Effect of Aging on the Interfacial Reaction between Sn-9Zn-xCr Solder and Cu Substrate

Lhe influences of adding 0.05, 0.1, 0.3, 0.5 wt.% Cr to Sn-9Zn alloy on growth of intermetallic compound layer (IMCs) at the interface of Sn-9Zn-xCr/Cu was investigated during aging treatment at 85degC and relative humidity from 20% to 85% for 100 h, 200 h, 350 h, 500 h. Lhe results show that IMCs thickness of Sn-9Zn-Cr alloys is much thinner than that of Sn-9Zn alloy after aging, but there is little difference on IMCs thicknesses among Sn-9Zn-Cr alloys. It is of interest to note that IMCs growth rate of Sn-9Zn-Cr is about 1/4 times of that of Sn-9Zn alloy. We supposed the reason is that Cr can slow down diffusion rate of Zn in solder. It is quite reasonable to consider that reliability of Sn-9Zn-Cr solder joints is better than that of Sn-9Zn solder joints because of thinner intermetallic compound layer.