Formation of silicon reentrant cavity heat sinks using anisotropic etching and direct wafer bonding

A novel silicon reentrant cavity heat sink for enhanced liquid cooling of silicon multichip substances has been fabricated using a two-step anisotropic etching process followed by silicon direct wafer bonding. Cavity mouth openings ranging from 8 to 500 mu m have been batch fabricated with the two-step process. The reentrant cavities suppress the temperature overshoot normally associated with the transition between the free convection and nucleate boiling regimes of liquid immersion cooling. Nucleate boiling has been observed to occur at heater fluxes below 2 W/cm/sup 2/ for both increasing and decreasing heat flux conditions. Specific thermal contact resistances (heater fluid) of less than 0.6 K-cm/sup 2//W have been measured in Freon-22, R-113, and FC-72.<
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