Elliptic Micropillar Wick Evaporators for Thermal Management of High Flux Electronics

Advances in chip manufacturing technologies and ascending transistor numbers led to a drastic increase in the thermal loads of electronic components. Since increasing tem-peratures limits the performance and lifespan of electronic components, thermal engineers have focused on the thermal management of non-linearly increasing heat fluxes. No matter how sophisticated the system-level cooling technologies are to counteract increasing high heat fluxes, the temperature gradient on a chip becomes a bottleneck of thermal management. Spreading the high-density heat fluxes through low thermal resistance at the die level or chip level is necessary. Capillary-driven two-phase heat spreaders are remarked to spread high-density heat fluxes due to the liquids' high latent heat, enabling large heat transfer capacities with low thermal resistance. Therefore, two-phase heat spreader embedded chip/electronic packaging solutions have become essential for efficient heat removal and better electronic performance. A well-designed embedded evaporator can meet the high heat fluxes observed on the chip. A proper evaporator design requires accurate performance assessment of a microarray structure, thereof, capturing complex multiphysics in wicking and evaporation. Recently, we developed a model that can capture complex physics (curvature effect, nonuniform heat flux, evaporation, thermocapillarity, etc.) in thin film evaporation from microarrays. In this study, we propose elliptic micropillars as a novel wick structure to meet higher and denser heat removal requirements in two-phase heat spreaders. We investigated the effect of various ellipse aspect ratios (c= 1, 1.5, 2, 2.5, 3, 3.5) on unidirectional capillary flow and thin-film evaporation in elliptic micropillar evaporators while keeping other relevant geometrical parameters (the pitch, height, and porosity) constant. Despite the porosity and height being constant, elliptic micropillars with higher aspect ratios provide substantially improved permeability. Although elliptic micropillars have longer perimeters compared to circular ones, no significant thermal resistance variation is observed due to the lower curvatures attributed to a higher per-meability. Overall, the current study demonstrates a substantial improvement in the heat removal capacity of micropillar wick evaporators with elliptical pillars compared to legacy cylindrical pillars.