Whenever someone has difficulty soldering, and I find out they are using unleaded solder, I always give the same advice:
USE LEADED SOLDER
USE LEADED SOLDER
USE LEADED SOLDER
Lead-free solder is a disaster. Stay away from it.
USE LEADED SOLDER
USE LEADED SOLDER
USE LEADED SOLDER
Lead-free solder is a disaster. Stay away from it.
I use Kester K100LD and it is absolutely fantastic. Unless you really know your stuff you can't tell a difference.
Please stop giving outdated advice like this.
You know what is 100% as good as leaded solder? Actual leaded solder!
You remember that giant class-action against the Heathkit company for all the people they poisoned with leaded solder? Don't remember it? That's because it never happened!
If your soldering consists of soldering pins onto Arduino nano boards, or whipping up a prototype or two with your JLCPCB boards, you'll be fine with leaded solder.