PCB Impedance control

   Impedance control , various signals will be transmitted in the conductors in the circuit board. In order to increase its transmission rate, its frequency must be increased. If the line itself is due to different factors such as etching, lamination thickness, wire width, etc., it will Causes changes in impedance value and distorts the signal. Therefore, the impedance value of conductors on high-speed circuit boards should be controlled within a certain range, which is called "impedance control".

    The impedance of a PCB trace will be determined by its inductive and capacitive inductance, resistance, and conductance coefficients. The main factors that affect the impedance of PCB traces are: the width of the copper wire, the thickness of the copper wire, the dielectric constant of the medium, the thickness of the medium, the thickness of the pad, the path of the ground wire, the wiring around the wire, etc. PCB impedance ranges from 25 to 120 ohms.

   In real life, PCB transmission lines usually consist of a wire trace, one or more reference layers, and insulating material. Traces and board layers form the controlled impedance. PCBs will often be multi-layered and the controlled impedance can be constructed in various ways. However, regardless of the method used, the impedance value will be determined by its physical structure and the electronic properties of the insulating material.