Printed Circuit Design & Fab - July 2008 - (Page 35)

EMERGING tEchnoloGiES Conclusion Nanotechnology provides many useful tools to enhance the properties and processing of electronic materials. The enhanced materials and processes will have to prove their reliability and economic value to compete, but the sheer volume of opportunities and potential solutions suggests we’ll be seeing a lot more nanomaterials in our industry. pcd&f Ed.: This article is excerpted from a paper in the proceedings of the 2007 SMTA Pan Pacific Microelectronics Symposium and is printed with permission. rEFErEncES FiGurE 6. Printed 30 nm silver layer processed at 150°C. 1. A. rae and A. Skipor, “nanotechnology and room Temperature Assembly, SMTA: Emerging Technologies Summit, Sept. 25, 2006. ” 2. C. r. M. Wronski, “The Size Dependence of the Melting Point of Small Particles of Tin, Brit J. Appl. Phys., vol. 18, 1967. ” 3. Ph. Buffat and J. P Borel, “Size effect on the Melting Temperature of . Gold Particles, Physical Review A, vol. 13, no. 6, June 1976. ” 4. S. l. lai, J. y. Guo, v. Petrova, G. ramanath, l. H. Allen, “Size-Dependent Meeting Properties of Small Tin Particles: nanocalorimetric Measurements, Physical Review Letters, vol. 77, no. 1, July 1996. ” 5. leslie H. Allen, “nanocalorimetry Studies of Materials: Melting Point Depression and Magic nanostructures, NNUN Abstracts 2002/Materi” als, Physics, Process & Characterization, 2002, p. 40. 6. M. Zhang, et al, “Size Dependent Melting Point Depression of nanostructures: nanocalorimetric Measurements, Physical Review B, vol. ” 62, no. 15, october 2000. 7. Kevin Grossklaus, Melting and Coalescence Behavior of Tin nanoparticles for use in low Temperature Solder Applications, Purdue university, master’s thesis, August 2007. 8. lin-yin Hsiao and Jengong Duh, “Synthesis and Characterization of lead free Solders with Sn-3.5Ag-xCu (x=0.2,0.5,1.0) Alloy nanopar” ticles by the Chemical reduction Method, J. of the Electrochemical Society, 152, (9), 2005. 9. Savas Berber, young-Kyun Kwon and David Tamanek, “Bonding and energy Dissipation in a nanohook Assembly, Physical Review of Let” ters, vol. 91, no. 16, october 2003. 10.university of Akron news, “uA Synthetic Gecko Foot-Hairs leading to reusable Adhesives, uakron.edu/news/articles/uamain_1293.php, ” Aug. 12, 2005. 11. liehui Ge, Sunny Sethi, lihie Ci, Pulickel Ajayan and Ali Dhinojwala, “Carbon nanotube-based Synthetic Gecko Tapes, Proceedings of the ” National Academy of Sciences of the United States of America, vol. 104, no. 26, June 26, 2007. 12.Alan rae, “nanosolder – What’s next?” International Conference on Soldering and reliability, May 16, 2008. constituents must be controlled; nanoparticles, by their nature, are reactive. Sinterable systems. Many of the same issues of surface reactivity apply to sinterable systems (e.g., ink-jettable silver). Surface control is key to controlling reactivity, but the same compromises apply as in adhesives; particles have to be disagglomerated, remain in suspension and achieve a practical concentration and shelf life. The issue is compounded by the fact that many printing systems need relatively low viscosities (tens of centipoises – between the viscosity of water and milk) and many of the inorganic fillers to disperse have high specific gravity compared with the organic pigments we use in many applications. Silver, for instance, has a specific gravity of >11 (much greater than that of organic materials). nano-solder. One of the main issues in nano-solder production is the use of tin. It is a very reactive metal and readily oxidizes. (Most of the dross forming on SnPb solder is actually tin oxide.) It is, however, possible to produce tin particles in a reducing environment. Manufacturing oxide-free tin particles, integration of metal particles with flux, and electronics assembly are the focus of the iNEMI Nano-Solder Project. This work is enhanced by a project funded by the National Science Foundation at Purdue University and MetaMateria Partners that is exploring the mechanism of nano-solder consolidation.12 The electron microscopy facility at the Purdue University Birck Nanotechnology Center is carrying out in-situ characterization of the melting behavior of tin and tin alloy nanoparticles. This analysis will be crucial for understanding the melting behavior of nanoparticles intended for use in a solder, and will allow the behavior of individual particles to be correlated with the behavior of a solder paste. This type of fundamental understanding of particle and paste behavior will be necessary for understanding and resolving the challenges related to developing a useable nano-solder. nanotube “dry” adhesives. Several challenges include producing the material in the correct form, verifying the theoretical strength and conductivity parameters, designing device interconnects and verifying processability and reliability – and doing it all economically. Nevertheless, this is a game-changing route to assembly that could have real benefits for electronics assemblers. JULY 2008 acknowlEdGMEntS The authors gratefully acknowledge the support and contributions of colleagues at nanoDynamics, MetaMateria Partners, Motorola, Purdue university, Delphi, and ineMI. alan raE, Ph.D., is vice president of innovations for nanoDynamics (nanodynamics.com) and chair of the ineMI research Committee; area@nanodynamics.com. andrEw SkiPor, Ph.D., is a distinguished member of the technical staff and distinguished innovator, a nanotechnology leader for Motorola labs (motorola.com), and chairs of the ineMI Pb-Free nano-Solder Project. Marc chaSon is an ineMI consultant and president of Marc Chason and Associates. printEd circuit dESign & fAB 35 http://uakron.edu/news/articles/uamain_1293.php, http://nanodynamics.com

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