Hello Jerry,

I absolutely agree that the trend over the past 8 to 10 years has been
towards full forced convection and with good reason.  As I am sure you know
it is very difficult to get a solid, uniform reflow profile using 100% IR.
This is especially true when it comes to boards with a mix of high and low
mass components.  That is why we developed our 100% Full Forced Convection
oven as we followed the market trend.

However, it is also true that many people are "prejudiced" against IR
because of the difficulity many companies have had in controlling the
temperature over the course of a day.  At Heraeus we have worked with
Quartz IR emitters since the 1950's and know how to control them very well.
 Ok, I don't want this to sound like a commercial, but I'm trying to give
you a background on us.

So, once the Full Forced Convection oven is in place, we went back to look
at the benefits of having optional IR emitters installed. We found (as a
result of the study we commisioned) that, in certain situations cutting on
the IR emitters in certain areas of the oven (i.e. not all zones), there
are advantages.

Specifically, with BGA soldering, having IR with convection is a very
effective way of getting heat under the chip.  There have also been
demonstrations that the combination can help eliminate tombstoning.

I hope this helps explain matters a little better.  Thank you for the
comments.

Douglas H. Bennett
Sales Engineer
Heraeus Amersil, Inc.
Atlanta, GA, USA
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