Contact area measurement of micron-sized metal-coated polymer particles under compression

Abstract

The contact problem of a sphere under compression by a rigid plate is pertinent to understanding electrical contact formation in anisotropic conductive adhesive (ACA) applications. However, no work has experimentally verified existing contact models for the metal-coated sphere-plate contact problem. Herein, compression tests on metal-coated polymer spheres were performed by flat punch nanoindentation with in-situ scanning electron microscopy (SEM) monitoring, and the resultant contact area was measured using SEM images. The obtained results were compared to Tatara and Abbott-Firestone models, along with finite element analysis (FEA). The measured contact area falls between Tatara and Abbott–Firestone models, indicating a mixture of elastic and plastic deformation. The contact area as a function of force is dominated by the polymer core and independent of the metal coating for the thin metal coatings tested. The work provides guidelines for bonding parameters for ACA assembly.