(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.
(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.