The composition of intermetallic compounds in Sn-Ag-Bi-In solders on Cu substrates

84Sn-3Ag-3Bi-10In and 89Sn-3Ag-3Bi-5In solders were subjected to reflow and solid state aging. The intermetallic compounds that formed at the interfaces between the solders and the Cu substrates and those that formed in the bulk solders in both test conditions were investigated. In the as-reflow samples, the intermetallic compounds were identified as Cu
₃
Sn and Cu
₆
Sn
₅
. After solid state aging, these compounds became Cu
₆
(Sn,In)
₅
and Cu
₃
(Sn,In). The compounds that formed in the bulk solders were zeta phase, the solid solution of Ag
₃
Sn and Ag
₂
In.