Brian -

Wow, you found me out!  I'll come clean. I used to be a writer for the
Seinfeld show but now, with the show off the air,  I go around making up
information about SMT and reflow.

Okay, I'll get off the caffeinated coffee if you'll stop plugging your ovens
on the Technet.  Talk about testy, my oh my.

With all due respect to you, the solutions you propose are valid and worth
trying. I frankly think you should keep things generic and not mention the
name and model of your oven in capital letters at every opportunity.  And I
never said that it was the only way (read it again, slowly).  However, I did
say that differential heating is unnecessary in this application.  Sorry to
take the wind out of your convection, but it is.

No I do not work for a reflow manufacturer.  I did at one time work for
Vitronics as Reflow Product Manager for 7 years.  By coincidence, did a bit
reflow, too.  A lot of reflow and a lot of applications, as a matter of fact.
And yes, we did experiment with differential heating.  And yes, I did a number
of applications with BGAs and what I described worked as I described it -
without differential heating.  I did additional work during my years with
GSS/Array Technology with BGA and intrusive reflow.  So gosh - I guess I do
have some first hand experience with SMT and reflow and I might actually know
what I'm talking about (maybe).  Sorry to disappoint you.

One line of thought that arose from the work I did in this area is that in
many cases, not only is differential heating not required, but raises
questions regarding stresses on the substrate laminate.  Think about it, if
you are creating a 30 - 40 deg C difference between two portions of the
laminate, typically .063" apart, what is this doing in terms of stress?  Now
here's an experiment for ETS (or someone else to undertake)!

In my work as a consultant (oh god, one of those)  I regularly am called upon
by both end users and equipment manufacturers to benchmark test their
eqiupment for them.  Over the years I have tested most of the major offerings
from HELLER, ELECTROVERT, ERSA, RESEARCH, VITRONICS, SOLTEC, BTU, SMTECH and
CONCEPTRONIC (touche').  Many of these manufacturers have also developed
differential heating -some work better than others.  I respect the fact that
these companies and ETS have spent big bucks in R&D to develop this
capability.  I question if it is really needed.  Most likley, it is an attempt
to create a market differentiator for a product area that is viewed by the
industry at large as a commodity.  This is sad as well, because as you know
from your experience with ovens, not all reflow ovens are created equal. The
process may likely be viewed as a commodity but the equipment should be less
so.

Keep on experimenting Brian and keep on inputting into the Technet. But please
keep it generic (or we'll have to sic Capn' Jack on you).  I'm going to have
that cup of decaf now, thanks.

Phil Zarrow
ITM, Inc.

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