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Conventional lead-free solders, with a solder alloy particle size in the micrometer range, present some major disadvantages, such as relatively high melting temperatures, which can result in defects and build up stresses during reflow processing, and limited application for high density, ultra- small pitch electronic applications. By decreasing the size of the solder alloy particles to the nanometer range, one can both decrease the melting temperature of the solder alloy and use such solders in very fine pitch applications. Besides lower melting temperature, particles in the nanometer size range present many other extraordinary properties, such as, large surface area per unit volume, large surface energy, supermagnetism, extraordinary optical properties, self- purification properties and quantum size effects. It is all these extraordinary properties that have attracted the attention of both scientific and technological communities all over the world. The main focus of this paper is the recent development of both composite solders and pure nano-solder pastes and their application as electronic interconnect materials. The paper starts by giving and introduction to the subject of nanoparticles, including definitions, advantages and general applications. This is followed by a section dealing with the main manufacturing processes presently being used to manufacture solder alloy nanoparticles. The two main sections of this article deal with composite solders and pure nanosolder pastes. The first part, regarding composite solders, deals with the issues related to adding nanoreinforcements into conventional micrometer-sized solders and the effect of such reinforcements on both the mechanical and physical properties of solder alloys. The second part deals with pure nano-solder pastes and their application in electronic interconnect applications.