and modified. Finally, some methods for suppressing synchronous switching noise during output PCB design are summarized.2. Simultaneous Switching Noise (SSN) Reliability Test MethodReliability testing is to expose equipment to various possible extreme working conditions for verification, and to find system design defects. For synchronous switching noise, we can design test cases from the mechanism and common hazards. For example, when a large number of buses switch at the same time, crosstalk noise will be introduced on adjacent pins. In this case, it is necessary to impose a special service load on the device under test during test design, so that the bus is exposed to as much as possible Under the condition of large crosstalk, use an oscilloscope to observe whether the bus signal quality and timing are acceptable. Taking the 16-bit parallel bus as an example, in order to maximize this effect, when designing the test message, 15 of the 16 signals have the same transition direction, that is, all 15 signal lines transition from 0 to 1 at the same time. At the same time, let another interfered signal line jump from 1 to 0. A loop program can be designed to allow 16 lines to traverse this test scenario in turn.In addition, synchronous switching noise may also affect sensitive signals on the return path. This is a very bad working state of the parallel bus. In order to verify whether the product works reliably under this working condition, it is necessary to add a special SSN test packets for verification. If the bus under test is 16 bits wide, to make all 16 signal lines flip synchronously, the message content should be: FFFF 0000; if the bus under test is 32 bits wide, to make all 32 signal lines flip synchronously, the test message The content should be: FFFF FFFF 0000 0000.Of course, the working environment of the device may also be high or low temperature, and the impact of temperature on the circuit is very significant. For example, the capacitance of the capacitor will change at low temperature and high temperature, and the internal timing parameters of the device will drift at low temperature. At high temperature, the impedance of PCB traces becomes larger, etc. Therefore, when performing the above SSN reliability test, it is necessary to increase the temperature stress to verify the reliability of the system.3. Synchronous switching noise suppression methodThrough the analysis of the abnormal problem of Serdes link, it can be seen that the impact of synchronous switching noise on circuit reliability is increasing. With the continuous improvement of device speed, this impact will become more obvious. Then, how to avoid the harm caused by SSN problem as much as possible What? Generally, when designing a single-board PCB, we can refer to the following rules for design.(1) For DDR storage devices, it is best not to run the data bus on the same layer to reduce the impact on the reference plane noise in the case of SSN; it can be considered to be placed on the same layer as the address bus, and the data bus is preferentially referred to its I/O power supply.(2) Sensitive signals such as Serdes try to avoid walking on the edge of the reference plane.(3) Sensitive signals such as Serdes and RAM data bus should be separated as far as possible on the PCB, and placed on different wiring layers to avoid referring to the same power plane.(4) In the case of satisfying the flow, the power plane should not be too large. When there are high-speed I/O signals or Serdes sensitive signals refer to this plane, do ground laying where the power supply is not used.(5) The power plane cannot have a large area without high-frequency decoupling capacitors. It is recommended to add decoupling capacitors especially where there are high-speed signal cross-segmentation on the edge of the plane. The decoupling capacitors can use discrete capacitors or embedded capacitors.(6) Carry out simulation analysis and evaluation of power plane resonance, and try to avoid resonance with the operating frequency of storage devices.(7) Add enough decoupling capacitors to the power input end close to the chip to stabilize the voltage, and it is best to use L-type or π-type LC filter circuits.(8) The wiring layer of the I/O is preferably close to the TOP surface to reduce the loop inductance caused by the signal layer change.(9) When the pins of the logic chip are arranged, the synchronous I/Os that are stacked together are spread out to reduce the loop inductance caused by space coupling, and the unused pins are grounded or power processed to increase the return path.(10) Add a bypass capacitor in the chip or select a chip packaged with low impedance characteristics.(11) For the suppression of synchronous switching noise at very high frequencies, high-impedance electromagnetic surface structure (EB G) can be considered. When using EB G structure as the PCB substrate, it can be integrated in the microstrip circuit substrate with a wide resistance When combined with other circuit components organically, it can save circuit space.SummarizeIn general, according to the bus structure of the logic unit or I/O interface on the board mentioned in the article, the test method of constructing a special message during the test phase and making these interfaces flip synchronously can quickly find design defects and expose the circuit board. The potential problem of synchronous switching noise is eliminated, and the reliability of the board is improved. At the same time, the method of suppressing synchronous switching noise summarized according to specific problems is not only the principle to be followed in the early design stage, but also the solution to the problem in the later stage. In the future, we can also use the equivalent model method to simulate and analyze the possible risk of synchronous switching noise on the board in the early stage to avoid problems in advance. It is also possible to design a programmable SSN test program, so that chip manufacturers can embed it in the controller, which can be directly invoked and verified during the reliability test stage to enhance the testability of the single board.The above is the analysis of synchronous switching noise problems in PCB design introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.
07-25

