Characterization of ternary Cu-Sn-Au bulk alloys and thin films

Abstract

The variation of the microstructure and corresponding properties of several Cu-based Au alloys with differing Sn contents was investigated. Both bulk alloys and thin films of the same composition were studied to determine whether characterization of the bulk alloys could be used to predict the optimal thin film composition. For bulk alloys with less than 10% Sn content, the electrical resistivity and hardness were found to be only slightly increased over those of a Cu-Au alloy with no added Sn ; however they increase rapidly with further increases in Sn content. A microstructural study indicated that these changes in properties are primarily attributable to the formation of a hard ε-Cu3Sn phase. The characteristic needle shape of these preciptated particles, as well as their volume fraction, seems to contribute to the embrittlement of the alloy. The orientation relationship between α-Cu and the ε-Cu3Sn precipitate was found to be {fx191-1} and {fx191-2} The relative variation in resistivity as a function of Sn concentration was the same for the thin film and the bulk alloy, although their absolute values were different because of surface oxidation and small grain size in thin films. Given the observed microstructural similarity, the similar composition depen dence leads to the conclusion that the properties of bulk alloys may be used to make reasonable predictions about the behavior of thin films in systems in which the thin film phase composition is the equilibrium one by heat treatment. © 1984 AIME.