Reliability and failure analysis of lead-free solder joints for PBGA package under a cyclic bending load

Nowadays, interest in the bending reliability of ball grid array packages has increased with the increase in mobile devices. Initially, bending tests were conducted to certify the safety of an electronic package during the manufacturing and shipping processes. But recently, the purpose of the bending test has changed: cyclic bending tests are being used to evaluate the electronic package's endurance against handling damage such as bending, twisting and key pressure. Furthermore, the bending test is being adopted as an alternative to a drop test. In this study, a four-point cyclic bending test was performed under various loading levels to investigate the fatigue behavior of solder joints with chemical compositions of 95.5Sn4.0Ag0.5Cu and 63Sn37Pb. It was found that the lead-free solder has a longer fatigue life than the lead-contained solder when the applied load is low. A finite element analysis (FEA) with plasticity and creep constitutive equations was conducted because there are no suitable sensors to measure stress and strain of solder ball joints directly. From the analysis results, it was found that the inelastic energy dissipation could be used as a good damage parameter. Also, from the inspection of the failure site and the FEA, it was found that the fatigue crack initiated at the exterior solder joints and propagated into the inner solder joints.