Hi Phil & Steve & Kate,
Sorry guys, but I cannot agree with you.
A "tent" profile will always have larger temperature differences between
components with different thermal masses than a "ramp-soak-spike"
profile--it's simple physics. Granted in a convection-dominated oven the
temperature differences will be smaller than with IR-dominated ovens, but
they still will be there and are large enough for the SJs of larger
components not to properly wet. You need to put thermocouples at the SJs of
different-sized components--I did. You get about 15C differences at peak
reflow between larger components (not even BGAs) and chip components with a
"ramp-soak-spike" profile ina 7-zone forced conection oven. I guarantee you,
that the delta-Ts in a "tent"-profile are larger. You certainly can work
around that, but why would you want to.
About Steve's points:
1) is invalid--would only apply to a less than efficient oven design--most
show distinct zone separations;
2) you getless 'popcornoing' because the larger componets run colder, which
means you can got SJs that are not properly wetted;
3) this is absolutely wrong--it violates basic heat transfer.
Phil is right, the fluxes are not the problem.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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