Online Condition Monitoring Methodology for Power Electronics Package Reliability Assessment

This paper introduces an online condition monitoring strategy that utilizes a transient heat pulse to detect package thermal performance degradation. The metric employed is the temperature-dependent transient thermal impedance ”Zth(t,Tamb).” The proposed methodology offers quantitative insights into the package thermal performance degradation and effectively pinpoints the presence of multiple failure mechanisms. A Thermal Test Chip assembled in a Power Quad Flat No-Lead package was used in this study to demonstrate the methodology. The packaged devices were first characterized to determine the transient pulse duration, a critical parameter to monitor a specific region of interest. Subsequently, the package thermal performance degradation was continuously monitored online during Thermo-Mechanical Cycling Lifetime experiments. The validity of the measurement results was later confirmed through acoustic imaging and cross-sectional analysis. The changes observed in Zth(t,Tamb) over thermal cycling corresponds to the delamination of the active metal layers on the die and cohesive failure on the die-attach. This paper further includes a comparative summary, highlighting the distinctions between the proposed and industrystandard test methods. In conclusion, the importance of online condition monitoring to detect early signs of failure was emphasized, and the proposed methodology's practical applicability in real-life scenarios was briefly discussed.