I see no problem with this practice, particularly if the jar is
not warmed up and only opened for a minute, then
put back in the fridge.  Be careful not to allow water to condense
on the paste, particularly if you are using water-cleanable paste.
I like the clever caulk gun/cartridge idea that was mentioned.
I think the idea that the whole jar of paste must be used immediately
is an exageration of the deleterious effects that humid air has on
solder paste.  They exist, but they don't occur that quickly.

However, don't reuse paste that has been on the stencil already,
recycle it.  Paste that has been exposed to air for many hours
is likely to have some of it's solvent evaporated or picked up
water from humidity in the air.  Also, the paste may have picked
up other contaminants from the stencil.

I have many small samples of many different pastes for SIR
evaluations in my fridge, and I have few problems with paste from
previously opened jars.  Sometimes a previously open jar
is the only sample I can find.

Ask the manufacturer of the paste you use for his recommendations.
Most of  us run shelf life evaluations and know whether paste can
be use after the jar is opened.  In most cases, I'd say it can.

Karen Tellefsen
Alpha Metals

----------
From: West, Jim <[log in to unmask]>
To: [log in to unmask]
Subject: [TN] Solder paste refrigerated after the container is opened.
Date: Wednesday, February 23, 2000 4:28 PM

Hi Techneters,

This questions is mostly geared towards the small manufacturers that does
not use that much paste, but all comments are welcomed.  Most manufactures
recommend you store your paste in a refrigerator and keep the temperature
at
32-50°F.  We do this, but since we do not use that much paste, we will open
a jar and apply the required amount of paste on our stencil.  Our biggest
production amount only requires us to apply paste to our stencil maybe
twice
or three times a day.  I was told by an outside source that once we open
the
jar of paste we can not put it back in the refrigerator.  One reason they
said was we are exposing the paste to the air and once this happens you
need
to use the paste ASAP.  That's a problem for us since we do not use that
much to begin with.  Currently, we will open the jar and take what we need
and then put the jar back into the refrigerator, it may be two days before
we need to use the paste again.  How do the small shops handle their paste?


Thanks in advance,

Jim West

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