Have you ever had bad experiences with black Varnish for thermal measuremen ts? We use this varnish for 10 years without problems, in many different pr ojects, but this time wenn it is applied, many short circuits appear over t he PCB in different positions... Strange thing is that I used the same varnish again over an old version PCB and it was ok... There were some minimal layout changes between old versio n and the new version, but the layout rules are the same. Also tried differ ent PCB manufactures, with same result. Maybe this new batch was contaminated with something in the production line , but the controls there are extremelly rigid...
And yes, I already made the thermal measurements without the varnish, were no big deviations from the old measurements, but still I need to indentify where does this weakeness come from.