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October 1998

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Subject:
From:
"McMonagle, Michael R." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Sat, 31 Oct 1998 08:36:02 -0600
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Tim,
        What type of system are you performing the rework on? With a
board of this density, it is critical that you are properly soaking the
board with adequate preheat (bottom and top), along with a slower reflow
ramp to minimize/prevent the possibility of bowing the perimeter of the
PBGA. Outside of the shorting issue, you have a real danger of causing
damage to wire bonds and ball connections. Also check your airflow
velocity at the nozzle, you may have to reduce it. Nozzle designs
inherently have higher velocity at the corners, so you need to try to
compensate without compromising the rest of your flow. Good luck....

Mike McMonagle
PCA Process Engineering Supervisor
K*Tec Electronics
1111 Gillingham Lane
Sugar Land, TX  77478
(281) 243-5639 Phone
(281) 243-5539 Fax
[log in to unmask]

> -----Original Message-----
> From: Stammely, Tim [SMTP:[log in to unmask]]
> Sent: Saturday, October 31, 1998 6:29 AM
> To:   [log in to unmask]
> Subject:      [TN] BGA rework question
>
> Hello all,
>
> We are trying to remove and replace two ORCA 432 pin BGA's on a big
> 14-layer
> board. We are getting alot of shorts after the rework(I'm x-ray
> inspecting).
> At first we tried solder pasting the pads with a mini stencil, but the
> amount of bridging we got caused me to try just fluxing the pads and
> letting
> the solder balls collapse, but we still got a lot of shorts. I am also
> noticing a lot of board warpage  during the rework heat cycle and it
> also
> appears that during reflow if I watch the component, the corners of
> the BGA
> collapse very early and the component almost appears to be bowing.
> Most of
> the shorts we are getting are in the corners where this last
> observation
> occurs making me think it is causing the shorts. Any suggestions on
> how to
> eliminate this problem?
>
> Thanks,
>
> Tim Stammely
> Manufacturing/Process Engineer
> MSI
> Manassas, VA
>
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