Daan:
                I hear what you are saying and I have not done ppm studies
on the wave soldering nor reflow oven environments.  It seems to me that  it
is difficult to shut out ambient when you have an open chamber. Gases will
travel upstream due to the law of diffusion. The nitrogen will help the flux
to shield the soldering process but not 100%.
        Just my two cents
        Ramon


> -----Original Message-----
> From: d. terstegge [SMTP:[log in to unmask]]
> Sent: Wednesday, March 10, 2004 10:27 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] Nitrogen Purity Question/Survey
>
> Hi Ramon,
>
> A good reflow oven is designed in such a way that there's very little
> mixing with ambient air, depending of course on the amount of nitrogen
> that's going in.  With cryogenic nitrogen you should be able to achieve
> levels below 100 ppm O2 in the reflow zone.
> If the nitrogen sole purpose is to open up the process window then this
> may be of lesser importance, but to prevent oxidation and keep
> solderability of OSP boards it's the ppm-level of O2 that can (according
> to literature) make the difference between succes and failure.
> And 0.5% is a lot of ppm's !!
>
> Daan Terstegge
> Thales Communications
> Unclassified mail
> Personal Website: http://www.smtinfo.net
>
> >>> [log in to unmask] 03/10/04 01:57pm >>>
>         Dave:
>                 For wave soldering and reflow oven  the 99.5 % would be
> more
> than necessary. Ambient air which is about 40 percent O2 is all around
> the
> machine and very quickly will mix with the injected N2. If it was for
> a
> close chamber such as it is used on semiconductor fabs, then it would
> make a
> difference if O2 was not desirable in a particular process. Your
> decision
> should be based on what is more economical.
>         Regards,
>         Ramon
>
> > -----Original Message-----
> > From: Dave Hillman [SMTP:[log in to unmask]]
> > Sent: Tuesday, March 09, 2004 1:00 PM
> > 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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