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Nickel-boron plating pitting problem in MEMS probe card

Q. Hello I am Kim.
I am currently working as a plating engineer in a manufacturer of probe cards based on MEMS (micro electro-mechanical systems) manufacturing technology.

I'm looking for guidance on an intermittent pitting defect that has appeared in our acid nickel-boron (Ni-B) electroplating line.

• Process parameters
- Bath pH : 3.9 (spec 3.9-4.1)
- Temperature: 45-50 °C
- Current density : 2.0 ASD (0.50 A)

• Defect description
- Circular pits across the surface (see photos).
- Defect appears on some lots, not all.
- A completely new bath showed the same issue <2 months after make-up.

• Troubleshooting done so far
1. Re-made the bath - pits returned.
2. pH, boron content, and temperature within spec.
3. Adding the Ni-B wetting/leveling additive reduces, but does not eliminate, the defect.

• Questions
1. Which additional checks would you recommend (Hull-cell, surface-tension, CVS, etc.)?
2. Could marginal wetting-agent depletion, combined with current crowding, explain the lot-to-lot behaviour?
3. Would lowering the current density or using pulse/pulse-reverse plating be an effective fix?

Any insights or similar experiences would be greatly appreciated.

Thank you in advance!

Kim

Bomin Kim
- Korea
July 30, 2025

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