Minimization of the Thermal Interface Resistance of Power SMD Assemblies for High-Temperature Applications

Heat removal from power SMDs in a D²PAK package for high temperature applications is investigated. The components are mounted on a glass fiber reinforced (FR4) printed circuit board (PCB) by soldering whereby the solder pad for the D²PAK is realized as array of "thermal vias "for an improved conduction of the power loss from the component side to the bottom side of the PCB. A novel heat conduction foil as thermal interface materials (TIM) between PCB and a cooling block acts as electrical insulation. Thermal investigations of described set-ups based on simulation and measurements were carried out at an ambient temperature of 150degC and a cooling block temperature of 80degC in order to comply for ambient conditions as in an engine compartment of a car. Results were compared from set-ups with different pad geometry, different number of thermal vias (99, 143, and 224 per pad), and different TIM-foils. In either case an effective reduction of the thermal interface resistance could be obtained by enlarging the pad area with respect to the pad size of the SMD.