Why is edge clearance important?

During board routing (milling), the router bit has a tolerance of +/- 0.1-0.2 mm. If copper is too close to the edge, the router may expose copper, causing shorts to adjacent boards in panels, corrosion of exposed copper, or cosmetic defects. V-scoring has even larger tolerances (+/- 0.3-0.5 mm). Adequate clearance prevents yield loss.

Typical clearance values?

Standard: 0.25 mm (10 mil) minimum for routed edges. V-score: 0.38 mm (15 mil) minimum due to wider scoring tolerance. For planes (ground/power pours): 0.5 mm (20 mil) recommended to avoid copper slivers. Castellated edges (half-vias): 0 mm clearance allowed, plated edge is intentional. Some fabs require 0.3 mm minimum for all copper.

Edge clearance for RF boards?

RF boards often need ground plane extending to the edge for shielding and controlled impedance at connectors. Solutions: use castellated vias or plated edge technology (copper-plated board edge for grounding). Otherwise, maintain 0.5 mm ground plane setback and add stitching vias near the edge. Edge-plating adds cost but provides superior grounding.

Electronic Design Automation

Board Edge Clearance

Board Edge Clearance is the minimum distance between any copper feature (traces, pads, planes) and the PCB board outline. This setback prevents copper exposure during board routing (±0.1-0.2 mm tolerance), V-scoring (±0.3-0.5 mm tolerance), and panel depanelization. Standard clearance is 0.25 mm (10 mil) for routed edges, 0.38 mm (15 mil) for V-scored edges, and 0.5 mm (20 mil) for copper planes to avoid thin slivers.

Category: Electronic Design Automation

Standard: 0.25-0.5 mm

Understanding Board Edge Clearance

PCB fabrication separates individual boards from panels using routing (milling a channel around the board) or V-scoring (cutting a V-groove and snapping). Both processes have mechanical tolerances that may shift the actual edge from the designed outline. Copper features within the tolerance zone risk being exposed, cut, or creating copper slivers along the edge.

DRC (Design Rule Check) in PCB layout tools enforces edge clearance as a constraint. The rule applies to all copper layers. Edge connectors and castellated vias are exceptions where copper intentionally meets the board edge, typically specified as separate rules.

Edge Clearance Rules

Routed edge: ≥0.25 mm (10 mil)
V-scored edge: ≥0.38 mm (15 mil)
Copper planes: ≥0.5 mm (20 mil)
Castellated: 0 mm (intentional)

Router tolerance: ±0.1-0.2 mm
V-score tolerance: ±0.3-0.5 mm

Clearance by Edge Type

Edge Type	Clearance	Tolerance	Notes
Routed	0.25 mm	±0.15 mm	Most common
V-scored	0.38 mm	±0.40 mm	Panel separation
Plated edge	0 mm	N/A	Ground contact
Tab-routed	0.25 mm	±0.25 mm	Breakaway tabs

Common Questions

Frequently Asked Questions

Why important?

Router tolerance ±0.15 mm can expose copper. Exposed copper causes shorts, corrosion, cosmetic defects. Prevents yield loss.

Typical values?

Routed: 0.25 mm. V-scored: 0.38 mm. Planes: 0.5 mm. Castellated: 0 mm (intentional edge copper).

RF boards?

Ground plane to edge for shielding: use edge plating or castellated vias. Otherwise 0.5 mm setback with stitching vias near edge.

Related Terms

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