A systematic comparison of various thermal interface materials for applications with surface-mounted (DirectFETTM) MOSFETs

Increasing power densities of power electronics with reduced volume requires increased efforts in cooling as little surface and material are available for thermal conduction. A systematic comparison of the thermal resistance of a wide selection of thermal interface materials (TIMs) ranging from solid Al₂O₃ to elastomeric interface materials as well as thermal greases is investigated in this work. In contrast to the ideal testing conditions used by the TIM manufacturers, a practical application setup using a surface-mounted MOSFET (DirectFET^TM) pressed on a heatsink is used. Thereby, additional influences on the thermal resistance due to surface finish or non-homogeneous pressure are considered in the results. The effective contacting area as well as different pressure levels are investigated. On the basis of a B6C converter bridge, it will be shown, how the proper choice of TIM affects the mechanical and thermal design of a converter.