Comparison of IGBT short-circuit failure “ohmic mode”: Epoxy molded package versus silicone gel module for new fail-safe and interruptible power converters

An epoxy molded package is compared with a silicone gel module with IGBTs chips in short-circuit failure modes with respect to critical energy, I2Tmelting and explosion energy capabilities. Special importance was attached to “ohmic mode” assessment and ageing of the failed chips. The molded technology yields a very low and stable Rsc (<10 mΩ) as a “residual ohmic value” of the dies in low energy short-circuit failure, which is analysed through a complete reverse. Continuous thermal cycling tests over a medium time duration (>1000 h) also exhibit an acceptable drift of the Rsc property (<20%). The silicone gel module clearly exhibits an unstable Rsc value due to damage of the “free moving” wire-bonding on the chips. The authors show that the paralleled wires connections and the multiple parallel melting pits allow a sort of active redundancy and a possible on-state operation. All these results are used for the design of new and original failsafe converters. These topologies use only one paralleled safety leg that is spontaneously and directly connected in series with the failed devices, through the low Rsc value of the failed chips, without any additional complexity or extra cost.