Dielectric Breakdown Characteristics of Silicone Gel for (U)WBG Power Modules Under High Slew-Rate Square Wave Stress

With the rapid expansion of emerging applications requiring high efficiency, high power density, and fast switching speeds, (ultra) wide bandgap ((U)WBG) power electronic modules are increasingly replacing conventional silicon-based counterparts due to their superior electrical, thermal, and switching characteristics. As a widely used encapsulation material, the dielectric properties of silicone gel (SG) determine the operational reliability of power modules. Therefore, the breakdown behavior of SG under practical high–slew-rate square-wave stresses warrants investigation. In this paper, the breakdown tests under bipolar square waves with various rise times at a fixed 50 kHz frequency were conducted on SG samples. Results show that the breakdown voltage of SG is positively correlated with the rise time: As the rise time decreases from 250 ns to 50 ns, the mean breakdown voltage drops from 4.60 kV to 2.79 kV, with a 39.35% reduction. A two-parameter Weibull analysis indicates steep slopes (β≫1) across conditions, implying relatively clustered breakdown voltages; shorter rise times tend to preserve high determinism while lowering characteristic strength. The breakdown behavior is interpreted by space charge dynamics. This study highlights the critical importance of incorporating waveform parameters into the insulation design and evaluation process for (U)WBG power modules.