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Why don't they mark SMD caps?

Discussion in 'Hobby Electronics' started by David L. Jones, Jul 23, 2009.

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  1. An interesting question was posted on another forum:
    "can you get (ceramic) SMD caps (1206,0805 etc) with the values printed on
    them?".

    My first response was that I've very rarely seen this (like maybe once), and
    while it is possible (see
    http://www.synrad.com/search_apps/application_briefs/117-2.htm), you
    basically can't get labeled ones, they are almost always without markings.

    It got me to thinking, why is it so?
    My guess would be that it's due to the surface finish (or lack thereof) on
    ceramic capacitors, and/or the delicate nature of their multi-layer
    construction means they could be more easily damaged or properties altered
    by the process.
    As opposed to most SMD resistors that have a coating on them which would
    allow for easy and accurate printing using various technologies.

    Any know the real reason(s) why ceramic SMD caps don't have markings?

    Dave.
     
  2. Dennis

    Dennis Guest

    It done purely to give techs the shits when building proto's or fault
    finding. :)
     
  3. Shaun

    Shaun Guest

    I doult very much any manufacter would coat SMD caps as it would increase
    the height to capacitor sits above the board, increasing the mounted
    inductance, a crital factor when designing high frequecny boards.
    Manufactuers spend a lot of money trying to reduce this unwanted property.

    see http://www.avx.co.il/docs/techinfo/licadesign.pdf
    or
    http://www.kemet.com/kemet/web/home...721E006EF53C/$file/Sun Paper on ESL & ESR.pdf
    although these articles deal with via placement they discuss the need to
    reduce the size of the loop that current flows in, a loop that would be
    increased if a capacitor had an extra coating on it.
     
  4. Dennis

    Dennis Guest

    Coating or encapsulation? Coating could be insignificantly thin.
     
  5. Shaun

    Shaun Guest

    It might be possible but I can't think of any non-conductive material that
    could be layered thin enough and still go through a wave solder machine.
     
  6. Tim Williams

    Tim Williams Guest

    Um, so what about the stuff they put on resistors?

    Ink is incredibly thin stuff.

    Tim
     
  7. Shaun

    Shaun Guest

    I didn't think an ink would withstand the the temperature (thinking
    along the lines of markings either being etchings or printed then
    encapsulated) but I have found an ink that could withstand the temperature,
    can even be used on ceramic materials, only problem is it has the be air
    brush stenciled, manufacture states it's not suitable for stamp or roller
    application.
    Okay so I've got no idea why such an ink isn't used to directly print to
    the capacitor,

    Shaun
     
  8. chip caps are bare. That is why they are hygroscopic too.
     
  9. Not ink. It is a baked on enamel. Axial resistors get fired in an
    oven after they are painted. That is why the stripes hold there color
    through thermal cycling.
     
  10. There are plenty of SMD chip cap makers that emblazon a value ID marking
    on their caps.

    The fact is more likely that you are using a size of cap that does not
    allow such a marking. I would say that 0805 is the smallest size I have
    seen markings on.
     
  11. Rich Grise

    Rich Grise Guest

    Money.

    It's way too expensive to mark teeny tiny little parts that nobody's
    ever going to look at anyway - the reels are clearly marked, and they're
    loaded into the stuffing machine, and that's the last human interaction
    the parts will ever see.

    If you're hand-prototyping, you'd either have to mark them yourself
    or mark the tape carrier or bin or envelope where you're keeping them.

    Hope This Helps!
    Rich
     
  12. Rich Grise

    Rich Grise Guest

    They'd also be a little hard to solder in. ;-)

    Cheers!
    Rich
     
  13. GregS

    GregS Guest

    I learned how to solder the little resistors, and that requires the microscope.
    They still look small. The iron looks like a bat and the tweezers a claw, and
    the little resistor looks like a speck.

    I would need a stronger scope to read any lettering on it.
    Some larger parts have little two letter codes on them and I don't even want to know what they mean.

    greg
     
  14. Then why do they mark the exact same size resistors?
    Resistors are generally cheaper than caps, so it would make more sense not
    to mark the resistors to increase the margin, so it would be the other way
    around, if that's the real reason.

    Dave.
     
  15. Can you provide links?
    No, the original person who asked the question specifically stated sizes as
    big as 1206.
    So it has nothing to do with physical size.
    Can't say I've seen the values ever printed on caps even larger than 1206.

    The question is about whay it's common to mark SMD resistors, but not common
    to mark SMD caps.

    Dave.
     
  16. No. They _DO_ mark resistors and resistors are generally even cheaper than
    capacitors.
     

  17. Caps with markings did NOT have a higher price schedule, dipshit.
     
  18. Wrong again. Markings fell out of vogue as part size decreased to the
    point where it was labor intensive to even examine the marking.
     
  19. krw

    krw Guest

    Then why are they still there on resistors of the same size, DimBulb?
     
  20. SMD resistors get a ceramic glaze coating over the applied resistance
    medium. It gets fired on. The lettering is usually fired glaze as well.
    The resistance medium is hygroscopic, so they have to seal it up.

    multilayer chip caps CANNOT be fired in an oven that way. They barely
    make it through the reflow process.
     
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