Types of Thermal Interface Material
Thermal Interface Material (TIM) fills gaps between mating surfaces to improve heat transfer between components in electronics and other high power applications. TIMs have a critical impact on the performance of a device, and selecting the right type is vital to successful production. TIMs can come in the form of thermal paste, grease, silicone adhesive, or pads. Each format has its own unique characteristics that make it more or less suitable for specific applications.
The primary function of a TIM is to fill the microscopic air pockets between two mating surfaces that reduces heat transfer. The gaps created by rough or wavy machined surfaces can be very difficult to contact and have low thermal conductivity due to their filled with air. The TIM replaces this air with a soft, thermally conductive material to greatly improve the connection and reduce thermal resistance.
Grease is the oldest class of TIM, and it remains popular as one of the easiest ways to fill these gaps. The thick, sticky consistency allows the material to be easily spread and conformed to surfaces, but this also increases its surface area in contact with the bare metal, which raises thermal conductivity by a factor of five or more over bare aluminum or copper.
Pads are a more recent development that are easier to handle, generally don’t have dry-out issues, and can be pre-applied for an assembly process. Often made from non-silicone or silicone elastomers, these soft and highly thermally conductive materials are easy to press down on the bonded areas with little force. They also have the added benefit of being able to tolerate more rough surfaces than pastes. For more demanding applications, a new class of advanced TIMs based on pyrolytic graphite are now available. These can move large amounts of heat in tight spaces, such as the tiny gaps between a microprocessor and its metal housing or a Ball Grid Array (BGA) package.