After designing a printed circuit board, a contract manufacturer will create reliable PCBs based on the design. However, a CM needs more than just the raw materials to produce your boards; they also need a good recipe. That recipe is in the manufacturing documentation created; therefore, the documentation must be complete and accurate. The Gerber file is one of the most important documents created for this process, as it helps guide the bare board fabrication. To understand the process, consider these Gerber files explained from a historical perspective.
After designing a printed circuit board, a contract manufacturer will create reliable PCBs based on the design. However, a CM needs more than just the raw materials to produce your boards; they also need a good recipe. That recipe is in the manufacturing documentation created; therefore, the documentation must be complete and accurate. The Gerber file is one of the most important documents created for this process, as it helps guide the bare board fabrication. To understand the process, consider these Gerber files explained from a historical perspective.
| Gerber Files Explained: FAQ | |
|---|---|
| Q: What does Gerber fabrication data encompass?
Q: What is the viewing angle for Gerber files?
Q: Are Gerber files equivalent to drawings? |
A: Gerber data acts like a physical model for the PCB. The CAM team can compensate drawings to account for manufacturing deviations. Gerber data is also the basis for panelization.
A: The Gerber file viewing angle is always top-down (i.e., staring into the board from the top side). Never mirror or flip layers in Gerber artwork.
A: Gerber files have to incorporate additional data beyond the drawings, such as data resolution. Additionally, CAM operators can interpret additional manufacturing requirements from the Gerber files (edge-plated connectors for gold plating, which through-holes are vias, etc.). |
Gerber Files Explained: What Is a Gerber File?
Gerber files are open ASCII vector format files that contain information on each physical board layer of your PCB design. Circuit board objects, like copper traces, vias, pads, solder masks, and silkscreen images, are all represented by a flash or draw code and defined by a series of vector coordinates. PCB manufacturers use these files to translate the details of a design into the physical properties of the PCB. The PCB design software typically generates Gerber files, although the process will vary with each CAD tool. Most of today’s Gerber file generation is according to the RS-274X Gerber format, which supersedes obsolete formats such as the RS-274-D Gerber standard. Gerber data does not have to have a specific identifying file name as a text file but often has a common extension such as .gb or .gbr.
The Use of Gerber FIles In PCB Manufacturing
Gerber file history traces back to the needs of the original vector photoplotters. A Gerber file contained minimal plotter configuration information and X/Y coordinates followed by a flash or drawing command indicating which aperture position to use as basic plotter instructions. The Gerber data has increased in functionality over the year; it now includes additional configuration information and macro and aperture definitions.
An older vector photoplotter would take many hours for larger pieces of film with a lot of line drawing, but this is now minutes with a laser plotter. Today’s laser plotters still use the same Gerber information, but the older vector plotters’ aperture restrictions no longer apply. The laser plotters convert the Gerber coordinates into a raster file, and that information instructs the laser plotter on how to create the films. For example, the aperture definitions convey the thickness and sizes of the traces and pads, while the drawing commands define lines, polygon fills, or flashes. Then, the laser sweeps across the film, exposing the image.
Time does not sit still, though, and the world of Gerber files continues to change. Circuit board manufacturers have begun using direct laser imaging to create PCB images directly onto the copper, bypassing the need for film. New database formats also capture PCB images that contain much more intelligent board design data, such as net connectivity data. But it’s safe to say that Gerber files will remain in their current form for some time, and designers must be aware of their part in PCB manufacturing.
How To Generate Gerber Files in a PCB Design
After completing the design and final check, the next step is to generate the Gerber files for the PCB manufacturer. The process varies according to the PCB design software; some older tools may require many steps to set up and generate files, but today, most CAD packages have simplified creating these files.
Typically, the Gerber files you will need to produce will be individual files for each physical layer of the board. If your PCB design is a six-layer board with four signal layers and two planes for power and ground, you must output those layers into six Gerber files. Additionally, you will need to generate a separate Gerber file for the top and bottom solder mask layers, the top and bottom silkscreen layers (if required), and the top and bottom solder paste layers (if required). The amount of silkscreen and paste layers will depend on whether your design requires silkscreen and paste on both the board’s top and bottom. Some manufacturers may ask for additional Gerber layers for board outlines or fabrication and assembly information, but those requests are usually for unique design configurations.
Before creating the files, designers must also configure the Gerber file generator so that the units, formats, and standards align consistently with the designer’s and manufacturer’s standards. Although not a Gerber file, an NC drill file generates along with the Gerber files. This file instructs the drilling machines used by the board fabricator where to drill the holes in the board. This file is similar to a Gerber formatted file, containing drill size information and vector data for the different drill locations.
Your Contract Manufacturer Can Explain All Aspects of PCB Manufacturing
Lastly, document Gerber, NC Drill, and other manufacturing files well so that a contract manufacturer can build the board according to your intent. To finalize the process, designers must create fabrication and assembly drawings, pick-and-place data, test data, a schematic netlist, and a readme file. The best thing designers can do is work ahead with a CM to get Gerber files explained (among other manufacturing files).
