Can solder go bad?

Can solder go bad–Yes! I hear from so many people who tell me they have been struggling for years to learn how to get a good clean, solid solder joint with little success, so what’s the problem? One reason that I had not considered until recently is that solder can go bad, really! How can a mixture of lead and tin go bad? Well most folks actually purchase solder with flux in it, often referred to as rosin core or multicore. These solders typically have about 3% rosin flux in them. And, believe it or not that can cause the solder to go bad over time. How much time, well typically the expiration date stamped on the label gives you about 2-3 years from the date of manufacture, not purchase. After that date, and depending on the lead content, the flux will begin to react with the lead and eventually get to the point where it won’t work effectively. Solder with more than 70% lead will usually react faster and only last a couple years.

Now, I have a roll of Kester rosin core solder that I have been using for about 20 years, so how do I get away with it? First, I typically also use a little dab of rosin paste flux but you shouldn’t do that on circuit boards or decoders since you can’t easily clean off the residue. I also don’t store it in a humid environment which can speed up the reaction process.

So what do I recommend? Well, if you check around on Amazon and eBay you will find that Kester 44 rosin core solder is available in small clear plastic dispensers that can contain over 50′ of solder wire (depending on diameter). I have such a container that I save for electronics projects and I replace it when it gets old. That should be enough to last most folks for 3 years. If you need more then split a pound with some friends and share the cost.

I save the old stuff for rail joints and other places where I can clean off the residue. And for those tough jobs where 3% flux isn’t enough you can purchase a small container of rosin flux paste to apply separately. You can also buy solder that does not contain the flux and apply the paste flux. Keep your rosin core solder in a dry place and once you get past the expiration date, if it starts to give you problems its time to buy a new roll.


  • Richard Williams

    Interesting postings. I too have had a roll of Kester 60/40 rosin core solder for an extended period of time. I got mine back in the mid 1970s and it was just this week that I used it all up. It never failed to give me a clean solder joint. I have used a bit of extra rosin flux to facilitate heat transfer. What it did do is get a bit of an oxidation on the outside of the solder over time. I solved that issue by wiping it clean with some isopropyl on a clean cloth. I learned this from a NASA high reliability soldering technique class I got in the military. In fact they insisted that solder be wiped like this before using to even remove oils from your hand. I am interested in understanding the reference to the solder going bad from the flux. Can you give me a pointer?

  • Thank you