What Are Gerber Files, and Why Should PCB Designers Use Them?
Printed circuit board (PCB) designers are tasked with creating innovative, functional, and efficient designs for boards to be utilized in a myriad number of products. Some may be very basic designs such as for simple appliances or standard calculators, while others may be significant technological masterpieces that become part of rocket guidance systems, automotive controls, or leading-edge smartphone components.
Whatever the PCB design project, the end result of the design phase is most often a series of Gerber files, that will be utilized by the manufacturer of the board to actually complete the fabrication. Those Gerber files must be complete and accurate to enable the board providers to manufacture boards that perform as the designer intended without failures or design flaws. These problems could result in the inability to fabricate the board without going back to the designer with questions or to work out basic design problems.
Gerber files are the ‘gold standard’ in PCB design for passing manufacturing information details to the fabricator of the boards. Multiple Gerber files are typically required for a single PCB, with separate files for describing individual board layers, silkscreen details, and much more.
Problems with Gerber Files
Once PCB design is completed and Gerber files have been generated for the manufacturer, there are a number of potential problems inherent in the process:
Missing files – CAD programs are not all created equal. Some create individual files for every type of data and every board layer. It is the designer’s responsibility to ensure that every file needed to manufacture the board to design specifications is prepared for the manufacturer. Not only does the designer need to make sure all files needed for fabrication are provided, it has been known to happen that designers neglect to send Gerber files at all. Be sure to supply manufacturers with the full complement of files needed to produce the boards successfully.
Zero byte files – Gerber files could be created that do not contain the information needed for fabrication. This is easily checked by the designer through validating the file sizes in the file directory. Zero-length files are a give-away that something is missing from the creation of the Gerber files.
Formats – Gerber files can be generated in 274D and 274X formats. The preferred format is 274X as it includes embedded aperture information within the file contents. 274D requires a manual step by the fabricator to enter aperture information, creating an opportunity for errors in manufacturing.
File labeling – incomplete or confusing file naming can generate confusion for the manufacturer, resulting in production delays or even mistakes in the board produced. This can be costly and time-consuming. Detailed labeling can avoid such confusion and delays.
Missing aperture lists – when 274X format is utilized the aperture information is contained within the Gerber files. But using 274D requires that the designer supply aperture list information in order for the manufacturer to understand the designer’s specifications.
Missing Excellon drill file or tool list – this information is critical to the fabricator to understand where the PCB holes should be placed, sizes of the holes, and specifically what tool should be used to drill them. Tool information can be included within the drill file, but could also be provided on a separate file. Providing this information eliminates the need for guesswork, manual entry, or delays in manufacturing.
Inner clearances that are not sufficient – providing sufficient clearances can help ensure that drilling will not will not cause shorts to inner copper layers of the board by exceeding the minimum clearance between a drill hole and the adjacent inner layer copper.
Not designing for manufacturing – the most creative and technically innovative PCB design is of no use if it cannot be manufactured. Consideration for fabrication techniques and capabilities is an integral part of successful PCB design.
Avoiding Gerber File Problems
There are a number of steps PCB design individuals and firms can take to avoid or at least minimize problems with Gerber files:
- Document and implement best practices that include checking for file lengths, completeness of information being sent to fabricators, and any documentation the supplier requires. Peer reviews are useful in catching some problems or omissions, as well.
- Utilize sophisticated computer aided design (CAD) software in the design process. This will catch any obvious errors in design even before the Gerber files are created.
- Validate files with a Gerber file viewer. This allows the designer to validate the actual size of the final board, check pin outs to verify pin orderings, and even print the board to scale for size confirmation.
- CAD software – utilize up-to-date software that provides at least basic analysis of the design before creating Gerber files for fabrication.
- PCB layout – software is available at economical prices (even at no charge) that is specifically designed for printed circuit board design. Such tools streamline layout design and help avoid errors in manufacturing.
- Design for Manufacturing (DFM) – DFM tools can help PCB designers ensure that their designs will be compatible with computer aided manufacturing (CAM) software utilized in the actual fabrication of the boards.
Streamlining the PCB Creation Process
By combining the use of design best practices and self-checks of Gerber files before sending them to manufacturers, designers can speed the process and avoid many delays. By implementing sophisticated tools such as CAD, PCB layout software, and DFM products, designers greatly reduce the potential for manufacturing errors and delays.