Dissolution behaviors of the Ni and Ni3Sn4 phase in molten lead-free solders

This study investigates the dissolution behavior of metallic substrates-Ni and IMC-Ni₃Sn₄ phase in molten Sn, SAC, SC, SB and SZ at 240, 270, and 300°C. The dissolution rates of the Ni substrate in molten solder follow the order Sn >; SAC >; SC >; SB >; SZ. Many the Ni₃Sn₄ phases with a small grain size were formed at the Sn/Ni system. Because a small grain could provide more groove to let Ni atoms dissolve in the molten Sn, the largest dissolution rate is in the Sn/Ni system. The dense Ni₅(Zn, Sn)₂₁ phase was formed in the SZ/Ni system. This dense layer inhibited the Ni atoms to dissolve into the molten solder. Thus, the SZ/Ni system has the lowest dissolution rate. The dissolution rate of the Ni₃Sn₄ substrate in molten solders follows the order Sn >; SAC >; SC >; SB at 240°C and Sn >; SC >; SAC >; SB at 300°C. There is no any IMC found in the Sn/Ni₃Sn₄ and SB/Ni systems. The (Cu, Ni)₆Sn₅ was observed in the SAC/Ni₃Sn₄ and SC/Ni₃Sn₄ systems. In the SZ/Ni₃Sn₄ system, the Ni₅(Zn,Sn)₂₁ phase was formed at the interface. Meanwhile, the Zn atoms diffused toward the Ni₃Sn₄ substrate to incorporate the sublattice of the Ni₃Sn₄ phase. Finally, the Ni₃(Sn,Zn)₄ layer was observed below the Ni₅(Zn,Sn)₂₁ phase.