Steve, Angie and Sean:

In a message from Steve Gregory it was suggested to use the first two zones
and disable the last two zones. This might be a difficult thing to do. I
don't have experience with the Heller but I know that some ovens limit the
amount of wattage that can be applied in a given zone. Often times the
reflow zone is allowed to use more watts than other zones because it is the
zone that works the hardest (hottest temp).

I also am worried about the way you use only some of the zones. I would
recommend using all zones as that is the way the machine was designed to be
used. Rather than turning off some zones why not just have a slower rise
rate? Or if your solder paste allows for it you could include a soak, which
would also allow your high mass spots on the board to catch up to the low
mass areas. This would reduce Delta T's across the board (although you
mention that the board is not very high in mass).

Just my 2 cents.

Brian Stumm
ETS, LLC


>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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