In PCB (Printed Circuit Board) production, output files serve as the crucial link between design and manufacturing. These files contain all the necessary information for manufacturing, from the layout and electrical connections to hole placements, trace thicknesses, and other critical data. Without these standardized output files, PCB manufacturing cannot proceed smoothly.
This article will provide a comprehensive overview of three key PCB manufacturing output file formats—Gerber, ODB++, and Excellon. We will explore their structures, advantages, and limitations to help designers choose the most suitable format for their projects and avoid common pitfalls during production.
Gerber File Format
The History and Evolution of Gerber Files
Gerber is one of the most widely used PCB manufacturing standards, originating in the 1970s. The format was named after Gerber Scientific, the company that first developed it to streamline the manufacturing process. Gerber files are primarily used to describe the graphical data of the PCB, such as traces, pads, silkscreen layers, and more.
Basic Structure and Content of Gerber Files
A Gerber file consists of vector data and command codes that describe the layout of each layer in the PCB design. The most common Gerber format is RS-274X, which contains vectorized graphics, including traces, pads, and drill hole information. Typically, Gerber files are accompanied by a drill file (Excellon) to ensure the accurate placement of holes in the PCB.
Common Gerber File Extensions and Applications
Gerber files typically use the extensions *.gbr or *.ger, and they come in various types, including:
Copper Layers: Top (T), Bottom (B)
Solder Mask Layers: Top Mask (TSM), Bottom Mask (BSM)
Silkscreen Layers: Top Silkscreen (TSK), Bottom Silkscreen (BSK)
Drill Files: Contain hole data for mechanical processing
How to Generate and View Gerber Files
Gerber files can be generated using PCB design software such as Altium Designer, KiCad, or Eagle. Designers need to ensure that the generated Gerber files conform to the manufacturer’s specifications. To verify the accuracy of these files, Gerber viewers such as GerberLogix or ViewMate can be used.
Advantages and Disadvantages of Gerber Files
Advantages:
Widely supported and compatible with most PCB manufacturers.
Simple and straightforward, ideal for traditional PCB manufacturing processes.
Disadvantages:
Can result in large file sizes due to redundancy.
Lacks 3D data support and is limited to 2D graphics, making it less suitable for complex designs.
ODB++ File Format
The Background and Evolution of ODB++
ODB++ is a newer PCB output format developed by Mentor Graphics (now part of Siemens). Unlike Gerber, ODB++ offers more comprehensive data and is designed to better support the needs of modern, complex PCB designs, especially those used in high-frequency or multi-layer applications.
Structure and Components of ODB++ Files
ODB++ files contain a full range of manufacturing data, including layer definitions, material specifications, soldering process information, impedance control, and component placements. This integrated format provides a single file that can hold all the necessary information for manufacturing, which simplifies communication between designers and manufacturers.
Differences Between ODB++ and Gerber
While Gerber files are focused on 2D graphical data, ODB++ is a more comprehensive format that includes multiple layers, 3D data, assembly information, and other manufacturing details. ODB++ is a “single file” format, unlike Gerber, which uses multiple files to represent different aspects of the design.
The Advantages of ODB++ in Modern PCB Manufacturing
ODB++ can accommodate more detailed information, reducing errors and inconsistencies during the manufacturing process. Its higher level of automation allows it to integrate more effectively with CAM (Computer-Aided Manufacturing) systems, making it well-suited for complex and high-performance designs.
How to Generate and Use ODB++ Files
As with Gerber files, ODB++ files are generated through PCB design software. Designers must ensure that all design information is included and accurate. It is important to confirm with manufacturers whether they support ODB++ and which version is required.
Excellon File Format
The Definition and History of Excellon Files
Excellon files are a specialized format used to describe drill hole data in PCB manufacturing. Originally developed by the Excellon company, this format is now the industry standard for conveying drilling information, such as hole positions, sizes, and depths.
Structure and Content of Excellon Files
An Excellon file typically consists of a series of drill commands specifying the X and Y coordinates for each hole, along with the hole diameter and type (e.g., via holes, mounting holes). While Excellon files are critical for hole data, they do not include the graphical layout of the PCB, which is handled by Gerber files.
