In-situ monitoring of package strain during HTRB test based on fiber-optic sensors

Leakage current is a key reliability indicator for power semiconductor devices, as its evolution under stress directly reflects degradation mechanisms. High Temperature Reverse Bias (HTRB) testing provides a standardized procedure to monitor this parameter over prolonged operation under elevated temperature and high reverse-bias conditions. Beyond electrical degradation, the test can also reveal reliability issues associated with thermally induced mechanical stress, which may alter the epoxy mold compound package. To investigate this phenomenon, this study presents a novel approach for real-time strain monitoring of the package during HTRB. As sensor, fiber-optic technology was considered. Particularly, Fiber Bragg Grating (FBG) strain sensors were glued on a TO-247 high-voltage Silicon diode. To validate the proposed methodology, two distinct bonding configurations of the FBG sensor were evaluated. In configuration (a), the FBG is bonded along its full length using an epoxy layer, whereas in configuration (b) the fiber is attached to the package only at two discrete points. In both cases, the measured strain variations exhibit a clear correlation with the evolution of the leakage current, confirming that mechanical deformation influences the leakage current behavior under stress conditions. These results demonstrate the feasibility of using FBG-based strain monitoring to track package deformation and its coupled electro-thermal response during HTRB qualification.