Grant: $270,422 - National Science Foundation - Jul. 6, 2009
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Award Description: This Award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). TECHNICAL SUMMARY: Sn-based alloy coatings have been used for many years in the manufacture of electronic components to enhance solderability and prevent corrosion. Recent environmental legislation has forced the elimination of Pb in these parts, which has enabled the re-emergence of tin whiskers, i.e. thin filaments that grow from the surface and can ultimately cause short circuits. Whisker-induced failures have been documented in numerous systems (satellites, aviation systems, medical devices, etc.) and represent a significant risk for manufacturers of high reliability systems. Despite significant research, many fundamental aspects of whisker formation are still not understood. Part of the difficulty is that multiple materials processes interact to create the whiskers (e.g. interdiffusion, phase transformations, stress generation and relaxation, etc.) so that it is difficult to identify the underlying mechanisms. Moreover, many processing variables (film thickness, grain size, plating conditions, etc.) have been shown to play a role in whisker formation. This makes it difficult to compare the results of different studies done under different conditions. The proposed research program is designed to identify the fundamental mechanisms that govern whisker formation by focusing on the several questions: 1. Which processes control stress in the Sn layer? 2. How is the stress evolution related to whisker formation? 3. What causes whiskers to nucleate at particular sites? 4. How does the addition of Pb prevent whisker formation? 5) How can we use our understanding of whisker formation to prevent their occurrence? Real-time thin film diagnostics will be used to quantify the simultaneous temporal evolution of several critical parameters such as film stress, intermetallic phase formation and whisker density, using carefully controlled samples. These kinetic studies will be complemented by electron microscopy studies to determine the underlying atomic-scale mechanisms behind these processes as well as whisker nucleation. Microstructure, film thickness, and Sn content in Pb-Sn alloys will be varied systematically to isolate and identify different kinetic processes that contribute to whisker formation. Analytical models will be used to interpret the measurements and to develop predictive capability for assessing reliability.
Project Description: Research was begun on several activities focused on measuring the fundamental kinetic processes controlling whisker growth. These parts of the project are specifically: a) measurements of stress relaxation kinetics in Sn and Pb-Snlayers and b) comparison of stress/phase transformation kinetics/whisker growth in layers with different thickness.
Jobs Summary: Prof. Eric Chason, the PI, was supported on the project-retained position. Jake Wasserman worked full-time as an undergraduate research assistant over the summer. This was a new position created for this project. In the future, Jake Wasserman will continue as research assistant (10 hrs/we) and Nitin Jadhav (current graduate student) will be supported ¼ time starting in October. A new graduate student supported on a fellowship will also be working on the project. She will receive support from this project when her fellowship terminates in May. (Total jobs reported: 1)
Project Status: Less Than 50% Completed
This award's data was last updated on Jul. 6, 2009. Help expand these official descriptions using the wiki below.