13.1 Impedance | General

At high transmission frequencies, traces become “transmission lines” and start behaving like components. To avoid transmission errors, such as reflections, impedance matching is required. “Impedance”, indicated by the symbol “Z”, is a measure of the opposition to electrical flow in an AC circuit. It is measured in ohms and is also referred to as the apparent impedance or resistance to alternating current.
The impedance depends, among other things, on:

• Conductor width
• Conductor height
• Conductor spacing
• Distance from reference layer
• Solder mask thickness
• Relative permittivity of the dielectric

At KSG, the impedance value can be measured on a measurement coupon and recorded in a test log.