I can’t post links, but Tech Ingredients released an excellent YT vid today on TIMs. All kinds of good stuff in there that would make for good Level1 content. The indium foil is esp interesting. It starts to plastically deform at 40 psi and fills voids.
Also, whether 2 flat pieces of metal need a TIM. People always say you do, but I’m with Tech Ingredients. I mean, it’s good general advice, but if you own 5k grit sandpaper and understand what flat is, then you don’t need grease.
Is there a distinction between interface beneath and/or above the heatspreader?
Or better to have direct contact cooler to cpu?
I presume soldered cpus gain the least from being de-lidded and even liquidmetal between it and the heatspreader, then real thin layer between heatspreader and actual cooling block?
But never bothered checking, so grease is fine for me!
The flow of heat through the whole system, starting with the silicon, is important. You will be limited by the weak link, which is generally at an interface between two bodies. The bodies (copper, aluminum, heat pipes, etc) are very efficient at transferring energy (conduction) with the exception of thermal pastes. The liquid is an insulator that suspends solid conductors.
You might be interested in googling how Yeti coffee tumblers work. There are some good teardowns that explain how they limit heat flow (conduction, convection, and radiation). You might be surprised to see that copper is used as an insulator.
A soldered heatspreader is ideal because the solder body is conductive and its interface makes intimate contact on the atomic scale. But soldering isn’t easy. You need very tight manufacturing tolerances. Solder is drawn into joints by capillary action and will preferentially fill narrow gaps over large gaps.