Reaction properties and interfacial intermetallics for Sn-xAg-0.5Cu solders as a function of Ag content

Wetting and interfacial reactions were investigated for Sn-xAg-0.5Cu alloys, in which the Ag content had a variation from x = 1.0 to x = 4.0. Differential scanning calorimetry (DSC) was used to investigate the range of the melting temperature and the solidification temperature by measuring the endothermic and the exothermic heat flow, respectively. Low Ag contents increased the melting temperature ranges and deteriorated the wetting properties such as zero cross time and wetting force measured at two seconds. The extent of undercooling increased and the thickness of intermetallic compounds (IMC) decreased as the Ag content decreased. As the Ag content decreased, the initial IMC thickness decreased due to the large undercooling and, during the solid aging at 170 °C, the IMC growth slightly decelerated because of the small diffusion coefficient. For the application of good drop shock reliability, Sn-Ag-Cu solder of low Ag content should be beneficial due to the restraint of the IMC growth (Cu₆Sn₅ and Cu₃Sn) and of the coarse plate-like IMC (Ag₃Sn).