How to prevent electric arc on a precision contact
Sounds like the current is rather high- it is good to use tens of mA to detect a normal switch closure because of minimum wetting current requirements. 

If it isn’t damaging the PCB you can use it if you detect the closure rather than opening. 12V won’t jump a significant distance (you can look it up, probably tens of microns), however when opening you can get ionization effects that allow the arc to be sustained over a relatively large distances. 

Edit: Dielectric strength of air (at STP) is 3E6 V/m so 12V will jump 4um. It might be a bit less if the parts are pointy.