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January 2005

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From:
"Fazioli, Dan (ACLE)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Fazioli, Dan (ACLE)
Date:
Thu, 6 Jan 2005 13:07:21 -0700
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Hi Roger,

First, you indicate that the PWB design has passed short-term vibration
testing without incident in the past.  What exactly is that short-term
vibration testing that the PWB passed?  Has a qualification vibration
test or an ESS vibration testing been done?  If the answers to the above
questions indicate that the design approach is structurally sound, then
it tends to indicate that the problem is associated with workmanship.  


Secondly, does this CCA use ENIG as a final finish on the solder pads?
And if so, have you considered that the presence of ENIG might be
resulting in the "black-pad" contamination issue that is well known as
the Black-line nickel (BLN) low level defect associated with ENIG that
can occur unpredictably for even the best PWB manufacturers, that goes
undetected and ultimately results in improperly formed solder joints
creating failures due to fractures in the solder joints that cause
electrical opens and/or intermittences during ESS vibration and
temperature testing and/or actual field exposures to the same types of
environments.

Regards,
faz


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roger Stoops
Sent: Thursday, January 06, 2005 1:19 PM
To: [log in to unmask]
Subject: [TN] Solder Joint Failures after Short-term Vibration

Hello all,

We are having an ongoing problem with solder joint failures on a 144-pin
PQFP processor, after short-term vibration. The board layout and
mechanical mounting apparatus were designed with vibration in mind, and
have passed vibration testing in the past. The same processor is used on
a dozen other assemblies, none of which have this problem.

The solder joints appear to exhibit dewetting, although there is a toe
and heel fillet.  The heel fillet is unusually large, and the top of the
PQFP lead has a grainy appearance instead of a matte or shiny
appearance.  Some leads can be pushed off the solder joint with very
little pressure.  Sn62Pb36Ag2 solder is being used, and our EMS provider
continues to claim that boards meet IPC-A-610 class 2 requirements.

Any ideas as to what may be causing solder joint failures? 


Also, any suggestions or recommendations (preferred) for a test house to
provide x-ray, microsection and composition analysis?

TIA & Best Regards,

Roger M. Stoops, CID+
Trimble Navigation Ltd., Dayton, OH, USA
Ph: +01 937.245.5288
Fax: +01 937.233.7511

Oh, and BTW, changing EMS providers is not an option...

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