Liquid cooling using integrated microscale heat exchangers are a promising future technology to address issues associated with integrated circuit thermal management. This paper reports the first results of microchannel heat exchangers fabricated directly in the back of silicon chips with integrated front side heaters and temperature sensors. These chips were mounted on organic substrates using C4 bumps and underfill and then these packages were mounted onto a motherboard using μPGA (Micro-Pin Grid Array) socket. The chips contained two metallic heaters; a 10 mm × 13 mm heater in order to provide uniform heating and a small 400 μm × 400 μm heater in order to simulate hotspots on actual microprocessors. The chips had multiple metallic temperature sensors distributed over the die area. Three different designs covering different widths and depths of microchannels were fabricated. The smallest width was 61 μm and the smallest depth was 180 μm. Thermal resistances and pressure drops of the three designs were measured. The best thermal resistance (junction to outlet of fluid) of 0.09 °C-cm2/W, was obtained using a 61 μm wide and 272 μm deep microchannel. The chips were also tested under non-uniform heating conditions by powering the hotspot heaters up to a heat flux of 1250 W/cm2.   This paper was also originally published as part of the Proceedings of the ASME 2005 Heat Transfer Summer Conference.

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