How to Merge Multiple Gerber Files: Complete Guide for PCB Engineers

The first time I needed to combine multiple PCB designs into a single Gerber package, I spent far too long searching for the right approach. Whether you’re trying to panelize different boards together, combine layers from separate exports, or merge silkscreen files with assembly drawings, knowing how to merge Gerber files properly saves both time and manufacturing costs. This guide covers every scenario where merging Gerber files makes sense and walks through the practical methods to accomplish it.

Why Merge Multiple Gerber Files?

There are several situations where PCB engineers need to merge Gerber files, and each requires a slightly different approach.

Common Reasons for Gerber File Merging

Scenario	Purpose	Typical Approach
Panelization	Combine multiple boards into one manufacturing panel	Merge all layers + add panel features
Layer combining	Merge silkscreen with assembly layer	Combine specific layers only
Mixed designs	Different boards on same panel	Full file set merging
Revision consolidation	Combine old and new design sections	Selective layer merging
Logo/artwork addition	Add graphics to existing design	Single layer merge
Cost reduction	Multiple prototypes in one order	Full panelization merge

Understanding your specific goal determines which merging method works best. Panelizing requires merging corresponding layers from multiple designs while maintaining alignment. Adding a logo to silkscreen only requires merging a single layer.

Understanding Gerber File Structure for Merging

Before merging Gerber files, you need to understand what you’re combining. Each Gerber file represents a single layer—merging combines the graphical data from multiple files while maintaining the coordinate system.

Layer Matching Requirements

When merging multiple PCB designs, corresponding layers must be combined:

Source Board 1	Source Board 2	Merged Output
board1.GTL	board2.GTL	panel.GTL
board1.GBL	board2.GBL	panel.GBL
board1.GTS	board2.GTS	panel.GTS
board1.GBS	board2.GBS	panel.GBS
board1.GTO	board2.GTO	panel.GTO
board1.GBO	board2.GBO	panel.GBO
board1.GKO	board2.GKO	panel.GKO
board1.DRL	board2.DRL	panel.DRL

The merging process reads each layer file, applies coordinate offsets to position boards correctly, and writes combined output files that contain data from all source boards.

Critical Merge Considerations

Factor	Importance	Notes
Coordinate origin	Critical	All boards must use consistent origin reference
Units	Critical	Don’t mix inch and metric within a merge
Format	Important	RS-274X recommended for all files
Layer count	Critical	All boards must have same layer count
Aperture definitions	Important	May need consolidation
Board specifications	Critical	Same thickness, copper weight, finish

Methods to Merge Multiple Gerber Files

You have several options for merging Gerber files, ranging from free command-line tools to professional CAM software.

Method 1: GerberPanelizer (Free GUI Tool)

GerberPanelizer is a free Windows application that merges Gerber files through a visual interface. It’s designed primarily for panelization but works for any Gerber merging task.

Step-by-step process:

1. Prepare source files: Organize each board’s Gerbers in separate folders with proper naming (.GTL, .GBL, .GTS, etc.)
2. Rename outline files: If using KiCad, rename .gm1 files to .gko (the extension GerberPanelizer expects for board outlines)
3. Create new project: Open GerberPanelizer, select File → New
4. Set panel dimensions: Configure panel size in Panel Properties (e.g., 100x100mm)
5. Import boards: Drag each Gerber folder onto the workspace. Boards appear in the layout area.
6. Arrange boards: Use Board Placement → Autopack or manually position boards. Right-click boards to add instances for duplicates.
7. Add breakaway features: If panelizing, use Breaktabs → Create Breaktabs to add mouse bites between boards
8. Verify panel: All boards should show green status indicating valid panel configuration
9. Export merged Gerbers: File → Export Merged Gerbers. Select an empty output directory.
10. Verify output: Open merged files in a Gerber viewer to confirm correct merging

GerberPanelizer tips:

• Files merge by extension—all .GTL files become one merged .GTL
• Board outline should only appear in .GKO file, not duplicated in other layers
• Save project file before exporting (exports cannot be edited later)
• Tool generates preview images showing front and back of merged panel

Method 2: GerbMerge (Command Line Tool)

GerbMerge is a Python-based command-line tool for merging RS-274X Gerber files. It’s powerful for automated workflows and scripting.

Installation:

pip install gerbmerge

Basic usage:

Create a configuration file (merge.cfg) defining your boards:

[MergeOutputFiles]Prefix = merged[JobBoard1]BoardFile = board1/board1*TopLayer = board1.GTL*BottomLayer = board1.GBL…[JobBoard2]BoardFile = board2/board2*TopLayer = board2.GTL…

Run the merge:

gerbmerge merge.cfg layout.txt

GerbMerge features:

• Automatic board placement optimization
• Manual placement via layout file
• Support for different board orientations (rotation)
• Excellon drill file merging
• Configurable panel dimensions

Limitations:

• Requires rectangular board outlines
• Configuration file syntax has learning curve
• Maximum 26 unique drill sizes in merged output

Method 3: CAM350 (Professional CAM Software)

CAM350 is industry-standard CAM software with comprehensive Gerber merging capabilities.

