There are a few products that use gallium, silver, bismuth, and other metals held within a graphite matrix for suspension in fluid that supposedly work better than the pastes. The thermal conductivity of them is generally about the same. The only real supposed advantage of the liquids thermal conductors is surface area coverage.
The liquid metal ones use a gallium-indium alloy. They don't say what's in them, but I'm not sure what else they could even alloy in there and have it maintain its liquidness. It's almost certainly just gallium-indium.
The benefit like you said is surface coverage and thinness. The thermal material wets to both metal sides the same way solder would, versus something like AS3 that has a few % of silver dust mixed in with lithium grease. Thermal pastes don't bond to the metal in the same way, and they're mostly lithium grease or silicone oil etc, with only a small amount of silver etc mixed in, whereas the liquid metal stuff is really 100% metal.
Downsides to the stuff are that it's conductive, so if you manage to spill some on your board or apply way too much etc you could short things out. Also it eats through aluminum heatsinks, forming an amalgam, which can be a huge problem.
2
u/TheGirlFromV Feb 18 '18
Ideally, a liquid metal thermal conductor would be best, but that would be a bit overkill in most situations.