Circuits Assembly - July 2008 - (Page 32)

Emerging Technologies of printing techniques with a thermally removable binder. Even at 80 nm, significant densification and conductivity development is seen above 125°C (Figures 2 and 3). These show promise for die attach, conductor printing and electrical connections. The iNEMI Nano-Solder Project is working to put these materials into a printable solder paste. The project team is characterizing the metals and working to develop a proof of concept demonstration, using a model similar to the SnAgCu system developed for Pb-free solders (inemi.org/cms/projects/ba/Pbfree_nano-solder.html). Nano-solders could potentially be available within the next three years. A method has been developed to synthesize Pb-free solders such as SnAg3.5Cux (x=0.2, 0.5, 1.0) by chemical reduction methods.8 Sinterable silver systems are currently available from such companies as Cabot, Cima NanoTech and NanoDynamics. Enhanced adhesives. Nanomaterials can enhance mechanical properties of adhesives (even a 0.1% addition of multi-wall carbon nanotubes can raise the flexural strength of an unfilled epoxy by 30%), as well as electrical properties because of the large number of potential contact or tunneling events when nanosized particles are present. A reduction of 10x in particle size (for example, from 1 µm to 100 nm) with the same weight content yields a 10 x 10 x 10 (1000-fold) increase in the number of particles present. Several iNEMI members are participating in a University of Binghamton SPIR project (Strategic Partnership for Industrial Resurgence, http://watson.binghamton.edu/level2/industry.html#SPIR) to quantify effects of nanoparticles – metal and carbon-based – in resin-based systems, in order to get a consistent dataset to characterize performance. Information from this project will be published. Nano-attach technologies. Hook-andloop fasteners (e.g., Velcro) used the ideas generated by plant burrs to create a new fastening paradigm. An extension would be to use carbon nanotubes, as suggested by researchers at Michigan State Univer32 sity in 2003.9 Simulation of entangled carbon nanotubes demonstrated nanotubes made in Figure 2. Concurved shapes could ductive network be used to develop produced using heatvery high-strength treated 80 nm silver. room temperature Figure 3. Resistivity as a function of process interconnects. temperature for a 30 nm silver. Note the signifiAnother innovative application of cant increase in conductivity as low as 125°C. nanotechnology is bio-mimetic nanointer-particle distance is lowered as attach. Textured dry adhesives, based on the particle size decreases for a given the gecko foot approach (bio-inspired) content. At the sub 5 µm level, many where nano-sized hairs attach to surface colloids agglomerate at concentrations roughness using van der Waals forces, of only 3 to 5%. have been the subject of a great deal of · Dispersion. Nanoparticles supplied as research.10,11 Bio-inspired materials sysdry powders are notoriously difficult tems using carbon nanotubes or polymer to disperse in viscous liquids. The tennano-filaments have been demonstrated dency now is to supply them as disperat a number of research locations with sions in compatible liquids or polymer strengths far higher than those that commaster batches. fortably attach a gecko to a ceiling! · Segregation. By varying the hydrophoThe iNEMI Nano-Attach research bic/hydrophilic nature of the surface project is identifying and attempting to coating, it is possible to encourage the demonstrate these types of nano-adhematerial to disperse in a similar medision techniques that have the potential to um or to preferentially congregate on replace traditional solder or conductive a second phase or at the surface (Figadhesive assembly processes currently ures 4 and 5). employed in electronics manufacturing. · Reactivity. Reaction with catalysts, fillers or other constituents must be conImplementation Challenges trolled; nanoparticles, by their nature, Percolation and particles. The addition of are reactive. fine particles to improve polymer system Sinterable systems. Many of the same conductivity has been well documented issues of surface reactivity apply to sinterin the literature. However, duplicating the able systems (e.g., ink-jettable silver). Surperformance in real-life systems tends to face control is key to controlling reactivbe much more complex. Nano-product ity, but the same compromises apply as in implementation can only be achieved if adhesives; particles have to be disagglomthe following factors are addressed: erated, remain in suspension and achieve · Protective coating. Virtually all nanoa practical concentration and shelf life. metals need a protective coating that The issue is compounded by the fact that permits dispersion in liquids and many printing systems need relatively low prevents oxidation or self-sintering. viscosities (tens of centipoises – between Uncoated silver will sinter to itself at the viscosity of water and milk) and many room temperature, and uncoated copof the inorganic fillers to disperse have per will quickly turn black. Uncoated high specific gravity compared with the aluminum and many other metals are organic pigments we use in many applipyrophoric. Coatings may be applied cations. Silver, for instance, has a specific in vapor phase by precipitation or gravity of >11 (much greater than that of chemical reaction. organic materials). · Agglomeration. Nanomaterials have Nano-solder. One of the main issues high surface energy and tend to stick in nano-solder production is the use of to each other. Because the number of tin. It is a very reactive metal and readparticles per unit volume is high, the circuitsassembly.com Circuits Assembly JULY 2008 http://inemi.org/cms/projects/ba/Pb-free_nano-solder.html http://inemi.org/cms/projects/ba/Pb-free_nano-solder.html http://watson.binghamton.edu/level2/industry.html#SPIR http://watson.binghamton.edu/level2/industry.html#SPIR http://circuitsassembly.com

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Circuits Assembly - July 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business Global Sourcing On the Forefront Screen Printing Tech Tips Will Electronics Follow the Sun? ‘Warm’ Manufacturing Heats Up Reputation Trumps Recession, China ‘Web Circuits’ A Novel Non-VOC Conformal Coating Krypton: Benchmarking Customer Satisfaction 2008-09 CIRCUITS ASSEMBLY Buyers Guide Wave Soldering Pb-Free Lessons Learned Process Doctor Materials World SMTA Int'l Product Preview Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - July 2008

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