PCB board rapid manufacturing system

Rapid Manufacturing System of PCB Board Based on Laser Direct Writing Circuit Technology

The research and development of new electronic products needs to go through the process of product design, production processing and debugging, among which, the design and manufacture of PCB board is one of the most critical links. Most components can be purchased in the market as finished products, and PCB boards must be designed and manufactured according to different products; therefore, the cycle length of PCB board design and manufacturing has a great impact on the development cycle of new products.

At present, according to the production process of the PCB board factory, even if only one sample PCB board is produced, it is the same as the process flow of producing a large number of PCB boards, which requires data preparation, light drawing, blanking, drilling, metallized holes, etc. Film or screen printing, exposure, graphic plating, etching, solder resist coating, tin spraying, silk screen characters, appearance processing and cleaning, etc. Dozens of processes. In this production mode, it usually takes at least a few days to a week from the confirmation of the PCB design documents by the designer and the PCB manufacturer to the final completion of the PCB manufacturing. This process can meet the production cycle needs of batch products, but it is not suitable for the production of sample PCB boards. In the stage of the first prototype, in view of the fact that there will always be some uncertain risks in technology, the design and commissioning time of the product is uncontrollable, and problems often arise in design, commissioning, design modification, and commissioning. In this case, Prototype PCB manufacturing cycles of several days are unacceptable.

In order to solve the problem of a long production cycle of a single sample PCB board, a rapid manufacturing system for PCB boards has been developed in recent years, which can complete the manufacture of sample PCB boards within 1 working day at the fastest. This paper introduces and compares the three common PCB board rapid manufacturing systems at present, and gives the process technology of the PCB board rapid manufacturing system based on laser direct writing circuit technology.

1. PCB board rapid manufacturing system

The common process steps of the PCB rapid manufacturing system are as follows: 1) Drilling and metallization holes; 2) Making circuit graphics; 3) Making solder resist graphics; 4) Making character graphics; 5) Soldering anti-oxidation treatment. Among them, the key steps that affect the quality of the finished PCB board are the production of metallized holes and circuit graphics.

PCB board rapid manufacturing system can be divided into three categories according to the working principle of circuit graphics production: chemical etching, physical engraving and laser direct writing processing.

1) Chemical etching. The chemical etching method is to use a chemical etching solution to remove the insulating material that needs to be removed from the substrate to produce a suitable circuit pattern. The chemical etching method has a certain impact on environmental protection due to the use of a series of acid and alkali reagents, and there are many chemical etching processes, the process is relatively complicated, and it is more difficult to implement than the other two methods, so it is not the main promotion now. Way.

2) Physical engraving. The principle of the physical engraving method is to convert the line information of the circuit board into three-dimensional position information, and then control the engraving tool to move along the XYZ axis guide rail through the stepping motor, so as to control the engraving tool to carve on the blank circuit board. According to this method, the production time of a typical double-sided circuit board is about 1 to 2 hours, and a sample PCB board can be made within 1 day; The processing cannot be well guaranteed. For example, when the hole diameter is less than 150 μm, the processing cost will be greatly increased due to the fragility of the mechanical drill bit, and the processing progress will also be affected.

3) Laser direct writing. The principle of laser direct writing is to select lasers of different wavelengths according to the different materials of the object to be processed, and use high-power laser beams to irradiate the surface of the material to cause a photochemical reaction on the surface of the material, and finally process the desired circuit pattern. Compared with the physical engraving method, because of the high energy density of the laser beam and the fast processing speed during the processing, it basically has no effect on the non-laser irradiated parts, and there is no mechanical contact with the processed parts, so laser processing will not affect the processed material. Mechanical stress, at the same time, the metal layer can be removed cleanly and without residue, and the circuit pattern can be processed.

2. Laser direct writing circuit technology

Laser direct writing circuit technology is a technology that uses the principle of laser direct writing to process the required circuit patterns on the copper-clad layer or gold-plated layer of the PCB.

At present, the most advanced laser processing equipment on the market mainly uses lasers with two spectrums of green light or purple light for processing, and it is already possible to completely use laser direct writing technology to complete the production of circuit graphics. The metal layer can be removed quickly with a single laser beam without any mask during processing. Especially based on the 355nm ultraviolet laser, most of the materials that make up the PCB board substrate can be processed, including copper, polymer resin materials and glass fibers.

The thermal shock to the material is smaller by using the ultraviolet laser.

