Definition

Impedance control maintains trace characteristic impedance within specified tolerance - typically ±10%, tighter (±5%) available at premium. Requires: controlled dielectric thickness (prepreg/core selection), trace width accuracy, and consistent Dk. Fabricators measure impedance on test coupons using TDR. Achieving tight impedance tolerance requires specifying stackup details or letting the fabricator design it to your target impedance. Cost premium for controlled impedance: 10-20% over standard fabrication. Essential for high-speed digital (DDR, PCIe, USB) and all RF designs. Request impedance test reports for critical applications.