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Tensile properties and fracture mechanisms of Cu/Sn-4Ag solder joints aged at 180 degrees C for different times were investigated at the strain rates of 1.25 x 10(-4) s(-1) and 1.25 x 10(-1) s(-1) At the low strain rate, it was found that the tensile strength of the solder joints decreased with increasing aging time in principle. though the tendency was not monotonously at the early stage of aging, and all the solder joints had similar tensile curves but different fracture morphologies and fracture processes. At the high strain rate, tensile strength of the solder joints was much higher and decreased monotonously with increasing aging time, with identical fracture process and fractographies. Evolution of the Cu/Sn-4Ag interfacial morphology during aging process and the effect of aging on tensile property of the Sn-4Ag alloy were also involved for further analysis. Based on the experimental results and observations, the fracture processes were revealed and some factors controlling the tensile strength of solder joints were discussed qualitatively (C) 2009 Elsevier B.V. All rights reserved