Signal Sweeping Technique to Decouple the Influence of Junction Temperature and Bondwire Lift-off in Condition Monitoring for Multichip IGBT Modules

Abstract:
This paper proposes a measurement technique applied to an unbiased multi-chip power module that is able to distinguish between junction temperature variation and bondwire lift-off. Compared with traditional approaches, the proposed technique requires only one test to monitor and discriminate these two conditions. The proposed technique relies upon the injection of high frequency/low power signals into the Gate-Emitter terminals of an IGBT and then analysing the corresponding frequency response of the Gate-Emitter circuit. It is verified that the imaginary part of the Gate-Emitter impedance (ZGE, Imag) changes in opposite directions. A high number of bondwire lift-offs leads to an increase of ZGE, Imag, whereas junction temperature rise leads to a drop in ZGE, Imag. Furthermore, it is shown that the real part of Gate-Emitter impedance ZGE, Real increases with both increased number of bondwire lift-offs and rise in junction temperature. In this paper, a small-signal model for the Gate-Emitter circuit of a 3.3 kV / 100 A IGBT power module is developed and its frequency response is examined and analysed with SaberRD. Furthermore, practical tests are also carried out with a network analyser.