FPC flexible board impedance control circuit is also called impedance strip. The principle of impedance control is that when the current that needs to pass through the line is greater than the maximum value that the line can withstand, it is necessary to use impedance to control the excess current. So how to control the value of the impedance line? The following five aspects will affect the resistance of the impedance line.

1. Different substrates lead to different impedance values

The difference of the base material has a great influence on the flexible printed circuit boards. The resistance value of each material is different, and even the resistance value of each part of the same material will not be exactly the same. Just as there are no two leaves alike in the world. The impedance lines on the impedance board generally use substrates with good material stability. If a material with poor stability is used, the resistance value of the material will change greatly. Once the required impedance value is exceeded, the impedance line control line cannot be used.

2.  Impedance changes due to material thickness

This reason has a lot in common with the reasons for the above aspect.

3. Line width and gap

The difference in line width and gap between impedance lines will lead to changes in the resistance value. The impedance line is used as a resistor, so the width of the line is the size of the resistance value. What about the line spacing? The current passing between the lines will generate a magnetic field, and the magnetic field can also generate current (generator principle, which is why it is shielded). At this time, the current will change, which indirectly leads to inaccurate impedance control data.

4. Etching tolerances can cause impedance variations

Etching is a kind of corrosion to the line, which will affect the thickness and width of the line. Etching can only be kept within a range, or there are deviations, which are the reasons for the resistance changes.

5. Electroplating Copper Tolerance

The impact of this depends on the process flow. In some processes, since the electroplating is before etching, the impedance will not be affected at this time. However, most of the FPC flexible boards have been etched when electroplating is completed. At this time, copper will also be attached to the impedance line, which will cause the resistance of the impedance line to change.