Comparing Excellon with Gerber and ODB++
Excellon files are used exclusively for hole data, while Gerber and ODB++ are used to describe the electrical layout and other features of the PCB. Excellon and Gerber are often used together, as Gerber files contain the electrical design, and Excellon files handle the hole drilling specifications.
The Role of Excellon Files in Drilling Data
Excellon files ensure that drill holes are precisely placed and sized according to the design requirements. This prevents drilling errors that could affect the performance or manufacturability of the PCB.
How to Generate Excellon Files
Most PCB design software can automatically generate Excellon files during the design process. Designers must ensure that hole sizes, hole types, and locations are accurately specified to prevent any discrepancies during manufacturing.
How to Choose the Right Output File Format
Choosing the File Format During the Design Stage
Selecting the right file format during the design phase is crucial. For simpler designs, Gerber may suffice, but for more complex multi-layer boards or designs requiring precise assembly data, ODB++ may be a better choice.
Manufacturer Requirements for File Formats
Different manufacturers may have specific requirements for the file formats they support. Designers should always check with their manufacturers to ensure compatibility and avoid potential issues during production.
Criteria for Choosing Between Gerber, ODB++, and Excellon
Choosing the right format depends on the complexity of the design, the manufacturer’s capabilities, and the specific requirements of the project. Gerber is ideal for standard designs, while ODB++ is better for high-performance, complex designs.
Making the Best Format Choice for Your PCB Project
A well-rounded approach involves considering design complexity, production requirements, and the manufacturer’s preferences. Understanding the strengths and weaknesses of each format will help you make an informed decision and avoid unnecessary delays in the production process.
File Format Conversion and Compatibility Issues
Converting Between Gerber and ODB++ Files
In some cases, designers may need to convert between Gerber and ODB++ files. While these formats differ in structure, conversion tools can help with this process, minimizing data loss and ensuring compatibility.
Common Issues in File Conversion and Solutions
Common issues during file conversion include data loss, misalignment of layers, and inconsistencies in the design. To mitigate these issues, designers should use trusted software for conversions and perform thorough validation of the resulting files.
Improving Output File Compatibility
To improve compatibility, designers should adhere to industry standards and avoid custom formats whenever possible. This ensures that files remain compatible across different platforms and with various manufacturers.
Verifying and Checking Output Files
Quality Checking Output Files
Before sending output files to the manufacturer, designers should conduct thorough checks. Tools like GerberLogix, ViewMate, or CAM350 can help verify the files to ensure no errors are present.
Verifying File Content and Data Integrity
It’s essential to confirm that all layers, drill holes, and other design elements are correctly represented in the output files. Missing or incorrect data can result in manufacturing delays or errors.
Common Output File Verification Tools
Popular verification tools include GerberLogix, ViewMate, ZofzPCB, and others, which help check for issues like layer misalignment, missing drill holes, or incorrect file formatting.
Future Trends: Evolution of PCB Output File Formats
The Impact of Emerging Technologies on Output File Formats
As technologies like AI and automation continue to advance, PCB design and manufacturing output files may evolve to incorporate more sophisticated data, such as 3D design and real-time monitoring for quality control.
File Format Optimization in Automated and Smart Manufacturing
With the rise of automated PCB manufacturing, output files will need to become more standardized and optimized for faster, error-free production. Future advancements may focus on reducing the complexity and size of files while improving their accuracy.
Future Standards: How They Will Influence Output File Format Choices
Emerging standards may address the limitations of current file formats, such as 3D data support, file compression, and enhanced compatibility between design and manufacturing software.
Conclusion
Summary: Key Differences Between Gerber, ODB++, and Excellon
Each output file format—Gerber, ODB++, and Excellon—has its own advantages and use cases. Gerber is suitable for simpler designs, ODB++ excels in more complex, multi-layer applications, and Excellon focuses on drill data.
Best Practices for Choosing PCB Output File Formats
The key to successful PCB production is understanding the strengths and limitations of each file format and choosing the one that best aligns with your design complexity, manufacturer requirements, and project specifications. Adhering to best practices in file generation and verification will ensure smoother production and higher-quality PCBs.