| Metal nanoparticles(NPs)are the key raw materials for conductive nano-inks of printing electronics and interconnected nano-pastes in microelectronic packaging.Their characteristics with excellent electrical/thermal conductivity and high-temperature operation have been attracted widespread attention.Among them,the easy migration of nano-Ag and oxidation of nano-Cu were seriously restricted in the industrial development.However,Cu@Ag NPs also take into account the high electrical/thermal conductivity of Cu and Ag,and overcome the ease of Ag migration and Cu oxidation,making it one of the most potential new materials for printing electronics and packaging.Currently,the research on Cu@Ag NPs mainly focused on catalysis,battery,biomedicine,and other fields.The behavior of room/low temperature(<200°C)sintering,the evolution law of core-shell interface,the behavior of electrochemical migration(ECM),and the principium of shear deformation were still indistinct.Hence,it is of great importance to clarify the above problems to break through the development of interconnected materials in the field of electronic manufacturing and packaging.In this thesis,Cu@Ag NPs synthesized by sonochemical method were investigated as the fundamental material.A highly compatible Cu@Ag nano-ink/paste was obtained.The room/low temperature sintering behavior of Cu@Ag NPs under different energy fields of ultrasound,photon,heat,and pressure was investigated systematically,respectively.The behavior of ECM and the shear deformation were discussed in detail.The reaction behavior of Cu NPs prepared by weak reduction and sonochemistry was compared and analyzed.With the effect of acoustic cavitation and acoustic flow,Cu nucleation sites were greatly increased,and the soft template growth function of polyvinylpyrrolidone(PVP)was eliminated,and the structure of the cladding layer also transformed PVP molecular chains into the electrostatic adsorption of dehydroascorbic acid.And the theoretical sintering temperature of Cu NPs can be effectively reduced to 200°C.Eventually,these effects provided a novel idea for the preparation of Cu@Ag NPs with excellent dispersion,tiny size particle,and core-shell structure.Therefore,Cu@Ag NPs with an average size of 52 nm were obtained.It also exhibited high temperature antioxidation at 139°C and room temperature storage for up to 60 days.The sintering behavior of Cu@Ag NPs by pulse photon was expounded.During the process of heating,the“dewetting”behavior of Ag shell was found to form Ag nanobumps(Ag NBs).They could efficiently drive to sintering with the large radius of curvature,resulting in the conductive films with considerable conductivity(61μΩ·cm)and low porosity(19.9%)at 150°C.Compared with thermal sintering,the films prepared by high-energy photonic sintering have a resistivity as low as 2.16μΩ·cm,a porosity as low as 0.5%,and a surface roughness as 15.4 nm.It was mainly attributed to the optical thermal coupling of high-energy photon and metal particles,which made the surface metallic layer rapidly heating and cooling to produce an ultracold environment,thereby forming a supersaturated Cu-Ag solid solution,and then the conductivity was significantly improved.Additionally,the influence of nano-Cu on the ECM migration behavior of sintered Cu@Ag electrodes was analyzed,and the anti-ECM behaviors of Cu@Ag electrode after photonic and heat sintering were contrasted.At the low-electric intensity(E),the sintered Cu@Ag electrode could not be failed within 2000 s.With the increase of E,the total failure time(t _A)was shortened to 36 s,which was increased by 4.6 times compared to the sintered nano-Ag.During the photon sintering,when the photon energy(P_e)increased from 0 to 8.04 J/m~2,and t_a increased from 91 s to 411 s,which increased by 3.2 and 18.7 times compared to thermal sintered Cu@Ag and Ag,respectively.Because the process of photonic sintering generated a large amount of supersaturated Cu/Ag solid solution and nano twin,they created a significant hindrance to Ag migration.The effects of power ultrasonic sintering on the microstructure and shear strength of Cu@Ag NPs were comparatively studied.When the pressure temperature>250℃,the holding time>15 min,and the pressure>10 MPa,the shear strength could be 152 MPa,the porosity was 2.3%,the average grain size was 157.8 nm,and the content of Cu desolubilization phase reached 13.9%.The behaviors of dewetting of Ag shell,softening and decomposition of cladding layer,solid solution between Cu and Ag,and precipitation of second-phase Cu particles were proposed.However,when the sintering temperature>150℃,2 s<ultrasonic time<6 s,and ultrasonic power>150 W,the shear strength was also as high as 153 MPa,the porosity was as low as 0.5%,and the solid solubility of Ag/Cu-rich phase increases to 12.82%/3.45%,the average grain size shrunk to 83.6 nm,the content of Cu desolubilization phase decreased to 8.2%,and a large amount of Ag-Cu interstitial solid solution was found.Furthermore,the deformation and erosion at the interface also occurred.Therefore,under the combined action of such high solubility between Cu and Ag,controllable precipitation of Cu desolubilization particles,grain refinement,and local micro-deformation and erosion of interface,the ultrasonic sintered structure could achieve the ultrahigh strength at a lower temperature(150℃)and higher efficiency(6 s).Eventually,the low-temperature sintering behavior of Cu@Ag NPs under different energy fields was compared and summarized.And the supersaturated Cu-Ag nanoalloy structure with excellent oxidation resistance,ECM resistance,shear deformation resistance,and electrical conductivity was obtained under the action of ultrasound or photon. |
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