Detecting 2 oz copper on PCB

Discussion in 'General Electronics Chat' started by Roderick Young, Nov 15, 2015.

  1. Roderick Young

    Thread Starter Member

    Feb 22, 2015
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    Suppose I ordered a PCB with 2 oz copper from a fab, but wanted to verify that they really used the 2 oz copper that I paid for. Would I be able to tell the difference from 1 oz copper simply by sliding my finger over the traces? If anyone has direct experience with this, I'd love to hear it.
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Can be easily measured with micrometer if you have a void and a trace of appropriate size for the micrometer.
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
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    When I've etched my boards, I can tell the difference between 0.5 and 1 ounce by looking at the traces from an angle. Might be obscured with a soldermask...

    upload_2015-11-15_10-36-20.png
     
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  4. WBahn

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    Mar 31, 2012
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    The thickness of a sheet of typical 20# paper is about 3.8 mils. So if your traces are at least half the thickness of a piece of typing paper, then it is probably 2 oz copper. If it is less than that, it is probably 1 oz (unless it is a LOT less). If you have regions of bare copper than doing a comparison under a microscope or even with a magnifying glass is pretty easy. If you have a soldermask then it is a lot more difficult.
     
  5. cmartinez

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    Jan 17, 2007
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    you could try to carefully shave off a little copper from the board with a sharp knife (maybe even a razor blade)... then measure its thickness with a caliper...
     
  6. #12

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  7. Roderick Young

    Thread Starter Member

    Feb 22, 2015
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    I'm not curious enough to actually purchase a caliper for measuring. I do have a cheap plastic caliper, but it doesn't have that kind of resolution. Were it not for the solder mask, I think the finger test might do it. I can distinguish between a 20# sheet of paper and a thinner one easily by sliding my finger across it when it's flat on the desk.
     
  8. cmartinez

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    Jan 17, 2007
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    If you have a 1 oz board to compare it with, and a jeweler-type magnifier, you could shave a small strip from each board and compare it visually.
    The human eye is very accurate for gauging purposes, if you give it something to be used as a dimensional reference.
     
  9. joeyd999

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    Jun 6, 2011
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    Did you ever consider asking for a certificate of compliance from the fab house?
     
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  10. WBahn

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    I wonder how much good that will actually do. The certificate of compliance is only as good as your faith in it veracity.

    If you already have sufficiently little faith that they aren't going to try to cheat you by using 1 oz copper when they said they would use 2 oz copper, what good would a certificate of compliance from them that says that they used 2 oz copper really be? Unless it comes from an independent testing firm, if they are going to lie when they say they will use 2 oz copper, then you have to assume they are going to lie and say that they did use 2 oz copper.

    The other possibility is that they are so incompetent that they used 1 oz copper by mistake (and, to be fair, even the most competent houses WILL make mistakes from time to time), but once again, the certificate of compliance will likely show that they used 2 oz copper because they think that they did use 2 oz copper. It depends on what their internal compliance procedures are like and, in particular, whether they are based on sign-offs only or whether they involve physical verification by someone other than the person that did the work.
     
  11. joeyd999

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    Actually, I should have said 'Certificate of Conformance'.

    I agree with everything you say, save this: such a certificate is a legal document and publishing one carries certain and specific responsibilities. Does this imply the publisher will be truthful? No. But it gives you recourse when the crap hits the fan (i.e. someone dies in a fire because your PCB materials were underrated for the application).

    Edit: Oh, and asking for one is a great way to vet the vendor. If they refuse, it's a big red flag. Most reputable vendors supply a certificate upon shipping the material. You don't even need to ask for it.
     
    Last edited: Nov 15, 2015
  12. WBahn

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    Unfortunately, that only matters if the company issuing it is within your legal reach. If you're using a cut-rate Chinese PBC house, your legal recourse may be next to worthless, particularly if you are a small fry. But still, it IS something. If nothing else, it might shift the responsibility away from you, and that's not nothing.
     
  13. #12

    Expert

    Nov 30, 2010
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    I work in the physical world more than most people. Good measuring equipment is mandatory. I use everything from a dial gauge to a 100 foot tape measure, and usually carry at least 3 thermometers, 3 electrical meters, and 3 devices to measure angles. So very happy to be back in business after a year off duty with a back injury! Today, I had to scrub my hands with a green scratch pad and cut a loose piece of skin off.:)

    As for you, you can use the green scratch pad to scrub your copper before assembling the circuits.:p
     
  14. joeyd999

    AAC Fanatic!

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    Are you saying "beer can cold" is not good enough?
     
  15. Roderick Young

    Thread Starter Member

    Feb 22, 2015
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    Just looking for an easy test for a hobbyist. If I was still working, we would have had a whole department to audit this kind of thing, but I'm trying to do things on the cheap. Retirement is sort of like being a teenager again - time is more available than money, so I try to be clever with minimal tools wherever possible.
     
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  16. pilko

    Senior Member

    Dec 8, 2008
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    Plastic calipers usually have a Vernier scale, If so, It will have enough resolution for your purpose.
     
  17. DickCappels

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    Aug 21, 2008
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    WBahn's suggestion in post #4 is a good one. If you don't have a sheet of 20# paper you can use a "Typical" human hair, which will be near 3.9 mills in diameter.
     
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  18. PeterCoxSmith

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    Feb 23, 2015
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    You are not curious enough but you are suspicious enough. Seems a bit strange.
     
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  19. DickCappels

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    Aug 21, 2008
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    Maybe this is too simple: Pick a trace, calculate the resistance you would expect if it were 2 oz copper. Measure the resistance.

    If you don't have an ohmmeter that goes that low you can make a (for example) 1 amp current source from a heat-sinked LM317 and apply that to the trace. Using your DVM you can measure the voltage drop. All of my DVM's have resolution down to 100 microvolts.

    Of course this might not be useful if your PCB doesn't have any traces that are long enough.
     
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  20. Roderick Young

    Thread Starter Member

    Feb 22, 2015
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    It would be accurate to say I'm not suspicious enough, either. I actually don't have a 2 oz board in hand, at least not yet, and have no reason such as anecdotal information to doubt the supplier. I guess I'm a creature of contradictions. I'll pay someone to change the oil and filter on our car, but won't spend on tools unless there is no choice. In the case of an oil change, occasionally I'll look in there right after to see if they actually put a new filter on, but not always.
     
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