7 Checks to Make Before Sending Gerber Files to PCB Manufacturing

Exporting a PCB design is not the same as verifying the manufacturing package.

Your board may look correct in the original design application, but the fabricator normally works from exported Gerber, drill and supporting files. A missing outline, displaced drill file or incorrect layer can therefore survive unnoticed until somebody inspects the actual deliverable.

The safest habit is simple:

Review the files you are going to send, not only the design from which they were generated.

This article presents seven practical checks you can incorporate into a PCB release workflow. They are useful whether you created the board, received the files from a customer or need to approve a manufacturing package without access to its original PCB design system.

1. Confirm that the manufacturing package is complete

Begin by extracting the package into a new review directory. Keep the original archive unchanged so that you can trace the reviewed files back to the exact delivery or release.

A typical bare-board package may include:

Top and bottom copper
One or more internal copper layers
Top and bottom solder mask
Top and bottom silkscreen, when used
Solder-paste layers when assembly or stencil data is required
A board outline or profile
Plated and non-plated drill files
Routing or slot data
Fabrication drawings and special instructions

Do not assume that filenames prove the package is complete. Extensions such as .GTL, .GBL, .GTS and .GKO are common conventions, but different PCB applications use different naming schemes. Some exporters give every layer the generic .GBR extension.

If you need help interpreting unfamiliar names, this Gerber file-extension reference explains the most common copper, mask, paste, silkscreen, outline and drill extensions.

Compare the package against both the intended layer stack and the manufacturer's submission requirements. A file can be valid Gerber data and still represent the wrong layer—or the wrong project.

2. Open all related layers together

Looking at individual files is useful, but it is not enough. Load the complete set into an independent PCB manufacturing-file viewer and display the layers in one workspace.

Combining the layers makes several problems immediately visible:

A file uses a different origin
A layer is unexpectedly empty or very small
Content lies far outside the board area
Drill holes are displaced from their pads
The outline belongs to another board or revision
A mechanical drawing has been mistaken for the production outline

Assign contrasting colors, change layer order and toggle visibility one file at a time. Transparency is especially useful when checking copper, mask and drill relationships.

Modern Gerber X2 data can contain attributes that identify a file's function and side. These attributes reduce ambiguity, but they do not remove the need to inspect the rendered content. For more background, see What Is the Gerber File Format?.

3. Verify the board outline and dimensions

The board outline should form a clear, closed representation of the intended finished profile. Display it with the copper and drill layers and look for:

Duplicate or overlapping contours
Open or broken segments
Unrelated construction geometry
Missing internal cutouts
Routing information on an unexpected layer
Copper or drill features outside the intended profile

Measure the overall width and height and compare them with the mechanical specification. Check important cutouts, mounting-hole positions and connector locations as well.

This is also a useful way to detect an incorrect unit interpretation. A board that should be 100 mm wide but appears at a dramatically different size is a warning to review the export units and coordinate format before proceeding.

4. Check drill-to-copper alignment

Gerber layers describe graphical PCB artwork, while hole information is commonly delivered in one or more Excellon drill files. Because these datasets may be exported separately, they must share compatible coordinates, units and origins.

Overlay the drill files with the copper layers and zoom into representative areas around:

Through-hole component pads
Vias
Mounting holes
Tooling holes
Plated slots
Non-plated mechanical features

The holes should be centered where expected. Check several areas across the board rather than inspecting only one corner; a scale or format error may become more apparent farther from the origin.

Review the available drill-tool diameters and make sure plated and non-plated data have not been omitted or confused. The Excellon drill-file guide provides a more detailed explanation of tool definitions, coordinates, units and zero suppression.

If a drill layer is displaced, do not assume the fabricator will infer the intended correction. Determine whether the cause is an export setting, a different origin, incorrect units or coordinate-format interpretation.

5. Inspect copper, solder mask and silkscreen relationships

Now review the production layers individually and in meaningful combinations.

Copper

Look for missing or obviously unexpected tracks, pads, flashes and copper areas. Query aperture information when an object has an unexpected shape or width.

Solder mask

Overlay mask and copper. Confirm that the intended pads are exposed and that the rendered openings align correctly. Remember that solder-mask output commonly describes the openings rather than the material that remains.

Silkscreen

Inspect reference designators, polarity marks and other printed objects near pads, holes and the board edge. Visual review does not replace the manufacturer's clearance rules, but it can reveal obviously misplaced or unexpected content.

Mechanical data

Make sure dimensions, notes or construction geometry have not accidentally been included on a production layer. Conversely, check that required routed slots and cutouts have not been left only in a drawing that the fabricator may treat as informational.

6. Measure critical features

Visual inspection can tell you that geometry appears plausible. Measurement helps confirm that it is correct.

Which dimensions matter depends on the board, but useful candidates include:

Overall board width and height
Mounting-hole spacing
Connector positions relative to board edges
Cutout dimensions
Board-edge clearances
Distances between selected pads or mechanical features
The size and position of test-fixture locations

Use snapping when available so measurements reference the actual pads, tracks or other geometry instead of approximate screen positions.

For ODB++ or compatible Gerber X3 datasets, additional component and net information may be available. This can help reviewers inspect designators, placement, rotations, pins and connectivity alongside the visible layers. See viewing PCB components and nets for an example of this richer inspection workflow.

7. Compare the release with the approved revision

For a revised board, checking that the new files look reasonable is only half the task. You should also confirm that the differences match the intended engineering change.

Compare corresponding layers from the new and previously approved releases. A graphical comparison can reveal:

Added or removed tracks
Moved or resized pads
Changed copper pours
Unexpected regeneration differences
Changes on layers that were supposed to remain untouched

Review both the visible changes and their absence. If the engineering change should have affected a particular layer but the comparison shows no difference, the wrong output may have been included.

GerbView can display added, removed and unchanged geometry using different colors. The Gerber comparison tutorial shows the basic workflow.

Warning signs that deserve investigation

Pause the release if you encounter any of the following:

A required layer is missing, empty or unexpectedly small
The outline appears more than once or does not enclose the board
Drill holes do not align with their copper pads
One layer uses a different origin, scale or unit interpretation
Visible content extends far outside the expected board area
Aperture or drill-tool information is missing or produces strange geometry
The revision comparison contains unexplained changes
A generic filename cannot be matched confidently to a layer function

An unusual display does not always mean that the data is wrong, but it should be understood before the package is approved.

Keep a record of the review

Once the package has passed inspection, archive the exact approved dataset with its revision identifier and any fabrication notes. A PDF or printed review document can also help communicate the layer set, dimensions or marked areas to colleagues who do not use PCB CAM software.

For confidential designs, consider whether the review tool should process files locally. An offline Gerber viewer avoids uploading the PCB data to a browser-based service, although workstation, network and storage security still remain your responsibility.

Where GerbView fits

GerbView is a Windows application for viewing, measuring, comparing, printing and converting PCB manufacturing files. It supports Gerber RS-274D and RS-274X, Gerber X2/X3 attributes, Excellon drill data and ODB++Design datasets.

It can load multiple files as layers, inspect apertures and drill tools, align layers that use different origins, measure geometry, compare Gerber revisions and create documentation in formats such as PDF and DXF.

If you want a broader introduction to the files exchanged between PCB design and production, read Understanding PCB Manufacturing File Formats.

Final thought

No visual checklist can prove that a board is electrically correct or manufacturable under a particular factory's rules. Independent file inspection should complement—not replace—electrical rule checks, automated DFM analysis and the manufacturer's own review.

It does, however, answer one essential question before fabrication begins: