Capillary Flows of Highly Filled Epoxy/Ni Suspensions for Conductive Adhesive Applications
Epoxy/Ni adhesives can be used as integrated circuit (IC) packaging materials due to their lower cost than epoxy/Ag adhesives with acceptable electrical conductivity. In this study, stable and unstable capillary flows of highly filled epoxy/Ni suspensions were investigated with and without cure at room temperature, via the capillary rheometer and syringe extrusion. Variations of the bulk electrical conductivity in these processes were discussed as well. Axial filtration of the polymer binder occurs under the static pressure for Epon815C/Ni/DETA adhesive with 50 wt% of Ni in syringe, resulting in an unstable flow and a cross-sectional filler concentration or electrical conductivity gradient. In dynamic capillary extrusion, lower resin viscosity and apparent shear rates enhance the flow instability and filtering of polymeric binder for epoxy/Ni suspensions with 75 wt% of Ni, thus facilitating a change in bulk electrical conductivity during processing. With increasing shear rates, the force oscillation frequency and force magnitudes increase. Incorporation of Ni nanopowders promotes a stable flow, yet the occurrence of agglomerates somewhat nullifies this advantage. Additionally, different rheological behaviors result as cure proceeds with different resins. Also, occurrence of the agglomerates leads to flow instabilities during processing with cure.