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 Sn(3)Nd in the microstructure of the solder alloys. A snowflake-like Sn(3)Nd was observed when Nd a parts per thousand currency sign 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 /s, and a 190 mu m 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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