Steve and everyone -
No need to be confused, Steve.  Justin -use the ramp profile because it works
best, rather than because you have to.
Sorry, Werner, but I disagree.  I have profiled literally hundreds of boards
with convection dominant ovens, ranging from 3 to 12 zones with a ramp
profile and minimal gradient.  A couple of weeks ago, we did a "mothah board"
for a client that was thick as a brick (0.129") loaded with QFPs and BGAs in
an 8 zone oven and attained a 14 deg C max. gradient.  Have done other very
complex boards (in terms of surface geometry and mass) and have had 9 deg C
gradients.
Yes, Steve is correct - some solder paste formulations recommend ramp OVER a
ramp-soak-spike.  Particularly OA formulations that might dry out prematurely
during soak in a convection dominant oven.  Had a case in Australia a few
years ago where a ramp profile saved the day (over ramp soak spike) with an
OA solder paste.
Hey, maybe it defines analytical physics.  But then again, aeronautical
engineers tell us a bumblebee shouldn't be able to fly.
While it is not for every application, everyone should at least try and
experiment with the ramp profile.
Phil Zarrow
ITM, Inc.
Durham, NH  USA
www.ITM-SMT.com

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