There is no single minimum trace width or spacing that is correct for every PCB. The rule set must satisfy the intended fabrication process and the circuit requirements at the same time. Separate these constraints so an easy-to-manufacture route is not mistaken for an electrically adequate route.
Start with process rules by construction
Ask for manufacturable width and spacing for the actual copper thickness, layer type and material. Etching and plating influence the finished geometry. Distinguish nominal CAD dimensions from finished acceptance limits, and identify any local fine-pitch escape that needs separate review.
Apply electrical constraints by net class
Power conductors need loss and thermal review; controlled-impedance signals need a defined cross-section; sensitive nets need coupling review. High-voltage separation comes from the applicable insulation design, environment and product requirements. A generic fabrication clearance cannot replace those electrical requirements.
Inspect copper features beyond traces
Copper pours, thermal reliefs, teardrops, plane openings and unused pads also create small gaps or necks. Refill zones and rerun checks before exporting. Review the generated data so a CAD display setting does not conceal an unintended island or narrow connection.
Resolve conflicts intentionally
A fine-pitch component may need a short narrower escape than the rest of its route. Record the exception, review its electrical impact and confirm manufacturing acceptance. Avoid weakening the global rules simply to remove one local violation; that can hide unrelated problems elsewhere.
Example: two meanings of clearance
A dense low-voltage signal region and an isolated power region may use the same copper weight but need different clearances. Assign separate constraints and a visible boundary. If the board-wide minimum is lowered for the signal breakout, the isolation region must retain its independent requirements.
Design review checklist
- Set layer- and net-specific constraints where needed.
- Check finished copper assumptions with the fabricator.
- Review neck-downs, pours and thermal reliefs.
- Keep every approved exception traceable to a location and reason.