Person:
Wong, C. P.

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Now showing 1 - 2 of 2
  • Item
    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.
  • Item
    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.