Influence of Joint Arrangement on the Fracture Behavior of Lead-Free Solder Joints

The capability to standardize the fracture strength of solder joints is an effective tool to investigate the reliability of electronic devices. To achieve this purpose, in this research, the influences of joint arrangement (loading arm and load sharing) on the level of constraint imposed on joint deformation, fracture energy, and generally, fracture behavior of solder joints were investigated. Fracture behavior of solder joints using double-cantilever-beam (DCB) specimens as a function of loading arm and load sharing (i.e., the distance between two solder joints) was studied under mode I loading conditions at a strain rate of 0.03 s−1. By increasing the loading arm, the fracture force, Fci, decreased linearly, while the critical strain energy release rate for crack initiation, Jci, increased from a loading arm of 12.7 mm to 38.1 mm and then remained almost unchanged for loading arms of 38.1 mm to 71.1 mm. Plastic deformation in the solder layer and criteria such as opening stress (i.e., the predominant stress component in DCB specimen) and stress triaxiality factor were calculated. It was shown that for the larger loading arms (from 38.1 mm to 71.1 mm), the fracture behavior was as a normal DCB specimen (i.e., the normal stress caused by bending was predominant and normal stress caused by tensile loading could be ignored). For the loading arm of less than 38.1 mm, the fracture behavior was similar to that of tensile-type specimens (i.e., the normal stress caused by bending decreased significantly by decreasing the loading arm and normal stress caused by tensile loading became considerable). Variations in the distance between two solder joints did not affect the Jci value, while Fci was influenced by the joint arrangement. This behavior was attributed to stress distribution in the solder layer.