A thermal interface material (shortened to TIM) is any material that is inserted between two components in order to enhance the thermal coupling between them. A common use is heat dissipation, in which the TIM is inserted between a heat-producing device (e.g. an integrated circuit) and a heat-dissipating device (e.g. a heat sink). There are intensive studies in developing several kinds of TIM with different target applications. At each interface, a thermal resistance exists and impedes heat dissipation. In addition, the electronic performance and device lifetime can degrade dramatically under continuous overheating and large thermal stress at the interfaces. Many recent efforts have been dedicated to developing and improving TIMs: These effort include minimizing the thermal boundary resistance between layers and enhancing thermal management performance, while addressing application requirements such as low

thermal stress In mechanics and thermodynamics, thermal stress is mechanical stress created by any change in temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, m ...

between materials of different thermal expansion coefficients, low

elastic modulus An elastic modulus (also known as modulus of elasticity (MOE)) is a quantity that describes an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. Definition The elastic modu ...

viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...

, as well as ensuring flexibility and reusability. * Thermal paste: Mostly used in the

electronics industry The electronics industry is the industry (economics), industry that produces electronic devices. It emerged in the 20th century and is today one of the largest global industries. Contemporary society uses a vast array of electronic devices that ar ...

, thermal pastes provide a very thin bond line and therefore a very small thermal resistance. They have no mechanical strength (other than the surface tension of the paste and the resulting adhesive effect) and require an external mechanical fixation mechanism. Because they do not cure, thermal pastes are typically only used where the material can be contained, or in thin applications where the

of the paste will allow it to stay in position during use. * Thermal adhesive: As with thermal pastes, thermal adhesives provide a very thin bond line, but provide additional mechanical strength to the bond after curing. While curing TIMs like thermal adhesives may be used outside of a semiconductor package, often they are used in inside of a thermal package, as their curing properties can improve reliability over different thermal stresses. Thermal adhesives come in both single-part formulations as well as two-part formulations, often containing additives to improve thermal conductivity, including solid fillers (metal oxides, carbon black,

carbon nanotubes A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range (nanoscale). They are one of the allotropes of carbon. Two broad classes of carbon nanotubes are recognized: * ''Single-walled carbon nanotubes'' (''SWC ...

, etc.), or liquid metal droplets. *Thermal gap filler: This could be described as "curing thermal paste" or "non-adhesive thermal glue". It provides thicker bond lines than the thermal paste, as it cures while still allowing an easy disassembly, thanks to limited adhesiveness. * Thermally conductive pad: As opposed to previous TIMs that come in a fluidic form, thermal pads are manufactured and used in a solid state (albeit often soft). Mostly made of

silicone In Organosilicon chemistry, organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (, where R = Organyl group, organic group). They are typically colorless oils or elastomer, rubber ...

or silicone-like material, thermal pads have the advantage of being easy to apply. They provide thicker bond lines (ranging in thickness from larger than a few hundred μm to a few mm) to accommodate non-flat interfaces and even multi-component interfaces, but will usually need higher force to press the heat sink onto the heat source, so that the thermal pad conforms to the bonded surfaces. *Thermal tape: These materials adhere to the bonded surfaces, require no curing time, they are easy to apply. Similar to thermal pads, they are typically shipped in a solid but flexible form and come in a variety of thicknesses larger than a few hundred μm. * Phase-change materials (PCM): Naturally sticky materials, used in place of thermal pastes. Its application is similar to solid pads. After achieving a melting point of 55–60 degrees, it changes to a half-liquid status and fills all gaps between the heat source and the heat sink. *Metal thermal interface materials (metal TIMs): Metallic materials offer substantially higher bulk

thermal conductivity The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low ...

as well as the lowest thermal interface resistance. This high conductivity translates to less sensitivity to bondline thicknesses and coplanarity issues than polymeric TIMs. Common metals used as TIMs include the relatively soft and compliant indium alloys, as well as sintered silver.

References

{{Reflist Computer hardware cooling Heat exchangers Heat transfer Materials science

See also

References