Abstract
A new lead free alloy, Sn-6Bi-2Ag-0.5Cu, has been developed by mechanical alloying and has great potential as a lead-free solder system. Initial trials on the manufacture of solder joints with this alloy revealed that a high quality bond with copper could be formed. Its melting range of 193.87°C to 209.88°C is slightly higher than that of eutectic tin-lead solder. Examination of the microstructure of the as-soldered joints revealed that it mainly consists of small bismuth (1 µm to 2 µm) and Ag3Sn (1 µm) particles finely dispersed in a nearly pure tin matrix with a small amount of η-Cu6Sn5 particles. The Cu-Sn intermetallic compound (IMC) layer formed at solder-copper interface is the η-Cu6Sn5 phase with grain size of 2 µm. The shear strength of the solder joint is higher than that of Sn-37Pb or Sn-3.5Ag. Under shear loading, fracture occurred at IMC layer-solder interface as well as in the bulk of solder.
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