LIBRARYSilkscreen, soldermask, and polarity marks.

Silkscreen and soldermask are the board's labels and its protective coat. Silkscreen prints reference designators, pin-1 dots, and polarity marks that make a board buildable and debuggable. Soldermask is the colored layer that covers the copper and keeps solder only where you want it.

What soldermask does

Soldermask is the thin lacquer, usually green, that coats the copper everywhere except the pads. It stops solder from bridging between close pins, protects the copper from oxidation, and insulates traces you might otherwise touch. The openings in the mask define where solder can wet, so on a fine-pitch part the mask openings matter as much as the pads.

The silkscreen legend

Silkscreen is the printed text and symbols on top of the mask. A good legend gives every part its reference designator (R1, C3, U2) so you can find it, marks pin 1 on every chip, and shows polarity on the parts that have it: the band on a diode, the stripe or plus on an electrolytic capacitor, the marked cathode on an LED, and the pin-1 corner on a connector.

Keep silk off the pads

Silkscreen ink over a pad stops solder wetting and ruins the joint, so the fab and the design rules push silk clear of copper openings. When a reference designator will not fit beside its part without touching a pad, move the text; do not shrink it onto the pad. Legible silk that sits in the free space is the goal.

A title block earns its space

Print a small title block somewhere on the copper or silk: the board name, a version, and a date. When you are holding three revisions of the same board, the one thing that tells them apart is the version you printed on them. It costs nothing and saves an afternoon of confusion at the bench.