There at least two reasons solder won’t melt on a copper pipe. Copper is an excellent conductor of heat. What ever you are using to heat the pipe is not supplying heat. As fast as you heat the pipe the copper will conduct the heat away.
How do you get solder to flow up?
Quote from Youtube video: So then what i do is apply a thin layer of that to the pipe you don't need a ton of the flux. Just a little bit to make sure that it's on the pipe. And the solder will flow upward.
How do you prevent soldering balls?
Ways to prevent solder balls from being created
- Make sure the PCB boards are not stored in humid environments.
- Ensure that the board is properly dried or preheated (to evaporate trace water amounts) before printing.
- Clean the printing stencil properly before application of solder paste.
