Very interesting. At what point in time did you see measurable changes in performance?
What was the first property to fail? Print, hot slump, or wetting?
We did some similar testing and found the results to be type dependent. Type 3 performing better than Type 4, with different properties failing first.
Guy
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, September 27, 2011 3:00 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Paste Shelf Life Extension
I can tell you that some major military and avionics manufacturers and CEMs use a ten-day limit on paste removed from refrigeration, as long as it is in sealed tubes, and the tubes are kept re-sealed immediately after dispensing to the printer, and the tubes are not re-refrigerated after initial removal from the fridge.
This was done based on qualification results of the individual paste candidates, which was then added to the original solder paste qualification results. Paste was tested for viscosity, wetting, slumping, etc., etc., every day for a period of 20 days, without seeing any degradation of paste or increase in DPMO (in fact, it improved!). Then the agreed-upon pot life was agreed to be 1/2 the qualified time, to err on the side of caution, and that was 10 days. This has been working extremely well for at least 4 years now.
I have done that for three different pastes, from two paste manufacturers. All were water soluble, standard Sn 63.
I would NOT allow that to be done with jars of pastes, only paste received in sealed Semco cartridges. Once you open a jar of paste, you should never return leftover paste to the jar. For jars, a 3-day pot life might very well be as long as I dared to use it. The amount of exposure and the inability to seal a jar very well are the reasons I do not use paste in jar form if I can possibly help it. Too many bad experiences with operators leaving jars open, mixing one alloy with another, mixing different flux types, partially closing the cover without putting the internal air purger back in, etc., etc. None of those things is very likely to happen if the paste is in a sealed Semco cartridge.
In order to cause no harm, I am not advocating this for anyone else unless you perform the qualification for your paste and your printing processes. But it is a very good thing to undertake as you will learn a lot about how your paste and your handling processes hold up under worst-case scenarios. You should do this in July or August under high humidity conditions (in North America anyway) if possible.
dean
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Amol Kane
Sent: Tuesday, September 27, 2011 11:51 AM
To: [log in to unmask]
Subject: Re: [TN] Solder Paste Shelf Life Extension
Leland,
After going thru the technet archives, talking to our paste manufacturers, and reading their SOPs for paste handling, we concluded that 7 days at RT was the usable limit (as long as the paste tube/tub is sealed). We have been using that time limit with no paste issues.
How did you arrive at the 3 days? (experimentation, past experience etc?). what I am getting is that there may be no need to re-certify after 3 days
Regards,
Amol Kane | Process Engineer
Catalyst Manufacturing Services, Inc.
941 Route 38, Owego NY 13827
Phone: (607) 687-7669 Extn 349 | Website: www.catalystems.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Tuesday, September 27, 2011 11:42 AM
To: [log in to unmask]
Subject: [TN] Solder Paste Shelf Life Extension
Folks,
Quick question here...
We have a rule here to scrap solder paste after it's been out of the fridge for 3 days. If we recertify and extend the expiration date by first verifying the proper viscosity, is it permissible to return the paste to the jar that was used for the viscosity testing?
Thanks for your help,
Leland
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