Does anyone have a ballpark figure for the thermal resitance of a typical solder resist?
I (ideally) have a T220 fastened down on one side of the pcb with ~1.5sq in copper (1oz on 1.6mm FR4). N - number of vias in this copper area through the pcb to a (little) larger area of copper which mates with the heatsink/case.
I would like, for various reasons, to have a solder resist on the solder side but am concerned lest it has a significant thermal resistance.
Would,say, ENIG be a better bet hereover the thermally mateing surface?