Common Faults of Mechanical Screen Printing and The Countermeasures
1. Reason And Countermeasures:
1) There is a gap on the blade edge of the scraper – grinding scraper.
2) The pressure of the scraper is too small – increase the pressure of the scraper.
3) The distance between the screen and the printed circuit board is too large – adjust the screen distance.
4) The warpage of the screen frame causes uneven pressure on the scraper – replace the screen frame, re-stretch the screen, and make the screen plate.
5) The viscosity of the printing material is too large – the printing material is prepared and used after it has been stabilized for a period of time.
6) The screen mask is too thick, the amount of printed material is small, and the screen printing wire is too thin – the mask thickness should be controlled when the screen is made (direct method).
7) The screen printing speed is too fast – appropriately slow down the screen printing speed.
8) Improper selection of printing material and too high screen mesh – replace the printing material and choose a screen with a slightly lower mesh.
9) Push back the uneven printing material – adjust the squeegee.
1) The blade edge of the scraper becomes round – sharpen the blade edge of the scraper.
2) The screen printing angle of the squeegee is too small – appropriately increase the screen printing angle of the squeegee.
3) The viscosity of the printing material is too low – use a printing material with a high viscosity.
4) Poor mixing of solvent and printing material – screen printing after fully stirring the printing material.
5) Wipe the screen with a solvent, and perform screen printing before the solvent has completely evaporated – after scrubbing the screen, wait for the solvent to evaporate before screen printing.
6) The mesh number of the screen is too low – use a high-mesh screen to make a screen.
3. The screen printing pattern is poor, spots appear, and the printing material coating is uneven.
1) The thixotropy of the printing material is not good – adjust the printing material according to the data or change to a new printing material.
2) Slow screen pick-up after printing – adjust the viscosity of the printing material, increase the tension of the screen, and enhance the elasticity of the wind.
3) The screen graphics are too close to the edge of the screen frame – use a larger screen frame to make the screen, and make the smaller graphics in the center of the screen.
4) Poor imaging of printing materials caused by static electricity – eliminate static electricity.
5) The angle of the scraper is too small – adjust the angle of the scraper.
6) Uneven screen printing speed – adjust the squeegee speed or repair the screen printing machine.
4. Screen Printing Graphics With Pinholes
1) When the screen is made, the screen mask is unevenly coated, and the screen pattern has pinholes – repair the screen with screen glue.
2) Impurities are mixed in the printing material to block the mesh holes – scrub the screen.
3) Dust in the air is attached to the screen graphics – scrub the screen to remove dust.
4) The surface of the printed board is not cleaned, and there is dust attached to the screen – clean the screen, and the surface of the printed board is fully cleaned.
When wiping the screen, accidentally scratch the screen into small pinholes – to repair the screen, wipe the screen gently with a soft cloth.
5. Short Screen Life
1) The surface of the printed board is uneven or has burrs. During the screen printing process, the screen is in contact with it, which deforms the screen graphics or produces small holes – surface treatment.
2) The tension of the screen is not appropriate – adjust the tension (self-tensioning), and the fixed stretched net must be stretched again to make the screen.
3) Improper selection of the screen-making emulsion – According to the screen printing conditions, select the appropriate screen-making emulsion.
6. Precautions for The Operation of The Screen Printer
1) Regardless of the printing material dripping on any part of the screen printing machine, it must be wiped clean immediately.
2) The movable parts of the screen printing machine must be lubricated every day.
3) After adjusting the machine, the screws must be tightened.
4) The installation of the screen printer must be kept horizontal
5) The suction cup is very important in screen printing, be sure not to bruise it.
6) It is not allowed to get the solvent on the suction cup.
7) The vacuum pump dust collector must be cleaned once a month to ensure suction and prolong the service life of the pump.
8) The operator must master the rules of using the screen printer.
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