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Thermal Design of Power Module to Minimize Peak Transient Temperature

Fig. 1. Steady-state thermal performance of the power module: (a) the impact of the heat transfer coefficient on the heat spreading effect; (b) the impact of the geometry of the heat spreader on the thermal resistance.
This study focuses on the impact of the geometry of the heat spreader and the heat transfer coefficient of the heat exchanger on the steady-state and transient thermal performances of power semiconductor modules. Results show that the steady-state thermal resistances along the thermal flow path change with heat transfer coefficients owing to limited heat spreading effect as shown in Fig.1(a). Thicker heat spreader helps to reduce the steady-state thermal resistance. However, the impact becomes smaller with higher heat transfer coefficient as shown in Fig. 1(b). The transient thermal response of the power module is a highly localized and passive phenomenon. The transient thermal performance is mainly affected by the thermal capacitance in the power module as shown in Fig. 2(a). As shown in Fig. 2(b), to minimize the transient thermal impedance without sacrificing weight, cost, and so on, the thickness of the heat-spreader should be selected to match the thermal time constant to the transient duration. Based on these results, a methodology is proposed to conservatively select the thickness of the heat spreader to maintain the silicon junction at a required peak transient temperature. The methodology is exemplified and verified by a thermal design for a medium-voltage power module.

Fig. 2. Transient thermal performance of the power module: (a) the impact of the heat transfer coefficient on the thermal impedance; (b) design the thickness of the heat spreader based on transient duration.
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