Comparison of joint level impact fatigue resistance and board level drop test

The purpose of the present study is to investigate the behavior of solder joints under high strain rate repeated loading during micro-impact testing. SAC 105 and SAC 305 solder alloys on electrolytic nickel-gold and copper-OSP pads were used in this study. In doing so, the dependency on factors such as impact energy and solder alloy was studied.In terms of solder alloy, lower silver containing tin-silver-copper based alloys are beneficial in high strain rate cyclic loading due to the increased ductility of the alloy. The majority of the failures observed on the SAC305 assemblies were intermetallic fracture, while the SAC 105 assemblies exhibited mostly solder failure modes. As the strain rate decreased, failure modes transitioned from brittle to ductile failure for the SAC305 assemblies. This transition was not the same for the two alloys. Reliability in board-level drop testing was compared to the results obtained from the micro-impact fatigue testing. Assemblies built using SAC 105 tended to outlast SAC305 assemblies, due to the increased ductility of the lower Ag containing solder. Failure modes correlated well between drop testing and joint level impact fatigue testing. It was found that the impact energy was a useful metric in determining the reliability of the solder joint.