Soldering is a process in which two or more metal items are joined together. They are heated with a soldering iron. A filler metal called solder, with a relatively low melting point melts and flows into the joint, mixing with and melting a little of the items being soldered. Soft soldering is characterized by the melting point of the filler metal, which is below 400°C. Some metals such as iron are rarely soldered, because their melting point is too high. 