Definition

Controlled impedance refers to PCB traces manufactured to achieve a specific characteristic impedance within a defined tolerance (typically ±10%). This requires controlling trace width, dielectric thickness, and material Dk with precision. Fabricators adjust trace widths during CAM to compensate for etch variations. Test coupons with TDR (time domain reflectometry) measurement verify impedance on production panels. Controlled impedance is essential for high-speed digital, RF, and any signal where reflections would cause errors.