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Mitigation of Tin Whiskers in Electroplated Tin Coatings by Effective Doping: The Role of Surface and Subsurface
Başlık:
Mitigation of Tin Whiskers in Electroplated Tin Coatings by Effective Doping: The Role of Surface and Subsurface
Yazar:
Bhassyvasantha, Sherin, author.
ISBN:
9780438052116
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (101 pages)
Genel Not:
Source: Masters Abstracts International, Volume: 57-06M(E).
Advisors: Bhaskar S. Majumdar Committee members: David T. Burleigh; Liliya Frolova; Paul A. Fueierer.
Özet:
The major objectives of this research on tin whiskers were the following: (i) to identify the primary mechanisms through which whiskers are mitigated in In doped Sn, and, (ii) to develop and characterize co-electrodeposited Sn-In alloy coating on Cu substrate thereby eliminating the need for multi-layered electroplating for mitigation of whiskers. Much of the attention was focused on 1-2 microm thick electroplating on Cu and bronze substrates, although thicker coatings up to 15 microm thick were also fabricated by the co-deposition technique. The thin coatings exhibited columnar microstructure similar to pure Sn samples, and thus microstructure did not appear to be a major reason for whisker mitigation.
Therefore, the research focused on the surface oxide and sub-surface region to evaluate their role on whisker mitigation. Notably, it is believed that a tenacious oxide layer prevents the supply of vacancies, which are needed to relax in-plane compressive stress in the plating that is the driver for whisker nucleation and growth. The surface measurements using Auger Electron Spectroscopy (AES) and X-Ray Photoelectron Spectroscopy (XPS) along with detailed analysis demonstrate that In addition has three important effects: (i) a mixed surface oxide layer that consists of SnO2, In 2O3, and a defective oxide of the form Sn(1-x)InxO( 2-y). In particular, the latter can serve as key locations where vacancies can be generated, which can then travel to the columnar grain boundaries and relax in-plane compressive stress in the film [60]; (ii) enrichment of indium at grain boundaries likely driven by the diffusion of oxygen below the oxide layer, and, (iii) sub-surface segregation of In that would reduce stress next to the surface oxide, a critical location where whiskers are nucleated. While all these effects contribute to stress reduction, it is believed that vacancy generation likely had the largest influence on whisker mitigation. Partial confirmation of a less tenacious oxide layer was obtained using cyclic voltammetry (CV) analysis. The CV results showed the absence of a strong protective tenacious oxide in indium doped Sn sample compared to a tenacious layer for pure electroplated Sn.
Significant progress was also made in co-depositing Sn-In alloy, since it avoids multilayer Sn-In-Sn deposition for whisker mitigation. Cyclic voltammetry stripping (CVS) studies provided partial understanding of the effects of bath composition, including additive and chelating agent additions, and electric potential on the electrodeposition process and resultant deposit composition and microstructure. Indium concentrations of 3 to 30 wt. % in a Sn matrix have been successfully obtained to date, however additional cyclic voltammetry stripping results will be needed to optimize coating conditions and additive levels. Surface studies also were conducted on Sn-Pb electrodeposits in order to draw comparison to whisker mitigation mechanisms observed in Sn-In alloy. In this case only SnO was observed in the oxide layer, without any presence of Pb. However, here too sub-surface segregation of Pb was observed that was greater in depth than Sn-In. The surface related whisker mitigation mechanisms for Sn-Pb are discussed.
Notlar:
School code: 0295
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(694407.1) | 694407-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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