And since Chemistry and Physics are sub-branches of metallurgy, then metallurgy must be a wonderful thing; QED.
Regards
Eric Dawson
> -----Original Message-----
> From: TechNet [SMTP:[log in to unmask]] On Behalf Of Bev Christian
> Sent: Friday, March 12, 2004 02:32
> To: [log in to unmask]
> Subject: Re: [TN] Nitrogen Purity Question/Survey NTC
>
> Dave,
> CHEMISTRY is a wonderful thing. :)
> Bev
>
> -----Original Message-----
> From: Dave Hillman [mailto:[log in to unmask]]
> Sent: March 12, 2004 9:29 AM
> To: [log in to unmask]
> Subject: Re: [TN] Nitrogen Purity Question/Survey
>
>
> 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]
>
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