Pathways for Alkali Ion Transport in Mold Compounds

Abstract

The mobility of potassium ions in a molding compound designed for electronic device insulation has been investigated by a charge attachment induced transport (CAIT) experiment. Two different transport pathways have been identified, i.) through the bulk of the sample and ii.) along boundaries of silica grains embedded in the organic components of the molding compound. The corresponding diffusion coefficients for K+ transport are DB = 1.8 × 10−21 cm2 s−1 for the bulk and DGB = 5.4 × 10−20 cm2 s−1 for the grain boundary. The effective activation energy for charge carrier transport amounts to 1.57 eV.

Effect of interfacial transport on the diffusivity of highly filled polymers

“…Wapner et al [9] used insitu infrared spectroscopic and a scanning Kelvin probe, and found that water diffusion along an epoxy-iron interface was two orders of magnitude higher that bulk diffusion. Motta et al [10] found a 30 times higher interfacial ion diffusivity for silica fillers embedded in epoxy mold compound using a charge induced transport experiment. Rocha et al [11] studied a fiber-reinforced epoxy and found that a fit between macroscopic numerical simulations and experimentally data for the overall diffusivity was only possible when introducing a 1.5-3.5 times higher interfacial diffusivity compared to the bulk for a 1-4 μm thick interface region around the glass fibers.…”