Yield Behavior of Moderately Filled Epoxy/Ni Suspensions

Abstract Epoxy/nickel (Ni) adhesives can be used as integrated circuit (IC) packaging materials due to their lower cost than epoxy/silver (Ag) adhesives with acceptable electrical conductivity. In this work, yield behavior was studied for moderately filled bisphenol-A based epoxy/Ni suspensions (10–60 wt% of Ni). Effects of the preshear history, resin viscosity, temperature, particle size, solid loading, as well as different yield stress determination methods were investigated. The preshear effect manifests itself in successive shear rate sweeps with the same sample. Consequently, an initial shear rate sweep was employed to serve as preshear conditioning and obtain reproducible results on all samples. Shear thinning generally occurs for epoxy/Ni suspensions. The fractal dimension (D f) may be employed to describe these flocculated structures, and a higher D f value was observed for Epon815C/Ni system as compared to Epon830/Ni system. The Arrhenius equation describes the temperature dependence of suspension viscositys adequately. Incorporation of Ni nanopowder significantly reduces flow and the activation energy for yielding. The stronger van der Waals attractions created within the nanoparticles lead to larger yield stress. Also, different yield stress values are calculated using different determination methods. Keywords: YIELDINGEPOXY/NI SUSPENSIONRHEOLOGY