How to Prepare Gerber Files for PCB Manufacturing
Which Gerber and drill files are needed, how to export them from KiCad and Altium, and the most common file mistakes that delay PCB production.
Table of contents 7 sections
Gerber files are the universal language a PCB manufacturer needs to produce your board. A missing or incorrect layer can delay production by days or result in the wrong board being made.
In short: export all copper, solder mask, silkscreen and board outline layers in Gerber format (RS-274X or X2), export drill data in Excellon format, and send everything in a single ZIP file.
What is a Gerber file?
Gerber is a vector format that describes each layer of a PCB as a separate file. Today’s standard, RS-274X (extended Gerber), and its successor Gerber X2 also carry additional information such as layer function inside the file. The old RS-274D format should no longer be used.
Which files are needed?
| Layer | Common extension | Description |
|---|---|---|
| Top copper | .GTL | Conductive traces and pads on the top side |
| Bottom copper | .GBL | Conductive traces on the bottom side |
| Inner layers | .G2, .G3 … | Inner copper layers on multilayer boards |
| Top / bottom solder mask | .GTS / .GBS | Areas where the solder mask is opened |
| Top / bottom silkscreen | .GTO / .GBO | Component designators, logos and markings |
| Top / bottom paste | .GTP / .GBP | For the solder paste stencil; required for assembly |
| Board outline | .GKO / .GM1 | The board edge and internal cut-outs |
| Drill file | .DRL / .TXT | Hole positions and sizes in Excellon format |
Extensions vary between design tools; what matters is that each layer can be clearly identified. Plated (PTH) and non-plated (NPTH) holes can be supplied in separate files.
Exporting Gerbers from KiCad and Altium
KiCad
- In the PCB editor, open File → Fabrication Outputs → Gerbers.
- Select the copper, mask, silkscreen, paste and Edge.Cuts layers.
- Enable the Gerber X2 option and generate the files.
- From the same dialog, use Generate Drill Files to create the Excellon file.
Altium Designer
- Use File → Fabrication Outputs → Gerber Files to choose layers and units.
- Export the drill file with NC Drill Files using the same units and precision.
- Open the outputs in a Gerber viewer to check them.
Opening the files in a free Gerber viewer (such as KiCad GerbView) before sending them and checking that the layers line up catches most errors before they reach the manufacturer.
The most common mistakes
- Missing board outline layer: the manufacturer cannot tell where to cut the board.
- Drill and Gerber files in different units or zero formats: holes appear offset.
- Missing solder mask openings: pads are covered by mask and cannot be soldered.
- Traces and spacing below the manufacturer’s capability: most manufacturers’ standard capability is around 0.15 mm (6 mil) trace/space; finer values cost more.
- Silkscreen overlapping pads: reduces solderability.
Watch out: sending your design file (e.g. .kicad_pcb or .PcbDoc) is not a substitute for Gerbers. Manufacturers may use different software versions; always send Gerber and drill files.
Information needed for a quote
- Gerber ZIP containing all layers
- Excellon drill file (PTH/NPTH)
- Board dimensions and layer count
- Board thickness (usually 1.6 mm) and copper weight (e.g. 1 oz)
- Surface finish (HASL, ENIG, etc.), solder mask and silkscreen colour
- Quantity and panel preference
Upload your Gerber ZIP and get offers based on layer count, thickness and surface finish.