Chip stacks are a crucial building block in advanced 3D microsystem architectures and can accommodate shorter interconnect distances between devices, reduced power dissipation, and improved electrical performance. Although enhanced conduction can serve to transfer the dissipated heat to the top and sides of the package and/or down to the underlying PCB, effective thermal management of stacked chips remains a most difficult challenge. Immersion cooling techniques, which provide convective and/or ebullient heat transfer, along with buoyant fluid flow, in the narrow gaps separating adjacent chips, are a most promising alternative to conduction cooling of three-dimensional chip stacks. Application of the available theories, correlations, and experimental data are shown to reveal that passive immersion cooling-relying on natural convection and/or pool boiling - could provide the requisite thermal management capability for 3D chip stacks anticipated for use in much of the portable equipment category. Alternatively, pumped flow of dielectric liquids through the microgaps in 3D stacks, providing single phase and/or flow boiling heat absorption, could meet many of the most extreme thermal management requirements for high-performance 3D microsystems. Use of deionized water is shown to provide an order of magnitude improvement in heat dissipation relative to the available dielectric fluids.
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