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September 2005

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Subject:
From:
Dennis Fritz <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Tue, 6 Sep 2005 11:06:26 EDT
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In a message dated 9/6/2005 9:36:25 AM Eastern Daylight Time,
[log in to unmask] writes:

"...in  order to ensure a well insulation between traces, we do
sandblasting (very  little and tiny) pcb's after etching.
this is to remove the bonding  material that remains on the board after
removing the copper. This is the  only way to achieve a very good SIR
result."


For removal of traces of the adhesion promotion material  (zinc, etc) that
are applied to copper foil, some companies have resorted to  chemical treatments
such as alkaline permanganate. This is similar to "desmear"  of the drilled
holes before metallization.   I think alkaline etching  of inner layers leaves
more of this "adhesion promotion" treatment in the rough  epoxy between
traces, than say cupric chloride etching.  However, the foil  vendors should comment
whether any secondary treatment of etched layers is now  needed to meet very
high (Telcordia?) SIR readings.  I suspect that lower  "tooth" foil does not
embed as much adhesion promotor as the older, rougher  foils used ten years
ago.  Certainly, drum side treatmented foil should  embed little adhesion
promoter.

Also, there may be a patent to two concerning specific  chemical cyles - it
has been like ten years since this high SIR need was  recognized.

I have not heard of using sandblast to accomplish this same  epoxy surface
treatment.

Dennis Fritz
MacDermid, Inc.

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