Using Digital Image Correlation Method to Evaluate Fracture Parameters of Lead-Free Solder

Abstract

Newly developed lead-free solder alloys, which contain doping some elements such as Ni, Bi, Sb, Al,..., have improved properties with respect to the conventional solder alloys, particularly in terms of resistance to creep. Their high performances are specifically desired in applications of power electronics where they are used for the electrical interconnections between the components. Studies on their resistance to rupture remain relatively limited. Yet the comprehension of fracture behavior is essential for the correct design of the electronic packages which must be robust against fatigue and vibrations loads. In this study, rupture of notched specimens fabricated from the InnoLot lead-free solder alloy is investigated. The tests are performed with the help of a micro-tensile testing machine equipped with an optical system for full-field measurements with Digital Image Correlation. The images are taken at successive steps of deformation and the displacement field is measured in a region of interest which is the singularity dominated zone surrounding the plastic zone at the crack tip. The procedure consists then in comparing the measured field with the theoretical field given by the Williams’ solution. The stress intensity factor is calculated by fitting the analytical fields to the experimental data. The effects of the size and shape of the zone of data collection, as well as that of the number of terms considered in the Williams’s expansion series, are examined in the study. A method is also proposed for the automatic crack tip detection.