Thermal and Mechanical Analyses of Clamping Area on the Performance of Press-Pack IGBT in Series-Connection Stack Application

Abstract

Press-pack insulated gate bipolar transistors (PP-IGBTs) are commonly connected in series and stacked together with heatsinks using an exterior clamping fixture in order to achieve high-voltage dc-link levels. A suitable contact area between the clamping fixture and the device is essential to ensuring optimal PP-IGBT thermomechanical performance, especially for the first and last devices in a stack. In this study, the effects of the clamping area on collector deformation, temperature, and stress distributions are investigated by means of the finite-element method (FEM). Moreover, this article analyzes the influence of heatsink thickness to maximize the stress evenness of the terminal PP-IGBT and reduce the overall length of the stack system. The results indicate that the collector lid is prone to warpage due to thermal expansion, which results in a decrease in the effective contact area between component layers. As the contact resistance increases, the chips accumulate considerable heat. Increasing the clamping area at this point can adequately compensate for the warp deformation and can also improve the stress uniformity of the chips. Finally, an experiment making use of stress-sensitive film has been carried out to verify the developed FEM models.