Control of nanosilver sintering attained through organic binder burnout
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Thomas G. Lei Department of Materials Science and Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
Jesus N. Calata Center for Power Electronics Systems and Department of Materials Science and Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
Guo-Quan Lu Center for Power Electronics Systems, Department of Materials Science and Engineering, and Bradley Department of Electrical and Computer Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (Received 13 May 2007; accepted 5 September 2007)
Control of the low-temperature sintering of nanosilver particles was attained by dispersing and stabilizing nanosilver particles into a paste form using the selected organic binder systems. As demonstrated by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), with the existing binder systems, undesirable premature coalescence of nanosilver particles was prevented and the metastable structure was retained until the binder burned out at relatively higher temperatures. Enhanced densification was achieved upon the binder burnout because at the relatively higher temperatures the densification mechanisms, e.g., grain-boundary or lattice diffusion, become more dominant. We propose that the onset of sintering, extent of densification, and final grain size can be controlled by either the size of the initial nanosilver particles or the binder systems with different burnout characteristics.
I. INTRODUCTION
Compared with the sintering behavior of micrometerscale materials, nanoscale particles have unique characteristics that include significantly lower sintering temperatures.1,2 The potential of sintering nanomaterials at very low temperatures opens the door to many novel applications. Specifically, sintered nanosilver has been proposed for semiconductor device interconnect applications.3,4 The potential advantages of sintered nanometal interconnection over existing solder-based systems are numerous. First, solder has to be melted to form the interconnection. The consequence is that the operating temperature has to be below the melting point. If a higher temperature is required, a higher-melting-temperature alloy must be used, which in turn requires an increasingly
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Address all correspondence to this author. e-mail: [email protected] Present address: 352600 Campus Box, Department of Mechanical Engineering, University of Washington, Seattle, WA 98195. DOI: 10.1557/JMR.2007.0440 3494
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J. Mater. Res., Vol. 22, No. 12, Dec 2007 Downloaded: 14 Mar 2015
higher process temperature. On the other hand, the sintered joint is formed at a temperature substantially lower than the melting point, thus enabling the joint to operate at temperatures at or higher than the process temperature. Second, solder joints are susceptible to fatigue failure because the operating temperature range is close to the melting point. Sintered joints operate far below the melting point and thus ar
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