[TriEmbed] OK, the oven is starting to perform
pete at soper.us
Wed Oct 15 21:10:30 CDT 2014
Thanks again for all the ideas and references! The probes are $10 each
from an inexpensive source (Digikey wants roughly 2-3X that much).
Either the super glue or Colin Ladd's method with "cast alumina" sounds
like the way to go for a couple of the probes.
But I got the probes to stay in place for a change and an actual
soldering run exactly matched a dry run with no paste: except for being
about 30 seconds out of phase the board temperature in four places
nearly exactly matched the Kester profile I've been using (but the paste
is actually made by Nordson EFD). Just 72 hours ago I would have
insisted this oven couldn't begin to accomplish this, but it did. No
doubt different board sizes, variety of components, places in the
drawer, etc, still bring about a lot of variability, but I may have
finally gotten the upper hand.
The three key fixes are:
1) Plugging up the air leaks
2) Arranging for the PCB to be held by its edges so there is air
under it as well as above it
3) Giving the oven intervals that are 2/3 as long as it thinks they
are (i.e. each of it's 10 second temp periods actually lasts 15 seconds)
Here's what the latest board looks like:
And here's the thermocouple data (the four probes agreed so closely they
rendered as a single line. The graph to the left is the desired profile).
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