Resistance to oxidation at 150°C of sub-micrometer diameter silver-coated copper particles produced by wet chemical synthesis and immersion plating

Sub-micrometer diameter Cu particles fabricated in air by wet synthesis at 80°C for 2 h were immersion plated with Ag to produce an inexpensive conductive paste filler aimed at achieving fine printed patterns. Increasing the volume ratio of hydrazine hydrate to ammonium hydroxide used during wet synthesis was found to accelerate the rate of reduction and increase the yield of Cu particles to as much as 97.56% when an optimal ratio of 3:7 was used. The resulting particles (average size = 0.56 μm) exhibited excellent dispersion, with the use of an optimal Ag concentration of 15 mass% in their subsequent immersion plating producing a continuous Ag shell and a 0.62 μm average diameter. Increasing the Ag concentration beyond this, however, resulted in abrupt agglomeration between the particles, as well as the formation of cavities and spherical pure Ag particles. Those particles produced under optimal conditions experienced only a slight weight increase of 0.4% after 75 min exposure to air at 150°C, suggesting that they have an excellent resistance to oxidation at this temperature.