Use of multicomponent phase diagrams for predicting phase evolution in solder/conductor systems

Although the complete phase equilibrium is never reached in interconnection applications, the assumption of local equilibrium at the interfaces is gen erally valid in most systems composed of dissimilar materials. Therefore, t he tie lines in ternary (or multicomponent) phase diagrams-together with th e relevant stability diagrams and the mass balance requirements-can be used for predicting the phase sequences (i.e. diffusion paths) formed, for exam ple, in solder/conductor joints. Generally, binary phase diagrams alone can not, provide sufficient information on the phase formation in solder/conduc tor systems because they do not bear any information on the relative stabil ities between different binary phases in multicomponent systems. As example s, the formation of intermetallic compounds in several solder/conductor sys tems with Au- or Cu- metallization was studied with the help of ternary pha se diagrams as well as experimentally. The phase diagrams were calculated u sing thermodynamic methods. The experimental results confirmed that the dep endence of formation of intermetallic compounds on temperature and solder c omposition is clearly represented by the phase diagrams supplemented with t he stability diagrams.