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July 1999

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Subject:
From:
Bev Christian <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 28 Jul 1999 12:36:44 -0400
Content-Type:
text/plain
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text/plain (105 lines)
Dewey, Marion,
Hey, be easy on Werner our res expert on reliability.  If I knew half as
much German as he knows English I would be happy!   :)

regards,
Bev
Nortel Networks
> -----Original Message-----
> From: Marion A. Graybeal [SMTP:[log in to unmask]]
> Sent: Wednesday, July 28, 1999 11:44 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] Freeze Spray and BGAs
>
> Werner,
>
> I see that you and Dan Quail attended the same school (potatoe).
>
> Marion Graybeal
> ----- Original Message -----
> From: Werner Engelmaier <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Wednesday, July 28, 1999 10:07 AM
> Subject: Re: [TN] Freeze Spray and BGAs
>
>
> >Hi Darrelt,
> >What happened to your BGA is pretty obvious. Just consider what is
> physically
> >happening when you hit iot with the freeze spray.
> >You hit the BGA with the freeze spry from the top, I am sure. This
> quickly
> >cools the top layer of the BGA, the rest of the BGA to a lesser degree.
> That
> >sets up differential thermal shrinking (the opposite of thermal expansion
> on
> >heating), which causes the BGA to warp like a potatoe chip with the top
> >surface being concave. This puts tremendous tensile stresses on the
> solder
> >joints, as well as on other parts in the BGA depending on construction.
> On
> >top of which, the PCB does not cool very much at all (the BGA shields it
> from
> >the freeze spray) and sets up shear stresses between the BGA and the PCB.
> >I would not at all be surprised if failure analysis shows fractured
> solder
> >joints. likely in combination of soldering pads ripped out of the polymer
> >matrix.
> >
> >Werner Engelmaier
> >Engelmaier Associates, L.C.
> >Electronic Packaging, Interconnection and Reliability Consulting
> >7 Jasmine Run
> >Ormond Beach, FL  32174  USA
> >Phone: 904-437-8747, Fax: 904-437-8737
> >E-mail: [log in to unmask], Website: www.engelmaier.com
> >
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