| In recent years,copper nanoparticles have become a hot topic in the field of conductive ink for excellent electrical conductivity,which is comparable to silver,and relatively low cost.However,due to their active chemical properties,copper nanoparticles tend to oxidize when exposed to air,resulting in the formation of copper oxide on the surface.For the application in conductive printing,the presence of copper oxide,which is considered non-electrical conductive,causes two major problems: one is the significant drop on electrical conductivity,the other is the increase in sintering temperature.Therefore,a facile way to enhance the oxidation resistance of copper nanoparticles is in need f or exploit.In this study,a two-step fabrication method was developed to synthesis Cu@Sn core-shell nanoparticle.The first step is the preparation of copper nanoparticles via polyol method with diethylene glycol as the solvent,CTAB as the surfactant and PVP as the dispersant.By varying the amount of surfactant CTAB and dispersant PVP,copper nanoparticles with 50 nm in diameter were successfully synthesis when the added amount of CTAB and PVP are 1.7 g,2 g,respectively.The second step is an electroles s plating process.A complexing agent is employed to lower the standard electrode potential of Cu2+/Cu,so that the displacement reaction between Cu and Sn2+ can carry on,resulting in a layer of Sn attached to the surface of copper nanoparticle,thus a co re-shell structure was formed.By studying the influence of complexing agent concentration,reaction temperature,drying method and reactant concentration on the displacement reaction,a set of optimum parameters was found.The core-shell structure of Cu@Sn nanoparticle was verified by TEM,HRTEM,SAED,STEM,element mapping characterization.The structure was found to be a three layer Cu-Cu6Sn5-Sn core-shell structure.And the thickness of the shell layer is 2-4 nm.TG analysis has verified that the oxidat ion temperature of Cu@Sn nanopariticle is 220 ?,which is 120 ? higher than copper nanoparticle,demonstrating that the outer layer of Sn does enhance the oxidation resistance of copper nanoparticle.By ultrasonicly mixing dry Cu@Sn nanoparticle powder with a mixed solvent?containing 50% of ethanol,40% of ethylene glycol and 10% of glycerol?,a conductive ink with 20 wt% conductive filler was prepared.Pen-on-Paper technique and stencil printing technique were employed to fabricate conductive patterns.Cu@Sn nanoparticle conductive patterns were sinter ed at various temperature and time.The lowest resistivity 1.48×10-6 ?·m was reached when the pattern was sintered at 260 ? for 60 min.A small bulb experiment was carried out to verify the conductive nature of Cu@Sn nanoparticle patterns.The application in high temperature solder was preliminarily studied by connecting copper plates with a Cu@Sn nanoparticles preform.When the sandwich structure was reflowed at 250 ? for 30 min,a joint with shear strenghth of 11.24 MPa was formed. |
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