Ken
In the two places I have worked the same approach has been taken: vias
are either filled or open, it doesn't matter which so long as it isn't
partially filled.  And this is on a "per via" basis, so mixed condition
on a board is OK.

As for flux trapped during wave, I have been involved in one instance
where this was thought to be an issue, where the spec for the part
claimed a clearance under the part of 0 to 4 thou.  In this case we
started out masking the vias under that particular part, but after
running some experiments we stopped masking and had no problems (on a
population of several hundred thousand).  The experiment consisted of
running unmasked boards through the normal process (SMT - manual - wave
- wash), and then cutting the leads of the component and removing it
from the board.  Ion chromatography showed trace amounts of residue,
well under the limits.  When we did any process changes we verified the
findings were still true.

So - if you think you may have a problem, check your worst case.

Usual disclaimer: not exactly as illustrated, mileage may vary, 4 to 6
weeks for delivery, do not try this at home, opinions are my own.

regards,

Graham Collins
Process Engineer,
Litton Systems Canada Limited
(902) 873-2000 ext 215


> -----Original Message-----
> From: Ken Patel [SMTP:[log in to unmask]]
> Sent: Tuesday, December 02, 1997 2:45 PM
> To:   [log in to unmask]
> Subject:      [TN] Reliability: Via plugging V/S keeping them open
>
> Is there any recommendation from the reliability point of view whether
> to
> plug the all non-vias or keep the vias open and let it be filled up
> during
> wave solder operation?
>
> Any comment/concern in removing the flux trapped during wave process
> from
> underneath the standard QFP's.
>
> This question is asked to standardize the fab requirements for all
> those go
> trough standard wave solder process.
>
> re,
> ken patel
> ______________________________________________________
> Ken Patel                       Phone:  (408) 490-6804
> 575 Cottonwood Dr.              Fax:    (408) 490-6859
> Milpitas, CA 95035              Beeper: (888) 769-1808
>

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