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Random errors - process or not?

Discussion in 'Manufacturing and Related Processes' started by Colin Pitman, Sep 10, 2017.

  1. Colin Pitman

    Colin Pitman Member

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    Not sure which part of the forum this belongs in, but I'll put it here for now.

    We make PCBs. Some with hundreds of components each. 1 PCB in several thousand might (for example) have a solder bridge short-circuiting two components together. It never happens in the same place, and can happen on any type of PCB (we make several hundred different types for some 20 - 30 different customers).

    The customer finds a defective one and asks me to complete an 8D report on the RC and CA. What can I possibly put down for this? It's a total fluke. Out of a million component joints, there will always be one with a solder bridge that isn't picked up by inspection...

    What would you put?!
     
  2. Andy Nichols

    Andy Nichols Moderator Staff Member

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    Colin:
    Welcome to the forum. As a past QM responsible for both pcb design quality and supplier quality, I'd suggest that you set up (if you don't have it) a system to track (pardon the pun) the faults on a diagram of the boards, by part number. You might be surprised, if you don't already do that, where these shorts occur. Experience shows it's often at a point of narrowest track/pad clearance etc. made worse by the way the board is presented to the soldering process (what process do you use?) Without analysis, it's hard to show if it is purely random. As far as responses to customers, it's too easy to issue a CAR for such events. Don't worry about how to respond to thoughtless requests like this. It's far better to meet with the customer and explain what you're doing, the random nature of the defects and so on. It might be their board design, after all. Best to work closely with SQA than answer mindless CARS/8Ds etc.
     
  3. Colin Pitman

    Colin Pitman Member

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    Thanks for the welcome and the response Andy. We don't use diagrams, but instead record component references of components involved. There are no trends that I can see. Solder bridging was an example, and there are lots of other one-off problems that we experience. I guess my core question was how do you decide what is a real issue and what isn't, and how that decision is communicated back to the customer. If I read your post right, are you basically saying that it's ok for me to push back sometimes when the customer requests a CAR/8D report for silly things?
     
  4. Andy Nichols

    Andy Nichols Moderator Staff Member

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    Well read! That's exactly what I'm saying...

    I would, however, encourage some type of diagramming of failures as much as the raw data may indicate some form of randomness, I believe it's of use, especially when "pushing back" if you can show a basic defect diagram (you could plot them location-wise against the ident layer of the cad file, for example) or something like a Paynter chart.
     
    Colin Pitman, Bev D and yodon like this.
  5. Ben Johnson

    Ben Johnson Member

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    If you want to be an arse tell them the RC is poor PCB design and the CA is for them to re-design it. :) But on a serious note, I completely agree with Andy's comments on being open and look into diagram mapping faults. Welcome to forum, I also have experience with PCB Manufacturing Quality and picky customers.
     
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