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What is the best high temperature plating material for OF copper wire?

 

We're developing a high temperature (450° C) electro-magnet coil for a space (vacuum) application with a required operating life time of ~ 6,000 hours on orbit. Our baseline conductor is 16 AWG solid OF copper. Our baseline insulation is woven fiberglass (E-glass) sleeving with a wall thickness of about 0.005".

We're planning to either wet wind or vacuum encapsulate the coils using a high temperature ceramic, water based potting compound to maximize the effective thermal conductivity of the coil and to create a structural sound coil to withstand launch vibration and thousands of thermal cycles.

One of our technical concerns is the potential for oxidation of the OF copper from exposure to any residual oxygen from the potting compound. Our baseline solution is to plate the wire to offer oxidation resistance. However, another big concern is resistance increase of the conductor due to diffusion between the plating and the copper at 450 °C for 6,000 hours since our on orbit power consumption requirement is fixed.

What is the best choice of plating for our application? Nickel?, Nickel/Gold?, Gold?, Platinum?, Silver? Aluminum? Nickel, Gold and Platinum appear to have the highest solubility into copper but also create the least impact to resistance.

Randy Aadland
- Redmond, Washington

Nickel would be your lowest cost option. Unless you are running at very high frequencies, the nickel diffusion into the surface of the copper will probably have very little impact on the resistance of the wire.

Mark Christianson
semiconductor reliability - Hayward, California, USA
April 7, 2011