Gerber files are the universal language between PCB designers and manufacturers. If you've ever exported a ZIP from KiCad and wondered what's actually inside — or why your manufacturer keeps asking for "corrected Gerbers" — this guide breaks it all down.
Gerber is an open standard (RS-274X and the newer X2) that describes each physical layer of a PCB as a 2D image. Think of it as a set of transparent overlays — one for copper traces, one for silkscreen, one for soldermask, one for drill holes. Stack them all together and you have a complete manufacturing blueprint.
Your EDA tool (KiCad, Altium, Eagle, OrCAD) generates these files from your PCB layout. The manufacturer's CAM software reads them to create the photolithography masks, drill programs, and inspection routines.
| Extension | Layer | What It Contains |
|---|---|---|
.gtl / .F_Cu.gbr | Front Copper | All traces, pads, and copper fills on the top layer |
.gbl / .B_Cu.gbr | Back Copper | All traces, pads, and copper fills on the bottom layer |
.gts / .F_Mask.gbr | Front Soldermask | Areas where soldermask is REMOVED (exposed copper) |
.gbs / .B_Mask.gbr | Back Soldermask | Areas where soldermask is REMOVED on back |
.gto / .F_Silk.gbr | Front Silkscreen | Text, logos, component outlines on top |
.gbo / .B_Silk.gbr | Back Silkscreen | Text and graphics on bottom |
.gtp / .F_Paste.gbr | Front Paste | Stencil openings for solder paste (SMT assembly only) |
.gbp / .B_Paste.gbr | Back Paste | Stencil openings for back-side SMT |
.gko / .Edge_Cuts.gbr | Board Outline | The physical shape of the PCB — dimensions and cutouts |
.drl | Drill File | Hole positions, sizes, and whether they're plated (PTH) or non-plated (NPTH) |
.gbrjob | Job File | Metadata — layer stackup, board size, materials (X2 format) |
Older tools use the 3-letter extensions (.gtl, .gbl). KiCad 6+ and modern tools use descriptive names (.F_Cu.gbr, .B_Cu.gbr). Both are valid Gerber — the manufacturer's CAM handles either. Just be consistent within a single export.
Before you send Gerbers to any manufacturer, verify these items. Most delays and quality issues come from mistakes in this list.
Open the Edge_Cuts file in a Gerber viewer. The outline must be a closed polygon with no gaps. A 1μm gap means the manufacturer can't define the board boundary. Use "measure" tools to check corners meet exactly.
For a 2-layer board, you need minimum: F_Cu, B_Cu, F_Mask, B_Mask, F_Silk, B_Silk, Edge_Cuts, and drill files. Missing a silkscreen layer isn't critical. Missing a copper layer is. Missing the board outline means they literally can't cut your board.
Two formats exist: Excellon (most common) and Gerber X2 drill. Check that:
Minimum 0.2mm (8mil) from any copper feature to the board edge. Closer than that and the routing bit may cut into traces. For cost reduction, 0.3mm is safer.
Check for narrow strips of soldermask between pads. If the gap is less than 0.1mm, the mask will peel during manufacturing. Your DRC should catch this, but visual inspection in a Gerber viewer catches what DRC misses.
Designing in mm but exporting drill files in inches (or vice versa). The board comes back 25.4x the wrong size. Always verify drill file units before sending.
If you're ordering assembly (PCBA), you need paste layers (.gtp/.gbp). Without them, the stencil can't be cut and SMT placement can't happen. Many designers forget these because they only focus on fabrication layers.
Sometimes the back copper layer gets mirrored in export. Check that back-layer pads align with front-layer pads when overlaid. Misaligned layers = boards that can't be assembled.
Older tools sometimes generate duplicate aperture codes. Modern CAM software handles this, but it can cause warnings that slow down your order. Run your Gerbers through a viewer first.
The router bit is typically 2-3mm wide. If your traces are within 0.2mm of the edge, there's a real chance they get cut. Move critical traces inward.
When we receive Gerbers, here's our internal checklist:
If all checks pass, we can have your board in production within hours. If something fails, we'll send you a DRC report with exact coordinates so you can fix it fast.
Not sure if your Gerbers are correct? Send us the ZIP — we'll run a full DRC and tell you exactly what needs fixing before production. No charge, no obligation.
💬 Send Gerbers via WhatsAppOr email: jsdg@mayio.cloud