Developing a lead-free solder alloy Sn-Bi-Ag-Cu by mechanical alloying

• Published in: Journal of electronic materials Vol. 29; no. 8; pp. 1015 - 1020
• Main Authors: WU, C. M. L, HUANG, M. L, LAI, J. K. L, CHAN, Y. C
• Format: Journal Article
• Language: English
• Published: New York, NY Institute of Electrical and Electronics Engineers 01.08.2000; Springer Nature B.V
• Subjects: Applied sciences; Brazing. Soldering; Exact sciences and technology; Joining, thermal cutting: metallurgical aspects; Metals. Metallurgy; Intermetallic compound; Mechanical properties; Shear strength; Powder metallurgy; Mechanical alloying; Tin base alloys; Solder; Bismuth alloy; Manufacturing process; Silver alloy; Soldered joint; Microstructure; Soldering; Fractography
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-000-0166-5

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 degree C to 209.88 degree 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 mu m to 2 mu m) and Ag sub(3)Sn (1 mu m) particles finely dispersed in a nearly pure tin matrix with a small amount of eta -Cu sub(6)Sn sub(5) particles. The Cu-Sn intermetallic compound (IMC) layer formed at solder-copper interface is the eta -Cu sub(6)Sn sub(5) phase with grain size of 2 mu m. 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.