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Zinc w/Trivalent Passivization Compatibility with NiCu EMI Gasket

Q. We've designed a power conversion product with a steel sheet metal housing. The housing, as well as internal steel parts, are zinc plated with trivalent passivization. This particular product requires EMI gaskets, which for a variety of reasons, were selected to be nickel-copper fabric over foam core. The original intended operating environment was indoor, 90% max RH, non-condensing. However, a key customer has asked about applying the unit outdoors in a suitable enclosure, with active measures to ensure no condensation. We need to ensure the electrical integrity of this interface for 10+ years. Incremental increase in contact resistance is OK. 10X is not.

1. NiCu is far from from zinc on the galvanic index. Is this interface likely to galvanically corrode with occasional (hard to quantify) condensation?
2. Passivated zinc is a common finish for us, but is there a reasonable cost effective, electrically conductive finish for steel that would be significantly more robust?
3. Similar EMI gaskets with tin plating are available from other manufacturers. Tin is slightly closer to zinc on the galvanic index. Is this worth considering, or would it be only a minor improvement, if at all?

John O'Connor
Product Designer - Merrimack, New Hampshire, USA
September 6, 2017