An analysis of local deformation of SnAgCu solder joint using digital image correlation

The changeover from eutectic Sn-Pb solders to lead-free solders has been driven by environmental concerns and market accessibility in the last few years. Though a number of creep constitutive laws of lead-free solder have been reported due to the importance of creep in solder joint failure in the electronic packaging, these constitutive laws often show great variations across the applicable stress range. In-situ measurement of strain fields in micro regions can help make the creep model more realistic. In this study, shear tests have been carried out on small solder joints in order to gain insight into the factors affecting solder properties. In order to measure the strain in solder joints, the Digital Image Correlation Method (DICM) has been used. The experimental results proved that there are two mechanisms that disturb the uniform deformation in solder joint. One is the interfacial strain concentration which has a dimension of less than 30μm and the other is spreading across interfaces from the locally deformed area, which has a size from about 50μm to 100μm. The existence of these local concentrations of creep strain is thought to be at least one of the causes of the variations in the published creep parameters. The deformation of solder joint on the shear test has also been modeled using Finite Element Method (FEM), and a three-layered model has been proposed to simulate the experimental results.