Signal energy in a propagating signal in a microstrip crowds the side of the signal line closest to the reference plane, and the dielectric between the signal trace and the reference plane, so the skin effect of the bottom surface of the conductor in contact with the PCB dielectric will be more critical than the ENIG coated surface of the Cu trace. If the Ni was the adhesion layer between the Cu and the dielectric, it can be expected to show a larger effect on loss.
Best regards,
Leo
Leo M. Higgins III, Ph.D.
Sr. Vice President, Engg and Technology
ASAT, Inc.
13809 Research Blvd., Suite 635
Austin, Texas 78750
office phone 512-249-4758
mobile 512-423-2002
[log in to unmask]
www.asat.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dwight Mattix
Sent: Wednesday, June 13, 2007 1:25 PM
To: [log in to unmask]
Subject: Re: [TN] Nickel barrier and RF applications
The lossy effects of Ni are long established. However, many successfully
use it at high freq.
In many (most?) cases the Ni effects can be modeled and tuned in circuit
design.
fwiw, We have a satcom mobile earthstation app with complex microstrip
filters and couplers running at 14GHz on ENIG.
Going on 20 years now and still producing/updating the system, still using
ENIG.
for the record:
ENIG is the worst surface finish we've ever used.
Except for everything else we've tried. ;^)
dw
At 10:57 AM 6/13/2007, Stadem, Richard D. wrote:
>Inge and Vlad
>Keep in mind that Paymon is reflowing the entire assembly, not just
>reworking a BGA site.
>Therefore what you just described is happening over the entire assembly
>to all of the solder joints.
>This cumulative effect could theoretically create a noticeable
>improvement in the RF performance of the circuitry.
>
>-----Original Message-----
>From: Hfjord [mailto:[log in to unmask]]
>Sent: Wednesday, June 13, 2007 12:13 PM
>To: 'TechNet E-Mail Forum'; Stadem, Richard D.
>Subject: SV: [TN] Nickel barrier and RF applications
>
>For each repeated reflow, more and more nickel participates in building
>nickel/tin intermetallics. These IMCs are not ferromagnetic. So, let's
>assume that Paymon's electroless nickel is just some 2-3 micrometers
>thick, which is not unusual, then a growth of the IMC by some 0.1 to 0.5
>micrometer for each reflow will probably have a positive effect = less
>magnetic.
>Just an analogue thought
>Inge
>
>
>I think, there is one question to ask. If ENIG (or rather the presence
>of Ni) is the source of the problem, then why does 2nd reflow improves
>the yield?
>
>
>Regards,
>
>Vladimir
>AMD
>
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