Study On Preparation Of Silver Nanoparticles And Performance Of Low-temperature Sintering

Electronic products have become an indispensable part of life.With the development of microelectronic devices with the characteristics of miniaturization,high density and high power,higher standards have been required for integration processes and packaging materials.Silver nanoparticle has received extensive attention as conductive medium for flexible printed circuits and a type of interface material for the connection of high-power devices.However,the difficulties in controlling the morphology and structure,low purity of the particles,and high synthesis cost are still the main problems that inhibit the application of silver nanomaterials.Therefore,to meet the demands for microelectronic materials technology development,it is urgent to develop silver nanoparticles with controllable morphology and structure,ease to sinter and low-cost silver nanoparticles.In this paper,polyvinylpyrrolidone(PVP)is used as a protective agent,and polyhydric alcohol is used as a solvent and a reducing agent to develop silver nanoparticles of two different sizes.We optimized the reaction conditions by studying the effect of reaction conditions on the silver nanoparticles morphology and size and yielded silver nanoparticles with controlled morphology and structure,high purity and low-cost.The sintering performance of silver nanoparticles was discussed in the study.(1)Using polyethylene glycol as the reducing agent and solvent,the influences of PEG molecular weight,PVP dosage,temperature and time were studied on the silver nanoparticles morphology and size.When PEG400 was used,with small particle size and narrow particle size distribution was obtained.The particle size of products gradually decreased with the increase of the amount of PVP.The particle size decreased first and then increased with increasing temperature.When m(AgNO3):m(PVP)is 1 g/g,the temperature is 120 ? and reaction time is 120 min,products with high sphericity and small particle size were obtained,with an average particle size as low as 30 nm.(2)The mixed solution of PEG and ethylene glycol was used as reducing agent and solvent.The effects of PVP molecular weight and dosage,the mass ratio of PEG to EG,reaction temperature and time has been investigated on the silver nanoparticles morphology and size.Adjusting the molecular weight and the amount of PVP directly affects the passivation of the Ag crystal plane,which in turn affects the morphology and size of the products.As the temperature increases,the particle size of silver nanoparticles first increases and then decreases.When the mass ratio of PEG to EG is 1:1,the particle size distribution is the narrowest.Under the conditions of m(AgNO3):m(PVP)=1g/g and reaction temperature of 120? and continuous reaction time of 120 min,silver nanoparticles with an average particle size of 80 nm can be synthesized.(3)Using silver nanoparticles as filler,conductive ink and sintered silver solder has been prepared separately.The silver ink-30 and silver ink-80 were prepared according to the different silver nanoparticles size,and printed on the polyimide(PI)film by screen printing technology.It was found that as the sintering temperature increased,the grain size of silver nanoparticles gradually increased and the degree of densification gradually increased via XRD.When the sintering temperature is 320? and the sintering time is 30 min,the resistivity of the printed circuit is as low as 9.6 ??·cm and 7.5 ??·cm,respectively.Silver solder-30 and silver solder-80 were prepared according to the different silver nanoparticles size.The effects of solder formula,hot pressing temperature and pressure on the shear properties of the solder sintered joint were studied.The shear strength of the solder sintered joint increases significantly with the increase of sintering temperature and pressure.At the same time,it was found that the sintering difficulty of the solder was inversely related to the content of residual organic matter on the surface of silver nanoparticles.Finally,the reliability experiment using two silver solders as bonding DBC substrates was studied.Under sintering temperature at 250?,pressure at 10 MPa and bonding time for 30 min,silver solder-30 and silver solder-80 sintered joint have the average shear strength as high as 46.9 MPa and 43.8 MPa,respectively.