PCB circuit board impedance refers to the resistance and reactance parameters, which play a hindrance to AC. Impedance processing is essential in the production of PCB circuit boards.
1, PCB line (bottom) to consider the plug mounting electronic components, plug after considering the electrical conductivity and the signal transmission performance and other issues, so it will require impedance as low as possible, the resistivity is lower than 1 per sq cm * 10-6.
2, PCB circuit board in the production process to go through heavy copper, tin plating (or electroless plating, thermal spray or tin), such as solder connector fabrication process, and these links all the material used must ensure that the resistivity of bottom, to ensure the overall low impedance circuit board meet product quality requirements, the normal operation.
3, PCB circuit board tin plating is the most likely problem in the whole circuit board production, and it is the key link to affect the impedance. The biggest flaw is the electroless tin coating color change (which is easy to oxidation and deliquescence), brazing is poor, will cause the circuit board to welding, resulting in high impedance electric performance is poor or the entire board performance is not stable.
4, PCB circuit board in a variety of signal transmission, and when must improve its frequency to improve the transmission rate, if the line itself for etching, laminate thickness, width and other factors, will cause the change of impedance is, signal distortion, resulting in a decline in circuit board performance, so we need to control the impedance value in a certain range.
As to why the PCB circuit board has to be impedance, I believe we all know very well. PCB circuit board impedance will directly affect the stability and performance of the circuit board, so in order to ensure the overall performance and quality of the PCB circuit board, impedance is needed.