Embedded two-phase cooling of high flux electronics using a directly bonded FEEDS manifold

This work presents the experimental design, bonding, and testing of a two-phase, embedded FEEDS manifold-microchannel cooler for cooling of high flux electronics. The ultimate goal of this work is to achieve 0.025 cm²-K/W thermal resistance at 1 kW/cm² heat flux and evaporator exit vapor qualities at or exceeding 90% at less than 10% absolute pressure drop. Unlike previous experiments by the authors of this work, in which the header, manifold, and Si chip were press-fit together, in the present work, the header and manifold are formed as one unit, and the chip and header-manifold unit are bonded together using a proprietary soldering technique. These improvements remove all possible flow leakage points, ensuring that all of the fluid flows through the micro-grooved heat transfer surface, thereby improving thermal performance and preventing avoidable early onset of critical heat flux. In addition, this approach also reduces package weight and volume, and allows for better flow distribution due to larger internal flow area made possible from the manifold fabrication technology. This work will briefly describe the procedure used to metalize and solder the chip to the manifold, as well as leakage and pressure tests to ensure the system can handle the expected loads. It will then detail calibration of experimental apparatus, and the single-phase and two-phase experiments performed with the cooler, focusing on overall heat transfer coefficient and pressure drop results. In the end, single-phase experiments revealed the presence of microchannel clogging, which acts to increase pressure drop, reduce heat transfer coefficient, and introduce hotspots. The presence of hotspots was confirmed using an infrared camera. Two-phase tests achieved heat fluxes in excess of 560 W/cm², and peak fin conductances between 200 kW/m²-K and 280 kW/m²-K at vapor qualities between 21-35%, respectively. However, higher heat fluxes, conductances, and vapor qualities are expected with removal or prevention of hotspots resulting from microchannel clogging.