This study examines the epitaxial growth of the intermetallic compound (IMC) of Cu6Sn5 (or (Cu,Ni)6Sn5) that forms at the interface between molten Sn-based lead-free solders and non-textured polycrystalline Cu substrates. Sn, Sn-Cu, Sn-Cu-Ni and Sn-Ag-Cu solders were investigated. The dominant growing planes in a hexagonal structure of this IMC on Cu substrates are (101) and (102). Addition of trace Ni into Sn-Cu solders leads to an increase in (101) growth and a decrease in (102) growth. The presence of Ag in Sn-Ag-Cu solders facilitates (102) growth and suppresses (101) growth. Such an epitaxial growth should have a large influence on the mechanical and electrical characteristics of the Sn-based solder/Cu joints.
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