FE-investigation of the stress/strain and fracture mechanics properties of intermetallic phase regions in leadfree solder interconnects

This main objective of this paper is to use a finite element analysis of the state of stress and strain within an intermetallic layer at the interface of a lead-free solder joint for an investigation of the comparatively unknown fracture mechanics properties and critical state of stress of intermetallic compounds. For this purpose we discuss the magnitude and sign of the stresses and strains (tensile vs. compressive) as a function of various parameters involved, such as the thermo-mechanical properties of the materials that constitute the joint, the geometry of the intermetallic phase (stress concentrations), and a potential change in volume during its formation. The stresses and strains are then used to calculate stored energies. From these an estimate for the energy release rates and related fracture mechanics properties of the intermetallics, as a function of the various parameters mentioned before, is obtained. The results of this paper can be used for guidance to indicate which materials and geometry parameters are crucial in order to optimize the interfacial quality from the (theoretical) viewpoint of mechanics