Hi ,

There is no point in getting scared. Yes the "noise" created by welding are wide bandwith in nature and are quite strong to kill the weak at heart ICs. For these circuits there are specific IC / Gates from guys Maxim who make them with extra ESD protection on the pins.

Particularly bad is the time when the arc is truck - all electronics that are not designed to handle this will go for a spin. In our case we have got 8051 MCUs for total TIG machine control and have found aspects like isolation transformers, floating grounds and Farady cages more useful than any of the Sckottky diodes or snubbers...

But your problem appears to be different - the MCU PCB's are not powered when the welding is done - so instead of designing PCBs that can be removed, why not just ensure that all signal / power to these PCB's are through removable connectors. Just
disconnect the connectors and not the PCB ?

Raghu