Electro-thermal modelling and Tj estimation of wire-bonded IGBT power module with multi-chip switches subject to wire-bond lift-off

Abstract

Wire-bonded multi-chip IGBT power modules constitute the heart of high-current power electronic motor drives. The most common failure mechanism is the degradation of the top-side wires. This deterioration impacts the electrical path and the individual dies’ temperature. The temperature is thus not only a stressor, but also a failure precursor. It is thus typically sensed in health monitoring methods based on damage-accumulation-models and failure precursors. One way to estimate the temperature is through the on-state voltage at low load current as a temperature sensitive electrical parameter. The on-state voltage being sensitive to the quality of the top-side connection, the obtained temperature estimate is drifting with degradation. This drift typically leads to under-estimating the temperature, thus reducing the precision of health monitoring. Drift compensation methods based on re-calibration are effective in single-chip switches, but their performances are not viable in multi-chip switches. This is due to the different temperature and current conditions during the calibration and the estimation phases. This paper addresses the relation between wire-bond degradation and temperature in multi-chip switches and proposes a simple model to explain and reproduce the electro-thermal behaviours. The model is based on experimental results where the degradation of wire-bonds is reproduced by cutting the wires sequentially. The model is further used to explain the drift in temperature estimation and the performance of the drift compensation methods based on re-calibration. Overall, the paper provides new results and understandings of the thermo-electrical behaviour of multi-chip power IGBT modules subject to wear-out.

Keywords

• health monitoring
• igbt power module
• power cycling
• temperature estimation
• wire-bond degradation