This paper reviews the development of screen printing applied to the production of printed circuit boards, and lists the progress of screen printing machinery in the past ten years. Among them, some domestic PCB printing materials are introduced in detail. It is pointed out that only the innovations of screen printing materials, equipment and processes can enable them to expand into high-tech fields and have an advantage in PCB manufacturing. The current PCB process defects and new processes are also discussed.
Keywords screen printing printed circuit board printing Abstract This paper reviews the developing course of screenp rintingused in PCB production and the progress of screen printing materials and equipment during the past ten years. Some China made PCB printing pastes are discussed in detail. It points out that only only by creating new materials, equipment and processes, can screen printing grow into high-tech field and occupation a dominant position in PCB industry. It also expounds some shortcomings inpresent PCB process and some new tentative ideas about process are offered.
First, on the printed circuit board to understand the printed circuit board (PrintedCircuitBoard referred to as PCB) First of all to understand what is printed circuit and printed circuit.
A printed circuit is a conductive pattern that provides electrical connections between components on an insulating substrate. It does not include printed components.
The so-called printed circuit refers to a conductive pattern that is made of a printed circuit, a printed component, or a combination thereof formed on an insulating substrate according to a predetermined design.
Printed circuit or printed circuit board called PCB.
PCB is an important basic electronic component in the electronics industry. Almost every type of electronic device, from electronic watches and calculators to giant electronic computers, telecommunications electronic devices, and space vehicles that run hundreds of millions of times per second, as long as there are electronic components such as integrated circuits, for the sake of electrical Interconnections are inseparable from the PCB. It can be said that in the development of all electronic products, especially intelligent electronic products, the most basic success factor is the PCB design, documentation and manufacturing technology of the product.
The PCB has the following functions in various electronic devices.
1) Provides mechanical support for fixing and assembling various electronic components such as integrated circuits.
2. Implement wiring, electrical connection, or electrical insulation between various electronic components such as integrated circuits. Provide the required electrical characteristics, such as characteristic impedance.
3) Provides solder mask patterns for automatic soldering to provide identification characters and graphics for component insertion, inspection, and repair.
After the electronic device adopts the PCB, due to the consistency of the same type of PCB, the error of manual wiring is avoided, and the automatic insertion or mounting of the electronic components, the automatic soldering, and the automatic detection can be realized. It ensures the quality of electronic equipment, improves labor productivity, reduces costs, and facilitates maintenance.
PCBs have evolved from single-sided to double-sided, multi-layered and flexible, and still maintain their respective development trends. Due to the continuous development of high-precision, high-density, and high-reliability, and constantly reducing the size, cost, and performance, PCBs still maintain a strong vitality in the future development of electronic devices. Second, screen printing in the production of printed circuit boards 1 "Intimidation" inspiration Screen printing can enter the PCB industry, has experienced a very tortuous process. Before the 1990s, for about 20 years, the PCB industry did not have a "good impression" of screen printing. At that time, PCB experts and scholars concluded that silk screen printing is "silk screen printing is not suitable for precision PCB manufacturing." . For example, the book "Printed Circuit Technology" published by Science Press (first edition, May 1987, Beijing) wrote: "The screen miss printing technology is suitable for resolution and dimensional accuracy requirements are not too high." "Printing - etching" and graphic electroplating manufacturing of printed boards." Realistically, screen printing at that time really did not have the ability to provide services for precision PCB production. For example, in the 1970s, the author used screen printing to produce PCB solder resist patterns, and the hardships he had made when making solder mask printing plates were still fresh. At that time, because there was no good plate-making material (such as screen-printing adhesive) on the market, we had to make a solder mask printing plate with the film transfer method. The process of making a solder mask printing plate by the film transfer method is briefly described below.
(1) A positive-working photographic negative film obtained by a photographic method and having a solder resist pattern.
(2) Preparation of PVA (polyvinyl alcohol) liquid photosensitive resist (glue).
(3) Apply PVA photoresist to the copper-clad board (PCB substrate) by centrifugal chucking.
(4) Exposure→Development→Film→Retouch→Etching.
Note: (1) ~ (4) for the traditional PCB manufacturing process.
(5) Spray paint several times until the recessed area on the copper-clad board is filled with the paint film (the paint film on the copper-clad board should be removed).
Note: (1) ~ (5) is actually a template for solder mask printing plates.
(6) Squeeze the stencil of the sprayed lacquer (pattern needs to be trimmed) tightly to the screen mesh plate, and quickly wipe with the solvent (turpentine) on the squeegee surface of the screen plate until the paint film on the solder mask plate is completely transferred. To the screen version.
