Raj,

We have many customers (AT&T, Apple, IBM, Motorola, etc.)
 who would be happy to help you understand the cost vs benefit ratio
for nitrogen in convection reflow.  It depends a great deal upon your
components and paste.  The finer the pitch (less than 20 mil) and the
lower the solids paste (5% and less), the lower the oxygen level you
want to have to get good soldering.

Give me a call if you'de like and I can put you in touch with users
processing similar parts to you.

Mark Nowotarski
Manager, Advanced Soldering Development
Praxair Inc.
Tarrytown NY USA
tel 914 345 6452