2021

High Speed PCB Design Specifications

High-speed PCB design is a necessary stage in the development of my country's electronics industry, mainly to ensure the stability and compatibility of electronic products. High-speed PCB design is a very complex and highly professional job, which requires relatively high requirements for the professionalism and work experience of designers.In addition, in the process of high-speed PCB design, there are many rules required, but in these rules, conflicts and contradictions often occur, resulting in the failure of high-speed PCB design work to proceed smoothly. Therefore, in this case, designers need to make corresponding judgments based on their own high-speed PCB design experience and the actual situation of the design, and carry out effective solutions to ensure the smooth development of high-speed PCB design work and ensure that electronic The stability and security of the digital system also play a very important role and significance in the realization of its functions.1. Analysis of high-speed PCB design rulesIn order to improve the quality of high-speed PCB design, it is necessary to have a certain understanding of design rules, such as: layout, wiring, etc., so as to ensure the pertinence in high-speed PCB design. The specific content is as follows:1.1 LayoutIn the process of high-speed PCB layout, it is necessary to start from the overall point of view and plan according to the principle of whole to detail to ensure the accuracy of high-speed PCB design. Then, in the process of high-speed PCB layout design, the specific content is as follows:(1) In the process of high-speed PCB layout design, it is necessary to misalign the connection between high-frequency components as much as possible to reduce their distribution parameters and mutual electromagnetic interference. At the same time, for components that are susceptible to interference, they must not be too close to each other, and a certain distance is kept between input and output components, which can reduce interference to components.(2) If the components are heavy, they should be fixed by brackets, and then the corresponding welding work should be carried out. However, for those large and heavy components that generate heat, they must not be installed on the printed board, but should be installed on the chassis bottom plate of the whole machine, and the heat dissipation problem should be considered, so as to ensure the rationality of the layout.(3) For the components near the circuit board, a certain distance should be kept from the circuit board, which should be controlled within 2mm under normal circumstances. At the same time, the best shape of the circuit board should be a rectangle. In addition, when the size of the circuit board is 200mm×150mm, the mechanical strength of the circuit board must be considered to ensure the rationality of the high-speed PCB design.1.2 Wiring(1) The wires used at the input and output terminals must try to avoid the phenomenon of adjacent parallels. It is best to use the ground wire between the wires, so as to ensure the rationality of the wiring.(2) The minimum width of the printed guide is mainly determined by the adhesion strength between the wire and the substrate and the current value flowing between them. At the same time, in the process of high-speed PCB layout design, if the thickness of the copper foil is 0.05mm, the width is 1mm~15mm, and the passing current is less than 2A, the temperature will not be higher than 3°C. In addition, for integrated current, especially for digital circuits, the wire width of 0.02mm~0.3mm is generally selected to ensure the stability of the system operation. However, in the process of high-speed PCB design, there are errors, so the error must be controlled. Generally, it should be controlled between 5mm and 8mm.2.High-speed PCB design content analysisIn the process of high-speed PCB design, there are many contents involved, such as: preliminary preparation work, layout design, wiring design, etc. Only by understanding each link in detail and strengthening the design, can high-speed PCB be guaranteed. Regarding the quality of the design, the following is a brief introduction of some experience in design for these aspects:2.1 PreparationsThe preparation work in the early stage of high-speed PCB design directly affects the development of design work and the speed of design work. Therefore, in the process of high-speed PCB design, detailed preparations must be made. According to the design work experience of the designer, it can be expanded from the following aspects:(1) Make a detailed circuit diagram. The accuracy and comprehensiveness of the circuit diagram directly affect the quality of high-speed PCB design, although the computer can be used to make corresponding adjustments and changes to high-speed PCB design. However, in the process of affecting the degree, if a component is changed, the overall layout degree will change accordingly, which will affect the quality and process of high-speed PCB design. Therefore, according to the relevant experience of the designer, the corresponding circuit diagram must be prepared, so as to ensure the accuracy of high-speed PCB design and the quality of the design.(2) Encapsulation of circuit components. Circuit component encapsulation is an important basis for high-speed PCB design, but in the process of designing encapsulation, it must be based on the physical object and a certain amount of space must be reserved. In the process of space reservation, it should be calculated according to the corresponding data and information, and random estimation cannot occur. This is mainly to avoid the stability of high-speed PCB design products. If the situation is relatively serious, there will be scrapped Phenomenon.(3) The actual size and size of the product exterior. The actual size and size of the exterior directly affects the size of the high-speed PCB. Therefore, in the process of high-speed PCB design, it is necessary to combine high-speed PCB design and external design with each other. At the same time, in the design process, if the adjustable components on the external panel, connectors and switching components are installed on the high-speed PCB, then the high-speed PCB and the external should be comprehensively considered to ensure good coordination and design together, so as to ensure The quality of high-speed PCB design.2.2 Rationality of high-speed PCB sizeHigh-speed PCB size is a very important item in the design. In the process of high-speed PCB design, if the size of the high-speed PCB is relatively large, the printed lines will be relatively long, so the impedance will increase accordingly, and the anti-noise ability will also decrease accordingly. If the size of the high-speed PCB is relatively small, the heat dissipation performance of the components will be relatively poor, the installation will be relatively difficult, and the interference will be relatively large. Therefore, in the process of high-speed PCB design, the size must be designed according to the actual situation of the circuit, which can further ensure the accuracy of high-speed PCB design.2.3 Overall layout design of high-speed PCBLayout design is an overall plan of high-speed PCB design, so in the process of high-speed PCB design, we must pay enough attention to the overall layout design. Then, in the process of specific design, it can be expanded from the following aspects:(1) In general, electronic circuits are composed of input stages, intermediate stages, and output stages. Therefore, in the process of high-speed PCB design, the overall layout should follow the signal flow, and the circuit unit position should be reasonably laid out, so as to ensure the stability of various signal transmissions. (2) In the process of circuit layout design of each functional unit, it is mainly based on components, and the corresponding layout is carried out around this central point, thereby ensuring the integrity of high-speed PCB design. (3) For the layout design of special components, a relatively suitable position should be set according to its particularity. (4) In the process of high-speed PCB design, if there are some relatively heavy components, the position of the fixed bracket should be designed, and the balance of each part should be paid attention to, which provides relatively convenient conditions for later production. (5) For components with relatively high heat generation performance, the corresponding heat dissipation must be set, or a corresponding heat dissipation method should be adopted to ensure the stability of the components.2.4 High-speed PCB layout design(1) Both digital signals and high-frequency analog signals have harmonics. Therefore, in the design process, the printed wire must not be designed with right angles and included angles at the corners, and the design shape of the arc can be used, which can play a role in radiation protection. (2) In the design process, if the area of high-speed PCB copper foil is relatively large, it can be designed in the form of a grid. The main purpose is to avoid deformation.2.5 Ground Wire DesignGround wire design is a very important content in high-speed PCB design, which can be developed from the following aspects: (1) Ground wire design is a very important content in high-speed PCB design, and its structure must be detailed Understanding, which mainly includes: system ground, shielding ground, digital ground and analog ground and other aspects. (2) During the design process, try to use a thicker ground wire, which can ensure the stability of the current operation and allow 3 times the current to flow. (3) In the process of ground wire design, each ground wire structure must form a closed loop, which can play the role of healthy noise and effectively reduce the phenomenon of potential difference.SummarizeTo sum up, this article briefly analyzes and elaborates on the relevant content of some rules of high-speed PCB design, and from the rationality of high-speed PCB size, the overall layout design of high-speed PCB, high-speed PCB wiring design, ground wire design, etc. On the one hand, the experience of its design is briefly discussed. Its main purpose is to ensure the quality and progress of high-speed PCB, and provide important support for the development of my country's electronic industry.The above is the design experience of high-speed PCB introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.
