Growth of intermetallic compounds in the Au-In system: Experimental study and 1-D modelling

The gold-indium system is of primary interest for bonding processes such as solid-liquid interdiffusion bonding. In order to optimize the manufacturing parameters, it is essential to know which intermetallic compounds (IMCs) are formed when solid Au and liquid In are brought into close contact with each other, and what are their growth kinetics. For this purpose, we fabricated diffusion couples above and below the melting point of In (for T=250 and 150 °C  respectively). Three IMCs, identified as AuIn2, AuIn and Au7In3, are always observed in the reaction zone, even after short times. AuIn2 is the thickest and fastest growing layer and AuIn is only present as a thin layer. Whereas AuIn2 and AuIn exhibit an equiaxed structure, Au7In3 is found to grow as columnar grains. The diffusion coefficients in each phase were determined by means of a 1-D finite difference modelling of In diffusion. The values are consistent and can be used to predict the growth rate as a function of temperature and time, i.e. to simulate a whole bonding process with finite thicknesses.