Electrochemical Migration and Rapid Whisker Growth of Zn and Bi Dopings in Sn-3.0Ag-0.5Cu Solder in 3wt.% NaCl Solution
Electrochemical migration (ECM) tests and rapid whisker growth on Sn-3.0Ag-0.5Cu solder candidates doped with Zn and Bi on Cu-plated FR-4 printed circuit board were conducted by applying constant voltage. The results showed that dendritic shape were different when the doped metals were different. When Zn was doped in SAC solder, dendrites looked like tree trunk, while that of Bi doping looked like rose, which was due to the different composition of SAC candidates. Comparing the length of dendrites at the same condition, it could be concluded that dendrite growth might be suppressed by Bi addition, which the contrary effect suitable to Zn addition. EDAX results showed that the main content on dendrites was Sn with or without Bi doping, while the main content was Zn, Sn, and Ag with Zn doping and Zn/Bi dopings. Whisker growth test verified that Sn accounted for a majority (larger than 95wt.%), no difference could be seen on whiskers of SAC solder candidates although the contents of SAC solder candidate were differently. The whisker growth rate were not different although the doped metals were different largely. Both dendrite growth and rapid whisker growth of SAC solder candidates doped with Zn and Bi were harmful to micro/nanoelectronic packaging attributing to bridge short circuit in PWBs industries.
Zhong Cao, Xueqiang Cao, Lixian Sun, Yinghe He
L. Hua et al., "Electrochemical Migration and Rapid Whisker Growth of Zn and Bi Dopings in Sn-3.0Ag-0.5Cu Solder in 3wt.% NaCl Solution", Advanced Materials Research, Vols. 239-242, pp. 1751-1760, 2011