Preparation And Modification Of Copper Nanoparticles And Highly-conductive Copper Films

Copper has excellent electrical conductivity and thermal conductivity. It can be widely used as the electrical connection structure of the electronic device. Nano copper is a new micro and nano joining material. Copper nanoparticles can be dispersed in a specific solvent to prepare a colloid of copper. Electrical connection structures can be made from copper colloid. There are two major problems. One is to improve the chemical stability and dispersion of colloidal copper. The other is fabricating highly conductive electrical connections at a lower temperature. The preparation and dispersion stability mechanism of colloidal copper were studied through experiments. Copper colloid with high dispersion stability and excellent chemical stability was obtained. In order to apply copper colloids to electrical connect, nano copper films are made from copper colloids. Content of organic and heat treatment process were studied to get copper films with high electrical conductivity. Under suitable conditions a copper film was gotten,whose electrical resistivity is close to the electrical resistivity of pure copper.Firstly, synthesis of copper nanoparticles was under liquid phase by SDS-PVP double-template method. The reaction was between hydrazine and copper sulfate. The concentration of SDS was fixed to 9m M, copper nanoparticles was prepared with a particle size of 60-100 nm.the copper nanoparticles were coated with a layer of organic. It makes copper nanoparticles dispersed in water, be free of oxidation after saving two months in the air. Also it is helpful for the copper nanoparticles to be dispersed stably in solution after the reaction, deionized water or isopropanol. The dispersion stability and stability mechanism of copper colloid were studied at different conditions(concentration of PVP, p H, dispersion medium).Stable copper colloid at least four months was gotten, when PVP concentration was 10g/L and the value of p H was10±0.5.Secondly, copper films were made from colloidal copper by suction filtration, suspension coating, spreading, etc. The heat treatment was conducted to improve the conductivity of copper films. SDS, PVP, copper nanoparticles coated with organic were heated in Ar and air. The results showed that the Cu films should be sintered at 250 oC, 500 oC in a tube furnace. The conductivities of the copper films were improved under Ar atmosphere, by changing the heating rate, sintering temperature, holding time. On the condition that heating rate was 5oC/min, sinter temperature was 500 oC and holding time was 3h,2.5x102μΩ·cm was received in the copper film.Finally, the resistivity of the copper film was reduced through controlling organic content in the copper film before sintering, further. After copper colloid was washed twice in isopropanol, Cu film sintered at 500 oC for 1h.The resistivity is less than 10μΩ·cm.During the preparation of colloidal copper, the copper concentration(30mmol/L) was increased to 3 times of original. And copper nanoparticles were washed once with dilute sulfuric acid. After sintered 30 min at 250 oC,copper film has a resistivity of 30μΩ·cm.