07-24

2021

Digital Circuit PCB Design

High Speed Design of Digital Circuit PCB Based on SIIn recent years, with the rapid development of integrated circuit technology, the speed of its work is getting higher and higher. This brings about a problem. The smaller the volume, the larger the layout and wiring density of the circuit, the faster the output switching speed of the integrated circuit, and at the same time the signal operating frequency continues to increase. Therefore, how to deal with high-speed signals and ensure system design performance has become a design capability. key factor for success.With the rapid increase of the clock frequency of the electronic system and the steepening of the signal edge, the influence of the trace interconnection and layer characteristics of the printed circuit board on the electrical performance of the system is becoming more and more important. For low-frequency designs, the influence of trace interconnection and board layers can be ignored. When the operating frequency of the system exceeds 50MHz, on the one hand, the influence of the transmission line must be considered in the interconnection relationship, and on the other hand, the electrical parameters of the printed circuit board should also be considered when evaluating the system performance. Therefore, the design of high-speed systems must face timing issues caused by interconnect delays and signal integrity (signal quality) issues such as crosstalk and transmission line effects. How to take into account the signal integrity factor in system design and plate design, and take effective control measures, has become a hot topic among system design engineers and PCB design industry.1.The method to ensure the signal integrity of the PCB board1.1 IsolationDevices on the PCB have various edgerates and various capacitive noises. The most direct way to improve signal integrity is to physically separate them on the PCB according to their different margins and sensitivities.1.2 Impedance, Reflection and TerminationImpedance control and termination are fundamental issues in high-speed design. It is also a core issue in every RF circuit design. However, the operating frequency of some digital circuits exceeds that of RF circuits, and the impedance and terminal load are still not considered in the design. Impedance mismatch will have the following fatal effects on digital circuits:(1) The digital signal will be reflected between the input terminal of the receiving device and the output terminal of the transmitting device, and the reflected signal will bounce back and propagate along the two ends of the line until it is completely absorbed at last;(2) The reflected signal causes the ringing effect of the signal passing through the transmission line, and the ringing will affect the voltage and signal delay or even completely deteriorate the signal;(3) The mismatched signal path may cause the signal to radiate to the environment; the problems caused by the impedance mismatch can be reduced by the terminal load. Usually one or two separate terminal loads are placed on the signal line close to the receiver, and the simple way is to connect a low-value exclusion in series. Termination limits the rise time of the signal and can partially absorb reflected energy. It is worth noting that termination does not completely eliminate the destructive effects caused by impedance mismatches. However, with careful selection of the proper device, termination can effectively control signal integrity. Not all wiring needs impedance control, it is up to the designer to decide whether to match. There are various rules in various applications, but generally follow the rules between the wiring length and the rise time of the signal, that is, the general impedance control rule is that when the wiring length is greater than 1/6 of the rise time, impedance matching must be performed .1.3 Layers and Layer SegmentationOne issue that is often overlooked by digital designers is current propagation in the loop. For example, assuming a unidirectional signal is transmitted between two gates (as shown in Figure 2), the current will propagate in the loop from gate A to gate B, and then return to gate A through the ground connection. Here There are two potential problems:(1) The ground should be connected by a path with low impedance value. If a path with a high impedance value is used, then there will be a voltage drop at the ground pin of Figure 2, which will destroy the ground reference of all devices and reduce the input noise margin;(2) The loop area caused by the current loop is as small as possible. The loop is equivalent to the antenna. Generally speaking, a large loop area will increase the chance of loop radiation and conduction. Every PCB designer hopes that the return current is directly along the signal line, so that the smallest loop area can be obtained;Using a large-area ground layer can solve the above problems at the same time. The large area ground provides low impedance between all ground points while allowing loop currents to travel directly through the respective signal paths.A common mistake made by PCB designers is to open a slot in the ground plane (as shown in Figure 3a). Figure 3(a) shows the current flow when the signal line bypasses the slot in the ground plane. The loop current will be forced to bypass the slot, which will necessarily create a large circulating loop. Figure 3(b) shows the current flow when the ground plane is not slotted. Generally speaking, the ground plane cannot be slotted. However, there are also situations where slotting cannot be avoided. When it occurs, the designer of the PCB must ensure that no signal path passes through the slotted part.Attention should also be paid to the area between layers in the power layer with mirror image differences. The power layer and ground layer of the PCB have radiation at the edge of the board. Electromagnetic energy radiating from the edges may damage adjacent connection plates. The solution is to shrink the power plane so that it overlaps the ground plane by a fixed distance. This can reduce the electromagnetic radiation energy value in the direct area outside the board, and reduce the influence of electromagnetic leakage on adjacent boards.1.4 Signal wiringThe most important thing to ensure signal integrity is the physical routing of the signal lines. High-speed signals cannot propagate in discontinuous signal lines. The right corner shown in Figure 4(a) is a problematic wiring method that is usually easier to commit. Such wiring has no problem at low frequencies, but it will radiate at high frequencies. It should be replaced by a 45o in Figure 4(b) or two 45-degree corners in Figure 4(c).In high-speed circuit design, if there is no special reason for signal wiring, all short-circuits should be eliminated as much as possible. Short-circuits are like radiation caused by impedance mismatch of signal lines. In addition, special attention should be paid to the wiring of differential pairs in the wiring of high-speed circuit design. The differential pair is driven by two completely complementary signal lines, and the differential pair can well avoid noise interference and improve the S/N rate. However, the differential pair signal line has particularly high requirements for wiring: (1) the two lines must be as close as possible to the wiring; (2) the two lines must be exactly the same length;1.5 Overcoming CrosstalkIn PCB design, crosstalk is another problem worthy of attention. When the spacing between signal lines is too small, the electromagnetic regions between signal lines will affect each other, resulting in signal degradation and crosstalk.Crosstalk can be resolved by increasing the spacing of the signal lines. However, PCB designers are usually constrained by the increasingly tight wiring space and narrow signal line spacing. Since there are no more choices in the design, it is inevitable to introduce some crosstalk problems into the design. Many relevant rules for reliable spacing are given in the literature. The commonly used rule is the 3W rule, that is, the spacing between adjacent signal lines should be at least 3 times the width of the signal line. However, the actual acceptable signal line spacing depends on the actual application, working environment and design redundancy and other factors. Therefore, when the crosstalk problem is unavoidable, the crosstalk should be quantified, and the designer can determine the signal integrity effect and evaluate the crosstalk effect of the system through computer simulation.in conclusionSignal integrity is one of the most important issues throughout the design of high-speed digital circuits. Here are several methods to ensure signal integrity in digital circuit design: (1) Physically isolate sensitive components from noise devices; (2) Impedance control, reflection and signal terminal matching; (3) Use continuous power and ground plane layers; (4) Try to avoid using right angles in wiring; (5) Differential pair wiring lengths are equal; (6) In high-speed circuit design The problem of crosstalk should be considered; (7) The power supply should be decoupled.In the design process of the PCB board, the factors of signal integrity are fully considered, and effective control measures are taken, so that a safe and reliable high-speed circuit can be designed. The author's innovation point: signal integrity (SI) has become a new hot topic in today's PCB design industry. This paper expounds typical signal integrity problems in high-speed PCB circuit design. It describes the manifestations of signal integrity problems, and focuses on analyzing several common problems that affect signal integrity - crosstalk, electromagnetic interference and reflection. And pointedly put forward specific solutions to the problems. In circuit design, taking corresponding measures can effectively improve signal integrity.The above is the SI-based digital circuit PCB high-speed design technology introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.
07-23

