Electrical conduction characteristics of solid metal anisotropic conductive adhesive particles

Anisotropic Conductive Adhesives (ACAs) have been used in fine pitch electronics packaging for over a decade and provide a high density and low temperature bonding method in a range of niche applications. In an ACA assembly, individual particles act as electrical conductors, providing current paths for fine pitch electronics interconnections. This paper presents a model of the electrical conduction characteristics of the solid metal particles used in some ACAs. Conduction through such ACA particles results from contact between the component and substrate pads and the particle, which is deformed by the assembly process. In order to investigate the effect of the extent of particle deformation, or transformation degree, upon the particle resistance, the particle transformation factor is defined. A mathematical model of the electrical resistance of an ACA particle, which is an integral function of the transformation factor and the particle geomehy, has been developed from a physical model of the ACA particle. MuthCAD software has been used to provide solutions for this function. According to these numerical solutions, the greater the particle transformation, the lower the particle resistance will be. In conclusion, it is shown that the ACA particle resistance is determined by the particle transformation and the particle geometries. Finally, the resistance function will explain the conductive mechanism of a deformed metal ACA particle.