Merging process in CAM350:

1. Import first design: File → Import → AutoImport. Select directory containing first board’s Gerbers.
2. Import drill data separately: File → Import → Drill Data. Select Excellon file.
3. Save as CAM file: File → Save to preserve imported data
4. Merge additional boards: File → Merge. Select second board’s CAM file or import its Gerbers.
5. Position merged board: Right-click to place at desired offset
6. Repeat for additional boards: Merge as many boards as needed
7. Consolidate layers: For each layer type, use Edit → Move To Layer to combine corresponding layers from all boards onto single output layers
8. Add panel features: Draw board outline, add V-score lines or routing paths
9. Export merged Gerbers: File → Export → Gerber Data
10. Export merged drills: File → Export → Drill Data

CAM350 advantages:

• Full editing capabilities during merge
• DFM checking on merged panel
• Professional-grade layer management
• Handles complex aperture definitions

Method 4: Merging Within PCB Design Software

If you have access to original design files (not just Gerbers), merging within your CAD tool is often easier.

Altium Designer:

• Use Embedded Board Array feature
• Place → Embedded Board Array
• Select source PCB files
• Configure array dimensions
• Export Gerbers from panel document

KiCad:

• File → Append Board to add designs to current PCB
• Manually arrange appended boards
• Add panel outline and breakaway features
• Plot combined Gerbers

Eagle:

• Use panelize.ulp script
• Run ULP → panelize.ulp
• Configure array parameters
• Generate Gerbers via CAM processor

Merging Specific Layer Types

Different merging scenarios require attention to specific layer behaviors.

Merging Copper Layers

Copper layer merging is straightforward—graphical data simply combines. Ensure adequate spacing between boards to prevent shorts during manufacturing.

Consideration	Requirement
Minimum spacing	0.5mm between copper from different boards
Ground planes	May need adjustment at board edges
Thermal relief	Verify pour settings don’t create issues

Merging Solder Mask Layers

Solder mask files are typically negative polarity—drawn areas represent openings. When merging, maintain this polarity consistently.

Watch for:

• Polarity consistency between source files
• Expansion settings from original designs
• Coverage of routing/tab areas in panel

Merging Silkscreen Layers

Silkscreen merges require attention to text overlap and readability.

Issue	Solution
Overlapping text	Adjust board spacing or edit merged output
Different fonts	Accept inconsistency or standardize before merge
Logo addition	Merge logo file with existing silkscreen layer

Merging Drill Files

Drill file (Excellon) merging requires special attention because drill files contain tool definitions that must be consolidated.

Drill merging challenges:

• Different tool numbering in source files
• Exceeding maximum tool count (typically 26-99 depending on manufacturer)
• Coordinate format inconsistencies
• Plated vs. non-plated hole separation

Best practice: Verify merged drill file in Gerber viewer overlaid with copper layers to confirm hole positions align with pads.

Merging Board Outline Layers

When combining multiple boards, the original board outlines become internal routing paths, and a new panel outline encompasses all boards.

Original Files	Merged Result
Board 1 outline	Internal routing path
Board 2 outline	Internal routing path
Panel boundary	New outer outline
Breakaway tabs	Added between boards

Common Merging Problems and Solutions

Gerber merging can introduce issues that weren’t present in original files.

Alignment Problems

Symptom: Layers don’t align correctly in merged output

Causes and fixes:

Cause	Solution
Different origins	Standardize origin before merging
Coordinate format mismatch	Convert all files to same format
Unit inconsistency	Convert all to mm or all to inches
Scaling issues	Verify no scaling applied during merge

Drill Misalignment

Symptom: Drill holes offset from copper pads

Common causes:

• Different coordinate origins between Gerber and drill exports
• Trailing vs. leading zero format mismatch
• Inch vs. metric unit confusion

Solution: Open merged files in viewer, overlay drill layer on copper, and verify alignment before sending to manufacturer.

Aperture Conflicts

Symptom: Strange pad shapes or missing features

Cause: D-code conflicts when merging files with different aperture definitions

Solution: Use merge tool that properly consolidates aperture lists, or manually verify aperture table in merged output.

Missing Layers

Symptom: Some layers don’t appear in merged output

Cause: File extension mismatch or layer mapping errors

Solution: Verify all source files use consistent naming conventions before merging.

Best Practices for Merging Gerber Files

Follow these guidelines to ensure successful merges.

