How does Gerber Format File Work?

2019-12-02 17:31Writer: qyadminReading:

PCB gerber backup

      The EAGLE Schematic/PCB editor keeps up to 10 backups of your board and schematics. reflecting the board start at the last times you saved you work.  This can be very valuable if you screw something up, but I've always been a bit frustrated. that it isn't easier to look at those files to see what changed in which revision.  (EAGLE won't  open the backup files, so you have to rename each backup before you can look at it.  And EAGLE won't open many files at one time, so that you can compare them side-by-side, either.) Now, one way to look at a PCB is to generate gerbers (the standard "plotter format" for PCBs). and use one of the gerber viewers to look at those. 

       This has the advantage of simplifying the "picture".  AND most gerber viewers will load up many layers of a PCB so that you can see them all together.  I realized that it would also let you display many copies of the same layer, so that you could "flip" through them. and notice changes.  In fact, the gerber viewer I use (gerbv, an open-source utility that runs on Windows, Macs, and Linuxes). has a display mode where the layer  displayed with their colors XORed together.  (In theory, this is an option to allow you to look at many layers at once. although in reality how well it works depends on the actual bit patterns of the colors used for each layer.)

       But, if you DO pick your layer colors , you can display two (or more) layers that are almost the same. and have the differences. HIGHLIGHTED for you!  This seemed close to ideal for visualizing the changes in a PCB design.  Well, for small changes, anyway.  We'll have to see how the community feels about its usefulness. All it needed was some sort of script that would go through all the backup files. generate appropriate gerber files. and then load up the gerber viewer having given each file an appropriate set of color, color mixing mode. and other display parameters.  It seems to be somewhat useful.

PCB Manufacturing and Gerber Files

          A Gerber PCB file  encoded. and compressed with specifications used by software developed for creating. and editing Printed Circuit Board (PCB) designs and layouts. and this file  classified as a CAD file. while these PCB design applications  categorized as CAD software. As the name suggests, a Gerber PCB file  integrated with Gerber CAD encoding. and compression standards. "CAD" in CAD software stands for Computer-Aided Design. and these Gerber PCB files  saved in the GBX format and  affixed with the .gbx extension.

         Certain Computer Aided Manufacturing applications use these GBX files. for its project output files. These CAD and CAM programs. can also  used to simulate certain functionalities.  implemented into a GBX design layout project. by the author of the GBX file. The PentaLogix ViewMate software can  used to open and view the content of these GBX files. and the data stored in a GBX file includes digital 3D objects and images.  numerical and statistical data, formatting. and layout design elements among other metadata info. corresponding to a particular GBX project.

         Launch a .gbx file, or any other file on your PC, by double-clicking it. If your file associations are set up. the application that's meant to open your .gbx file will open it. It's possible you may need to download obuyse the correct application. It's also possible that you have the correct application on your PC. but .gbx files aren't yet associated with it. In this case, when you try to open a .gbx file, you can tell Windows which application is the correct one for that file. From then on, opening a  .gbx file will open the correct application.

     So how are Gerber files used in PCB manufacturing? In the subtractive method of PCB manufacture. the PCB starts as a sheet of substrate materialencased in copper on one or both sides. Gerber files used to provide a picture of where the PCB copper should remain at the end of the process. 
Gerber Format File

