Abstract
The purpose of this study is to investigate the effect of addition of trace Ni and Ge into Sn-6.4Sb-3.9Ag（mass%）lead-free solder
on its mechanical properties using miniature size specimens. As the solder alloy in which trace Ni and Ge are added, Sn-6.4Sb-
3.9Ag-0.25Ni-0.003Ge（mass%）lead-free solder was prepared. Tensile test and fatigue test were conducted at 25℃ and 200℃.
0.1% proof stress and tensile strength of both solder increase with increasing strain rate and decrease with increasing temperature.
Although tensile strength of both alloys are almost equal at 25℃ and 200℃, that of Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge is superior to
that of Sn-6.4Sb-3.9Ag when the strain rate is 2.0×10-1 s-1. In contrast, elongation of Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge is inferior to
that of Sn-6.4Sb-3.9Ag at 25℃. Furthermore, it was confirmed that the relationship between inelastic strain range and the number
of cycles to fatigue failure obeys the Manson-Coffin equation and both alloys have excellent fatigue properties even at 200℃. From
the results of electron backscatter diffraction pattern analysis, it was found that the crack grows at high angle grain boundaries with
continuous recrystallization in Sn-6.4Sb-3.9Ag at 200℃. In Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge, the crack grows at grain boundaries
formed by solidification.
