Very interesting. I can see that in an IR preheat wave solder machine, but I don't understand why the closed loop feedback in a convection oven would fail to properly compensate for the change in temperature. I think the variables at work influence performance on an SMT line through different mechanisms. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask] Sent: Monday, September 15, 2003 7:17 PM To: [log in to unmask] Subject: Re: [TN] Effects of humidity on soldering 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 --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------