What Frequency?
Since they are using Duroid, I think it is save to assume it is for RF.
Nickel is a barrier to RF.
Depending on the Frequency, Power level and loss acceptance, ENIG may be acceptable but will not give as good as a performance as HASL.
Unfortunately many RF designs require enclosing the circuit to minimize leakage and HASL is not flat enough to seal against well.
You might suggest IAg as you will get both flat surface and less loss due to finish (RF skin effect).
I am not sure if the Dk of the finish metals will have any real effect, but am certain that best RF performance does not come with Nickel based finishes.
Call me if you want to discuss further.
Hope it helps,
FNK

Frank N Kimmey CID+
Principal PCB Designer
Powerwave Technologies Inc
Office 916-941-3159
Fax 916-941-3195
Cellular 916-670-0645

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Kathy
Sent: Tuesday, November 29, 2005 3:01 PM
To: [log in to unmask]
Subject: [TN]


I am posting this ? for a colleague:



"We are fabricating some boards for a customer that will be 1 oz of copper
on Duroid 6010.  They are considering two surface finishes:  HASL (Hot Air
Levelled Solder) and 150u" Nickel under 5-10 u" Gold.



The question they are asking is as follows:  What are the dielectric
properities of the Nickel/Gold finish vs. those of the HASL finish.



Does anyone know the answer?  I figured that the insulating material (the
Duriod) and the conductor thickness (copper) would have the largest
influence on dielectric performance and that the surface finish would have a
negligible impact on performance.  Is this true?"



Thanks!








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