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From:
"Whittaker, Dewey (EHCOE)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Whittaker, Dewey (EHCOE)
Date:
Mon, 4 Mar 2013 15:07:25 +0000
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Mike,
Good advice, given it started out as a pipe dream.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Monday, March 04, 2013 7:55 AM
To: [log in to unmask]
Subject: Re: [TN] how is "oxygen-free" defined and measured?

To answer your question literally as asked.
I used to profile the ppm in reflow machines by putting a copper pipe on the
O2 meter which was on a trolley. The pipe was long enough to pass through the reflow machine. You then position the trolley so the other end of the pipe is sampling the entry to the machine and then push it in a bit and take a reading and so on. This is a time consuming process as it takes a while for the readings to stabilize each time. It can give accurate readings and these might be different than the readings from the ovens own system which may not have the sampling point at conveyor level.
Remember the Sod's Law of the Laboratory when doing this: Hot glass looks the same as cold glass. (modified in this case to copper) Commercially available Copper based thick film inks usually state O2 max 10ppm.
Resistivity goes up with O2 ppm as the copper oxidises. So how many ppm you need to control to depends on the conductivity you require. 
A typical firing profile for these inks would peak around 900C and last about 60 minutes. 
.
I would say this all is bit beyond your average reflow system so I imagine that what you asked is not literally what you meant. 
I imagine you have some copper filled polymer ink and that will just need a profile to cure the polymer which possibly could be within a larger reflow oven's capability (or a box oven), probably the ppm requirement will be similar. If you have some magic nano-particle based material, that might give you a claimed much reduced temperature and other interesting properties, good luck with that. 


Regards 
 
Mike Fenner
Bonding Services & Products
M: +44 [0] 7810 526 317
T: +44 [0] 1865 522 663



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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