In a message dated 4/2/2005 3:50:20 PM Central Standard Time,
w8ji@contesting.com writes:
Apparently this is just a problem with a few metals used in
solder? Or is it the flux?
Tom:
I'm no chemist, that's for sure. I was working as a manufacturing manager in
a high volume electronics assembly plant at the time. But I will say all our
efforts were directed at removing flux residue after waveline or reflow
soldering, so I guess the enabler was the flux. At least proper cleaning of
flux
residue after soldering eliminated the dentrite growth problem. To test the
cleaning process, a piece of test equipment was used that measured the
conductivity of a container of deionized water and then measured it again after
an
assembled and washed board had been immersed and agitated. If any flux
residues
washed off the board and caused the conductivity of the deionized water to rise
beyond spec, we had to check the board washers, make corrections and re-wash
and re-test that lot of boards.
Because the freon used in the chemical-type board washers was banned and
because maintaining a deionizing plant for the water-type washers was a big
task,
I was glad when no-clean fluxes were developed. We adapted no-clean flux to
the waveline flux fountains and solder paste manufacturers adapted it to their
formulations of solder paste. We were able to eliminate the board cleaning
process and that was a happy day.
BTW, all this was going on in a plant manufacturing 2-way radios and cell
phones. We were using fine pitch smt ic's and close spacing on board traces.
Jim W9TM
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