Modular Heat Sink for Chip-Scale GaN Transistors in Multilevel Converters

Pallo, N., Kharangate, C., Modeer, T., Schaadt, J., Asheghi, M., Goodson, K.E., and Pilawa-Podgurski, R., "Modular Heat Sink for Chip Scale GaN Transistors in Multilevel Converters," Proceedings of the Applied Power Electronics Conference, San Antonio, TX, March 4-8,

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The flying capacitor multilevel topology shows promise for high power density inverter designs and presents new cooling challenges. Typical implementations feature a number of
coplanar power transistors, including those with top-cooled, flipchip packages, assembled on a single printed circuit board or array of switching cell daughter boards. Cooling each transistor requires the use of a compressible thermal interface material to compensate for component height tolerance and to provide electrical insulation. However, this interface material presents a high impedance in the thermal path. Thus, a modular approach for forced-air heat sinking is proposed, where variation in height can be accommodated per device while electrical isolation may no longer be necessary. This scheme allows a thinner, less compliant, and higher performance interface material to be used.  Additionally, a 3D-printed manifold is presented as a means to favorably direct forced-air across the cooling surfaces.

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