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What kind of process did the problem come from? Print process? FQC? Human error? Scratch? Dent?

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Some soldermask got scraped or corroded off after manufacture (if it wasn't there to begin with, it would be coated with the board finish--solder or ENIG or whatever), and some mild corrosive agent (possibly flux residue, but also possibly just water) caused the formation of verdigris around the exposed copper.

If the soldermask was corroded off, it's likely the same corrosive agent (would have to be flux residue in this case; water wouldn't eat away the soldermask) was responsible for both that and the verdigris.

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Looks to me like it's corrosion, a scratch wouldn't remove material of varying thickness on the solder mask.

It could have resulted if the PCB manufacturer did not thoroughly clean the boards of etching solution. Another possibility is if there was some other solvent that was on the board and prevented the solder mask from adhering to the board.

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Looks like only mechanical wear because the board is only scratched where you have mask over copper, but not where you have mask over a gap.

Corrosive agents typically won't attack both copper and mask and they would attack the mask more isotropically.

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    \$\begingroup\$ Also abrasion clearly visible where it hasn’t penetrated the solder mask, although it’s strange that the SMT resistor is unscathed. The bare copper immediately above and below suggests that the damage happened prior to the board being populated \$\endgroup\$
    – Frog
    Commented Mar 23, 2023 at 8:58
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    \$\begingroup\$ @Frog good spot. Must have been prior to assembly because otherwise the large colder bump would have also made that scratch pattern impossible. \$\endgroup\$
    – tobalt
    Commented Mar 23, 2023 at 9:08

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