static electric arcing

Discussion in 'The Projects Forum' started by jmartens1978, Nov 8, 2012.

  1. jmartens1978

    Thread Starter New Member

    Nov 8, 2012
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    I have a project that I am working on and would like some input from anyone that has some knowledge on High Voltage Arcing on PCBs.

    Problem: I have a PCB that is enclosed in a plastic enclosure that has metal pins and switch that extend to the outside of the enclosure. Static electrical shock is hitting those pins and switches and the high voltage from that shock appears to be traveling through the circuit and taking out ICs. When I transferred the shock into the pins I noticed that there was arcing from trace to trace and trace to pads trough out the PCB coming from the trace connected to the external switch and pins. The system is a 9v system and the static generator that I used to test the PCB was a Van de Graff generator 10-060. The PCB is extremely compact.

    My solution: My solution whether it will work or not is to place ground rings around the external pins on the PCB and the external mechanical switch on the PCB. I am hoping to force the high voltage from the static shock to arc to ground (taking the high voltage straight back to the battery) as soon as it enters the PCB and not travel down the trace to other parts of the circuit. As a back up just in case the static shock does not have a high enough voltage to arc I have MOVs in line with the traces connected to the external parts to hopefully lessen the effects of the higher voltage spike.

    I primarily want to force an arc to ground at the point where the high voltage spike enters the PCB. I have little knowledge of high voltage in PCBs.

    Questions: Do you think this will work? If not I am open to suggestions. What is the best way to construct the ground ring to guarantee the static shock will arc to the GND ring every time?

    Thank you,
    Jed
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Post your circuit diagram, including the generator connection and everything else. A pircture is worth a thousand words.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    Why are you using a Van de Graff generator for a static test? That seems excessive. There are standardized static tests used for electronic devices. I would suggest you test to those standards, if possible.

    To protect against high static discharge you may need to use a spark-gap suppressor as well as the MOVS. You also should have some resistance in series with all the pins (as high as possible without disrupting the circuit operation).
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Something I wrote for the book. While it doesn't directly answer your question, some of it applies.

    ElectroStatic Discharge
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    Maybe his logic is: if anything can survive a Van de Graaff generator, then it can survive anything else short of a direct hit from a lightening bolt.

    Small Van de Graaff generators produce potentials of 200kV and more.

    Most ESD meters only go up to 20kV.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    All I can say is "Good luck with that." :rolleyes:
     
  7. jmartens1978

    Thread Starter New Member

    Nov 8, 2012
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    I am using a small Van de Graaff generator with the logic if it survives this it can survive about anything. This also seem to guarentee that I got a stong shock everytime. What devices are used for standard static testing? This is my first project in dealing with a static shock taking out my electronical device through an extrenal switch and pins that extend out side the plastic housing designed to make contact with a metal surface.

    Based on my test setup I am recieving approximately 15kv -20kv from the Van de Graaf generator.
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Device Sensitivity and Testing, By The ESD Association.

    I've actually done such testing after ordering a nice high voltage cap. A transistor curve tracer gave the 1,500 volts spec'd to our test.

    BTW, our unit passed this test.

    Google "human finger ESD model" for more.
     
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