Design, assembly and commissioning of a test apparatus for characterizing thermal interface materials

While thermal interface materials (TIMs), such as greases, compliant polymers, metallic foils and phase change materials, are commonly used in most electronic and microelectronic applications their in-situ thermomechanical characteristics are not well understood. Analytical models are available for idealized surface geometries, including conforming rough surfaces and non-conforming, smooth surfaces, but models are typically not available for real surfaces that combine both surface roughness and waviness, especially for interfaces that incorporate interstitial materials to promote compliance. As a result, thermal interface materials are usually characterized experimentally, in adherence to guidelines described in ASTM standard D 5470-95 which does not provide for changes in material thickness during the application of a load. This paper details the design and construction of a test apparatus that exceeds all specifications stipulated in ASTM D 5470-95 and can be used to accurately characterize thermal interface materials, including the precise measurement of changes in in-situ materials thickness resulting from loading and thermal expansion.