Design of the Contact Metallizations for Gold-Tin Eutectic Solder-A Thermodynamic-Kinetic Analysis

This dissertation focuses on the design of reliable interconnections using Au-20wt.%Sn solder with the assistance of thermodynamic calculations. In this work, three commonly encountered contact metallizations, namely Ni, Cu, and Pt, have been selected. In order to assess the reliability of the Au-20wt.%Sn|X (X=Ni, Cu and Pt) interconnections from the metallurgical viewpoint, firstly, the phase diagrams of the Au-Sn-X ternary systems have been thermodynamically established with the Calphad method. Secondly, the diffusion couple method was employed to study the interfacial reactions experimentally. The microstructures of the as-soldered and subsequently aged Au-20wt.%Sn|X interconnections were characterized by means of scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (EDX) and scanning transmission electron microscopy with EDX. The observed interfacial reaction phenomena have been rationalized by combining the experimental results with the thermodynamic considerations. Emphasis has also been placed on collecting the mechanical properties of the IMCs formed at the solder/Cu and Ni interfaces since these values are essential for evaluating the reliability of the interconnections. The results in this dissertation show that Au-20wt.%Sn|Pt was more thermally stable than Au-20wt.%Sn|Ni and Au-20wt.%Sn|Cu when these as-soldered reaction couples were subsequently aged at 150 °C for a long-term. When a short bonding time is employed, Pt contact metallization is superior to the Ni and Cu contact metallizations for the Au-20wt.%Sn solder.