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Wong,
C. P.
Wong,
C. P.
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ItemMonolayer protection for eletrochemical migration control in silver nanocomposite(Georgia Institute of Technology, 2006-09-12) Li, Yi ; Wong, C. P.The authors introduced an effective approach of using monolayer-protected silver nanoparticles to reduce silver migration for electronic device interconnect applications. Formation of surface complex between the carboxylate anion and surface silver ion reduces the solubility and diffusivity significantly of migration components and therefore contributes to effective migration control. A fundamental understanding of the mechanism of silver migration control was conducted by studying the current-voltage relationships of the nanocomposites with a migration model. The control of silver migration enables the application of the silver composites in fine pitch and high performance electronic device interconnects.
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ItemMicrowave assisted patterning of vertically aligned carbon nanotubes onto polymer substrates(Georgia Institute of Technology, 2006-07) Sunden, Erik Oscar ; Moon, Jack K. ; Wong, C. P. ; King, William P. ; Graham, SamuelThis paper presents a low pressure hot embossing method for transferring patterns of vertically aligned carbon nanotubes into thermoplastic substrates. The procedure utilizes the synthesis of carbon nanotubes in discrete patterns on silicon substrates through the vapor liquid solid growth mechanism. The nanotube pattern and silicon stamp is placed on top of a polycarbonate film and locally heated above the glass transition temperature using microwave processing. The weight of the silicon substrate presses the nanotubes into the polycarbonate, resulting in the complete transfer of vertically aligned patterns. The technique is a rapid processing method, which could be used to integrate aligned nanomaterials with MEMS and flexible electronics that are fabricated on a wide range of thermoplastic polymer materials.
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ItemA Novel Aluminum-Filled Composite Dielectric for Embedded Passive Applications(Georgia Institute of Technology, 2006-05) Wong, C. P. ; Xu, Jianwen ; Moon, Kyoung-Sik ; Tison, Christopher K.This paper presents the development of a novel aluminum- filled high dielectric constant composite for embedded passive applications. Aluminum is well known as a low-cost and fast self-passivation metal. The self-passivation forms a nanoscale insulating boundary outside of the metallic spheres, which has dramatic effects on the electrical, mechanical, and chemical behaviors of the resulting composites. Influences of aluminum particle size and filler loading on the dielectric properties of composites were studied. Because of the self-passivated insulating oxide layer of fine aluminum spheres, a high loading level of aluminum can be used while the composite materials continues to be insulating. Dielectric property measurement demonstrated that, for composites containing 80wt%3.0 maluminum, a dielectric constant of 109 and a low dissipation factor of about 0.02 can be achieved. The dielectric constant of epoxy-aluminum composites increased almost 30 times as compared with that of the pure epoxy matrix, which is about 3.5. Die shear tests showed that at such loading level, materials still had good processability and good adhesion toward the substrate. Bulk resistivity measurement, high-resolution transmission electron microscope (HRTEM) observation, and thermogravimetric analysis (TGA) were conducted to characterize the aluminum powders in order to understand the dielectric behavior of aluminumfilled composites. Bimodal aluminum-filled composites were also systematically studied in order to further increase the dielectric constant. Ouchiyama–Tanaka’s model was used to calculate the theoretical maximum packing fraction (MPF) of bimodal systems. Based on the calculation, rheology studies were performed to find the optimum bimodal filler volume fraction ratio that led to the best packing efficiency of bimodal fillers. It was found that the viscosity of polymer composites showed a minimum at optimum bimodal filler volume fraction ratio. A high dielectric constant of 160 (@10 kHz) with a low dissipation factor of less than 0.025 was achieved with the optimized bimodal aluminum composites. The developed aluminum composite is a promising candidate material for embedded capacitor applications.
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ItemStudy and Characterization on the Nanocomposite Underfill for Flip Chip Applications(Georgia Institute of Technology, 2006-03) Wong, C. P. ; Sun, Yangyang ; Zhang, ZhuqingThe nanosilica filled composite is a promising material for the no-flow underfill in flip-chip application. However, as the filler size decreases into the nano length scale, the rheological, mechanical, and thermal mechanical properties of the composite change significantly. The filler–filler and filler–polymer interactions have a profound impact on the material properties. The purpose of this paper is to achieve an in-depth understanding of the effect of the filler size and surface treatment on material properties and therefore to design a nanocomposite formulation with desirable material properties for no-flow underfill applications. Mono-dispersed nanosilica filler of 100 nm in size were used in this study. An epoxy/anhydride mixture was used as the base resin formulation. The nanosilica fillers were incorporated into the resin mixture to different filler loadings from 5 wt% to 40 wt% with or without silane coupling agents as the surface treatment. UV-Visible spectroscopy showed that the underfills with nano-size filler were transparent in the visible region even at high filler loading. The curing behavior and the Tg of the nanocomposite were studied using a modulated differential scanning calorimerter. It was found that the presence of the nanosilica could hinder the curing reaction, especially at the late stage of cure. The Tgs of the nanocomposites with untreated silica were found to decrease with the increasing filler loading. The measurement of the dynamic moduli from dynamic mechanical analyzer indicated that there was a secondary relaxation related to the filler–polymer interface. The coefficient of thermal expansion of the nanocomposite was measured using a thermal mechanical analyzer. The rheology of the nanocomposite was studied using a stress rheometer. It was found that the filler treatment could significantly reduce the viscosity of the nanocomposite and improve the processing capability of the underfill. Density measurements and moisture absorption experiments both indicated that the addition of nanosilica could increase the free volume of materials. The dispersion of the nanosilica in the cured composite materials was observed using scanning electron microscopy. Control samples with micron-size silica fillers were formulated and characterized for comparison.
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ItemElectrical Property Improvement of Electrically Conductive Adhesives Through In-Situ Replacement by Short-Chain Difunctional Acids(Georgia Institute of Technology, 2006-03) Wong, C. P. ; Li, Yi ; Moon, Kyoung-SikTo improve the electrical properties of electrically conductive adhesives (ECAs), short-chain difunctional acids, such as malonic acid (acid M), adipic acid (acid A), and terephthalic acid (acid T) were introduced into a typical isotropic conductive adhesive formulation. By in-situ replacement of the commonly used surfactant-stearic acid in silver(Ag) flakes, such difunctional acids can increase the conductivity of ECAs. With the addition of malonic acid and adipic acid, which only have short chain single-bond hydrocarbon between the dicarboxylic groups, the conductivity of the typical conductive adhesives was improved significantly. Terephthalic acid, however, deteriorates the conductivity due to the rigid aromatic structure in the molecule. Dynamic mechanical analysis and thermomechanical study indicated the improved electrical properties with malonic and adipic acids were achieved without negatively affecting the mechanical and physical properties of ECAs.