The production problem
An ENIG surface can appear normal initially yet show black spots, yellowing or localized corrosion after salt-spray or corrosive-gas exposure.
Diagnostic sequence
- Document nickel-phosphorus condition, gold thickness and the initial surface.
- Check final rinsing, ionic residue and drying after immersion gold.
- Compare untreated and treated samples from the same lot.
- For severe defects, strip gold locally and inspect the nickel layer.
Control direction
- Exclude black-pad and gross plating defects before protection trials.
- Reduce residues that can accelerate localized electrochemical corrosion.
- Evaluate pore-sealing protection only on an otherwise acceptable gold finish.
Validation before production release
Salt-spray appearance with full test conditions
Nickel inspection after gold stripping
Contact resistance
Solderability
What this approach cannot repair
Pore-sealing protection is risk reduction, not replating. It cannot repair exposed copper, missing gold or an already corroded nickel layer.