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Role of Gerber File in PCB Manufacturing

What is a Gerber File?

A Gerber file is a standard file format used in the printed circuit board (PCB) industry to describe the printed circuit board images: copper layers, solder mask, legend, drill data, etc. It is the de facto standard used by PCB fabrication houses.^1

Gerber files are intermediate files between PCB design software and manufacturing machines. PCB designers export Gerber files from PCB CAD software and send these files to PCB manufacturers. The PCB manufacturers import the Gerber files into Computer-Aided Manufacturing (CAM) software to prepare data for each manufacturing stage.^1

A Gerber file contains 2D binary images of copper layers, solder mask, legend, etc. Each Gerber file corresponds to one image.^1

History of Gerber Format

The Gerber format was originally introduced by Gerber Systems Corp., a division of Gerber Scientific, founded by Joseph Gerber.^2 The Gerber file format has evolved over the years:

Year Format Version Description
1980 Gerber X1 Vector based, limited aperture shapes
1998 Gerber RS-274X Extended version of X1, added custom apertures and attributes
2014 Gerber X2 Successor to RS-274X, added additional metadata ^1

Ucamco acquired the Gerber format from Gerber Scientific in 1998 and now manages the format.^2 In 2014, Ucamco introduced the Gerber X2 format, adding new capabilities and formally standardizing the format as IPC-2581.^3

Role of Gerber Files in PCB Manufacturing Process

Gerber files play a crucial role throughout the PCB manufacturing process. Here is an overview of how Gerber files are used in each step:

1. PCB Design

PCB designers create the schematic and PCB layout using Electronic Design Automation (EDA) or PCB CAD software. Once the design is complete, the designer exports Gerber files representing each layer of the PCB:

  • Copper layers
  • Solder mask
  • Silkscreen
  • Drill data

The number of Gerber files depends on the number of layers in the PCB. A simple double-sided PCB might have 5-6 Gerber files, while a complex multi-layer PCB could have 20 or more.^4

2. Gerber File Review

The PCB designer reviews the generated Gerber files using a Gerber viewer to check for any errors or discrepancies. Catching issues at this stage prevents problems later in manufacturing.

Some aspects to check in the Gerber review include:

  • Proper alignment of layers
  • Correct drill sizes and locations
  • Width of traces and spacing between features
  • Presence of all required files (one file for each layer)

3. Quoting and Planning

The PCB designer sends the Gerber files to the PCB manufacturer for fabrication. The manufacturer imports the Gerber files into their CAM software to assess the design and provide a quote.

Information obtained from the Gerber files used for quoting includes:

  • PCB dimensions
  • Number of layers
  • Drill sizes and counts
  • Smallest traces and spaces
  • Surface finishes
  • Special requirements

Based on the Gerber data, the manufacturer plans out:

  • Required materials
  • Equipment and processes to be used
  • Production schedule

4. CAM and Tooling

Once the order is placed, the manufacturer performs more in-depth planning and preparation using the Gerber files.

In Computer-Aided Manufacturing (CAM), the Gerber data is used with the manufacturer’s software to:

  • Perform design rule checks (DRC)
  • Prepare detailed instructions for machines
  • Program drilling and routing equipment
  • Generate photoplots and stencils
  • Panelize the design

Proper tooling is essential to avoid production issues and delays. Errors in the Gerber data can result in scrap and rework.

5. Fabrication

With the Gerber data prepared, the PCB fabrication process can begin. The data from the Gerber files drives the manufacturing machines.

Key fabrication steps using Gerber data:

Fabrication Step Gerber Data Used
Imaging Layer Gerbers
Etching Copper Gerbers
Solder Mask Mask Gerbers
Silkscreen Legend Gerbers
Drilling Drill Gerbers
Routing Outline Gerbers

The Gerber data must be accurate for proper alignment of layers, fully etched copper patterns, correct registration of soldermask and legend, and precise drilling of holes.

6. Quality Assurance

After fabrication, the manufactured PCBs are inspected to ensure they meet quality standards and match the design intent. Gerber files can assist with quality assurance.

