A method for determining elastic properties of micron-sized polymer particles by using flat punch test

Micron-sized metal coated polymer particles are used in developing anisotropic conductive adhesives (ACA). The mechanical properties of polymer particles are of crucial importance for the reliability and design of ACA. In this paper we present a method to determine the mechanical properties of polymer sphere particles under large deformation by using a flat punch test-soft elastic sphere against a rigid flat. Finite element analyses have been carried out to study large deformation contacts. It has been shown that the classical Hertz solution works only for very small sphere deformation (less than 1% compression strain) and Tatara's solution works well for sphere compression up to 20%, beyond that large strain effect should be considered. For compression less than 20%, both the compression stress-strain curves and lateral expansion strain-compression strain curves can be normalized by a function of the Poisson ratio. Based on the finite element results, explicit equations describing these relations are presented for determining the Young's modulus and Poisson ratio of polymer particles at large deformation. The proposed method has been applied to analyze the experimental results of typical polymer particles used for conductive adhesives from a specially built capacitance-based flat punch test. (c) 2006 Elsevier B.V. All rights reserved.