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I have received several parts from a PCB manufacturer which should have been inspected to IPC-A-600 Class 2 but were instead inspected to IPC-A-600 Class 3.

I believe I have received PCBs inspected to a higher degree of accuracy, meaning potentially less defects. But I'd like to know the potential negative impacts of excessive inspection.

I think I have identified a few below:

  1. Increased cost due to higher accuracy inspection techniques (it may be the techniques used are identical but with more stringent inspection criteria applied to Class 3 than 1 and 2)
  2. Increased costs due to greater amount of scrappage.
  3. Increased costs due to larger quantities of solder used.

Are the above reasonable? Are there any others?

FYI, I was only charged for Class 2. So Happy Days…I think?

313Ctron
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    It seems obvious to me but why haven't you spoken with the supplier to see what they have done and ask them to justify their inspection choice. – Andy aka Sep 17 '21 at 12:40
  • I have actually spoken to them. It was a mistake during their setup process that wasn't identified until I raised it with them. While it's unlikely to happen again, I'd still like to know the negatives of over inspected PCBs, hence my questions... – 313Ctron Sep 17 '21 at 13:08
  • So, of the three questions you asked above, what did they say? – Andy aka Sep 17 '21 at 13:10
  • They didn't really want to be specific. I also haven't got a breakdown of the various costs or processes. They just said that I would be charged for Class 2 and they were sorry. But now I'm intrigued to know more, and since they are being rather cagey, I've come to SE to see what other people may think in the hope a gaining a better understanding. – 313Ctron Sep 17 '21 at 13:21
  • You should ask them on the (somewhat false) basis that you are considering going to a higher level of testing and that you'd like to know the implications. You may actually decide to go for class 3. That's where you'll get your better answers. – Andy aka Sep 17 '21 at 13:40
  • Good idea. In the meantime however, I'd like to ask the community for their thoughts on the topic. – 313Ctron Sep 17 '21 at 13:53
  • Good luck dude!! – Andy aka Sep 17 '21 at 14:53

2 Answers2

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It could be that your contractor's production line is tuned for construction and testing to Class 3, and for some reason it's less trouble and/or less expensive for them to simply bill you for Class 2 and build and test to a higher spec than to build and test to Class 2.

Scott Seidman
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I very much doubt there's a significant downside to class 3 inspection when you specified class 2. After all, class 3 is for critical equipment so your boards were inspected to tighter tolerances, etc. I obviously was not a party to your conversation with the manufacturer but I think that what you are interpreting as "caginess" is really just them not seeing it as a problem that requires much extra thought or explanation.

As for your points: a lot of the class 2 vs class 3 differences are pretty straightforward "50% overhang vs 25% overhang" type tolerances and it's entirely possible that they inspect to class 3 automatically since that also satisfies class 2 criteria without having to worry about mixing up two sets of criteria. Also some of the class 2 criteria - while more permissive - are trickier to inspect. As a (made up) example: class 3 might specify 100% solder coverage on a terminal but class 2 might allow 75% coverage on a vertical portion if the terminal height is 1mm or less and 50% coverage if the terminal height is more than 1mm but then also requires horizontal coverage of more than 75%, etc.

Increased costs due to scrapping defective boards could be there, but they didn't get passed along to you and I think you'd be as likely to see rework costs. And unless you're going by some really fly-by-night place I doubt they're scrapping a bunch.

Increased solder cost: unlikely, unless you've specified some exotic solder. The standard itself doesn't really translate into class 3 = more solder. In fact, excessive solder that obscures inspection of a joint could be a failure condition.

vir
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