2021

High-Speed Circuit Crosstalk Issues

Suppression of Crosstalk Problems in High Speed Circuit PCB DesignWith the rapid development of PCB design, its high speed and miniaturization have become a trend. On the one hand, due to the smaller size of the PCB circuit board, the wiring density is greatly increased; on the other hand, the signal frequency becomes higher and the edge becomes steeper. In this way, in the design of high-frequency circuit PCB circuit boards, the problem of crosstalk between signals cannot be ignored more and more. This is an important consideration in the design of high-frequency PCB circuit boards. Through the analysis of the crosstalk problem, the crosstalk problem can be quickly found, located and solved in the PCB design. So how does crosstalk arise? What factors are related? What is the effect on the PCB circuit? And how to control it?1. The generation of crosstalk problemMutual inductance and mutual capacitance between signal transmission lines are two important factors that cause crosstalk problems. Signal transmission lines include printed lines, wires and cable bundles, etc. Crosstalk is the coupling of electrical signals from one transmission line to another. When the alternating current of the signal passes through the transmission line, a magnetic field is generated around it. When the electromagnetic fields generated by different transmission lines are superimposed and interact, crosstalk occurs.In digital circuits, since it is mainly a pulse circuit, crosstalk occurs during the transition of the signal. The faster the signal changes, the greater the crosstalk will be.As shown in Figure 1, the changing signal propagating from A to B along the transmission line produces a coupled signal on the transmission line CD. When the varying signal returns to a stable DC level, the coupled signal is no longer present.Crosstalk can be divided into capacitive coupling crosstalk (Sc) and inductive coupling crosstalk (Sl).Capacitive coupling crosstalk is when there is signal transmission on the interference line, due to the change of the signal edge voltage, in the area near the signal edge, the distributed capacitance on the interference line will induce a time-varying electric field, and the victim line is in this electric field , so the changing electric field induces a current in the victim wire. This results in capacitively coupled crosstalk. as shown in picture 2.Inductive coupling crosstalk means that when the signal propagates on the interference line, due to the change of the signal current, a time-varying magnetic field will be generated by the action of the distributed inductance in the vicinity of the signal transition, and the changing magnetic field will be induced on the victim line. Noise voltage, and then form inductive coupling current, the resulting crosstalk is inductive coupling crosstalk. As shown in Figure 3.2. Parameter factors affecting crosstalk(1) The influence of the coupling length of the signal transmission line on crosstalk: the coupling length of the signal transmission line is different, and the degree of crosstalk generated is different. The far-end crosstalk is proportional to the length of the signal transmission line, the longer the coupling length, the greater the crosstalk. As for near-end crosstalk, only when the coupling length is less than the saturation length, the crosstalk increases with the increase of the coupling length, and when the coupling length is greater than the saturation length, the near-end crosstalk is a stable value.(2) The effect of line spacing on crosstalk: line spacing is inversely proportional to crosstalk. When the line spacing is greater than or equal to 3 times the line width, the crosstalk is very small.(3) The influence of signal rise time on crosstalk: In high-speed PCB design, the speed of signal rise time has a great influence on signal crosstalk. As the rise time becomes shorter, especially when the parallel trace length is less than the saturation length, the crosstalk voltage amplitude will decrease rapidly. Therefore, devices with fast edge rates are increasingly used in modern high-speed board designs.(4) The effect of the thickness of the medium layer on the crosstalk: The crosstalk is inversely proportional to the thickness of the medium. The thinner the dielectric, the less crosstalk it will cause.3. The influence of crosstalk on high-speed PCB circuitsCrosstalk is ubiquitous in high-speed and high-density PCB circuits. Each of its signal transmission line pairs interacts with its nearest signal line. In high-speed PCB design, it is necessary to correctly deal with the crosstalk problem of signal lines and improve the anti-interference ability of signal lines. Generally, crosstalk has the following two effects on high-speed PCB circuits.(1) Crosstalk causes false triggering: Signal crosstalk is an important part of the signal integrity problems faced by high-speed PCB design. Functional errors in digital circuits caused by crosstalk are the most common one.(2) Trigger delay caused by crosstalk: In digital circuit design, timing is an important consideration. Due to the existence of crosstalk, the timing delay is caused.4. Suppression of crosstalk problemsCrosstalk is a problem that needs to be focused on in high-speed PCB design. Although it is impossible to eliminate crosstalk, it can still be suppressed within a tolerable range technically. The whole process of high-speed PCB design includes steps such as circuit design, chip selection, schematic design, PCB layout and wiring. It is necessary to find crosstalk in different steps and take measures to suppress it in order to reduce interference. .The problem of controlling crosstalk can be considered from the following aspects:4.1 Suppress crosstalk by controlling signalsThe transition rate of the transmitted signal edge also has an effect on the suppression of crosstalk. The faster its conversion rate, the greater the impact on crosstalk. Therefore, when selecting devices, try to choose slow devices while meeting the design specifications, and avoid mixing different types of signals, because fast-changing signals have potential crosstalk hazards to slow-changing signals. Through the PCB circuit design, the impedance of the signal transmission line is matched. It is necessary to match the terminal impedance of the near end or the far end of the transmission line with the impedance of the transmission line as much as possible, so as to suppress the amplitude of the crosstalk, and then achieve the purpose of suppressing the crosstalk.4.2 Adopt shielding measuresProviding package ground for high-speed signals is an effective way to solve the crosstalk problem. However, the ground wrap increases the amount of routing, which makes the limited routing area more crowded.The shielding of the ground wire requires that the distance between the ground points meet certain requirements, which is generally less than twice the length of the signal change edge. At the same time, the ground wire will also increase the distributed capacitance of the signal, which will increase the impedance of the transmission line and slow down the signal edge.4.3 Suppress crosstalk from product designFor sensitive internal circuits, it is necessary to prevent the injection of external interference signals; at the same time, it is also necessary to prevent crosstalk between internal noise circuits and other signal lines, especially crosstalk between I/O signal lines.4.4 Suppress crosstalk through PCB wiring layer and wiring spacingThrough reasonable setting of wiring layers and wiring spacing, effectively shortening the length of parallel signal lines and increasing the spacing of signal transmission lines, crosstalk can be effectively suppressed.Increasing the distance between printed lines can reduce capacitive coupling, and inserting a ground wire between printed lines is more effective in reducing capacitive crosstalk. It is relatively difficult to suppress inductive coupling. The number of loops should be reduced as much as possible, and the signal loops are prohibited from sharing the same wire. At the same time, because the crosstalk generated by capacitive coupling and inductive coupling increases with the increase of the load impedance of the disturbed line, so reduce the load to reduce the influence of coupling interference.When conditions permit, try to increase the distance between traces and reduce the length of parallel traces. If necessary, you can use a fixed maximum parallel length push wiring method, that is, jog traces. This wiring method can effectively suppress crosstalk. As shown in Figure 4.The signal layer adjacent to the ground wire should be equipped with low-level analog signal lines and high-speed digital signal lines, while the signal layer farther from the ground wire should be equipped with low-level signal lines and high-level analog signal lines.Reduce parallel wiring, especially the wiring between the input end and the output end, and parallel wiring should be strictly prohibited. In this way, feedback coupling can be avoided, thereby effectively suppressing the occurrence of crosstalk.In PCB design, the corner of the printed wire generally takes an obtuse angle of 135 degrees. The clock line should be adjacent to the ground layer, and the line width should be as large as possible. The line width of each clock line should be the same.The line width of the power line and ground line should be increased as much as possible. Generally, the signal line width of digital circuits should be between 8mil and 10mil, and the line spacing should be between 6mil and 8mil. For devices with a pitch of 0.5mm, the wiring width should not be less than 12mil, and the high-speed signal lines should be designed as striplines or embedded microstrip lines.If the two signal layers are adjacent, the wiring should be carried out in an orthogonal direction to reduce the coupling between layers. By termination, the far-end and near-end impedance of the transmission line can be matched with the transmission line, thereby reducing crosstalk.In PCB design, a unified ground is generally used, and digital circuits and analog circuits are partitioned for layout and wiring. The digital ground and the analog ground should be separated, and the wiring cannot cross the partition gap, otherwise the crosstalk will be sharply enhanced.SummarizeCrosstalk is ubiquitous in high-speed and high-density PCB design, and the influence of crosstalk on circuits cannot be ignored. In order to reduce crosstalk, the most effective way is to reduce bad signal coupling, reduce the possibility of crosstalk as much as possible in PCB design, and minimize the influence of crosstalk. The above is some experience combined with PCB design, and I have read some related professional books, and put forward some solutions to the crosstalk problem in high-speed and high-density PCB design, for colleagues in the future High-speed and high-density PCB design learn from.The above is the suppression method of crosstalk problem in high-speed circuit PCB design introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.
07-22

