Sn whisker growth behavior, over periods of time up to 10,080 h at room temperature, was examined for Sn and Sn-Cu, Sn-Ag, Sn-Bi, and Sn-Pb coatings electroplated on copper in 2 lm and 5 lm thicknesses to understand the effects of the alloying elements on whisker formation. Sn-Ag and Sn-Bi coatings were found to significantly suppress Sn whisker formation compared with the pure Sn coatings, whereas whisker growth was enhanced by Sn-Cu coatings. In addition, annealed Sn and Sn-Pb coatings were found to suppress Sn whisker formation, as is well known. Compared with the 2-lm-thick coatings, the 5-lm-thick coatings had high whisker resistance, except for the Sn-Cu coating. Whisker growth was correlated with coating crystal texture and its stability during storage, crystal grain microstructure, and the formation of intermetallic compounds at Sn grain boundaries and substrate-coating interfaces.

In the present study, the degradation of the Ag-epoxy conductive adhesive/Sn interface at 85°C and 85% relative humidity was investigated through a variety of microstructural analyses. After the humidity test, the interfacial electrical resistance increased, and the interface was easily separated by external stress. Transmission electron microscopic (TEM) analyses indicated that two different Sn oxides, namely SnO and SnO 2 , were formed inhomogeneously at the interface in the humidity test. In addition, many voids were formed at the interface between Sn oxides and Sn plating. These Sn oxides and voids were the cause of the interfacial degradation.

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