Passive Immersion Cooling of 3-D Stacked Dies

Three-dimensional die stacking increases integrated circuit (IC) density, providing increased capabilities and improved electrical performance on a smaller printed circuit board (PCB) footprint area. However, these advantages come at the expense of higher volumetric heat generation rates and decreased thermal and mechanical access to the die areas. Passive immersion cooling, allowing for buoyancy-driven fluid flow between stacked dies, can provide high heat transfer coefficients directly on the die surfaces, can easily accommodate a wide variety of interconnect schemes, and is scalable to any number of dies. A methodology for the optimization of immersion cooled 3-D stacked dies is presented, including the effects of confinement on natural convection and channel boiling. Optimum die spacings for both single and two phase cooling with saturated FC-72 are found to be on the order of half a millimeter for typical microelectronics geometries and to yield heat densities of 10-50 W/cm³ in natural convection and 100-500 W/cm³ in channel boiling.