NOVELTY - Preparing metal nanoparticles, comprises reacting an insoluble complex of a metal salt with a reducing agent in a reaction mixture comprising a first surfactant, a second surfactant, and a third surfactant, where the first surfactant comprises a primary amine, the second surfactant comprises a secondary amine, and the third surfactant comprises a chelating agent comprising a diamine.    USE - The process is useful for preparing metal nanoparticles, preferably copper nanoparticles (claimed), which are useful: in the applications of nanoelectronics and photonics materials e.g. micro-electromechanical systems and nanoelectromechanical system, in biomaterials, as biomarkers, diagnostics and sensors, and in nanomaterials e.g. in polymers, textiles, fuel cell layers, composites and solar energy materials; and in antimicrobial formulations, antibiotic and antifungal agents, in coatings, plastics and textiles, and in diet supplements.    ADVANTAGE - The copper nanoparticles: ensure high uniformity of material and very rapid fusion processes (less than 1 minute) for fast assembly processes; and provide higher electrical and thermal conductivity compared to SAC materials and other lead-based solder replacements.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) forming copper nanoparticles (200) comprising: forming a first solution comprising a copper salt, a first surfactant, a second surfactant, and third surfactant; allowing an insoluble complex of the copper salt to form from the first solution; combining a second solution comprising a reducing agent with the insoluble complex, to form a reaction mixture; and forming copper nanoparticles from the insoluble complex; and    (2) the copper nanoparticles prepared by the process, having a fusion temperature of less than or equal to 200 degrees C, and comprising the first, second and third surfactants.    DESCRIPTION OF DRAWING(S) - The figure shows a presumed structure of the copper nanoparticles prepared by the processes.    Copper nanoparticle (200)    Dense core (202)    Lower density shell (204)    Surfactant layer (206)