Hi Steve.
What maximum impurity level?  Well, we are running at pretty high levels of impure nitrogen as our oven is running on air.  

We run RMA paste, on fine pitch, double sided, with no issues or adverse effects.  We do have nitrogen (from stored liquid) available and hooked up to the oven but found that the defect rate was lower running air vs nitrogen - particularly tombstoning where we had a design with incorrect pad geometry. 

We do still use the nitrogen in the wave solder machine, and find it very beneficial there.  I'd consider going back to using it in reflow if I was changing to a low residue flux - but experiments would be necessary.

I agree with the words put to paper (or internet) by Phil Zarrow, "I am not, based upon my experience, an advocate of using nitrogen in the reflow process, but I remain open-minded on the subject." http://www.circuitsassembly.com/mag/2001/08/0108front.htm  (have to credit that since Phil also is on TechNet!!!)

Have a good weekend.

 - Graham Collins

regards

Graham Collins
Process Engineer, Northrop Grumman
Atlantic Facility of the Litton Systems Canada business unit.
(902) 873-2000 ext 6215

>>> [log in to unmask] 08/31/01 12:51PM >>>
Our facility is considering changing from stored liquid nitrogen at 99.9999%
purity to onsite generated at 99.5% purity (5000ppm impure).  Our reflow
manufacturer recommends a maximum of 180ppm oxygen in the nitrogen
environment.   What problems could occur if the 180ppm level is breached?
What maximum impurity levels have been observed without any adverse effects?

Thanks in advance for your inputs.

Steve Shoda
BAE SYSTEMS Controls
Fort Wayne, IN

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