Formation and Growth of Intermetallic Compounds at the Interface between Pb-free Solder and Cu-Zn alloy UBM

摘要

Sn-Ag-Cu(SAC) solder containing a small amount of Zn has been revealed to be beneficial in suppressing the formation and growth of intermetallic compounds(IMCs) at the solder joints. In this study, Instead of adding Zn into the SAC solder, we used Cu-20wt%Zn alloy UBM, which was deposited on the Cu pads using electroplating to improve the easy oxidation of solder alloy system including Zn. The growth of interfacial IMCs between SAC solder and Cu-Zn UBM were investigated during soldering at 260°C for 20s and thermal aging at 150°C up to 1000 h, and compared with Cu UBM. In the case of Cu UBM, a typical bilayer of Cu{sub}6Sn{sub}5 and Cu{sub}3Sn was observed at the solder joint interfaces. The growth rate of Cu-Sn IMC layers was much higher than that on Cu-Zn UBM. While in the case of Cu-Zn UBM, the growth of Cu-Sn IMC layers and the formation of large Ag{sub}3Sn plates at the solder joints were remarkably depressed by Zn element in Cu-Zn UBM. Especially, Cu{sub}3Sn IMC layer was strongly suppressed during thermal aging. In addition, Kirkendall voids were not formed at the SAC solder/Cu-Zn UBM interface.