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PCB Arcing/spark gap

Discussion in 'Electronic Design' started by Bob Stephens, May 4, 2004.

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  1. Bob Stephens

    Bob Stephens Guest

    A while back there was a discussion here about the minimum inter - trace
    distance to prevent unintentional spark gaps on PCB's. Anyone know of a
    table or a rule of thumb for spacing vs. applied voltage for inner layers?
    I've googled a fair amount and haven't really come up with anything.


  2. Active8

    Active8 Guest

    We probably included links in that recent thread. You know, when you
    go to google, if you click on the "groups" link and find this
    group's archive, you can then select to search within this group
    only. When I'm looking for a past thread, I'll search on the names
    of the posters that I remember participating, the year, and as much
    of the subject line as I can remember. Text in the body of the posts
    can also be helpful. Ferinstance, I kinda remember someone posting a
    link to an article that covered "crosstalk" between the traces, so I
    might use that keyword, also.
  3. Bob Stephens

    Bob Stephens Guest

    Thanks Mike. I wasn't aware of that feature in Google.

  4. Jim Meyer

    Jim Meyer Guest

    Breakdown voltages for PC boards are highly process dependant.
    Your question can only be answered by a particular board manufacturer
    for one particular type of board.

  5. James Meyer

    James Meyer Guest

    Note the "inner layers" part of the original post. That spec should be
    completely under control of the board manufacturer and not affected (much) by
    subsequent processing of the board.

  6. Terry Given

    Terry Given Guest

    ......and thereafter depends on the type/amount of crude deposited on the
    board during assembly/testing/shipping/installation/operation of

  7. Terry Given

    Terry Given Guest

    oops, didnt see that - you are quite right, the aforementioned crud issues
    are irrelevant - assuming the inner layer traces come out (eg via/pad)
    sufficiently far from each other.

    I have however looked into this issue in particular, when looking at
    designing planar smps transformers to run from 1kVdc. I never got a
    satisfactory answer from the pcb manufacturers. IIRC Coombs' printed
    circuits handbook gives you an idea of the dielectric strength of the
    laminate itself, but the real issue is the dielectric strength of, and the
    presence of voids in, the resin (b-stage prepreg IIRR). Making sure there
    are no voids is the hard bit.

  8. James Meyer

    James Meyer Guest

    If high voltage is a sufficient issue, the board manufacturer can test
    the breakdown voltage per board and only ship boards that pass the test. Of
    course, you will have to pay a premium for that sort of testing.

  9. Terry Given

    Terry Given Guest

    individual testing was the only solution I could find, too. In the end I
    didnt use a planar for that app - the total cost was too high, mostly due to
    the type of switch I could use (1700V) restricting frequency, thereby fixing
    Np,Nz at high values, which makes it difficult in planar.

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