I'm going to venture to guess that a $100+ million dollar aircraft has a far superior thermal cooling system than your home PC. That is not a concern of the Air Force I do not think. It would be quite humorous to imagine an LM employee walking into their nearest Fry's Electronics to purchase some off-the-shelf thermal paste for F-22 avionics.
I think *you* might be surprised. There are always going to be air gaps under heatsinks that need to be filled (even if you're water, fuel, or even LN cooling). What do you use? That's right, thermal paste.