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May 1999

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Subject:
From:
Jim Marsico 516-595-5879 <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 13 May 1999 07:26:00 -0500
Content-Type:
TEXT/PLAIN
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TEXT/PLAIN (33 lines)
Good Day Technet:

First, a little background...  We're in production using a 228 ceramic BGA for
a military contract.  The base material of the component is gold plated nickel,
prior to solder ball attachment.  The gold plating is very thin, around .25
microns.  We've been experiencing approximately 5% (components, that is, not
solder joints) open circuits found at in-circuit testing (ICT).  Upon removal
of the BGA (Air-Vac system) from the board, the specific ball location where
the open was identified at ICT shows no solder remaining on the component,
where all other locations has solder remaining.  What does remain is a dull,
gray, crystalline metallization.

SEM/EDX analysis shows Ni/Sn and Cu/Sn.  It is presumed that the Ni/Sn is the
intermetallic layer created from the nickel base material and the tin in the
solder.  What puzzles me is the presence of the copper-tin crystallites.  Since
there is no copper in the solder or on the component, is it possible that this
copper has migrated all the way up from the board pad to the component/solder
interface?

Thanks in advance...

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