PCB Impedance Control
It is critical to control signals perfectly as the PCB design is more and more complex. Here impedance control plays a great role, that’s because if fails to control impedance, it will lead to considerable signal reflection and distortion. In other words, a prefect impedance control actually means a prefect PCB design.
The conductor in the circuit board will have various signal transmission. We have to increase its frequency to improve the transmission rate. Value of impedance will change slightly by etching, stack thickness, wire width and other factors, finally leading to the signal distortion. Therefore, high-speed circuit board conductors, the impedance value should be controlled within a certain range, usually the value of PCB impedance range is 25 to 120 ohms.
Factors that influence the PCB impedance are as follows: width of conductor, thickness of conductor, constant of dielectric, thickness of dielectric, space between conductors if differential impedance, thickness of solder mask, and constant of solder mask oil.