Phase Change Material Heat Sink for Transient Cooling of High-Power Devices

Abstract

This paper reports a heat sink that uses a composite phase change material (PCM) made from a copper foam infused with a Field's metal eutectic alloy that melts at 60°C to achieve both high cooling and the ability to buffer transient temperature spikes. We integrate this composite PCM heat sink with circuit board mounted gallium nitride (GaN) devices that dissipate heat flux as large as 50 W/cm2. To design the PCM heat sink and understand its behavior, we developed a three-dimensional finite element method (FEM) simulation of the integrated assembly. We fabricated and characterized five composite PCM heat sink devices, where each device had a different PCM thermal buffer. The thermal buffers had varying Cu volume fraction and thickness. The PCM heat sinks were integrated with top-cooled or bottom-cooled GaN devices on printed circuit boards. Measurements of PCM heat sink performance showed that during phase change, the device junction temperature was reduced by 10-20°C compared to a solid Cu reference heat sink, depending on the device heating power which was as high as 6 W. The PCM heat sink cooling time was increased by up to 2X compared to a solid Cu heat sink of the same geometry. Finally, we developed and validated a reduced order resistance-capacitance (RC) circuit model that can guide the design of future PCM heat sinks. This work demonstrates the potential for PCM heat sinks to be integrated with high power GaN devices and shows methods for the design and modeling of PCM heat sinks.