Study On Coarsening Kinetics And Nanomechanic Behavior Of Au-Sn Eutectic Alloys

Au-Sn eutectic alloy is an irreplaceable lead-free solder used in 250-350?range in microelectronic packaging field.However,at present,there are still great technical difficulties in the microstructure control and fabrication of Au-Sn eutectic alloys,which is mainly attributed to the unclear evolution and deformation mechanism of the AuSn and Au₅Sn phases of complex hexagonal structures in eutectic structures.Therefore,in this study,SEM,EBSD,XRD and other characterization methods were used to quantitatively reveal the coarsening kinetic behavior of the alloy by analyzing the growth law of the layer structure and equiaxial structure of the Au-Sn eutectic alloy during the heat treatment.The selective nanomechanical experiments were carried out on the eutectic structure,AuSn phase and Au₅Sn phase of lamellar at different strain rates,in order to reveal the deformation mechanism of the two phases under the lamellar and equiaxial morphology.This study will provide an effective theoretical basis for the preparation and development of Au-Sn alloy solder.The specific results are as follows:(1)Annealing the Au-Sn eutectic alloy in the range of 160-220?,the microstructure of Au-Sn eutectic alloy laminates becomes coarser and the lamellar spacing increases gradually.The kinetic behavior of the coarsening of the lamellar structure of Au-Sn eutectic alloy can be expressed as?²=₀²+kt,and the coarsening activation energy was about 119.28±18.51 kJ/mol.The coarsening mechanism of laminar structure is mainly in the form of laminar splitting and terminal migration,which is close to interfacial diffusion control.(2)Under the annealing temperature range of 160-220?,The phase of AuSn and Au₅Sn will undergo continuous coarsening and growing in the heat treatment after equiaxial,and no phase transition will occur in the two phases.The coarsening kinetic behavior of equiaxial two-phase can be expressed as³=₀³+kt.In the growth process of equiaxial AuSn and Au₅Sn phases,grain boundary diffusion plays a certain role in tissue coarsening,but coarsening is mainly dependent on volume diffusion control mechanism.(3)Two alloys of the Au-15Sn and Au-30Sn were prepared,and Au₅Sn and AuSn grains with phase size satisfying nanomechanical characterization were obtained.The results showed that the Au₅Sn phase was more rigid and brittle than AuSn phase,and the microhardness of Au₅Sn and AuSn were 139.8 HV and 89.7 HV,respectively.(4)The nanomechanical experiments show that the nano-hardness of Au₅Sn phase decreases with the increase of strain rate.The strain rate sensitivity index m=-0.0472,the leading deformation mechanism may be twin.The nano-hardness of AuSn phase first decreases and then increases with the increase of strain rate.At the strain rate of 0.01s^-1-0.1 s^-1,the strain rate sensitivity index of the AuSn phase m=-0.0361,and the dominant deformation mechanism of the AuSn phase may be twinning.When the strain rate is 0.1s^-1-0.2 s^-1,the strain rate sensitivity index of the AuSn phase m=0.0742,and the deformation of the AuSn phase may be dominated by the slip mechanism.(5)The results of nanomechanical experiments were performed on the Au-Sn eutectic lamellar structure with phase interface showed that the nano-hardness of the lamellar structure gradually decreased with the increase of strain rate.and the strain rate sensitivity index of lamellar structure m=-0.0201,indicating that the plastic deformation of lamellar structure may be dominated by twins.