Shining the light on what your PCB fabricator does with your data

Article from Circuit Mechanix Magazine:

Circuit Mechanix Mar 2016 - Cover

Shining the light on what your PCB fabricator does with your data

After the design process is complete and the fabrication data, is generated and checked (I’m sure everyone reading this checks their data before giving it to the fabricator) it’s sent to the fabricator and after a few days some PCB’s arrive back, just like the PCB’s that were designed. It’s simple right?
But what has the fabricator done to / with your data?
Have you asked for your fabricator to check the gerbers against a netlist?
Is the panel data reviewed before production commences?
Why is it even important?

Like all these things, it’s impossible to know until the question is asked! The next time PCB data is sent to your fabrication company why not ask them a few things:

  1. Ask them to make a list of the changes they make. With the best will in the world the design rules the design is checked against are often not set up to the manufacturers constraints. This kind of information will help you understand what they need better.
  2. Most of the time PCB’s are supplied in panels, how they are aligned can cause issues with your product (where the breakouts are for example) or possibly the manufacturing process. Having a review on the panel data and possibly having the assembler look at it, (if the design complexity demands it) can help smooth out the assembly process.
  3. If you’ve provided your fabricator with a netlist to check the gerbers against, have you checked to make sure they can read it? Is your fabricator carrying out this check?
  4. There is normally some kind or test report generated when this process. Getting the results of this ensures that not only can they read the netlist and you’re generating it in the right format, but that it’s being carried out. Asking the fabricator to do this is often
    needed as sometimes the principle of ‘if it’s not asked for it’s not needed’ is used.
  5. The netlist will also help give the fabricator the data they need to test the bare boards. But of course, is this carried out? If it’s not, faults in bare board test will not show up until the
    board had been populated and testing is being carried out. If it’s being asked for, make sure that a copy of the test report is included with the delivered PCB’s.
  6. Time and money may be saved if bare board test is deemed unnecessary, but imagine the lost time and money is there’s an error on some or all of the populated boards. Really it’s a false economy.
  7. The next thing that’s interesting to look at is plated through holes. The hole size given in your design – is it treated as the finished hole size or the drill size? Surely the difference doesn’t matter? In a hole for a large transistor this is certainly not going to make much difference. But a small hole for a fine wire or lead may end up being smaller that expected as the plating can reduce the hole size by 0.1mm. Sometimes this counts.

Knowing this kind of information about how your fabricator works will help a designer enhance their designs by enabling them to work with the fabricator more effectively. Also going through the post design manufacturing review shouldn’t take as long as it sounds, but it could save a mess up and they cost far more time and money.
Circuit Mechanix © 2016

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