Investigation of Dissolution Behavior of Metallic Substrates and Intermetallic Compound in Molten Lead-free Solders

This study investigates the dissolution behavior of the metallic substrates Cu and Ag and the intermetallic compound (IMC)-Ag 3 Sn in molten Sn, Sn-3.0Ag-0.5Cu, Sn-58Bi and Sn-9Zn (in wt.%) at 300, 270 and 240°C. The dissolution rates of both Cu and Ag in molten solder follow the order Sn > Sn-3.0Ag-0.5Cu >Sn-58Bi > Sn-9Zn. Planar Cu 3 Sn and scalloped Cu 6 Sn 5 phases in Cu/solders and the scalloped Ag 3 Sn phase in Ag/solders are observed at the metallic substrate/solder interface. The dissolution mechanism is controlled by grain boundary diffusion. The planar Cu 5 Zn 8 layer formed in the Sn-9Zn/Cu systems. AgZn 3 , Ag5Zn 8 and AgZn phases are found in the Sn-9Zn/Ag system and the dissolution mechanism is controlled by lattice diffusion. Massive Ag 3 Sn phases dissolved into the solders and formed during solidification processes in the Ag 3 Sn/Sn or Sn-3.0Ag-0.5Cu systems. AgZn 3 and Ag 5 Zn 8 phases are formed at the Sn-9Zn/Ag 3 Sn interface. Zn atoms diffuse through Ag-Zn IMCs to form (Ag, Zn)Sn 4 and Sn-rich regions between Ag 5 Zn 8 and Ag 3 Sn.