Soldering is a joining process for connecting various metal materials together with the aid of a molten filler metal (solder), the melting temperature of which lies below that of the base materials. The base materials are coated without melting themselves. Work sometimes takes place with the addition of pastes or powered flux (e.g. soldering grease), which clean the workpiece surface, improve the coatability and solder flow and are intended to prevent the formation of surface films.

Depending on the type of solder application it is possible to distinguish between joint soldering and surface soldering. Usually, electrically-heated solder guns are used for soft soldering, whilst petrol or gasoline-driven solder lamps are used for soft and hard soldering. With electrical resistance soldering the solder, flux and workpiece are heated between electrodes from copper or tungsten and joined together. With induction soldering the soldering process takes place in conjunction with the influence of an electric field of high frequency alternating current. Furnace soldering under protective gas is particularly significant in device engineering.