2021

Circuit board modification process analysis

Due to design changes, manufacturing and other reasons, modification work is almost inevitable in many electrical and electronic product development units. The so-called modification refers to the modification of the function of the product in order to meet the new standard. Such as changes in circuit connections or components due to changes in design schemes and technical status, that is, the increase or decrease of wires, the increase or decrease or change of components, and the corresponding structural changes brought about.The aerospace standard QJ2940A-2001 stipulates: "The modification of the printed circuit board assembly refers to the change of the connection characteristics. The change of this characteristic is achieved by cutting off the printed wires, adding components, and cutting and adding wires (leads) connections. of.” Modifications to printed circuit board assemblies are usually due to design changes and requirements for reliability and safety. For some products, this kind of modification is helpless, and in many cases it is inevitable. For example, when a printed circuit board needs to be changed in design, there are usually two options: one is to realize the design change through modification. The advantages of this approach are obvious: short cycle, low cost, and easy implementation. The disadvantage is that the modification and the risks brought by the modification must be fully demonstrated, such as the fixing method of the modified components, the quality of the solder joints, and the safety distance. Refitting is often accompanied by many unexpected situations, such as the impact on peripheral devices, the performance of modified parts in various environmental experiments, etc. The second is to re-board and re-weld. The advantage of this method is that the risk is controlled, and it can completely solve a series of problems caused by modification; the disadvantage is very obvious: all components must have enough margin (for many expensive components, this is actually very difficult) Do it); the environmental tests that have been completed must be carried out again, and these two points and the delay caused by these two factors are unbearable for many research and development units.1. Modification of printed circuit board assembliesThe modification of the printed circuit board assembly usually includes the addition of components, the modification of the connection of components, and the cutting of the printed wires in the inner layer of the multilayer printed circuit board.1. The principle of circuit board modificationGenerally speaking, the quality of modified products will not decrease, there should be no hidden dangers, and even the product quality will be better. According to the relevant regulations in QJ2940A-2001, the printed circuit board modification should follow the following principles: within any 25 cm2 area on any printed circuit board assembly, the total number of modifications should not exceed 2; only when the printed circuit board does not change Components can be added only when the structural size is limited; the component wires should be covered with corresponding insulating materials; the extension of the lead wires should be limited to prevent subsequent vibration problems; the first bonding point on the extended wire should be away from the component to the wire The distance between the solder joints should not be greater than 15mm.2. Common circuit board modification methods(1) Addition of components: The traditional method of adding components can usually be divided into: installing additional components on the soldering surface of the printed circuit board, installing additional components on the component surface of the printed circuit board, installing additional components on the terminal block There are several methods of adding components, using adhesive mounting to add components, and adding components through lead mounting of adjacent components. The above methods need to be flexibly selected according to the actual situation.(2) Modification of component connection: The modification of component connection generally includes the following methods: welding after winding and connecting with extended component leads; welding of component leads and vertical leads installed in existing holes; installation of double In-line package components, soldered or not soldered on the cut-off leads (this method can only be used if the leads that need to be cut do not exceed one-third of the number of leads on each side of the dual-in-line package ); Installed on the cut-off lead with welded or unsoldered wire connector; Add a wire to the metallized hole inserted with a flat cross-section lead; Add a wire to the lead of the flat package device; Insulation of the lead of the component.2. Case analysis of actual circuit board modification1. Problems to be considered in circuit board modificationIn actual work, it is necessary to install 4 pull-up resistors on a welded printed circuit board (the printed circuit board has been subjected to conformal coating and glue dispensing reinforcement). Before the modification, we mainly considered the following factors.(1) The packaging form of adding resistors: There are two types of resistor packaging options: plug-in and surface mount. Among them, the plug-in resistor is convenient to lead directly, but it is relatively large in size and relatively heavy in weight. After installation, it is necessary to consider the way of its mechanical reinforcement. If the mechanical reinforcement is not proper, it is easy to cause problems in the subsequent mechanical vibration test. Surface-mount resistor leads are relatively inconvenient, but they are small in size, light in weight, and easy to mechanically strengthen. Therefore, the way to solder the lead wires is a problem that needs to be considered.(2) Selection of cement: The mechanical reinforcement of the added components is a process link that must be considered. Generally speaking, mechanical reinforcement and cementation can be considered in two ways. Since mechanical reinforcement usually requires punching holes to destroy the printed circuit board, the method of bonding is often used to mechanically reinforce the attachment. There are two main types of common adhesives to choose from—silicone rubber and epoxy resin glue. Among them, the bonding strength of silicone rubber is not as good as that of epoxy resin, but the release stress is small during the curing process, and its own elasticity is relatively large, which has a certain mechanical shock absorption effect; the bonding strength of epoxy resin is high, but the release stress during the curing process The stress is also large, and improper use is easy to break the metallized hole and damage the bonded components. Both have advantages and disadvantages, and you need to choose according to the actual situation. For example, when the components are dense and there are many metallized holes, it is better to use silicone rubber for bonding; when the space is relatively sufficient and there are not many metallized holes, it is better to use epoxy resin for bonding.(3) Selection of the bonding position: The bonding position should be selected in a place that is spacious, has fewer metallized holes, and is as far away from the frame as possible; the bonding position should not interfere with other components, mechanical installation frames, and heat dissipation frames. At the same time, the cemented position should also take into account the distance between the lead-out wire and the target welding point of the lead-out wire. The closer the distance, the better.(4) Selection of the routing path: the routing path from the resistor lead-out line to the target point is also a problem that must be considered. Generally speaking, lead-out wires should not cross other component bodies, pads and solder joints. If it is necessary to cross, reliable insulation measures must be taken. At the same time, the solder joints at both ends of the wire should not be subjected to obvious wire stress, and the connecting wire should be preformed after the wire path is determined to ensure that its own stress is minimized.2. Determination of circuit board modification planThe determination of the modification plan should start from the actual situation of the printed circuit board assembly to be modified, and consider various factors in a comprehensive and balanced manner. Here, we adopted the modification plan of "adding a small resistance board" - using the small resistance board made to weld the patch 0805 package resistor, the schematic diagram of the resistance board is shown in Figure 1. HY914 two-component epoxy resin glue is used between the resistance board and the modified board.The main advantages of adopting the method of "adding resistance boards" are as follows: First, the solder joints of adding components are reliable. On the resistance board, the resistance element installed can be normally welded on the pad, and the lead-out wire is welded on the lead-out wire pad. Add unreliable factors. Second, the bonding between the resistance board and the modified circuit board. Since the two circuit boards are both FR4 base materials, after the bonding is completed, the mismatch of thermal expansion coefficients between materials is greatly reduced. This greatly reduces the risk of component damage caused by inconsistent thermal expansion coefficients among printed circuit board substrates, components, and adhesives (the traditional modification method is to directly paste components on the surface of the printed circuit board) .3. Circuit board modification processThe printed circuit board refitting process is divided into 14 processes, including pre-installation preparation, resistance board welding, and cleaning, as shown in Figure 3.Circuit board modification process flow chart(a) Preparation before installation. Before installation, the tools and materials needed for modification should be ready for use.(b) Resistance plate welding. The welding of the resistance board adopts OK 037 soldering iron head, the welding time is 2~3 s, and the welding process uses R-type flux.(c) cleaning. For cleaning, use a dust-free cloth dipped in alcohol to scrub manually. After scrubbing, the solder joints should have a bright appearance and good wetting, and the printed circuit board should have no residues such as rosin and solder residue.(e) Inspection of solder joints.(e) Bonding: HY914 epoxy resin glue is first used for the bonding of printed circuit boards, and glue is applied on both sides of the bonding surface. The glue should be evenly applied and the amount of glue should be appropriate. 4 h. After HY914 is completely cured, apply GD414 one-component room temperature vulcanized silicone rubber evenly around the resistance plate. The glue should cover the edge of the resistance plate and cure for 21 hours.(f) Conductor treatment: Raychem 0.15 mm2 silver-plated conductors are used for the conductors. Measure the appropriate line length from the lead-out point of the resistance board to the target point, strip the head, and tin-coat it for later use. When measuring the length of the wire, the routing path should be fully considered, and try to avoid placing the cable above the component body, above the solder joint, above the component lead, above the metal ground hole, etc. If it is really impossible to avoid the above positions, necessary insulation measures must be taken to prohibit direct contact of the wires with the above positions.(g) To remove paint. The original three anti-paint is DBSF6101, and the thinner of the paint is V (toluene): V (n-butanol): V (butyl acetate) = 2:1:1 mixture. Here, its thinner is selected as the paint remover. Use a dust-free cloth to dip a small amount of paint remover and repeatedly wipe the surface of the target solder joint to achieve the paint removal effect. The wiping time should be controlled within 15 minutes. Long-term immersion will cause the pads of the printed circuit board to loosen, which will affect the reliability of the electrical connection.(h) Lead wire installation. Solder one end of the connecting wire to the lead-out pad of the resistor board, and solder the other end to the target soldering point.(i) cleaning. After the soldering is completed, wipe off the flux residues on the solder joints and their surroundings.(j) Inspection of solder joints. Check whether the solder joints are mis-welded, and under a magnifying glass of 5 times, whether the solder joints are bright and well wetted.(k) Touch-up paint. Repaint the three anti-paint on the resistance board, lead solder joints, etc., and let it dry naturally for 24 hours.(l) Wire bonding. Carry out dispensing reinforcement treatment on the outlet position of the lead-out line, and glue the lead-out line every 1 cm.(m) Inspection. Check whether the connection relationship is correct, whether the adhesive colloid is completely cured, whether there are missing paint parts, whether there are solder residues, rubber particles and other redundant substances.(n) Take pictures. Panoramic and partial multi-angle pictures of the modified printed circuit board should be taken for future reference.3. Circuit board test verificationAfter the modification is completed, test verification work is required. The printed circuit board has been subjected to board-level temperature cycle test and random mechanical vibration test. Here, the board-level test conditions and temperature cycle test conditions are selected as follows: temperature range -40~75°C; heating rate 10°C/min, cooling rate 5°C/min; high temperature for 2 h, low temperature for 1.5 h; cycle times 10 times . The mechanical test conditions are: 20~80 Hz, +3 dB/oct; 80~350 Hz, 0.04g2/Hz (g is the acceleration of gravity); 350~2 000 Hz, -3 dB/oct; the total root mean square value is 6.06 ; Loading direction, Z direction; Vibration time, 5 min before the temperature cycle and 15 min after the temperature cycle.After the above-mentioned temperature and mechanical environment tests, the printed circuit board, especially the modified part of the printed circuit board, was normal in appearance inspection, and the power-on test was normal, which further proved that the modification method is reliable and effective.SummarizeThe modification of printed circuit board assembly is a job with strong uncertainty, complex and changeable state, and various process implementation routes. This requires the craftsman to brainstorm, fully consider various pros and cons, select the best from the best, and come up with the best process implementation plan. In addition, refitting is a last resort. When conditions such as development progress and funds permit, priority should be given to rearranging printed circuit boards to ensure product quality.The above is a printed circuit board modification process method introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad, including MCU, voice IC, Bluetooth IC and modules, wifi modules. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS solutions, the development of Bluetooth audio, the development of children's toys, and the development of electronic education products.
07-21

