The phenomenon of rare earth (RE) additions inducing whisker growth in Sn-0.7Cu-Nd (0.1–5 wt.%Nd) solder is reported. The results showed that Nd exists as Sn3Nd in the microstructure of the solder alloys. A snowflake-like Sn3Nd was observed when Nd ≤ 0.5 wt.%. After exposure to ambient conditions, the Nd-bearing alloys have a strong tendency toward whisker growth, with a short incubation time for whisker nucleation (only several hours). All whiskers originated from the Sn-Nd compound, where whiskers grew relatively fast; the average growth rate of the five longest whiskers was approximately 4 Å/s, and a 190 μm whisker was observed within 480 h. Based on these results, it was predicted that whisker growth would be inevitable for all RE-bearing solders. The cause of this phenomenon is also discussed. Finally, the authors suggest that any solders doped with RE should be carefully considered again.
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Acknowledgements
This research was supported by the National Science Foundation of China (no. 50871119). The authors would like to thank Mrs. G.C. Ma and Mrs. H. Feng in this Institute for their assistance in SEM observation, and Mr. J.P. Daghfal and Dr. W. Warke for editorial assistance.
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Liu, M., Xian, AP. Tin Whisker Growth on the Surface of Sn-0.7Cu Lead-Free Solder with a Rare Earth (Nd) Addition. J. Electron. Mater. 38, 2353–2361 (2009). https://doi.org/10.1007/s11664-009-0926-9
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DOI: https://doi.org/10.1007/s11664-009-0926-9