FPC impedance board characteristics and impedance control

According to the transmission theory of signal, the signal is a function of time and distance variables, so the signal may change at every part of the line. Therefore, the ac Impedance of the line is determined, that is, the ratio of voltage change to current change is the Characteristic Impedance of the transmission line: the Characteristic Impedance of the transmission line is only related to the characteristics of the signal line itself. In practical circuits, the resistance of the wire itself is less than the distributed impedance of the system, especially in high-frequency circuits. The characteristic impedance mainly depends on the distributed impedance of the unit distributed capacitance of the wire and the distributed impedance of the unit distributed inductance. The characteristic impedance of an ideal transmission line depends only on the unit distributed capacitance and unit distributed inductance of the line.

There will be a variety of signal transmission in the conductor of the circuit board, when to improve the transmission rate and must increase its frequency, if the line itself due to etching, lamination thickness, wire width and other factors, will cause changes in impedance value, so that the signal distortion. Therefore, the impedance value of the conductor on the high-speed circuit board should be controlled within a certain range, known as "impedance control". The main factors affecting the impedance of THE FPC impedance board 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. Therefore, when designing FPC impedance board, we must control the impedance of the line on the board, so as to avoid signal reflection and other electromagnetic interference and signal integrity problems as far as possible, and ensure the stability of the actual use of FPC impedance board.