GBO File

What are GBO files and how to open them

Are you having problems opening a GBO file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your GBO files.

What is a GBO file?

A .GBO file is a Gerber Bottom Overlay file.

The Gerber Bottom Overlay file is a layer file used in PCB design export that contains the legend or silkscreen artwork printed on the bottom side of a printed circuit board. This includes component outlines, reference designators, logos and orientation marks that appear on the underside of the board. It serves purely as a visual guide for assembly, inspection, and labeling - it does not carry copper traces or electrical connectivity.

This file is produced by PCB design software when exporting fabrication data in the Gerber format (typically RS-274X or with modern Gerber X2/X3 attributes). During this export process "bottom overlay" is enabled, and the software writes the bottom side legend/silkscreen content to the .GBO file. After generation it is used by manufacturers, visualisers or editors to view the board bottom's printed markings. It is not usually modified at the CAM stage, though viewing and proofing in tools like GerbV is common. GERBV is verified to open this specific Gerber Bottom Overlay format. (Known-programs list includes GERBV.) Evidence: known programs include GERBV.

When naming, the extension ".gbo" acts as a convention to denote that the file contains the bottom overlay (silkscreen) layer. Many fabricators expect files labeled with GBO to correspond to the bottom legend layer. Other layers - such as bottom copper, bottom solder mask, etc. - use their own standard extensions like GBL, GBS. This naming helps with organizing the multiple files required for PCB fabrication.

Technical detail: this file is an ASCII-text vector image following the Gerber RS-274X standard, often with Gerber X2 attributes. The coordinate commands in the file describe the positions and shapes of the legend artwork. The internal "FileFunction" attribute in Gerber X2/X3 spec allows marking a file as Legend,Bottom to denote that its function is a bottom side silkscreen overlay.

How to open GBO files

We have identified one GBO opener that is compatible with this specific type of GBO file.

Programs that open Gerber Bottom Overlay files

Last updated: August 6, 2026

Various apps that use files with this extension

These apps are known to open certain types of GBO files. Remember, different programs may use GBO files for different purposes, so you may need to try out a few of them to be able to open your specific file.

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