(7) During the transfer process of the paint film, the paint film is difficult to be completely transferred to the screen plate. Therefore, the transferred screen pattern (paint film) needs to be trimmed, and this trimming method will make the solder mask. The accuracy of the graphics is greatly impaired.
Above, the author only briefly introduced the production process of the solder mask printing plate. The complications, inefficiency, high cost, and high labor intensity have already taken hold on the paper, and this process is used in PCB manufacturing. Hard to accept by PCB workers, it is impossible to make screen printing stand in the PCB manufacturing industry. Because of this, the status of screen printing in the PCB manufacturing industry is not only low but also at stake. In the late 1970s, when the dry film of solder mask was introduced, the process of making PCB solder resist patterns by screen printing was naturally left out of the PCB manufacturing industry.
In addition to the “low energy†exhibited in the production of PCB solder masks, screen printing has also had fierce collisions with other PCB fabrication processes during the fabrication of PCB resist patterns. During the 1960s and 1970s, there were protein gels, bone glues, and PVAs for PCB resists. Red glue (a mixture of iron oxide and rosin) must be used when using protein glue. Therefore, the process is extremely complicated and is rarely used. Bone gum has an unpleasant odor, is prone to mildew, is prone to moisture, and is therefore difficult to develop, especially in humid climate conditions. In addition, the glue film after the photocured bone glue easily falls off after absorbing moisture, thus limiting its use. In the early to mid-70s, PVA was the most widely used PCB resist. Later, DuPont's anti-corrosive dry film and domestic anti-corrosive dry film were put into operation. The resists in PCB manufacturing are basically PVA and resist. Dry film. During this period, screen printing has also tried to squeeze into the process of making PCB resist patterns. It should be certain that this idea was worthy of praise at the time. However, screen printing actually has a poor record in this “battlefieldâ€. The reason is mainly due to the unsuccessful resist printing materials. The main component of the anti-corrosion printing material in the initial stage was bitumen (adding a little solvent). Although this kind of printing material has good anti-corrosion properties, it has serious pollution to the copper-clad board and the environment and affects the health of operators. Such serious defects make the process of making resist patterns by screen printing unfavorable, and PCB workers prefer to use PVA or dry film.
Recalling the tortuous course of the application of screen printing in the PCB manufacturing technology, we can deeply feel that in an seemingly inadvertent atmosphere, various application technologies including screen printing are fiercely collided in the PCB manufacturing process. In this collision, whether to squeeze in or be squeezed out, all to see their own strength. The reason why screen printing in this period was in a tragic situation was that it was too poor and inferior. Screen printing, if you want to stand firm on the heel of PCB manufacturing and strive for greater achievements, you must practice “inner strength†and create advantages. Without strong technical advantages, you will not be able to squeeze even if you are squeezed. Only you may be mercilessly squeezed out. 2 î€ î€ î€ â€œ 内 内 内
As an old PCB worker and old screen printer worker, I deeply understood whether the acceptance of screen printing in PCB manufacturing technology depends entirely on whether screen printing has excellent screen printing materials and good processability. The tremendous progress of screen printing technology in the past decade has forced PCB workers to re-learn and gradually love and inseparable from screen printing. The development in recent years has made screen printing a good process adaptability and has become a controllable and easily controllable production process. Below we briefly introduce the progress of screen printing machinery in the past decade.
(1) Screen Printing Wire mesh screen is the most important part of screen printing. This is because it controls the flow and ink consumption of the ink. At the same time, it also determines the durability and quality of the screen, which determines the quality of the printing. In the past ten years, people can see high performance screen printing screens with good performance in the market, especially high-binding, high-tension, monofilament, flat-woven polyester (PET) screens. The introduction of a flat weaving screen with a diameter of 27 μm and up to 150 lines per cm has changed people's understanding of some important factors in printing, such as precision screen printing SMT technology, integrated circuit manufacturing technology, film Switch manufacturing technology, etc. have been confirmed. In addition, the excellent cross-linking properties of screens and screen-sensitive adhesives or photosensitive films are also an important factor in the production of high-quality screen printing plates. In order to ensure a good combination of screens and screen-printing materials, traditional The approach is to emphasize that plate-making operators must do a good job of pre-processing the already-stretched wire mesh. It includes the mechanical roughening of the new wire mesh and appropriate degreasing treatment. Currently, there is no need for roughening on the market. High-tension/high-bonding screens for fat-removal treatment are sold. This product not only saves time and simplifies the advantages of the process. The screen is more durable and its life is 2 to 3 times longer than ordinary screens. At the same time, in the development and research of new screens, we also noticed that the screens are wear-resistant, have high resolution, have a wide exposure time limit, and have excellent matching characteristics with photosensitive materials. The new screens have been commercialized in the domestic market. It is very easy to buy.
