Development of Scalable Silicon Heat Spreader for High Power Electronic Devices

Abstract

A silicon heat spreader, called hexcell, is presented to develop thin, strong, interconnected, and scalable heat transfer devices for high power electronics cooling. Several key technical aspects, reflected characteristics of fabrication, thermomechanical, hermetic sealing, and heat transfer on wick structures, have been performed to underlie the system integration. The hexcell prototypes are developed through microelectromechanical system photolithography and dry-etch processes, associated with eutectic bonding to form a sealed silicon chamber. Hexcells are structurally optimized to minimize the stress, expanding the maximum operating pressure and temperature ranges. As a result, the developed hexcells can survive 0.32 MPa pressure difference and are able to sustain an operating temperature over 135°C. Experimental results of both helium and vapor leakage tests indicate that eutectic bonding with limited bonding surface area may not provide hermetic sealing. Vacuum sealing is achieved by introducing epoxy to fill the leak pine-holes on the bonding interface. The developed hexcell wick exhibits good heat and mass transport performance, reaching a maximum 300 W/cm2 cooling capacity with 35°C superheat as demonstrated with a prototype of a 2×2 mm2 heating area.