Research On Thermal Reliability Of All-copper Interconnection Structure Based On Sintering Nano-copper Paste

Power electronic devices provide functions such as electrical energy conversion and circuit control in the electronics industry,and have played an increasingly critical role in recent years.With the continuous development of power devices in the direction of high-frequency rapid response,high integration,and high power conversion efficiency,the operating junction temperature of chips in high-power devices has gradually increased,and traditional packaging materials and processes have been difficult to meet performance requirements of high density packaging interconnection of high power chip.Copper nanoparticles have become a new generation of chip interconnection materials with considerable application prospects due to their excellent electrical and thermal properties,good electromigration resistance,and low economic cost.By sintering copper nanoparticles at low temperature,which can achieve the goal of high-temperature service of the interconnection structure.Low-temperature Cu-Cu interconnection technology based on sintered copper nanoparticles has become a research hotspot for scholars and related companies at home and abroad in the past decade.However,the chips in high-power devices may encounter high temperature,thermal shock,or even extreme temperature cycling conditions.The thermal stability of the corresponding interconnection structure has a crucial impact on the overall packaging performance and service reliability of the power device.Therefore,studying the thermal reliability of the all-copper interconnection structure based on low-temperature sintered nano-copper paste can provide theoretical support and scientific basis for the future practical application of high-density all-copper interconnection packaging technology of high-power chip.In this paper,through the optimization of process parameters,self-preparation of copper nanoparticles is carried out,and the microstructure characterization and sintering properties of the optimized copper nanoparticles were studied.the low-pressure and low pressure rapid sintering process is used to prepare all-copper interconnection structure,and its thermal reliability was evaluated.Thermal reliability evaluation is mainly divided into high temperature aging experiment and thermal shock experiment,and then the interconnection structure samples are tested for shear strength,and the influence of different thermal conditions on the interconnection performance of all-copper interconnect structure is studied by combining microstructure characterization and theoretical analysis.The main conclusions of this article are the following:(1)By adjusting the chemical reagents and synthetic process parameters used in the polyol method,copper nanoparticles with nearly spherical morphology were prepared,with a particle size range of 10-35 nm and an average particle size of 21.44 nm.A certain organic layer on the surface of copper nanoparticles plays a role in dispersing and preventing excessive oxidation of the particles.The self-prepared copper nanoparticles have a good sinterability.Under the air environment of sintering temperature of 280?,sintering pressure of 6 MPa and sintering duration of 10 min,the rapid sintering of all copper interconnection structure has achieved a high bonding strength with an average shear strength of 25.99 MPa;the organic solvent in the solder paste can significantly reduce the initial sintering temperature,and appropriately increasing the sintering temperature is beneficial to strengthen the as-sintered structure,thereby enhancing the bonding strength of the interconnection structure.(2)The thermal aging atmosphere has a significant effect on the bonding strength of the all-copper interconnection structure.After long-term air aging,due to severe oxidation,the sintered structure became loose,resulting in attenuation of the bonding strength.The average shear strength of the interconnection structure sintered at 220?was reduced to a minimum of 5.12 MPa.After long-term vacuum aging,a large-area micro-interconnection structure was formed,and the as-sintered structure was densified,resulting in an increase of the bonding strength.The average shear strength of the interconnection structure sintered at 280? rose to 20.03 MPa.In a low-oxygen environment,the organic layer on the surface of the particles evaporated slowly,which can play a continuous role in anti-oxidation within a certain period of time.The Cu atoms between the particles can be fully inter-diffused under the condition of constant temperature and low oxygen,which promotes the densification of the as-sintered structure,thereby strengthening the interconnectivity of the all-copper interconnection structure.(3)Thermal shock conditions have a certain effect on the thermal stability of all-copper interconnection structures.The bonding strength of the all-copper interconnection structure decreased first and then increased slightly with the number of thermal shock cycles.After 1000 cycles,the interconnection structures prepared by air sintering and vacuum sintering still maintained good bonding strength,and the average shear strength are respectively 23.24 MPa and 25.01 MPa.The micropores in the sintered layer will affect the conductivity of the all-copper interconnection structure to a certain extent,while the degree of oxidation and porosity of the sintered structure will affect the interconnection performance of the all-copper interconnection structure.After the thermal shock cycle of the interconnection structure,the as-sintered structure will show a loose to dense change process,and eventually a mixed micro-interconnection structure of copper and copper oxides will be formed.