Standard plumbing solder is flux-free and 50:50 tin to lead. Then, there is Acid Flux plumbing solder that should not be allowed in the same county as electronic solder. You can determine which is which by cutting off the end. Acid flux solder will have a visible core containing the acid. Typical acid-core solder is 40:60.

If the solder in question is either of those *DO NOT* use it for electronics under any circumstances. And if it is vintage tin/lead solder *DO NOT* even use it for plumbing.

Peter Wieck
Melrose Park, PA