Solder mask and silkscreen: colours and design rules
What the mask and the legend do, which colours you can choose and the layout rules that keep both clean and readable.
What the solder mask does
The solder mask is the coloured protective layer over the copper. It keeps solder only where it belongs (on the pads), protects the traces from oxidation and moisture, and reduces the risk of solder bridges between close pads. Pads and holes are left open.
What the silkscreen does
The silkscreen is the printed legend on top of the mask: reference designators, polarity marks, logos and test points. It does not influence the electrical function, but it makes assembly, testing and repair much easier.
Colours
- Solder mask: green is the standard; black, white, red and blue are also available. The calculator shows the colours that can currently be chosen; other colours than the standard carry a small surcharge, shown live.
- Silkscreen: white, black, red or yellow. White is the standard on FR4, black on aluminium (IMS) boards.
- Contrast: use a silkscreen colour that stands out from the mask — white on black or green, black on white. On a white mask the legend must be black.
- LED boards: a white mask reflects light and is a common choice for LED designs.
Design rules for the mask
- Mask opening: the opening is usually about 0.05 mm larger than the pad on each side; your CAD program applies this by default.
- Mask bridges: between pads of fine-pitch parts a thin strip of mask must remain. If the pad spacing is too small the bridge disappears and the openings merge; discuss very fine pitches with us.
- Via protection: decide whether vias are covered by mask or left open, and say so in the order.
- No mask on pads that must be soldered; make sure openings are on the correct side.
Design rules for the silkscreen
- Keep it off the pads. Silkscreen on a pad prevents soldering; it is removed or clipped at the opening.
- Size: very small text does not print legibly. As a rule of thumb, use letters at least 0.8 mm high with a line width of about 0.15 mm.
- Orientation: align the text in one or two directions so that it can be read in assembly.
- Do not print on bare copper or over holes.
Checking before you send
Open the Gerber set in a viewer and check that the mask openings sit on the pads and that the silkscreen does not touch them (see how to open and check Gerber files). Choose the colours in the price calculator or contact us.
Frequently asked questions
Why is a mask bridge between pads important?
A strip of solder mask between close pads keeps the solder from forming bridges during assembly. Check the distance between the pads of fine-pitch components.
How small can silkscreen text be?
A safe rule is letters at least 0.8 mm high and clear of pads; smaller text becomes hard to read.
Can silkscreen overlap pads?
It should not. Ink on a pad prevents good soldering, so keep text and outlines away from the solderable surface.
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