Electronic Assembly Technology with Lead (Pb)-free interconnection alloys is relatively new in comparison to the long history and experience with tin-lead eutectic solder. Compositional variations of the ternary tin-silver copper can have significant impact on the interconnection behavior under different loading conditions. While the popular solder alloy is a Sn-Ag-Cu three-component system, the interconnection itself can be a five or six component system owing to the different component termination and the printed wiring board finishes utilized. Understanding of the microstructural aspects of the lead free alloys is still in its infancy. New failure mechanisms, different from the ones seen with eutectic solders, have been reported. Influence of minor elements on the behavior of Pb-free solders is not adequately explored. There is an urgent need for a better understanding of lead free solders to ensure product performance and reliability under a broad range of use environment since their implementation has already started. In this course will be explored the fundamental materials aspects, microstructural aspects, unique failure modes & mechanisms along with a discussion of prevention methods.