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We developed a new lead-free solder alloy, an Sn-Ag-Cu base to which a small amount of Ni and Ge is added, to improve the mechanical properties of solder alloys. We examined creep deformation in bulk and through-hole (TH) form for two lead-free solder alloys, Sn-3.5Ag-0.5Cu-Ni-Ge and Sn-3.0Ag-0.5Cu, at elevated temperatures, finding that the creep rupture life of the Sn-3.5Ag-0.5Cu-Ni-Ge solder alloy was over three times better than that of the Sn-3.0Ag-0.5Cu solder at 398 K. Adding Ni to the solder appears to make microstructural development finer and more uniform. The Ni added to the solder readily combined with Cu to form stable intermetallic compounds of (Cu, Ni) 6 Sn 5 capable of improving the creep behavior of solder alloys. Moreover, microstructural characterization based on transmission electron microscopy analyses observing creep behavior in detail showed that such particles in the Sn-3.5Ag-0.5Cu-Ni-Ge solder alloy prevent dislocation and movement.

Sn-Ag-Cu-Ni-Ge solder alloy has been developed to improve the mechanical properties of the Sn-Ag-Cu base solders and prevent oxidation of those solders. In this paper, an interfacial reaction and microstructure between the solder and a Cu electrode were investigated under heat exposure conditions. It was found that intermetallic compounds growth at the interface of the solder and the Cu electrode was greatly affected by amounts of added elements. Adding Ni in the solder can suppress the formation and growth of intermetallic compounds (IMCs) such as Cu-Sn and decreasing the amount of adding Ag in the solder can prevent the formation and growth of Ag3Sn. Moreover, it was found that there was an effect of suppress the growth of the Cu3Sn formed on the interface of Cu and (Cu,Ni)6Sn5 by adding Ni from analysis results of EDX and TEM.

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A new lead-free solder alloy, Sn-Ag-Cu base adding a small amount of Ni, Ge, has been developed to improve their mechanical properties and prevent oxidation in solder alloys. In this paper, creep properties of two lead-free solder alloys, Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge (abbr. Sn-3.5Ag-0.5Cu-Ni-Ge) solder and Sn-3.0Ag-0.5Cu solder, were investigated at three temperatures ranging from 313K-398K. It was found that the creep strength of the Sn-3.5Ag-0.5Cu-Ni-Ge solder is higher than that of the Sn-3.0Ag-0.5Cu solder. Especially in the low stress region at 398K, the creep rupture time of the Sn-3.5Ag0.5Cu-Ni-Ge solder is about three times as long as that of the Sn-3.0Ag-0.5Cu solder. The microstructure of these solder alloys show that the addition of Ni was found to refine the effective grain size and provide a fine and uniform distribution of Ag3Sn in the solidified microstructure. The microstructure of the Sn-3.5Ag-0.5Cu-Ni-Ge solder is more stable than that of the Sn-3.0Ag-0.5Cu solder alloy after aging treatment at 398K, 1000 h. TEM observation was also performed, showing that precipitations of (Cu, Ni)6 Sn5, the diameter of which are about 0.5 μm, are distributed in the Ag3Sn/β-Sn phase eutectic area of the Sn-3.5Ag-0.5Cu-Ni-Ge solder after creep test at 398K, 5MPa. It is thought that the precipitations of (Cu, Ni)6 Sn5 contribute to creep strength in the Sn-3.5Ag-0.5Cu-Ni-Ge solder alloy.