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.