Soldermask is the liquid photoimageable coating, usually green but also red, blue, black, white or clear, applied over the outer layers and opened only at pads and other exposed features. It prevents solder bridges between close pads, protects copper from oxidation and handling, and adds some insulation. Mask openings run slightly larger than the pads, and the narrow web of mask between fine-pitch pads, the mask dam, has a minimum width the fabricator can hold.
Soldermask dam between the QFN pads is under 3 mils, the fab will gang-relieve it, so watch for bridging.
Also heard as
- solder mask
- solder resist
- mask
- LPI
- LPSM
Related terms
Tenting
Covering a via with soldermask or film so its hole is sealed over instead of left open.
Silkscreen
Printed ink layer on a board showing reference designators, outlines, polarity marks and logos.
Bridging
Solder defect in which solder joins two pads or leads that should be separate, creating a short.
Pad
Exposed copper area on a board where a component lead or terminal is soldered.