Study On The Preparation And Properties Of Electrically Conductive Adhesive Based On Silver-coated Core-shell Composite Particles And Epoxy Resin

High-performance electrically conductive adhesives (ECA) have attracted wide attention for their advantages such as environmental-friendship, simple operation, and better line resolution, however, most of the present available ECA can't meet requirements of sophisticated electronic manufacture industry because of the high volume resistivity (ρv), high density and high costs. In order to overcome these above problems, monodispersed silver-coated silica core-shell composite particles (Ag/SiO2) with controllable shell thickness (TAg) and diameters (D) were used as conductive fillers. The influences of TAg and D of the conductive filler particles on theρv of their based ECA were investigated. Based on the point of the interface of polymer matrix and conductive fillers, we proposed the ethylenediamine to modify the surface of the conductive filler. The as-fabricated ECAs show a relative high conductivity and low conductive percolation threshold, which is reasonably explained by the conductive percolation theory and equivalent circuit diagram. Their main results show as follows.Using monodispersed silica particles with D ranging from 400 to 1500 nm as templates, which were synthesized by changing reaction temperature of the sol-gel reaction of tetraethyl silicate in the presence of ammonia as a catalyst, monodispersed Ag/SiO2 with controllable TAg were prepared by adjusting the concentration of the silver precursor. The ECAs were fabricated by using Ag/SiO2 as conductive fillers. The influences of TAg and D of conductive fillers onρv and costs of the ECA were investigated. When the templates with a constant diameter were used, theρv of the ECA decreased with increasing TAg. When the TAg was increased, theρv of the ECA firstly swiftly decreased, then reached a certain value. On the other hand, at TAg=50 nm, theρv of the ECA increased with increasing the diameter of silica templates. In order to decrease the cost of ECAs, Ag/SiO2 core-shell composite microspheres with relatively thicker silver layer is more effective than Ag/SiO2 core-shell composite sub-microspheres with relatively thinner sliver layers. Using silver coated glass microsphere composite particles (Ag/GM) synthesized by liquid chemical reduction method as raw materials, and boiling water and ethylenediamine as surface modification agents, Ag/GM was modified. It has been discovered that boiling water can partly remove the low molecular weight polyvinylpyrrolidone on the surface of Ag/GM originally and ethylenediamine can also partly replace the polyvinylpyrrolidone on the surface of Ag/GM originally. We used these Ag/GMs as conductive fillers to fabricate EC As. Compared with the Ag/GM synthesized by chemical reduction method and modified with boiling water, the Ag/GM modified with ethylenediamine are dispersed in the epoxy adhesive more effectively and the interface energy between them and epoxy resin matrix is reduced because of the formation of the chemical bonding between the epoxy resin and the ethylenediamine adsorbed on the surface of Ag/GM. The as-fabricated ECAs show a relative high conductivity and low conductive percolation threshold, which is reasonably explained by the conductive percolation theory and equivalent circuit diagram.