Effects of Ag on the Kirkendall void formation of Sn-xAg/Cu solder joints

Abstract

Binary Sn-Ag solders with varying amounts of Ag (0.5, 2.0, and 3.5 wt %) were reacted with Cu under bump metallurgy (UBM) which was electroplated with bis-sodium sulfopropyl-disulfide additive, and the characteristics of Kirkendall void formation at the solder joints were investigated. The results indicate that the propensity to form Kirkendall voids at the solder joint decreased with the Ag content. Subsequent Auger electron spectroscopy analyses showed that Ag dissolved in the Cu UBM reduced the segregation of S to the Cu(3)Sn/Cu interface, which suppressed the nucleation of Kirkendall voids at the interface. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488629]