Thermal analysis of power cycling effects on high power IGBT modules by the boundary element method

The technology of high power IGBT modules has been significantly improved t hese last years against thermal fatigue. Nowadays, the most frequently obse rved failure mode, due to thermal fatigue, is the solder cracks between the copper base plate and the DCB (Direct Copper Bonding) substrate. Specific simulation tools are needed to carry out reliability researches and to deve lop device lifetime models. In other respects, accurate temperature and flu x distributions are essential when computing thermomechanical stresses in o rder to assess the lifetime of high power modules in real operating conditi ons. This study presents an analysis method based on the boundary element m ethod (BEM) to investigate thermal behavior of high power semiconductor pac kages submitted to power cycling constraints. The paper describes the bound ary integral equation which has been solved using the BEM and applied to th e case of a high power IGBT module package (3.3kV-1.2kA). A validation of t he numerical tool is presented by comparison with experimental measurements . Finally, the paper points out the effect of the IGBT silicon chips positi on on the DCB substrate on the thermal constraints. In particular. a light shifting of the silicon chips may be sufficient to delay significantly the initiation and the propagation of the cracks, allowing a higher device life time of the studied module.