From fundamental physical considerations, we have derived a set of partial differential equations describing wetting and spreading. These equations are derived using a variational thermodynamic principle applied to a two-component alloy system with three (vapor, liquid and solid) phases. The method naturally includes time dependent chemical interactions between substrate and liquid and also non-classical (diffuse interface) effects. (The latter are important for applications where the system size approaches nanometer dimensions).

Numerical solution of the equations is being performed for specific wetting geometries and parameter values. Results will be compared to predictions of simpler theories and experimental results. The importance of solute transport and its influence on the surface energy will be examined. A sensitivity analysis will determine those factors that dominate in the wetting process. We will use the model to determine how to interpret the measurements of the wetting balance to best aid in the design solder joints for fine-pitch electronics. Subsequently, these tools will be applied to thin film breakup, heterogeneous nucleation on shaped particles and VLS nanowire growth. |