The ultraviolet laser has high photon energy. When the ultraviolet laser is irradiated on the surface of the processed material, the molecules on the surface of the material absorb the photons in the ultraviolet laser, interact with their own electrons, and directly destroy the chemical bonds connecting the atomic components of the material, breaking the molecular chain. The broken small molecules are ejected strongly outwards in the form of an explosion, breaking away from the surface of the material.

The use of laser processing has great advantages in the stability of processing accuracy and the operation and maintenance of later equipment. The theoretical use time of the laser generator, the core component of the laser processing equipment, is usually 100,000 hours, and the actual service life is generally more than 5 years; the laser beam emitted by the laser generator can maintain a relatively stable state for a long period of time In this way, the inconsistency of processing accuracy caused by the wear and tear of milling cutters and drills in traditional physical engraving methods can be avoided; in terms of daily maintenance of equipment, laser processing equipment only needs to be dust-proof and clean, and does not need to be lubricated And other operations can greatly reduce the maintenance costs of later equipment operation.

3. PCB board process technology

3.1 Drilling

In terms of drilling, there are three methods of using ultraviolet laser to process holes: laser punching, laser trepanning and laser spiral processing.

1) Laser punching. The process method is to keep the position of the laser beam unchanged, set a high repetition rate laser pulse, and continuously process the position of the hole. The pulse frequency of laser processing equipment can generally be set to 250-300kHz, and the depth of the hole will increase at each pulse width. In this process, the size of the hole depends on the focused spot size. The focus spot diameter of ultraviolet laser processing equipment can be as small as 15μm, so this process can complete the processing of smaller diameter holes, especially suitable for the processing of blind holes.

2) Laser perforation. The process method is to set the laser beam at the position of the hole, and make a circular motion around the outer circumference of the hole. After the first round, a circular groove will be machined at the position of the outer circumference of the hole. Every time you walk around, the depth of the groove will increase a little. When processing from the top of the PCB to the bottom, after the bottom is pierced, the material of the cylinder connected to the bottom will fall off during processing, forming a through hole. This process method is suitable for processing through holes, but not suitable for processing blind holes, because if the hole is not pierced, the cylindrical material in the center area of the hole will remain in the middle of the hole during processing.

3) Laser spiral processing. The process method is to set the laser beam to start processing from the center of the hole and move outward from the center in a spiral manner. As the laser beam moves, the depth and diameter of the hole grows. This process method is suitable for processing large-sized holes.

In actual processing, the above three process methods can be selected according to the type and size of the hole, and the copper on the surface layer can be directly removed by adjusting the laser pulse frequency and energy, and then the lower layer material can be removed. Compared with other lasers, the bottom of blind holes processed by ultraviolet laser is cleaner and free from carbonization, which provides a good surface treatment for post-process metallized holes.

In view of the characteristics of laser processing, it has considerable advantages in processing micro-holes and blind holes. However, in actual production, for PCB boards with a thickness of more than 0.5mm, when processing through holes with a diameter of more than 0.8mm, the efficiency of drilling with laser equipment is not as high as that of drilling with physical engraving machines; For PCB boards with a thickness > 0.5mm, it is preferable to use a physical engraving machine for drilling.

3.2 Metallized holes

After the hole is formed, metallized hole treatment is required to achieve the effect that the hole is metallized and penetrated. Metallized holes should have good mechanical toughness and electrical conductivity. There are two methods of metallized holes: physical metallized holes and chemical metallized holes.

1) Physical metallization holes. The principle is to use conductive paste to make the holes conduct electricity. The minimum diameter of the through hole that the system can process is 0.4mm, and the maximum diameter-to-depth ratio of the hole is 1:4. The contact resistance after the metallized hole is about 20mΩ. The technological process of physical metallization holes is as follows: a. Paste the special protective film on both sides of the PCB board; b. Use laser processing equipment to drill holes (for through holes with PCB board thickness > 0.5mm and hole diameter > 0.8mm, physical engraving machine drilling can be given priority); c. Place the PCB board on the vacuum adsorption table, and use a rubber scraper to apply the conductive paste on the protective film on one side of the PCB board by brushing; d. Turn on the vacuum adsorption function, and suck the conductive paste into the hole under the action of vacuum; e. Flip the PCB board, repeat steps c and d; f. Remove the protective film, and cure the conductive paste in an oven with a curing temperature of 160°C and a curing time of 30 minutes. The advantage of physical metallized holes is that it is easy to operate, does not need to use electroplating process, and does not use chemicals in the process, which is more environmentally friendly; but the penetration reliability of metallized holes is not as good as that of chemical plating process.

