In the printed circuit boards, all wires and traces are already having an impedance against the flow of the current. This is because the traces and wires are made of copper and copper is the element having lowest resistivity. The traces and wires of copper are almost perfect conductors and their DC resistance is also low.
The Nature of Impedance
To define impedance an argument can be developed with the case that the traces and wires of copper are having potentially significant in having the impedance. This logic can be elaborated as follows.
1.Each of the traces of the copper are having series impedance and is also distributed along the traces and is also inversely related to the cross sectional area of the traces. However, it is admittedly very small but is not zero.
2.Each of the traces is also having certain capacitance amid the trace itself and the path which is returning the signal to the traces, and is not dependent on the trace of the path. This is because of its distributed nature and is also related to the width of the traces and the material of the dielectric.
3.Assuming the traces having resistance very small and is also in the relation of the distributed inductance along with its capacitance, then the traces would look like the distributed LC circuit which is driving the current.
4.Until and unless the traces are being designed very carefully in an intelligent environment, the impedance of the traces would be uncontrolled, which may cause different problems. This is why the impedance is always varying at different points in the entire printed circuit boards.
5.In only a few cases, the control of the impedance in the printed circuit boards is important where the current reading are required to be accurate, however controlling the impedance is very important in the design of printed circuit boards, and for this we need to define impedance nature.