Translating 60F = 15C 85F =29.4C

I think you will find that most paste suppliers set an upper limit of about
30C for max room temp storage. Paste life is going to come down fairly
rapidly above that and at 40 is going from months to days. Above 40 hours.
So storing in a temp limited environment makes sense.
Don't forget if you are storing at a lower temp than your usage temp you
will then have to wait a long time for it to come back to operating
temperature - and not open containers before they have done so. 
So better to store at your day time ambient, which is likely to be higher
than 15C. 
Limiting the rate of issue from long term to line store is also a good way
of keeping paste quality consistent.

If you do have to use previously opened paste: Use new paste to preload
stencil and then the previous day's opened to top up. That will minimise any
variations that may have become present.

Keep in mind when setting procedures that though no one wants unnecessary
waste, money spent on paste is a very small part of your buy (typically
<0.X%)and therefore many times less than cost of paste that doesn't work. 
Your main driver therefore is quality of work.


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

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Richard D. Krug
Sent: Wednesday, March 13, 2013 12:40 PM
To: [log in to unmask]
Subject: [TN] Cooling of Solder Paste Overnight

It has been proposed that we take left over solder paste and store at ~60 F
overnight to extend life and integrity of paste.  This would be paste in its
original tube or jar, not recovered from a stencil.  We are located in
Florida.  During the summer, when the AC is reduced overnight, temperature
in the building gets to ~85 F.  

Has anyone done this?  What are the pro's and con's?  

Dick Krug, CSSBB, CSMTPE
Senior Process Engineer
Sparton Complex Systems
30167 Power Line Road
Brooksville, FL  34602-8299
p (352) 540-4012  (Internal Ext. 2012)
[log in to unmask]

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