Nanomechanics of Polymer Particles

Metal-coated polymer particles with diameter from 500nm to 30μm are increasingly used in electronics and microsystem. Recently the focus has been put on metal-coated polymer particles used in Anisotropic Conductive Adhesive, such as in Liquid Crystal Displays. In these applications, the characterization, analysis and control of mechanical properties of the conductive particles are of crucial importance. Due to the inherent complexity of the spherical geometry, characterization of the metal-coated polymer particles possesses great challenges. A nanoindentation-based flat-punch method has been recently developed for testing the mechanical properties of the particles with deformation up to 80%. This method has been proved applicable for the investigation of single micron sized particles and also makes it possible to locate the individual particles tested in the SEM. A series of polymer particles and metal-coated polymer particles with various diameters have been tested. The thickness of metal coating is around 50nm. The particles show yielding, hardening and fracture behavior. It has been observed that the surface metal-coating displays an interesting strengthening effect on the mechanical behaviour of polymer particles. This strengthening effect gradually diminishes when the delamination between gold coating and polymer core occurs. Subsequently the mechanical behaviours of coated polymer particles resemble that of non-coated ones. The technique could be used to design/manufacture more effective conductive particles.