High temperature aging study of intermetallic compound formation of Sn-3.5Ag and Sn-4.0Ag-0.5Cu solders on electroless Ni (P) metallization

The Sn-3.5Ag and Sn-4.0Ag-0.5Cu solders on electroless Ni-immersion Au metallization exhibited different interfacial morphology after high temperature storage (HTS) testing at 150/spl deg/C. Ni/sub 3/Sn/sub 4/ intermetallic compounds (IMCs) were found in the Sn-Ag system, while in the Sn-Ag-Cu system, spalling grains of (Cu,Ni)/sub 6/Sn/sub 5/ IMC were observed after long aging, along with a thick (Ni,Cu)/sub 3/Sn/sub 4/ IMC layer which adheres to the P rich electroless Ni coating. Kirkendall voids were found between the Sn-Ag and electroless Ni interface after 168 and 500 hour thermal aging, while a clear gap existed at the interface after 1000 hour aging, as a result of the growth of the micro-voids. In the Sn-Ag-Cu system, Kirkendall voids were found inside grains of the Sn-Ni-Cu ternary interfacial compound after 500 and 1000 hour aging.