Bev,
If you are experienced chemist,you can explain everythink, even stuff that
does make no sense.
I am keeping in front of me few pieces of electrolytic gold plated PCB (
2.5 micron of electrolytic Gold over 5 micron of electrolytic Nickel ) .. I
took one piece of such PCB and put it into immersion Silver solution. Just
imagine - this stupid Silver solution never attended chemistry lessons and
probably this is why I got immersion Silver over Gold. Any ideas why ???
But it seems,that metalurgy is working. Plated surface change its color
slowly and it seems,that silver is being dissolved into Gold.
Edward
Edward Szpruch
Eltek Ltd
P.O.Box 159 ; 49101 Petah Tikva Israel
Tel ++972 3 9395050 , Fax ++972 3 9309581
e-mail [log in to unmask]
> -----Original Message-----
> From: Bev Christian [SMTP:[log in to unmask]]
> Sent: ו מרץ 12 2004 16:32
> 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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