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.

The purpose of the present study is to investigate the melting properties, microstructures, tensile properties and fatigue properties of Sn 5Sb(0.050.50)Ni (mass%) high-temperature lead-free solders. The solidus temperature and liquidus temperature of the Sn5SbNi solders are approximately equal to those of the Sn5Sb alloy. From the result of EPMA mapping analysis and the SnSbNi ternary phase diagram, the Sn 5SbNi solders are found to consist of ¢-Sn, SbSn and NiSb phases. As the amount of Ni in the Sn5SbNi solder increases, the number of NiSb phases increases and the phases are coarsened so that the 0.1% proof stress and tensile strength increase, and the elongation decreases at 25°C. In contrast, the effects of the Ni content on the tensile properties are negligible at 150°C and 200°C. The fatigue ductility exponent ¡ of the Sn 5SbNi solders is smaller than that of the Sn5Sb solder at 25°C. At 150°C and 200°C, the ¡ values of Sn5Sb0.05Ni and Sn5Sb0.10Ni remain small, whereas those of Sn5Sb0.25Ni and Sn5Sb0.50Ni increase. This means that the Sn5SbNi solders with 0.050.10 mass% Ni have superior fatigue properties to the Sn5Sb solder in the temperature range from 25°C to 200°C.

The effect of the addition volume of Ni on the microstructures and tensile and fatigue properties of Sn-6.4Sb-3.9Ag (mass%) was investigated using micro-size specimens. The addition of Ni into Sn-6.4Sb-3.9Ag tends to increase the number of grains formed in the solidification process and produce a high-angle grain boundary. An amount of 0.1% proof stress of Sn-6.4Sb-3.9Ag decreases with an increase in the Ni addition volume at a strain rate of 2.0 × 10−1 s−1. The effect of the addition of Ni into Sn-6.4Sb-3.9Ag on tensile strength is negligible at both 25 °C and 175 °C. The elongation of Sn-6.4Sb-3.9Ag decreases with an increase in the Ni addition volume at 25 °C according to the fracture mode change from ductile chisel point fracture to shear fracture. The effect of the addition of Ni into Sn-6.4Sb-3.9Ag on the elongation is negligible at 175 °C. The low cycle fatigue test result shows that the fatigue life does not degrade even at 175 °C in all alloys investigated. The fatigue life of Sn-6.4Sb-3.9Ag-0.4Ni (mass%) is superior to those of Sn-6.4Sb-3.9Ag and Sn-6.4Sb-3.9Ag-0.03Ni (mass%) in the high cycle fatigue area. The electron back scattering diffraction (EBSD) analysis result shows that fine recrystallized grains are generated at the cracked area in Sn-6.4Sb-3.9Ag-0.4Ni in the fatigue test at 175 °C, and the crack progresses in a complex manner at the grain boundaries.

Tensile and low cycle fatigue properties of Sn-5Sb (mass%) and Sn-10Sb (mass%) were investigated using miniature size specimens, and fracture behaviors of the specimens were observed. Tensile strength and 0.1% proof stress of both alloys decrease with increasing the temperature. The tensile strength and 0.1% proof stress of Sn-10Sb are higher than those of Sn-5Sb at 25°C. Elongation of Sn-5Sb decreases with increasing the temperature except for a strain rate of 2 × 10−1 s−1, while Sn-10Sb increases with increasing temperature. Although elongation of Sn-10Sb is lower than that of Sn-5Sb at 25°C, the difference between them is small at 150°C. Chisel-point fracture was observed in both alloys regardless of conditions of the tensile test. The low cycle fatigue lives of Sn-5Sb and Sn-10Sb alloys obey the Manson–Coffin equation, and the fatigue ductility exponent, α, was 0.54 for Sn-5Sb and 0.46 for Sn-10Sb in the temperature range from 25°C to 150°C. On the basis of the observation of fractured specimens and the investigation of α, it was clarified that the crack progress can be delayed by the formation of coarse SbSn compounds in the Sn-Sb alloy, and thus the fatigue properties can be improved.

Tensile properties of Sn-5Sb (mass%) and Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge (mass%) were investigated using miniature size specimens and obtained results were compared. Tensile strength of both alloys increase with increasing the strain rate and decrease with increasing the temperature. Although similar dependency to the temperature is observed in 0.1% proof stress, the effect of the strain rate on it is obscure. The tensile strength and the 0.1% proof stress of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge are higher than those of Sn-5Sb. The elongation of Sn-5Sb is relatively stable at the range from 0.4 to 0.6. The elongation of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge which is approximately 0.3, is inferior to that of Sn-5Sb. On the basis of investigation of stress exponent, n, it was clarified that dispersion strengthening by Ag3Sn particulates in Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge is effective to prevent the degradation of creep resistance compared with Sn-5Sb that is strengthened by solid-solution of Sb in β-Sn phases and dispersion of SbSn compounds.