| https://www.eptac.com/soldertips/whats-with-the-expiration-dates-on-solder-paste-or-wire/
don’t want to be liable for failures in the field due to old material. As for the cored wire solder, similar storage issues apply, but more to the point, the real concern is the changing activity of the flux in the core due to its corrosive or acidity properties working
Blackfox Training Institute, LLC | https://www.blackfox.com/how-to-remove-oxidation-from-soldering-iron-tips/
) Apply flux cored solder on the oxidized tip. Once the flux is activated it starts a chemical reaction that removes the oxidation. Clean the tip with a brass wool or automatic tip cleaners Repeat the steps above until the tip is visibly clean If the tip is still not clean after this process, move on to the next step