2021

Printed Circuit Board Sketch Design

The so-called printed circuit board sketch is a design drawing that can accurately reflect the position and connection of components on the printed circuit board, and refers to the basis for drawing a black and white base map. In the sketch, it is required that the position of the pads, the spacing of the pads, the interconnection between the pads, the direction and shape of the printed wires, and the overall size of the entire board, etc., should be based on the actual size of the printed board (or according to a certain The ratio) is drawn as a basis for the printed board. Drawing sketches is the key and main workload for patterning printed boards. The design of the sketch can be designed by hand or by computer-aided design. Manual design requires the design of the sketch on the drawing. Using a computer to design a printed board, although you can draw a black and white base map directly on the computer without designing a sketch on paper, the design principle of the sketch still needs to be reflected in the application process of the CAD software.Manual design is generally to accurately mark a series of requirements such as the position, size, conductive pattern, wire width and spacing of the connection pad (pad) and hole on the fixed-size grid paper, and can add text descriptions. Computer-aided design (CAD), with the help of CAD software, according to the circuit schematic diagram and wire list, the design data such as the structural parameters, electrical requirements, design rules and component catalogs of the printed circuit board are input into the computer. According to these instructions, the computer automatically completes functions such as wiring, graphics compilation, netlist generation, and design specification verification. Its structural graphics can be displayed by the terminal, and the design can be modified by human-computer interaction. After completion, a series of data tapes (disks) will be provided.Sketches usually include the following types of drawings: layout sketches, original graphics (or conductive graphics, in the form of drawings or CAD graphics data, handed over to printed circuit board manufacturers), solder mask drawings, marked character drawings, mechanical processing drawings and assembly drawings etc. The layout sketch is the key to designing a printed circuit board. According to the layout sketch, design the mechanical processing drawing, electrical assembly drawing and photographic base drawing. Design the solder resist map and mark character map (referred to as character map) according to the photographic base map.The layout sketch is a technical document that marks all the size ranges and grid positions on the printed circuit board according to the requirements of the electrical schematic diagram or logic diagram. It includes conductive patterns, component sizes and types, hole locations, and instructions necessary to manufacture printed circuit boards, which can be indicated by one or more sketches. In general, printed circuit board graphics and design data are expressed on a sketch as much as possible.1. Principles of printed circuit board sketch designOnce the prep work is done, it's time to start sketching. In addition to paying attention to dealing with various types of interference and solving grounding problems, the main principle of sketch layout design is to ensure that the printed wires do not cross the ground connection. It is not easy to do this well, and the main workload of sketch design is also to draw non-intersecting one-line diagrams. By rearranging the position of the components, the components are connected according to the circuit on the same plane, and the connections between each other cannot cross. If you encounter a cross, you need to re-adjust the arrangement position and direction of the components to solve or avoid this situation. Therefore, when designing a sketch, first draw a single-line diagram that does not intersect.1.1 Points to note when drawing non-intersecting one-line diagrams1) Components are installed on the component surface, which forms a mirror image relationship with the soldering surface, and special attention should be paid to multi-lead components.2) Printed wires have certain width and spacing requirements. The wires of discrete components are generally about 1.5 to 3.0 mm, and the wire spacing is determined by the insulation resistance and breakdown voltage between wires. When the insulation resistance exceeds 20 MΩ, the distance between the two lines is 1.5mm, the allowable working voltage is 300V, and the distance between the two lines is 1.0mm, the allowable working voltage is 220V. Therefore, when drawing a single-line non-intersecting diagram, the spacing between wires should not be too dense.3) The drawing of the schematic diagram is generally based on the principle of signal flow process and reflecting the function of components in the diagram, so as to facilitate the analysis and reading of the circuit, and never consider the size, shape and arrangement order of the lead wires of the components, so the principle There are many lines crossing in the figure. This has no effect on the reading diagram, but the crossover phenomenon is not allowed in the printed board. Therefore, in typesetting, first draw a single-line non-intersecting diagram. By rearranging the positions of the components, the connections between the components on the same plane do not cross. In case of crossing, you can rearrange the positions and directions of the components. to solve.When it is difficult to avoid wire crossing, the spacing and span of components can be appropriately increased, and the "short wiring" method can also be used. When it is really complicated, double-sided panels can be used. When drawing single lines that do not intersect, first draw with a pencil, and gradually adjust the layout until it conforms to the electrical schematic diagram.At the beginning of the design process, do not prematurely determine the arrangement position and direction of each component to solve or avoid this situation (wire crossing). In a more complex circuit, sometimes it is difficult not to cross at all. For example, in order to solve the problem that two wires do not cross, one turns around and becomes very long. This should be avoided in the design, because it not only increases the printed line. Density, and it is very likely that there will be interference in the circuit due to the length of the line. For this reason, "flying wires" can be used to solve the problem of too long printed wires, but the "flying wires" should not be too many. "Flying wire" means cutting off one at the intersection of the printed lines and connecting it with a short wire from the component surface of the board. This phenomenon is only used accidentally when it is absolutely necessary. If there are too many "flying lines", it will affect the quality of the board, and it cannot be regarded as a successful work.After the non-intersecting one-line diagram is basically finished, you can start to draw the typesetting sketch. The position and size of components are required to be roughly fixed. The printed wires are arranged, and try to be short, few, and sparse. It usually takes several iterations to adjust the position and direction of components several times to achieve a satisfactory result.In order to make a black and white base map of the printed board, a formal layout sketch should be drawn. It is required that the layout size, pad position, connection and direction of printed wires, size and position of each hole on the board, etc., must be the same as the actual layout and clearly marked. The ratio of the figure can be determined according to the density and precision of the graphics on the printed board, and can take different ratios such as 1:1, 2:1, 4:1, etc.1.2 Analysis circuit schematic diagramThe degree of analysis of technical data such as principle design ideas and the use of the whole machine determines the initiative in the process of printed circuit design. The following objectives should be achieved through the analysis of the schematic diagram.1) Find possible sources of interference in the line and sensitive components that are susceptible to interference.2) Familiarize yourself with each component that appears in the schematic diagram, master the outline size, package form, lead mode, pin arrangement sequence, function and shape of each pin, etc. of each component, and determine which components need to be installed due to heat generation Heat sink and calculate the heat dissipation area, determine which components are mounted on the board, which are off the board, etc.3) Determine the type of printed board: single-sided or double-sided. Single-sided: It is often used in discrete component circuits, because the discrete components have fewer leads and the arrangement position is easy to change flexibly. Double-sided: It is mostly used in circuits with more integrated circuits, especially dual-in-line packaged devices. Because the lead spacing of the device is small and the number is large (as few as 8 pins, as many as 40 pins or more), it is very difficult to lay out printed lines on one side without crossing, and it is almost impossible to realize more complex circuits.4) Determine the installation method, arrangement method and pad routing form of components. According to different characteristics, there are often the following corresponding relationships: horizontal installation of components → regular arrangement → circular pads, vertical installation of components → irregular arrangement → island-shaped pads.5) Determine the external connection method.2.The steps to draw a PCB sketch2.1 Drawing of a single-sided printed board sketchAccording to the size of the sketch, take graph paper or coordinate paper (there should be a certain margin).Draw the outline size of the layout, and leave a certain space under the outline to explain the technical requirements of the drawing.Leave a certain blank distance (usually 5-10mm) around the board without pads and wires. Draw each process hole on the board (including the fixing holes of each component on the printed board substrate), and the center of the process hole is generally taken at the intersection of the coordinate grid.Use a pencil to draw the outline of each component (should be drawn in the order of the position of the components on the single-line non-intersecting sketch), pay attention to make the outline size of each component correspond to the real thing, and the spacing of the components should be uniform. It is not necessary to draw outlines for small components that are used more, such as resistors, small capacitors, and low-power transistors, but you must be aware of them. Determine and mark the position of each pad. The pads with precision requirements should be marked strictly according to the size. If there is no size requirement, the components should be arranged evenly and neatly (more attention should be paid to the regular arrangement). The position of the pads should not be considered whether the pads are neat and consistent, but should be determined according to the size and shape of the components. In the end, it should be ensured that the components are evenly spaced, neat and moderately dense after assembly.For the sake of simplicity, to draw the printed wire, it is only necessary to mark the direction and path of the wire with a thin line. It is not necessary to draw according to the actual width of the printed wire, but the distance between the wires must be considered.After repeatedly checking the sketch drawn by the pencil is correct, retrace the solder joints and printed wires with a drawing pen, and wipe off the physical outline of the component after tracing to make the sketch clear.Indicate the size of the pad and the width of the wire, and indicate the technical requirements of the printed board.The technical requirements are as follows: 1) pad outer diameter, inner diameter, wire width, pad spacing and tolerance; 2) board material and board thickness; board dimensions and tolerances; 3) board coating requirements (referring to gold, silver, lead tin alloy, etc.); 4) the use of flux and flux on the board surface; 5) other specific requirements, etc.2.2 Drawing of double-sided printed board sketchIn addition to the design and drawing process of the double-sided printed board sketch above, the following points should also be considered.The components are arranged on one side (side A), and the main printed wires are arranged on the non-component side (side B). The printed wires on both sides should try to avoid parallel layout, and should try to be perpendicular to each other to reduce interference.It is best to arrange the printed wires on both sides separately. If drawing on one side, use two colors to show the difference, and indicate which side they are on. The corresponding pads on both sides should be strictly one-to-one. The method can be to lead the center of one side of the pad to the other side through the needle punching method. When drawing the wires on the component surface, pay attention to avoiding the component casing, shielding cover, etc.The printed lines that need to be connected between the two sides need to be realized with metallized holes.2.3 Precautions for circuit board sketch drawingWhen drawing a printed circuit board sketch, the following should be noted.1) Familiar with the circuit principle. The so-called familiarity with the circuit principle means knowing the composition and working principle of the circuit, such as the ins and outs of the signal, the flow of the working current, and the relationship between components and unit circuits, so as to ensure the electrical performance during wiring.2) Collect component data. In order to ensure the location, size and correct arrangement of components, the external dimensions, installation dimensions, and pin arrangement of components and accessories in the circuit should be collected as comprehensively as possible for reference when implementing wiring.3) Determine the position of the fixture. The fixing part refers to the relative position between the printed circuit board and the casing. The position of the potentiometer, variable capacitor, battery pole piece, pulley and printed circuit board fixing hole in the circuit cannot be changed arbitrarily to prevent them from being damaged after wiring. Printed line damage or rewiring For the position of the fixture, in addition to marking its shape or outline and locating its size, the solder joints should also be marked. When part of the "site" is "occupied" by the fixture, an appropriate amount of margins with a certain width should be reserved.4) Select the sketch scale and sketch proof. The sketch of the printed circuit board is the basis for making the printed circuit board. In order to make the sketch convenient and accurate, the sketch of the printed circuit board is usually enlarged than the real thing. After drawing, it will be photographed and copied and reduced to a ratio of 1:1, so that the deficiencies in the drawing can be reduced and compensated accordingly. Commonly used ratios are doubled (ie 2:1) or magnified 5 times (ie 5:1). The magnification is based on the distance between wires or pads. In order to draw accurate printed circuit board sketches, reasonable and clean wiring, and beautiful appearance, it is best to use light-colored coordinate paper. When the coordinate paper has a large grid of 10mm×10mm and a small grid of 2.5mm×2.5mm, when the ratio of 2.5:1 is selected, the large grid is equivalent to 4mm×4mm, the small grid is equivalent to 1mm×1mm, and other ratios are as follows And so on.SummarizeTo sum up, we can design a sketch of a printed circuit board that meets the requirements, and improve the PCB design process.The above is the sketch design method of the printed circuit board introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.
07-20

