old solder flux

[Ralph Mowery]

Does the flux in solder really get old ?

I have some of the older 60/40 flux core that is over 20 years old and
never had any problems with it.

Just getting into the SMD soldering and the tubes of solder paste have
an expiration date on them of about a year and some want to be kept in
the refrigerator when not being used. Also bought some liquid flux and
it mentions an expiration date about a year or so later.

Just being a home user it may take me years to use the stuff. I know
lots of things have an expired or use by date on them,but that does not
really mean much. I think the government just requires a date on some
items.

[Ian Malcolm]

Ralph Mowery <rmower...@earthlink.net> wrote:
> Does the flux in solder really get old ?
>

> Just getting into the SMD soldering and the tubes of solder paste have
> an expiration date on them of about a year and some want to be kept in
> the refrigerator when not being used. Also bought some liquid flux and
> it mentions an expiration date about a year or so later.

The problem with solder paste is surface oxidisation of the very small
particles of solder in it, and possibly saponification of the flux due to
its reaction with the oxidised solder. Keep it refrigerated in a ziplock
bag or hermetically sealed container with a silica gel sachet to control
humidity, at the lowest possible storage temperature as the rate of
degradation doubles with every 10 deg C increas in temperature, and allow
it to warm to room temperature an hour before use.

Fluxes are a more complex matter. Liquid Rosin fluxes are unlikely to
degrade over decades if securely stoppered. Liquid Synthetic fluxes may
be more problematic and if any component can further polymerise, the
expiry date may be justified. If kept cool and well stoppered, in a dark
place or opaque bottle, the chances are that it will still be good well
after the expiry date. Gel fluxes may be stable or may tend to seperate
or degrade. Again, cool and dark may help.

Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL

[Michael Black]

On Fri, 29 Apr 2016, Ralph Mowery wrote:

>
> Does the flux in solder really get old ?
>
> I have some of the older 60/40 flux core that is over 20 years old and
> never had any problems with it.
>

I once bought a roll of solder, maybe the price was great, and I thought
it wsa 60/40 or some slight variation, but it never worked. I remember
being puzzled at the time, but it's long enough ago that I don't know.
Maybe it was odd solder to begin with, but at the time I thought maybe it
was stale.

That said, other than that role, I've never had problems. I think I've
gone through two decent rolls over the decades (and small rolls) and other
than that one roll, I've never had problems.

I thought it was when the solder was soldered that problems arose. I
remember having problems desoldering old tube equipment, the flux gone or
something, only by adding some new solder did the old flow properly.


Michael

[N_Cook]

A pot of solder "paste" (pretty solid now) I use, is expiry dated 1996,
I just locally mix in a blob of flux to make a small amount useable each
time

[Jon Elson]

Ralph Mowery wrote:

>
>
> Does the flux in solder really get old ?
>

Certain formulas definitely CAN! Also, the outside of the solder wire
slowly accumulates more oxide, making the flux's job harder.

> I have some of the older 60/40 flux core that is over 20 years old and
> never had any problems with it.
>
> Just getting into the SMD soldering and the tubes of solder paste have
> an expiration date on them of about a year and some want to be kept in
> the refrigerator when not being used. Also bought some liquid flux and
> it mentions an expiration date about a year or so later.
>

Paste has a lot of other properties than just flux. It has to spread
through the solder stencil, leave nice "bricks" that don't slump, then do
the flux job during reflow, and then either be washed off or not cause
problems if the "no clean" type. A lot of jobs for one material.

If you let it sit at room temp for too long, it separates, and has to be
remixed.

> Just being a home user it may take me years to use the stuff. I know
> lots of things have an expired or use by date on them,but that does not
> really mean much. I think the government just requires a date on some
> items.

I have had paste go bad on me, started to look like tiny cottage cheese in
the jar, and didn't reflow well when used on a board. I added liquid flux
to it, but that only helped a little. So, I had to get new stuff.

Jon