Why do PCB boards need to be impedance?

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The pcb board impedance refers to the resistance and the parameters of the reactance, which hinder the AC. Impedance processing is essential in the production of pcb boards. The reasons are as follows:

1. PCB circuit should consider plugging and installing electronic components. After plugging, consider the conductive performance and signal transmission performance. Therefore, the lower the impedance, the better the resistivity should be less than 1/TImes per square centimeter; 10-6 or less.

2, PCB circuit board in the production process to experience the process of copper, electroplating tin, solder joints and other processes, and the materials used in these links must ensure the bottom of the resistivity, in order to ensure that the overall impedance of the circuit board is low to meet product quality requirements. , can run normally.

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3. The tin plating of the PCB circuit board is the most prone to problems in the whole circuit board production, and is the key link affecting the impedance. The biggest defect of the electroless tin plating layer is that it is easy to discolor and the brazing property is poor, which may cause the circuit board to be difficult to be soldered, and the impedance is too high, resulting in poor electrical conductivity or instability of the whole board performance.

4. There are various signal transmissions in the conductors of the PCB circuit board.（PCB Assembly manufacturer china） When the transmission rate is increased, the frequency must be increased. If the line itself is different due to etching, laminate thickness, wire width, etc., the impedance value will change. The signal is distorted, resulting in reduced performance of the board, so it is necessary to control the impedance value within a certain range.

For the electronics industry, according to the investigation, the most deadly weakness of the electroless tin plating layer is that it is easy to change color, poor solderability leads to difficult soldering, and the impedance is too high, resulting in poor conductivity or unstable performance of the whole board. The line is shorted to burn or fire.