(2) Screen-type photosensitive materials Today, we can purchase many high-resolution screen-sensitive or photosensitive films in the market, especially water-based photosensitive films (direct-printing photosensitive films). The process is simple and the film thickness is uniform and controllable. In particular, the water-based photosensitive film with a film thickness of 80 to 140 μm can be used in some special applications. At the same time, it also provides a new field for screen printing. Reliable material base.
According to the latest screen printing information, U.S. Edeleon recently introduced a 400-μm-thick photosensitive film for various electronic applications and high-density textile printing.
(3) screen printing materials (ink)
The progress of screen printing materials, especially the development of functional inks, not only benefits ordinary screen printing (for example, UV inks never block mesh), but it also directly leads to screen printing technology and products. High-tech. For example, conductive silver paste printing in a thin film switch; solder paste (lead tin alloy) for interconnecting SMD, SMC (chip component) and PCB in SMT technology; semiconductor layer CdS (cadmium sulfide) in solar battery, CdTe (cadmium telluride) and screen printing of electrode layer carbon (C), silver (Ag), silver + indium (Ag + In), magnetic ink, thick film IC ink, and the like. As far as PCB printing materials are concerned, the quality and printing process of PCB printing materials today is truly different from that of 20 years ago. Table 1 shows the use and characteristics of some PCB inks. Table 1 Uses and Features of PCB Ink Variety Uses and Features Dilute alkaline developing liquid resist LPR-ER is used for multilayer PCB inner layer production and high-precision high-frequency PCB graphic production. The minimum wire diameter can reach 30μm or less. Short exposure time, rapid development, easy release, corrosion resistance, excellent resistance to plating, easy to operate UV curable liquid resist UR-ER is mostly used for single-panel and non-metallized hole PCB graphics production. Curing speed, corrosion resistance, excellent plating resistance, easy stripping, dense protective film, no penetration in the etching solution dilute alkali developing solder mask ink LPR-SRGLPR-SRM for high-density PCB insulation protection. High development accuracy (40μm)
Keywords screen printing printed circuit board printing Abstract This paper reviews the developing course of screenp rintingused in PCB production and the progress of screen printing materials and equipment during the past ten years. Some China made PCB printing pastes are discussed in detail. It points out that only only by creating new materials, equipment and processes, can screen printing grow into high-tech field and occupation a dominant position in PCB industry. It also expounds some shortcomings inpresent PCB process and some new tentative ideas about process are offered.
First, on the printed circuit board to understand the printed circuit board (PrintedCircuitBoard referred to as PCB) First of all to understand what is printed circuit and printed circuit.
A printed circuit is a conductive pattern that provides electrical connections between components on an insulating substrate. It does not include printed components.
The so-called printed circuit refers to a conductive pattern that is made of a printed circuit, a printed component, or a combination thereof formed on an insulating substrate according to a predetermined design.
Printed circuit or printed circuit board called PCB.
PCB is an important basic electronic component in the electronics industry. Almost every type of electronic device, from electronic watches and calculators to giant electronic computers, telecommunications electronic devices, and space vehicles that run hundreds of millions of times per second, as long as there are electronic components such as integrated circuits, for the sake of electrical Interconnections are inseparable from the PCB. It can be said that in the development of all electronic products, especially intelligent electronic products, the most basic success factor is the PCB design, documentation and manufacturing technology of the product.
The PCB has the following functions in various electronic devices.
1) Provides mechanical support for fixing and assembling various electronic components such as integrated circuits.
2. Implement wiring, electrical connection, or electrical insulation between various electronic components such as integrated circuits. Provide the required electrical characteristics, such as characteristic impedance.
3) Provides solder mask patterns for automatic soldering to provide identification characters and graphics for component insertion, inspection, and repair.
After the electronic device adopts the PCB, due to the consistency of the same type of PCB, the error of manual wiring is avoided, and the automatic insertion or mounting of the electronic components, the automatic soldering, and the automatic detection can be realized. It ensures the quality of electronic equipment, improves labor productivity, reduces costs, and facilitates maintenance.
