Does solder mask provide electrical insulation?

Thread Starter


Joined Apr 16, 2010
I just received some prototype PCB's for a project. These are the first PCB's I have laid out in many years and I made a couple of mistakes.

One is that I have the heat sink for an IRLZ44N touching a track. The track goes to the MOSFET's source and the heat sink is electrically connected to the drain. However, the track is covered with solder mask. Is that good enough for electrical isolation? I know that I can trim the base of the heat sink slightly, or put a piece of tape between the heat sink and the track, but is it necessary?

Last edited:


Joined Apr 5, 2008

A soldermask is only to prevent the solder to jump to other pins.

Solder Mask
A solder mask is a thin polymer coating on your board which surrounds your pads to help prevent solder from
bridging between pins. This is essential for surface mount and fine pitch devices. The solder mask typically
covers everything except pads and vias. Your PCB program will automatically remove solder mask from pads
and vias. The gap it leaves between the pad and the solder mask is known as the “mask expansion”. The mask
expansion should usually be set to at least a few thou. Be careful not to make it too big, or there might be no
solder mask between very fine pitch devices.
Attached the complete PDF.