Investigation of internal package structure based on the analysis of dynamic temperature response

This paper presents the investigations of internal package structure based on the analyses of device dynamic thermal responses to power step excitation recorded in various cooling conditions. The analyses are carried out for two theoretically identical power devices representing different technological generations. As demonstrated in the paper, both thermal and electrical behaviors of these devices differ substantially. The time constant spectra and the cumulative structure functions calculated from the recorded thermal responses revealed deep internal differences between the devices. These results were confirmed also by measurements of device geometries taken after the disassembly of their packages. Owing to the proposed approach it was possible also to generate compact thermal models of both devices in the form RC Cauer ladders whose elements could be attributed some physical meaning. These models were finally validated with the measurements showing excellent accuracy of thermal simulation.