PCBs have evolved from single-sided to double-sided, multi-layered and flexible, and still maintain their respective development trends. Due to the continuous development of high-precision, high-density, and high-reliability, and constantly reducing the size, cost, and performance, PCBs still maintain a strong vitality in the future development of electronic devices. Second, screen printing in the production of printed circuit boards 1 "Intimidation" inspiration Screen printing can enter the PCB industry, has experienced a very tortuous process. Before the 1990s, for about 20 years, the PCB industry did not have a "good impression" of screen printing. At that time, PCB experts and scholars concluded that silk screen printing is "silk screen printing is not suitable for precision PCB manufacturing." . For example, the book "Printed Circuit Technology" published by Science Press (first edition, May 1987, Beijing) wrote: "The screen miss printing technology is suitable for resolution and dimensional accuracy requirements are not too high." "Printing - etching" and graphic electroplating manufacturing of printed boards." Realistically, screen printing at that time really did not have the ability to provide services for precision PCB production. For example, in the 1970s, the author used screen printing to produce PCB solder resist patterns, and the hardships he had made when making solder mask printing plates were still fresh. At that time, because there was no good plate-making material (such as screen-printing adhesive) on the market, we had to make a solder mask printing plate with the film transfer method. The process of making a solder mask printing plate by the film transfer method is briefly described below.
(1) A positive-working photographic negative film obtained by a photographic method and having a solder resist pattern.
(2) Preparation of PVA (polyvinyl alcohol) liquid photosensitive resist (glue).
(3) Apply PVA photoresist to the copper-clad board (PCB substrate) by centrifugal chucking.
(4) Exposure→Development→Film→Retouch→Etching.
Note: (1) ~ (4) for the traditional PCB manufacturing process.
(5) Spray paint several times until the recessed area on the copper-clad board is filled with the paint film (the paint film on the copper-clad board should be removed).
Note: (1) ~ (5) is actually a template for solder mask printing plates.
(6) Squeeze the stencil of the sprayed lacquer (pattern needs to be trimmed) tightly to the screen mesh plate, and quickly wipe with the solvent (turpentine) on the squeegee surface of the screen plate until the paint film on the solder mask plate is completely transferred. To the screen version.
(7) During the transfer process of the paint film, the paint film is difficult to be completely transferred to the screen plate. Therefore, the transferred screen pattern (paint film) needs to be trimmed, and this trimming method will make the solder mask. The accuracy of the graphics is greatly impaired.
Above, the author only briefly introduced the production process of the solder mask printing plate. The complications, inefficiency, high cost, and high labor intensity have already taken hold on the paper, and this process is used in PCB manufacturing. Hard to accept by PCB workers, it is impossible to make screen printing stand in the PCB manufacturing industry. Because of this, the status of screen printing in the PCB manufacturing industry is not only low but also at stake. In the late 1970s, when the dry film of solder mask was introduced, the process of making PCB solder resist patterns by screen printing was naturally left out of the PCB manufacturing industry.
In addition to the “low energy†exhibited in the production of PCB solder masks, screen printing has also had fierce collisions with other PCB fabrication processes during the fabrication of PCB resist patterns. During the 1960s and 1970s, there were protein gels, bone glues, and PVAs for PCB resists. Red glue (a mixture of iron oxide and rosin) must be used when using protein glue. Therefore, the process is extremely complicated and is rarely used. Bone gum has an unpleasant odor, is prone to mildew, is prone to moisture, and is therefore difficult to develop, especially in humid climate conditions. In addition, the glue film after the photocured bone glue easily falls off after absorbing moisture, thus limiting its use. In the early to mid-70s, PVA was the most widely used PCB resist. Later, DuPont's anti-corrosive dry film and domestic anti-corrosive dry film were put into operation. The resists in PCB manufacturing are basically PVA and resist. Dry film. During this period, screen printing has also tried to squeeze into the process of making PCB resist patterns. It should be certain that this idea was worthy of praise at the time. However, screen printing actually has a poor record in this “battlefieldâ€. The reason is mainly due to the unsuccessful resist printing materials. The main component of the anti-corrosion printing material in the initial stage was bitumen (adding a little solvent). Although this kind of printing material has good anti-corrosion properties, it has serious pollution to the copper-clad board and the environment and affects the health of operators. Such serious defects make the process of making resist patterns by screen printing unfavorable, and PCB workers prefer to use PVA or dry film.
