1.PCB Manufacturing Pre-requisites
The Gerber RS-274X file format is used for PCB manufacturing data submission to fabrication house. This is output of PCB design file. Why not PCB Design file handed over to manufacturer? One of the reasons is almost all product hardware concept related information is present in PCB design file. For example, Bill of Material can be very easily generated from this PCB design file. It contains active connectivity information from where entiredesign can be copied. The gerber files do not include BOM and active connectivity information. The gerber files are image of active layers and connections but they are just “images of all active PCB layers”.
So they are relatively safe to submit to third parties such as PCBs fabrication houses etc.The gerber format was emerged from applications where it was applied to re-generategraphics or images i.e., from plotters industry. It isused in electronics PCBs manufacturing industry in the same way. It generates PCB traces, pads, vias, clearances and all other electrical and non-electrical information contained in a design file. All PCB CAD softwares are capable to generate gerber files.All the electronics engineers who have designedand manufactured PCBs will have used this option.
Gerber file outputs these four parts:
- X/Y Coordinates
- Configuration Parameters
- Drawing Commands
- Aperture Definitions
The PCB manufacturer creates photo plots from the given Gerber files data. The higher the resolution of gerber files data the better the plots created for PCB fabrication.
2.What should include in Gerbers
The gerber data is very critical to produce. It should be generated very carefully. Usually, any layer missed during gerber files generation will interpreted by manufacturer that there was no layer in the original design. The PCB produced will be off course faulty and cannot be used. A faulty gerber data will produce faulty PCB output.Before generating gerber files in Eagle software the PCB design engineer should very clear to include necessary layers ad information in Gerber CAM processor of Eagle software.
3.Eagle Output File Format
The eagle PCB Design software generates gerber files on popular RS-274X format however it is slightly tricky to understand the file extensions. The drill files are created and saved separately in Exelon format. For gerber files creation it provides a separate software utility called CAM (Computer Aided Manufacturing) processor or only processor.
In eagle there are two main terms the processor and the job. The processor is explained already. The job is a set of tasks composed so that each task reads specific layer information from PCB design file and creates gerber file.
CAD softwares create one file for each PCB design layer. So for 20-conductive layers PCB design there will be 20 gerber files, additive to top and bottom legend, keepout, top and bottom paste, top and bottom solder mask layers. When it is to submit data for manufacturing or quotation purposes the Gerber files folder should be in*.zip or *.rar format.In Eagle software the following extension for layers are produced in gerber generation.
- GTL Top Copper Layer
- GTS Top Soldermask Layer
- GTO Top Silkscreen Layer
- GBL Bottom copper Layer
- GBS Bottom Soldrmask Layer
- GBO Bottom Silkscreen Layer
- TXT Drills Layer
- GML/GKO *Board Outline or Keepout Layer
- 6 layer board also need internal layers information also
- GL2 Inner Layer2
- GL3 Inner Layer3
- GL4 Inner Layer4
- GL5 Inner Layer5
Along with layers information, holes location and size of drills also part of gerber data produced before submission to a manufacturer. It is called NC drill file and data is incomplete without these files. The purpose of Gerber files is to create X/Y Coordinates, Configuration Parameters, Drawing Commands and Aperture Definitions of each layer mentioned in software. The Eagle software scans the each layer entire PCB file to create these four parameters for each separate layer.
However, to generate a PCB Design file into CAM Processor:
Usually, the CAM processor is a dialog box that takes design file as an input and allows optional settings and generates output files.
To open CAM Processor click File> CAM Processor
OR alternatively, in Control Panel’s main menu File > New > CAM Job
thenselect PCB board: go to file> selecta job file>execute the job.
to load a PCB design file.
Figure 1: Eagle PCB software CAM Processor
Start CAM processor from Eagle software as shown in Figure 1.
Figure 2: Selecting CAM Processor File Format
Select format of output files and necessary options in the CAM processor as in Figure 2.
Figure 3: Layer names in Eagle CAM Processor
Produce output files as shown in Figure 3.
For fabrication data to be handed over to manufacturer it is necessary that it should be accurate and complete. Ay missing information will cause a faulty and hence garbage PCB.Eagle software like other softwares produces files in Gerber RS-274X format. For successful gerber files creation one should have clear knowledge of Eagle CAM processor. It is a good practice to verify metadata files against each layer with their three charactersextension.For gerber data verification known online and offline installable softwares are available which show the exact image what data is generated. Verify and match gerber data before submitting it to fabrication house. Besides PCB layers metadata NC drill files are also required by the PCB fabrication house so produce separately, verify and match with original design file before forwarding it.3