ABSTRACT
This chapter presents a comprehensive mechanics approach for solder reliability and integrity. This approach is capable of predicting the integrity and reliability of solder joint material under fatigue loading without viscoplastic damage considerations. It also presents the comprehensive damage model describing life prediction of the solder material under thermomechanical fatigue (TMF) loading. The method is based on the theory of damage mechanics, which makes possible a macroscopic description of the successive material deterioration caused by the presence of micro-cracks and -voids in engineering materials. A damage mechanics model based on the thermodynamic theory of irreversible processes with internal state variables is proposed and used to provide a unified approach in characterizing the cyclic behavior of a typical solder material. With the introduction of a damage effect tensor, the constitutive equations are derived to enable the formulation of a fatigue damage dissipative potential function and a fatigue damage criterion. The fatigue evolution is subsequently developed on the basis of the hypothesis that the overall damage is induced by the accumulation of fatigue and plastic damage. This damage mechanics approach offers a systematic and versatile means that is effective in modeling the entire process of material failure, ranging from damage initiation and propagation leading eventually to macro-crack initiation and growth. As the model takes into account the load history effect and the interaction between plasticity damage and fatigue damage, with the aid of a modified general-purpose finite element program, the method can readily be applied to estimate the fatigue life of solder joints under different loading conditions.
