The Track widths and isolation gaps are defined in the DRC parameters of your CAD system in a little as 0.001mm (1µm) steps.
These are taken by manufacturer to be the nominal values and are used to help set the parameters for production.
The values should be based on a “Right First Time Design for Manufacturing” principle and functionality of the PCB.
Track widths and isolation gaps are important as they define the current load, impedance and electronic signal integrity for a PCB.
Therefore, the track widths chosen depend upon the actual functionality of the PCB. For example, high current requires wider traces and isolation gaps as normal signal tacks.
The main factors that influence the final track widths and isolation gaps are listed below:
- Base Copper Thickness.
- Track Width to Height Ratio.
- Type of Imaging Process (Di vs Conventional).
- Copper Balance.
- The Etching Process.
As a manufacturer we know how to manage and compensate for the factors above.
However, it is not possible to fully compensate for each one and thus tolerances are introduced.
When measuring a track width. you must do so where the copper meets the laminate, not the top of track.
In accordance with the IPC A-600 the acceptable tolerance for track widths and isolation gaps is 20%.