Solder paste (a bit of noob, maybe some science)

[MyHeadHz]

I was considering branching out from through-hole components into SMD.  The sticking point for me is the shelf life of solder paste, because it would mean needing a 1 week lead time and $15 of solder paste overhead before every session. So I researched a bit in the archives here.

There seem to be some disagreements among the members here.  There are 3 basic groups of ideas that make it unusable: 1.  evaporation makes it dry out.  2.  the metal powder/micro-balls settle out of the flux.  3.  Some necessary solvent evaporates and renders it useless, or the hygroscopic flux won't work with too much water (water displacement).

(It is also worth noting that everyone seems to agree that there is no chemistry changes going on.)

So it's still not so clear.   However, some of these three causes might have viable solutions for the home gamer.

There has been involving ultrasonic cleaners that might be able to re-suspend these particles, or re-constitute dried out paste.  Perhaps a similar process could work if the solvent has been displaced by water, but with a drying phase first.

Ultimately, the goal would be to have a simple process of preparing/preserving old solder paste for use whenever, to save cost and time.  That, and I'm trying to find an excuse to buy an ultrasonic cleaner after watching that video.

Think any of this is plausible, or is it a dead end?

[GerryR]

Well, just go ahead and get the Ultrasonic Cleaner,    I keep my solder paste in the refrigerator, which prolongs its life.

[JustMeHere]

My 3+ year old solder paste tube still works well enough.  For low scale production, I wouldn't worry about it.

[pmercier]

I've some chineese solder paste that aged for 3 year now on my bench at normal temperature with no particular care about storage (bad bad bad boy).
It's still usable but a little too "pasty". When i need some i just take some and mix it with little isopropyl alcool and use it quickly. Perhaps not the best thing to do, but ... it work for me.