Research On The SiC Compound Nano-silver Paste And Its Low-temperature Sintering Mechanism

At present,sintered silver is the only low-temperature interconnect and high-temperature service thermal interface material successfully applied in the industrial field.However,due to the short industrial application time,there are still some shortcomings that limit the rapid development of sintered silver.First,the existing sintering process takes a long time.In addition,the sintering process of nano-silver is accompanied by densification shrinkage of the structure,and the interconnected joints with insufficient structure evolution will further shrink during long-term service in a high temperature state,causing the interconnect joint to fail.In response to the above problems,this paper mainly studies the following:In this paper,silver particles with an average particle size of 55 nm were prepared by reducing silver nitrate with sodium citrate.The surface of the silver nanoparticles was uniformly coated with a 0.7 nm thick coating by observation of high-resolution transmission electron microscopy.The nanoparticles were added into different solvents to prepare alcohol-based paste.By comparing the microtopography of sintered structure of different solvent pastes,ethylene glycol was selected as the organic solvent of paste in the paper.Raman and differential thermal analysis of the above alcohol-based paste showed that the alcohol-based paste prepared in the paper has excellent sintering performance.In order to prevent the further evolution of sintered silver microstructure during service,silicon carbide(Si C)nanoparticles were composited in the prepared alcohol-based silver nanoparticle paste.The sintering process of Si C nanoparticle composite paste was studied by scanning electron microscopy,transmission electron microscopy and energy dispersive spectro scopy.It was found that the composite of Si C nanoparticles hindered the densification and shrinkage evolution of sintered microstructure,and refined the sintered structure.The porosity of the refined sintered structure increased from 14.1 % to 28.5 %;the grain size decreased from 375.9 nm to 140.8 nm;the thermal conductivity decreased from 306 W/m·K to 184 W/m·K,but it was still more than three times the thermal conductivity of conventional thermal interface materials.In order to shorten the sintering time of nano-silver,the paper optimized the prepared nano-silver by partially replacing the sodium citrate with sodium sulphate to reduce the silver nitrate.At the same time,the coating layer was washed several times to reduce the solvent content of the paste,and the temperature at which the solvent was completely volatilized and the coating layer was rapidly decomposed during the sintering process of the paste was lowered.On this basis,a new rapid hot-pressing sintering process was proposed.The microstructure evolution process of rapid-hot pressing before and after Si C nanoparticle composites was analyzed by transmission electron microscopy and transmission kikuchi diffraction(TKD).When the composite content of Si C nanoparticles was 5%,the porosity of the sintered microstructure increased from 15.2 % to 17.1 %,the grain size decreased from 67.5 nm to 60.6 nm,and the resistivity increased from 3.9 ??·cm to 4.6 ??·cm.The interconnected joints were prepared by rapid hot-pressing sintering.By studying the effects of sintering temperature,auxiliary pressure and sintering time on the shear strength of interconnected joints,the optimal parameter for the preparation of interconnected joints was obtained,that is,the auxiliary pressure was 8MPa,the sintering temperature was 275 °C and the sintering time was 50 s.The interconnected joint prepared based on this process had a shear strength of up to 68.8 MPa.Due to the short hot-press sintering time,the joint structure evolution was not sufficient,and more severe shrinkage occurred during the service process,and the failure of the interconnected joint occurred.The composite of Si C nanoparticles improved the high temperature service stability and long-term service reliability of interconnected joints by refining the sintered structure and hindering the densification and shrinkage evolution of the sintered structure during service.For the sintered joint with a composite content of 5%,the decreased proportion of the 250 °C high temperature shear strength reduced from 45.6 % to 16.3 %;for the sintered joint with a composite content of 2%,the shear strength increased from 46.6 MPa to 81.4 MPa after thermal shock for 200 cycles,with an increase of 75 %.