A CPU is a very power-hungry component that needs to be kept cool or risk overheating and permanent damage. It’s essential that PC builders use a high-quality CPU thermal paste to transfer heat from the processor to the cooling solution. The best thermal pastes have a density that allows them to fill seemingly minor flaws or air bubbles between the CPU and the cooler or heat sink.
These imperfections can prevent the two surfaces from coming into full contact and transferring heat efficiently. The best thermal pastes also have a very low viscosity so they spread easily and are able to fill in all the gaps, creating an even surface that helps with cooling.
While the application method has become something of a hotly debated topic among some enthusiasts, real-world benchmarks (Linus Tech Tips) have shown that the most important factors in a good thermal performance are the thickness and viscosity of the paste itself and the thermal conductivity between the CPU core and the heat spreader. Keeping these factors in mind, the best way to apply thermal paste is to put a pea-sized drop directly onto the center of the processor and clamp down the heat sink on top.
Then, using a card, paper, plastic or a piece of cardboard, smooth out the paste and make sure it is spread evenly. Do not use bare hands or fingers as these can contain oils that may interfere with the performance of the thermal paste. It is recommended to reapply the thermal paste every couple of months or so, to keep it in good condition.