Thermal Decoupling in Power Electronics Modules Using Thermal Pyrolytic Graphite

The device within a power electronics module package will fail if the maximum junction temperature is not within the device's permissible maximum temperature rating specified by the manufacturer. Modern electronic miniaturization demands multi-chip module (MCM) packaging providing different semiconductor technology integration, reduced number of component interconnects, and lower power supply. But the huge amount of heat generated by each chip produces thermal coupling among devices, leading to an increase in the junction temperature. The power device specifications in the datasheet assume the devices being mounted on a suitable heatsink. Wide bandgap (WBG) devices like silicon carbide (SiC) devices can generally sustain a maximum junction temperature of about 175 °C – 200 °C. The junction temperature of the WBG devices becomes severe in a high-density high-power module. This highlights the need for a thermal management system to limit the maximum junction temperature within the device's permissible range. As a result, the power module needs to be connected to a heatsink to effectively increase the surface area of the heat dissipation junctions. A high conductivity material based heatsink extracts heat effectively from the module as the thermal resistance value remains low. In this paper, preliminary thermal analysis is done for a high density high-power module where the high in-plane thermal conductivity of thermal pyrolytic graphite (TPG) is exploited in substrate as well as heatsink designs. TPG brings down the junction temperature to a considerably lower level, leading to a safer power module functioning. This paper focuses on the design and proper alignment of the substrate and heatsink with respect to the module layout so that maximum junction temperature is reduced by proper heat extraction far below the operating temperature of the devices and also extent of reduction of the thermal coupling among the power devices placed next to each other on the same plane within the power module.