Design and Fabrication of a Substrate Integrated Phase Change Thermal Buffer Heat Sink

Recent power electronics cooling efforts have shown that bringing the cooling mechanism directly into the device substrate can achieve reduced package thermal resistance and reduced system pumping requirements while maintaining traditional circuit manufacturing processes. At the same time, it has been demonstrated that effective compact methods of managing electronic temperature excursions from brief power surges or other transient events include the use of a solid-liquid phase change material (PCM), but tight integration into the electronics package without degrading overall cooling has proven difficult. Recognizing that such a thermal buffer heat sink (TBHS) would enable lighter weight, more compact cooling hardware for vehicle power electronic modules, the U.S. Army Research Laboratory has developed a method for integrating and assembling a PCM-based TBHS within a power electronics substrate. The TBHS design builds upon both the author’s previous efforts in substrate integrated cooling and design trade studies sponsored by the Department of Energy. By fabricating the PCM cavities alongside the fluidic passages on the backside of a ceramic substrate, the PCM thermal bottleneck can be minimized, and a compact solution can be found. Low fabrication temperature limits imposed by the presence of an integrated PCM can be circumvented by using a room temperature curing silicone bonding layer for assembly. The prototype fabrication plan is presented along with steady and transient thermal models to verify performance of the integrated heatsink. A representative design is shown to have a steady state thermal resistivity of less than 0.4 cm2K/W, with the convective rate of the cooling fluid being the dominant factor. Transient analysis shows peak temperature suppression due to the effect of phase change heat absorption, including a 4°C reduction under a pulsed loading condition.