old solder flux

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

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

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

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

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.

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