Polymer Engineering Faculty Research


Stable and Unstable Capillary Flows of Highly-Filled Epoxy/Nickel Suspensions

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Epoxy/nickel adhesives can be used as integrated circuit (IC) packaging materials due to their lower cost than epoxy/silver 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 rheometry and syringe extrusion. Variations of the bulk electrical conductivity in these processes were discussed as well. Axial filtration of the polymer binder occurs under a static pressure for a cured epoxy/Ni system, Epon 815 C/Ni/diethylenetriamine (DETA) adhesive with 50 wt% of Ni in the 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, both average force and force oscillation frequency increase. Incorporation of Ni nanopowder 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 instability during processing with cure.

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Journal of Adhesion Science and Technology





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