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There is no greater reward than spending long hours designing the smallest details of a PCB and finally getting the finished PCB from the manufacturer.
The wait may seem like an eternity from the moment you first handed him the design files, but when you find the package with the finished board on your doorstep - it's like an engineering Christmas! We'll walk you through the entire design process in our PCB Fabrication Basics series.
Let's start with a visual representation of an electrical circuit in the form of a draft design and then move on to packaging all theoretical research into a physical form, represented by radio components and conductive tracks. Right now, it's time to move on to the post-project and PCB fabrication processes.
At this stage, you are faced with the task of putting together all the files and documentation that the PCB manufacturer will need to successfully manufacture your multilayer PCB. And when he has everything he needs, you will only have to sit and wait for the package.
But how does the manufacturer know how to make your PCB?
It cannot use source files generated by your favorite CAD system. You need to send him Gerber and Excellon Drill files.
If you've never made a PCB, the expressions "Gerber, Excellon and NC Drill files" may seem incomprehensible. After all, can't you just send the circuit and PCB design files from the PCB design application to the manufacturer and let them do the rest?
If only everything was that simple. As we all know, much computer-aided design (CAD) systems exist for printed circuit boards. Different CAD systems have their file formats. Just imagine if a manufacturer needed to be constantly aware of all the file formats of each CAD system. That would be complete madness!
Instead of using the PCB design system's file formats, each PCB design system supports intermediate production files called "Gerber".
These files describe the conductive traces of each layer of the printed circuit board in a manner understandable by the computer-aided manufacturing (CAM) system.
The developed Gerber files initially contained instructions for a photoplotter that created an image of a printed circuit board using light on an unexposed film sheet. These days, Gerber files control a laser plotter that plots all the traces, mounting holes, and vias on a printed circuit board.
The peculiarity of Gerber files is that each File you generate will be associated with a specific layer of the PCB design and have its unique file extension.
To date, the standard file extensions that you can work with in CAD/SAP are as follows:
It is also worth remembering that several Gerber file formats are available - Gerber RS-274D and Gerber RS-274X. The older D format uses two files to describe one PCB layer. The newer X format combines all information from two files into one File.
When managing design data, it's much easier to keep track of one File per layer instead of two. We always recommend that you use the Gerber RS-274X format. There is no reason to abandon this format these days.
You may have noticed something missing from the table above - a link to a file with holes. You will need to send this second File to the PCB manufacturer along with the Gerber files. The NC Drill Hole File (for CNC machines) will be used to precisely define where to drill holes on the PCB and their dimensions.
Let's make a reservation right away that you might have heard about the NC Drill file, which meant the Excellon file, designed for the drilling and tracing machine formerly manufactured by Excellon Corporation.
Now that you have a basic understanding of what Gerber and NC Drill files are let's turn to a typical PCB design system and see how to create files in this system.
One of the popular CAD systems includes a handy SAP engine that allows you to upload an SAP file and quickly generate files for your project.
In our example, we'll upload a Gerber RS-274X SAP file, and from that, we'll get five separate Gerber files for the LED Flasher project we completed in the PCB Design Basics series.
1. Open the PCB design (.brd) File in the CAD control panel;
2. Select the CAM Processor tool at the top of the window, or select File>> CAM Processor to open the CAM Processor Dialog;
3. No SAP task has been loaded yet, so let's add one. Select File >> Open >> Job (File >> Open >> Task). Then navigate to the default project folder, and select the gerb274x. Cam file and click Open.
4. As you can see, new tabs for each SAP file will now be generated as a result of this task. Click the Process Job button to create all Gerber files.
And that's it! With the click of a button, you generate all the Gerber files you need, which you can then send to the PCB manufacturer. If you return to the CAD control panel, you will see the newly created Gerber files listed next to the existing project files.
Hole File Formation
Since the Gerber files you just generated contain all the necessary information a manufacturer needs to produce each PCB layer, they do not contain information about the holes to be drilled. You need a file that lists the location and size of each hole.
Fortunately, generating such a file in modern CAD is as simple as creating Gerber files.
1. Select the CAM Processor tool at the top of the window, or select File>> CAM Processor to open the CAM Processor Dialog ;
2. First, you need to download the SAP task for drilling holes. Select File >> Open >> Job (File >> Open >> Task). Then navigate to the default project folder, and select the excellent. Cam file and click Open.
3. Now there will be only one tab, Generate drill data (Generate data about the holes), in which the data from the layers 44 Drills (44 Holes with plated) and 45 Holes (45 Holes without plated) will be summarized - exactly what you need. Click the Process Job button to create this File.
You now have all the necessary files to send to the PCB manufacturer to make the bare board. The key word here is "empty board".
If you want the manufacturer to install all the electronic components on the board, doing what is called “PCB contract assembly ", then you will most likely need to send additional files to the manufacturer, such as a bill of materials (BOM - Bill of materials).
Note that although we have used the standard Gerber SAP design file to generate the files, some PCB manufacturers also offer their SAP design files for download. After uploading such a file, a task template will generate Gerber files in a specific manufacturer's format.
Before you generate Gerber files, check with your PCB manufacturer to see if they offer a native-format CAD file. If not, you can safely use the Gerber RS274X standard format CAD project available in the CAD system.
All articles on this blog are written so that you can most likely design a printed circuit board in CAD so that a real product can be made from the finished project in the future.
Sometimes this doesn't work because you can accidentally silkscreen a pad, or there might be a break in the circuit. The difference between a finished project and a production-ready project can be huge in any situation.
Therefore, before you consider sending any Gerber or NC Drill files to a manufacturer, we always recommend checking everything carefully to ensure that what you have designed is reflected in the generated files.