Synthesis and Properties of Pulse Electrodeposited Lead-Free Tin-Based Sn/ZrSiO 4 Nanocomposite Coatings
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INTRODUCTION
IN the electronic industry, the most common solder materials are lead–tin alloys. However, increased health concerns over the toxicity of Pb in Pb-Sn solders have promoted the development of new lead-free solder alloys for electronic packaging.[1] Among the various lead-free solders, eutectic Sn-Cu alloy has been the most recommended candidate. The melting point of the eutectic Sn-Cu alloy is 490 K (217 C), just a little bit higher than that of the melting point of the conventional eutectic Pb-Sn alloy [456 K (183 C)]. Sn-based alloys are widely used in electronic and electrical contact points due to their low densities, good conducting properties, and good corrosion resistance properties.[2–4] Though these alloys are perfect replacements for lead-based solders, their poor mechanical properties make their durability less than satisfactory.[5] Tin-based solder coatings wear out very easily when exposed to moderate to high temperature and also in sliding systems. Therefore, the understanding of wear behavior of Sn-based systems in important in electrical contact
SUMIT BHATTACHARYA, Master’s Student, and SIDDHARTHA DAS and KARABI DAS, Professors, are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India. Contact e-mail: karabi@metal. iitkgp.ernet.in ASHUTOSH SHARMA, Research Professor, formerly with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, is now with the Department of Materials Science and Engineering, University of Seoul, Seoul, South Korea. Manuscript submitted April 11, 2015. Article published online January 5, 2016 1292—VOLUME 47A, MARCH 2016
applications. Moreover, with aging there is formation of whiskers on the surface, which may cause short circuiting in electronic packages leading to complete device failure.[1–5] These alloys are prone to the formation of undesirable reaction compounds with the copper substrate, such as Cu6Sn5, Cu3Sn, which are deleterious to soldering properties.[6] Therefore, the nano-sized ceramic particle-reinforced Sn metal matrix composites have been attracting scientific interest in recent years, since nanostructured materials are expected to have special physical, mechanical, and tribological properties.[7–12] Recently, Sharma et al. have demonstrated that CeO2 nanoparticles in Sn matrix improve the microhardness several times.[10] In a similar study conducted by this group, they also successfully mitigated whisker growth by manipulating the residual stress in solder matrix by using CeO2 nanoparticles.[11] In another recent study, it is also demonstrated that use of La2O3, not only improves the strength but also the ductility of the solder if the distribution of nanoparticles is homogeneous.[12] Nanocomposite solders also have been shown to exhibit better electromigration behavior.[13] The reinforcing particles serve to suppress grainboundary sliding, large intermetallic compound formation, whisker formation, and grain growth, thereby
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