Nanocomposites and nanomaterials

Electrical resistivity of Sn95.5Ag3.8Cu0.7 alloys, modified by nickel admixtures
O. Tkach, Yu. Plevachuk, V. Sklyarchuk, Y. Kulyk, R. Serkiz 
Department of Metal Physics, Ivan Franko National University of Lviv, Lviv, Kyrylo i Mephodiy Str. 8, 79005 Lviv, Ukraine.
E-mail: ntkacholga@gmail.com

A scientific interest for Sn-based nanocomposite alloys with minor nanosized additions of metals, oxides and carbon relates to the possible application of these materials as an alternative to commercial lead-free solders. As pointed out in recent literature reviews, improved mechanical properties and a reinforced microstructure of solder joints using nanocomposite Sn--Ag--Cu (SAC) alloys compared to those without nanoinclusions, revealed new possibilities for the development of currently used commercial lead-free solders. The main profit of the nanosized additions is related to a suppression of the extensive growth of the Cu6Sn5 intermetallic compound at the solder/Cu interface towards the solder side. This is achieved due to the spreading of nanoparticles over the IMC's surface, thereby suppressing the growth of Cu6Sn5 at the interface as well as in the bulk solder. In particular, the adsorbed nanoparticles at the IMC layer interface hinder the diffusion of Sn atoms from the bulk solder towards the interface and thereby suppress the IMC growth. Compared to the solid state, there is a limited number of papers dealing with experimental investigations of nanocomposite SAC solders in the liquid state after melting as well as in the semi-solid state. It was shown that minor metal nanoadditions have an impact on the microstructure of solidified SAC solders, but practically without any significant change of the melting temperatures. The effect of small nanosized (up to 3 wt.%) nickel impurities on the electrical resistivity of Sn95.5Ag3.8Cu0.7 (SAC387) alloy was investigated. It was shown that the resistivity gradually increases with increasing impurity content of Ni. The resistivity data provide additional information on the influence of admixtures on the structure and physicochemical properties of the metal matrix, which is important for understanding the microstructural transformations in a liquid state and for modeling the processes of melting and solidification.