Lifetime Assessment of Solder Joints of BGA Package in Board Level Drop Test

Abstract

Leaded and lead-free BGA packages were tested in board level drop test defined in the JEDEC standard. The results of experiment were employed to modify the Darveaux model to extend its application to the drop test by re-calculating the values of the parameters contained in this model. FEA models with different materials, height and pitch of solder balls were established. The characteristic of the impact applied on the PCB assembly in the drop test is the very high peak acceleration and very short pulse duration. The stress and strain of the typical nodes in these models were calculated in LS-DYNA, which is very appropriate for the simulations under these conditions. The average strain energy density was also calculated to predict the lifetime of solder joints in these different material and geometrical conditions through this modified Darveaux model. The experiment and simulation reveal that the solder joints in the corners of the package suffer much higher plastic strain and are more susceptible to fail. The mainly failure mechanism in board level drop test is the plastic-strain-induced crack at the interface between the solder balls and the pads in the packages. Lead-free solder joints have longer lifetime in board level drop test than leaded ones because of their relatively higher elastic modulus and yield stress. Optimal height and pitch of solder balls exist, which lead to lowest plastic strain and best performance in the drop test