Numerical modeling of the performance of thermal interface materials
Pour Shahid Saeed Abadi, Parisa
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Thermal interface materials are needed for improving thermal contacts, such as those in microelectronics. Finite element modeling is conducted to understand the factors that govern the performance of thermal interface materials of controlled thickness in the form of thermal pastes or paste-coated-sheets between copper surfaces of controlled roughness. Good agreement is found between modeling and experimental results that involve copper proximate surfaces of controlled roughness sandwiching the thermal interface material of controlled thickness. Comparative evaluation is made on two contrasting pastes, namely a carbon black paste and a commercial metal particle paste. The carbon black paste is lower in thickness than the metal particle paste, so it gives better performance. The performance of both pastes is more influenced by the paste-copper interfacial conductance than the paste thermal conductivity. The effects of pressure, paste thickness and copper surface roughness on the performance are mainly due to the change in the fractional filling of the valleys in the copper surface topography. In case of paste-coated sheets, the coating on both sides of a core sheet is the carbon black paste and it serves to improve the conformability. The core sheets are copper foil, aluminum foil, indium foil and flexible graphite. Flexible graphite (made from exfoliated graphite) is advantageous in its low elastic modulus, whereas copper and aluminum foils are advantageous in their high thermal conductivity. Indium is advantageous in its low elastic modulus compared to copper or aluminum and in its high thermal conductivity compared to flexible graphite. Among the four types of core sheet with identical thickness, coated indium foil gives the best performance for a range of foil thickness, which is 6-112 μm for the case of smooth (15 μm roughness) proximate surfaces and 117-320 μm for the case of rough (0.01 μm roughness) proximate surfaces. Aluminum foil gives the best performance for a thickness range of 112-2000 μm in the case of smooth proximate surfaces. For thicknesses below these ranges, flexible graphite performs the best. For thicknesses above these ranges, copper foil performs the best.