Load Sharing Between Discrete Solder Joints in Bending: Effect of Spacing and Joint Properties

The fracture loads of copper-solder-copper double cantilever beam (DCB) specimens containing two discrete solder joints were measured and found to be maximum at a certain characteristic joint spacing. A finite-element model (FEM) showed that this corresponded to a minimization of the solder peel stress and an optimal load sharing among the two joints. This behavior was also analytically modeled using both a continuous foundation model and a simplified discrete foundation model, which isolated the effects of joint geometry and the bending stiffness of the solder and substrates. The model predictions of the characteristic joint spacing for both DCB and three-point bending configurations were satisfactorily compared with the FEM and the experimental data. The proposed approach is useful in predicting the load sharing among the multiple solder joints typical of surface mount microelectronic devices and in designing joint with maximum strength.