Electrical conductive characteristics of anisotropic conductive adhesive particles

In anisotropic conductive adhesive (ACA) interconnections, the particles are electrical conductors providing current paths in the fine pitch electronic packaging as well as physical parts connecting with the chip bumps and the substrate pads through the mechanical deformation interfaces. The primary object of this fundamental research is to reveal the electrical conductive characteristics of Ni/Au coated resin particles. Such an ACA particle resistance is resulted from two metal coated layers, which are two parallel resistors in the circuit determined by the particle transformation degree. In order to investigate the effect of the particle transformation degree upon the particle resistance, the particle transformation factor is defined. The mathematical electrical resistance function of an ACA particle, an integral function of the transformation factor and the particle geometries, resin diameter nickel layer thickness, and gold layer thickness, is worked out from the physical model of an ACA particle. To carry out the solutions of the function, MathCAD software is applied. According to the numerical solutions, the deeper the particle transformation, the thicker the metal coated layer thicknesses and the longer the resin diameter are, the lower the particle resistance is. In conclusion, it is stated that the ACA particle resistance is determined by the particle transformation and the particle geometries, however the transformation and the nickel layer thickness are more sensitive than the resin diameter and the gold layer thickness. Finally, the resistance function will explain the conductive mechanism of the deformed ACA particle.