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Wong, C. P.

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Author: Lu, Daoqiang × End date: 1999 × Start date: 1999 × Has files: Yes ×

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Now showing 1 - 3 of 3
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    A Study of Lubricants on Silver Flakes for Microelectronics Conductive Adhesives
    (Georgia Institute of Technology, 1999-09) Wong, C. P. ; Lu, Daoqiang
    Conductive adhesives are composites of polymer matrixes and metal fillers (conductive elements). Silver (Ag) flakes are widely used as fillers for electrically conductive adhesives (ECA’s). Generally, there is a thin layer of organic lubricant coated on the commercial Ag flake surface. This lubricant layer is needed for eliminating the Ag particle agglomeration while dispersing the Ag filler into the polymeric resin. Therefore the lubricant influences rheology, conductivity, and other properties of ECA’s. The nature of the lubricant on a Ag flake and the interaction between the lubricant and the Ag flake surface were studied by diffuse reflectance infrared spectroscopy (DRIR). Thermal decomposition of the lubricant was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). In addition, the effects of some chemical compounds on lubricant removal and the enhancement of conductivity of the ECA were also investigated. It was found that 1) a chemical bonding was formed on the Ag flake surface between the lubricant and Ag; 2) the short chain acids replaced the long chain lubricants; 3) an ether and a poly(ethylene glycol) enhanced electrical conductivity by partially removing the Ag flake lubricants.
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    Mechanisms Underlying the Unstable Contact Resistance of Conductive Adhesives
    (Georgia Institute of Technology, 1999-07) Wong, C. P. ; Lu, Daoqiang ; Tong, Quinn K.
    One critical obstacle of current conductive adhesives is their unstable contact resistance with nonnoble metal finished components during high temperature and humidity aging. It is commonly accepted that metal oxide formation at the interface between the conductive adhesive and the nonnoble metal surface is responsible for the contact resistance shift. Two different mechanisms, simple oxidation and galvanic corrosion, both can cause metal oxide formation, but no prior work has been conducted to confirm which mechanism is the dominant one. Therefore, this study is aimed at identifying the main mechanism for the metal oxide formation and the unstable contact resistance phenomenon of current conductive adhesives. A contact resistance test device, which consists of metal wire segments and conductive adhesive dots, is specially designed for this study. Adhesives and metal wires are carefully selected and experiments are systematically designed. Based on the results of this systematic study, galvanic corrosion has been identified as the underlying mechanism for the metal oxide formation and for the observed unstable contact resistance phenomenon of conductive adhesives.
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    Conductivity Mechanisms of Isotropic Conductive Adhesives (ICA’s)
    (Georgia Institute of Technology, 1999-07) Wong, C. P. ; Lu, Daoqiang ; Tong, Quinn K.
    Isotropic conductive adhesives (ICA’s) are usually composites of adhesive resins with conductive fillers (mainly silver flakes). The adhesive pastes before cure usually have low electrical conductivity. The conductive adhesives become highly conductive only after the adhesives are cured and solidified. The mechanisms of conductivity achievement in conductive adhesives were discussed. Experiments were carefully designed in order to determine the roles of adhesive shrinkage and silver (Ag) flake lubricant removal on adhesive conductivity achievement during cure. The conductivity establishment of the selected adhesive pastes and the cure shrinkage of the corresponding adhesive resins during cure were studied. Then conductivity developments of some metallic fillers and ICA pastes with external pressures were studied by using a specially designed test device. In addition, conductivity, resin cure shrinkage, and Ag flake lubricant behavior of an ICA which was cured at room temperature (25 ℃) were investigated. Based on the results, it was found that cure shrinkage of the resin, rather than lubricant removal, was the prerequisite for conductivity development of conductive adhesives. In addition, an explanation of how cure shrinkage could cause conductivity achievement of conductive adhesives during cure was proposed in this paper.