A Guide to Thermal Greases

Thermal grease, also known as thermal paste or thermal interface material, is a thermally conductive material used to connect a heat source to a thermal spreading device. Thanks to their diversity and performance, thermal grease can be found in many thermal settings, such as heat sinks. Thermal grease can greatly improve a system’s overall thermal conductivity and effectiveness. In this blog, we will discuss the use of thermal grease, what it does, and its chemical properties.

Thermal grease is often used in computing devices, commonly residing in the central processing unit (CPU). CPUs create a significant amount of thermal energy that must be removed to function optimally. The electrically non-conductive thermal grease is applied directly to the casing of the CPU package. These casings, or thermal spreaders, are thermally conductive. Nevertheless, the casing protects the semiconductor material and integrated circuit from thermal grease and other external factors. Next, a heat sink, thermal spreader, heat pipe, or vapor chamber, connects to the thermal grease. The goal of the grease is to minimize air pockets between the semiconductor chip’s heat spreader and the thermally conductive material that moves thermal energy away from the heat source.

Air, a great thermal insulator, prevents heat transfer from a source to the thermal management device. The liquid properties of thermal grease allow it to enter the microchasms of both the heat source surface and the surface of the thermal spreading accessory. Without thermal grease, a heat source in direct contact with a thermal accessory would develop air pockets between the two devices, reducing the thermal management system’s thermal conductivity. The use of thermal grease eliminates these porkcets and therefore improves the effectiveness of the thermal management accessories. That said, thermal grease is not only used to improve efficiency. Without it, operation of the heat source would risk damaging the internal semiconductor and integrated circuit.

The electrically-insulative and thermally-conductive nature of thermal grease allows manufacturers and builders to use it in nearly all electronic applications requiring connectivity between thermal management devices. However, specific chemical compositions are required to achieve these properties. There are two main compounds that make up thermal grease: a polymer base, known as a matrix, and a liquid or micronized metal filler. The ratio between these two compounds will determine the thermal and electrical conductivity properties of the grease. Different greases have different ratios and therefore varying benefits and drawbacks.

Thermal greases that consist of high concentrations of metal compounds have higher thermal conductivity than those with low concentrations. Depending on the polymer’s electrical conductivity properties, a thermal grease with high metal-concentration will also have higher electrical conductivity properties, which increase the risk of electrically shorting the heat source or circuit. Designs that use a lower-metal concentration do not have this risk, but also provide a much lower thermal conductivity. Finally, based on the polymer chemistry of the liquid matrix, thermal grease can sometimes act as an adhesive, and thermal greases with adhesive properties are sometimes called thermal glue. These adhesives can be in many forms, such as solid-form tape or more traditional glues.

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