Recalling the tortuous course of the application of screen printing in the PCB manufacturing technology, we can deeply feel that in an seemingly inadvertent atmosphere, various application technologies including screen printing are fiercely collided in the PCB manufacturing process. In this collision, whether to squeeze in or be squeezed out, all to see their own strength. The reason why screen printing in this period was in a tragic situation was that it was too poor and inferior. Screen printing, if you want to stand firm on the heel of PCB manufacturing and strive for greater achievements, you must practice “inner strength†and create advantages. Without strong technical advantages, you will not be able to squeeze even if you are squeezed. Only you may be mercilessly squeezed out. 2 î€ î€ î€ â€œ 内 内 内
As an old PCB worker and old screen printer worker, I deeply understood whether the acceptance of screen printing in PCB manufacturing technology depends entirely on whether screen printing has excellent screen printing materials and good processability. The tremendous progress of screen printing technology in the past decade has forced PCB workers to re-learn and gradually love and inseparable from screen printing. The development in recent years has made screen printing a good process adaptability and has become a controllable and easily controllable production process. Below we briefly introduce the progress of screen printing machinery in the past decade.
(1) Screen Printing Wire mesh screen is the most important part of screen printing. This is because it controls the flow and ink consumption of the ink. At the same time, it also determines the durability and quality of the screen, which determines the quality of the printing. In the past ten years, people can see high performance screen printing screens with good performance in the market, especially high-binding, high-tension, monofilament, flat-woven polyester (PET) screens. The introduction of a flat weaving screen with a diameter of 27 μm and up to 150 lines per cm has changed people's understanding of some important factors in printing, such as precision screen printing SMT technology, integrated circuit manufacturing technology, film Switch manufacturing technology, etc. have been confirmed. In addition, the excellent cross-linking properties of screens and screen-sensitive adhesives or photosensitive films are also an important factor in the production of high-quality screen printing plates. In order to ensure a good combination of screens and screen-printing materials, traditional The approach is to emphasize that plate-making operators must do a good job of pre-processing the already-stretched wire mesh. It includes the mechanical roughening of the new wire mesh and appropriate degreasing treatment. Currently, there is no need for roughening on the market. High-tension/high-bonding screens for fat-removal treatment are sold. This product not only saves time and simplifies the advantages of the process. The screen is more durable and its life is 2 to 3 times longer than ordinary screens. At the same time, in the development and research of new screens, we also noticed that the screens are wear-resistant, have high resolution, have a wide exposure time limit, and have excellent matching characteristics with photosensitive materials. The new screens have been commercialized in the domestic market. It is very easy to buy.
(2) Screen-type photosensitive materials Today, we can purchase many high-resolution screen-sensitive or photosensitive films in the market, especially water-based photosensitive films (direct-printing photosensitive films). The process is simple and the film thickness is uniform and controllable. In particular, the water-based photosensitive film with a film thickness of 80 to 140 μm can be used in some special applications. At the same time, it also provides a new field for screen printing. Reliable material base.
According to the latest screen printing information, U.S. Edeleon recently introduced a 400-μm-thick photosensitive film for various electronic applications and high-density textile printing.
(3) screen printing materials (ink)
The progress of screen printing materials, especially the development of functional inks, not only benefits ordinary screen printing (for example, UV inks never block mesh), but it also directly leads to screen printing technology and products. High-tech. For example, conductive silver paste printing in a thin film switch; solder paste (lead tin alloy) for interconnecting SMD, SMC (chip component) and PCB in SMT technology; semiconductor layer CdS (cadmium sulfide) in solar battery, CdTe (cadmium telluride) and screen printing of electrode layer carbon (C), silver (Ag), silver + indium (Ag + In), magnetic ink, thick film IC ink, and the like. As far as PCB printing materials are concerned, the quality and printing process of PCB printing materials today is truly different from that of 20 years ago. Table 1 shows the use and characteristics of some PCB inks. Table 1 Uses and Features of PCB Ink Variety Uses and Features Dilute alkaline developing liquid resist LPR-ER is used for multilayer PCB inner layer production and high-precision high-frequency PCB graphic production. The minimum wire diameter can reach 30μm or less. Short exposure time, rapid development, easy release, corrosion resistance, excellent resistance to plating, easy to operate UV curable liquid resist UR-ER is mostly used for single-panel and non-metallized hole PCB graphics production. Curing speed, corrosion resistance, excellent plating resistance, easy stripping, dense protective film, no penetration in the etching solution dilute alkali developing solder mask ink LPR-SRGLPR-SRM for high-density PCB insulation protection. High development accuracy (40μm)
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