General > General Technical Chat

Bizarre and Unexplainable High-Impedance "Shorts" Across PCB

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floobydust:
The PC boards are defective- it could be a contaminated bath at the PCB fab.
If it's dissimilar metals i.e. copper and tin aqueous, there would be a 1/2 cell galvanic potential seen between traces as well. Dry, a thermal EMF would be seen.
I don't think tin whiskers develop fast though.
I have seen shorts due to copper specs caused by dust. I just used a power supply at high current to clear them, as proof.

station240:

--- Quote from: tom66 on September 06, 2021, 05:25:15 pm ---I then heated the board up in that area at 400C with a hot air gun for 30 seconds.  Result: problem gone.  And no matter what I do, flex the board, heat it up with an iron, tap it in the area, it doesn't come back.

--- End quote ---

I wonder if this indicates there is water (or a solvent) trapped between the inner layers.
Worth asking a few different PCB fabs if this is an issue they have seen, and what the possible cause could be ?

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