What is impedance?

In circuits with resistance, inductance, and capacitance, the impediment to alternating current is called impedance. Impedance is usually expressed by Z, which is a complex number. The real part is called resistance, and the imaginary part is called reactance. Among them, the obstruction effect of capacitors in the circuit on alternating current is called capacitive reactance. For the inductive reactance, the blocking effect of the capacitor and the inductance on the alternating current in the circuit is collectively called reactance. The unit of impedance is ohm.

2. Why do PCB circuit board manufacturers make impedance in the production of circuit boards?

PCB circuit board impedance refers to the parameters of resistance and reactance, which hinders the alternating current. In the production of PCB circuit boards, impedance processing is essential.

1. PCB circuit (bottom board) should consider plugging and installing electronic components. After plugging, consideration should be given to conductive performance and signal transmission performance. Therefore, the lower the impedance, the better, and the resistivity should be lower than 10-6 per square centimeter the following.

2. The PCB circuit board production process must go through the process of making copper, electroplating tin (or electroless plating, or thermal spray tin), connector soldering, etc., and the materials used in these links must ensure the resistivity bottom to ensure the circuit The overall impedance of the board is low to meet the product quality requirements and can operate normally.

3. The tin plating of the PCB circuit board is the most prone to problems in the production of the entire circuit board, and is the key link that affects the impedance. The biggest defects of the electroless tin plating layer are easy discoloration (both easy to oxidize or deliquesce) and poor brazing, which will lead to difficult soldering of the circuit board, high impedance and poor conductivity or unstable performance of the whole board.

4. There will be various signal transmissions in the conductors in the PCB circuit board. When the transmission rate must be increased to increase its transmission rate, if the circuit itself is different due to factors such as etching, stack thickness, wire width, etc., the impedance value will change. In order to distort the signal, the performance of the circuit board is reduced, so you need to control the impedance value within a certain range.