Epoxies are inherently excellent electrical insulators. Adhesives, sealants, coatings, potting, encapsulation and impregnating compounds are widely employed in electronic and electrical applications. Choosing the right epoxy not only depends on its dielectric properties, but also on a number of properties such as temperature resistance, mechanical strength, chemical resistance and resistance to thermal and mechanical shocks and cycles. These factors are greatly affected by the choice of the curing agent. Amine type curing agents are commonly used for bonding, sealing, coating and impregnation applications. Anhydride type curing agents are commonly used for potting and encapsulation applications, owing to their low exotherm and long pot life. Before selecting an epoxy for your application, it is first important to understand the various dielectric properties of insulation materials:
Volume and Surface Resistivity: Volume resistivity quantifies how effectively a material can resist the flow of electric current along its thickness. Surface resistivity measures the material’s ability to resist the passage of electric current along its surface. Higher the resistivity, better is its insulative properties. The volume resistivity of an epoxy is measured using the ASTM D257 test method and typically it measures > 1011 ohm-cm at 25°C for an unfilled system.Dielectric Strength and Dissipation Factor: Dielectric strength measures a material’s ability to resist flow of electric current along its thickness without breaking down. It is typically measured in volts/mil. Dielectric constant is the measurement of the rate of loss of energy under an alternating field. Dielectric strength for an epoxy is measured using the ASTM D149 test method and dissipation factor is measured using the ASTM D150 test method. For a 0.125 inch thick specimen, an epoxy’s dielectric strength typically measures in the range of 420 – 480 volts/mil.
Arc Resistance: Arc resistance measures the time durability of a dielectric material against a high voltage arc discharge. It is measured using the ASTM D495 test method. Typically, epoxies can hold up to the arc for 90-300 seconds.
Kohesi Bond offers a vast selection of epoxy compounds with varying dielectric properties. Specific grades meet various industrial certifications such as NASA standards for low outgassing (ASTM E-595). Our products can withstand extremely high and low temperatures. Notably, KB 1040-2 is an optically clear, cryogenically serviceable product that offers resistivity of > 1015 ohm-cm. Additionally, it is capable of passing NASA’s low outgassing specifications. Kohesi Bond’s technical specialists can help you find the best solution for your electronic application.