How to Send the Most Complete PCB Documentation Package to Fabrication
Getting through the PCB design and development stage is always cause for celebration. You just cleared through the last PCB documentation and fabrication project hurdles, whether it was securing quantities for new components, finalizing environmental testing, or getting that green light from your EMC (Electromagnetic Compliance) engineer. Your PCB project is now in the “released” status with all approval signatures in place, and it’s time to hand it over to production. This path of transitioning and translating your design specifications into a set of workable files for your PCB manufacturer should be straightforward, but it never is.
It doesn’t take much to bring the production process to a halt with one missing PCB document that can easily blur the line of communication between what your specs are and what your PCB documentation depicts. The saying “the devil is in the details” couldn’t be more true when it comes to your PCB fabrication and assembly documentation. When generating a PCB footprint, your goal is to ensure your manufacturer doesn't delay production, pass on extra costs, or build a nonconforming PCB assembly. In this article, I'll show you how to build a complete PCB documentation package that hold to IPC standards, that a manufacturer will expect.
The Basics of PCB Documentation and Manufacturing Files
From a manufacturer perspective, it’s a major error when your package is missing one of the documentation pieces or sets referenced in your design files. An incomplete production documentation will most likely delay your project due to the time wasted clarifying and mitigating the issue. The table below shows a list of output files in various categories you should be familiar with:
Not only should your PCB documentation package be complete, but one must keep in mind that your manufacturer requires your package come in a format that is generally accepted by the PCB industry.
The most popular vendor-neutral file formats for PCB designs are Gerber files (either the standard RS-274-D or extended RS-274X), ODB++, and IPC 2581. These file sets provide the information CAM engineers need to create stencils for coper etching. The good news is most CAD systems can generate or export your design data in one of these formats. Other files that may be required are Gerber files in a fabrication drawing, Excellon/NC drill files, netlists, and bills of materials.
Note that not all manufacturers will accept files in your design software's native CAD format. There are a number of reasons for this, so it is best to check exactly what your fabricator needs and in what format they require before sending anything.
What Your PCB Documentation Should Include
So what should you include at a minimum? Most novice designers focus on creating a bill of materials and little else. While the list of requirements might change from one manufacture house to another, there are some minimum PCB documentation requirements:
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PCB data that includes:
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Gerber Files
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Drill Files
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Netlist Data
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PCB fabrication instructions that include:
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Slot and Hole Sizes
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Board Outline
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Finished Copper Weight
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Finished PCB Thickness
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Surface Finish
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Silkscreen Requirements
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Soldermask Requirements
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Bill of Materials (BOM) that includes:
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Component Quantities
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Reference Designators
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Brief Description
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Manufacturer Part Number
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Supplier Information
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With this information, your manufacturer can give you an accurate quote with an estimated delivery date, and more importantly, understand your design intent and build a PCB that conforms to your specific requirements.
Generating PCB Fabrication Outputs
Some PCB layout software does not include the tools you need to quickly generate fabrication outputs. You'll be forced to use an external program to create PCB fabrication files, usually from an ASCII version of your PCB layout. Programs that include integrated PCB manufacturing tools make it easy to quickly generate professional fabrication files. You'll be able to select a range of output files for your manufacturer in a single utility.
Complete PCB Documentation Data Package (Output Job Files)
What Does your Manufacturer Do with the Data Anyway?
Boards are typically fabricated in about 25 digitally controlled steps using production tools. Some designers think that the PCB fabrication data they submit, such as the Gerber files, directly drive aspects like the photoplotter, or that the drill files will directly be used by the drilling machine. However, that is not the case, and panelization is clear evidence of that. Let’s go over some of these factors.
Layer Stack Diagram
The first step your manufacturer performs with the data set you send them is load it into their CAM system to recreate your PCB’s model. This is the model that will actually drive the manufacturing process as the system converts the image files. That’s why your data has to clearly specify information that defines the function of each file on the stack, so it’s clear which is the top layer, the bottom layer, etc.
Drill Files
This file specifies geometric information that indicates the PCB material that should be removed and where it needs to be plated. The drilling machine must be able to read the geometric data that should be standard and specified by their diameter, start and end layer, and whether they are plated or not.
PCB Outline
Without the printed circuit board outline and knowing what area is the rigid-flex PCB and what isn’t, the board simply cannot be built. Your PCB layout should specify a closed solid contour without holes. The reason you don’t want to intentionally include holes is to avoid any confusing duplication since your drill file will contain a well-defined drill hole pattern.
Technical Drawing
While every manufacturer relies on your set of digital data as input to their production tooling system, actual technical drawings, such as mechanical, should be included. And while these drawings are not needed to process your PCB digitally, they are meant to be manually checked by a technician when needed. Also, one thing to remember is that drawings will never be used as a substitute for your digital data, whether it is for copper layers, solder masks, legends, drill patterns, or whatever other pattern your design includes.
Netlist
Always include a netlist with your documentation package. Why? Well, a netlist will help ensure your design is correctly transferred into the CAM system. After inputting your fabrication data into the CAM system, the first thing it generates is a netlist from the image, which they call a reference netlist. Due to potential errors, either from the software or the operator, this reference netlist is often compared against the job data by the CAM engineer to make sure any possible mistakes are caught.
Avoid Any Guess Work
If you’re still using a PCB design software tool that requires you to manually generate output documentation, pay close attention to the files you are outputting and keep them organized in a single repository. To put it simply - a complete PCB documentation package should contain all the files required by your manufacturer, organized in a file format and structure that is easily interpreted without any guesswork. Any redundant or errant files found by your manufacturer will only add delays to your manufacturing process, and that’s the last thing you want to deal with.
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