Damage initiation and propagation modeling using Energy Partitioning Damage Evolution model for Pb-free solder materials

Thermo-mechanical fatigue and damage has always been an issue for solder joint materials used in micro-electronic devices. Accurate prediction of the damage and crack is essential in order to predict the life of these joints. This paper presents a finite element modeling approach that is used in conjunction with Energy Partitioning Damage Evolution (EPDE) model to determine the state of damage, update the constitutive properties of material and determine the crack initiation and propagation site and time in BGA solder joints. A non-linear visco-plastic finite element modeling is used to successively initiate and propagate the crack. Constitutive properties of elements are updated based on the amount of damage that they accumulate in each step. Elements with excessive damage are eliminated from the structure. Finite element results show that as elements accumulate damage, they are softened and thus can stand more strain. Therefore, the damage accumulation rate decreases. It also shows the initiation site and propagation path very accurately which is confirmed with experiments.