2021

Differential Pair PCB Design

PCB Design Points for Differential Line PairsA differential pair is a pair of coupled transmission lines. Differential signaling is done by using two output drivers to drive the differential pair, one carrying the signal and the other carrying its complement. All we need is the voltage difference between the differential pairs that carry the information to be transmitted.1. Advantages of differential signal transmissionDifferential signaling has many advantages over single-ended signaling:(1) Strong anti-interference ability, because the coupling between the two differential lines is very good, when there is noise interference from the outside world, they are coupled to the two lines almost at the same time, and the receiving end only cares about the difference between the two signals , so the external common mode noise can be completely canceled;(2) It can effectively suppress EMI. For the same reason, because the polarities of the two signals are opposite, the electromagnetic fields radiated by them can cancel each other out. The tighter the coupling, the less electromagnetic energy will be released to the outside world;(3) Timing positioning is accurate. Since the switching change of the differential signal is located at the intersection of the two signals, unlike the single-ended signal, it is judged by the high and low threshold voltages, so it is less affected by the process and temperature, and can reduce the timing error. , but also more suitable for circuit design of low-amplitude signals.For PCB engineers, the most concerned thing is how to ensure that the advantages of differential signals can be fully utilized in actual wiring. Anyone who has been in contact with PCB design will understand the general requirements of differential wiring, that is, "equal length and equal distance". But all these rules are not used to apply mechanically, and many engineers seem to have not done an in-depth analysis of the actual design process of the differential line pair. The following will focus on discussing several common points in PCB differential signal PCB design.2. Key points of differential line pair PCB design2.1 IsometricThe purpose of equal length is to make the signal transmission delay on each line the same, so as to ensure that the polarities of the two differential signals are kept opposite at all times. Any difference in time delay between the two transmission lines will make part of the differential signal become a common-mode signal, seriously affecting the signal quality. Equal length is to make the wiring length of the two signal lines of the differential line pair the same as possible. Usually, the matching requirement for equal length of high-speed differential signals is within ±10 mils. Of course, this is a relatively high requirement. The real value can be calculated by allowing signal misalignment (skew, which can be found in the chip manual) and signal transmission delay (generally 180 picoseconds per inch).Due to device layout, pin distribution, etc., most of the differential line pairs generated by direct wiring are of unequal length, which requires manual winding. Manual winding is generally performed at the chip pins to reduce the impedance discontinuity of the differential line pair.2.2 IsometricEquidistance is to ensure the continuity of differential impedance between differential line pairs and reduce reflection. Differential impedance is an important parameter for designing a differential pair, and if it is discontinuous, it will affect signal integrity. Differential impedance can be regarded as the equivalent impedance of two single-ended signal lines in series. Usually, the equivalent impedance of a single-ended signal line is 50Ω, so in general, the differential impedance should be kept at 100Ω. Equidistance is to keep the distance between the differential line pairs equal (that is, parallel wiring), so as to ensure that the differential impedance of the differential line pair does not change throughout the process.The differential impedance is related to many parameters such as the line width, line spacing, printed board stacking sequence, and dielectric constant of the differential line pair. Some of these parameters can only be provided by the printed board manufacturer. Therefore, the printed board designer should contact Manufacturers negotiate together to determine parameters such as line spacing. It is worth noting that when a differential signal is transmitted on different layers of a multilayer PCB (especially when both inner and outer layers are routed), the line spacing must be adjusted in time to compensate for the characteristic impedance change caused by the dielectric constant change of the medium. Unequal distances have less impact on signal integrity than unequal lengths. When the equal length conflicts with the equal distance rules, the equal length should be satisfied first.2.3 Lamination of differential line pairs and printed boardsThe stacking setting of the PCB board is closely related to the coupling and shielding of the signal. There is a view that differential lines provide return paths for each other, so differential signals do not need a ground plane as a return path, which is a wrong understanding. Generally, the coupling between differential traces is small, often only accounting for 10% to 20% of the coupling degree, and more is the coupling to the ground, so the main return path of the differential traces still exists on the ground plane. In PCB design, differential signals are required to be close to at least one ground plane, and it is best to be close to the ground plane on both sides. The recommended stacking method is shown in Figure 2. The signal quality decreases from left to right, but all of them meet the basic requirements.Figure 2 Common stacking methodsLike high-speed single-ended lines, differential pairs also have integrity requirements for the reference ground plane. That is, on the path that a differential line pair passes, its reference ground plane must be continuous and no divisions may occur.2.4 The distance between the differential line pair and other signalsControlling the distance between the differential line pair and other signals can effectively reduce the interference of other signals on the differential line pair and suppress EMI. We know that the energy of the electromagnetic field decreases with the square of the distance. Generally, when the distance between the differential line pair and other signals is greater than 4 times the differential line width or 3 times the differential line spacing (whichever is larger), the distance between them The influence of time is extremely weak and can basically be ignored. The formula is as follows:L>4w and L>3d, wherein, L: the distance between the differential line pair and other signals; w: the line width of the differential line; d: the line spacing of the differential line pair.Here, other signals include other differential lines, single-ended lines, signal planes, and the like. At the same time, the distance between the differential line pair and the edge of its reference plane should also be calculated according to the above method. The purpose of this is to ensure the symmetry of the two differential lines and reduce common mode noise.2.5 Termination of Differential PairsAdding termination resistors to differential line pairs is an effective way to ensure impedance matching of differential transmission lines. The control of the terminal matching resistance should be based on different logic level interfaces, to select an appropriate resistance network and parallel connection with the load, so as to achieve the purpose of impedance matching. At present, the most commonly used differential signals are LVDS and LVPECL. The following will introduce the termination methods of these two signals respectively.(1) LVDS signal: LVDS is a low-swing differential signal technology, and its transmission rate is generally above several hundred Mb/s. The driver for the LVDS signal consists of a current source that drives the differential line, typically at 3.5 mA. Generally, the termination resistor only needs to be connected in the middle of the positive and negative signals.(2) LVPECL signal: LVPECL level signal is also one of the differential signal levels suitable for high-speed transmission, and its transmission rate can reach 1 Gb/s. Each of its single-channel signals has a DC potential that is 2 V lower than the signal driving voltage. Therefore, when applying terminal matching, you cannot connect a resistor between the positive and negative differential lines, but only perform single-ended matching on each channel. ,As shown in Figure 6.It should be noted that with the development of microelectronics technology, many device manufacturers have been able to make the terminal matching resistor inside the device (you can find it in the chip manual) to reduce the work of PCB designers. At this time, the termination can no longer be performed, otherwise the signal quality will be affected instead.2.6 Other issues to pay attention toWhen designing the PCB of differential line pairs, you should also pay attention to the following issues: minimize the use of vias and other factors that cause impedance discontinuity; do not use 90° broken lines, and use arcs or 45° broken lines instead; Add ground plane isolation between differential line pairs to prevent crosstalk between each other;Don't just ensure that the total length of the traces is equal, but try to make each section of the traces equal (for the division of impedance discontinuities, such as sockets); if not necessary, try not to add test pads on the differential lines.SummarizeDue to its excellent performance, the differential line pair has gradually become a common method in the design of high-speed digital circuits. In high-speed digital PCB design, the use of differential line pairs to transmit high-speed signals, on the one hand, is of great benefit to the signal integrity and low power consumption of the PCB system, and on the other hand, it also puts forward a higher level for PCB designers. Require. As a PCB design engineer, we should have a deep understanding of the relevant concepts of transmission line theory, carefully analyze the causes of various distortion phenomena, and find out reasonable and effective solutions; we must continue to summarize some of the experience accumulated in the work in order to achieve satisfactory design results. .The above are the key points of PCB design for differential line pairs introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.
07-18

