A Gerber file is a vector image file format used for printed circuit board (PCB) design. Gerber files are used to communicate design data from CAD software to PCB fabrication equipment. There are different types of Gerber files that contain information about different layers and aspects of the PCB design. Understanding the different Gerber file extensions created by various PCB design software can help ensure proper file handoff from design to manufacturing.

Common Gerber File Extensions

Here are some of the most common Gerber file extensions you may encounter:

• .gbr – Standard Gerber RS-274X file. Contains 2D vector data for a single PCB layer.
• .gko – Layer stack information. Specifies layer order and properties.
• .gbo – Bottom copper layer. Vector data for bottom copper PCB traces.
• .gts – Top copper layer. Vector data for top copper PCB traces.
• .gto – Top silkscreen overlay. Vector data for top silkscreen and markings.
• .gtp – Top solder paste layer. Vector data for solder paste layer.
• .gbl – Bottom solder mask layer. Vector data for bottom solder mask.
• .gbs – Bottom silkscreen overlay. Vector data for bottom silkscreen.
• .gm1 – Mechanical layer 1. Vector data for board outline and contours.
• .gml – Mechanical layer n. Additional mechanical layer data.
• .gpo – Pin/pad layer. Location of component pins and vias.
• .drd – Drill data. Locations and sizes of drill holes.

Other file extensions may be used by specific software tools. It’s important to understand what information each file contains as they must align properly for successful PCB fabrication.

Gerber File Extensions from Major PCB Design Tools

Here are some details on the specific Gerber file extensions generated by the most common PCB design software packages:

Altium Designer

• .GBL – Bottom layer
• .GBO – Bottom overlay
• .GBS – Bottom solder resist
• .GD1 – Drill drawing
• .GG1 – Drill guide
• .GM1 – Mechanical layer 1
• .GM2 – Mechanical layer 2
• .GM3 – Mechanical layer 3
• .GM4 – Mechanical layer 4
• .GM5 – Mechanical layer 5
• .GM6 – Mechanical layer 6
• .GM7 – Mechanical layer 7
• .GM8 – Mechanical layer 8
• .GM9 – Mechanical layer 9
• .GM10 – Mechanical layer 10
• .GM11 – Mechanical layer 11
• .GM12 – Mechanical layer 12
• .GM13 – Mechanical layer 13
• .GM14 – Mechanical layer 14
• .GM15 – Mechanical layer 15
• .GML – Mechanical layer
• .GPB – Bottom pad master
• .GPT – Top pad master
• .GTO – Top overlay
• .GTP – Top paste
• .GTS – Top layer
• .TXT – Drill report
• .CSV – Drill report

Altium Designer generates a complete set of Gerber and drill files needed for fabrication. The file extensions clearly indicate the layer or data each file contains.

Eagle

• .dri – Drill report
• .brd – Board file
• .sch – Schematic
• .BOT – Bottom copper layer
• .TOP – Top copper layer
• .SLK – Silkscreen layer
• .plc – Top paste mask
• .stc – Solder stop mask top
• .sts – Solder stop mask bottom
• .cpy – Copper layers
• .oln – Outline
• .drd – NC drill file
• .tap – Autorouter file

The Eagle CAD software uses shorthand file extensions for the various Gerber layers. .BOT and .TOP indicate top and bottom copper layers.

KiCad

• .kicad_pcb – Board file
• .net – Netlist file
• .pdf – Printout file
• _NPTH.drl – Non-plated drill file
• _PTH.drl – Plated drill file
• .gbr – Gerber files per layer:
  • F.Cu – Front copper
  • B.Cu – Back copper
  • F.SilkS – Front silkscreen
  • B.SilkS – Back silkscreen
  • F.Mask – Front solder mask
  • B.Mask – Back solder mask
  • Edge.Cuts – Board outline

KiCad outputs each PCB layer and drill data into separate Gerber files with prefixes indicating the layer. This makes it easy to identify the contents of each file.

OrCAD/Allegro

• .brd – Board file
• .sch – Schematic
• .sol – Forward annotation netlist
• .bd – Back annotation netlist
• _BOTTOM.gbr – Bottom copper
• _TOP.gbr – Top copper
• _SILKSCREENBOTTOM.gbr – Bottom silkscreen
• _SILKSCREENTOP.gbr – Top silkscreen
• _SOLDERMASKBOTTOM.gbr – Bottom soldermask
• _SOLDERMASKTOP.gbr – Top soldermask
• _OUTLINE.gbr – Board outline
• _DRILL.txt – Drill report
• _NPTH.drl – Non-plated holes
• _PTH.drl – Plated holes

OrCAD/Allegro prepends layer information to the start of each Gerber filename for clarity. Separate drill files are generated for plated and non-plated holes.

