Gordon,

Keep in mind that you (or your assembly shop) probably demand solder mask
over bare copper (SMOBC) in your prints.  That means the only place nickel
and gold  will be plated on the board in where the solder mask doesn't cover
the copper traces, i.e. pads and vias.  Since the pads are then covered with
solder, the signal at that point will either a) travel down the solder to
the lead (in the case of a QFP), or b) in the case of a BGA, travel down a
copper trace to the nickel plating, through 200 micro inches of plating and
up the solder sphere.  The effect can be considered negligible.  The only
place signals will effectively travel down the nickel/gold plating is in the
vias.  At this point, you have to consider, how much of an affect will the
plating material have, compared to the shape of the signal path (i.e.,
making a L shaped bend when the trace reaches the via).

Best Regards

Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]


> -----Original Message-----
> From: Gordon Falconer [SMTP:[log in to unmask]]
> Sent: Monday, May 14, 2001 2:26 PM
> To:   [log in to unmask]
> Subject:      [TN] Electroless Nickel / Immersion Gold
>
>         Can anyone tell me if there are any probblems using Electroless
> Nickel
> (5micron) / Immersion Gold (0.1 micron) as a surface finish on High
> Frequency boards (10GHz). Particularly,is nickel a poor conductor at High
> Frequencies?
>
>
> Regards
> Gordon Falconer
> Process Engineer
> Zot Engineering Ltd
>
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