Thermal epoxy is any adhesive epoxy that has one or more substances added to it to enhance thermal, or heat, transfer. These epoxies can be electrically conductive or not conductive, depending on the thermal additive used. Silver and other metal-based thermal additives are usually electrically conductive, and thermal epoxies that contain these additives must be applied very carefully so as not to cause electrical shorts. Ceramic-based additives are not electrically conductive but are also not as efficient at thermal conduction.
Manufacturers make thermal epoxies that are designed to work as high-performance engineering adhesives and structural adhesives in a wide range of applications and environments. These include aircraft, boats, marine equipment, cars, surfboards, snowboards, and bicycles, among others. There are thermal formulations for almost every application imaginable, including those that cure while under water, those that remain very flexible or get quite rigid when cured, those resistant to fire or high heat, and even those certified by the U.S. National Aeronautics and Space Administration (NASA) for low outgassing.
Heat can damage or destroy electrical components, and today’s high-speed computer components produce a large amount of heat that must be removed. Devices called heat sinks are used to pull heat away from an object and dissipate the heat to the air, sometimes with the help of a cooling fan. Heat sinks are made from metal alloys designed to have excellent thermal conduction properties, and they have specially designed fins to help conduct and remove the heat. They are almost always mounted to a surface using a special adhesive thermal epoxy.
When used in computer applications, a thermal epoxy can help fill microscopic voids that occur in the surfaces of heat sinks and other devices. These voids occur in the manufacturing process. When two objects are mounted together, for instance a chip and a heat sink, the voids fill with air. Air is a very poor thermal conductor, so a substance is introduced to fill the voids and help conduct the heat to the heat sink for removal. The substance used can be thermal grease, thermal tape, thermal pads or, if the device needs to be secured to the mounting surface, thermal epoxy.
When applying thermal epoxy it is very important to use the least possible amount required to fill any voids and make the bond. If a too-thick coat of epoxy is applied, the electrical conductivity of the epoxy will be degraded. Once the epoxy has cured, the bond between the two surfaces is permanent. Epoxies should only be used in well-ventilated areas, and the manufacturer’s instructions should always be followed for best results.