Importance of electric resistance monitoring in shear test

The reliability and the accompanying fatigue law for solder joints are a challenge for the aerospace and defense industries. Due to the service loadings and the lifetime requirements, fatigue laws must take into account plastic and viscous damages for solder joint materials. This paper presents an innovative test bench developed for the fatigue analysis of assembled packages. Two failure criteria are discussed: the electrical criterion, based on the monitoring of electrical resistance, and the mechanical criteria, based on force magnitude. The monitoring of the electrical resistance is able to detect the failure of a single solder ball, which represents a failure for a functional component. The electrical failure is reached without significant change in the mechanical parameters and the electrical criterion is always reached before the mechanical failure. The electrical criterion can be used to define the limit for the calculation of stabilized values of the mechanical parameters. This work opens up a fatigue Design of Experiment in order to define, based on experimental results, a fatigue law for solder joint which takes into account creep-fatigue interaction.