Use of a SPICE-based Transfer Function to Model the Absolute Humidity in a Power Semiconductor Module

Abstract:
Power electronics may be significantly impacted by the environmental conditions (relative humidity, temperature) during their field operation. Particularly, moisture can initiate and/or accelerate different failure mechanisms for semiconductors. A better knowledge of the moisture level at silicon chip level is therefore an essential prerequisite to estimate the power electronic lifetime. In this study the kinetics of the moisture ingress into silicone gel was investigated experimentally and theoretically using mathematical models being derived either from the Fick’s first (i.e. Quasi Steady State model) or second law (i.e. Full Transient model) of diffusion. Since both mathematical models gave very equivalent solutions, we made use of the electrical analogy from the QSS model to convert its mathematical equation into a SPICE-like model. The obtained SPICE simulations are matching the theoretical model enabling the quantification of the humidity moisture uptake at the silicone gel-chip interface over time. The SPICE model allows to input any mission profile (i.e. temperature, relative humidity) any customer is experiencing in the field.