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September 2000

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Subject:
From:
"Cyker, Howard A (Howie)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 11 Sep 2000 11:45:11 -0400
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Julien,

We have processed many devices similar to what you describe.  You would have
to assure that the solder paste we are using has sufficient "tack"
(influenced by viscosity, flux formulation, metal content) to hold the QFP
in place as the board moves.  Another factor affecting tack is time and
temperature.  Generally, a higher ambient temperature will cause the paste
to slump and lose tackiness.  Similarly, the longer the solder paste is
exposed (either after printing, or on the stencil) prior to pick & place,
the lower the tack.  Also, increasing the placement force of the pick &
place machine can push the leads deeper into the solder paste to hold the
part more securely, however pushing too far can also cause the device to
slide off the pads during placement (it probably will slide before you
deform the leads).  It may also cause the paste to squeeze out from the pads
causing solder shorts or solder balls.   How heavy are your parts?  We have
been successful with parts in the 35 gram range.

> Howard A. Cyker
> Lucent Technologies
> Email [log in to unmask]
> Phone 978-960-2964
> Fax 978-960-1187
Pager 888-961-2336



> ----------
> From:         Julien Bouchard[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Julien Bouchard
> Sent:         Monday, September 11, 2000 11:03 AM
> To:   [log in to unmask]
> Subject:      [TN] Displacement of PQFP with heat slug
>
> Hi everybody,
>         We currently have problems with some PQFP ( 208 and 240 pins )
> that have a
> piece of metal mold inside the IC to enhance the thermal exchange. Because
> of this metal, the IC is very heavy, in comparaison of other IC. After
> they
> have been place by the pick and place machine, they often move from there
> original position when the conveyor start or stop. It seem that the IC is
> so
> heavy, and is inertia is taller than the retention force of the paste. We
> try a lot of solution, but none of them give a good and constant result.
>         We want to know if someone have similar problem and if a good
> solutions
> have been found. Thank you.
>
> Julien Bouchard
> Matrox - Process Engineer
> Email : [log in to unmask]
>
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