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The reliability of a solder ball joint with a Sn-Ag-Cu-Ni-Ge lead-free alloy, which is expected to be an advanced lead-free solder, was investigated under heat exposure conditions. Solder ball joints with a eutectic Sn-Ag alloy and a ternary Sn-Ag-Cu alloy were also prepared to compare with that of the Sn-Ag-Cu-Ni-Ge alloy. Microstructual observations of the cross sections of the solder ball joints were conducted to investigate microstructural evolutions in the solders and the growth kinetics of reaction layers formed at joint interfaces. The influence of heat exposure treatment on joint strength was investigated by ball shear test. Moreover, the influence of surface treatment of a Cu pad on the reliability of the solder joint was also investigated.

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 impact properties of solder ball joints with Sn-Ag-Cu-Ni-Ge lead-free solders and Cu electrodes were investigated in the aged conditions at 393 K. The impact properties evaluated was compared with Sn-Ag and Sn-Ag-Cu solder joints. The impact properties of Sn-AgCu-Ni-Ge joints were superior to those of Sn-Ag and Sn-Ag-Cu joints. In the cases of Sn-Ag and Sn-Ag-Cu joints, fracture mainly occurred in the intermetallic compounds (IMC) layer formed in the joint interface regardless of aging treatment. On the contrary, main fracture mode was solder fracture in as-reflow Sn-Ag-Cu-Ni-Ge joints. Although the main fracture mode gradually changed from solder fracture to IMC fracture upon aging, Sn-Ag-Cu-Ni-Ge joints had excellent impact reliability compared with Sn-Ag and Sn-Ag-Cu joints even after aging at 393 K for 1000 h.

An influence of content of Ni and Ag in a Sn-Ag-Cu-Ni-Ge lead-free solder has been investigated on microstructure and joint strength of the soldered joint under heat exposure conditions. The growth kinetics of the reaction layer formed at the joint interface has been investigated, and the apparent activation energy of the reaction layer growth has been also examined. Moreover, the soldered joints with Sn-Ag and Sn-Ag-Cu solders were prepared and were compared with the joints with the Sn-Ag-Cu-Ni-Ge solders.