Hi Rob - it is my understanding that a typical solder reflow oven is not 
capable on achieving and maintaining the inert atmosphere you would need 
to achieve for the sintering of copper ink, at least in terms of my 
interpretation of sintering copper. We are able to achieve a 10 ppm O2 
contamination level in our reflow ovens due to some really good attention 
to the nitrogen copper line connections running from the nitrogen tanks to 
the reflow ovens. I don't know if that O2 contamination level is 
sufficient for your process. Also, the typical reflow oven can only 
maintain very low O2 contamination levels by pushing a high volume of N2 
to avoid having air "drag in" from the entrance and exit openings of the 
equipment.  There are a host of other oven options more suited for 
creating a consistent, maintainable inert atmosphere  - the SMT soldering 
process doesn't necessarily require a very pure inert reflow atmosphere to 
get the benefit of improved wetting. Hope this helps.

Dave Hillman
Rockwell Collins



From:   Robert James <[log in to unmask]>
To:     <[log in to unmask]>
Date:   03/01/2013 04:30 PM
Subject:        [TN] how is "oxygen-free" defined and measured?
Sent by:        TechNet <[log in to unmask]>



Hi Everyone,
I am trying to sinter some copper ink using a solder reflow oven.  To 
prevent oxidation of the copper as the temperature is elevated, I'd like 
to purge the system with nitrogen to displace the oxygen before the temp 
is ramped (the oven allows me to do this).  I'm unsure, however, what the 
exact requirement is - for 'oxygen-free' processes, what level of O2 is 
typically allowed? How is it measured?  From what I've seen, there are 
basically two types of O2 sensors - relatively inexpensive ones designed 
for determining whether an atmosphere is breathable, or those with ppm 
accuracy.  The former may not be sensitive enough, the latter are horribly 
expensive and not particularly well suited to being placed inside a reflow 
oven.  What is commonly used in the industry?  Any advice or 
recommendations would be greatly appreciated.

regards,
Rob




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