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oldest is a fused metal alloy used to create a permanent bond between metal work pieces. The word welding comes from the English word half soudur, via Old French solduree and soulder, from the Latin solidare, meaning "to make solid" [3]. In fact, the weld must be melted in order to adhere and connect the parts, so that an alloy suitable for use as welding will have a lower melting point than the parts to be joined. Whenever possible, the weld must also be resistant to oxidative and corrosive effects that degrade the joint over time. Welding which is intended for use in the manufacture of electrical connections between electronic components also tends to have favorable electrical characteristics.

Soft solder typically has a melting point range of 360 to 720 K (360 to 720 K), and is commonly used in electronics, plumbing and sheet metal work. Manual welding uses a welder or a welding gun. Alloys that melt between 180 and 190 ° C (450 and 460 K) are the most commonly used. Welding made with alloys with a melting point above 450 ° C (740 K) is referred to as "hard welding", "silver welding" or brazing.

In specific proportions, some alloys may become eutectic, that is, their melting point is the same as their freezing point. Non-eutectic alloys have markedly different solidus and liquidus temperatures, and within that range exist as a paste of solid particles in a melting of the lower melting phase. In electrical work, if the joint is altered in the pasty state before it has completely solidified, a poor electrical connection may occur; the use of eutectic welding reduces this problem. The pasty state of a non-eutectic weld can be exploited in the plumbing, since it allows molding of the weld during cooling, to ensure the sealing of the pipes, resulting in a so-called "friction joint".

For electrical and electronic work, welding wire is available in a range of thicknesses for welding by hand, and with cores containing flux. It is also available as a paste or as a preformed sheet in the form of matching the workpiece, most suitable for mechanized mass production. Lead and tin alloys were commonly used in the past and are still available; are particularly suitable for welding by hand. Lead-free soldering has increased in use due to regulatory requirements plus the health and environmental benefits of avoiding lead-based electronic components. They are used almost exclusively today in consumer electronics. Plumbers often use welding rods, much thicker than the wire used for electrical appliances. Jewelers often use welding on thin sheets, which they cut into fragments.