Impedance Control on PCB

1.Introduction
The development of wireless communications requires more compact electronic devices. Further, the more precise for electric products, the more special technology is needed for their main board. A PCB (printed circuit board) planar inductor is one that is printed directly on the PCB board with a copper track employed as the turn of the windings, thereby the conventional inductor flat. Efforts have been made on its design and calculation as well as its applications. The frequency dependence of a PCB inductor must be considered at higher frequencies. The effective trace resistance of a multi-turn spiral inductor operating at high frequencies is known to increase dramatically above its DC value, due to proximity effect or current crowding.

2.Why need to control impedance?
We need controlled impedances because the function of a wire or trace is to transfer signal power. Maximum signal power is achieved with matching impedances. The same considerations apply to signal transfer through traces on a PCB. When board traces carry high frequency signals, care must be taken to design traces matching the impedance of the driver and receiver devices. The longer the trace or the higher the frequencies, the higher is the need to control the trace impedance.
PCB manufacturers control impedance by varying the dimensions and spacing of the trace or laminate. We at Wonderful PCB Technology Co., Ltd experience an increase in demands for multi layers with controlled impedance. An estimated 75% of the multi layer PCB’s with eight layers or more are designed with controlled impedance.

3.Controlled impedances on PCBA manufacturer traces.
Any impedance mismatch can be extremely difficult to analyze once a PCB is loaded with components. Components have a range of tolerances, so that one bath of components may tolerate an impedance mismatch, while another batch might not. Moreover, a component’s characteristics may come and go. Thus, if changing a component appears to cure a problem, the components may become the suspects instead of the trace. Component selection becomes the solution, and build costs are driven up, while all the time the real fault- race impedance mismatch-goes undetected!
For these reasons, a PCB designer will specify trace impedance and tolerance, and should work with the PCB manufacturer to ensure that the PCB meets the specifications.

4.The future of PCB impedance control.
In near future virtually all PCB’s will likely include at least some impedance requirements. As the operating speed of electronic circuits has increased, so has the need for PCBs to have controlled impedances and the majority of PCB manufacturers are producing them.