Abstract:

In this study, a Mahalanobis distance approach to identify anomalies in trench field stop IGBTs was implemented. The goal of this work is early warning of IGBT degradation to achieve failure avoidance. Ten trench field stop IGBTs were aged by electrical-thermal stress under a resistive load until their failure. Collector-emitter voltage and collector-emitter current were identified as precursor parameters to trench field stop IGBT failure. X-ray analyses of the aged parts showed die attach degradation which has likely led to the changes observed in the precursor parameters. These two parameters were used as input to calculate the Mahalanobis distance (MD). The initial values of the precursor parameters recorded were labeled as healthy data and the subsequent values were labeled as test data. The MD values obtained from the healthy data were transformed using a Box-Cox transform to a normal distribution and three sigma limits were obtained from the transformed data. The upper three sigma limit of the transformed MD healthy data was used as a threshold to detect degradation. An anomaly was said to have occurred when the transformed MD test data crossed the upper threshold. This MD approach detected degradation in all the IGBTs tested before failure with the maximum detection time being 84% before failure.

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