Thermal paste application is an often overlooked aspect of PC assembly. This is a shame, because good thermal paste can make or break the performance of your CPU.
The best way to avoid problems with thermal transfer is to apply a very thin layer of the product. This will eliminate air gaps between the silicon die and the heat sink, and improve thermal conduction. A thick layer, however, can increase the distance between the two metals and reduce efficiency.
Most thermal pastes are based on ceramic or metallic materials suspended in a binder. Depending on their chemical make-up, these materials can either be electrically conductive (like aluminum oxide), or non-conductive (like ARCTIC MX-4).
When choosing a thermal paste, the most important factor is that it should be easy to apply and spread evenly. It should also be stable for thousands of hours without drying or flaking.
A few tips for thermal paste application:
Use a clean coffee filter or lint-free cloth with IPA or ArctiClean Thermal Material Remover to clean the surface of the processor(s). Wipe until you can no longer see any oil residue on the surface of the silicon. Avoid using your bare finger, as this will leave its oils on the surface and degrade the thermal interface.