2004 Volume 45 Issue 3 Pages 714-720
The interfacial reactions and the interface microstructures between Sn-3.5Ag-(0.7Cu) lead-free solders and Fe-42Ni substrate were investigated at the reaction temperature of 250°C. Joint strength was also evaluated. The Sn-3.5Ag joint shows the double reaction layers of FeSn2. Ni from Fe-42Ni dissolves into molten Sn-3.5Ag solder during soldering and forms Ni3Sn4 compounds with the eutectic network of Ag3Sn/β-Sn in solder layer during solidification. For the Sn-3.5Ag-0.7Cu jont, the Cu addition in Sn-3.5Ag changes the microstructure of solder and interfacial reaction layers. Ni dissolved into solder melt reacts with Sn and Cu to form a η-phase of Cu-Ni-Sn compound during the soldering without the formations of Ni3Sn4 compound. At the reaction interface, fine particles of FeSn2 can be found near to the reaction layer instead of the faceted compound of FeSn2 in the second reaction layer for the Sn-Ag joint. Sn-3.5Ag-0.7Cu joint increases the joint strength by about 30—40 MPa higher than that of Sn-3.5Ag joints.