Junction temperature distributions with hot spots and uniform and non-uniform heat fluxes in direct-to-die passive two-phase immersion cooling

Hot spots as well as uniform and non-uniform heat fluxes within integrated circuits, exert a significant influence on the thermal management of both heterogeneous integration and three-dimensional packaging. To address this challenge, this study introduces an innovative approach that utilizes a Cu-Si-based flat thermosyphon heat sink (FTHS) to implement direct-to-die passive two-phase immersion cooling. Specifically, the effects of the fill ratio, tilt angle, and variable heat flux distributions were explored. A thermal test chip (TTC) was employed to adjust heat flux across three distinct heating zones to create diverse experimental scenarios. The junction temperature distributions, along with both overall and spreading thermal resistances, were assessed. Key findings indicated that the non-uniformly increasing heat flux distribution across the three heating zones enhanced the heat transfer capacity by 110% compared to that of the uniform heat flux distribution, while improving the temperature uniformity by 10 °C. In addition, compared to baseline configurations, the Cu-Si-based FTHS integrated into data center servers could extend the lifespan of electronic components by a factor of 9.85 while reducing the room air cooling load by 33.17 kJ/kg. The maximum coefficient of performance and measured fan power consumption were 217 and 1 W, respectively. These findings underscore the potential of integrating direct-to-die passive two-phase immersion cooling within Cu-Si-based FTHS and demonstrate how a non-uniformly increasing heat flux distribution can improve thermal design and reduce energy consumption. This study further provides optimization recommendations for the layout of high-performance digital logic chips and high-bandwidth memory in heterogeneous integration.