Failure of intermetallic solder ball due to stress shielding and amplification effects

The shielding and amplification effects between microcracks have been the unsolved problem in intermetallic solder ball failure. This study investigated the interaction between multiple edge cracks in solder ball to quantify the effects of shielding and amplification on the crack driving force based on stress singularity approach. The finite element model of two parallel edge cracks subjected to mixed-mode loading was developed. The effect of crack length between the two parallel edge cracks on stress intensity factor was evaluated. Macrocrack was found to provide shielding to the smaller crack or microcrack. In parallel edge cracks, the shielding effect reduces as the distance between the two parallel edge cracks increases. When two colinear cracks are closer together, the stress increases and shows amplification effect. It is found that when we compare both shielding and amplification, the distance between the two crack tips must be shorter to give a better effect.