Low Cycle Fatigue Testing of Ball Grid Array Solder Joints under Mixed-Mode Loading Conditions

Abstract

To give a proper and accurate estimation of the fatigue life of ball grid array (BGA) solder joints, a mechanical fatigue test method under mixed-mode loading is proposed. Experiments were conducted with 63Sn∕37Pb and Sn∕3.5Ag∕0.75Cu solder joints in room temperature. The mechanical low cycle fatigue tests were performed under several loading angles. The loading angle is controlled by several grips which have specific surface angle to the loading direction. Constant displacement controlled tests are performed using a micro-mechanical test apparatus. It was found that the normal deformation significantly affects the fatigue life of the solder joint. Throughout the whole test conditions at room temperature, Sn∕3.5Ag∕0.75Cu solder alloy had longer fatigue life than 63Sn∕37Pb alloy. Failure patterns of the fatigue tests were observed and discussed. A morrow energy model was examined and found to be a proper low cycle fatigue model for solder joints under mixed mode loading condition.