Abstract
Although low-cycle fatigue properties of solder materials have long been studied, high-cycle fatigue properties have rarely been investigated. In particular, there is not much research evaluating high-cycle fatigue properties using the strain control method due to difficulties such as the control of small strain. In this study, the low-cycle and high-cycle fatigue properties of Sn-Ag-Cu solder were investigated by torsional fatigue test with strain control. Experimental results show that when fatigue life was evaluated in the inelastic strain range, the fatigue ductility exponent differed between the low-cycle region and highcycle region, and was large in the low-cycle region and small in the high-cycle region. However, when fatigue life was evaluated using inelastic strain energy density, a power law was found over a wide range from the low-cycle region to the high-cycle region. Thus, when cumulative damage in the high-cycle fatigue region is evaluated by using only a MansonCoffin plot in the conventional low-cycle region, the results overestimate the cumulative damage. To predict the fatigue life accurately, it is necessary to consider changes in the fatigue ductility exponent of the Manson-Coffin model or to use inelastic strain energy density.
