In a message dated 7/10/98 2:21:26 PM Pacific Daylight Time, [log in to unmask]
writes:

Hi Brian!!

      Just to clarify a couple of points from my last post:

>  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).

Yes that is correct, but what I was suggesting they do is IF they still wanted
to not use two zones, was to not use the last two zones instead of not using
the first two...just to give the boards more of a chance to cool down before
they came outside the oven. With the Heller ovens, you can't go higher than
300 degrees C. set-points, and you can put em' in any zone you want to...

>  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).

That's what I said too, but in rare occasions there's been times that I've had
to push the spike deeper inside the oven so that the solder was at least solid
before the board exited the oven...that was back when I found out about the
exhaust requirement for Conceptronic ovens and how the exhaust played a
critical role in cooling. I had to push the spike back inside the oven until
we could get a new exhaust fan installed on the roof. That's the reason I said
what I did, IF they insisted on not using two zones. But Brian is right, use
all the zones you have...much more control that way.

But speaking of exhaust and cooling, guess what I found in the Heller manual?
(oh by the way, the manual I have is for the 1500W, 1700W, 1800W, and 1900W
ovens) Page 64 of Troubleshooting, Section-XIV-(Board cooling is insufficient)
Item 5. "In an air cooled machine, verify there is sufficient exhaust
connected to the exhaust port of the cooling module." So Heller ovens also use
the exhaust to assist with cooling. The 1900's need 600 cfm so that's another
thing to check.

-Steve Gregory-

(Here's your change...GRIN...Have a good weekend buddy!!)------>  >  Just my 2
cents.

>  Brian Stumm

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