A dielectric loss investigation of moisture in epoxy-glass composites

Dielectric loss has been used to study moisture absorption-desorption equilibria and kinetics in epoxy-glass composites. Measurements were made at a temperature of 90°C and a frequency of 200 Hz to maximize sensitivity to interfacial or Maxwell-Wagner polarization. Exposure to various partial pressures of moisture at that temperature permitted a kinetics analysis from which an estimate was made of the diffusivity of water in the composites. Values of dielectric loss at saturation were used to establish a moisture/dielectric loss calibration at 90°C which can be used to estimate the macroscopic internal moisture content of coupon samples and printed circuit cards and boards. Dielectric loss measurements offer promise as a screening technique for resin-glass coupler development.