Investigation of microstructure and mechanical properties of novel Sn-0.5Ag-0.7Cu solders containing small amount of Ni

This work investigates the effects of small additions (0.05 and 0.1 wt.\%) of Ni on the microstructure and mechanical properties of low Ag content Sn-0.5Ag-0.7Cu (SAC (0507)) lead-free solder alloy. The addition of 0.05Ni resulted in the microstructural refinement, uniform distribution of the Ag3Sn and (Cu, Ni)(6-)Sn-5 intermetallic compounds (IMCs) and small primary beta-Sn grains. This apparently enhances the mechanical strength and microhardness. However, the addition of 0.1Ni leads to the formation of relatively high fraction of the primary beta-Sn phase and the IMCs appeared abrasive within the matrix. As a result, the SAC (0507)-0.1Ni solder exhibits low tensile strength, microhardness and large elongation, which produce a soft and highly compliant bulk solder. In addition, the strength of all studied alloys increases with increasing strain rate and decreasing testing temperature, showing strong strain rate and temperature dependence. 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. (c) 2013 Elsevier Ltd. All rights reserved.