Alloys based on the Sn-0.7Cu-xNi system are potential Pb-free solders. In this paper we report on the solidification characteristics and microstructures of Sn-0.7Cu alloys containing 0-1,000 ppm nickel. The microstructural observations show that increasing the nickel content reduces the volume fraction of primary Sn, thus generating a more-eutectic microstructure. In an attempt to better understand the changes in solderability with Ni additions, fluidity tests were carried out using the Ragone method for small incremental increases in nickel content. The maximum fluidity length was found to vary strongly with nickel content. Additionally, the distribution of nickel within samples was investigated using synchrotron micro X-ray fluorescence.
Three binary Sn-Cu solder alloys of near-eutectic composition have been directionally solidified at different growth rates. The competition between primary tetragonal Sn cells/dendrites and eutectic is interpreted with the coupled zone concept. It is also found that SnCu is a weakly irregular eutectic system with Cu 6 Sn 5 leading the eutectic, but two different eutectic morphologies (coarse and fine) form simultaneously during eutectic growth. At higher growth rates, the eutectic interface breaks down into a cellular eutectic with the fine eutectic in the centre of the cells and the coarse one at the cell boundaries. This is explained by the segregation of Pb impurities ahead of the eutectic interface.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.