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The increasing scientific interest in Sn-based nanocomposite alloys with minor additions of oxides, metals and carbon in nanosized form is explained by the possible application of these materials as an alternative to commercial lead-free solders. As pointed out in recent literature reviews, the improved mechanical properties and reinforced microstructure of solder joints using nanocomposite Sn-Ag-Cu (SAC) alloys, compared to those without nanoinclusions, revealed new possibilities for the development of the currently used commercial lead-free solders. The main benefit of the nanosized additions is related to the suppression of the extensive growth of the Cu6Sn5 intermetallic compound (IMC) 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 on the interface as well as in the bulk solder. In particular, the adsorbed nanoparticles on 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 has been 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 conductivity of Sn95.5Ag3.8Cu0.7 (SAC387) alloy has been investigated. It has been shown that the electrical conductivity gradually decreases with an increase in the impurity content of Ni. Conductivity, as a structure-sensitive transport characteristic of the liquid state of a substance, is important for modeling the processes of melting and solidification. The conductivity 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. Morphology of the samples was examined using REMMA-102-02 Scanning Electron Microscope- Analyzer (JCS SELMI, Sumy, Ukraine). [ABSTRACT FROM AUTHOR]