The influence of cyclic strain-hardening exponents on fatigue ductility exponents for Sn-Bi solid solution alloys and Sn-Ag-Cu microsolder joints was investigated. In Sn-Bi solid solution alloys, the fatigue ductility exponent in Coffin-Manson’s law was confirmed to increase with a decrease in the cyclic strain-hardening exponent. On the other hand, in the Sn-Ag-Cu miniature solder joint, the fatigue ductility exponent increases with a rise in temperature and strain holding. Thus, the fatigue ductility exponents are closely related to the cyclic strain-hardening exponent: the former increases due to the depression of the latter with a rise in temperature and increase in intermetallic compound particle size during strain holding. The results differ for the creep damage mechanism (grain boundary fracture), which is the main reason for the life depression in large-size specimens.

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