Thanks everybody for your opinions. I value them even if they differ
from mine. I agree nitrogen is an expense and I understand paste
suppliers have done their best to try and formulate a paste that will
provide the benefits of nitrogen without the expense. As my good friend
Lee Parker said, "Back in the good old days" we did things because they
were right and did not eliminate them because it cost 5-10 cents a
board. Face it, the EMS's are more interested in margins than quality.
The more competitive we force the EMS to be the less quality we get.
Management has to understand they are in the business to make a profit
too. It then becomes the OEM's responsibility to continuously monitor
and realign their processes. You cannot leave it up to the EMS to
monitor it themselves.
There are instances where nitrogen can cause problems by overexciting
the solder. In some cases we very selectively turned it off ourselves.
But 99.9% of the time it was of a benefit. As we move into more and
more Pb-free processes and using Pb-free components in a Sn/Pb process
it does inhibit better wetting. I researched several of the major paste
suppliers and they all claim their pastes work in either environment.
None say that their pastes wet better in a oxygen rich environment.
They are trying to sell paste and use nitrogen elimination as a selling
tool.
The bottom line is no where is there a requirement or even a strong
suggestion that nitrogen is required. I was hoping for a "Best
Practices" or "Best in Class" report. Again, thank you for your incite
and opinions.
Russell Nowland
Alcatel-Lucent
Supply Base Engineer
Address: 14000 Quail Spring Parkway, Suite 300
Oklahoma City, OK 73134
email: [log in to unmask]
Desk: 405-302-1660
Cell: 405-203-0034
Fax: 405-302-1622
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, December 18, 2006 5:03 PM
To: [log in to unmask]
Subject: Re: [TN] Nitrogen usage
To expand on that, there are many OEMs and a few CEMs that are running
true 6 sigma, but it goes much beyond the ICT, 5Dx and AOI level.
Most of the work must be done BEFORE the assembly level, not as a result
of assembly processes. You cannot achieve 6Sigma at the production level
alone. In fact, I would estimate at least 70% of the efforts need to be
focused on the parts and pwb vendors, not the other way around. Crap
coming in pretty much ensures crap going out, no way around it.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Monday, December 18, 2006 3:38 PM
To: [log in to unmask]
Subject: Re: [TN] Nitrogen usage
Heh Heh,
If you can find ANY Tier anything CM running TRUE 6 sigma first pass
yield based on ICT, 5Dx and optical AOI inspection - no "touch up" let
me know and I will use them.........
John Burke
(408) 515 4992
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, December 18, 2006 1:28 PM
To: [log in to unmask]
Subject: Re: [TN] Nitrogen usage
IPC can only provide guidelines to achieve an acceptable yield. If a
company can demonstrate that it has control over the solderability of
its components and pwbs such that it can achieve 6 sigma DPMO without
nitrogen, why would they be "required" to use nitrogen? If IPC were to
"require" nitrogen, how much of a ppm of oxygen is acceptable? While the
use of a nitrogen blanket is a good practice in most cases, many
companies find the decrease in DPMO is so small that it is not cost
effective to run nitrogen. There are many other variables that need to
be controlled, nitrogen is just one of the factors and it is not
anywhere close to being the most important, unless, of course there are
little or no controls put in place to preserve the solderability of the
parts and pwbs. Some ovens use nitrogen so excessively that they are
useless, so why bother to turn it on? Other ovens with a properly
designed reflow chamber use the nitrogen efficiently such that you can
achieve an O2 level of less than 75 ppm inside the reflow chamber,
without having to go through 10 billion liters of nitrogen per hour to
achieve that reading. This is why there is no "requirement" for
nitrogen.
Most of the newer solder pastes are actually formulated to do away with
the nitrogen requirement. If you are not using one, I would suggest you
get a sample and start performing a qualification.
As to tombstoning, it has been my experience that the addition of
nitrogen increases tombstoning (does not make it better), for the very
reason it improves the surface tension which leads to improved wetting.
In the industry, many companies turn off the nitrogen for assemblies
heavily populated with 0402's or smaller. This is a common practice.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Russ Nowland
Sent: Monday, December 18, 2006 12:07 PM
To: [log in to unmask]
Subject: [TN] Nitrogen usage
Hello Technetter's,
Sometimes in life you find yourself in a pickle and wonder how the heck
you got there. It always brings me to that famous quote "It is hard to
soar with the eagles when you work with a bunch of turkeys".
I have a question: I am working with and "MAJOR" EMS that does not use
nitrogen with either Sn/Pb or Pb-free reflow. In this day and age I
have never heard of this. They have it available but will only use it
if I require it. At a price, of course. They don't seem to take into
account it will improve their yields as well.
Is there an IPC, NEMI, or any other standard that requires/recommends N2
usage for either Sn/Pb or Pb-free reflow process?
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