Suppressing Ni3Sn4 formation in the Sn–Ag–Cu solder joints with Ni–P/Pd/Au surface finish

The interfacial reactions of Sn–3.0Ag–0.5Cu solder jointed with electroless Ni–P/immersion Au (ENIG) and electroless Ni–P/electroless Pd/immersion Au (ENEPIG) were investigated. Cu 6 Sn 5 grew rather slower in ENEPIG samples among all aging conditions as compared with ENIG. Furthermore, the second phase, Ni 3 Sn 4 , started to form in the ENIG aged joints, but not in the ENEPIG aged joints. It was demonstrated that ENEPIG could inhibit the formation of Ni 3 Sn 4 , which further decreased the growth of columnar Kirkendall voids inside the Ni 3 P layer. With less voids formed in the Ni 3 P layer, it is expected that the reliability of ENEPIG joints would be superior to that of ENIG joints. Detailed mechanisms of Ni 3 Sn 4 suppression and void formation were discussed and proposed.