2021

Common SMT Design Questions

Although SMT has been used in our country for more than 20 years, due to various reasons, in some enterprises that design and produce multi-variety and small-batch products, PCB designers are still unfamiliar with SMT production equipment and processes, and cannot Good application of PCB design specifications and situations where the concepts of manufacturability are vague. As a result, there is a lack of practical experience in the selection of manufacturing process, selection of components and PCB materials, pad design, PCB layout design, thermal design, stress design, and testability design when actually designing products, and repeated revisions are required. or redesign.The hidden dangers of quality defects caused by bad design in SMT manufacturing are very large. If the PCB layout design does not meet the specification requirements, it will cause poor manufacturability, increase the process flow and process difficulty, affect equipment utilization, reduce production efficiency, and waste man-hours. Delaying the construction period, the most serious thing is that it will cause a large number of welding defects, which will inevitably lead to PCBA repairs. We know that rework will bring hidden dangers to quality, and may damage components (some components are irreversible) and printed circuit boards, directly affecting product reliability. In the worst case, it will lead to revision or redesign, prolonging the actual product development cycle.Common problems in SMT printed circuit board design are: no design reference mark, PCB process edge, PCB shape and size; unreasonable component layout; incorrect pad structure size; incorrect via hole design; solder mask and The silk screen is not standardized; the PCB material, thickness and width dimension ratio are not suitable; the PCB shape is irregular and not made into a jigsaw board, etc. The following will explain one by one and put forward the correct design requirements while analyzing the problem.1. Bench markFiducial marks are used to correct errors caused by PCB processing and deformation, as well as for PCB positioning and component positioning. In the whole SMT process flow, the relevant automation equipment needs to use the reference mark set on the PCB light board for accuracy calibration, such as: placement machine, silk screen printing machine, AOI, flying probe tester and automatic rework station, etc. Some PCBAs in production are assembled online without setting the benchmark mark. We know that in addition to standard shape fiducial marks, screen printing machines and placement machines can also use through-hole device soldering rings, soldering holes, and mounting device pads as fiducial marks. Many problems will cause batch repairs. It is recommended that as long as the PCB with SMD devices is wiring, the upper reference mark should be set.2. PCB process sideThe PCB should leave a certain edge to facilitate the clamping of the equipment, that is, the process edge. Generally, along the direction of PCB welding transmission, two sides should leave at least 5 mm of process side, and components and pads are not allowed to be placed within this range. Generally, the process side can be arranged on a pair of long sides.3. PCB size is too smallIn order to improve the placement efficiency, when the PCB size is less than 70 mm × 70 mm, it should be designed as a jigsaw board, and some special-shaped boards also need to be jigsawed. As shown in Figure 1, after the board passed the review of the design specifications, a panel was made, but the process side was added to the short side, and the process side should be added to the long side direction, that is, the direction of the SMT production line clamping transmission. Suggestion: When the material level of the placement machine and the feeder are sufficient, put the top surface and bottom surface of the PCB on the same side, which can save the production cost of a steel mesh and reduce the time for replacing the placement program once; Combine multiple PCBs in one project into the same large board. This can greatly improve placement efficiency and finished product efficiency.4. Pad width sizeIf the pad width is too small, the soldering surface of the pins will be small, the amount of solder will be small, the strength of the solder joints will be insufficient, and the resistance to vibration and electrical conductivity will be poor. Aerospace and military products require that the width of the pad should be the same as or 1.1 times the width of the component pins, and civilian products can be reduced by 0.9 times under the limitation of high-density wiring.5. Placement of componentsWhen the components are close to the edge of the printed board, there will be the following problems: (a) It is not conducive to automatic assembly; (b) Mechanical stress concentration; (c) Easy to damage during turnover; (d) Metallized holes and pads are easy to be pulled hurt. It is generally required that components are not allowed to be placed within 3 mm from the process edge, clamping edge or printed board edge. When placing components near the edge of the printed board, the long side of the component should be parallel to the edge of the printed board. For chip ceramic capacitors, after high temperature aging or use for a period of time, it will be found that their failures have a common feature, mostly located near the edge of the panel, screws and sockets. close to the edge of the PCB, as shown in Figure 4.6. Component placement directionA certain maintenance space should be reserved around large devices to facilitate the operation of the heating head of the repair equipment. When placing components near the edge of a large device, the long side of the component should be parallel to the edge of the device.7. Location of key and valuable componentsThe proximity of critical and valuable components to areas of high stress concentration can easily lead to solder joint fatigue or solder joint fracture. Do not place it on the corners and edges of the PCB, nor near connectors, mounting holes, slots, cuts, gaps, and corners of the panel. As shown in Figures 9 and 10. BGA device inspection generally adopts non-destructive X-ray inspection method.8. ViaVias are not allowed on pads. Vias on the pads will cause the solder to melt and leak into the metallized hole or the bottom layer through the via holes during soldering, causing defects such as too little solder in the solder joints, virtual soldering, tombstones, and thermal stress. Vias are generally not set under the device. When the device package is smaller than 0805, it is easy to cause a short circuit; when the via is solder masked, the thicker solder mask will hold up the device, causing desoldering, tombstone and virtual soldering, etc. .9. Wing pin design requirementsThe soles of the wing pins should all sit on the pads. Ensure that a solder joint is formed at the heel of the pin, that is, the main solder joint. Whether the solder joint is formed here is the key point to ensure the welding strength of this type of pin. Ensure that the solder pad extends more than 0.3 mm from the toe of the pin.10. BGA layout requirementsEarly design specifications do not recommend placing BGA devices on both sides, but the demand for thin and light electronic products is becoming more and more urgent in practical applications. For example, in the case product, 10 BGA devices are installed on the top surface of the PCB, and 6 BGA devices are installed on the bottom surface of the PCB. It has become the norm to place BGA devices on both sides. The temperature cycle life of the solder joints in the PCBA assembly state has a lot to do with the assembly density, especially when the array terminals are assembled at the same position on both sides of the PCB, the life of the joints will be reduced by about 50%.11. Electrical connector aperture ratioThe aperture ratio of the electrical connector should be set reasonably. The large aperture ratio leads to a large gap between the hole wall and the pin, and it is easy to cause a short circuit through tin when soldering. For special cases, such as the J30J micro-rectangular electrical connector, the minimum welding gap is 0.136 mm, which is smaller than the minimum safety gap of 0.2 mm for through-hole device welding. It is easy to cause tin connection during soldering. An oval hole can be set to increase the gap between the two pads. The gap can reach 0.25 mm, which can effectively prevent short circuit during welding.Process summaryAccording to the actual application experience, the following 8 measures are adopted, and the standardization of PCB design can be quickly, comprehensively and effectively applied within the enterprise, eliminating bad design and realizing manufacturability design.(1) Formulate internal PCB design specification standards (or guidelines) and review systems;(2) Set up the post of PCB design specification process designer in the enterprise;(3) Purchase professional PCB design specification software tools;(4) Establish training plans and files for PCB designers, and confirm that all PCB designers have undergone manufacturability design training;(5) Make full use of the internal network of the enterprise, establish a fast and effective way to obtain PCB design standard information, and establish a fast and effective implementation process for feedback, approval and approval of PCB design issues;(6) Establish a PCB design defect case library, which is a green channel for different designers and craftsmen to obtain and update in daily work;(7) Effective communication and collaboration between PCB designers and SMT processing plants; (8) SMT processing plants provide timely feedback to customers, and continuously improve and perfect product PCB design.The above are the common problems and solutions of SMT printed circuit board design introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad, including MCU, voice IC, Bluetooth IC and modules, wifi modules. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS solutions, the development of Bluetooth audio, the development of children's toys, and the development of electronic education products.

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