Environmental concerns, increasing complexity, and demands for reliability of solder joints in electronic systems provide an impetus to find alternatives to existing lead-tin solder and fluxes in common use. Several practical obstacles need to be overcome before an alternative to lead containing solder systems can be reliably implemented for electronic applications. Also new solders will have different failure criteria that must be established. A strategy for developing composite solders that permit tailoring the mechanical properties for the application, as well as stabilizing the microstructure to achieve optimal performance under service conditions is described. Stabilizing the microstructure will prevent mechanical property evolution over the life of the component, and this would substantially simplify the prediction of solder joint lifetimes. A research program to develop relevant quantitative descriptions of microstructural evolution and property variation in eutectic Sn-3.5%Ag solder with and without composite strengthening is summarized.
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