Study On Nano Silver Die Attach Materials Prepared By Spark Ablation And Its Bonding Performancer

With the development of the third generation semiconductor devices towards miniaturization,high density and high power,higher requirements are put forward for the performance of packaging die attach material.Due to the problems of poor thermal stability,low bonding strength and poor thermal conductivity,the traditional die attach material can not meet the needs of"low-temperature sintering and high-temperature service"of the third generation semiconductor devices.Due to small size effect,metal nano materials can realize low-temperature sintering,and the sintered body shows the excellent physical properties of bulk metal.It has important application prospects and research value in the field of packaging and die attach.At present,silver nanoparticles are mainly prepared by chemical method,but this method is difficult to prepare silver particles with high purity and ultra-fine size.In recent years,spark ablation method has been focused on because of its green environmental protection and rapid preparation.This method can simply and continuously prepare metal nanoparticles with ultra-fine size and high surface purity with a single bulk metal target,but few people have studied the bonding performance of silver nanoparticles prepared by this method.In this thesis,high purity spherical silver particles with average particle sizes of 5±3 nm and 20±15 nm were prepared by diffusion and stamping deposition.The effects of spark energy and gas flow on particle size,morphology and thickness of deposition layer were systematically studied,and the optimal preparation parameters were determined.The effect of gas flow on the size distribution of silver nanoparticles is deduced experimentally and theoretically,and a quantitative model of the evolution of silver nanoparticles is proposed.The model provides a new experimental and theoretical basis for understanding the growth kinetics of ultrafine silver nanoparticles prepared by spark ablation.In this thesis,the nano silver deposition layer prepared under the best parameters is used in the sintering experiment,and its bonding performance are studied.The results show that the shear strength of silver joint is 22.1 MPa after sintering at 260?and 2 MPa.After pressureless annealing at 300?,the resistivity of the deposited layer is 1.73×10^-7?·m,about 11 times that of bulk silver.On this basis,a new method of solvent assisted sintering was proposed,and the mechanism of solvent assisted sintering of silver nanoparticles was revealed.When the sintering conditions are 180?and 2 MPa,there is no bond between the untreated nano silver joint and the substrate,while the shear strength of the silver joint treated with ethylene glycol can reach 37.08 MPa.Cross section EDS line scanning shows that a thickness of 0.8?m is formed between the die attach layer and the substrate,which indicates that the sintered silver joint with high bonding strength has been successfully prepared.This study confirmed the feasibility of nano silver prepared by spark ablation in the field of packaging and die attach.The proposed nano particle size evolution model and solvent assisted sintering theory have important guiding significance for understanding the particle size evolution and improving the sintering performance.