Hi Grant! Just wanted to thank you and the rest of the Technet community for your assistance. We have also run a number of DOE investigations to understand the interaction of O2 levels and solder joint formation. Both the internal and external data sources put the O2 level in the primary reflow zone in the range of 100-300 ppm - pretty neat how everyone is arriving at similar values (physics is a wonderful thing). The nitrogen purity level is a primary driver when using on-site gas generation in comparison to the use of cryogenic N2. The posed question/survey was a sanity check to get one final review of our overall review of N2 options. Thanks again for everyone's responses. Dave <[log in to unmask] m> To: <[log in to unmask]>, <[log in to unmask]> cc: 03/11/2004 02:13 Subject: RE: [TN] Nitrogen Purity Question/Survey PM Hi Dave, At a previous employer, one the engineers did an excellent DOE to determine the actual threshold of Nitrogen level necessary to significantly reduce BGA voids. The number came to 250 ppm of O2 in the oven as the "bare minimum" to make it worth it. Our process then became one of actually measuring the Nitrogen level at change-over and waiting/verify that the O2 was below 250 ppm. We would actually, get down around 25-50 but we would have to turn off the supplemental cooling fans on the exit conveyor because the air would reflect off an exiting board and shoot into the oven. Otherwise the O2 level would shoot up to 150 ppm every time a board would exit. I did find that if the fans were sharply angled away from the oven opening, we could keep it from contaminating the nitrogen levels. Worth considering since large dense boards would generally be too hot to handle right out of the oven, even with the supplemental cooling fans. Although many other engineers would use Nitrogen to improve the appearance of the solder joints, the only reason for dropping O2 levels to 250 ppm was to control BGA voids. If voids are already under control, or you can switch solder paste formulations to control voids, then the low O2 ppms would not be necessary. Ryan Grant -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Hillman Sent: Tuesday, March 09, 2004 11:00 AM To: [log in to unmask] Subject: [TN] Nitrogen Purity Question/Survey Hi folks! Question for those folks using nitrogen for an inert atmosphere in their reflow processes or as a blanket gas on their wave solder processes. Cryogenic nitrogen is typically 99.998% purity (in terms of O2 content). On-site nitrogen generation equipment can deliver N2 gas ranging from 99.5% to 99.99% purity (again, in terms of O2 content). What gas purity level are you using in your processes and do you have a rationale for selecting that purity level? The reason for the question is that I am involved in an exercise of comparing on-site nitrogen generation versus cryogenic nitrogen supplies. Thanks in advance for you assistance. Dave Hillman Rockwell Collins [log in to unmask] --------------------------------------------------- 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 -----------------------------------------------------