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May 2014

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From:
Mike Fenner <[log in to unmask]>
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Date:
Fri, 2 May 2014 20:40:14 +0100
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My opinion? For T3 applications it is difficult to justify the expense of
nitrogen and probably for most T4.
There is a visual difference, solder resists are not darkened for example,
but generally you only notice on a side by side comparison. Possibly
cleaning is simplified for similar reasons - a reduction in oxidative
degradation of organics which in this case would be the flux. For sure with
low or so called zero residue flux types, nitrogen is a process requirement.
For some older no clean formulations there might be/have been some benefit.
For Current no cleans pastes which leave around 50% (guide number) the
presence or absence of oxygen above that amount of flux is not so
significant.
(Current lead free paste formulations and leaded products derived from them,
are easily back in place on the "paste progress curve" after lagging from
the Pb-free diversion).

The downside of inerting apart from the material cost and extra process
monitoring is that the surface tension of the solder can be effectively
increased; this offsets any increase in spread, leading to an increase in
probability of tombstoning. Not a good thing with lead free in particular as
high tin alloys have a higher ST than Sn/Pb.
There is any amount of papers on this topic available and I am sure your
friendly paste supplier and wannabe supplier can send you their favourites.
The savings can be very significant. Certainly you could at the very least
use the published data to make a case to run a trial. In that you could run
a series of test boards at increasing levels of oxygen to determine the max
amount of oxygen permissible to maintain your desired quality levels. That
would make sense anyway. The chances are high you would find approx
209,460PPM O2 is acceptable. :)

Regards

Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jim West
Sent: Friday, May 02, 2014 6:50 PM
To: [log in to unmask]
Subject: [TN] Use of Nitrogen (reflow ovens)

Good Friday all,

Wondering how many out there, using both lead and lead-free solder, are
using nitrogen with your reflow process?  At a previous factory, we did not
use nitrogen as part of our reflow process and where I'm working today, we
use Nitrogen on all our lines.  I had success without nitrogen and we are
having success with nitrogen.  At the APEX show, I spoke with at least one
reflow oven manufacture about their oven and what they feel about the use of
nitrogen and they pretty much said they are selling less ovens with
nitrogen.  To the point of 90%+ of their ovens are sold without the nitrogen
option.  As most know, nitrogen is very expensive and I would like to
justify not using nitrogen in the future, but I have an uphill climb due to
my parent company suggesting we use nitrogen based on a policy created over
7 years ago.  Based on our product mix, I'm of the opinion we don't need
nitrogen.

What are your thoughts on using nitrogen with the reflow process?

Has anyone gone through the process of eliminating the use of nitrogen and
had success afterwards?

Thanks,
Jim


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