Anisotropic Conductive Adhesives (ACAs) consist of a
polymer adhesive matrix containing fine conductive particles
dispersed either randomly, or more rarely in an ordered way.
The primary objective of this experimental research was to
understand the effects of a non-uniform bond thickness due to
non co-planarity of the component or substrate terminations
in ACA assemblies. This has been achieved through
measurements of the conductivity variations of ACA joints in
a number of ACA assemblies, where the component bump
plane and substrate plane were deliberately held in different
degrees of relative rotation from parallel during adhesive
cure. Measurements of the joint resistances versus rotational
angle, for a constant bonding force, were made for 10 levels
of rotation of the chips relative to the substrates. The results
showed that the resistances of the joints in the assemblies
exhibited three distinct types of behaviour: stable joint
resistances; gradually increasing resistances and unstable
resistances. In conclusion, it is shown that ACA joints are
very sensitive to the uniformity of the bond thickness, as the
larger the rotations were, the lower and less uniform the joint
conductivities were, however, the joints were uniform if the
rotation angles were controlled within certain limits