Tensile test behavior of the eutectic Sn-Ag solder joint in ball grid array assemblies

Abstract

In this study, the mechanical behavior of a eutectic Sn-3.5Ag ball-grid array (BGA) assembly was evaluated by tensile testing at strain rates of 10⁻⁴ and 10⁻⁵ s⁻¹ at various homologous temperatures. The maximum strength of the eutectic Sn-3.5Ag ball-grid array assembly decreased as the testing temperatures increased and the testing strain rates decreased. Two types of fracture modes were found during the tensile tests depending on the strain rates and homologous temperatures. At a strain rate of 10⁻⁴ s⁻¹ and at homologous temperatures lower than 0.65, the crack propagation occurred at the angle 45 deg with the tensile axis and along the Ag₃Sn/Sn interfaces. However, at strain rates lower than 10⁻⁴ s⁻¹ or at homologous temperatures higher than 0.65, the tensile crack formed by linking the creep voids that propagate normal to the tensile axis. A transgranular creep fracture was found on the failed surfaces of Sn-3.5Ag ball-grid array assemblies.