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September 2000

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Subject:
From:
Ryan Grant <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 18 Sep 2000 08:20:14 -0600
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Arturo,
        Warping BGAs are the usual cause of shorts in the corners and are
usually caused by the reflow profile.  BGAs have a natural tendency to warp
due to CTE and package thermal mismatch as you have seen at rework.

        However, if the BGA was reflowing fine, and all of a sudden, with
the same reflow profile, it now warps in the corners; it is likely the fault
of the component.  If that is the case, you can usually isolate it to a
specific date code.  Most plastic BGAs have their tops injection molded.
The heat and pressure can leave residual stress in the component.  This
stress will relieve itself by warping the component during reflow.  You can
often times see warped packages prior to reflow as well.

I hope this helps
Thanks

Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]


> -----Original Message-----
> From: Arturo Urias [SMTP:[log in to unmask]]
> Sent: Friday, September 15, 2000 5:09 PM
> To:   [log in to unmask]
> Subject:      [TN] BGA bridges
>
> I have been experiencing bridges on some 1.27mm pitch BGAs.
> The bridges always happen in the corners, and my suspicion
> is that the BGAs (yes, the components) are warping downward
> to the point of creating the bridges on the corners, where the
> distance from the BGA to the pwb is shortest.
> I have seen this phenomena while reworking the BGAs, but I am
> a little surprise to see it during the oven reflow.
> Any ideas what is causing the bridges?
> Thanks!
>
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