Before welding to clean up the circuit board and wires, oil, paint and other dirty clean and, if necessary, use alcohol. Clean up after the welding point using a soldering iron to heat on rosin or solder paste, and use the electric iron soldering points on the tin (ie let hang tin soldering point). Two or more welding points using the electric iron, tin and so that they are connected together. On the tin melt tin use electric iron head directly touch the solder wire, soldering iron temperature reaches the melting temperature solder wire melting. Weld metal is too big electric iron can not be heated to solder melting temperature of the metal being welded, it should increase the wattage of electric iron. I wish you success.