Rules ensure defined constraints, not ever-smaller minima. Review widths, spacing, copper weight, holes, annular rings, and mask together for the actual structure. DRC proves compliance with current settings, not their correctness or manufacturing/electrical approval.
Collect all four input types before setting rules
Inputs comprise layer copper weight/stackup; hole types, spans, and finished definitions; fabricator-approved combinations; and net/product requirements. High-voltage spacing, sensitive analog, differential impedance, and high current each need their own basis, not ordinary-signal minima.
Würth Basic Design Guide V1.0 separates inner/outer layers, finished copper weight, holes, and mask, demonstrating dependencies. Its values are supplier-specific and require confirmation elsewhere. This page uses the classification to organize CAD settings.
Group rules by object rather than applying one board-wide rule
| Rule Group | Input Basis | Output Content |
|---|---|---|
| Standard Copper Graphics | Layer-specific, finished copper, and manufacturing window | Trace width, copper spacing, and boundary |
| Vias and Pads | Drill diameter, finished hole, hole position, and alignment | Via pad, keep-out, and via group |
| Solder Mask | Window opening, bridge width, alignment, and package | Pad windows and exception zones |
| Critical Networks | Electrical, thermal, timing, and product requirements | Special category and constraints |
| Mechanical Area | Edge milling, slots, mounting, and panelization | Copper to edge and keep-out areas |
Check priorities: ordinary-net rules can override fine-pitch exceptions or critical nets and yield wrong results. After import, inspect representative objects to confirm actual application.
Why is nominal hole ring calculation insufficient?
Engineering example: 0.60 mm pad and 0.30 mm hole give nominal annular width (0.60－0.30)÷2＝0.15 mm. A 0.05 mm center offset leaves 0.10 mm geometrically in that direction, before other dimensional/geometry deviations. This explains combined effects, not a universal acceptance limit.
Specify drill versus plated finished diameter. Manufactured residual rings depend on tolerances/criteria, not CAD nominal dimensions alone. Define separate through-hole, blind-via, and microvia rules, checking spans and lands.
Trace width and spacing must match copper thickness and task
Heavy copper changes etched cross sections, undercut control, and inner-layer resin fill. Thin-copper minima cannot simply transfer. Critical nets also need impedance, current, and temperature checks; etchability does not establish function. Retain manufacturing/electrical rules and resolve conflicts through layout/structure.
Another example: 0.50 mm available between pads must hold two 0.10 mm traces, 0.10 mm between, and 0.10 mm each side: 0.10×2＋0.10×3＝0.50 mm. This exactly consumes nominal space without geometric margin. Copper weight, hole occupancy, and tolerances still need review before manufacturability claims.
Local exceptions should leave reviewable reasons
- Locate DRC exceptions by net, layer, coordinates, and rule identifier.
- Distinguish wrong settings, genuine conflicts, and justified special structures.
- Develop concrete layout fixes where possible; submit special processes for manufacturing review.
- Approved exceptions need scope, reason, supplemental inspection, and approver.
- Recheck revisions, remove obsolete waivers, and retain historical links.
Do not loosen global rules merely to clear error counts. Limit one component's special clearance to its objects/area. Recheck actual copper weight/structure before copying exceptions to new projects.
How manufacturing feedback returns to design files
| Manufacturing Comments | Design Review | Closed Record |
|---|---|---|
| Increase Trace Spacing | Layout space and adjacent network | Revision and DRC results |
| Adjust hole or pad | Wire escape, connections, and package | Via Group and Representative Section |
| Trace Width Compensation | Impedance and sensitive RF geometry | Allowable range and controlled layout |
| Solder mask window adjustment | Assembly and Solder Bridge Relationship | Window layer and first article inspection |
Keep approved rules, exceptions, and drawings at one revision. CAM changes without CAD updates recur on repeat orders or supplier changes; return final geometry and impacts to design.
How to verify rules are actually effective
Review representative heavy-copper layers, fine-pitch areas, holes, edges, and critical nets against approved CAD rules. Run full DRC and close exceptions, then independently view exported holes/mask/outline for new export ambiguities.
Retain sensitive first-article dimensions, cross sections, or electrical results to assess rule/process alignment. For systematic deviation, analyze inputs, compensation, and process windows instead of replacing targets with one board's incidental result. This develops reusable experience.
Electrical isolation spacing does not come solely from manufacturing minima. Product tasks determine conditions/bases; check applicable standard revisions rather than inventing universal safety values in ordinary fabrication rules.
Representative checks for rule priority and units
Large rule sets combine global, net-class, regional, and individual constraints. Confirm software precedence, then inspect which rule actually applies to a special object. A higher global rule may override an apparently configured special value.
Check internal constraints/rounding as well as display after millimeter/inch changes. Use known holes, widths, and edge distances to confirm common units. Do not change global minima to suppress unit-error alarms.
Check waivers cover exactly approved objects. A local waiver expanded to an entire package/net can hide real conflicts. Record scope/reason and recheck location/applicability after revisions.
Distinguish design-object distances from finished acceptance distances. Compensation/shape changes occur in fabrication; state rule purposes clearly. Design must assess whether proposed changes affect sensitive geometry, beyond accepting fewer final alarms.
Export the current rule revision and necessary exception summary. Receivers need not execute all internal CAD settings, but must know special regions and changes requiring approval. Link rules to drawings so software checks support executable designs.
Frequently Asked Questions
Does importing factory rules enable fully automatic release?
Still check copper weight, stackup, net requirements, rule priority, and local exceptions.
Does zero DRC errors establish a correct design?
It is only a rule-check result. Continue to Combined Parameters, Manufacturing Combination and Document List.
Source material and applicable scope
- Würth Elektronik, “Basic Design Guide”; V1.0; checked on 2026-10-17; relevant sections: Basic Design Rules, inner/outer copper, PTH, solder mask, and other tables. Supports classification by copper weight, holes, and layers. Supplier values are not transferred; calculations/exception workflows are engineering guidance.
