Prediction of electrical contact resistance for anisotropic conductive adhesive assemblies

Anisotropic conductive adhesive (ACA) assembly is emerging as one of the most flexible and cost effective packaging interconnect methods in the microelectronics industry. One of the major impediments to the full realization of the fine pitch ( < 200 mum) capabilities of this assembly method is accurate prediction and control of electrical contact resistance. This paper presents a detailed review and direct comparisons of the different models that have been used to predict electrical contact resistance in ACA interconnects. It is found that large discrepancies exist among these models and between contact resistance values experimentally measured and what these models predict. The governing equations and assumptions underlying the models and their implications are examined, and possible rationales for the observed discrepancies, and future directions for developing improved models are identified. The study shows that important issues generally not considered in current models are tunneling resistance, multimaterial layers, edge effect, rough surfaces, elastic recovery and residual forces, interaction between nearby particles, and variation on the radii of multiple particles.