The effects of current stressing at 104 A/cm2 on Cu/42Sn-58Bi/Cu reaction couples with a one-dimensional structure at 23°C, 50°C, and 114°C were investigated. The microstructural evolution during electromigration was examined using scanning electron microscopy. The temperature dependence of the coarsening of the Bi-rich phase, the dominant migrating entity, and hillock/whisker formation in eutectic Sn-Bi were investigated under high current density. During current stressing at 104 A/cm2, the average size of the Bi-rich phase remained the same at 23°C, increased at 50°C, and shrank at 140°C. Bi accumulated near the anode side at both high (50°C, 140°C) and low temperature (23°C). At high temperatures, both Sn and Bi diffused towards the anode side, but Bi moved ahead of Sn during current stressing. However, at low temperatures, Sn reversed its direction of migration to the cathode side. Pure Bi hillocks/whiskers and a mixed structure of Sn and Bi hillocks were extruded as a consequence of compressive stress from electromigration- induced mass flow towards the anode side.
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The authors acknowledge financial support of this work from the the New Century Excellent Talent Support Program, Ministry of Education, and the Funding Project PHR (IHLB).
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Xu, G., He, H. & Guo, F. Temperature-Dependent Phase Segregation in Cu/42Sn-58Bi/Cu Reaction Couples under High Current Density. J. Electron. Mater. 38, 273–283 (2009). https://doi.org/10.1007/s11664-008-0562-9
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DOI: https://doi.org/10.1007/s11664-008-0562-9