2) Chemically metallized holes. The principle is the principle of electroless plating. The process is divided into four basic steps: pre-dipping→activation→microetching→electroless copper plating. The details are as follows: a. The pre-soaking process can choose a solution whose main chemical composition is 5% Na2CO3. Under heating conditions, it can remove sweat stains, oil stains, etc. produced by the PCB board in the previous process; b. The black hole liquid can be used in the activation process, and its main chemical liquid composition is C (graphite) particle solution. The main function of this solution is to complete the uniform layer of conductive carbon film on the inner wall of the hole; c. 5% Na2S2O8 solution can be used in the micro-etching process, which mainly completes the dissolution of carbon black on the surface of the base material after black holes; d. The electroless copper plating process can choose a CuSO4 solution whose main chemical composition is 10%. The main function of this solution is to serve as a conductive substance for electroplating to realize metallized holes. At present, the more advanced desktop chemical metallization hole equipment has optimized the anode plate and added a reverse pulse electroplating power supply. The combination of these two technologies can effectively ensure the uniformity of electroplated copper thickness.

3.3 Line graphics production

In terms of circuit pattern forming and processing, the use of ultraviolet laser equipment can realize direct writing of circuit patterns on the metal coating layer of PCB boards. In actual production, setting a laser beam with short pulse time and high pulse energy has less thermal shock effect on the circuit, and has a better effect on processing fine-pitch circuits and radio frequency microwave circuits.

3.4 Production of solder mask graphics and character graphics

The solder mask layer is a protective film with a specific pattern formed on the surface of the PCB board during PCB board production. The production principle of solder resist graphics and character graphics is to use screen printing ink to the surface of the PCB board, and then use heating to cure it. The specific process steps are as follows: printing photosensitive solder resist ink→solder resist graphic exposure→solder resist graphic development→printing photosensitive character ink→character graphic exposure→character graphic development→solder resist and character ink thermal curing.

When printing ink, the PCB board rapid manufacturing system does not use the method of making a screen mold, but uses a laser printer to directly print the photosensitive material into the film sheet required for printing ink. This does not require the waiting time (usually 1d) for making the screen mold, thus greatly shortening the production cycle, and the whole process can be completed within 1 to 2 hours.

3.5 Flux anti-oxidation treatment

The principle of soldering anti-oxidation treatment is to use chemical reagents to react with the copper surface, and an organic film layer of a certain thickness can be formed on the bare copper. The organic film layer can effectively isolate the pad of the copper layer from the air, prevent the pad from being oxidized, and ensure soldering performance. The process can be completed within 1 to 2 hours through four simple operations, that is, degreasing → micro-etching → pickling → film formation, as follows.

1) The degreasing process can choose a solution whose main chemical composition is 5% Na2CO3. Under heating conditions, it can remove sweat stains and oil stains on the PCB board in the previous process.

2) A 5% Na2S2O8 solution can be used in the micro-etching process, and a rough copper surface can be formed after micro-etching, which is convenient for film formation. The thickness of the microetch directly affects the film formation rate, so to form a stable film thickness, it is very important to maintain the stability of the microetch thickness. Generally, it is more appropriate to control the microetch thickness at 1.0-1.5 μm.

3) The pickling process can use 1% dilute H2SO4 solution, the main purpose is to remove the oxides that may be produced by the PCB board due to contact with air in the previous process.

4) OSP organic reagent can be used in the film forming process. The solution can form a layer of hydrophobic organic protective film with a thickness of 0.3-0.4 μm on the copper surface through chemical reaction. This film is used to protect the copper surface in the normal environment. It will no longer continue to oxidize, and at high welding temperatures, the protective film is easily removed by flux, and can form a firm solder joint with molten tin in a very short time.

The solderability of PCB boards treated in the above way can be preserved for up to 3 months if they are stored in vacuum packaging. After the extended period, the solderability of the pad will decrease.

epilogue

The PCB board rapid manufacturing system based on laser direct writing circuit technology solves the problem of insufficient precision of physical engraving; and because it adopts non-contact processing, there is no mechanical stress on the PCB board, which can further improve the reliability of the circuit. It is a good choice for making sample PCB boards. It should be pointed out that the PCB board processed by this system can not guarantee the quality reliability in a long period of time because it has only undergone simple soldering anti-oxidation treatment, so it is only suitable for the verification of the design scheme, and cannot be used. For formal industrial product delivery.

The above is the PCB board rapid manufacturing system based on laser direct writing circuit technology 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.