Examination of Electromigration Effects in Sn-Bi Based Solder Joints

A study of the effect of the variation of processing parameters on the microstructure of Pb free solder joints, and their performance under current stressing. The effect of varying reflow temperature, under bump metallurgy and solder joint geometry on the microstructure of assemblies was examined. Effects were examined of different current densities and temperatures on Bi migration in Sn-Bi based solder joints. A model of Bi accumulation in these structures was constructed and used to predicted mean times to failure.

Bio: Eric Cotts is a professor in the Materials Science program, and in the Physics department, at Binghamton University. He received his BS degree from Cornell University in 1978 and his PhD degree from the University of Illinois at Urbana-Champaign in 1983. His research group studies phase transformations in metal systems, with a focus on applications for microelectronic devices. Studies of the dependence of nucleation rates of undercooled Sn on impurity content provide insight in to control of microstructure and recommendations for the processing of interconnects. Examination of the effects of thermal history and current stressing on the microstructure of SnBi-based solders lead to expressions for the mean time to failure as a function of current density, temperature, metallization and solder joint geometry.