While I don't have data to support paste manufacturer's recommendations, I've used 3 levels of "shelf life" based on the manufacturer's recommendations.  
	Refrigerated un-opened - typically 6 months
	Out of refrigerator - typically 1-2 weeks  - Jar may be open, but paste never foes back into jar
	On stencil - typically 8 hours but may be shortened based on relative humidity (out of the 30-70% range)

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

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Amol Kane
Sent: Monday, June 20, 2011 2:28 PM
To: [log in to unmask]
Subject: [TN] Solderpaste Storage and Use

I am re-writing our solderpaste use and storage procedures for water soluble and no clean fluxes (SnPb and Lead-free) to say, in essence the following:

"To be stored per the manufacturer's recommendations (usually upto 10C), must be at room temperature before it is dispensed on the stencil (at least an hour thawing is required). Maximum use period to be 8 hours. Re-refrigeration and use beyond 8 hours not permitted"

The pushback is to the prohibition of re-refrigeration (for use the next day) after it is thawed and use beyond 8 hours requirement. These requirements are due to concerns with moisture absorption by the solderpaste once thawed (affecting slump) and flux activity (due to ageing)

What criteria are all the learned folks on technet using for solderpaste management? Is there any literature available that looks at solderpaste use limits on time and temperature?

A logical solution would be to do a DOE to look at these parameters, but I am being asked to come up with something ASAP:).   love how these things work!




Thanks in advance


Amol


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