Time-lapse imaging of bismuth precipitation and coarsening on the surface of Sn-Sg-Cu-Bi solder joints after thermal cycling
File(s)
Published version
Author(s)
Hsieh, Chen-Lin
Coyle, Richard J
Gourlay, Christopher M
Type
Journal Article
Abstract
Adding bismuth to Sn-Ag-Cu solder compositions can significantly improve reliability in thermal cycling, but there are uncertainties in how bismuth precipitates and coarsens in Sn-Ag-Cu-Bi solders containing > 3 wt.% Bi. Here we apply time-lapse imaging in a scanning electron microscope to study bismuth precipitation and coarsening at room temperature on the polished surface of Sn-2.25-0.5Ag-6Bi ball grid array solder joints after thermal cycling. It is shown that (Bi) precipitates on the surface within 2 h after polishing and then coarsens by a combination of Ostwald ripening, coalescence ripening, and competition between two orientation relationships. Time-lapse imaging revealed that coalescence causes an increase in the local bismuth particle size and the formation of anomalously large (Bi) particles. The accumulation of bismuth on the polished surface increases far beyond the equilibrium volume fraction for this alloy. The bismuth particle size distributions are significantly wider than expected from Lifshitz–Slyozov–Wagner (LSW) theory, that assumes only Ostwald ripening, which is shown to be because coalescence creates anomalously large particles. This study shows the important role of bismuth precipitate coalescence within the coarsening mechanism in Sn-2.25-0.5Ag-6Bi solder joints.
Date Issued
2025-04-01
Date Acceptance
2025-01-03
Citation
Journal of Electronic Materials, 2025, 54 (4), pp.2657-2671
ISSN
0361-5235
Publisher
Springer Science and Business Media LLC
Start Page
2657
End Page
2671
Journal / Book Title
Journal of Electronic Materials
Volume
54
Issue
4
Copyright Statement
© The Author(s) 2025 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
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Publication Status
Published
Date Publish Online
2025-02-03