Thermal Stability and Sulfidizing Resistance of High Reflective Multilayered Sn/Ag₃Sn and Sn/Ag Films Electrodeposited on Cu Alloy Sheets

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• 作者：Song-Zhu Kure-Chu ; ^{chusongz@iwate-u.ac.jp" class="auth_mail" title="E-mail the corresponding author} ; Toru Ogasawara ; Rong-bin Ye ; Hitoshi Yashiro ; Kuniaki Sasaki
• 关键词：Sn/Ag3Sn/Ag ; electrodeposition ; reflectivity ; thermal stability ; sulfidizing resistance
• 刊名：Electrochimica Acta
• 出版年：2016
• 出版时间：10 September 2016
• 年：2016
• 卷：212
• 期：Complete
• 页码：380-389
• 全文大小：4430 K

文摘

We reported multilayered Sn/Ag₃Sn and Sn/Ag films with Ag thickness of 20–300 nm that electroplated on a reflowed Sn layer on Cu alloy sheets as promising coating materials for LED lead-frames. The morphology, surface roughness, crystalline structure, and reflectance of multilayered Sn/Ag-based films are more dependent on plating baths than on Ag thickness. The Sn/Ag₃Sn film obtained from a cyanide Ag bath exhibited high specular reflectivity of 65–70% (480 nm), whereas the Sn/Ag films from a cyanide-free bath showed a high total reflectivity of 94% similar to commercial Ag films. The reflectance of both the multilayered Sn/Ag₃Sn and Sn/Ag films almost unchanged even after heating at 373 K for 120 h, in comparison with the apparent drop for a commercial Ag film. Moreover, the multilayered Sn/Ag₃Sn films, both the as-deposited and the annealed specimens, remained the reflectivity even after immersing in a 0.2 ml/L (NH₄)₂S_x solution for 60 min. The excellent sulfidizing resistance of the Sn/Ag₃Sn films can be attributed to the chemically stable Ag₃Sn alloy layer with improved corrosion resistance and the protective SnO/SnO₂ thin film on the surface, thus inhibiting the chemical reaction of Ag and S^2– ions.