Effect of stacked structure on breakdown characteristics of power module insulation materials under frequency-dependent electric stress

Power modules are prone to partial discharge at the triple junction points of metal electrodes, silicone gel, and ceramic substrate, which can easily result in insulation breakdown. This paper investigated ceramic substrates' insulation breakdown and damage characteristics with different stacked structures and interface morphologies under high-frequency electrical stress based on discharge parameter statistics, trap distribution measurements, and material damage characterization. The study showed that the partial discharges of gel-solid insulation with different stacking structures are more intense with increasing frequency. Compared with the single-layer substrate of the same thickness, the partial discharge initial voltage and breakdown voltage of the double-layer substrate increased by 56.31% and 39.67%, respectively. In contrast, the maximum discharge amplitude, average discharge amplitude, and pulse repetition frequency decreased by 30.1%, 74.2%, and 15.6%, respectively. The trends of partial discharge initial voltage, breakdown voltage, maximum discharge amplitude, and discharge pulse repetition frequency remain unchanged with the addition of the metal interlayer, and the average discharge amplitude shows an upward trend due to the decrease in the number of small-amplitude discharges as a result of the weakening of the discharges. Further, the rougher surface of the substrate made the silicone gel filling more compact, which caused the enhancement of deep trap energy level and density, resulting in the difficulty of inducing electricity generation of the ceramic substrate. With the optimization of the stacked structure, the damage caused by the material melting and discharge problem due to the high-frequency thermal effect was also relatively weakened. The study's results can provide a reference for the design of the IGBT package insulation structure.