Conductive adhesive development concept using a bimodal distribution of Ag-particles

Summary form only given. This work aims to develop a conductive adhesive (CA) with a bimodal metal particle distribution to obtain optimum electrical performance without losing mechanical impact strength. Research shows that nanoparticle filled systems can produce higher conductivity at lower particle loading levels. This is attributed to the open nature of agglomerates that make up the conductive network in nanoparticle filled polymers. However, it is difficult to control rheology when applying this type of CA in the stencil printing process. The objective of this work is to introduce nanoparticles in micro-size metal particles to form a bimodal distribution in the polymer matrix. Previous examinations of Ag-filled particles reveal that micro-sized particle fillers appear as full density Ag flakes, while nanoparticle fillers appear as highly porous agglomerates, similar to open-cell foams. Little study has been carried out on the cross-sectional area of a particle-particle contact in CA, but some initial results indicate that the real contact area is several orders of magnitude smaller than that estimated from simple geometric considerations. In this study, TEM is used as the main measurement method to analyse the nanoparticle distribution. The volume nanoparticle percentage in the micro-size particle varies from 2.7 wt% to 13.8 wt%, and the total metal content is in the range of 60-80 wt%. The change of contact area and contact behaviour with various volume ratios of nano-size and micro-size particles was also studied. Electrical resistivity and mechanical strength were measured and compared for different filler loading levels.