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A low-temperature metallurgical joining method in which the solder (joining material) has a much lower melting point than the surfaces to be joined (substrates). Because of its lower melting point, solder can be melted and brought into contact with the substrates without melting them. During the soldering process, molten solder wets the substrate surfaces (spreads over them) and solidifies on cooling to form a solid joint.
The most important technological applications of solders are in the assembly of electronic devices, where they are used to make metallic joints between conducting wires, films, or contacts. They are also used for the routine low-temperature joining of copper plumbing fixtures and other devices. In addition, solder is used in the fusible joints of fire safety devices and other high-temperature detectors; the solder joint liquefies if the ambient temperature exceeds the solder's melting point, releasing a sprinkler head or triggering some other protective operation.
Tin or indium content is included in solder to facilitate bonding to the metals that are most commonly soldered, such as copper (Cu), nickel (Ni), and gold (Au). Tin and indium form stable intermetallic compounds with copper and nickel, and indium also forms intermetallics with gold. The intermetallic reaction at the solder-substrate interface creates a strong, stable bond. See Alloy, Intermetallic compounds
the process of joining solid materials by means of molten solder. Soldering involves a mutual dissolving and diffusion of the material being joined and the solder; the gap between the parts being joined is thus filled. Soldering results in solid joints for items made of steel, cast iron, glass, graphite, and ceramic and synthetic materials. The numerous methods of soldering are classified according to the means of heating, the conditions under which the gap is filled, the method of cleaning the surface, the formation of the seam, and other factors.
Metal soldering, the most common type of soldering, is arbitrarily divided into soldering with hard and soft solders. When hard solders are used, joints are heated by gas torches, electric arcs, or high-frequency currents in muffle, tunnel-type, and other furnaces. Soldering with soft solders can be done with soldering irons or gas torches; it can also be done by immersion in molten solder and by other means.
REFERENCESLashko, N. F., and S. V. Lashko. Paika melallov, 2nd ed. Moscow, 1967.
Petrunin, I. E., S. N. Lotsmanov, and G. A. Nikolaev. Paika metallov, 2nd ed. Moscow, 1973.