The Preparation Of Nano Cu@Ag And Performance Research Of Nano Cu@Ag Aqueous Condutive Ink

The research and development of paper and plastic-based(such as PET, PP and PE) electronic products have become important, with the development of electronic products in the direction of high accuracy, high flexibility, digitization and diversification. As the glass transition temperature of these paper and plastic substrate are within 150℃, the traditional micron and sub-micron conductive fillers have couldn’t meet the needs of printed electronics now. The high cost of nano silver conductive ink and the instability of nano copper conductive ink limit its commercialization. Therefore, the development of conductive ink of low sintering temperature and low-cost is very important. As the conductive filler, the research and development of nano Cu@Ag, not only can solve the problem of the oxidation of nano copper, but also can reduce the costs of the silver nanoparticles. Also, the conductive interconnects can be fabricated by Ag migration between Cu@Ag core-shell nanoparticles at the low temperature, which can reduce the sintering temperature of conductive ink. The research and development of nano Cu@Ag conductive ink is expected to solve the current technology problem of the high cost and high sintering temperature of conductive ink and become more and more important.Firstly, copper nanoparticles could be obtained via the reduction of Cu2+ions by using cetyltrimethylammonium bromide (CTAB) as the dispersing agent and sodium citrate (Na3C6H5O7) as the complexing agent under an excess of sodium hydroxide (NaOH) and sodium borohydride (NaBH4) in aqueous solution under nitrogen atmosphere. The influence of the NaBH4 concentration, NaOH concentration, and Na3C6H5O7 concentration on the phase of copper nanoparticles were studied. Characterization of these nanoparticles by XRD, TEM, HRTEM and UV-Vis confirmed the phase of nano copper. The results showed that 3～20 nm copper nanoparticles with well dispersibility in water were synthesized when the concentration of CuSO4 was 1mol/L, the concentration of NaBH4 was 1mol/L, the concentration of NaOH was 0.4 mol/L and the concentration of Na3C6H5O7 was 0.2 mol/L, at the temperature of 30℃ under nitrogen atmosphere.Secondly, the formation of Cu@Ag core-shell nanoparticles was driven by transmetalation reaction on the surface of copper nanoparticles, where the Ag+ ions were reduced by the copper atoms present on the particles’surface. First of all, the residual NaBH4 of the nano copper colloidal must be removed completely before preparing Cu@Ag core-shell nanoparticles. This was achieved by adding H2SO4. Then, the solution was adjusted to different pH value by adding different amounts of NaOH solution before adding silver nitrate. To obtain a homogeneous Ag coating on Cu nanoparticles, various Cu-Ag nanoparticles were synthesized with the change of pH value, temperature and Cu/Ag molar ratio. To obtain the Cu@Ag core-shell nanoparticles with well dispersibility in water, various Cu@Ag core-shell nanoparticles were synthesized with the change of temperature and the concentration of CTAB. Characterization of these nanoparticles by XRD, TEM, HRTEM, SEM, UV-Vis, EDS and DSC-TGA confirmed the core-shell structure and oxidation resistance. The results showed that Cu@Ag core-shell nanoparticles with well dispersibility in water were synthesized at pH 7 at 35℃ under nitrogen atmosphere when the concentration of CTAB was 0.1 mol/L. The diameter of these Cu@Ag core-shell nanoparticles which were stable up to about 265℃ in the air and were not oxidized for three month varies from 3 to 50 nm.Finally, nano Cu@Ag conductive ink were prepared using Cu@Ag nanoparticles as conductive filler, water-based acrylic resin (AC-3137) as the binder, ethylene glycol as the leveling agent, glycerol as the humectants and deionized water as the solvent while the dispersants were different, such as CT-5010, XH-9015z and BYK-348. The results showed that the BYK-348 was optimal for conductive ink. The influence of the content of conductive filler and sintering temperature on conductivity of the conductive ink was studied and the Cu@Ag conductive pattern were directly fabricated on ordinary photo paper using a roller pen filled with Cu@Ag nano ink. The resistivity of the written patterns was measured using a four-point probe (GDSKDY-1L). The results showed that the resistivity of the conductive Cu@Ag film obtained from the nano ink was low to 1S.67μΩ·cm when thermal sintered at 150℃ for 1 h under a nitrogen flow.