What is the Accepted format of a PCB file During Manufacturing?

When designing printed circuit boards (PCBs), it is important to understand the file formats that PCB manufacturers accept. Choosing the right file format ensures proper communication of the PCB design data and avoids errors or delays during manufacturing. The most commonly accepted PCB file formats are gerber, DXF, and ODB++. Understanding when and how to use each format is key for a smooth PCB fabrication process.

Gerber File Format

Gerber is the most universally accepted file format in PCB manufacturing. It was developed by Gerber Systems Corporation and has been adopted as a standard across the industry. Gerber files use vector graphics to represent different layers and features of a PCB design.

Here are some key things to know about the Gerber file format:

• Vector Graphic: Gerber files use vector graphics to represent pads, tracks, holes, etc. as geometric shapes rather than bitmaps. This allows lossless scaling without affecting image quality.
• Layers: A Gerber file represents a single layer, such as copper, solder mask, silkscreen, etc. A complete set of Gerber files is required to fully convey the PCB design.
• Extensions: Standard Gerber file extensions are .GBR, .GTL, .GTO, .GTP, .GTS, .GM1, etc. indicating different layer types.
• Versatility: Gerber can represent various PCB features - conductors, apertures, regions, cutouts, etc. Limited only by the capabilities of the design software used.
• Ubiquity: Gerber is recognized by all PCB manufacturers and assembly houses globally. It has been the standard since the 1980s.

Gerber files can be generated from all major PCB design software packages like Altium, Eagle, OrCAD, KiCad, etc. Overall, the Gerber format provides an efficient and reliable means of transferring PCB design data to manufacturers.

DXF File Format

DXF stands for Drawing Exchange Format. It was originally developed by Autodesk for CAD software data interoperability. DXF has since been adopted for PCB design file transfer as well.

Here are some key details about the DXF file format:

• ASCII or Binary: DXF files can be saved as ASCII text or Binary data. Binary files are smaller but ASCII offers more compatibility.
• Vector Data: Like Gerber, DXF represents designs as geometric vectors rather than bitmaps. This allows for clean scaling.
• Layers: DXF does not inherently support layers. Additional coding is required to convey layers.
• PCB Objects: DXF can represent pads, tracks, holes, outlines, etc. Limited only by software capabilities.
• Extensions: .DXF is the standard extension for DXF files.
• Advantages: DXF offers better representation of drilled holes. It can also represent testpoints, annotations, etc.
• Disadvantages: Lack of native layer support. Large file sizes compared to Gerber.

While DXF offers some advantages, Gerber remains the primary format for PCB fabrication data exchange. DXF is acceptable but best used alongside Gerber files rather than as a standalone format.

ODB++ File Format

ODB++ (or ODB+) is a relatively new standard for exchanging PCB design data. It was developed by a consortium of major PCB software and manufacturing companies in the early 2000s.

Here are some key things to know about ODB++ format:

• Zip Archive: ODB++ files use the .ZIP format. An ODB++ file contains multiple XML files representing the PCB data.
• XML Data: ODB++ uses Extensible Markup Language (XML) to store PCB objects like pads, tracks, etc.
• Native Layers: ODB++ fully supports layers without additional coding needed.
• Rich Feature Set: ODB++ can represent a very extensive range of PCB features - from basic tracks/pads to complex cutouts, plane layers, etc.
• Single File: ODB++ combines the entire board layout into a single .zip file instead of separate layer-based files.
• Compressed Size: Due to XML data and compression, ODB++ files are significantly smaller than Gerber or DXF files.
• Limited Support: While growing, ODB++ has not yet been universally adopted across the PCB industry. Most manufacturers accept it, but not all assembly houses.

The ODB++ format offers size and feature advantages but Gerber remains more widely supported. ODB++ is best used in conjunction with Gerber data for compatibility.

Summary of Key File Formats

Here is a summary comparison of the three main PCB file formats for manufacturing:

Choosing the Right File Format

So which file format should you use? Here are some guidelines:

• For standard PCB fabrication, provide Gerber files as a baseline since they are universally supported.
• Include DXF files if your design has complex holes or cutouts that are better represented in DXF.
• Use ODB++ files as a supplementary format for enhanced data exchange, but not as standalone.
• For advanced PCB technologies like HDI or rigorously controlled impedance, ODB++ provides the most design detail.
• Provide data in both Gerber and ODB++ formats when working with strict tolerances or high-complexity boards.
• Always check with your manufacturer about their preferred file formats. Some may require specific formats.

