Almost every PCB board has a soldermask applied on one side or two sides, to protect the copper surface and prevent solder shorting between components during assembly. This article will introduce how to apply soldermask to a printed circuit board.
1. The panels will be cleaned up at first and brushed to remove all tarnishes on the copper surface and then brought into the yellow room.
2. Each panel is given a final cleaning to remove dust from the surface and loaded into the vertical coater. The coating machine covers both sides of the panel with the epoxy soldermask ink at the same time. These two operations ensure that the ink completely encloses the copper tracking.
3. The panels are then racked and gone through a drier, which makes the solder resist hard enough to be printed. The operator has to check whether the coating is complete and even.
4. Afterwards, a UV printer is used for the imaging of the coated panels. Then mount the films on the machine and place the panel onto the registration pins. Make sure the film and the copper layer are precisely aligned. The UV lamps in the machine harden the ink where the film is clear, that is where we need soldermask on the finished board.
5. The imaged panels are put on a conveyor into the developer which strips off the unhardened and unwanted solder resist. Later the required resist will be further cured in an oven to provide a robust and permanent coating. Make a final inspection for the alignment of the soldermask on the panel and make sure that there are no traces of ink on the pads or through the holes. Even slight traces will influence the solderability of the finished PCB.
According to these steps, you can apply your simple diy PCB solder mask at home.