Collaborative Research: Mechanisms and Processing Strategies for Sn Whisker Mitigation

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The growth of tin whiskers on fine pitched tin-plated electrical interconnect lines poses catastrophic short circuit problems in lead-free electronic components. In the past, this problem was mitigated by adding a few percent lead, which is no longer permissible due to a world-wide ban on lead. This research is aimed at developing robust strategies for mitigating tin-whisker growth by two different mechanisms. One path proposed is to alter the plating chemistry by adding dopants in the electroplating bath to emulate mechanisms that enable lead to impart whisker growth resistance to tin. Another is to modify deposition conditions to promote a near-equiaxed grain structure instead of typically prevalent columnar grains, allowing absorption of mass flow without whisker growth. To achieve this, the project will integrate an intellectual component of alloy-design/microstructure with a deliverable manufacturing component. To aid alloy-design, molecular dynamics (MD) simulations will be performed to provide insight into the influence of dopant elements on grain boundary energy and diffusivity in tin. The expected outcomes will be stress reduction in the tin plating as well as insight into the key mechanisms of whisker formation, including the impact of process conditions on the size and density of whiskers produced.If successful, the process technology proposed here will have significant impact on the electronics manufacturing industry. The results will be particularly relevant for the power, space and military electronics industries, where lifetimes are measured in decades making whisker formation an egregious problem. The work will integrate research and graduate student training at New Mexico Tech and Washington State University by fostering discovery, interactions with the industry, dissemination of results in conferences, as well as mentoring of undergraduate and high school students. It will provide students with hands-on experience in an industrially relevant technology, where materials processing, microstructure, mechanics, and thermodynamics are all tied together in a single problem of world-wide impact.