ELEMENT OF THE MONTH
Each month we will explore elements of interest from the periodic table, with a brief history of discovery and development, and a review of uses and applications.
TIN – ATOMIC NUMBER: 50 – CHEMICAL SYMBOL: SN
Tin is a soft whitish metal with a yellowish tinge, known to mankind for around 5,000 years. Its abundance is approximately 2ppm of the earth’s crust.
It rarely exists as native metal and is mostly present as stannic oxide (cassiterite), which is reduced to tin metal in smelting furnaces.
Pure tin is very ductile at normal temperatures but can turn to a powder below a temperature of 13C
WHERE IS TIN USED?
As a Pure Element
Pure tin has few uses as a solid material, but is extensively used to coat other materials such as steel (tin) cans. A bed of molten tin is used in flat glass plate production to produce a very smooth parallel surface (Pilkington process)
As an Alloy
One of the first uses of tin was as an alloy with copper that heralded the beginning of the bronze age. Tools and weapons that were previously hewn from stone were easier to fabricate in bronze and were more effective. In recent times, a wide range of alloys has been developed to provide industry with solders (tin-lead, tin-silver-copper, tin bismuth), electronic contacts (copper-tin, copper-tin-zinc, copper-nickel-tin), and bearing materials (tin-lead- copper-antimony-arsenic)
As a Compound
Niobium-tin intermetallic compounds exhibit superconductor characteristics that maintain high current flow at high magnetic flux density, up to 30 teslas, and are used in the Large Hadron Collider at CERN European Organization for Nuclear Research. At the other end of the scale, tin (stannous) fluoride is used in toothpaste to reduce dental erosion and cavities.
As a Coating
Electroplated tin is widely used to protect substrates such as steel, and as a solderable layer for copper-based connectors and contacts. Lower cost or environmentally friendly tin-based alloys can be electroplated as alternatives to chromium (tin-cobalt), palladium (tin-nickel), cadmium (tin-zinc), lead (tin-bismuth). Immersion tin coatings are widely used in the printed circuit board manufacturing industry to provide a very flat solderable surface suitable for high density circuit tracks and component pads.
Here are some key parameters for Tin, quantifiable using instruments from Helmut Fischer GmbH
- Composition of tin alloy solder bump contacts on BGA electronic components with an instrument utilising the XRF technique, such as XDV-µ
- Hardness and modulus of elasticity of thin copper alloy foils and strips in the connector industry, using the Instrumented Indentation Test
- Minimum 3% lead content of high reliability tin-lead solders with instruments such as XDAL 237
- Screen electronic components and assemblies for prohibited substances such as lead using a high end XRF system such as XDV-SDD