Mechanical stress state consideration for enhanced electromigration life prediction in aluminum wire bonds

Abstract

In this study, 5 [mil] aluminum wire bonds are subjected to elevated ambient temperatures, current densities, and mechanical stresses using a novel accelerated testing mechanism. Failure of a wire bond in this study was a 10 % increase in electrical resistance. Temperature coefficient of resistance experiments in this study identified the wire temperatures resulting from joule heating and thermomechanical stress evaluations were completed using ANSYS to extract relevant stresses occurring at each experimental condition. Collection of the failure data and analysis of the results indicate that mechanical stress interacts with current density and that the introduction of externally applied mechanical stress reduces the lifetime of a wire bond. Comparisons have been drawn between time to failure estimates for Black's equation for electromigration and three model forms developed from the results of this study. The comparison indicates that Black's equation is insufficient when mechanical stresses interact with current density and that mechanical stress ought to be considered in the future when completing reliability evaluations for wired interconnects in high-temperature systems.