Thesis
Elimination of whisker growth by indium addition in electroplated tin on copper substrate
Washington State University
Master of Science (MS), Washington State University
2017
Handle:
https://hdl.handle.net/2376/103579
Abstract
Copper lead-frames in electronic packages are often electroplated with 1-5 µm thick tin film, from which long whiskers grow with passage of time, potentially causing electrical shorts between neighboring circuitry. Whisker growth from Sn coatings is a serious reliability concern in electronics, particularly when the required service life is over a decade, e.g., in aerospace and defense applications. Until recently, whisker growth from tin coatings was mitigated by the addition of a small amount of Pb. However, current requirements for lead-free electronics preclude using Pb as an additive, requiring an alternate approach to whisker mitigation. In this work, we have presented the results of In-alloying on whisker growth from 3 µm and 6 µm thick electroplated Sn films and compared the results with a baseline sample of pure Sn, a control sample of tri-layer Sn-Sn-Sn, all subjected to identical thermal treatments. It is shown that when 5-10% indium is incorporated throughout the thickness of the Sn films, whisker growth is completely eliminated. The reasons behind this mitigation were experimentally explored using Focused ion beam (FIB), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Previous work had shown that while In addition reduces grain boundary diffusivity, it does not fully account for the observed dramatic reduction of whisker growth. FIB was used to assess the role of internal interfaces, and XRD was used to elucidate the role of Cu-In intermetallic formation. Finite element modelling was utilized to investigate the role of In-incorporation in the surface-oxide, as revealed by XPS and AES. Based on the analyses, it was inferred that the observed mitigation due to In addition occurs due to a multitude of factors, including reduction of grain boundary diffusivity, reduction of the driving force for whisker growth due to incorporation of In in the native Sn-oxide film on the surface of Sn, and the alteration of grain structure of Sn due to In-incorporation. Finally, we have reported a new method for co-electrodeposition of Sn-In alloys, and the impact of co-deposited Sn-In platings on the susceptibility to whisker growth.
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Details
- Title
- Elimination of whisker growth by indium addition in electroplated tin on copper substrate
- Creators
- Susmriti Das Mahapatra
- Contributors
- Indranath Dutta (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Mechanical and Materials Engineering, School of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; [Pullman, Washington] :
- Identifiers
- 99900525028501842
- Language
- English
- Resource Type
- Thesis