Definition

Dielectric Constant (Dk), also called relative permittivity (εr), describes how much a material can store electrical energy compared to a vacuum. Higher Dk slows signal propagation and allows smaller trace geometries for a given impedance. FR-4 has Dk around 4.2-4.5, while PTFE-based materials range from 2.1-3.0. Dk stability over frequency and temperature is critical for controlled impedance designs. Dk also affects capacitance between traces and planes.