Study on synthesis of ultrafine Cu–Ag core–shell powders with high electrical conductivity

Cu–Ag composite powders with high electrical conductivity were synthesized by electroless plating of silver sulfate, copper powders with eco-friendly sodium citrate as reducing agent, dispersant and chelating agent in an aqueous system. The influences of sodium citrate/Ag ratio on Ag coatings of Cu powders were investigated. Ag was formed a dense coating on the surface of Cu powders at a molar ratio of sodium citrate/Ag = 0.07/1. SEM showed an uniformity of Ag coatings on Cu powders. SEM-EDX also revealed that Cu cores were covered by Ag shells on the whole. The surface composition analysis by XPS indicated that without Cu or Ag atoms in the surface were oxidized. The resistivity measurements of Cu–Ag paste shows that they have closer resistivity as the pure silver pasteʹs after 250 °C for 30 min heat-treatment (2.55 × 10−4 Ω cm) and 350 °C for 30 min heat-treatment (1.425 × 10−4 Ω cm).