Thermal Interface: Pad Or Paste
In order to reduce the thermal interface resistance between the CPU die and the surface of the heat sink, either thermal pads or paste are used as so-called thermal interface material (TIM).
Application of the predominantly pre-assembled pads is quite simple to figure out: remove the protective film, assemble cooler, turn on your PC, and that's it. The downsides of the pads are that they can only be used once, and when upgrading your processor, cleaning the contact surface is not all that easy.
For this reason, those who regularly change the CPU should opt for thermal paste instead of a pad.
Thermal conductivity of various thermal pastes.
When using thermal paste, you should take care that you do not apply it too thickly. The paste should only expel the air (λ = 0.035 W/mK) from the interface between the cooler and the die. As a rule, an amount equal in size to two or three grains of rice is usually quite sufficient. Using more generally does more harm than good. After all, the thermal conductivity of your standard paste is usually two powers of ten less than that of the cooling material. As practical tests of the various pastes have shown, the die temperature can be reduced by up to three or four degrees Celsius using a high-quality thermal paste.