Design Of The Nano-silver Conductive Network And Its Effect On The Performance Of Conductive Composite

Polymer based conductive composites have been considered as the important connect materials because of the advantages of light weight, low processing temperature, fine pitch interconnect and easily processed into variety of shapes. However, there are some issues such as low conductivity and poor electrical stability that need to be solved. In order to solve these problems, we prepared a variety of conductive composites by designing the structure of silver nanoparticles and improving the preparation process. The four kind of conductive networks, which contain the nano-silver sintered type, the flexible silver nanochain linked type, the nano-silver selective distribution type, the uniform arranged type, were built. In addition, effects of the morphology of silver nanoparticles and conductive network on conductivity and electrical stability were also investigated.Ag+-TEOA complex was synthesized by silver nitrate and triethanolamine. FTIR and DSC curves shown that the thermal decomposition of Ag+-TEOA complex occurred at 150 oC. UV-vis and XRD results shown the decomposition product was nanosized silver, and TEM image shown that the silver nanoparticles, the average sizes of which were in the range of 5-24 nm, uniformly dispersed in epoxy matrix. DSC curves indicated that the product TEOA compound can accelerate the curing process of epoxy resin. The conductive adhesive was prepared by mixing Ag+-TEOA complex with the Ag-coated Cu flakes filled epoxy resin. The bulk resistivity of the cured conductive adhesive was as low as 6.27 10-4 Ω cm, the resistance of the cured conductive adhesive was only 6.7% increase after hydrothermal aging. SEM images indicated that the sintering of the silver nanoparticles anchored on the surface of Ag-coated Cu ?akes could effectively improve the oxidation resistance of Ag-coated Cu flakes. In addition, the Ag NPs nanoparticles also sintered between the fillers and formed nano-silver sintered type conductive network, which improved the conductivity and the aging properties of conductive adhesive.In order to impart flexibility for conductive composite, water-based polyurethane was used as matrix. Ag2O-TEOA complex was synthesized by silver oxide and triethanolamine. The WPU had been modified by silane and complex in succession. It was found that the aging property of conductive composites have been improved. The result of microstructure analysis shown that, during the process of modification, the hydrophobic silane segments that modified the polyurethane chains and simultaneously increased the crosslinking density, leading to the improvement of the water resistance of polyurethane. On the other hand, the sintering of the silver nanoparticles anchored on the surface of Ag-coated Cu ?akes also effectively improve the oxidation resistance of fillers. These effects synergistic improved the aging property of conductive composites.For further improve the flexibility of conductive composite, flexible silver nanochains were obtained by reducing the silver ions adsorbed on the DNA molecule chains. UV-vis and Raman spectroscopy revealed that the immobilization of Ag nanoparticles on DNA was attributed to the synergism of the two binding modes, e.g. electrostatic interaction and complexing action. Effect of the concentration of Ag+ and p H value on the morphology of silver nanochains were investigated. TEM images shown that the Ag nanoparticles regularly organized into bands along the DNA chains and formed silver nanochains. The curl silver nanochains overlaped between the microsized fillers and formed silver nanochains linked conductive network, which led to the improvement of the conductivity of conductive composites. The resistivity and the resistance change(during bending) of silver nanochains filled composites both have significantly decreased. When suffered deformation, the silver nanochains linked conductive network extended and the conductive paths still maintained, which improved the resistance stability of conductive composites. The bulk resistivity of conductive composite reduced from 6.93 10-4 Ω cm to 2.13 10-4 Ω cm, and the resistance change(R/R0) was only 3.65 when rolling at 4mm, while that of controlled sample reached to 8.89.Two kinds of silver nanochains filled composites had been prepared by direct blending method and foam template method, respectively, and the structure of conductive networks had also been investigated. It was found that the conductive network formed by blending method exhibited a random entangled status, whereas the conductive network formed by foam template method selective distributed in the narrow edges of the grid. Since the optimized conductive network, the amount of fillers could be reduced while maintaining the conductivity of conductive composites. When the filler content was 60 wt%, the sheet resistance of the conductive composite prepared by foam template method was 56 Ω/sq, less than that of the 65 wt% silver nanochains filled conductive composite prepared by blending method(98 Ω/sq).In order to reduce the amount of conductive fillers, while improving the electrical properties of conductive composite, we utilized layer-by-layer self-assembly method to make nanosilver based conductive multilayer film through the alternate deposition of the silver particles with positive charge and the cationic polyurethane. UV-vis and TEM indicated that the self-assembly of silver nanoparticles was an uniformly deposition process. The silver nanoparticles interluded in the gap of adjacent silver layer and formed uniform arranged type conductive network. The conductivity of conductive multilayer film was investigated. It was found that when the filler content was 48.3 wt%, the resistivity of conductive multilayer film was 3.23 Ω cm, less than that of the conductive composite filled with 60 wt% nano-silver(4.8Ω cm). It indicated that when maintaining the same conductivity, this kind of conductive network could significantly reduced the filler content. When the conductive multilayer subjected to bending deformation, the conductivity did not show significant changes. It was attributed to the fact that the silver nanoparticles oriented along the deformation direction and gathered into a bundle, a new conductive network was built to maintain the conductivity during deformation. The morphology of the conductive network of the laminated conductive films after thermo-compression was investigated. It was found that the conductive network sintered and formed more dense conpact, which improved the conductivity of conductive film.