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Thread: Conductive PCB substrate

  1. #11
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    I do work night shift

  2. #12
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    How about posting a picture of the board in question?

  3. #13
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    I will try and get a pick up soon.
    I found the board is FR2 - which IIRC does have some paper, wiki quotes as having low moisture resistance. living on Dartmoor means its always a bit on the damp side.
    Second attempt did the same and I also found that the default pads on the MOSFETs are too thin to be reliably etched with no issue. to get over this I widened the pins placements and increased there size - this mean bending the pins to get the MOSFETs in, but if it gives a more reliable circuit than I am fine with that.

  4. #14
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    Hi Guys/Gals,

    A VERY important point made earlier in this thread is the necessity of a resistor being present to turn the FET off.

    This is because the GATE of a FET requires mere micro amps to turn it on.

    Essentially a resistor from GATE to SOURCE in both cases of N-Channel or P-Channel FET's.

    Often with 5V logic circuits I use a 10K resistor.

    Think of it being that if you supplied the gate with a voltage to turn it on, then just removed the voltage, the gate is just left floating around in the breeze. The FET's internal gate capacitance is enough to keep it switched on in many cases hence using a resistor is the sure way to return it to OFF when the drive voltage is removed.


    Hope this helps.



    Regards,
    Morty.
    Last edited by mortifyu; 29-12-2016 at 16:54.

  5. #15
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    What sort of flux did you use? THIS is very important.
    And most importantly how did you clean it?
    Is it thru hole or SMT?

    With the limited description, your problem seems to be surface ionic contamination.
    Board leakage is then exacerbated by changes in humidity.
    "Will design analog circuitry for Beer."

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