The surface of a CPU or a heat sink is never entirely flat. If you place a heatsink directly on a CPU, there will be tiny, nearly invisible, gaps between the two. Since air conducts heat poorly, these gaps have a very negative effect on the heat transfer. Therefore, an interface material with a high thermal conductivity is needed to fill these gaps to improve heat conductivity between CPU and heatsink.
Here, you can decide between using thermal paste and thermal pads. But when should you use which solution? What are their differences and what advantages do both solutions have?
Thermal grease, thermal compound, thermal goop, thermal gunk or heat paste – thermal paste has lots of different names. It is a sticky paste applied directly on the heatsink or CPU and the most commonly used interface material in the electronics cooling area. Thermal compound with a good quality will provide the best possible performance. Unfortunately, to apply thermal paste can be quite messy. Also, thermal paste isn’t the best way to fill bigger gaps sometimes. Here, you can use thermal pads.
A tutorial how to properly apply thermal compound, can be found here:
Thermal pads are a lot easier to install than thermal grease. Unfortunately, they aren’t as effective as a thin layer of thermal paste. Some stock CPU coolers come with pads, because they’re nice and clean, and they’ll work fine.
But they are one-shot solutions only. You have to replace the pad if you ever remove the heatsink from its mounted position, because the heat of the operating CPU will have caused the thermal pad to conform the top. So, once you move the heatsink there will be new gaps between the surfaces. So never forget: If you dismount the heatsink, replace the thermal pad and remove all debris.
Avoid Common Mistakes
When using thermal pads or thermal paste, there are some mistakes that are often made. So, here are some ideas to avoid those:
Never use thermal compounds and thermal pads together. Just because you use both, the effect won’t increase. The reverse is true. Adding thermal grease on top of a thermal pad actually reduces the ability of heat to flow to the heatsink.
Also, never stack several pads on top of each other. Two or three pads on top of each other between the CPU and a heatsink might kill the CPU.