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July 1998

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Subject:
From:
"Stephen R. Gregory" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 10 Jul 1998 15:58:42 EDT
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In a message dated 7/10/98 11:48:17 AM Pacific Daylight Time,
[log in to unmask] writes:

> Steve,
>  I'm Angie's co-worker and she had to take off, so I offered to cover for
>  here,
>  The board being run is not very dense, 1 bga, 3 qfp's, hand-ful of other
>  ic's, and some passive.  Nothing special.  Our fans are both set to 100%
>  but still extremely hot.  Any other suggestions?
>
>  Sean M. Heffernan
>  Quadrus Manufacturing
>  [log in to unmask]
>  408-918-5132

Hi there Sean!

     So, Angie takes off when things get "interesting" huh? Just teasin'!!
Well, one thing I can think of was that Angie said before that you had the
first two zones turned off, and I guess I just have to ask why...I guess I can
understand that maybe the board really doesn't need all the zones to reflow
good, but maybe somehow by doing that you've changed the way the airflows
moves about the oven and that maybe causing your board to stay hot so long. I
don't know precisely the way the air moves in Heller's ovens, but I do know
that something as obscure as not having enough exhaust flow with Conceptronic
ovens would cause boards to come out hot...the way their cooling section was
designed is that the exhaust would draw ambient air from outside the oven at
the exit end to assist with cooling the assemblies as they exit, if you didn't
have at least 500cfm @ 1.0" in. hg, the boards would come out still liquidous
(plus it voided the warranty on the blower motors, the blowers also needed
that rate to keep them cool).

       If you used all zones you would be able to lower your set-points at the
end because by the time the boards came down to the spike zone they would be
closer to the max peak that you want to see, and thus wouldn't have to set
265. Or if you still want to turn 2 zones off, do the last two instead of the
first two, drive your spike zone back into the oven further and you'll have a
little more distance for the boards to cool before they pop outta the end...

      Hmmmmmm, something still don't sound right though...the boards shouldn't
be that hot with the temperatures that Angie said everything was set at. I
know Angie said that the oven was pretty new, but I'm wondering if your belt
speed is really 65cm per min...could be faster than what it's saying it
is...check that too.

      Wish I could be there and see things first hand....naw I don't, it's
Friday!!! (GRIN) Where's that Geoff Sikes at? Why isn't his butt out there
helping you out? (Just razzing Geoff, tell him hi for me!!)

-Steve Gregory-

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