Predicting Crack Initiation of Solder Joints with Varying Sizes Under Bending

Abstract

The critical strain energy release rate for crack initiation, Jci, was measured under mode I loading for SAC305 solder joints between two copper substrates. Fracture tests were performed using double cantilever beam specimens at a strain rate of 0.03 s−1. Different bond-line widths (i.e., joint size in the out-of-plane dimension) and thicknesses, were examined. The fracture force per unit width and Jci (the average value of four J-integral contours encircling the crack tip) were relatively insensitive to the width of the joint ranging from 8 mm to 21 mm. Variations in bond-line thickness (i.e., 150 μm, 250 μm and 450 μm) also had an insignificant influence on the fracture energy of solder joints. This behavior was explained in terms of stress distribution, crack-tip plastic zone area and triaxiality factor produced in the solder layer. Crack initiation in the specimens was then predicted using Jci as a property. Finally, a cohesive zone model was developed using a single set of parameters that was successfully used to predict the fracture loads of the joints with different sizes.