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When is it appropriate to add full fabrication notes instead of just a simple readme file, and when should I just send the Gerber file for fabrication? Each of those approaches to documentation – or lack thereof – may be appropriate depending on which stage you’re at in your design process.
For test boards, bench tools, or other boards that will never be used by anyone but you, you’ll probably use a prototype or run-as-sent service. For these boards and in these scenarios, you likely won’t have notes for UL marking, electrical testing, destructive testing, cross section analysis, and so on. The extra documentation you create at this stage may be minimal or none – you might in fact be sending in the Gerber file alone.
Or you might attach a readme file that says for example: Nonfunctional circuit for mechanical fit only. This will clue the fab house that the DFM checks they normally run — checks this board will fail — are not necessary.
Occasionally, we also see a fully documented fabrication drawing with a large note telling us to ignore fabrication notes in conflict with manufacturer’s standard processes.
When you’re developing a new product, you can expect to go through several iterations of your boards in order to prove out your subsystems before arriving at something that starts to resemble a finished product.
At this stage of development, when you’re ordering boards, you might want more control over elements like thickness or layer stack-up than you took with your test boards. Because you’re still in early development, keeping development moving along may be your priority. You might add an electrical test to make sure the board works as designed, but you’re not adding in a lot of process controls or special handling instructions that might slow development or add costs. Documentation becomes a little more robust here than what you needed for your test boards, but just enough to get what you need to continue development.
Once you get close to product release, your boards need to be pretty well-defined. At this stage, your documentation should include a full set of notes with specific callouts, material specification, silkscreen and solder mask, copper weight and plating thickness, test and inspection requirements, and so on.
As you move into the final rounds of development and then production, you’ll need to add more documentation including detailed manufacturing requirements and inspection criteria to meet commercial standards. At this stage, you need full fabrication notes because quality is critical here – missing important documentation can be expensive and severely impact the quality of your final product.
Depending on what you’re designing, you might need even more documentation. If you’re designing for the transportation, medical, defense industries or another highly regulated industry, there’s a lot more documentation you’ll need.
In these scenarios, the sky’s the limit in terms of what standards you might have to meet and the accompanying documentation you need to supply. Destructive testing, IPC 6012 Class 3 or Class 3A, ITAR, FDA requirements – any of these may apply to the specific product you’re building. When you get into these areas, your notes may take up a full sheet in your drawing package and refer to design and manufacturing specifications that are hundreds of pages long.
These documents can cover not only quality manufacturing processes, but also things like materials sourcing, record keeping requirements, test specifications, labor and purchasing, ethics, handling, packaging, and any number of standards you may have to meet in order to bring your product to market.
As your boards get more complex and more complete, so should your fabrication notes. And while documentation itself is important, it is equally critical to create the right level of documentation for the development phase you’re in.
Often, developers add a full documentation set along with an order for low cost test boards. PCB manufacturers can’t deliver the same level of service for inexpensive test boards as they do for production boards, and it’ll save you time and money to set your expectations – and documentation – appropriately for what you’re ordering.
Some prototype or run-as-sent services will automatically delete anything that isn’t a Gerber file, and others might see pages of fabrication notes for a batch of test boards and stop the order to review the notes and call or email you to discuss what the need really is. Often, if someone really just needs some test boards but sent along a full set of canned fabrication notes, the end result is that the order for test boards is delayed while the PCB manufacturer vets the requirements with the customer.
To help ensure that your PCB manufacturer can get the boards you need in the timeframe and at the price point you need for your stage of product development, create and send only the fabrication notes that are relevant for that stage. You’ll save yourself time and money and get your product to market faster.
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