Degradation behavior and mechanism of polymer films for high-ohmic resistor protection in a heat and humid environment

•Performance of coated high-ohmic resistors in heat and humid resistance was studied.•Polymer films for resistor protection are mainly formed by phenolic and epoxy resins.•Hydrogen evolution reaction (HER) can occur on polymer film for a working resistor.•Corrosion resulted from OH− ions generated in HER may lead to polymer degradation.

The protection of polymer films is critical to the reliability of high-ohmic resistors working in a heat and humid environment, and temperature is the main factor resulting in failure of coated resistors. However, in this study hydrogen evolution reaction (HER) and corrosion reaction of OH− ions are found to be another two important factors determining the fate of coated resistors. When temperature effects can be neglected, corrosion resulted from OH− ions generated in HER may be the major reason of polymer degradation, the mechanism of which is discussed based on the polymer films mainly formed by phenolic and epoxy resins.