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From [log in to unmask] Mon Feb 3 16: |
04:11 1997 |
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<"3kkMD1.0.DZN.OrXzo"@ipc> |
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Bob Mesick offered to design and get built a solder pot into which
solder which had become laden with copper could be transferred so as
to allow the copper-tin IMC to rise to the surface so that it could be
scooped out. If such a pot were to be built, then it seems to me that
it would be good to have something a little better than a ladle to
transfer the solder from pot 1 to pot 2 and back again. How about
including a pump with heated transfer line?
I am curious about the need for such a machine. First, how many
operations are there that keep the wave solder machine running so
consistently that it can't be "shut down" (i.e., not operated, so that
the solder can be allowed to sit just above its liquidus temperature)
for a day every so often?
Second, why does the copper have to be removed? Apart from the fact
that J-STD-001 sets a limit on the copper in Table 5-1, the worst that
can be said for the presence of the copper in the solder is that it
makes it look kind of funny. If ignored, the copper level in the
solder does not continue to rise but reaches a steady state, since
fresh solder must continue to be added to the pot. Excess copper in
the solder is not a defect per Table 11-1, and in this standard,
"'must' and 'shall' are used to emphasize characteristics that must be
considered during the development of the process control program"
(Para. 1.5). The way I read this sentence, if the process control
program has determined that copper in solder is not worth controlling,
it doesn't have to be.
Gordon Davy
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