Preparation Of Nano Silver/graphene Composites And Their Application In Electrical Conductive Adhesives

Electrical conductive adhesives (ECAs) are widely used as packaging material forLight Emitting Diode (LED) due to their excellent electrical and thermal conductivity.With the development of LED to higher brightness and higher power, the properties ofECAs are needed for higher requirement. It is very necessary to prepare novel ECAs withhigh electrical and thermal conductivity to adapt to the development of LED. Due to theexcellent properties of nano silver and graphene, the preparation of nano silver/graphenecomposites and their effect on ECAs were investigated in this study.Graphite oxide was prepared with graphite powders by the modified Hummers’method. Then the nano silver/graphene composites were prepared by in-situ reductionusing AgNO3as silver precursor and NaBH4as reducing agent. The characterizationresults of the composites showed that, the silver nanoparticles (about30nm) have auniform distribution on the surface of thin graphene, and the morphology of graphene iscurled. The Raman signal intensity of the composites was10times than that of graphene.The reaction time, reaction temperature and the concentration of AgNO3werechanged to study the influence on the preparation of the composites. The results showedthat the reaction time has no influence on the size of nano silver in the composites; theadsorption peak of nano silver on the UV spectrum did not shifted. However, the reactiontemperature has influence on the size of nano silver in the composites. The size of thenano silver decreased with the increase of the reaction temperature, and the particle sizewere calculated by the XRD data, the size of nano silver with the reaction temperature of40°C,70°C and100°C was40.5nm、36.1nm and32.7nm respectively. Theconcentration of the AgNO3also has influence on the size of nano silvers in thecomposites. The particle size of nano silvers decreased firstly then increased with theincrease of AgNO3concentration. The size of nano silvers with the concentration ofAgNO3of3×10-3mol/L,4.5×10-3mol/L and6×10-3mol/L was36.1nm,31.1nm and33.4nm respectively. Then the prepared nano silver/graphene composites were introduced into silver flakesfilled ECAs. The effects of different weight ratios of composites to silver flakes on theproperties of ECAs were investigated. The results showed that the resistivity of the ECAsdecreased firstly and then increased with the increase of weight ratios of composites tosilver flakes. When the weight ratio of composites to silver flakes was20:80(%), theresistivity of the ECAs reached the lowest value of2.37×10-4Ω·cm. The lap shearstrength of the ECA decreased as the weight ratios of composites to silver flakes increased.However, the viscosity of the ECAs increased with increase of the weight ratios ofcomposites to silver flakes. The addition of composites causes a slight decrease in thermalstability of the ECA, but it still can be used at a relatively high temperature. As the contentof the conductive fillers was same, the thermal conductivity of the ECA with compositeswas about2times that of the ECA with pure silver flakes. Without composites, the thermalconductivity of the ECA increased as the content of silver flakes increased.