Effect of isothermal aging on interfacial IMC growth and fracture behavior of SnAgCu/Cu soldered joints

Abstract

The reliability of lead free electronic devices depends strongly on the reliability of the soldered joints while the later one was controlled, mainly, by the formation and growth of the interfacial intermetallic compounds (IMCs) between the solder matrix and the substrates. The morphological features, microstructural evolutions and growth kinetics of the IMCs on the interfacial of SnAgCu/Cu soldered joints, under as soldered and isothermal aging condition, were investigated. The three-dimensional IMCs feature was explored by etch the solder matrix out of the SnAgCu/Cu interface. The phases of IMCs were identified by energy dispersive X-ray (EDX). The thickness of the IMCs was measured by element mapping and phase constitution analysis. The SnAgCu/Cu soldered joints were isothermal aged at 125C, 150C and 175C respectively. The corresponding IMCs growth rate was formulated according to the data from various aging time. The growth kinetic of the IMCs was analyzed in the framework of diffusion principles. The tensile strength of the joint was evaluated by in-situ tensile test and the fracture mechanism was analyzed in accordingly. It was found that Cu6Sn5 was formed at the solder and Cu interface during reflowing. With the increase of aging time, the grain size of the interfacial Cu6Sn5 increased and its morphology was changed from scallop-like to needle-like and then to rod-like and finally to particles. The rod-like Ag3Sn phase was formed at the interface of solder and Cu6Sn5 layer with the increase of the aging time. The growth of the IMCs was found follows Arrhenius’s diffusion model and the corresponding diffusion factor and active energy were obtained by data fitting. The IMCs growth rate was found increases with the increase of the aging temperature. The fracture site of the soldered joints was changed from the solder matrix to the interfacial Cu6Sn5 layer with the increase of the aging time.