Comparison of current sharing among paralleled devices in wire-bonded and planar power modules

The full circuit models of two power modules carrying insulated-gate bipolar transistors (IGBT) are obtained using electro-magnetic simulation. Simulation of the full circuit models shows that the planar IGBT module excels the wire-bonded IGBT module in the current sharing capability. The gate inductances and resistances are found to be 60% less in the planar interconnect module than in the wire-bonded module. As a result, the power module with planar interconnects yields faster response, which decreases the switching energy imbalance caused by the time lags. The variation of the threshold voltages has a significant effect on the switching energy distribution among the devices. The IGBT with lower threshold voltage tends to be turned on earlier and turned off later than the IGBT with higher threshold voltage. Therefore, a substantial amount of current will travel through the IGBT with lower threshold voltage during switching transient. The continuous operation of the power modules leads to junction temperature imbalance on the IGBTs. The thermal imbalance can further cause imbalance of energy dissipation. Simulation shows that the planar module layout can decrease the impact of layout impedances, thermal imbalance, and process variations.