Solderability, IMC evolution, and shear behavior of low-Ag Sn0.7Ag0.5Cu-BiNi/Cu solder joint

The solderability, intermetallic compounds (IMC) evolution, and shear behavior of the low-Ag Sn0.7Ag0.5Cu-3.5Bi-0.05Ni (SAC0705-BiNi)/Cu solder joint was investigated by comparing with Sn0.7Ag0.5Cu (SAC0705)/Cu and Sn3.0Ag0.5Cu (SAC305)/Cu solder joints. Experimental results demonstrated that the melting temperature of Sn0.7Ag0.5Cu-BiNi solder alloy was lower than that of SAC0705 and SAC305 solder. But the melting range of Sn0.7Ag0.5Cu-BiNi was wider. Compared with the other two kinds of alloys, SAC0705-BiNi showed the best wettability. SAC0705/Cu, SAC0705-BiNi/Cu, and SAC305 solder joints appeared similar IMC morphologies and grain size at the beginning of soldering, but evolved to different appearance as the soldering process proceeded. The growth rate of the IMC grains in SAC0705-BiNi/Cu solder joint was the lowest because of the refinement of Ni. SAC0705-BiNi/Cu solder joint showed the highest shear strength before and after being aged, mainly due to the enhancement of solid solution strengthening and dispersion strengthening of Bi and Ni in the bulk solder, as well as the refinement of Ni at the soldering interface.