The performance and fracture mechanism of solder joints under mechanical reliability test

The drop resistance and fracture behavior of Sn–37Pb, Sn–3.0Ag–0.5Cu (SAC305), Sn–1.0Ag–0.5Cu (SAC105), and Sn–8.5Zn–0.5Ag–0.01Al–0.1 Ga (SnZn-5e) solder ball joints under the board-level drop test (BLDT) and the ball impact test (BIT) were studied. The results show that the drop reliabilities in terms of the characteristic life ratio from the Weibul plot are SnZn-5e : Sn–37Pb:SAC105:SAC305 = 3.1:2.9:2.1:1. It was observed that failure of Sn–37Pb occurred at the eutectic tin–lead phase whereas it took place at the brittle interface between the (Cu,Ni)6Sn5 inter-metallic compound and Ni layer in SAC305. The failure of SAC105 was found to be located within the solder matrix as well as at the interface of the inter-metallic compound. The failure of SnZn-5e depends on the morphology of the interfacial inter-metallic compound. The failure modes of Sn–37Pb and SAC305 after the BIT were similar to those after the BLDT. The maximum impact force (Fmax) and the initial fracture energy (E) from the BIT can be used to evaluate the drop reliability of solder joints.