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Soldering wire is a fusible alloy, typically of tin and silver or lead, that has been extruded into an easily handled form. Shaping solder into wire allows it to be wound on a spool for easy storage and unwound for use as necessary. Some soldering wire is a solid alloy, while other varieties comes with a flux core. Soldering wire can be made of many different compounds, and some alloys are more useful than others for particular jobs. Various tin and lead alloys were historically used for applications such as electronics and plumbing, though lead may be replaced by metals such as silver and antimony for health or environmental concerns.
Types of soldering wire are typically differentiated by their thicknesses and the metals they are made of. Thin wire is typically useful for delicate electronics work, while thicker options can be good for plumbing work or to solder together wires. A eutectic mixture of 63% tin and 37% lead was a very popular form of wire solder for working on electronics, since this type of mixture has a discrete melting point rather than a general range. Alloys with higher lead content were more popular for applications such as plumbing as these will typically solidify more slowly, which can be advantageous when joining pipes.
Due in part to concerns over lead poisoning, a variety of other metals are also used in soldering wire. Certain governments have enacted laws that require these lead free solders, while others provide tax benefits for using them. Some materials that have replaced lead in soldering wire include silver, antimony, copper, and zinc.
Each alloy used in soldering wire typically melts somewhere between 190 and 840 degrees Fahrenheit (90 to 450 Celsius). Solder that uses metals such as antimony and silver typically has a slightly higher melting point than comparable lead variants. Brass wire that is composed solely of copper and zinc is typically used in brazing, which is a similar process that involves metals with melting points higher than 840 degrees Fahrenheit (450 Celsius).
Flux cored soldering wire typically contains one or more internal veins of acid or rosin based materials. This type of wire solder makes it unnecessary to apply external flux during the soldering process. As the wire solder is uncoiled and heated, the internal flux melts as well. This allows the flux to remove any metal oxides on the components that are being joined. Acid core wire is usually used for plumbing applications, while rosin wire is useful in electronics soldering.