Rate dependence of bending fatigue failure characteristics of lead-free solder joint

This study concerns the failure mechanism of a lead-free SAC305 solder joint under the isothermal bending fatigue condition. For this, series of bending fatigue tests are carried out with the variations of bending displacement and frequency, and FEM analysis is conducted to examine the relationship between mechanical behavior of a solder joint and fatigue life cycle. The results of this investigation suggest that the isothermal fatigue of a solder joint is strongly affected by plastic deformation process of SAC solder. It is found that the failure life cycle ´N_f´ fits well to the model suggested by Coffin-Manson, that is N_f ~ (Deltaepsiv_p)^-2.3. This result indicates that fatigue failure is determined by accumulation of damage by plastic deformation of solder. The fractography of a solder joint also supports our conclusion because crack is found to propagate along the solder matrix near to IMC interface.