A Method of Damage Mechanics Analysis for Solder Material

This paper presents a method of damage mechanics analysis for solder joint material stressed to extensive plastic deformation. The material chosen for the current work is the 60Sn-40Pb eutectic alloy due to its wide use. The analysis is based on the thermodynamic theory of irreversible processes. With the introduction of a set of internal state variables, known as damage variables, and a damage effect tensor, a damage dissipative potential function is proposed to enable the formulation of the constitutive equations of elasticity and plasticity coupled with damage. The equations of damage evolution are also derived to monitor damage initiation and growth. Before a damage analysis can be performed with a finite element analysis, the mechanical properties of the chosen solder joint material and its damage variables must first be determined. A method of experimental analysis was developed and used to successfully measure the highly strain sensitive 60Sn-40Pb solder material. The measured properties are presented and various characteristics of the solder material are examined and discussed.