How do I request impedance control?

Tell us four things: 1. The target impedance, for example 50 Ω single-ended or 100 Ω differential. 2. The tolerance. ±10% is typical. 3. Which layers carry the controlled traces, and their width and spacing. 4. Your stack-up. If you do not have one, ask us to recommend one. Put this in the notes field of your quote or RFQ, or attach a stack-up drawing. Impedance-controlled boards are reviewed by an engineer, who confirms the stack-up and the price before production.