pcb isolation distance and soldermask

Thread Starter


Joined Sep 20, 2005
Say I have some 230V and 12V traces that should be double isolated. I look up the clearance and creepage, and get the proper isolation distance for pcb layout.
Now for the question, often I see this gap left without soldermask, what are the advantages/disadvantages?
I would think that the path would be less prone to creepage with normal soldermask?


Joined Oct 15, 2009
The solder mask is typically avoided as it may have micro voids,etc.. that can trap contaminates/moisture,etc... that could cause arc over/reduction in the creepage/clearance distances..
Quite often people also use a physically routed (milled away) gap that is applied post solder mask to ensure consistent gap/help with preventing carbonization,etc... as well as allowing greater surface distance vs air distances


Joined Jan 23, 2018
For separating such large voltage differences I have used separations of at least 1/4 inch (=7mm) or more if possible. It is safer to have more than the minimum allowable gap if you can.