In a message dated 9/11/2003 12:56:03 PM US Eastern Standard Time,
[log in to unmask] writes:
There is a presumption (not supported with data) here that when it rains, and
the humidity goes up, we historically have experienced more solder defects
I have seen and documented this condition at two different factories during
my employment at each.  The cause was not, however, humidity but rather the
drop in atmospheric pressure associated with the storm front.  Each of those
factories was a positive pressure HVAC set up for the building, meant to keep
dust, etc., from entering each time a door was opened.  The effect of a
significant and rapid decrease in atmospheric pressure was to cause a corresponding
increase in exhaust volume through each exhaust port, including the wave solder
machine.  This increased exhaust caused a recordable change in the temperature
of the preheaters and therefore the boards as they made contact with the wave,
altering the profile and defect rate.  We had lines running 24/7 with around
200-300 ppm, so just a dozen or so solder defects could triple the ppm numbers
for a shift.

Jon Moore

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