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Electrodeposition of Sn-Rich, Au-Sn Solder Films
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- Author / Creator
- Watt, Charles S
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Eutectic and near-eutectic tin (Sn) solder alloys have been indispensable when interconnecting and packaging electronic devices in the assembly of modern electronic circuits. Legislation has necessitated the implementation of lead (Pb)-free solder alternatives to replace near-eutectic Sn-Pb solders that were the most commonly used materials in the electronics industry. The Sn-rich eutectic alloy (90 wt% Sn) in the gold–tin (Au-Sn) system offers a potentially cheaper alternative to the Au-rich eutectic alloy (20 wt% Sn) for optoelectronic and microelectromechanical systems (MEMS) device packaging and may be applicable as a Pb-free solder for microelectronic packaging.
A simple electrodeposition method is utilized to fabricate Sn-rich, Au–Sn solder films, including the eutectic composition. The electrolyte is composed of a solution of Sn chloride and ammonium citrate. Gold is added to the electrolyte in the form of either a Au nanoparticle (<20 nm) suspension, prepared with Na citrate, or by directly adding Au powder (500–800 nm particles). The resultant electrolytes are used to electrodeposit eutectic and near-eutectic alloy films. Uniform thicknesses and compositions are obtained with the direct addition of Au powder. Gold content in the deposits increases with increasing Au particle loading in the electrolyte and increasing current density.
The intermetallic interactions and phase evolution in solder interconnections play an important role in the understanding the reliability and optimizing the solder process. The interactions between the Sn matrix and Au particles are examined. Room temperature aging leads to the formation of AuSn4 at the Au particle-Sn matrix interface. Reflow of deposits with near-eutectic compositions results in the formation of Sn and AuSn4. -
- Subjects / Keywords
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- Graduation date
- Fall 2015
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.