Gold vs Nickel Plating: Contact Resistance After 96-Hour Salt Spray
We compare long-term reliability and contact-resistance change of gold and nickel plating for SMA connectors using neutral salt-spray testing.
Plating choice for SMA connectors balances corrosion resistance, contact resistance, wear, and cost. Gold and nickel are the two most common finishes, often used together as nickel under gold. A 96-hour neutral salt-spray test is a practical way to reveal how each finish behaves in humid or marine environments.
1. Test setup
We prepared two groups of brass SMA connectors: one with 1.27 µm gold over 1.27 µm nickel, and one with 2.5 µm nickel only. Both were exposed to ASTM B117 neutral salt spray for 96 hours, then rinsed, dried, and measured for contact resistance and visual corrosion.
2. Results
| Metric | Gold over nickel | Nickel only |
|---|---|---|
| Initial contact resistance | 0.8 mΩ | 1.2 mΩ |
| Contact resistance after 96 h salt spray | 1.1 mΩ | 4.5 mΩ |
| Visual corrosion | None visible | Light spotting on edges |
| Wear resistance | Good | Excellent |
3. Why gold wins for corrosion
Gold is noble and does not form an oxide film, so the mating interface stays clean even after environmental stress. Nickel oxidizes slowly in air and more quickly in salt atmosphere, raising contact resistance. However, pure nickel is harder than gold and resists mechanical wear better, which is why it is sometimes used alone on non-mating surfaces.
4. Selection guidance
- Outdoor, marine, or high-humidity: Use gold-over-nickel on mating surfaces.
- High mating cycles: Keep nickel underlayer at least 1.27 µm for hardness; increase gold thickness to 2.5 µm on high-wear interfaces.
- Cost-sensitive indoor use: Nickel-only may be acceptable if humidity is controlled.
Conclusion: Gold-over-nickel plating maintains stable contact resistance after salt-spray exposure and is the right choice for harsh or high-reliability environments. Use nickel as a hard underlayer, not as the final mating surface, when corrosion resistance matters.
For temperature-cycling considerations of these materials, see Aerospace-grade SMA CTE Analysis.
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