GOALI - The Effect of Changing to Pb Free Solders on Manufacturing Processes: Evolution of Solder Joint Microstructure

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This GOALI project is a collaboration with Universal Instruments Corporation to study how a transition to lead (Pb)-free solders will affect manufacturing processes for electronic packaging. A comprehensive treatment of solder joint reliability requires at least three major research efforts: (1) Development of a fundamental understanding of solder joint microstructure (grain size/structure, phase regions, intermetallics), including the ability to predict microstructure at any given time during any given thermal history. (2) Development of constitutive relations which quantify deformation properties as functions of temperature, strain rate, and detailed microstructure. (3) Development of damage functions that quantify the progression of damage for given temperature, strain/stress (or integrated functions thereof such as ductility exhaustion) and microstructure. In principle, after characterizing these relations, establishing a predictive capability for the mechanical behavior and reliability of Pb free solder joints is relatively straightforward, although extensive, mechanical modeling is required. This capability would allow the prediction of accelerated test results for specific solder based assemblies, as well as the interpretation of experimental results and extrapolation to service conditions. However, without the ability to predict the variation of important aspects of the microstructure over the history of the joint, efforts 2 and 3 above become at best semi-empirical and highly questionable for purposes of extrapolation. Particular complications are the effects of the progress of damage and the (often cyclic) effects of the thermal mismatch induced deformations. This project addresses significant issues related to environmentally benign manufacturing, with specific emphasis on manufacturing electronics. It is expected that advancements in fundamental knowledge of material behavior and processing of this material substitution will be made. There is direct involvement of undergraduate and graduate students through both research and an educational component, strengthen by the industrial collaboration.