● Thoroughly cleaned
● Covered with liquid mask
● Tack-dry the mask
● Film made of gerber files
● Aligne film
● Wash off uncured mask
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Solder mask, also known as solder resist. It is applied to the surface of the printed circuit board to prevent conductors from touching tin prevent electrical short cuicuit between conductors due to moisture or caused by chemicals.
Since the introduction of Liquid Photo Imageable Solder Masks (LPI) in the late 1980's, it has continued to be applied on printed circuit boards, such as rigid, rigid/flex, and flexible PCBs. LPI solder mask is by far the most common type of solder resist used today. LPI is more reliable, can be printed very accurately, and makes better contact with the surface of the board and the copper features on which they're applied to protect. LPI solder mask is an epoxy based material, so it is very durable and nearly impossible to remove once they have been cured. There is a variety of methods to apply LPISM ink, such as screen printing, curtain coating, electrostatic spray, air spray and so on.
Liquid Photo Imageable Solder Mask
Liquid Photo Imageable Solder Mask is normally applied to printed circuit board in the following steps:
1. The plate should be thoroughly cleaned to ensure no dust particles are trapped on the surface.
2. The plates are completely covered on both sides with the liquid mask.
3. The coated plates are placed in an oven to tack-dry the mask.
4. A film is made of the solder mask gerber files. Where you want to apply mask to the board, the film will be clear. Where the mask should be removed will be black on the film.
5. The tack-dried boards are placed into a UV developer and the film is precisely aligned over the board. The black area on the film will prevent the UV light from curing the mask where it is not wanted.
6. After the mask is exposed to the UV lamps, the uncured mask is washed off.