Creep Properties and Microstructure of the Sn-Ag-Cu-Ni-Ge Lead-Free Solder Alloy

Abstract

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.

Comparative study on tensile creep behavior of SN-9ZN, SN-0.7CU and SN-49ZN-1CU solders

“…The minimum or steady state creep rate is one of the most important parameters for fundamental studies of creep behaviour. The stress dependence of the minimum creep rate is generally described by using power law equation [11].…”

“…Further, creep deformation is the most common deformation mechanism in solder joints due to its high homologous temperatures. Even at room temperatures, the conditions of creep is easily reached [9][10][11] Many tests have been conducted using impression creep and indentation creep to investigate creep strength of Lead free solders [9]. But the results of such creep studies are considerably affected by the shape of indenter.…”

“…But the results of such creep studies are considerably affected by the shape of indenter. Hence, tensile creep studies would be more appropriate for systematic study of creep behaviour [10][11].  Load Application System: This mechanism is used to apply a force or load on the test specimen.…”