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5.1 Causes and Countermeasures:
1) There is a notch on the scraper blade - grinding scraper.
2) The scraper pressure is too small - increase the scraper pressure.
3) The spacing between the screen and the PCB is too large - adjust the spacing.
4) The warpage of the frame causes the pressure of the squeegee to be non-uniform - replace the frame, re-stretch the net, and make the screen.
5) The printing material viscosity is too large - mix the printing material and use it after stabilizing for a period of time after the preparation.
6) The screen mask is too thick, the amount of printed material is small, and the screen printing wire is too thin - the thickness of the mask must be controlled when making the screen (direct method).
7) Screen printing speed is too fast - Slow down screen printing speed.
8) Choose improper printing materials and high screen mesh - change the printing material and use a screen mesh screen with a slightly lower mesh.
9) Push back the print uneven - adjust the squeegee.
5.2 Ink seepage
1) Scraper blade round - sharpening scraper blade.
2) Scraper screen printing angle is too small - properly adjust the scraper screen printing angle.
3) The viscosity of the printing material is too low - change the printing material with high viscosity.
4) Poor mixing of solvent and printing material - After the printing material is fully stirred, it is screen printed.
5) Wipe the screen with solvent, and screen-print the solvent without completely evaporating. After cleaning the screen, wait for the solvent to evaporate before screen printing.
6) The number of screen meshes is too low - use high-mesh screen mesh screens.
5.3 bad screen printing patterns, spots, uneven coating material
1) The thixotropy of the printed material is not good - mix the materials according to the data or use new materials.
2) Post-printing screens slowed down from the grid—adjusting the viscosity of the printing material, increasing the tension of the stretching net, and increasing the elasticity of the wind.
3) The screen pattern is too close to the edge of the frame – use a large screen frame to make a smaller screen and make a smaller picture in the center of the screen.
4) Poor image formation caused by static electricity - Elimination of static electricity.
5) The scraper angle is too small - adjust the scraper angle.
6) Uneven screen printing speed - adjust the speed of the squeegee or repair the screen printer.
5.4 Screen Printing with Pinholes
1) When the screen is made, the screen mask is unevenly coated, and the screen pattern has pinholes. The screen is used to repair the screen.
2) Impurities mixed in the printed material block the mesh - scrub the screen.
3) The dust in the air adheres to the screen pattern - scrub the screen plate to remove dust.
4) The surface of the printed board is not cleaned, and dust adheres to the screen-cleaning screen, and the surface of the printed board is fully cleaned.
When wiping the screen, accidentally scratch the screen into small pinholes - repair the screen, wipe the screen gently with a soft cloth.
5.5 Short Screen Life
1) The surface of the printed board is uneven or burr. In the process of screen printing, the screen is in contact with it, so that the screen pattern is deformed or a small hole is generated - surface treatment is performed.
2) Insufficient size of the screen tension - adjust the tension (self-tension), fixed stretch net must be re-stretched plate.
3) Improper selection of screen-forming emulsions. - Select the appropriate screen-forming emulsion according to the screen printing conditions.
5.6 Screen Printing Operation Precautions
1) The printed material must be wiped clean immediately, regardless of whether it is placed on any part of the screen printer.
2) The active part of the screen printer must be lubricated daily.
3) After adjusting the machine, the screws must be tightened.
4) Screen printer installation must be kept horizontal
5) The suction cup is very important in screen printing, be sure not to bruise.
6) Do not allow solvent to get onto the suction cup.
7) The vacuum cleaner must be cleaned once a month to ensure suction and extend the life of the pump.
8) The operator must master the rules of use of screen printers.
The faults and countermeasures in pcb screen printing (4)
5. Mechanical screen printing common faults and causes
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