Influence of Thermal Cross Coupling at Power Modules

The thermal impedance of the semiconductors in Power Modules is always measured for a single chip, without the influence of other surrounding dies. This article describes the increase of the junction temperature of powersemiconductors due to the cross coupling of the Rth of components placed close to each other. The influence of different module structures, such as baseplate-less modules, modules with baseplate, material-thicknesses and different materials is provided. Introduction Today power-applications are getting more and more compact to save cost, space, and weight. For the same reason the layout of PowerModules has to be optimized. Also the integration factor is getting higher. In the past single half bridges and separated rectifiers were used, nowadays PIM ́s are used. But this trend is leading to a high concentration of thermal losses, associated with a high influence of the thermal cross coupling to the real thermal impedance of the application. Since the thermal impedance for the semiconductor of a powermodule is given only for single semiconductors without cross coupling, it is important for the designer of power electronic equipment to know how much the thermal resistance will increase, by chips and modules placed close together. As integration and power concentration is going forward it becomes more and more important for the designer of frequency converters to deal also with the influence of cross coupling. Therefore, as long as no thermal cross coupling is provided for Power Modules, the increase of thermal impedance for the application has to be estimated based on the internal distances of semiconductors in the module. 0. Basic Module Construction and Simulation Considerations For the simulation the following basic module constructions were used. The used chipset is a 150A – 158mm2 IGBT loaded with 85W and in the case of a half-bridge configuration a 150A FRED, loaded with 25W is used, which can be estimated as typical for a fully loaded 150A module in drive applications. For the different simulations mainly the number of chips and the position at the heatsink was alternated. In some cases also the thickness of the substrate and the thermal grease. Si Chip Sn 100um Cu 300um