Why should PCB circuit boards do impedance?

pcb circuit board impedance refers to the resistance and reactance of the parameters, which act as a barrier to alternating current. Impedance processing is essential in pcb circuit board production. The reasons are as follows:

1.We should consider the connection and installation of electronic components of PCB circuit(bottom of the board). After the connection, the conductivity and signal transmission performance should be considered. Therefore, the lower the impedance, the better.

2.During the production process of PCB, the process of copper-plating, tin-plating (Immersion Tin, HASL), connector soldering and other production links should be experienced, and the materials used in these links must ensure the low resistivity to ensure that the overall impedance of PCB can meet the product quality requirements and can operate normally.

3.The tin plating of PCB is the most likely problem in the whole PCB production, and is the key link affecting the impedance. The biggest defects of electro tin plating coating are easy to change color (easy to oxidize or deliquescence) and poor solderability, which will lead to difficult soldering of PCB, high impedance and poor conductivity or unstable performance of the whole board.

4.There will be various signals transmitted in the conductor of PCB.When the frequency must be increased in order to improve the transmission rate, if the circuit itself is different due to etching, stackup thickness, wire width and other factors, the impedance value will change, the signal will be distorted, and the performance of the circuit board will decline. Therefore, it is necessary to control the impedance value within a certain range.