Lead-free Solder Reaction With The Substrate Ni Interface Research And Au-pb-sn Ternary Thermodynamic Optimization

Failure of the joint is one of the main reasons of failure of semiconductor devices, while the microstructure of the joint can greatly influence its performance. So many studies of the interfacial reaction between solder and substrate during both the process of soldering and service of the device are helpful to design of solder composition, soldering process, prediction and control of the microstructure of the interface and forecasting of the life of semiconductor devices.Lead-tin solder alloys have been widely used in the modern electronics industry because their low melting points, good wettability, good corrosion resistance and reasonable electrical conductivity. However, due to increasing environmental and health concerns and legislation restriction over the use of lead, many different solder alloys have been proposed as potential Pb-free solder candidates and the most promising Pb-free solders fall into the Sn-based alloys, for instance, Sn-Ag alloys, Sn-Bi alloys and Sn-In alloys. Ni coats are often plated as an Under Bump Metallurgy (UBM) layer on the substrate before the electronic components are soldered. The subject of this work is to study the interface between solder and substrate from the phase equilibria information and microstructure evolution:1. The interfacial reactions between different composition Sn-Bi alloys and Ni substrate at 423K for different aging time were studied. Using CALPHAD method and combination of the experimental apparatuses (optical microscope, SEM, EPMA), the mechanisms for the formation of intermetallic compound at the interface were analyzed and explained.2. Using CALPHAD method, the Ni-Sn binary system was optimized. A set of consistent parameters was obtained, on the base of which, intermetallic formation and its sequence between pure Sn and Ni substrate were predicted.3. Using the CALPHAD method, the experimental phase diagrams and thermodynamics data was collected, critically assessed and the uniform and newest lattice stability was adopted. The Au-Pb binary system was optimized. A set of consistent parameters was obtained. The Au-Pb-Sn was extrapolated by integrating Au-Sn and Pb-Sn binary systems, and a series of the vertical sections and isothermal section were calculated and compared with the experimental data.