On Thursday, March 9, 2017 at 1:16:50 AM UTC-5, wrote:
"** Thin mica (0.05mm) is still the best performing insulator material for semiconductors you can get at a sensible price AND will easily handle 200V or more. Just a smear of white, silicone grease on each side and you are there. "

Actually it should not be smeared. Just a dab will do you, and when the force is applied whether by screw or other means it is better because there are no air pockets in it.


In small transistors, I put a tiny dab right in the center of the transistor. On larger devices, I tend to spread it to cover at least half the heatsink. On hybrid modules I tend to give it a complete thin peanut butter coating.

I was taught that compound should be applied by a dot and let it spread out by the compression of the mounting technique to prevent an air pocket. What I've found out is that very few mounting methods compress the device sufficiently to spread and force most of the compound out.

You've done your share of STK replacements - how many did you remove to discover the compound was in the center but never spread towards the outer edges?

I use Dow Corning 340 which is a very dense and heavy compound, and this stuff takes a lot of force to compress it all the way across the back of a large heatsink.