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Post subject: question on silver plating
Posted: Wed Mar 05, 2008 3:19 pm
Joined: Fri Feb 22, 2008 4:01 pm
For RF power delivery, it is a common practice to silver plate copper wire or strip or coil. Over time the part gets tarnished in color. Questions:
(1) Does the corrosion matter?
(2) How to prevent corrosion/tarnishing?
Thanks for your response.
Posted: Thu Mar 06, 2008 5:25 am
Joined: Fri Feb 17, 2006 12:07 pm
Location: London UK
Much depends on the application.
For antenna use, for example, 2 critical factors are frequency and antenna current.
As the radio frequency increases, loss mechanisms of a surface nature such as dielectric loss in surface contaminants (such as oxides) are significant. Also the conductivity loss becomes significant because it is a constant per wavelength, and there will be a larger number of wavelengths at higher frequencies. Copper has a high bulk conductivity but copper oxide film on the surface increases the surface resistance and hence loss. Silver compounds form more slowly in contact with air, except for silver sulfide. This is the black tarnish seen on silver. However, its conductivity is no too bad and only becomes significant in really critical applications such as in some high Q filters or first stage receiver circuits where very low noise factors are needed.
Plating with gold is then used for these very critical applications.
Where antenna currents are high, for example high Q small loop antennas, conductivity is important in order to ensure good efficiency and avoid heating effects at high power. Where antenna current is low, for example multiple element wideband structures with high feed impedance, the material used is not critical. I have used zinc galvanized steel at UHF with no discernable deterioration compared to copper elements.