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-Ni
3
Sn
4
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 Ni
3
Sn
4
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 Ni
5
(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 Ni
3
Sn
4
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/Ni
3
Sn
4
and SB/Ni systems. The (Cu, Ni)
6
Sn
5
was observed in the SAC/Ni
3
Sn
4
and SC/Ni
3
Sn
4
systems. In the SZ/Ni
3
Sn
4
system, the Ni
5
(Zn,Sn)
21
phase was formed at the interface. Meanwhile, the Zn atoms diffused toward the Ni
3
Sn
4
substrate to incorporate the sublattice of the Ni
3
Sn
4
phase. Finally, the Ni
3
(Sn,Zn)
4
layer was observed below the Ni
5
(Zn,Sn)
21
phase.