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