What file format defines the outline?

In Gerber output, the board outline is typically on the Edge.Cuts or Mechanical layer, exported as a separate .GKO or .GM1 file. In ODB++ and IPC-2581 formats, it is part of the profile definition. The outline must be a single, closed polygon with no gaps. Arcs are defined by center point and radius. Most fabricators accept 0.1 mm line width for the outline.

Minimum inner radius?

Router bits are typically 1.0-2.0 mm diameter, so the minimum inner corner radius is 0.5-1.0 mm. Attempting a sharp 90-degree inner corner will result in a radiused corner matching the router bit radius. If a sharp corner is required, use a drill hole at the corner to create a relief. Slots also require minimum width equal to the router bit diameter.

Board outline tolerance?

Standard routing tolerance: +/- 0.15 mm. Precision routing: +/- 0.10 mm. V-scoring: +/- 0.3-0.5 mm (less precise). Dimension tolerance affects enclosure fit, connector alignment, and board-to-board spacing. Specify critical dimensions with tighter tolerances and identify datum features for alignment.

Electronic Design Automation

Board Outline

The Board Outline is the mechanical boundary layer that defines the physical shape, dimensions, and internal cutouts of a PCB. It is the reference for router path programming during fabrication, panelization layout, and enclosure mechanical integration. The outline must be a single, closed polygon with minimum inner corner radii of 0.5-1.0 mm (matching router bit radius). Standard dimensional tolerance is ±0.15 mm.

Category: Electronic Design Automation

Tolerance: ±0.15 mm

Understanding Board Outlines

The outline drives multiple fabrication processes: panel layout (maximizing boards per panel for cost), router programming (CNC path), V-score placement, and electrical test fixture design. A well-defined outline with proper tolerances prevents mechanical fit issues in the final product.

Internal cutouts (for connectors, airflow, or cable routing) follow the same rules as the outer edge. Each cutout must be a closed polygon with corners radiused to the router bit diameter. Plated internal cutouts (for edge connectors) require additional processing steps.

Outline Specifications

Router bit diameter: 1.0-2.0 mm
Min inner radius: 0.5-1.0 mm
Min slot width: 1.0 mm

Tolerance:
Standard: ±0.15 mm
Precision: ±0.10 mm
V-score: ±0.30-0.50 mm

Outline Output Files

Format	File Extension	Layer Name
Gerber (Protel)	.GKO	Keep-Out
Gerber (KiCad)	-Edge_Cuts.gbr	Edge.Cuts
Gerber (Altium)	.GM1	Mechanical 1
ODB++	profile	Profile

Common Questions

Frequently Asked Questions

File format?

Gerber: .GKO or .GM1 (separate layer). ODB++/IPC-2581: profile definition. Must be closed polygon, no gaps.

Inner radius?

Min 0.5-1.0 mm (router bit radius). Sharp corners get radiused. Use drill relief for true sharp corners.

Tolerance?

Standard: ±0.15 mm. Precision: ±0.10 mm. V-score: ±0.30-0.50 mm. Critical dims get tighter specs.

Related Terms

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