Traditional power electronics for military and fast computing applications are bulky and heavy. The “mechanical design” of electronic structure and “materials” of construction of the components have limitations in performance under very high temperature conditions. The major concern here is “thermal management.” To be more specific, this refers to removal of high-concentration hotspot heat flux >5 kW/cm2, background heat flux >1 kW/cm2, and “miniaturization” of device within a substrate thickness of <100 μm. We report on the novel applications of contact-based thermoelectric cooling (TEC) to successful implementations of high-conductivity materials - diamond substrate grown on gallium nitride (GaN)/AlGaN transistors to keep the hotspot temperature rise of device below 5 K. The requirement for smarter and faster functionality along with a compact design is considered here. These efforts have focused on the removal of higher levels of heat flux, heat transfer across interface of junction and substrate, advanced packaging and manufacturing concepts, and integration of TEC of GaN devices to nanoscale. The “structural reliability” is a concern and we have reported the same in terms of mean time to failure (cycles) of SAC305 (96.5% tin, 3% silver, 0.5% cu) solder joint by application of Engelmaier's failure model and evaluation of stresses in the structure. The mathematical equation of failure model incorporates the failure phenomena of fatigue and creep in addition to the dwell time, average solder temperature, and plastic strain accumulation. The approach to this problem is a nonlinear finite element analysis technique, which incorporates thermal, mechanical, and thermoelectric boundary conditions.
GaN is increasingly be ing used in a wide variety of power electronic applications. The piezoelectric nature of GaN, however, can result in defect generation and can modify the electrical performance of power devices, especially AlGaN/GaN high electron mobility transistors (HEMTs). The cooling mechanisms used to cool the GaN can create thermal gradients that can exaggerate this piezoelectric effect. In this study, multiphys ics finite element mode ling was used to determine the thermal gradients, the resulting thermo-mechanical stresses, and the attendant changes in the electric fields resulting from piezoelectric interaction seen in the HEMT. Devices were then tested on a probe station to va lidate the results of the mode ling. Evident dra in and gate current and on-resistance degradation were observed after a 30 minute voltage and current stress was applied to the HEMT.
Power electronic modules are exhibiting ever increasing power density as a result of compound semiconductor devices being placed in packages of decreasing size. This has led, in turn, to higher volumetric heat generation, which is driving the development of advanced thermal management approaches, including integration of single and two-phase microchannel coolers into the power electronics package. Reliable integration and operation of these coolers is essential for maintaining the performance and reliability of the power electronic system as a whole. This paper will present models for the critical failure mechanisms in microchannel coolers, including erosion/corrosion and cooler fracture.
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