Electrical Properties of Epoxy Resin after Thermal Aging under High Humidity

The electrical properties of epoxy resin after hygrothermal aging were studied. The volume resistivity, dielectric loss, permittivity, and breakdown strength were measured for samples aged at 95 °C at a relative humidity of 95 % for 180 h, 420 h, 660 h, and 1000 h. It was found that the volume resistivity decreases with aging time by an order of magnitude at 1000 h. The dielectric loss and permittivity significantly increase with aging time in the low-frequency range. However, the AC breakdown strength is not significantly changed after the hygrothermal aging. A comparison was made with another group of samples aged at 95 °C without moisture control. Through the FTIR (Fourier Transform Infrared Spectroscopy) analysis of the molecular structure variation, the change of electrical properties is attributed to the water absorption, decomposition and hydrolysis of epoxy resin during the hygrothermal aging process.