A damage integral approach to thermal fatigue of solder joints

A damage integral that provides a numerical accounting of accumulated fatigue damage in solder joints is defined. Eutectic Sn-Pb solder joints under shear loading are considered. The stress is calculated using state variable constitutive relations for inelastic deformation. The fatigue damage rate is described by means of a phenomenological crack growth law expressed in terms of a nominal stress intensity factor. The material parameters for this crack growth law are determined from isothermal fatigue data. Damage integral calculations are performed for solder joints fatigued to failure with either isothermal or thermomechanical cycles. The results indicate that the phenomenologies of fatigue damage in the cases considered may be equivalent for these two loading modes