A dielectric or substrate is an insulating material used in PCBs to isolate conductive layers (signal, ground, and power planes). Dielectric materials influence signal propagation speed, energy storage, and thermal stability.
Common dielectric materials include FR-4, PTFE, polyimide, and ceramic-based materials. Each type offers different electrical and mechanical properties suited to specific applications, such as high-frequency, high-temperature, or flexible circuits.
When you’re choosing a dielectric material for your circuit board, consider the following properties:
Dielectric constant (Dk) measures the ability of a material to store electrical energy in an electric field. It directly affects the capacitance between conductors and influences the propagation speed of signals through the material. Dk ranges between 2 and 10.
Dissipation factor (Df) determines the extent of signal loss in a dielectric material. The higher the Df, the higher the signal attenuation. Df ranges between 0.02 and 0.001. A lower dissipation factor means less signal loss. For high-speed designs, pick a material with Df<0.005.
Glass transition temperature (Tg) is the temperature at which the material transforms from a solid to a viscous state. Always choose a dielectric with Tg greater than the maximum operating temperature.