Thermal performance and stress analysis of heat spreaders for immersion cooling applications

This paper numerically investigates the thermal performance and stress analysis of enhanced Copper (Cu) spreaders for nucleate boiling immersion cooling of high-power electronic chips. The proposed spreaders take advantage of the remarkably high thermal conductivity of Cu (low thermal spreading resistance) and enhanced nucleate boiling heat transfer of dielectric liquid PF-5060 on Microporous Cu (MPC) coating. The spreaders topmost surfaces are smooth (Ra = 0.21 mu m), roughened (Ra = 1.44 mu m), and coated with an 80-mu m thick MPC layer. The spreader thicknesses (delta(Cu)) varied between 1.6 and 3.2 mm, the chip side length (L-C) between 10 and 30 mm, and chip thickness (delta(C)) between 200 and 500 mu m. The numerical results show that MPC spreaders remove the most significant quantity of thermal power (58-270 W) dissipated by underlying chips compared to plane (smooth and roughened) Cu spreaders (28-210 W). The MPC spreaders have the least total thermal resistance, and the corresponding maximum chip temperature (T-c,T-max) is low (67 degrees C) and in a considerable safe margin from the temperature limits set by the high-power chip industry (85-120 degrees C). The maximum Von-Mises stress (70 MPa) on the underlying chips cooled by MPC spreaders is 1/100 of the allowable yield strength of silicon (7 GPa) but much higher than those cooled by plane Cu spreaders (40-44 MPa). The total displacement or deformation due to the temperature gradient is 22 mu m and 4 mu m at the top face of the spreader and at the chip-spreader interface, respectively, for MPC spreaders cooling 500 mu m thick 10 x 10 mm underlying chips. The total displacement is much less (< 0.5 mu m) for all chips cooled by plane Cu spreaders or larger footprint area underlying chips (L-C = 20-30 mm) cooled by MPC spreaders. These numerical results demonstrate the capability of MPC spreaders for immersion cooling by nucleate boiling of dielectric liquid PF-5060 of high-power electronic chips.