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January 2001

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Subject:
From:
Gregg Klawson <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 31 Jan 2001 09:06:44 -0500
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We have just run several ENIG finished board assemblies through a 10 day
cycled system-level humidity test for the first time.  Our previous
experience base has been with HASL'd and/or conformal coated boards.  Two
issues have come up which we don't fully understand.

The first issue is that the boards have a light green to white translucent
residue areas which have formed on top of the Au surfaces which were not
soldered (via-hole lands).  SEM-EDS and FTIR shows these residues contain
water and nickel species, perhaps a nickel sulfate or carbonate.  Taking a
cotton swab with IPA and gently rubbing the residues causes small pieces of
Au to flake off revealing a dark surface (perhaps black).  It appears that
there was a pin hole in the gold and the underlying nickel corroded
producing the residue and corroding underneath the "good" gold area.

I'm wondering if this corrosion is "normal" for ENIG finished boards in
this type of environment?  Or do we potentially have some other
issue?   Any reliability concerns?  All the PWBs were built in the same
shop at different times.

Thanks in advance for your comments.  Second issue coming up in a separate
email to Technet.

Best regards,
Gregg Klawson
General Dynamics Communication Systems
Taunton, Massachusetts, USA
mailto:[log in to unmask]

The views expressed are the author's and do not necessarily reflect the
official position of General Dynamics or any of its subsidiaries.

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