Why do PCB circuit boards need impedance

The impedance of pcb circuit board refers to the parameters of resistance and reactance, which hinder the alternating current. In the production of pcb fabrication circuit boards, impedance processing is essential. The reasons are as follows:

1. The PCB circuit (bottom of the board) should consider plugging and installing electronic components. After plugging, the conductivity and signal transmission performance should be considered. Therefore, the lower the impedance, the better, and the resistivity should be less than 1×10 per square centimeter. -6 or less.

2. During the production process, PCB circuit boards have to go through process steps such as copper sinking, tin electroplating (or chemical plating, or thermal spray tin), connector soldering, etc., and the materials used in these links must ensure that the resistivity is low, in order to ensure The overall impedance of the circuit board is low to meet the product quality requirements and can operate normally.

3. The tinning of PCB circuit boards is the most prone to problems in the entire circuit board production, and it is a key link that affects impedance. The biggest defect of the electroless tin coating is easy discoloration (easy to be oxidized or deliquescent) and poor solderability, which will lead to difficult soldering of the circuit board, high impedance, poor electrical conductivity, or instability of the overall board performance.

4. There are various signal transmissions in the conductors in the PCB circuit board. When it is necessary to increase its frequency in order 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. , So that its signal is distorted and the performance of the circuit board is degraded, so it is necessary to control the impedance value within a certain range.

PCB Assembly Manufacturing impedance will directly affect the stability and performance of the circuit board, so in order to ensure the overall performance and quality, impedance is required. As the design of electronic products becomes more sophisticated and the difficulty of packaging increases, the improvement of SMT patch yield has become one of the key factors to reduce the cost of hardware manufacturing. BGA, IC are key components, and the one-time success rate of these components is the key point during soldering. PCB manufacturing has become a priority.