Solder mask or solder resist is a coating applied to a Printed Circuit Board (PCB) to protect the copper traces on the board and to stop electrical shorts. The solder mask is usually applied on both sides of the PCB i.e Top and Bottom to ensure reliability and performance.

The solder mask is a Liquid UV Photo-imageable Ink that is usually green in color. Other color options like red, blue, yellow, white, black and purple are also available. This is something you need to ask the PCB manufacturer.

In the image above, the light green line is the solder mask layer. As you can see, the solder mask covers the entire trace, leaving only the pads exposed which are required to make electrical connections.

What is the purpose of using a solder mask?

• To prevent short circuits and protect the copper traces on the board.
• To protect the traces from exposure to air which can cause oxidation and corrosion of traces.

What material is used for solder mask?

Resin is usually selected as the main material for solder mask because it works exceptionally well in terms of humidity resistance, insulation, solder resistance and high-temperature resistance.