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The diffusion of atoms and the growth behaviour of intermetallic compounds (IMCs) at both Sn–3·5Ag–0·5Cu/Cu and 63Sn–37Pb/Cu interfaces under isothermal aging and thermal shearing cycling conditions have been investigated. The results show that a Cu6Sn5 IMC layer is formed at both the Sn–Ag–Cu/Cu and Sn–Pb/Cu interfaces, and the morphology of Cu6Sn5 changes gradually from scallop structure to plate-like structure with increasing number of thermal shearing cycling, while two IMCs, Cu6Sn5 and Cu3Sn, are formed at the Sn–Ag–Cu/Cu and Sn–Pb/Cu interfaces after isothermal aging for 100 h. The IMC growth follows parabola growth kinetics, implying that the IMC growth is controlled by the diffusion of Cu atoms. In Sn–Ag–Cu solder, Ag3Sn, forming uniform particles after reflowing, congregates gradually to be chunk-like. [ABSTRACT FROM AUTHOR]