Diagramas De Fases

Phase Diagrams of Important Electronic Materials
A phase diagram is the most concise representation of the phase equilibria present in a system. Phase diagrams are indispensable in understanding phase transformations, solidifications, interfacial reactions, and the accompanying changes in microstructure. Know ledge of the phase equilibria of a material system is, therefore, critical for theimprovement of existing materials and the development of new materials. More significantly, with the rapid development of the thermodynamic modeling of phase diagrams, information that can be obtained from phase diagrams is no longer limited to the phase or the chemical (interfacial) stability between multiple phases. The driving forces for phase transformation, chemical reactions, and diffusionprocesses can now be estimated quantitatively once the proper thermodynamic modeling of a materials system has been performed. The knowledge of the driving forces can then be used to rationalize observed phenomena, or even to serve as inputs of kinetic models for quantitative predictions. With appropriate thermodynamic modeling, even the metastable phase equlibria and the driving forces involvingphase(s) can be accurately calculated. Thermodynamic modeling of phase diagrams is also quite helpful in simplifying the time-consuming experimental determination of phase diagrams. Moreover, thermodynamic modeling combined with kinetic modeling, such as solidification modeling and diffusion modeling, can significantly cut down the development time of new products.
The electronics industry facesaccelerating demands for products with higher functionality and grater portability and greater portability al lower prices. At the same time, environmental regulations demand the elimination of certain tonic element, such as lead, from electronic products. Central to these issues is the development of new and hatter material systems in a minimum amount of time. Phases diagrams, thermodynamic modeling,an appropriate kinetic modeling combined together can serve as a powerful tool to achieve this goal. The following articles address issues related to the thermodynamic modeling of phase diagrams for electronic materials, the combined use of the thermodynamic and kinetic modeling, and the application of phase diagrams in the development electronic materials.
The first article, by U.R. Kattner,discusses thermodynamic modeling for the development of an important class of electronic material, lead-free solder alloys. Phase diagrams and thermodynamic modeling are especially useful for the development of lead-free solder alloys and their matching metallizations because, in the systems, very good agreement between modeling and experimental observation can be achieved. This is because for mostof the solder alloys, which usually much below 230°C, even room temperature is at relatively high homologous temperatures and local thermodynamic equilibrium, can be established rather easily. In this article, the CALPHAD (calculation phase diagram) approach is introduced first. All the important binary systems related to soldering are reviewed. Important ternary and higher-order system are alsocovered. This paper clearly shows that the electronic solder and related materials as a whole combine to form one of the best-characterized materials systems in terms in terms of the thermodynamic description, and offer a great potential to demonstrate the usefulness of phase diagrams and thermodynamic modeling.
The second article, by U.R. Kattner, presents an excellent discussion on theapplication of combined thermodynamic and diffusion kinetic modeling to the development of new electronic material, including lead-free solders, their matching metallizations, and the appropriate diffusion bartier layers. In this article, the theoretical background is discussed first. An important new concept of local nominal composition is introduced. The local nominal-composition concept combined with...