Interfacial microstructure evolution between eutectic SnAgCu solder and Al/Ni(V)/Cu thin films

The evolution of interfacial microstructure of eutectic SnAgCu and SnPb solders on Al/Ni(V)/Cu thin films was investigated after various heat treatments. In the eutectic SnPb system, the Ni(V) layer was well protected after 20 reflow cycles at 220 degreesC. In the SnAgCu solder system, after 5 reflow cycles at 260 degreesC, the (Cu,Ni)(6)Sn-5 ternary phase formed and Sri was detected in the Ni(V) layer. After 20 reflow cycles, the Ni(V) layer disappeared and spalling of the (Cu,Ni)(6)Sn-5 was observed, which explains the transition to brittle failure mode after ball shear testing. The different interfacial reactions that occurred in the molten SnAgCu and SnPb systems were explained in terms of different solubilities of Cu in the two systems. The dissolution and formation of the (Cu,Ni)(6)Sn-5 phase were discussed on the basis of a Sn-Ni-Cu phase diagram. In the solid-state aging study of the SnAgCu samples annealed at 150 degreesC for up to 1000 h, the Ni(V) layer was intact and the intermetallic compound formed was Cu6Sn5 and not (Cu,Ni)(6)Sn-5, which is the same as was observed for the eutectic SnPb system.