Pads

• .sch – Schematic
• .pcb – Board file
• .apr – Auto-router file
• .asc – ASCII pick and place file
• .mnt – Information file
• .mnt2 – Extended information file
• .pnp – Pick and place data
• Bottom.gbr – Bottom copper layer
• Top.gbr – Top copper layer
• BottomOverlay.gbr – Bottom overlay
• TopOverlay.gbr – Top overlay
• BottomSolder.gbr – Bottom solder mask
• TopSolder.gbr – Top solder mask
• Outline.gbr – Board outline
• DrillFile.txt – Drill report
• DrillFile.npt – Non-plated holes
• DrillFile.pth – Plated holes

Pads software uses descriptive names for Gerber files, with no additional prefixes or suffixes. Drill files are differentiated by their file extensions.

Proteus

• .pdsprj – Main project file
• .DSN – Schematic design file
• .pdsbak – Backup project file
• .pdsshp – Shape file
• BottomCopper.gbr – Bottom copper layer
• BottomSilk.gbr – Bottom silkscreen layer
• BottomPaste.gbr – Bottom solder paste layer
• TopCopper.gbr – Top copper layer
• TopSilk.gbr – Top silkscreen layer
• TopPaste.gbr – Top solder paste layer
• SolderMaskBottom.gbr – Bottom solder mask
• SolderMaskTop.gbr – Top solder mask
• Profile.gbr – Board outline
• DrillDrawing.gbr – Drill drawing
• NC Drills.txt – Drill report
• Holes.xln – Plated and non-plated holes

Proteus appends a descriptive layer name to each Gerber file it generates. Drill data is contained in multiple report and data files.

Pulsonix

• .pson – Native Pulsonix board file
• .pdk – Packed design
• .cdr – Gerber design rule check report
• Bottom Copper.GM1 – Bottom copper
• Top Copper.GM1 – Top copper
• Bottom Paste.GBP – Bottom solder paste
• Bottom Solder.GTS – Bottom solder mask
• Top Paste.GTP – Top solder paste
• Top Solder.GBL – Top solder mask
• Profile.GM1 – Board outline
• Drill Map.TXT – Drill report
• NC Drills.DRL – Non-plated holes
• PTH Drills.DRL – Plated holes

Pulsonix uses a mixture of layer prefixes and suffixes for Gerber files. Drill files are differentiated by their extensions.

Xpedition

• .edb – Enterprise database board file
• .edx – Enterprise database library file
• .dat – ASCII export file
• bottom.gbr – Bottom copper layer
• top.gbr – Top copper layer
• bottom_paste.gbr – Bottom solder paste
• top_paste.gbr – Top solder paste
• bottom_soldermask.gbr – Bottom solder mask
• top_soldermask.gbr – Top solder mask
• profile.gbr – Board outline
• drill_report.txt – Drill report
• fabrication_drawing.pdf – Fabrication drawing

Xpedition uses simple descriptive names for Gerber files. Drill data is contained in a text report.

Gerber File Designators

In addition to file extensions, Gerber files may contain designators in the file name specifying further details:

• F – Front or top layer
• B – Back or bottom layer
• L1, L2, etc. – Layer numbers
• Inr – Inner layer
• Th – Through-hole plating layer
• SS – Solder side layer
• SP – Solder paste layer
• SM – Solder mask layer
• SR – Silkscreen layer
• C – Contour data
• D – Drill data

These one or two letter codes can provide more information about the file when combined with the main extension. For example, F_Cu.gbr indicates the top copper layer.

Spotting Potential Gerber Issues

When receiving Gerber files from a customer or another design source, here are some things to look out for:

• Missing critical layers – All copper, mask, paste, silkscreen layers should be present.
• Duplicate layers – May cause manufacturing errors if duplicated.
• Mislabeled layers – Double check layer file extensions match contents.
• Missing drill files – Fabrication cannot proceed without drill data.
• Non-standard naming – Unclear file contents if naming convention not followed.
• Mismatched data – Features between layers should align precisely.
• Incompatible files – Ensure all files adhere to RS-274X standard.
• Poor layer alignment – Layers must be precisely aligned for proper function.

Addressing any file issues with the design source early on can prevent costly mistakes during PCB fabrication and assembly.

Maximum Number of Gerber Layers

While it’s possible to have dozens of custom layers in a complex PCB design, most designs adhere to these key layers:

• Top copper
• Bottom copper
• Top silkscreen
• Bottom silkscreen
• Top soldermask
• Bottom soldermask
• Top solder paste
• Bottom solder paste
• Drill drawing
• Board outline/profile

This totals 10 essential Gerber layers for a standard design. More complex boards may need a few additional layers for internal power planes or other buried layers. But in most cases, keeping the layer count under 20 is recommended for manufacturing simplicity.

