RE: [SI-LIST] : Zo Variance From Plating Thickness Variation

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From: Tom Dagostino (tom_dagostino@mentorg.com)
Date: Fri Jan 14 2000 - 15:44:20 PST


David, define microwave frequencies and relate them to parts with 50 to 100
psec risetimes. 100ps is on the order of 3.5 GHz and 50 psec is about 7
GHz. Surface roughness I think comes into play at frequencies less than
this.

Tom Dagostino
ICX Modeling Group
tom_dagostino@mentor.com
503-685-1613

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Dave Hoover
Sent: Friday, January 14, 2000 10:49 AM
To: 'si-list@silab.eng.sun.com'
Subject: [SI-LIST] : Zo Variance From Plating Thickness Variation

Michael wrote.....

Dave [Groovy]: you're one SI'er who is intimately familiar with real world
PWB fab variances. Have you ever seen application problems that were due to
unevenness of finished trace geometry?

Michael Alderete
Aerojet
---------------------------------------------------------------------------

Michael [;-) Rut Oh..the secrets out]:

Honestly I haven't heard of any issues popped up in the field from
unevenness of finished trace geometry. My Industry Specs (IPC-6012)dictate
minimum copper thickness. If we have a process related issue that would
reduce the copper thickness below the values required we would generally
cull that out during cross section analysis. Also we would see it in the
Zo (and/or Zdiff) TDR results. Isolated spots (like major copper pitting)
would be highly visable and rejected at inspection.

>From an electrical standpoint, I haven't heard of any of our current
customers
who have had risetimes (and fall times) short enough to really see issues
from
minor plated copper variance. (Now if I was building microwave stuff I may
have had a different answer to this.....)

David Hoover

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