Arctic Silver 5 or similar thermal pastes are non conductive under regular circumstances. You need a lot of pressure in order to make it conductive
Arctic Silver 5 is quite sticky and tough to apply but it´s stable even after years of usage.
If on the other hand you want to use some liquid metal fluid, this one is 100% electrical conductive and not stable at all. In comparison to regular paste, it will evaporate sooner or later and leave a hard layer behind which is very hard to remove.
Just use whatever paste you like since the thermal difference will be 1-3° at best, even standard silicone paste ( the white stuff you use for power electronics ) is better than no paste at all.
Originally Posted by republicano
i often thought about this,the thermal paste is used to transfer heat over to the metal frame if it makes contact.
you would want to use arctic ceramic to be safe, non conductive insulating thermal paste, even though the 99% silver is the best for conductivity you would want make sure it doesnt get in contact with the motherboard.