Fatigue lifetimes of low-tin high-lead and tin-lead eutectic solders under total strain controlled tension-tension tests were studied in this paper. Based on the stress and strain micro-macro correlations, a modified Coffin-Manson law is obtained. The modified lifetime prediction formulas which had been used to predict the fatigue lifetime for low-tin high-lead solder, exhibiting cyclic hardening and then saturation, was found to apply to the eutectic solder, where substantial cyclic softening has been observed. This micromechanically based approach allows one to model the known physical phenomena in solders by modifying the appropriate parameters in the predictive micromechanically based constitutive equations.

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