The maximum number of layers is ultimately determined by the capabilities of the PCB fabrication equipment that will produce the boards. Most fabricators can reliably handle up to 20 layers without issue. Going above that may require special layer alignment techniques or additional handling steps. This can increase cost and lead time for very high layer count boards.

Why So Many Gerber Files?

With so many separate files, it may seem complicated compared to simpler image formats. But there are good reasons PCB design splits data into separate Gerber files:

Precision: Gerber files preserve vector data with extreme precision suitable for PCB fabrication equipment. Bitmaps and other images can lose quality.

Editability: Keeping layers separate as Gerber files enables making edits to a single layer without affecting others. This supports design revisions.

Layer alignment: Individual layers stack up precisely when loaded separately in fabrication equipment. Alignment can suffer if combined into one file.

Standardization: Gerber format is highly standardized, making files interchangeable between different PCB tools and manufacturers.

Error checking: The extensive RS-274X file format enables embedding quality control information to verify PCB data integrity during transfer and fabrication.

So while handling numerous Gerber files is more complex, the flexibility and precision they provide is critical for high-quality PCB manufacturing with minimal errors.

Gerber File Generation Tips

Here are some tips to generate clean, error-free Gerber files for fabrication:

• Always use the latest version of your PCB design software and keep CAD libraries up-to-date. Older versions may export inferior or non-standard gerbers.
• Ensure all required layers are output. Perform a thorough design rule check to clear all errors before generating gerbers.
• Use standard naming conventions for layers based on software defaults or fab house recommendations.
• Specify NC drill holes in a separate file from plated holes.
• Provide a detailed drill and pick-and-place drawing for assembly.
• Double check layer alignment across all layers and features.
• Include a text readme file that documents all output files.
• Compare board dimensions across all layers for consistency.
• Zip files to simplify transferring multiple gerbers and prevent data corruption.
• Validate Gerber format compatibility using a free online Gerber viewer.

Carefully following PCB design best practices and layer standards will help avoid issues transmitting design files for fabrication and assembly.

Gerber File Verification

Before sending Gerber files for PCB production, designers should perform several checks:

Visual inspection: Carefully examine each layer at high zoom levels against the source design for missing or incorrect geometry.

Layer alignment check: When overlaid in a Gerber viewer, all layers should precisely line up with no offsets between layers or features.

Design rule check: Use PCB CAD tools to validate trace widths, spacings, annular rings, and other rules adhere to fabrication specs.

Dimensional check: Confirm overall board dimensions match across layers and with the source design.

File format validation: Use online Gerber viewers like Gerbv to check files adhere to RS-274X format.

Naming convention check: Ensure layer file names match expectations and contain necessary identifiers.

Drill validation: Confirm drill files contain plated and non-plated holes specified in the design.

Fabricator pre-check: Submit files to manufacturer for preliminary review to catch problems early.

Automating comparisons between layers using PCB analysis tools helps catch inaccuracies before they become expensive fabrication errors.

Conclusion

Understanding PCB Gerber file extensions is key to properly manufacturing printed circuit board designs. While the array of separate layer files may seem complex, when generated properly they provide the accuracy and precision needed to translate from CAD to physical PCBs. By following layer standards, validating data, and carefully checking outputs, PCB designers can feel confident their Gerber files capture design intent without surprises during fabrication and assembly.

FQA

Question 1: What is the main purpose of Gerber files in PCB design?

Answer 1: The main purpose of Gerber files is to communicate complete PCB design data from CAD software to fabrication equipment. Gerber files contain vector instructions that precisely specify every conductive copper layer, mask layer, silkscreen, outline, and drill hole needed to manufacture the board.

Question 2: Can Gerber files contain multiple layers in one file?

Answer 2: It is possible to combine multiple layers into one Gerber file, but this is not recommended. The standard approach is maintaining each PCB layer or data type as a separate Gerber file. This provides maximum control and alignment during fabrication.

Question 3: What fabrication issues can incorrect Gerber files cause?

Answer 3: Incorrect Gerber files can lead to shorts, broken traces, improper hole sizes and locations, misaligned layers, and many other manufacturing defects. Missing layers or data in Gerber files may prevent fabrication altogether. Carefully validating Gerbers prevents expensive mistakes.

Question 4: How can you determine the function of a Gerber file without opening it?

Answer 4: The function of a Gerber file can often be determined from its file name and extension. Standard conventions include using suffixes or prefixes to designate layer types such as “_BottomCopper”, “F.Silk”, or “TopLevel”. Strict naming conventions help identify files.

Question 5: Can Gerber files be edited or combined after export?

Answer 5: While it is possible to edit or combine Gerber files using specialty CAM software, it is not recommended. For design changes it is always best to modify original CAD source files and then re-export fresh Gerber files. Manual manipulation of Gerbers can introduce errors.