A Study of EM Failure in a Micro-Scale Pb-Free Solder Joint using a Custom Lab-Scale X-Ray Computed Tomography System

The three-dimensional (3D) microstuructural evolution in a Pb-free solder system undergoing accelerated electromigration (EM) testing is characterized using a custom, lab-scale, cone-beam, micro x-ray computed tomography (mu XCT) instrument. A micro-scale Sn-0.7Cu butt -joint was subjected to a current density of 10(4)A/cm(2) at 100 degrees C. The experimentation was enabled by the design of a miniature fixture for in situ imaging under accelerating EM testing conditions. The fixture is friendly to surface imaging and mu XCT scanning. The migrating species, copper and tin, are observed volumetrically through substrate dissolution, solder build-up, and the formation of reaction products in the solder joint by mu XCT imaging. The migration of the copper substrate and the formation of copper-tin reaction products is quantified.