Soldermask in PCB production

PCB solder mask layer, refers to the printed circuit board to be on the part of the green ink. Soldermask windowed position is not on the ink, exposed copper to do surface treatment after welding components position, not windowed position are printed on the ink to prevent line oxidation, leakage.

PCB solder mask open window for three reasons
1. Hole pad window: plug-in hole pads need to open the window, open the window to weld the components, not open the window welding position will be covered by ink, resulting in device pins can not be welded.
2. PAD pad windowing: the location of the window is the location of the patch, the need for patch welding components, if you want to weld the location of the window is not open, and will be covered by ink, equal to the absence of pads.
3. Large copper surface window: sometimes need to improve the PCB alignment without increasing the width of the case of the alignment through the ability of high-current, usually in the PCB alignment on the tin, so the need for tinning the position of the need to open the window to deal with. removing solder from pcb

Why should the solder mask window be larger than the line PAD?
General window than the line pad, if the solder mask window area with the pad as large as the area, due to PCB manufacturing tolerances, it will not be able to avoid the solder mask green oil covered to the pad, so to take into account the process of board factory deviation, are to let the solder mask window area than the actual pad to expand the size of a certain number of the board by the general board factory production tolerances, it is recommended that the large overall 4-6mil.

What is the role of the solder mask?
1. To prevent solder spillage caused by short circuits and other issues.
2. In wave soldering when the bookmark slag welding layer is particularly important to prevent non-soldering points from stained solder and so on.
3. Can effectively protect the circuit against moisture. removing solder from pcb

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