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Wong,
C. P.
Wong,
C. P.
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ItemSynthesis of High-Quality Vertically Aligned Carbon Nanotubes on Bulk Copper Substrate for Thermal Management(Georgia Institute of Technology, 2010-05) Lin, Wei ; Zhang, Rongwei ; Moon, Kyoung-Sik ; Wong, C. P.Vertically aligned carbon nanotubes (VACNTs) grown on bulk copper substrate are of great importance for real-life commercial applications of carbon nanotubes (CNTs) as thermal interface materials in microelectronic packaging. However, their reproducible syntheses have been a great challenge so far. In this study, by introducing a well-controlled conformal Al₂O₃ support layer on the bulk copper substrate by atomic layer deposition, we reproducibly synthesized VACNTs of good alignment and high quality on the copper substrate. The alignment and the quality were characterized by scanning electron microscope, transmission electron microscope, and Raman spectroscopy. The key roles of the conformal Al₂O₃ support layer by atomic layer deposition are discussed. This progress may provide a real-life VACNT application for thermal management.
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ItemEnhanced Electrical Properties of Anisotropic Conductive Adhesive With $pi$ -Conjugated Self-Assembled Molecular Wire Junctions(Georgia Institute of Technology, 2009-09) Zhang, Rongwei ; Li, Yi ; Yim, Myung Jin ; Moon, Kyoung-Sik ; Lu, Daoqiang ; Wong, C. P.We have investigated the electrical properties of anisotropic conductive adhesive (ACA) joint using submicrometer- sized ( 500 nm in diameter) silver (Ag) particle as conductive filler with the effect of -conjugated self-assembled molecular wires. The ACAs with submicrometer-sized Ag particles have higher current carrying capability ( 3400 mA) than those with micro-sized Au-coated polymer particles ( 2000 mA) and Ag nanoparticles ( 2500 mA). More importantly, by construction of -conjugated self-assembled molecular wire junctions between conductive particles and integrated circuit (IC)/substrate, the electrical conductivity has increased by one order of magnitude and the current carrying capability of ACAs has improved by 600 mA. The crucial factors that govern the improved electrical properties are discussed based on the study of alignments and thermal stability of molecules on the submicrometer-sized Ag particle surface with surface-enhanced Raman spectroscopy (SERS), providing a fundamental understanding of conduction mechanism in ACA joints and guidelines for the formulation of high-performance ACAs in electronic packaging industry.
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ItemNovel Nano-Scale Conductive Films With Enhanced Electrical Performance and Reliability for High Performance Fine Pitch Interconnect(Georgia Institute of Technology, 2009-02) Li, Yi ; Yim, Myung Jin ; Moon, Kyoung-Sik ; Wong, C. P.In this paper, a novel nano-scale conductive film which combines the advantages of both traditional anisotropic conductive adhesives/films (ACAs/ACFs) and nonconductive adhesives/films (NCAs/NCFs) is introduced for next generation high-performance ultra-fine pitch packaging applications. This novel interconnect film possesses the properties of electrical conduction along the z direction with relatively low bonding pressure (ACF-like) and the ultra-fine pitch (< 30 μm) capability (NCF-like). The nano-scale conductive film also allows a lower bonding pressure than NCF to achieve a much lower joint resistance (over two orders of magnitude lower than typical ACF joints) and higher current carrying capability. With low temperature sintering of nano-silver fillers, the joint resistance of the nano-scale conductive film was as low as 10―5 Ohm. The reliability of the nano-scale conductive film after high temperature and humidity test (85°C/85% RH) was also improved compared to the NCF joints. The insertion loss of nano-scale conductive film joints up to 10 GHz was almost the same as that of the standard ACF or NCF joints, suggesting that the nano-scale conductive film is suitable for reliable high-frequency adhesive joints in microelectronics packaging.
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ItemInvestigation of electrical contact resistance for nonconductive film functionalized with Π -conjugated self-assembled molecules(Georgia Institute of Technology, 2007-02-26) Dong, Hai ; Li, Yi ; Yim, Myung Jin ; Moon, Kyoung-Sik ; Wong, C. P.Nonconductive adhesive/nonconductive film (NCA/NCF) bonding technology has attracted increasing research interests as lead-free interconnect. During bonding, heat and pressure are applied and the direct physical contacts between the two surfaces of integrated circuit bump and substrate bond pad can be achieved. The electrical contact resistance of a NCA/NCF joint is controlled by the pressure, roughness and NCA/NCF material properties. An accurate prediction of contact resistance can help guide experiment setup towards improving the electrical performance of NCA/NCF. In this study, a model is developed and correlated to experiments. The effects of NCA/NCF material properties on electrical contact resistance are investigated.
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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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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.
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ItemImproved Stability of Contact Resistance of Low Melting Point Alloy Incorporated Isotropically Conductive Adhesives(Georgia Institute of Technology, 2003-06) Wong, C. P. ; Moon, Kyoung-Sik ; Wu, JialiWith the driving force of “green” revolution in the electronics industry, tremendous efforts have been made in pursuing lead-free alternatives. Although lately lead-free alloys have drawn a lot of attention, their technical weaknesses, such as high processing temperature, poor wetting and high surface tension, limit their applications on the thermally sensitive, flexible, nonsolderable substrates and the ultra-fine pitch size flip chip interconnection. Conventional isotropically conductive adhesives (ICAs) have been used widely in surface mount and die-attach technologies for electrical interconnection and heat dissipation. The low temperature processing of ICAs is one of the major advantages over lead-free solders, which brings a low system stress, simple manufacture process and the like. In order to enhance the contact resistance of ICAs, the low melting point alloy (LMA) incorporating technology has been developed by our group. In this paper, LMA fusing methods were studied, since nonfused LMA in ICAs after a curing process can adversely affect the physical property and contact resistance stability. A differential scanning calorimeter (DSC) was used for the basic examination of depleting rate of LMAs in the typical ICAs. The cross-sectional morphology, LMA distribution and intermetallic compound were investigated by a scanning electron microscope (SEM). In addition, contact resistance for the ICA formulation incorporated with LMAs under elevated temperature and humidity was evaluated.