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21.
Venkat Iyer 《电子工业专用设备》2006,35(4):3-4,22
半导体封装主要是提供一个媒介,把精细的硅芯片连接到较粗糙间距的印制电路板上,并保护器件免于受潮。这些年间,虽然这个功能并未改变,但封装技术已远较从前复杂。由于芯片的性能逐步复杂封装已肩负着全部散热的责任,这些热量不能成为限制部件电子性能的因素。而且对便携式应用而言,由于空间越来越宝贵,也需要更小和更薄的封装。随着硅片工作频率的提高,走线电感需要减小。与此同时,封装方案必须具备成本效益以满足当前消费电子应用的价格目标。鉴于硅技术不断发展,封装不得不变得更轻薄、散热性能更佳、速度更快及成本更低!1引线封装市场上… 相似文献
22.
K. N. Srinivasan M. Selvam S. Venkata Krishna Iyer 《Journal of Applied Electrochemistry》1993,23(4):358-363
Electrodeposition of metals from solution is usually accompanied by the simultaneous discharge of hydrogen ions or water molecules. When hydrogen is liberated at an iron/steel surface during electrodeposition, a portion of the hydrogen is absorbed by the metal surface and then diffuses into the interior. The diffused hydrogen produces some detrimental effects, such as reduction in ductility and loss in mechanical strength, leading to hydrogen embrittlement. The present paper reports investigations on hydrogen permeation measurements in zinc-manganese alloy deposition using a modified electrode clamp for easy removal and fixing of the electrode. Hydrogen permeation studies indicate that the porosity of the deposit increases in the following order:Zn-Mn(14.3%), Zn-Mn(2.4%), Zn-Mn(24.8%) and Zn-Mn(37.5%).This is in agreement with the corrosion data obtained which indicates that Zn-Mn alloy deposits with low manganese content show better performance than pure zinc deposits. 相似文献
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Fluorescence quenching effect of single walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) on three most common fluorophores fluorescein, rhodamine 6G and quinine sulphate has been studied and compared. Comparative studies of quenching efficiency shows that SWCNTs are more efficient fluorescence quencher than the MWCNTs. Nature of Stern–Volmer plot was found to be highly non-linear indicating combined effect of dynamic and static quenching. The contribution of dynamic quenching component was assessed through the fluorescence lifetime measurements. Studies on vacuum annealed SWCNTs with low defect contents suggest that structural defects primarily contribute to the large quenching. Fluorescence quenching was found to be dominant even in the cases where adsorption was low implying that surface adsorption play a minor role in the quenching, except for rhodamine 6G. Adsorption isotherms have been studied using Langmuir and Freundlich models. Freundlich model was found to be closer in behaviour implying a multilayer adsorption of molecules on the surface. The contributions of metal nanoparticles and carbon impurities present in different allotropic forms to the fluorescence quenching were also assessed. We speculate that defect mediated nonradiative energy transfer through dipole–dipole coupling may be the dominant mechanism of high efficiency quenching by SWCNTs. 相似文献
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Ping Xu Kuan Chang Young Il Park Bin Zhang Leilei Kang Yunchen Du Rashi S. Iyer Hsing-Lin Wang 《Polymer》2013,54(2):485-489
Two water soluble conjugated polymers, poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and ammonium ion stabilized poly(phenylene vinylene) (P2), are found to be able to reduce noble metal ions to zero-valent metals via a direct chemical deposition technique. Au nanoparticle clusters can be obtained through reduction of Au3+ ions by PEDOT:PSS and the electronic coupling between them can be controlled by HAuCl4 concentration. Core/shell Ag/polymer nanostructures are prepared from reduction of Ag+ ions by P2, which have a ppb detection limit for 4-MBA using surface-enhanced Raman spectroscopy (SERS). This conjugated polymer mediated synthesis of metal nanoparticles may open a new avenue for fabricating nanomaterials and nanocomposites with tunable optical properties that are dominated by their structure and electronic coupling between nanoparticles. 相似文献
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S. Iyer J. McIntosh A. Bandyopadhyay N. Langrana A. Safari S. C. Danforth R. B. Clancy C. Gasdaska P. J. Whalen 《International Journal of Applied Ceramic Technology》2008,5(2):127-137
We present processing (green and sintered), part shrinkage and warping, microstructural characterization, and mechanical properties of Si3 N4 made by fused deposition of ceramics (FDC), using optical microscopy, scanning electron microscopy, and X-ray diffraction. The mechanical properties (fracture strength, fracture toughness, and Weibull modulus) are also reported. Proper FDC build parameters resulted in dense, homogeneous, near-net-shape Si3 N4 , with microstructures and mechanical properties similar to conventionally processed material. Mechanical properties are shown to be isotropic, while there is some degree of microstructural texturing (preferred β-Si3 N4 grain orientation) in sintered components. 相似文献
29.
The biodegradability of low density polyethylene (LDPE)/starch and LDPE/starch/starch acetate (STAc) blends was tested and observed to be dependent on STAc content. The binary and ternary blends containing up to a maximum concentration of 30% starch were examined for their thermal, mechanical, and morphological properties. The blends with no STAc or 2.5% STAc show almost no adherence of two phases. With 10% STAc, dispersion of starch was observed to increase with some adherence to LDPE. Tensile strength, elongation at break, and Izod impact strength of the blends decreased with increased starch content. However, incorporation of STAc along with starch improved all these properties, particularly elongation at break and toughness. The melt flow index was also improved on partial substitution of starch by STAc. Maximum biodegradability was observed for the blends containing 30% (starch + STAc). Cell growth was observed to increase with increasing concentration of (starch + STAc) in the blends. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2791–2802, 1999 相似文献
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