The solder mask is an essential element in printed circuit board manufacturing. Without a quality solder mask, most printed circuit boards wouldn’t last very long. There are several elements that go into creating an effective solder mask, and it’s a key feature of your printed circuit board’s makeup.
WHAT IS A SOLDER MASK
Solder mask is a material used to protect the copper on the circuit board with a protective layer of liquid photo imageable lacquer. This mask goes on both sides of the circuit board to protect the copper from problems that could lead to failure, such as oxidation, shorts from outside conductive influences, soldering, high voltage spikes or environmental factors and so forth.
When fabricating the printed circuit board, you’d spray the solder mask onto the production panel, then apply UV exposure with the correct solder mask pattern, then develop and dry the mask. You’ll typically recognize solder mask on printed circuit boards as being green, but other colors and even clear solder mask are also possible.
HOW TO MEASURE SOLDER MASK THICKNESS
While you want your solder mask to be thick enough to protect your circuits, it’s important to measure the solder mask to make sure it’s not too thick. On the side edges and top of the conductor, you’ll want a thickness greater than 7 micron. The maximum thickness for solder masks on finished copper parts of up to 35 micrometers is 40 micrometers. If the copper is thicker, the solder mask can be as thick as 80 micrometers.
Other good rules when it comes to solder mask include:
- Meet minimum annular ring requirements if the solder resist encroaches on lands
- Don’t allow exposed isolated pads
- Permit solder resist only when plated through holes not intended for solder fill
- Don’t let solder resist on test points or connector fingers