When it comes to impedance, many engineers have many problems with it. Because there are many variables which affects the value of controlled impedance in a printed circuit board as for FPC supplier, however, what is impedance and what should we consider when controlled impedance?

The definition of the Impedance?

Impedance is the sum of the resistance and reactance of an electrical circuit which is measured in Ohms. Impedance is an alternating current characteristic in which signal frequency is an important element. The longer the trace or the higher the frequency, the more imperative it becomes to control the trace impedance. Signal frequency is a vital factor for traces which connect to components requiring two to three hundred MHz or more.
Many different trace configurations would be used in printed circuit boards to achieve controlled impedance. We can control the impedance through spacing and dimensions of the circuit board traces.

Impedance Control Level available

Typically, FPC supplier tells you there are three levels of impedance control available for printed circuit boards.

1. Impedance Control 
Impedance control are widely used in high-end designs with a tight tolerance or unusual configuration. There are several different types of controlled impedance. In which characteristic impedance is common used. Other types include wave impedance, image impedance, and input impedance.

2. Impedance Watching 
Impedance Watching means compatibility in impedance. The impedance control trace will be determined by width of the trace and height of the dielectric,which can be adjusted as needed.

3. No Impedance Control 
Because the impedance tolerances in the design are not tight, correct impedance can be achieved by conforming to standard specifications without impedance control. Accurate impedance can provided by PCB manufacturer without extra steps, So, it’s the most cost-effective level.