Before we talk about the impedance control, let’s see how Wikipedia explains about this: Impedance control is an approach to the control of dynamic interaction between a manipulator and its environment. This type of control is suitable for environment interaction and object manipulation. Therefore, impedance control is required for some specific printed circuit boards.

1. For PCBs that need through holes component parts, once the parts are soldered, consider about the electrical conductivity and signal transmission performance ect., the lower the impedance control value is, the better. The resistivity should be no more than 1×10-6 square centimeters;

2. During the PCB fabrication process, the boards will experience with plating, hot air leveling and many other process, we have to make sure all the materials used are resistivity guaranteed, therefore to achieve the PCB quality requirement and the PCBs are well performed during actual use;

3. Hot air leveling is the essential one during the whole process, and it critical for impedance control. The biggest defective for chemical tin plating is its allochroic-friendly ( it is easy to oxidized or resolves in water), poor solderability features, these make it difficult to assemble the boards, and the high impedance value contributes to poor electrical conductive, or unstable performance of boards;

4. There are various signal transmission in printed circuit boards,  we have to improve the frequency if we require to improve the transmission speed. While the etching, stack-up thickness, trace width will affect the impedance value, and cause distorted signal, thus influence the PCB use. Therefore, we have to control the impedance value in to a certain value;

All in all, the impedance control will affect the actual performance of PCBs, in order to guarantee the PCB quality, impedance control is highly recommended for the design.