Intermetallic Growth and Contact Resistance of Tin Contacts After Aging

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: Cu6Sn5and Cu3Sn or Ni3Sn4depending 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.