Assessing the Impact of Lead-free Solders on the Long-term Reliability of Weapon System Electronics.

"Lead based solders have been used for decades to make conductive and structural connections in electronic assemblies. Whole manufacturing technologies are based on the melt, flow and wetting characteristics of these materials and establishing new solderplatforms requires substantial and pervasive changes in the industry. As industry moves away from the use of lead in electronic assemblies, the development of qualification standards for lead free solders and conductive adhesives is needed to ensurecontinued performance reliability. In the proposed work, TRI/Austin will develop procedures that can be used as a "standard of evaluation" for lead free solders, making it possible to compare them with each other and with well established lead/tinsolders. During Phase I, leading lead free solder alloys and conductive adhesives suitable for military applications will be cataloged. Standardized models to predict thermal-mechanical failure will be developed, given a formulation and a specifiedgeometry. A standardized stress test will be designed to validate the above model and enhance failure prediction. TRI's expertise in accelerated life testing will provide the basis for evaluating lead free solders using thermal models and in thesimulation of actual exposures to various "real world" environmental conditions. The proposed technology will be enhance the reliability of future missile and other weapons systems, and is applicable to Nationa