Demonstration of CTE-Matched Two-Phase Minichannel Heat Sink

Pumped two-phase cooling systems have been identified as effective thermal management solutions to remove a large amount of heat, provide excellent temperature uniformity across the device, and operate within low pumping power compared to their single-phase liquid-cooled counterparts. Regardless of the mechanism of heat transfer, effective materials for an efficient thermal management are those with high thermal conductivity to enhance the heat dissipation, and low coefficients of thermal expansion (CTE) to minimize thermal stress. In addition, the CTEs of the materials adjacent to each other must be close to each other to avoid a CTE mismatch, which is a main reason for the device failure. In this study, a low-CTE two-phase minichannel heat sink was fabricated and tested in moderately high heat fluxes. The evaporator was a double bonded copper (DBC) aluminum nitride (AlN), which was brazed into a Kovar enclosure. Both AlN and Kovar are CTE-matched. Also, the heat sink was a dielectric cooling system due to a low dielectric constant of AlN and using the refrigerant R245fa as the working fluid. The AlN substrate allows a direct mounting the electronic on the substrate without using a thermal interface material. The experiments were conducted at two flow rates with high inlet subcooling degrees. The heat sink operated above 183 W/cm
²
without any indication of partial dryout. At this heat flux, the measured thermal resistances for both flow rates culminated in values
$\sim \mathbf{0}.\mathbf{32}\ \mathbf{K}-\mathbf{cm}^{\mathbf{2}}/\mathbf{W}$
.