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Why service print on mass-produced PCB

Discussion in 'Electronic Design' started by Robert Latest, Jan 5, 2007.

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  1. Hi folks,

    While I was contemplating whether I should put a servive print on the PCB I'm
    currently working on (it's a hand-assembled low-quantity thingy with about
    100 SMD parts) I looked at commercial PCBs to see how they do it (all my
    libraries are homemade, and I hadn't ever bothered with the silk screen).
    What strikes me as odd is that these things (I'm looking at a couple of
    boards ripped out of old hard disks, and at a PC motherboard) have service
    prints at all. Top and bottom. I mean, these PCBs are only ever touched by
    quite illiterate pick-and-place robots and automated test equipment, and
    when they fail they are thrown away without ever being looked at, so why
    bother with a service print in such a cost-sensitive market?

    Just curious.

    robert
     
  2. If a pcb is manufactured totally by machine... and has been designed to
    be disposable upon failure... then there is no valid reason I can think
    of for using a silk screen. Are you assuming the pcbs you have looked
    at were not meant to be repaired?

    www.telstar-electronics.com
     
  3. Joel Kolstad

    Joel Kolstad Guest

    Hopefully that's because you're trying to save costs? :) Silkscreens are
    definitely convenient...
    Because your assumption that the boards are all machine assembled is probably
    wrong. Most PCBs are still touched by human hands for some manually inserted
    components, *especially* in high-volume markets where labor is cheap compared
    to the very specialized robots you need for "odd" shaped parts. See:
    http://www.pcstats.com/articleview.cfm?articleid=1722&page=1

    That being said, I imagine that the reason silkscreens are still so ubiquitous
    is largely due to convention and determining that -- in high volumes -- the
    price perhaps still is negligible.

    Joerg -- do your products all end up with silkscreens?

    ---Joel
     
  4. It could help in quality control - even if actual assembly is
    automatic, if there is a problem with a resistor placement it would be
    nice to know it is R234.
     
  5. Tim Wescott

    Tim Wescott Guest

    The MFE types like to take samples that have been rejected and figure
    out why, to see what process improvements they can make to improve
    yield. I'll bet that if you're printing _anything_ on the board there
    is little or no cost differential to printing the reference designators.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Posting from Google? See http://cfaj.freeshell.org/google/

    "Applied Control Theory for Embedded Systems" came out in April.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
  6. Others suggested why do it at all, and it reminded me of an ad I just saw,
    for a 'Infinity-ohm' SMT resistor with 2-D barcode, soldered to some
    extra SMT pads. The purpose was to identify a specific stuffing run (more
    precise designation than silkscreening on a bare board, and doesn't
    require a different machine like stick-on labels---plus it's less likely
    to peel off).
     
  7. jasen

    jasen Guest

    When PC motherboards fail in warranty they go back to the factory... and
    often come back as "refurbished".

    The silkscreen often also has useful stuff, like model number, labels for the
    various pin headers etc.

    Bye.
    Jasen
     
  8. PeteS

    PeteS Guest

    There's probably more cost in the addition of the silk layer at layout
    (necessary for prototype testing) than in the cost of retooling at the
    fab house plus the cost of printing for runs in many 10s of K.

    Once it's on there, why take it off might be another part of the answer.

    Cheers

    PeteS
     
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