Gerber File Preparation Guide for Small-Batch PCBs

Preparing accurate Gerber files is one of the most critical steps in getting a PCB designed, manufactured and assembled in the UK. Your Gerber files affect the turnaround time, costs, and final quality of your printed circuit boards. A complete and easy-to-read Gerber package allows your manufacturer to begin production right away, minimises communications back and forth, and prevents time-consuming and expensive mistakes.

In this article, we cover everything you need to prepare Gerber files for small-batch PCB fabrication and assembly in a step-by-step process.

What Are Gerber Files?

Gerber files are the industry-standard file format used to describe the copper traces, pads, soldermask, silkscreen, and other features of your printed circuit board. Think of Gerber files as the “blueprint” of your PCB. Every PCB manufacturer uses Gerber files to set up the CAM (Computer-Aided Manufacturing) process and create your boards as designed.

Gerber files are sometimes also referred to as Ger-X, RS-274X or GCDS files depending on the particular flavour of the Gerber format used.

For assembly, Gerber files are often accompanied by an assembly drill file, pick-and-place file (also called centroid file), and Bill of Materials (BOM). Pick-and-place and drill files contain X/Y locations and rotation information. The BOM lists component values, packages and manufacturer part numbers. In combination, all these files allow a PCB fabricator and assembler to build and populate your circuit board without guesswork.

Choose the Right Gerber Format

Most PCB manufacturers can work with the RS-274X format, the standard format for Gerber files. If your CAD software also supports the Gerber X2 format, that is even better. X2 files contain additional layer attributes. A manufacturer can use these to automatically determine layer roles and, for example, avoid stacking errors during assembly.

Make sure your files contain embedded aperture data so there is no ambiguity. Files with aperture definitions are also easier to process.

Include All Essential Layers

Your Gerber package should include all essential layers so the manufacturer can fabricate and assemble the board without having to request missing information. For a two-layer board, that usually means including:

• Top copper layer
• Bottom copper layer
• Top and bottom soldermask layers
• Top and bottom silkscreen (legend) layers
• Board outline or mechanical layer
• Drill file containing holes and vias
• Solder paste layers (top and bottom) if you need stencils for SMD assembly

If you are having the board assembled, you must also provide:

• Pick-and-place (centroid) file with component locations, rotations, and side information
• Bill of Materials (BOM) listing component reference designators, values, packages, and manufacturer part numbers

These extra files allow your assembler to place components on the correct side and order the correct parts for your board.

Recommended File Naming Convention

Using a consistent naming convention for your Gerber files and assembly-related data is helpful to avoid confusion and speed up the manufacturer’s CAM setup. We recommend the following convention:

• ProjectName_GTL.gbr – Top copper
• ProjectName_GBL.gbr – Bottom copper
• ProjectName_GTS.gbr – Top soldermask
• ProjectName_GBS.gbr – Bottom soldermask
• ProjectName_GTO.gbr – Top silkscreen
• ProjectName_GBO.gbr – Bottom silkscreen
• ProjectName.drl – Drill file

Finally, put all files into a single ZIP archive before sending them to your manufacturer.

Export Settings and Design Checks

The following settings are worth double-checking when you export your Gerber file.

• Units – Millimetres are used in most of Europe and the UK. Only if your manufacturer specifically asks you to do so, use inches.
• Coordinate format – The standard format, as recommended by your CAD tool
• Polarity – Make sure copper is set to positive image so pads and traces appear as copper-filled features
• Annular rings and trace widths – Match your manufacturer’s minimum design rules for the selected small-batch production technology
• Soldermask and silkscreen clearances – Make sure text of the silkscreen layer does not overlap pads

Finally, before sending your Gerber files to the manufacturer, open the generated files in a Gerber viewer and check that they look as expected. It is often easy to spot problems like mirrored layers, missing drills or other errors like wrong polarity before the board is fabricated.

Panelisation of Small Boards

If your board is very small, you might need to panelise it. Panelisation is the process of printing multiple copies of your PCB on a single production panel.

You can either design your own panel or ask your manufacturer to panelise your board for you. If you design the panel yourself, here are a few guidelines to keep in mind:

• Use V-scoring or tab-routing for easy breakout
• Leave at least 0.4 mm of copper between the V-cut line and any copper features
• Add tooling holes and make sure no components overlap the breakaway tabs

For small batch production, it is often easier and cheaper to let your manufacturer panelise your board according to their standard panel size.

Fiducials and Board Orientation

If you are getting your PCBs assembled, make sure to include fiducials on your PCB. Fiducials are small copper pads that help the pick-and-place machines to accurately locate the board. Place at least two fiducials, ideally three global fiducials, on the top side of your board in a triangular arrangement.

Also, make sure you clearly indicate pin 1 of ICs and connectors on the silkscreen or copper layer, so assembly errors are avoided.

Pick-and-Place and BOM Files

The pick-and-place (centroid) file you provide to your assembler must include the following information:

• Reference designator
• X and Y coordinates
• Rotation
• Component side (top or bottom)

The format and information in your BOM (Bill of Materials) file is critical to your assembler being able to source the right parts and give you an accurate quote. Provide your BOM in a clean, structured format (CSV or Excel) that lists the value, package, and manufacturer part numbers of all components.

Final Checklist Before Sending Files

Use this checklist before you send your files:

• All copper, mask, silkscreen, outline and drill layers are included
• Solder paste layers are included (if stencils will be used during assembly)
• Pick-and-place and BOM are attached if the board is going to be assembled
• README file that includes board thickness, material, finish and other special instructions
• Files are zipped into a single archive
• Files have been verified in a Gerber viewer and passed DRC checks

Following this checklist ensures a smooth production run with no unnecessary delays.

Why This Matters for Small-Batch PCBs

The main benefit of following this guide and preparing your Gerber files properly for small-batch PCB manufacturing is that it shortens the time from design to production. If you are ordering a small batch of PCBs, any delay often results in time and money being wasted. Missing or incorrect files often mean your manufacturer has to pause production and ask you for clarification, which adds days to your turnaround time.

On the other hand, good quality Gerber file make it easy for your UK PCB manufacturer to get started right away, produce high-quality boards, and keep costs predictable.

Need Expert Help with Your Gerber and Assembly Files?

Preparing Gerber and assembly files can be challenging, especially if you are new to PCB design or using a new CAD tool. PCB COMPANY UK helps engineers, makers and businesses prepare their Gerber and assembly files correctly the first time. We provide PCB design checks and prototype manufacturing as well as full PCB assembly services for small batches.

If you are looking for expert assistance, contact PCB COMPANY UK today – we will review your Gerber file for free and help you go from design to production with confidence.