Overall, the Gerber format remains the standard for reliability while ODB++ offers emerging advantages. Using both in combination provides the ideal solution.

Creating Manufacturing Files with PCB Design Software

All major PCB design applications allow generating manufacturing-ready files from completed designs. Here is an overview:

Altium Designer

• Gerber and ODB++ generation supported
• CAM (Computer Aided Manufacturing) editor to create output jobs
• Layer stack manager tocontrol file outputs
• Generate files directly from PCB editor

Eagle

• CAM processor to configure and generate Gerber and drilling files
• Dialog boxes to select layers for inclusion
• CAM jobs can be saved for reuse
• EPS, PDF, SVG exports also possible

KiCad

• In-built Gerber and drilling file generation
• Layer selector matrix to control outputs
• GUI plot dialog to configure file saving
• Can load custom Gerber settings files
• PDF and DXF exports also possible

OrCAD Allegro

• Manufacturing Tool to generate Gerber and drilling data
• Dialog selection of layers, features for output
• Interactive preview of artwork layers
• Reusable output configurations can be saved
• NC Drill support for drill files

Pads PCB

• Gerber and Excellon drill file generation
• Customizable with user-created output templates
• Dialog-driven plot interface
• Settings to control aperture handling and file splits
• Additional PDF, TIFF, DXF exports available

The specific steps vary across different software tools, but all provide streamlined interfaces to produce industry-standard PCB manufacturing files.

Handling Gerber Data

Since Gerber files are the most crucial output data, it is important to check them thoroughly before submitting to PCB fabrication. Here are some key points on handling Gerber data:

Layer Organization

• Ensure all required layers like copper layers, drill layers, solder mask, silkscreen, etc. are generated
• Verify layer naming conventions match industry standards
• Cross-check layer counts between PCB software and Gerber viewer

Data Completeness

• No gaps or missing data on the layers
• All relevant PCB features like pads, tracks, outlines, holes, etc. are defined
• Critical items like fiducials, vias, and holes are rendered

Polarity

• Dark areas correspond to copper features, clear areas represent substrate
• Polarity matches between layers, especially copper and solder mask
• No unintended polarity inversions are present

File Precision

• Coordinate and aperture precision is 0.001mm or better
• Decimal precision settings optimized for manufacturing
• No unintended rounding or loss of critical data

Image Quality

• Clean vector lines with no jaggies or raster effects
• Pad shapes and hole diameters are consistent
• Lines and spaces conform to manufacturing limits

Thoroughly vetting Gerber files using CAM software viewers and validation tools ensures your PCB data is accurate for fabrication. This prevents errors or ambiguities during manufacturing.

Conclusion

Understanding PCB file formats for manufacturing ensures the design data is smoothly transferred for fabrication and assembly. The universal standard remains Gerber, enhanced by emerging formats like ODB++. Using vector-based, layer-oriented data allows PCB designs to be reliably manufactured. Checking for completeness, polarity, precision, and quality in Gerber files verifies manufacturing-readiness. With the right file preparation, PCB designers can feel confident their boards will progress seamlessly from design into production.

Frequently Asked Questions

What are the main differences between Gerber and ODB++ formats?

The main differences are:

• Gerber uses individual files per layer while ODB++ combines all data into a single zip archive.
• Gerber relies on vector graphics while ODB++ uses XML data formats.
• ODB++ compresses the data while Gerber does not use compression.
• ODB++ fully supports PCB features while Gerber has limited capabilities.

Can I send Gerber files directly for PCB assembly?

Gerber files contain only fabrication data for PCB layers. They do not include assembly information like component placement, centroids, rotations, or bill of materials (BoM) data. For assembly, additional files like pick-and-place data, component libraries, and BoM are required alongside Gerber files.

What is the best file format for HDI PCB manufacturing?

For advanced PCB technologies like high-density interconnect (HDI), the ODB++ format provides the most detailed representation of the design. This allows more precise control over features like laser-drilled microvias. However, Gerber files are still recommended as a baseline for universal compatibility.

How do I convert Gerber data to PDF or image formats?

While Gerber files are designed for manufacturing, they can be converted to PDF or image formats like PNG for documentation purposes. This is done using free or paid CAM viewer tools which render the Gerber layers into graphical formats. Some PCB design software also allows direct Gerber to PDF conversion.

Can I directly import Gerber files into a PCB design tool?

Most PCB design tools do not support direct import of manufacturing Gerber data into an editable layout. Instead, they rely on proprietary native file formats for designing. However, there are tools like Eagle's retrofit feature that can import Gerber data for reference or validation.