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November 2006

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Subject:
From:
bob wettermann <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, bob wettermann <[log in to unmask]>
Date:
Fri, 17 Nov 2006 09:37:06 -0800
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All:

 Thanks for your responses.  One of the weaknesses  of this forum is the lack of ability to load photos and movies into the  thread to explain the case with pictures whihc are worth much more than  words in these cases.

  Perhaps I should explain the repair more thoroughly.

  We are suggesting to this customer (Class II, consumer grade product)  that we "cut off" the pad and epoxy down any remnant pad. This is much  less expensive Amercian labor than doing a complete IPC 7721 repair.

  The real issue that I am asking for input from the esteemed group on is the pull strength.....

  Thanks

  Bob

"Stadem, Richard D." <[log in to unmask]> wrote:  When the pad is lifted, it typically exposes the fiberglass weave
underneath the pad. This allows moisture, flux, solvents, etc,  to enter
the pwb and can cause problems later.
The answer to your question depends on what the assembly is used for,
and to what standard do you wish to comply with. IPC 610 and J-STD-001
do not allow missing pads, they require it be repaired.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of bob wettermann
Sent: Friday, November 17, 2006 9:11 AM
To: [log in to unmask]
Subject: [TN] One solder Ball Not Connected on a No Connect Pad After
Rework

This question to the group is about expected solder joint strength on a
BGA.

  The BGA in question is a 8 x 8mm plastic package  BGA using a LF
SAC305 soldering process. It has 64  x 0.018" balls holding it to  the
PCB.

  When removing this device for rework 3-4% of the time one of the
corner NO CONNECT pads comes off.

  The question is if we do nothing upon replacement of  a new device  to
the damaged pad will it really make a difference ??? We are arguing
that the holding strength of the reworked device would be approximately
the same because the change in overall surface area is marginally
impacted.


  Thanks

  Bob Wettermann


Bob Wettermann

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Bob Wettermann

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