The other problem is too much heat. If you heat the copper (or any metal to be soldered) to the point that it changes color then it will be impossible for the solder to properly flow. The copper should never change from the bright shiny color it is from cleaning it with sand paper. I would use 50/50 (tin/lead)and not the "environmentally safe" stuff they sell for plumbing. After cleaning with sand paper apply the flux. Then heat while applying the solder. When the copper gets hot enough to melt and flow the solder remove the heat and solder.
Posted on Sep 25, 2011, 8:32 AM from IP address 184.108.40.206