Preparation Of Ultra-Long Silver Nanowires And Its Application In Conductive Adhesives

As a substitute of tin lead solder,conductive adhesive plays an important role in the field of electronic packaging.However,compared with the traditional tin lead solder,the conductive adhesive possesses the relatively low conductive and mechanical properties.Silver nanowires can provide long-distance conductive path due to the one dimensional feature in a scale of micron level,and their diameters belong to nanometer scale,which has a range of advantages such as small size effect,lower melting point than bulk silver,and easier to form metallurgical connection in the curing process.Hence,silver nanowires are considered as conductive fillers for electronic packaging.In this thesis,silver nanowires were prepared by polyol method and solvothermal route respectively.There are many nanoparticles in the silver nanowires prepared by polyol method,while the morphology of silver nanowires prepared by solvothermal method is uniform and stable.The effects of reaction temperature,type of coating agent,proportion of coating agent and silver salt,type of nucleating agent and etching agent on the morphology of silver nanowires were studied in detail.High aspect ratio silver nanowires with diameter of 150 nm and length of more than 100μm were obtained by solvothermal reaction at 160℃for 2 h using PVP as the coating agent and ultra-low content NaCl as nucleating agent.The surface of silver nanowires was treated to improve its dispersion in resin matrix.The sintering phenomenon of silver nanowires was also investigated,and the relationship between the diameter and melting point of silver nanowires was deduced.The results show that the resistivity of conductive adhesive is 8.92×10^-5Ω·cm when the filling amount is 60%.However,the silver nanowires are easy to agglomerate and entangle,and the dispersibility needs to be improved.Therefore,silver nanowires and commercial flake silver powder were mixed to prepare composite conductive adhesive,and the effects of silver nanowires on flake silver powder were studied under the total filling amount of 60%,70%and 80%,respectively.The results show that the value of the conductivity filler can be reduced by adding the silver nanowires.When the total filling amount is adjusted to 70%with a ratio of silver nanowires of 15%,the conductive adhesive presents the optimal performance,and the volume resistivity is as low as 8.94×10^-5Ω·cm.In order to further improve the dispersion of conductive fillers,a kind of micro silver powder coated with aniline was prepared.The conductive adhesive composed of the silver powder and silver nanowires was used to study the effect of silver nanowires on the micro silver powder with the total filling amount of 60%,70%and 80%,respectively.As the filling amounts of micro silver powder are controlled to 70%and80%,the conductive adhesive delivers the excellent conductivity and dispersion.Furthermore,when the filling amount reaches 70%and the proportion of silver nanowires is 15%,the conductive adhesive with a volume resistivity of 4.33×10^-5Ω·cm is obtained.