Effect of additional elements on the low-cycle-fatigue characteristics of Sn-1.0Ag-0.7Cu solder obtained using a miniature-sized specimen

[Display omitted] •The fatigue life of four low-Ag solders varied with the addition Bi, Ni, Ge.•The stress range response and fracture mechanism were affected on the additions.•The fatigue life of the four solders can be expressed using the energy parameter.•The calculation of the simplified parameter without fatigue test is proposed.•The effects of additions were investigated via microstructural observations. The low-cycle-fatigue properties of lead-free solders based on Sn-1.0Ag-0.7Cu were investigated using miniature-sized specimens. Their mechanical properties were improved by adding bismuth, nickel, and germanium. The effects of additional elements upon the low-cycle-fatigue characteristics of Sn-1.0Ag-0.7Cu, Sn-1.0Ag-0.7Cu-2.0Bi, Sn-1.0Ag-0.7Cu-0.07Ni-0.01Ge, and Sn-1.0Ag-0.7Cu-2.0Bi-0.07Ni-0.01Ge were studied and found to change. The number of cycles to failure of the two solders with bismuth was shorter than those of the two without bismuth. Regarding added nickel and germanium, there were as many cycles to failure of Sn-1.0Ag-0.7Cu-0.07Ni-0.01Ge as there were to Sn-1.0Ag-0.7Cu without nickel or germanium. The stress amplitudes of the two solders with bismuth were higher than those without bismuth. The number of cycles to failure of four solders can be expressed using energy parameters. Microstructures were observed to investigate the differences in the stress range response (softening) and fracture mechanism.