What Is Tin?

Tin is a soft, silvery-white metallic element with atomic number 50 and the symbol Sn, derived from its Latin name stannum. It belongs to group 14 of the periodic table, sharing that column with carbon, silicon, germanium, and lead. Tin has been smelted from its principal ore, cassiterite (SnO2), since antiquity, and the ability to alloy it with copper to produce bronze made it one of the defining materials of prehistoric metallurgy. In modern engineering, tin's low melting point of 231.9 degrees Celsius, good electrical conductivity, resistance to corrosion, and ability to form alloys with many other metals make it indispensable to electronics manufacturing, surface finishing, and advanced materials.

Physical and Chemical Properties

Tin exists in two stable allotropes at atmospheric pressure. White tin (beta-tin) is the familiar metallic form with a body-centered tetragonal crystal structure and a density of 7.31 g/cm3; it is ductile and highly workable. Below 13.2 degrees Celsius, white tin transforms slowly into gray tin (alpha-tin), which has a diamond cubic structure and is brittle and semiconducting, a phenomenon known as tin pest. The transformation can be inhibited by small additions of bismuth, antimony, or lead, which is relevant for solder joints operating in cold environments. Tin's electrical conductivity is approximately 9.17 x 10^6 siemens per meter, lower than copper but adequate for thin film and plating applications. It is also superconducting below 3.72 K, a property studied in early experimental investigations of superconductivity. NIST maintains reference data on tin's thermophysical properties as part of its NIST Chemistry WebBook.

Electrical and Electronic Applications

Tin's dominant application in electronics is as the base constituent of solder alloys used to form electrical and mechanical connections between components and printed circuit boards. The eutectic tin-lead alloy at 63 percent tin and 37 percent lead has a melting point of 183 degrees Celsius and was the standard solder in electronics assembly for decades. Restrictions on lead under the European Union's RoHS directive and similar regulations worldwide prompted the industry to shift to lead-free alternatives, primarily tin-silver-copper (SAC) alloys such as SAC305, which contains 3 percent silver and 0.5 percent copper with the balance tin and melts at approximately 217 to 220 degrees Celsius. The properties and applications of tin electrodeposits in electronics are surveyed in technical publications from Advanced Plating Technologies. Tin is also used as a transparent conducting oxide in its dioxide form (SnO2), which functions as a transparent electrode in touchscreens, solar cells, and low-emissivity architectural glass. Tin-based perovskites are an active research area for photovoltaic and LED applications.

Metallurgical and Industrial Applications

Beyond electronics, tin is used to produce tin-plated steel, commonly called tinplate, for food and beverage packaging. The coating, typically 1 to 17 grams per square meter, provides a barrier against corrosion and a surface that bonds well to organic coatings. Tin bronzes, alloys with copper containing 4 to 20 percent tin, combine high strength, good wear resistance, and corrosion resistance for bearings, bushings, and marine hardware. Pewter, traditionally an alloy of tin with small percentages of copper and antimony, is used in decorative and tableware applications.

Applications

Tin has applications in a wide range of industries, including:

• Electronics assembly, as the primary constituent of lead-free solder alloys in surface-mount and through-hole soldering
• Semiconductor and photovoltaic manufacturing, where tin compounds serve as transparent conductive films
• Food packaging, through tin-plated steel for corrosion-resistant containers
• Bearing and wear-resistant components, via tin bronze alloys in industrial machinery