Soldering irons are used to melt the soft solder, with which components and printed circuit board are joined. Soldering with soldering irons is a soft soldering process. Soft soldering is characterized by having a melting point of the filler metal below approximately 400 °C (752 °F), whereas silver soldering and brazing use higher temperatures, typically requiring a flame or carbon arc torch to achieve the melting of the filler. Soft solder filler metals are typically alloys that have liquidus temperatures below 350°C. In the course of time, different types of soldering irons were developed; starting with the uncontrolled manual soldering iron up to microprocessor controlled soldering stations, with different power levels and a multitude of solder tips. They are available as electrically heated or as gas heated soldering irons.