Hi Tom -
Nitrogen in reflow will improve the surface tension of the molten solder.
With experiments demonstrating that BGAs can be placed as much as 30% off pad
center (Jeff Kennedy while at Ceridean and Mike Buseman while at Unisys) and
even 50% off center (Motorola -Austin) I don't think you really need to use
Nitrogen in your reflow - not for this reason.  I know that Motorola still
uses nitrogen on some of their ovens reflowing CSP and flip-chip but I believe
that this will likely eventually be phased out.  I would suggest not going to
the expense of nitrogen, regardless of whether your ovens are plumbed for
containment or not.
Regards,
Phil Zarrow
ITM, Inc.
Durham, NH  03824
www.ITM-SMT.com

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