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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+

  •  Post a screenshot of the connector.  You are one the right track with the shapes -- that sounds like the best method.

  •  Here's the screen shot as requested. The spark gaps are the triangular shapes. The single via is a 12 mil drill. I have to set the point of the triangle to 6 mils but at 2 oz copper, I'm not sure I can maintain that distance. Boards shops are telling me that there's a +/- 20% tolerance. Blue is top, red is bottom.

    Cheers,

    Ron Scott CID+

  • 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

  •  Greetings,

    I did increase the gap to 8 mils but was able to keep my gap from the spark gap to 6 mils. I dropped a power shape on the the spark gaps and it did'nt flag a DRC (how lucky). If I could possibly have 4 oz cu, I'd go with that but the spacing requirements would compromise my design. I have a ESD diode array in place already but my customer wanted the spark gaps too.

    Cheers,

    Ron Scott CID+

     

  • Hi Ron,

    My explanation is the feasibility of the 6 mil gap using 2oz surface copper at a planned fab house, not whether the DRC flag arises or not.
    As you may know, whether the DRC flag arises or not depends on the spacing constraint of shape to pin, even if the fab house can not keep the fab specifications.


    Regards,
    Tomo

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