Solder and Soldering Iron

The solder alloy used to join too pieces of metal, the "parent" metals, has a melting point less than that of either parent metal. When it is placed between the two parents, it slowly changes from a liquid to a solid. The soldering iron is used to melt the solder and it is then allowed to cool.

While the process of solidification is taking place, the solder alloy begins to form a new alloy with each of the parent metals. When the solder finally cools, therefore, the joint consists of five segments: parent metal #1; a new alloy of parent metal #1 and the solder alloy; the solder alloy itself; a new alloy of parent metal #2 and the sold alloy; and parent metal #2.

The primary function to the soldered junction, of course, is to provide a connection between the two parent metals. However, the junction is not a permanent one. In fact, an important characteristic of the soldered connection is that it can be broken apart with relative ease.