Growth of intermetallic compounds in the Sn-9Zn/Cu joint

We have studied the microstructure of the Sn-9Zn/Cu joint in soldering at temperatures ranging from 230 degrees C to 270 degrees C to understand the growth of the mechanism of intermetallic compound (IMC) formation. At the interface between the Sn-9Zn solder and Cu, the results show a scallop-type epsilon-CuZn4 and a layer-type gamma-Cu5Zn8, which grow at the interface between the Sn-9Zn solder and Cu. The activation energy of scallop-type epsilon-CuZn4 is 31 kJ/mol, and the growth is controlled by ripening. The activation energy of layer-type gamma-Cu5Zn8 is 26 kJ/mol, and the growth is controlled by the diffusion of Cu and Zn. Furthermore, in the molten Sn-9Zn solder, the results show eta-CuZn grains formed in the molten Sn-9Zn solder at 230 degrees C. When the soldering temperature increases to 250 degrees C and 270 degrees C, the phase of IMCs is epsilon-CuZn4.