A thermal grease (also known as a thermal compound, thermal interface material, TIM, heat sink paste or CPU grease) is a thermally conductive chemical substance used to improve the contact between heat sources such as processors and their respective thermal spreaders/heat sinks. The grease is usually applied in a thin layer between the components to fill any microscopic gaps and improve the quality of the contact. This in turn increases the thermal conductivity between the two surfaces, thus preventing overheating and protecting the microprocessor from damage.
Without the use of a thermal paste, direct contact between a processor and a heat sink would develop an array of air pockets that act as thermal insulation and drastically reduce the heat spreader’s ability to transfer and dissipate heat from the microprocessor. Using a small amount of thermal grease eliminates these tiny air gaps and significantly improves the performance and longevity of both the heat spreader and the microprocessor.
There are many different types of thermal greases available to consumers, all varying in price, temperature range and working consistency. The basic types of thermal grease are primarily made up of silicone and zinc oxide, although some more expensive products will include additional heat conductors such as silver or ceramic to further improve the efficiency of the paste.
When applying a thermal grease it is important that a thin layer is used, as any excess will act as an insulator and degrade the performance of both the microprocessor and the heatsink. A paper-thin layer should be sufficient for most situations. It is also important not to apply too much as this will cause the grease to cook into a hard, crusty substance that can significantly decrease the performance of the thermal transfer.