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unpopulated 4 layer board came back shorted between 3v3 and gnd. Cannot find the issue

frippe75

Hi!

 

The board has a short between 3v3 and gnd and I cannot find it using drc/erc.

I have overlaps for sure. Those are mainly due to me drilling in pads. I have gone through all overlaps related to gnd and 3v3 signals.

 

The dru is from OSHpark and their published tolerances for a 4layer board.

Tried measuing resistance on board but maybe my multimeter is too simple to show anything. But since the board is not populated and still shorted thats a bad idea.

 

From a schematic perspective the 3v3 and gnd cannot be shorted since they are not connected. Has to be on the board side, right?

 

Trying to determine if I should go back to OSHpark or not. Got three copies and they are the same so thinking this is a design issue more than anything else.

 

Any ideas?

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  • Am 17.02.19 um 16:24 schrieb Fredrik Tarnell:

    Hi!

    Tried measuing resistance on board but maybe my multimeter is too simple to show anything. But since the board is not populated and still shorted thats a bad idea.

     

    There is a simple but effective way to locate such shorts (also

    defective parts like shorted caps on populated boards:

     

    Take a laboratory power supply and inject a healthy but not damaging

    current into the short – here, say 1-2 amps.

     

    (If looking for a short on, say, a narrow thin trace pair, of course

    limit the current to maybe 0.1 amps, whatever the trace will survive.)

     

    Take a sensitive millivoltmeter (0.1 mV resolution or better) and start

    measuring voltage differences randomly across the board.

     

    The current causes a perceptible voltage drop along traces and even

    across ground planes, so you should soon find the place where the drop

    is steepest and the current is sinking into the short.

     

    Good luck!  Hans

     

Reply

  • Am 17.02.19 um 16:24 schrieb Fredrik Tarnell:

    Hi!

    Tried measuing resistance on board but maybe my multimeter is too simple to show anything. But since the board is not populated and still shorted thats a bad idea.

     

    There is a simple but effective way to locate such shorts (also

    defective parts like shorted caps on populated boards:

     

    Take a laboratory power supply and inject a healthy but not damaging

    current into the short – here, say 1-2 amps.

     

    (If looking for a short on, say, a narrow thin trace pair, of course

    limit the current to maybe 0.1 amps, whatever the trace will survive.)

     

    Take a sensitive millivoltmeter (0.1 mV resolution or better) and start

    measuring voltage differences randomly across the board.

     

    The current causes a perceptible voltage drop along traces and even

    across ground planes, so you should soon find the place where the drop

    is steepest and the current is sinking into the short.

     

    Good luck!  Hans

     

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