Briefly describe the relationship between screen printing and printed circuit board 2

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 “battlefield”. 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 Hard to practice "internal strength"
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.
Screen and screen printing sensitive adhesive or photosensitive film has excellent cross-linking, but also an important factor in the production of high-quality screen printing plate, in order to ensure the good combination of screen and screen photosensitive material, the traditional approach is to emphasize The plate-making operator has to do a pre-treatment work on the already stretched wire mesh, which includes mechanical roughening of the new wire mesh and appropriate degreasing.
At present, there are already high-tension/high-strength wire mesh screens that are not required to be roughened or fat-removed on the market. This type of product has the advantages of being time-saving and simplification of the process, and the screen is more durable and has a longer life than ordinary wires. The net is extended 2 to 3 times. 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 Usage and Features of PCB Ink Variety Uses and Features:
Dilute alkali liquid development liquid resist LPR-ER is used for multilayer PCB inner layer production and high-precision high-frequency PCB graphics 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.