Thermal performance of baseplate and direct substrate cooled power modules

In this paper a comparison of three coolers is presented: a coldplate onto which a conventional power module is mounted, a direct baseplate cooler and a direct substrate cooler. The direct baseplate and substrate coolers employed water jet impingement. By removing the baseplate the thermal resistance, mass and volume of the combined electronic package and cooler is reduced. At the same time potential improvements to reliability are realised through the removal of the bonded interface between the substrate and baseplate and the interface between the heat spreader and heat sink. For each cooler the heat transfer performance as a function pumping power was determined together with the transient thermal impedance. The effective heat transfer coefficient generated by the direct coolers (over 20 kW/m²K) was significantly higher than the coldplate (8 kW/m²K). Furthermore the total thermal resistance for the direct substrate cooler was lower than either the baseplate or coldplate cooled design variants, demonstrating that the heat transfer coefficient provided by jet impingement is high enough to obviate the need for a heat spreader plate. In addition the transient thermal impedance for the direct substrate cooler was substantially lower producing reduced levels of thermal cycling.