If you’ve ever built a model airplane or furniture that arrives unassembled, you know exactly how I felt last summer when I was building a tool shed from a DIY kit. I stared at all the pieces lying on the ground and thought, “now what am I supposed to do with all of this?” But as I soon discovered, each piece had a purpose, and eventually the tool shed came together (thankfully without too many left-over pieces). The entire ordeal reminded me of the early days of my career, when I first started learning the ropes of PCB design. I remember looking at all of the output files I was told to create and wondering, “now what am I supposed to do with all of this?”
The answer to this question is that each of those files has a very important part to play in the building of your printed circuit board. Your PCB must go through two major steps in its construction, fabrication of the bare board, and then assembly of components. Additionally, the final product must be inspected and tested before it is shipped back to you. Throughout this process, your contract manufacturer (CM) needs specific data and clear guidelines from you to do their job correctly. PCB manufacturing files are the best tools you can use to provide your CM with the necessary information they need to create the best PCB possible.
The PCB Manufacturing Files Used for Circuit Board Fabrication
The first thing your CM will do in manufacturing your PCB is send design data to the PCB fabricator. These files will be used for creating the different layers and images of the bare circuit board, as well as drilling the holes and routing around its exterior. The fabricator will first start with the files needed to make the images for the different board layers. Traditionally, these were Gerber formatted files that drove image creation through a photoplotter onto the film used for PCB fabrication. Now, however, a new file format known as IPC-2581 is beginning to replace the older manufacturing file formats, including Gerber.
IPC-2581 is not simply a Gerber file replacement, but rather an entire database with all the manufacturing data needed for fabrication, assembly, and testing. This new file format contains the image information (Gerber), the drill information (NC drill), American Standard Code for Information Interchange (ASCII) netlist data for testing, and much more. The benefit of IPC-2581 is that the PCB designer no longer needs to generate multiple separate files, but can instead simply output the design job as an IPC-2581 formatted file and submit that to the CM.
Along with creating all of the necessary layer images and laminating the board together, the fabricator will also work on drilling the holes in the board. This information would normally come from an Excellon formatted NC drill file, but is now also contained within the main IPC-2581 data file. Another important part of the data that is also in the IPC-2581 file is a netlist. The netlist allows the fabricator to conduct bare board testing to make sure that their fabrication process hasn’t introduced any unintended shorts.
The fabricator will also use the fabrication drawing that you created for additional information. The fab drawing should have complete dimensions, the locations of unique board features such as slots and holes, and layer stackup information. It is also common to include readme files with the information sent to the PCB fabricator for more specific details on the board, and this information can now also be included with the IPC-2581 file.
Once the fabrication of the board is complete, it will be sent back to the CM for assembly.
PCB Assembly and the Manufacturing Files Needed
Even before your CM sent the data out to the fabricator to create the boards, they were already working on the components that would be assembled onto the board. Using your bill of materials report (BOM), their purchasing agents were already at work sourcing, buying, and stocking the parts that would be needed. Once the boards are shipped back to the CM from the fabricator, the build kits are put together for PCB assembly.
Solder paste needs to be applied to the board for assembly, and the IPC-2581 file contains an image for that solder paste. The CM will build the stencils for applying the solder paste from this image as well as using it to verify that the correct solder has been applied to the board. Once the solder is in place, the pick and place equipment will use the component X & Y locations from the IPC-2581 file to place the parts on the board.
As with the fabricator, the CM will use the assembly drawing and readme information that you’ve created during PCB assembly. The drawings will show all of the component locations on the board with their reference designators as well as expanded views of the more complex assembly details. The drawings and readme files will also include specific instructions for board markings, conformal coating, and the many other details needed for complete board assembly.
The Files that are Used for Final Inspection and Test
The last part of the PCB manufacturing process is the inspection and testing of the completed product. Different image files combined with the BOM are used for programming the inspection equipment, and with an IPC-2581 file, all of this data is presented in the same file. The netlist data for functional testing is also in the same file, and that data is used for creating test fixtures and programming the test equipment. Through all of the manufacturing processes, any additional information and build instructions in readme files can help clarify the details of your circuit board.
PCB Manufacturing Files and Data and How They are Used
File or Data
NC Drill and Routing
XY Component Locations (Pick & Place)
Assembly (Solder Application)
Bill of Materials
Component procurement, Board Inspection
Bare Board & Functional Test, and Inspection
Board Fabrication & Assembly
As you can see, there is a lot of data and information needed to create your PCB. Fortunately, your CM can help you to wade through all of the data requirements so that you know exactly what they will need to work with. In addition, they can help you to understand what kind of board specifications you will need for your design and how best to configure the layer structure and materials for it.
|Tempo‘s Custom PCB Manufacturing Service|
At Tempo Automation, we can help you with this and every aspect of your PCB design. We are ready to work with you on your board design so that it goes through the manufacturing process without any problems.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium user, you can simply add these files to your PCB design software.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on PCB manufacturing files or how they’re used during fabrication and assembly, contact us.