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Constructing a "spark gap"

Goblin59

 I have a unique requirement for my current design. I have 12 data input lines that need to have ESD protection.I thought I had this problem solved with a zener diode array but the customer wants a "spark gap". This is supposed to be a small triangle of metal positioned 6 mils from the pad (oh, yes, the spark gap is between pins on a connector) on 2 oz copper. I've tried making small shapes (like testpoints) but that doesn't seem to work too well. Any ideas on how to handle this?

Cheers,

Ron Scott CID+

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  • First of all, you should confirm the manufacturability about the fab spec to your fab house.
    It is typically difficult to make the 6 mil gap at 2 oz copper on the surface layer.
    In our company, the 2 oz copper on the surface layer must not use to avoid a problem with the copper etching.

    I think there are two solutions.
    One is to space the gap than 8 mil, but the spark may be hard to occur compared with the 6 mil gap.
    The other is to change the copper thickness from 2 oz to 1 oz to maintain the 6 mil distance if possible electrically.
    A copper plating thickness is at least 1 oz (35um) typically.
    Which do you need the true 2 oz copper thickness or 2 oz copper plus plating thickness (about 3 oz) ?
    If the true 2 oz is ok electrically, it may be no problem with using 1 oz copper thickness with 1 oz plating thickness.

    And as an another advice,
    The spark operation will not be guaranteed although I have used the PCB technique, too.
    Naturally, the quality will be quite variable, especially at the 2 oz, it will become pronounced all the more.
    Therefore an ESD protection diode will be the best choice to get a definite effect.

    Hope this helps.
    Tomo
Reply
  • First of all, you should confirm the manufacturability about the fab spec to your fab house.
    It is typically difficult to make the 6 mil gap at 2 oz copper on the surface layer.
    In our company, the 2 oz copper on the surface layer must not use to avoid a problem with the copper etching.

    I think there are two solutions.
    One is to space the gap than 8 mil, but the spark may be hard to occur compared with the 6 mil gap.
    The other is to change the copper thickness from 2 oz to 1 oz to maintain the 6 mil distance if possible electrically.
    A copper plating thickness is at least 1 oz (35um) typically.
    Which do you need the true 2 oz copper thickness or 2 oz copper plus plating thickness (about 3 oz) ?
    If the true 2 oz is ok electrically, it may be no problem with using 1 oz copper thickness with 1 oz plating thickness.

    And as an another advice,
    The spark operation will not be guaranteed although I have used the PCB technique, too.
    Naturally, the quality will be quite variable, especially at the 2 oz, it will become pronounced all the more.
    Therefore an ESD protection diode will be the best choice to get a definite effect.

    Hope this helps.
    Tomo
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