Elevated temperature tests were performed on molybdenum wirebutton z-axis socket assemblies in an effort to develop and qualify ahigh footprint density burn-in socket for pinless modules. Stress testswere performed at 200° C, with periodic mating and unmating of thesubstrate from the socket. These tests revealed that after 172 hours ofstress, the mean contact resistance increased by over an order ofmagnitude. Individual measurements of the stressed circuit board, socketand substrate revealed that the substrate contributed the majority ofthe observed resistance increase and that the degradation was due todiffusion and oxidation of the Cr/Cu/Ni/Au pad metallurgy on the pinlessceramic substrates. The resistance contributions of the socket andcircuit board pads were also analyzed and various wire button contactmetallurgies were evaluated in order to minimize their role in thedegradation. Overall, this work demonstrates the importance ofmaintaining the integrity of all metallurgical interfaces when usingz-axis interconnects at elevated temperatures
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