Surace-Enhanced Two-Phase Cold Plate Designs for High Power Dissipation in Data Centers

Multi-chip modules (MCMs) have become a popular architecture adopted in datacenters to collocate computation, memory, and communications. Their high-power density brings considerable challenges to the use of conventional air-cooling. Higher facility temperatures are preferred because they enable heat capture and reuse as well as simpler heat rejection architectures with low water usage such as dry cooling. This push for higher coolant temperature, alongside the elevated power density, has placed an even more stringent requirement on minimizing the chip junction-to-coolant thermal resistance. Here, we developed a high-performance, energy-efficient, and scalable thermal management approach based on two-phase cooling using R1233zd(E) refrigerant. The approach utilizes custom copper and aluminum microchannel evaporators capable of dissipating heat loads up to 1 kW over a 76 mm × 76 mm MCM-relevant footprint. The custom high-aspect-ratio (~10) microchannel (300~550 μm) evaporators are designed and fabricated using either electrical discharge machining or skiving. Experiments showed that a skived copper cold plate with 550 μm channel width, 375 μm fin width, and 5.25 mm fin height can reach a junction-to-coolant thermal resistance < 0.0083 K/W at a 1 kW heat load. We employ surface structuring to enhance the refrigerant flow boiling performance. Etched aluminum is used due to its promotion of nucleation and rewetting arising from its roughness and wickability. Etching was carried out on an EDM aluminum fin plate with 300 μm channel width, 250 μm fin width, and 2.3 mm fin height. We observed a 1.7× higher refrigerant flow boiling heat transfer coefficient improvement after surface structuring, achieving a thermal resistance of 0.0085 K/W at 1,1 kW heat load. Our work demonstrates that two-phase cooling, favored by low-profile MCMs, can enhance the power density at the server level.