Pre-Merge Checklist

Step	Action
1	Verify all source boards DRC-clean
2	Confirm identical layer stackup
3	Standardize file naming conventions
4	Convert all files to RS-274X format
5	Use consistent coordinate units
6	Document board origins

During Merge

Step	Action
1	Import files from organized folder structure
2	Verify each board loads correctly
3	Check layer mapping before proceeding
4	Position boards with adequate spacing
5	Save intermediate work
6	Add panel features (outline, tabs, fiducials)

Post-Merge Verification

Check	Method
Layer alignment	Overlay all layers in viewer
Drill alignment	Overlay drill on copper layers
Board spacing	Measure in viewer
File completeness	Verify all layer files present
Aperture validity	Check for errors when loading
Manufacturer acceptance	Upload to online viewer/DFM tool

Useful Resources for Merging Gerber Files

Merging Tools

Tool	Type	Platform	URL
GerberPanelizer	GUI	Windows	github.com/ThisIsNotRocketScience/GerberTools
GerbMerge	CLI	Cross-platform	github.com/unwireddevices/gerbmerge
hm-panelizer	GUI	Cross-platform	github.com/halfmarble/hm-panelizer
KiKit	CLI/Plugin	Cross-platform	github.com/yaqwsx/KiKit
CAM350	Professional	Windows	downstreamtech.com
Camtastic	Professional	Windows	altium.com

Verification Tools

Tool	Purpose	URL
Gerbv	Free Gerber viewer	gerbv.github.io
KiCad GerbView	Free Gerber viewer	kicad.org
ViewMate	Free/paid viewer	pentalogix.com
HQDFM Online	Online DFM check	nextpcb.com
Ucamco Reference Viewer	Online viewer	gerber-viewer.ucamco.com

Manufacturer Online Viewers

Service	Notes
JLCPCB	Instant render, DFM feedback
PCBWay	Layer preview, pricing
OSH Park	Renders with purple mask
Seeed Studio	Panel preview

Frequently Asked Questions

Can I merge Gerber files from different CAD tools?

Yes, Gerber is a standardized format, so files from different CAD tools (KiCad, Eagle, Altium, OrCAD) can be merged together. However, you must ensure all files use the same format version (RS-274X recommended), consistent units, and compatible coordinate systems. The challenge is usually in file naming conventions—different tools use different extensions. Standardize naming to Protel conventions (.GTL, .GBL, etc.) before merging. Also verify that all source designs share identical specifications: same layer count, board thickness, copper weight, and surface finish.

How do I merge just one layer, like adding a logo to silkscreen?

To merge a single layer (such as adding a logo to existing silkscreen), you only need to combine the specific layer files. In GerberPanelizer, you can add a logo Gerber to the same folder as your board—files merge by extension, so both .GTO files combine automatically. In CAM350, import both files to the same layer and they’ll overlay. The key is positioning—apply a coordinate offset to the logo file so it appears in the correct location. Create the logo as a separate Gerber file with the same origin as your main design for easiest alignment.

What’s the maximum number of boards I can merge into one panel?

There’s no hard limit on the number of boards you can merge—the constraint is typically the maximum drill tool count. Most merging tools and manufacturers support 26-99 unique drill sizes across the merged panel. If your combined designs exceed this limit, you’ll need to standardize hole sizes across designs before merging. Physical constraints also apply: your merged panel must fit within your manufacturer’s maximum panel size (commonly 450x600mm for production). For prototype services, panels are typically limited to 100x100mm or similar, which practically limits the number of boards you can include.

Why do my merged drill files show holes in wrong positions?

Drill misalignment after merging almost always results from inconsistent coordinate settings between original Gerber and drill exports. Check three things: First, verify the coordinate origin used for drill export matches the Gerber origin. Second, confirm the coordinate format (leading/trailing zero suppression) is consistent. Third, ensure units match—mixing inch Gerbers with metric drill files causes 25.4x scaling errors. To diagnose, load merged output in a Gerber viewer and overlay the drill layer on top copper. If holes are systematically offset in one direction, the origin was different. If holes appear scaled wrong, you have a unit mismatch.

Should I merge Gerber files myself or let the manufacturer do it?

For standard panelization of identical boards, manufacturers typically handle this automatically and efficiently—they combine your design with other customers’ boards to fill their production panels. However, merge Gerber files yourself when you need multiple different designs on one panel (manufacturers charge extra for this), when you have specific panel configuration requirements, or when you want control over board arrangement and breakaway tab placement. For prototypes where you’re ordering from pooled services (OSH Park, JLCPCB), letting them panelize is usually more cost-effective. For production quantities or mixed-design panels, creating your own merged Gerbers gives you full control.

Conclusion

Merging multiple Gerber files is a fundamental skill for PCB engineers working with panelization, cost optimization, or complex multi-board projects. Whether you choose a free GUI tool like GerberPanelizer, a command-line solution like GerbMerge, or professional CAM software like CAM350, the principles remain the same: organize your source files consistently, merge corresponding layers correctly, verify the output thoroughly.

The most important step is verification. Always load your merged output in a Gerber viewer before sending to manufacturing. Check layer alignment, drill positions, board spacing, and panel outline. A few minutes of verification prevents expensive mistakes and manufacturing delays.

Start with simple merges—combining identical boards into a panel—before attempting complex multi-design merges. As you gain experience, you’ll develop workflows that reliably produce correct merged output, saving time and reducing your per-board manufacturing costs through efficient panelization.