Application of Screen Printing in PCB Production 2
1. PCB resist film printing The circuit design printed circuit board in the formation of a resist film, which is the resist film printing; it is done by screen printing. To form conductors such as circuits and pads on the copper clad laminate, two processing techniques are commonly used: one is the screen printing method and the other is photolithography. Lithography costs are high, with the increase of screen printing accuracy, screen printing method is applied more and more. Screen printing method that is pre-printed on the CCL resist film, and then chemically coated parts of the resist is not etched away, and then remove the resist film, to get the required conductive pattern. In the screen printing can be used in polyester or stainless steel wire, the two screen printing is relatively high precision. Plate can be used directly photosensitive plate or straight photosensitive plate. The use of direct plate, the thickness of photosensitive film coating to master, the general printing solder mask to (25 ~ 30) μm better. Anti-corrosion inks are generally alkali-soluble inks, printed on the CCL after the corrosion resistance of ferric chloride and other acidic solution. Screen printing scraper made of polyurethane rubber, a thickness of 8mm, the Shore hardness of about 70, scraper shape selection right angle, scraper and screen angle of (50 ~ 60) °, the printing should be properly controlled anti Etching film thickness after drying. Hole, increase revision workload. Screen printing after drying with far infrared bake 2min, but with natural drying, the temperature control (25 ~ 30) ℃, about 4h or longer some time. After drying the circuit board can enter the acidic etching process, after etching with 1% ~ 2% sodium hydroxide dilute alkali spray to the membrane. At this point the role of PCB resist film is completed.
2. Adhesive printing surface mount, the reference to the flow of solder and the installation of large shaped parts, screen printing adhesive used is generally purple-curable UV adhesive. The adhesive in the UV irradiation, the internal free radicals will absorb UV cause the entire adhesive crosslinking or polymerization reaction. In a short period of time to achieve a solid bond.
3 paste (paste) printed circuit boards are generally pre-installed on the substrate of the various components, and then the soldering. The purpose of solder paste printing is to attach the mounting components to the printed circuit board lands. Mass production, using this method can ensure its excellent welding performance. The solder is generally composed of solder particles, solvents, fluxes and other components. Its high viscosity, large friction coefficient. Commonly used flux is pewter, melting point at 183 ℃. Sludge printing and pulp printing is not the same, printing special attention to the scraper speed, it is necessary to slow and uniform. The only way to ensure the quality of the solder paste. In addition to pay special attention to prevent the oxidation of solder circuit, solder circuit is oxidized, which determines the welding quality. In some cases, solder may be applied properly, but the storage is not good, the circuit will be oxidized, and the welding will be poor. Therefore, it is necessary to prevent the oxidation reaction due to moisture and other reasons.
4. Mark the ink printing Figure 28 layer PCB board graphics symbols printed circuit board after the completion of the symbol is completed. Marking ink spectrophotometry solid and thermoset two categories, and each is divided into single-component and two-component two. Printed circuit board requirements on both sides (that is, the plug-in surface and the welding surface) must be screen printing mark ink. Different types of ink film thickness will be different, the film thickness on the quality of printed circuit boards have a considerable impact. Ink film thickness and a lot of process factors, so to integrate a variety of garden elements, according to the actual operation to control the thickness of the film. Screen printing in addition to the above areas of application, but also in the solder mask printing, printed circuit board and other areas of widespread use. Although screen printing has become an irreplaceable place in the PCB manufacturing industry today, it can handle even the most advanced and sophisticated circuit board production. However, the sophistication of the circuit board manufacturing is also increasing, so this screen printing technology put forward higher requirements.
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