Solder and Soldering Iron

The first step in making a soldered connection is to heat the solder alloy until it melts. In the most primitive form of soldering irons, this can be accomplished simply by heating a metal cylinder and using it to melt the alloy and attach it to the parent metals. However, most soldering irons are now heated by an electrical current that is designed to apply exactly the right amount of solder in precisely the correct position between the two parent metals.

The joining of two parent metals is usually more difficult than might be suggested by the foregoing description because most metals oxidize when exposed to air. That means that the faces (that is, the metal oxides that cover their surfaces) of the two parent metals must be cleaned before soldering can begin. In addition, care must be taken that the surfaces do not re-oxidize at the high temperature used in making the solder. The most common way of accomplishing this goal is to use an acidic flux in addition to the solder itself. An acidic flux is a material that can be mixed with the solder, but that melts at a temperature less than the solder's melting point. As soldering begins, therefore, the flux insures that any new oxide formed on the parent metals will be removed.