This is a result of either flux or some other chemical left on the board
and heated up. It promotes the tarnishing in select areas only. I
usually see this if too much flux was put on the assembly as a result of
a rework process. When the flux is activated with heat application, it
discolors the IAg. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kanaiyalal Patel
Sent: Tuesday, August 16, 2005 5:48 PM
To: [log in to unmask]
Subject: [TN] Yellow smudges on unmasked immersion silver plated area..

Hello fellow Technet members,
We are experiencing yellow smudges on unmasked thermal and ground lines
on the  immersion silver plated board. Pictures are on Steve's website.
http://www.stevezeva.homestead.com and click on "Picture Page 2" then
look for "Sierra Board.doc".
Wondering if you can provide some clue into what may be going wrong
here? Thanks. We are using watersoluble flux with acqueous cleaning. The
boards go thru doublesided reflow and no wave soldering.
Regards,
Ken



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