What is the significance of impedance for PCB? Why should PCB be impedance? This paper first introduces what is impedance and the type of impedance, then introduces why PCB circuit board should be impedance, and finally expounds the significance of impedance for PCB circuit board. Follow the small editor to understand.
1、 What is impedance
In a circuit with resistance, inductance and capacitance, the resistance to alternating current is called impedance. Impedance is often represented by Z, which is a complex number. The real part is called resistance, and the imaginary part is called reactance. The blocking effect of capacitance on AC in the circuit is called capacitive reactance, the blocking effect of inductance on AC in the circuit is called inductive reactance, and the blocking effect of capacitance and inductance on AC in the circuit is called reactance. The unit of impedance is Ohm.

2、 Solder resist type
(1) Characteristic impedance in electronic information products such as computers and wireless communications, the energy transmitted in the circuit of PCB is a square wave signal (called pulse) composed of voltage and time, and the resistance it encounters is called characteristic impedance.
(2) Two same signal waveforms with opposite polarities are input to the differential impedance driving end, which are respectively transmitted by two differential lines, and the two differential signals are subtracted at the receiving end. The differential impedance is the impedance zdiff between two lines.
(3) The impedance zoo of one of the two odd mode impedance lines to the ground is the same.
(4) The impedance zcom when two same signal waveforms of the same polarity are input to the even mode impedance driving end and the two lines are connected together.
(5) Common mode impedance is the impedance Zoe of one of the two lines to the ground. The impedance values of the two lines are consistent and usually larger than the odd mode impedance.
3、 Why do PCB circuit boards need impedance
PCB circuit board impedance refers to the parameters of resistance and reactance, which hinder AC power. In the production of PCB, impedance treatment is essential. The reasons are as follows:
1. The PCB circuit (bottom of the board) should be considered to plug and install electronic components. After the plug, the electrical conductivity and signal transmission performance should be considered. Therefore, the lower the impedance, the better, and the resistivity should be lower than 1 & times per square centimeter; Below 10-6.
2. During the production process of PCB circuit board, it is necessary to go through such process manufacturing links as copper deposition, electro tin plating (or chemical plating, or thermal tin spraying), connector soldering, and the materials used in these links must ensure the low resistivity, so as to ensure that the overall impedance of the circuit board can meet the product quality requirements and can operate normally.
3. The tin plating of PCB circuit board is the most likely problem in the whole circuit board manufacturing, and is the key link that affects the impedance. The biggest defects of electroless tin plating layer are easy to change color (i.e. easy to oxidize or deliquescence) and poor solderability, which will lead to difficult soldering of circuit board, poor conductivity or unstable performance of the whole board due to high impedance.
4. There will be various signal transmission in the conductor in the PCB circuit board. When it is necessary to increase its frequency in order to improve its transmission rate, the impedance value of the circuit itself will change due to different factors such as etching, lamination thickness and wire width, which will cause signal distortion and reduce the performance of the circuit board. Therefore, it is necessary to control the impedance value within a certain range.
4、 Significance of impedance to PCB
For the electronic industry, according to the industry survey, the most fatal weakness of the electroless tin plating layer is that it is easy to change color (i.e. easy to oxidize or deliquescence), poor solderability leads to difficult welding, high impedance leads to poor conductivity or unstable performance of the whole board, and easy to grow tin leads to short circuit of PCB circuit and even burning or fire.