Hi Sergio,

The dielectric thickness (H), soldermask thickness (H1), line width top (W)
& bottom(W1), spacing (S) & the circuit height (T) all have impact on the
impedance. The circuit height includes the base copper+plated copper & the
surface finish like HASL, ENIG / electrolytic nickel gold, Silver etc., But
the ENIG/electrolytic gold thickness being so small in comparison to the
overall copper thickness the impact on the impedance is negligible,
especially if you are talking about +/-10% for 50 Ohms or greater impedance
values. If you looking for say +/-5% or less or a Rambus design with 28 ohms
impedance than the effect of every component above becomes significant. Hope
this helps.

Thanks,
Krishnan


-----Original Message-----
From: Sergio T. Ruiz [mailto:[log in to unmask]]
Sent: Friday, September 19, 2003 12:48 AM
To: [log in to unmask]
Subject: [TN] controlled impedance..


hey guys...

thanks so much for all the great info on this list!

i have yet another questions..

i am working on a controlled impedance board with a twist..

the final coating on this board is nickel/gold..

does anyone have any experience as to how this effects the impedance of a
trace?

off hand, i am going to guess that since you are basically adding just
another conductive layer to the build, it shouldn't matter. and, since the
thickness of the layer should be negligible in the calculation..

but.. real experience sometimes thwarts my guesses..

thanks!


____
Sergio T. Ruiz
technology and MIS
Philway Products, Inc.
(419) 281-7777 x232

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