Intermetallic Growth Mechanism and Mechanical Properties of Post-Annealed SAC305 Solder Joints on Cu-Based Electrode Interfaces.

Intrinsic Cu- and Ni-added Cu electrodes were prepared to study Sn-3Ag-0.5Cu lead-free solder joints. Our work focused on three categories: (1) formation and role of intermetallic compounds, (2) structural and compositional change of intermetallic compounds due to thermal aging effects, and (3) mechanical bonding strength of solder joints. A series of SEM, EDX, and bonding test analyses were performed on two electrode types to study joint morphologies, the types of intermetallic compounds formed, and bonding strengths, respectively. As a result, after heat treatments at 150 °C for 10 h, 100 h, and 300 h, Cu6Sn5 and (Ni, Cu)3Sn4 were obtained at the interfaces of the intrinsic Cu electrode and the Ni-added Cu electrode, respectively. In the Ni-added Cu electrode samples, the growth rate of the intermetallic compounds was reduced, but the mechanical bonding strength had a higher value compared to that of the intrinsic Cu electrode. The bonding characteristics under different heat treatment conditions are also discussed.