A Micromachined Manifold Microchannel Cooler

Abstract

An improved MEMS fabricated, manifold microchannel cooler has been developed for single phase liquid, forced convection. The manifold design uses multiple channel sizes to minimize pressure drop, maximize heat transfer, and improve temperature uniformity across the area of the cooled device. A significant reduction is achieved in thermal resistance between the device and the cooling fluid. This is a critical need in modern electronic components because of the increasing demand for higher power levels and packaging densities. This paper discusses improvements in fabrication, alignment procedure, and packaging in comparison to our previously published work. A wide range of microchannel dimensions have been fabricated and tested to show the effect of channel size on performance. Testing results of the thermal transfer rates will be presented using silicon diodes as heat sources. A 25 mm × 8 mm × 3 mm (thick) silicon cooler was fabricated to cool two 6 mm square devices. The cooler was microfabricated with a silicon three wafer stack and the channels were etched using standard MEMS processing techniques including DRIE. This new device has modified the authors previously published work in a number of ways. First, fabrication sequence has been modified for better depth uniformity and a new alignment technique has been used that incorporates micro ball bearings as passive alignment pins. Second, triangular shaped inlets have been incorporated to further reduce pressure drop. Third, an aluminum nitride layer was incorporated into the layer stack to achieve electrical isolation between the device and the fluid. Finally, thermal characterization has been improved by using aluminum nitride chip resistors as surrogate heat sources with improved reliability and temperature uniformity over the heated area. Dimensional improvements have also been made to improve fluidic performance and lessen the potential of clogging. The manifold channels are 500 μm wide and 1mm deep with a 50 μm fin width. The microchannels are 150 μm deep with a width of 80 μm and a fin width of 40 μm. The aluminum nitride is bonded onto the top of the silicon channels then the chip resistors are bonded with a silver polyimide paste onto the aluminum nitride. The devices fluidic and thermal performance was measured. We have demonstrated an improvement over the previously published manifold microchannel cooler while also demonstrating the use as a multichip module. The manifold microchannel design minimizes the pressure drop across the channel while maximizing cooling potential and temperature uniformity across the area of the device. The experimental results have shown very promising thermal performance of this multi-chip manifold microchannel cooler. Thermal resistances less than 0.4 C/W were measured at flow rates of 400 ccm with a pressure drop of 5.6 psi. Tests were performed with heat fluxes up to 331 W/cm2 with a measured chip temperature rise of only 53C. The results of the testing show very good thermal performance of this device.