Oxygen-defective metal oxides, e.g., acceptor-doped CeO2, demonstrate exceptionally large electrostrictive responses compared to state-of-the-art electromechanically active ceramic materials.

Low contact angles in reactive wetting are often used as an indicator for strong solder connections. However, from a physical point of view, the so-called work of adhesion is the more justified measure, for which quantitative data are rare. Here, we present measurements for SnPb and SnBi solders on Cu and Ni base metallization. Surface tension and wetting angles are determined by the sessile drop method over the whole composition range of the solders. Provided comparable measurement conditions, the Young-Dupre equation is applied to determine interfacial energies and the work of adhesion. They reveal a characteristic dependence on the intermetallics formed in contact with the liquid solder, clearly supporting the concept of Eustathopoulos which assumes wetting angles are always in contact with the intermetallic of highest possible Sn content. The concentration dependence of the work of adhesion indicates significant segregation of Sn to the liquid-solid interface which significantly affects the bonding strength.

While reactive microsolder joints are of ubiquitous importance in modern electronics, the effects of joint miniaturization on wetting behavior remain largely unexplored. We elucidate this fundamental question of scalability by investigating the wettability of eutectic SnPb solder on Cu and Ni-electrodeposited metallization strips of varying widths. Contact angles are presented in dependence of the metallization width which is varied from 3 mm down to ∼100 μm. The measured angles clearly increase with decreasing metallization width. Based on the measurements and by modifying Young's equation, it is shown that the behavior of the wetting angle can be quantitatively understood with an "effective" triple-line energy of ϵt = (753 ± 31) × 10-9J/m for SnPb on Cu. The interpretation of this energy term is discussed in relation to the forming intermetallic phase and the ensuing surface roughness. A remarkable similarity between the experimentally observed size dependence and the crossed-groove perturbation model of Huh and Mason demonstrates that the rough intermetallic phase induces wetting hysteresis such that it is quantitatively well described by an effective triple-line energy.