Yes, it can have an effect.
Read this article: Reduction of High-Frequency Signal Loss Through the
Control of Conductor Geometry and Surface Metallization.
www.smta.org/files/SMTAI02-Brist.pdf  There are several other articles
out there on this subject as well, but this is one of the best.
The laminate properties have the most effect on signal loss in
high-impedance/high frequency circuits, but the surface finish also has
significant impact. This is due to the Hall effect, where only the
outermost 2 to 7 microns are used to pass the signal. I have seen
problems incurred from the changing of the finish in these types of
circuits, mostly in telecommunications assemblies. However, I saw the
same signal loss problems in a military gyroscope that was changed from
HASL to ENIG, and in several Bluetooth applications where a change from
ENIG to OSP or immersion silver inadvertently increased the performance.
Basically, electroless nickel has a much higher resistivity due to
impurities in the plating bath, etc, that can increase the resistivity
to as much as 100 uohms/cm, even higher in many cases. Compare that to
surface resistivity of copper, which is rated at 1.7 uohms/cm.

Not to mention that the solder joints on ENIG are not the same. They may
not be as reliable as those formed directly to copper. I would suggest
you perform a full qualification of the product with ENIG and compare
with silver before jumping in and using it.
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of ekalgren
Sent: Monday, November 07, 2005 10:02 AM
To: [log in to unmask]
Subject: [TN] RF Board Finish

Good morning, all.



I've got a question for the RF guys out there.  Is there a significant
difference between silver plating and gold plating when it comes to an
RF circuit board assembly?  My drawings call for silver but our vendor
sent gold.  I've been asked to find out if this will have a major impact
on performance.



Thanks for your help.



Eric Kalgren

Electrical Engineer

Continental Tool and Microwave Company

603-775-5200  ext. 333

[log in to unmask]




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