Reliability and Au embrittlement of lead free solders for BGA applications

Pb-free solder for electronics assemblies is fast becoming a reality, primarily because of market driven forces. This affects the entire electronic manufacturing industry, from component supplier to equipment manufacturer. While the industry has identified possible alternates to Sn-Pb solder alloy, much work still needs to be done, especially in the area of component and board level reliability, solder/surface interactions, and assembly process development. The reliability of Pb-free solder joints for BGA applications under temperature cycle conditions for three different packages is compared in this paper. Two Sn-Ag-Cu compositions are considered and their reliability is compared with Sn-Pb alloy. In addition, ball shear testing was performed after 0, 24, 48, 96, 192, 384, and 504 hours of high temperature aging. The results indicate that the solder joint reliability generally improves when Pb-free solder is used; however, the degree of improvement is package dependent. The ball shear data also favors Sn-Ag-Cu alloy over Sn-Pb alloy. The data also indicates that using Sn-Ag-Cu alloy for solder balls can possibly eliminate the Au embrittlement issue, often encountered in BGA type packages with Sn-Pb balls.