Abstract
The microstructure and the X-ray diffraction properties were studied for tin electroplates deposited from bright acid baths as well as from a stannate bath. Aging at 50°C for 7 years, largely converted 5µm coatings to various intermetallic compounds: Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> and Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn or Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> depending on the substrate. Dull tin electroplates showed low contact resistance also after aging in spite of a large proportion intermetallic phase at the surface. Bright tin from acid sulphate baths of three different formulations and in particular a tin-nickel alloy coating showed high contact resistances after aging. It seems very doubtful that bright tin could replace gold. Dull tin or tin-lead may offer better chances.
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