Steve,
I agree with Doug. You have little to loose by experimenting with the "old" paste. Open a jar and see if it works. We all do that with our "good" paste anyway. You know the drill, production says the paste is crappy, it doesn't print well, it causes solder balls, we're getting non-wetting, we're getting shorts, bla, bla, bla...The first thing engineering asks is 'have you tried a new jar of paste?'
Proof of this, I was once tasked with qualifying a new solderpaste. Just to throw in another data point, I grabbed an 18 month old "unopened" jar of (a big name brand) solderpaste (what the heck, I'm just curious). To my astonishment, that 18 month old paste out performed all the other brands with "new" jars. (For some reason, the sales rep REFUSES to recommend aging their paste)....O.K., not that aging the solderpaste that long improves performance, but it certainly didn't degrade enough to justify throwing in the recycle bin. (Legal disclaimer: 'results may vary')
Ryan Grant
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Thursday, February 20, 2003 6:07 AM
To: [log in to unmask]
Subject: Re: [TN] A generic question about solder paste shelf life..
Steve,
Guy Ramsey had some good comments, although he has an apparent allergy to
statistics <grin>.
From my perspective, I agree that the shelf life is usually longer than the
stated figure. I know conformal coatings more than I know solder paste,
but the principle is the same. Most coatings have a shelf life of one
year. In reality, the coatings stay good for 16-18 months, but 12 months
is what the manufacturer will guarantee. We have some materials here which
we use beyond stated shelf life, but only after we have done studies to
find out the true shelf life. You need to do tests, as Guy suggested, to
find where the true shelf life is.
For solder paste, and the paste gurus can take me to task if I'm wrong, you
have essentially three elements: the solder, the flux, and rheological
agents. If it stencil prints nicely, the rheological agents are still
intact. If the solder joints look good, the flux is doing its job. Keep
using it while you watch your hardware for increases in solder defects, or
until your stencil operator starts remarking "this dang paste don't flow
like it used to".
If you don't want to play with actual hardware (ya sissy), then use new
paste, but continue to use some of the paste characterization tests found
in J-STD-004 and J-STD-005/006 on the old paste. Do experimentation to
find out what the true life of the paste is. Unfortunately, this gets
complicated by the fact that you have now opened the jar. I suggest
filling the jar with nitrogen or some other inert gas to prevent oxygen
attacking the paste. Since this subject will likely come up again in the
future, spend the time now to answer the question of how big the window is.
Doug Pauls
Steve Gregory
<[log in to unmask] To: [log in to unmask]
M> cc:
Sent by: TechNet Subject: [TN] A generic question about solder paste shelf life..
<[log in to unmask]>
02/19/2003 07:31
PM
Please respond to
"TechNet E-Mail
Forum."; Please
respond to
SteveZeva
Hi all!
I have a generic question about solder paste shelf life. Should one hold as
gospel, the shelf-life that is stated by the manufacturer?
I know many will say yes, because that is what the manufacturer says they
will guarantee. But this seems to me, maybe, could be, a marketing
strategy.
Situation:
We ordered solder paste in January 2003, and received the paste from
distribution that was made October 17, 2002. According to the datasheet,
the paste has a shelf-life of 4-months in proper storage conditions. So
when we received the paste in January, we had less than one and a half
months to use it up. Well, we didn't use it all up, due to some production
push-outs from our customers, and some production being put on hold because
of engineering issues, also customer related.
In calling the paste manufacturer, we were told that the paste is probably
good for 6-months, but they wouldn't be able to give us anything to
document that because their internal procedures prevented that.
I'm just wondering if anybody else has run into this situation, and maybe
questioned it...
The way solder paste is packaged seems to me, a very robust way to keep it
from deteriorating. The jar normally has a tight-fitting plastic insert
that will not allow excess air to be in contact with the paste, and then on
top of the plastic insert, there usually is a sealed foil cover over the
opening of the jar. To me, that is very good packaging that should allow
solder paste to remain good for more than 4-months. My mom cans vegetables
and home-made soup with less packaging and it lasts for at least a few
years, I eat it and it's wonderful!
My real concern is that we throw-away perfectly good solder paste because
of what we're told what the shelf life is by the vendors. After all, who's
best interests is it in, if there's a short shelf-life? Has anybody done
and real studies of solder paste shelf life vs. performance?
At $70 a jar, this is not a cheap matter, and doesn't help with all this
lead-free craziness when you have to throw away perfectly-good paste...
-Steve Gregory-
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