Modeling and Experimental Verification of the Contact Resistance of a Novel Anisotropic Conductive Adhesive

The need to eliminate lead-based materials as a means of interconnection has renewed the electronics industry’s interest in using conductive adhesives for component attach, especially Anisotropic Conductive Adhesives (ACA). Typical ACAs require the application of pressure during the curing process, to establish the electrical connection and also to capture a monolayer of conductive particles between the mating surfaces. The novel ACA discussed in this paper uses a magnetic field to align the particles in the Z-axis direction during curing and eliminates the need for pressure. The application of the magnetic field allows for the formation of conductive chains between the mating surfaces, thereby eliminating lateral conductivity. This uniqueness of the novel ACA also accommodates for any coplanarity error and the formation of effective Z-axis conductivity, with a variety of lead and bump shapes. The novel ACA also enables mass curing of the adhesive, eliminating the need for sequential assembly. As part of the study presented in this paper, the conductive chains were modeled as series and parallel resistor networks in an insulating adhesive matrix. The number of particles in the chain and hence the number of interfaces between the particles is found to influence the initial contact resistance of the joints. The interfacial resistance is derived from the experimental run. Area array packages with and without bumps, reveal varying contact resistances as indicated by the model and experiment. This paper will present a model for the conductive chain formation in the novel ACA, and discuss the experimental results obtained to verify the joint contact resistance.