Electrical characterization of individual metal-coated polymer spheres used in isotropic conductive adhesives

Isotropic conductive adhesives (ICAs) filled with metal-coated polymer spheres (MPS) have been proposed to improve the mechanical reliability compared to conventional ICAs filled with silver flakes. The electrical properties of MPS play an important role in the electrical performance of macroscopic MPS-based ICAs. This article deals with the electrical characterization of individual MPS using a nanoindentation-based flat punch method, in which the resistance and the deformation of single MPS were monitored simultaneously. Four groups of silver-coated polymer spheres (AgPS) with identical polymer cores but different silver coating thicknesses were tested. The resistance of AgPS decreases gradually with increasing deformation degree of particles, and increases when the deformation of particles is reduced. In addition, the resistance of individual AgPS is dependent on the physical properties of the silver coating, such as thickness, uniformity, and porosity. The thicker the silver coating is, the lower and more stable the resistance of AgPS is.