Interfacial Reaction and Die Attach Properties of Zn-Sn High-Temperature Solders

Interfacial reaction and die attach properties of Zn-xSn (x = 20 wt.%, 30 wt.%, and 40 wt.%) solders on an aluminum nitride-direct bonded copper substrate were investigated. At the interface with Si die coated with Au/TiN thin layers, the TiN layer did not react with the solder and worked as a good protective layer. At the interface with Cu, CuZn5, and Cu5Zn8 IMC layers were formed, the thicknesses of which can be controlled by joining conditions such as peak temperature and holding time. During multiple reflow treatments at 260A degrees C, the die attach structure was quite stable. The shear strength of the Cu/solder/Cu joint with Zn-Sn solder was about 30 MPa to 34 MPa, which was higher than that of Pb-5Sn solder (26 MPa). The thermal conductivity of Zn-Sn alloys of 100 W/m K to 106 W/m K was sufficiently high and superior to those of Au-20Sn (59 W/m K) and Pb-5Sn (35 W/m K).