   The picture is then used to guide the creation of channels to remove copper from the board to leave. only the conductive traces used by the actual PCB. The standard convention is to use clear markings for areas. with no copper and black markings for the actual copper traces. But it doesn't stop there. Once the copper traces marked out, layers like the solder mask and silkscreen cover them. The Gerber file will also have pictures for these other layers. representations of locations of the board's drill holes. and even a designation of the board's size.
  Since Gerber files contain so much info, PCB Houses get up to 9 files - although they're making a two-layer PCB. Examples include:
• The copper traces for the top of the circuit board
  • The copper traces for the underside of the circuit board
  • A picture of the solder mask for the top layer
  • A picture of the solder mask for the bottom layer
  • Silkscreen imaging for the top layer
  • Silkscreen imaging for the bottom layer
  • The coordinates of all drill holes, as well as their properties
  • An outline of the physical board. with all the machining operations marked out, such as scoring. slots and internal cutouts
  • A simple text README file explaining the uses for all files
  Post-Design Process for Gerber Files
Many software applications lead to different methods to create Gerber files. including Cadence and Altium Designer. After design, a photoplotter transfers the Gerber to the PCB. The photoplotter prints out each of the files on one piece of film.
  Each PCB layer and the accompanying solder mask gets its own sheet. so a simple two-layer PCB needs a minimum of four sheets of film - one each for the top and bottom trace layers. and one each for the accompanying layers of solder mask.
  After printing, the photoplotter punches a "registration hole" through the lined-up films. The registration hole used as a guide to align the pieces of film onto the copper and substrate layers. so the film covers the substrate panel.
  A photo-sensitive film consisting of a layer of ultraviolet-hardened chemicals. then covers the PCB blueprint. Known as a "resist," this film. allows the PCB manufacturer to receive a perfect match for the photos on the Gerber file.
  Once the resist and the layer of substrate. have lined up using the registration holes from earlier. they receive a blast of ultraviolet light that passes. through the translucent parts of the film. hardening the photo resist. This indicates areas of copper trace that meant to remain as pathways. In contrast, the black ink prevents any light from getting to the areas that shouldn't harden. so they can later removed.
  This process repeats for each layer. including the solder mask layers and the silkscreen layers. When it comes to designing a Gerber file and transferring to a PCB. there are two considerations designers need to consider.
  1. Legacy Issues
Gerber file format used to drive controlled photoplotters. Today's PCB printers. are much more in line with a modern laser printer - something the Gerber file format wasn't built to handle. which causes issues when the files  used with current raster plotters to print PCBs:
  • Hole data can be absent. because the original photoplotters used for PCB manufacture didn't drill holes. Excellon numerical control files can used to augment the Gerber data. but even this is incomplete - it doesn't differentiate between through, blind. or buried holes. Technicians reading the data also have no idea whether they are offset. or using the correct scale.
  • No functional definition or mapping of the files. Nothing in the Gerber file itself tells the CAM technician whether it's a top, bottom or mirrored file. This is why most current Gerber files include a README.
  2. Design for Manufacture (DFM) Issues
Gerber files contain no way to read the "intent" of the PCB. There are also no protections against a PCB designer. building a PCB that is difficult or even impossible to create. One of the most common errors that PCB technicians need to watch out for is missing files. but other errors include:
  • Putting silkscreen onto the PCB pads
  • Putting features of the PCB too close to the outline of the PCB
  • Drilling holes twice, making them large 
PCB gerber backup 

   As long as designers and technicians recognize these. and other issues, the Gerber file format can. and will used for PCB design and manufacture well into the future.
  PCBCart features a smart DFM check system that is capable of implementing DFM. check on standard designs as long as PCB design file is input. which plays a crucial role in efficiency and accuracy improvement. Furthermore, the DFM check provided by us is free! 

How to use Gerber files 

     Gerber files are the industry’s preferred file format. for manufacturing printed circuit boards.  Most PCB design software has the ability to output. the design data in Gerber format to represent a design’s copper layer images, solder mask, legend. and drill and route data .  But, in the output process. it can be easy to  exclude important data required for manufacturing. or output data that contains design rule violations. such as insufficient solder mask clearance or deficient silkscreen line width.
      Advanced Circuits’ online tool, FreeDFM. offers a quick. and easy way to check your Gerber files. before submitting your order for manufacturing.  The free tool ensures. that all  the design rules  satisfied and all required data  included in your Gerber files.  Checking your files can save you time by avoiding CAM holds after your order has  placed and it can save you money. making sure your printed circuit boards  produced exactly as intended the first time.
      To use Advanced Circuits’ FreeDFM software. make sure that your Gerber files  placed in a single folder. and compressed as a .Zip.  Upload your .Zip file to FreeDFM. and provide the email address . where you would like to receive the detailed report. identifying any possible issues found.
     Next, our FreeDFM software will  identify the files. based on the standard naming conventions of most EDA software packages.  You may also  identify any of the files if the system was not able to match the file extension.  Click here to view a list of the most common Gerber file extensions file naming conventions.
     Once you submit your file. Advanced Circuits’ FreeDFM software will perform the automated checks for your PCB design. and send a detailed report outlining. any possible manufacturability issues found in your Gerber files.  The report  sent  to your inbox within minutes. and it will contain the location and description of the issues along. with a discount code for up to $100 off your next PCB fabrication order.

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