Ways Gerber data is used in PCB Quality control:

  • Automated Optical Inspection (AOI) compares PCBs to Gerber data
  • Electrical test fixtures verify connections per the Gerber netlist
  • Gerber files provide a reference to check against for visual inspection

If issues are found, referring to the original Gerber data can help trace the source of the problem, whether it’s a design error, Gerber generation issue, or manufacturing defect.

Best Practices for Gerber Files in PCB Manufacturing

Following some best practices when working with Gerber files can help ensure a smooth and error-free PCB manufacturing process.

  1. Use the Latest Gerber Format

Whenever possible, use the latest Gerber X2 format which adds powerful capabilities and improves efficiency:
– Embedded netlist and component data
– Layer stackup information
– Windowing and offset support
– Better parity with CAD data^3

  1. Adhere to Manufacturer Specifications

Check the PCB manufacturer’s specifications and follow their recommendations for Gerber file generation, such as:
– Required file formats
– Naming conventions
– Minimum feature sizes
– Supported drill sizes
– Soldermask clearances

  1. Perform Design Rule Checks

Use the EDA software’s Design Rule Check (DRC) to verify the PCB layout meets manufacturing constraints before generating Gerber files. Catching and fixing errors early avoids delays.

  1. Review Gerber Files

Always review the generated Gerber files before sending them for manufacturing. Use a Gerber viewer to check for:
– Complete set of files
– Presence of all features
– Correct alignment of layers
– Proper drill sizes and locations

  1. Include Reference Designators

Include reference designator text in the silkscreen layer Gerber. This is helpful for assembly and testing. Ensure text size is legible.

  1. Provide Drill Files

Include NC drill files in addition to the Gerber drill layer. Provide separate plated and non-plated drill files if applicable.

  1. Use Standard Naming Conventions

Follow standard naming conventions for Gerber files, such as the suggested naming in IPC-356. This makes it clear which file represents each PCB layer.^5

– MyPCB.GTL – Top (outer) copper layer
– MyPCB.GBL – Bottom (outer) copper layer
– MyPCB.GTS – Top soldermask
– MyPCB.GBS – Bottom soldermask
– MyPCB.GTO – Top silkscreen (legend)
– MyPCB.GBO – Bottom silkscreen
– MyPCB.TXT – Drill file

  1. Communicate Special Requirements

If the PCB has any special or non-standard requirements, communicate those clearly to the manufacturer and include relevant notes in the Gerber files.

  1. Protect Intellectual Property

If there are intellectual property concerns, consider using Gerber X2’s ability to remove sensitive data from the original CAD file when exporting the Gerber files.^3

By implementing these practices, PCB designers can help optimize the PCB manufacturing process, minimizing errors, delays, and costs.


What is the difference between Gerber RS-274X and Gerber X2?

Gerber RS-274X is the extended version of the original Gerber format. It added support for custom apertures and attributes. Gerber X2 is the successor to RS-274X introduced in 2014. X2 further extends the format’s capabilities with layer stackup data, embedded netlists, design intent, and more.^3

Can Gerber files be 3D?

No, Gerber files are always 2D representations of the PCB layers and features. They do not contain 3D model data.^6

What is the difference between Gerber and ODB++ Formats?

Gerber is an open, ASCII vector image format for PCB manufacturing data. ODB++ is a proprietary, intelligent database format developed by Mentor Graphics. Both can convey PCB fabrication data, but ODB++ includes netlist, component, and test point information.^7

Are Gerber files required for PCB Assembly?

Gerber files are primarily used for PCB fabrication data. While some assemblers may request them, Gerber files alone do not contain all the information needed for assembly. Additional files like pick & place, BOM, and centroid are typically required.^4

What happens if there are errors in the Gerber files?

Errors in Gerber files can lead to manufacturing defects if they are not caught in time. Problems can include misaligned layers, incorrect features, drill errors, and more. If a design error is found, new Gerber files must be generated after fixing the issue in the CAD software.^4