Understanding Gerber Layers: GKO vs Mechanical Layer

When preparing PCB design files for manufacturing, clarity and accuracy in layer usage are essential, not just for a smooth production process, but to avoid costly delays or revisions. One of the most common errors we’ve observed is the use of the GKO layer for mechanical outlines, which can lead to miscommunication during fabrication.

Let’s break down the difference between the GKO layer and the mechanical layer, and how to use them correctly.

What is the GKO Layer?

The GKO (Keep-Out) layer is primarily used to define restricted areas on a PCB — regions where no copper, components, or routing should occur. It's meant for internal design constraints, not for conveying physical board outlines or mechanical data to the fabricator.

 Intended Purpose: Defining no-go zones for routing and component placement.

 Not Meant For: Board dimensions or fabrication outlines.

What is the Mechanical Layer?

The mechanical layer (often named Mechanical 1 or simply MECH) is the correct place to define your board outline, cut-outs, mounting holes, and any fabrication notes. It communicates the physical characteristics of the PCB to the manufacturer.

 Intended Purpose: Board shape, tooling holes, cutouts, and mechanical dimensions.

 Use This for: Communicating mechanical requirements to your PCB fabricator.

Why the Confusion Happens

Many PCB design tools allow users to repurpose layers freely. In some design environments, the GKO layer can appear similar to a mechanical layer, especially when default settings are not customized. This often results in customers unintentionally placing board outlines or cutouts in the GKO layer, assuming it serves a dual function.

Risks of Using GKO for Mechanical Requirements

When mechanical details are incorrectly placed in the GKO layer:

• Critical information might be missed during CAM processing.

• Delays can occur if files need clarification or correction.

• Manufacturing errors may happen if the outline isn’t interpreted properly.

Best Practices

To avoid these issues:

1. Use a designated mechanical layer to define board outlines and dimensions.

1. Label your layers clearly in your Gerber files and fabrication drawings.

1. Cross-check before submission, especially when exporting from ECAD tools like Altium, Eagle, or KiCAD.

1. Include a readme or layer stack-up description with your file package if needed.

1. Consult your PCB manufacturer if you're unsure which layers to use.

Final Word

Mixing up the GKO and Mechanical layers might seem like a minor mistake, but it can cause major delays or even result in missed fabrication details. Do not place mechanical layer information — such as board outlines or cutouts — in the GKO layer, as it may be completely overlooked during manufacturing.

Need help preparing your files?

 Visit our PCB Design Guidelines