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I have some solder that is past the "expiration date" on it. How does solder expire? Is it still good? What happens if I use it?

It seems odd that solder could expire, so I'm just looking for some clarification. Thanks!

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    \$\begingroup\$ What type of solder? Solder paste does expire. \$\endgroup\$ Mar 29 '17 at 1:55
  • \$\begingroup\$ It is Kester with a rosin flux core. \$\endgroup\$
    – Stremdawg
    Mar 29 '17 at 2:42
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    \$\begingroup\$ If it is a spool of solder wire, and it looks OK and performs OK, I would probably say continue to use it. Solder paste definitely expires. Not sure what happens to it, though. \$\endgroup\$
    – mkeith
    Mar 29 '17 at 5:28
  • \$\begingroup\$ Found a spool of propper leaded solder made in Japan in the 70s a few years ago. Best solder I've used so far. \$\endgroup\$
    – winny
    Mar 29 '17 at 18:41
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Solder can definitely expire. This is because of the flux which can separate or in the case of solder paste dry out and become ineffective. The composition of the flux also matters as I have an at least 40 year old roll of Kester solder which still works brilliantly because it has a pine based flux, on the other hand I have a much newer roll of Alpha Metals solder which spatters because of an inconsistent flux mixture. The metal itself can also oxidize but it is so slow it is unlikely to matter and also depends on the type of metals used.

For hobby projects, if it still works then use it :)

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When it comes to metal, oxygen is the enemy.

Solder does not expire, Flux oxidizes and reduces the fluxes ability to keep oxides\oxygen away from the metal. If you doing production runs you need to watch the shelf life of the solder\flux. If you a hobbyist or for some prototyping situations you can keep a bottle of flux handy and dab a little more on to counter the effects of the oxidized flux, then clean the extra flux off. The biggest problem is extra flux and a reduced ability for expired flux to flow well.

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