My flux pen recently bit the dust. Fortunately the raw material was close at hand. Making solder flux from rosin is a snap — and a pine tree near my house was oozing big dollops of gum.
Harvesting the gum was a furtive operation. Under cover of darkness, I crept out and scraped some into a tin. Then I covered it in 99% isopropyl alcohol, swirled it around for a minute or two, and left it overnight to dissolve.
The next morning I jury-rigged a filter from a juice bottle and a coffee filter. It spilled all over the place, but we're doing things cheap, right? That clear amber liquid is pure rosin flux. (Well, not quite pure. It is better to heat the resin beforehand to drive off the turpentine.)
I would have added a few drops of glycerol if there had been any nearby, but the flux was fine as it was. It cleans up with a little more isopropyl alcohol. An easy way to dispense the flux is from a 10 ml needle-tip bottle. All I need now is to brush up my soldering technique. :)
Hints and tips
This project is dead Easy. Just try not to get sticky goo everywhere.