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Any way to identify SMD capacitors?

Discussion in 'General Electronics Chat' started by fastline, Sep 17, 2017.

  1. fastline

    fastline Member

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    Working on a motion control board that has failed. I have sourced one small SMD cap that is showing shorted? Seems odd to me but I am no pro with this. Is a shorted ceramic cap a typical failure mode?

    We have another identical board and I was going to compare the boards but I was curious, SMD resistors seems to follow a coding process but do capacitors by chance to identify them?
     
    Last edited: Sep 17, 2017
  2. dknguyen

    dknguyen Well-Known Member

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    Yes, shorted cap is a typical failure mode.

    I didn't even realize SMD resistors had a code of any kind.
     
  3. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    I choose to get resistors with a code. 103=10,000
    I have a very hard time getting caps with any numbers.
     
  4. dave

    Dave New Member

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  5. schmitt trigger

    schmitt trigger Active Member

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    SMT components have become so vanishingly small, that no longer carry any sort of labeling.
     
  6. JonSea

    JonSea Well-Known Member

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    Beware when "experts" use words like never and impossible. It is difficult to prove a negative, as the following pictures will attest. At some point resistors are simply too small to mark but those in the pictures are 0805 components. I believe 0603 resistors are marked as well.

    On the other hand, *I* have never seen 0805 or 0603 capacitors marked with values - I'm not sure why they are not.

    20170918_143436.jpg 20170918_143306.jpg
     
  7. tomizett

    tomizett Active Member

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    My experience is that surface mount caps (which I assume are MLCC's - generally buff/brown in colour) are awlays unmarked. I don't know why; it's pretty annoying.

    If you've an identical board then you're in luck as you should be able to measure the equivalent known good cap on that board. You can *probably* (maybe with a bit of informed guesswork) get a measurement in-circuit.

    I also agree with dknguyen - it's my understanding that MLCCs (multilayer ceramics), at least, are quite prone to failing short. In fact I read an app note recently (and I appologise that I can't find a link to it now) that painted them as quite unreliable all round, and also prone to failing open or low value.
    The "take home" message for me from that app note was that the way that they are soldered/mounted has a significant impact on the reliability, so I now avoid reworking them when I can. If I do have to, I'll re-flow with hot air rather then hand solder with an iron.

    Hope this helps.
     
  8. schmitt trigger

    schmitt trigger Active Member

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    JonSea; I'm not an "expert". But I see hundreds of boards every day at work.

    An 0805 is, for modern standards, an extremely large component. Resistors of that size can be indeed labeled. 0603 sometimes are also labeled.

    But the OP is talking about capacitors, and even larger devices like 1210, are never marked.

    Fastline:
    yes, they fail shorted. It is called flex-cracking. There are literally dozens of reports on the web discussing it. Below is one of them.
     

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