Ag3Sn compound formation was observed to evolve from the Cu side to the Ni side in Ni/Sn5Ag/Cu solder joint upon reflow process. The transformation of the interfacial compound phase at the Sn5Ag/Ni interface, i.e., from Ni3Sn4-based compound to Cu6Sn5-based compound, changes the interfacial energy state, which is the main driving force for the evolution of Ag3Sn compound formation. The evolution consequence of Ag3Sn compound suggests that Sn5Ag/(Cu,Ni)6Sn5 interface is the best energy-preferential heterogeneous nucleation site for the Ag3Sn compound phase, comparing to the Sn5Ag/Cu6Sn5 interface and the Sn5Ag/Ni3Sn4 interface. In addition, the lower Cu concentration near the Ni side is another added driving force for the heterogeneous nucleation of Ag3Sn phase at Sn5Ag/(Cu,Ni)6Sn5 interface.
- Intermetallic alloys