Effect of Silver Flakes and Particle Shape on the Steady Shear Viscosity of Isotropic Conductive Adhesives

This study investigated the effect of silver filler particle/flake shape on the rheological behavior of isotropic conductive adhesives (ICAs). Three types of epoxy systems were formulated with the following fillers: silver flakes, silver powder, and a mixture of silver flakes and silver powder. A volume fraction ranging from 0.2 to 0.8 silver fillers was added to the epoxy systems, and the corresponding viscosity of the paste was measured. The relationship between viscosity and volume fraction of ICAs is described through empirical models such as the Krieger–Dougherty, Quemada, and Eilers models. The studies showed that the shape of the filler influenced the viscosity of the suspension. For example, the silver flakes agglomerated at a lower volume fraction than silver flakes. In addition, an increase in the volume fraction reduced the distance between the particles and flakes, resulting in greater viscosity. In addition, the Krieger–Dougherty model yielded the best correlation between the measured viscosities and volume fraction.