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This paper explores the effect that compression of the conducting particles in Anisotropic Conductive Adhesive (ACA) assemblies has on the resistance of the joints. Particles within the same assembly were compressed by differing amounts by the action of two rigid, planar surfaces which form a wedge with the particles trapped between them. Using this method, it is found that optimum conduction is obtained when metal-coated polymer particles are compressed to a height between 80% and 100% of their original diameters (see Fig. 1 for definitions). Results on flip-chip assemblies with a pitch of 220 μm are presented. They are in agreement with the wedge experiment findings in that larger particles are shown to be able to better accommodate variations in the gap heights between chip and substrate. The wedge experiment has also been used to validate fluid flow based models of particle movement during assembly and statistical models of particle distribution after assembly is complete. The experiments also indicated the presence of thin insulating films between particles which offer an additional safety margin when considering shorting between neighbouring electrodes by clusters of particles.