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Whiskers: The Role of Electric Fields in the Formation Mechanism and Methods for Whisker Growth Mitigation

Borra, Venkata Shesha Vamsi
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1513381893591481

Abstract Details

2017, Doctor of Philosophy, University of Toledo, Electrical Engineering.
Electrically conductive hair-like structures, referred to as whiskers, can bridge the gap between densely spaced electronic components. This can cause current leakage and short circuits resulting in significant losses and, in some cases, catastrophic failures in the automotive, aerospace, electronics and other industries since 1946. Detecting a metal whiskers (MWs) is often a challenging task because of their random growth nature and very small size (diameters can be less than 1 µm, lengths vary from 1µm to several millimeters). Many decades ago the industry introduced whisker mitigating Pb in the solders used to fabricate electric and electronic parts. In recent years, this changed because the European Union (EU) passed a legislation in 2006, called “Restriction of the use of Certain Hazardous Substances (RoHS) in Electrical and Electronic Equipment”, which requires a reduction and elimination of the use of Pb in technology. Thus, the issue of undesirable and unpredictable whiskers growth has returned and there is a renewed interest in the mechanisms of formation of these structures. None of the whisker growth models proposed to date are capable of answering consistently and universally why whisker grow in the first place and why Pb addition suppresses their growth. Understanding MW nucleation and growth mechanism are of significant interest to this project, since this would potentially allow the development of new accelerated-failure testing methods of electronic components to replace existing testing methods which are generally found to be unreliable. In particular, this research is intended to study the effects of electric fields on the whisker growth, which according to the recently developed electrostatic theory[1] of whisker growth, are of crucial importance. This theory proposes that the imperfections on metal surfaces can form small patches of net positive or negative electric charge leading to the formation of the anomalous electric field (E), which governs the whisker development in those areas. Stress relaxation based theories are quite popular and effects of electric fields on the whisker growth were often overlooked in such theories and hypotheses. Several approaches to understand the role of electric fields in the whisker forming mechanism were considered in this work. The influence of E-fields, AC as well as DC, on both vacuum deposited films and electroplated film samples were studied. One of the approaches involved the use of strong high-frequency AC E-fields (optical fields) on the metal surface, which was realized by Surface Plasmon Polariton (SPP) excitations using a CW laser. Another approach was biasing sample using a DC field was carried out using either a parallel-capacitor geometry or a very localized electric field application, obtained by using a sharp conductive Atomic Force Microscope’s cantilever tip maintained at a known distance. The E-field of localized charged defects in glass formed by irradiation with gamma rays from a radioactive source was studied as well. In addition, an attempt was made to correlate the internal structure and the external striations on the whisker. Experimental validations of the massive whisker nucleation (MWN) concepts were accomplished. Whisker cross-section analysis was performed using focused-ion-beam (FIB) milling and the resulted samples were examined using scanning transmission electron microscopy (STEM). Finally, the possibility of mitigating whisker growth by using thin semiconducting sublayers such as a NiO intermediate layer between Cu and Sn was studied in this project, and a special attention was dedicated to investigate the presence and the effect of intermetallic compounds (IMCs)
Daniel Georgiev, Dr. (Committee Chair)
Vijay Devabhaktuni, Dr. (Committee Member)
Victor Karpov, Dr. (Committee Member)
Devinder Kaur, Dr. (Committee Member)
Anthony Johnson, Dr. (Committee Member)
Aerospace Materials; Chemical Engineering; Condensed Matter Physics; Electrical Engineering; Engineering; Experiments; Materials Science; Metallurgy; Nanoscience; Nanotechnology; Physics; Plasma Physics; Solid State Physics; Theoretical Physics
Tin; Sn whiskers; electrostatic theory; whisker mitigation; surface plasmon polariton SPP; focused ion beam FIB; scanning and transmission electron microscope SEM, TEM; atomic force microscope AFM; gamma radiation; thin films; nucleation; characterization

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Citations

  • Borra, V. S. V. (2017). Whiskers: The Role of Electric Fields in the Formation Mechanism and Methods for Whisker Growth Mitigation [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1513381893591481

    APA Style (7th edition)

  • Borra, Venkata Shesha Vamsi. Whiskers: The Role of Electric Fields in the Formation Mechanism and Methods for Whisker Growth Mitigation. 2017. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1513381893591481.

    MLA Style (8th edition)

  • Borra, Venkata Shesha Vamsi. "Whiskers: The Role of Electric Fields in the Formation Mechanism and Methods for Whisker Growth Mitigation." Doctoral dissertation, University of Toledo, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1513381893591481

    Chicago Manual of Style (17th edition)

toledo1513381893591481
303
© 2017, some rights reserved.Creative Commons License Whiskers: The Role of Electric Fields in the Formation Mechanism and Methods for Whisker Growth Mitigation by Venkata Shesha Vamsi Borra is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Toledo and OhioLINK.