Epoxy resins are widely used as insulation material in electrical and electronic applications. They are employed as adhesives, sealants, coatings, impregnants, moldings and potting compounds to produce void-free insulation around components. The selection of a specific epoxy formulation for a given application requires not only an understanding of desirable dielectric properties, but also many other characteristics such as physical and mechanical strength, chemical resistance, operating temperature range and thermal cycling, dimensional stability and resistance to shock and vibration.
The chart below summarizes some of the most important characteristics in evaluating the electrical performance of epoxies:
Dielectric Properties of Epoxy Insulation Materials
Volume Resistivity : The measurement of the ability of an insulating material to resist the passage of electric current through the thickness of a solid specimen under specified conditions. A typical unfilled epoxy has a volume resistivity of >1010 ohm-cm at 25°C.
Surface Resistivity :The measurement of the ability of an insulating material to resist the passage of electrical current along the surface of a solid specimen under specified conditioning. A typical unfilled epoxy has a surface resistivity of >1010 ohm-cm at 25°C.
Dielectric Constant :The measurement of the strength of a given specimen at a specified thickness and is expressed in volts/mil. Dielectric strength decreases with specimen thickness. Typical values for epoxy specimen 0.125 inches thick are in the 420-480 volts/mil range.
Arc Resistance :The measurement of the resistance to a specified high voltage, low current arc conditions in terms of seconds to insulator breakdown. Values for typical epoxies are in the 100-300 second range.
Dissipation Factor : The measurement of the energy lost to the dielectric material in an alternating field.