Electrical performance of isotropic conductive adhesives with copper and copper coated iron fillers

This paper describes a study of using copper coated iron (Cu/Fe) micron scale particles as conductive fillers in isotropic conductive adhesives (ICAs) for applications in electronics manufacture. The non-conductive native oxide on the surface of the Cu/Fe particles is tackled through use of a combination of an oxide-removing etching process followed by application of a self-assembled monolayer (SAM) coating to inhibit re-oxidation. This builds on previous work to replace silver flakes with lower cost copper particles, whilst use of iron cored particles potentially further reduces materials costs. Materials for conductivity tests were formulated by mixing the filler particles with a commercially available two component epoxy system. Tracks were then stencil printed using the formulated adhesives and cured at elevated temperature under an inert atmosphere. The surface composition was acquired using X-ray photoelectron spectroscopy. The resistances of the resulting conductive tracks were measured using the four-point probe method and from these the resistivity was calculated. The processes of etching and self-assembled monolayer coating are both shown to play important roles in reducing the amount of oxide on the particle surfaces and therefore improving the conductivity of the resulting adhesive.