Advanced Thermal Integration for HPC Packages with Two-Phase Immersion Cooling

Two-phase immersion cooling is a promising technology for cooling 2.5D/3D heterogeneous integration packages for 5G and AI applications. For the first time, this study applies two-phase immersion cooling to a chip on wafer on substrate (CoWoS) HPC package with a thermal design power (TDP) of up to 900 W. Two different boiler designs integrated on CoWoS packages are considered consisting of porous surface structures such as powder or mesh deposited on a solid copper base and vapor chamber base, respectively. The thermal characteristics of the two designs are examined and compared experimentally. It is shown that the boiler with a copper base has a junction-to-ambient thermal resistance (Ψ
JA
) of 0.0542 (°C/W). By contrast, the boiler with a vapor chamber base achieves a lower thermal resistance of Ψ
JA
= 0.0355 (°C/W) due to its enhanced heat spreading effect. The power density characterization is also investigated using monolithic die flip chip package. The boiler with a vapor chamber base shows superior cooling performance with the power density of up to 2 W/mm
²
if excess temperature is 50⁰C. Computational fluid dynamics (CFD) models of the two boiler designs are constructed and calibrated. A CFD model of a CoWoS HPC package is then established to investigate the thermal performance of the package under the two boiler designs. The simulation results are shown to be in excellent agreement with the experimental data. Accordingly, the feasibility of the proposed model for performing thermal analyses at the component-to-system level is confirmed. Overall, the results presented in this study confirm the ability of two-phase immersion cooling systems to meet the high power dissipation and density requirements of CoWoS platforms and other 2.5D/3D heterogeneous integration packages for HPC products.