Impedance control on PCBs

In the early 1990s, impedance control was limited to PCBs used in few specific market segments. Today, we find these requirements in many applications; all IOT objects, signal and graphic boards, modems, games, phoning, PCs, etc.

RF circuits are more and more complex and their impedance calculation could no longer be done with a simple formula. We now use specific software, which take into account all parameters, which have an influence on the value of the impedance.

Which parameters will influence the impedance and its control

The value of the impedance, measured in Ohms, will be influenced by 4 specific factors:

1. Dielectric thickness. As a reference, a thickness deviation of 0.025mm (1 mil.) will influence the impedance value by approximately 2 Ohm.

2. The Er value of the substrate. It is important to have a stable and low Er. A change of value of 0.1 translates into an evolution of 0.5 Ohm. As the impedance control tolerance becomes tighter, we will use higher performance materials.

3. Trace thickness. For this, we consider the base copper thickness, but also all the processes that will influence this thickness during the whole production process; this includes the plating and the surface treatment.

4. Trace width. As an example, we can assume that a change of width of 0.025 (1 mil) is equal to a change of impedance of 1 Ohm).

It is therefor paramount to make accurate calculation and according to the required tolerance to choose the right material & process. Therefor, we choose different types of laminates to match the required values and tolerances.

With numerous tests and verification throughout the whole manufacturing process, we are able to achieve your committed results and meet your specifications. A normal impedance control tolerance is +/- 10%. Under certain circumstances, we are able to offer tolerances of 8% or even 5%.

Please contact us to for more information.