Short note:
Magnetic interactions stop about kHz because the magnetic perm.. coffficient
goes to 1.
Thanks for relating your data.
Richard Haynes

-----Original Message-----
From: Barry Bates <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Friday, March 12, 1999 4:21 AM
Subject: Re: [TN] Effect of Surface Finish on RF Boards


>Michael,
>We have experienced unacceptable loss at 3GHz for 50 ohm
>microstrip transmission lines with the standard Ni Au finish on
>1/2 oz and 1oz copper using Rogers and Arlon PTFE based
>substrates.
>What we found OK was a cheat, we applied the standard Ni Au
>finish to all the exposed pads, ie solder, test, contact, etc.
>and we left the rest of the track bare Cu with the normal, thin
>Probama solder resist coating. The solder resist had to cover
>part of the Ni Au to ensure sufficient environmental protection.
>The solder also adds to the attenuation budget so be sparing with
>it. The higher the frequency the worse it gets.
>As far as I recall, Ni also does some of its attenuation via a
>lossy magnetic interaction with the EM wave.
>This gave the microwave guys the performance they were after.
>The detail I do not have but I recall that the losses went from
>many tenths of a dB to just about 1/4 dB for about 450mm long 50
>ohm track
>Regards,
>                Barry Bates
>
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