Limitations and Guidelines for Damage Estimation Based on Lifetime Models for High-Power IGBTs in Realistic Application Conditions

Statistical lifetime models for high-power insulated-gate bipolar transistors (IGBTs) are developed based on results from power-cycling experiments and relate lifetime expectancy to the well-defined conditions of a laboratory experiment. In most cases, predefined cyclic-stress conditions are repeatedly applied until the power device under test reaches its end of life. However, in real applications, power modules are exposed to nonrepetitive stress patterns that can be very different from the power-cycling conditions. A well-established lifetime estimation method suggests decomposing the stress pattern into individual components, whose damage can be calculated using a lifetime model. These damage contributions are then summed up in order to estimate the consumed or the remaining lifetime of a device. When comparing the estimation results to field measurements though, they often fail to match the real behavior of a power device. This article points out the uncertainties that appear in this process of applying a lifetime model on stress patterns deriving from field applications. The main purpose is to present typical sources of errors and discuss how severely these may impact the lifetime estimation.