Evolution of microstructure, thermal and creep properties of Ni-doped Sn-0.5Ag-0.7Cu low-Ag solder alloys for electronic applications

For development of lead-free solder for advance electrical components, the correlation of microstructure with thermal and creep properties of novel Ni-doped Sn-0.5Ag-0.7Cu (SAC (0507)) lead free solders has been investigated. Results showed that addition of 0.05Ni into the lead-free SAC (0507) solder led to the microstructural refinement, more uniform distribution of the Ag3Sn, (Cu,Ni)6Sn5 intermetallic compounds (IMCs) and small primary β-Sn grains. However, the SAC (0507)-0.1Ni alloy has relatively high fraction of the primary β-Sn phase and the IMCs appeared coarse within the matrix compared with the other examined alloys. DSC results showed that the addition of Ni did not produce any significant effect on the melting behavior. Interestingly, 0.05 wt.% Ni addition exhibited a drastically reduced undercooling to be 6.3 °C. In terms of creep behavior, the SAC (0507)-0.05Ni gave the highest creep resistance due to the fine dispersion of IMCs. Furthermore, 0.05 wt.% Ni addition can evidently increase the creep-rupture life, about 2.0 times greater than that of the baseline SAC (0507) and approximately 5.0 times better than that of SAC (0507)-0.1Ni solder. Meanwhile, the SAC (0507)-0.1Ni alloy shows lower creep resistance which is mainly attributable to smaller volume fraction of the precipitate phases. Based on the obtained stress exponents and activation energies, it is proposed that the dominant deformation mechanism in SAC (0507) solders is dislocation climb over the whole temperature range investigated.