Fabrication of Sn-Ag/CeO 2 Electro-Composite Solder by Pulse Electrodeposition
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INTRODUCTION
IN recent decades, researchers have been looking for lead-free solders because of the various legislations and the imposed ban on the usage of Pb-bearing materials. Various lead-free solders, either binary or multicomponent alloys, e.g., Sn-Cu, Sn-Ag, Sn-Zn, Sn-Bi, Sn-AgCu, Sn-Ag-RE, Sn-Zn-Al, Sn-Ag-Cu-In, etc., are being developed and studied.[1–3] For the microdevices where soldering materials are employed, i.e., flip chip packaging and ball grid arrays, it is necessary to ensure that the solder joints have adequate strength.[4–6] As the size of the interconnecting network in microelectronic packaging devices is getting finer over time, their reliability is causing a serious concern. The miniaturization of the packaging devices will lead to an increase in current density, and it may finally be damaged.[7] One of the attractive routes to ensure the solder joint’s reliability is via co-electrodeposition approach from aqueous suspension of ceramic micro/nanoparticles, nanotubes, or whiskers in an electrolyte.[8–11] Shin et al.[12] showed that with the incorporation of SiC nanoparticles in Sn-Bi matrix, the composite solder exhibited a finer eutectic microstructure with enhanced shear strength compared with Sn-Bi. On the other hand, Park et al.[13] demonstrated that the addition of carbon particles in the Sn matrix greatly increased their cycle performance. Recently, Choi et al.[14] co-electrodeposited multiwalled CNT in Sn matrix and found shear energy being improved by 50 pct and thus pointed out the novelty of the electrodeposition for producing the reliable solder joints. Various ceramic reinforcements, such as Al2O3, ZrO2, TiO2, SnO2, SiC, Y2O3 etc., have been already added into a solder alloy.[15–17] These reinforcements not only refine the microstructure and intermetallic ASHUTOSH SHARMA, Research Scholar, SUMIT BHATTACHARYA, Graduate Student, SIDDHARTHA DAS, Professor and Head, and KARABI DAS, Professor, are with the Department of Metallurgical and Materials Engineering, IIT Kharagpur, Kharagpur 721302, India. Contact e-mail: [email protected] Manuscript submitted November 9, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS A
compounds, but also increase the mechanical and thermal property, wear and corrosion resistance without sacrificing much the electrical performance of the materials. Currently, rare earth oxides are also being consistently used as reinforcing materials. Among the rare earth members, CeO2 is being widely used in mechanical, tribological, and microelectronic domain of research.[18–20] The CeO2 not only possesses excellent mechanical properties, but also attractive thermal and electrical properties. However, it is to be noted that micron-sized ceramic particles result in weaker particle matrix bonding that can deteriorate the mechanical, physical, and electrical properties of the nanocomposite solders.[21] Therefore, the prime objective of this research is to design a novel nanocomposite solder, near-eutectic Sn-Ag-containing nanocrystalline CeO2 particles for the first
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