RF/Microwave Die Attach of Gallium Nitride Devices Achieving Less Than 1 Voiding in a Flux-Free Environment

摘要

High power devices operating at high temperatures are sources of excessive heat generation, whether the application is automotive, RF/Microwave, military, or commercial power components. Removal of this excessive heat is necessary not only for proper operation of the device, but also for longevity and reliable performance. The attachment interface between a high power device and a particular substrate, whether metal, sapphire, ceramic, or other exotic material, must be essentially void free. Voids consisting of air pockets are very poor thermal conductors and jeopardize the efficient heat transfer to the heat sink or substrate. Reducing or eliminating voids is paramount to a successful die attach and may be verified by either X-Ray or SAM (scanning acoustical microscopy). Our studies consisted of soldering a gallium nitride die to a copper tungsten thermal spreader using an Au80Sn20 solder preform. The equipment used was a dedicated vacuum/pressure reflow furnace which has the capabilities to reduce voids by using a pressure differential controlled process. Our findings will review the successful achievement of essentially void free die attach with a void level of less than 1% as verified by X-Ray and SAM scans. As a result of not using flux and achieving a void free solder interface, long term reliability is enhanced due to the absence of corrosive flux residue which would likely degrade the device over time.