Study On Microstructure And Mechanical Properties Of AuSn20 Film Soldering Joints

With the continuous innovation of electronic manufacturing technology and the further requirements of solder joint reliability,the manufacturing technology,soldering performance,microstructure evolution and mechanical properties are still one of the central issues of electronic packaging at this stage.As the package density increases and the solder joint size continues to decrease,the use of AuSn20 solder films is becoming increasingly important.AuSn20 solder film,as one of the important forms of AuSn20 solder,has rarely been studied for its microstructure distribution and shear mechanical properties in practical applications.This paper prepared AuSn20 solder films with different thicknesses(3μm,6μm,9μm,12μm)by jet vapor deposition technology,and the microstructure of the solder joints with Au / Ni was studied.Then the lap joints of AuSn20 solder film and Au/Ni were studied,the effects of different AuSn20 solder film thicknesses and different strain rates on the shear strength of the joints were analyzed.This paper first briefly introduced the basic properties,application morphology,and forming methods of AuSn20 solder,and elaborates the research status of interface reactions between AuSn20 solder and different metal layers.Secondly,AuSn20 solder films with different thicknesses were prepared by jet vapor deposition technology,and preliminary tests were performed on the deposited AuSn20 solder films.Then the microstructure analysis of the sandwich structure of AuSn20 solder film and Au/Ni joint was performed,and the element diffusion trend in the solder layer was explained.Finally,the shear strength test was performed on the lap joint of AuSn20 solder film and Au/Ni,and the fracture was observed.The analysis results showed that as the strain rate increases,the shear strength of AuSn20 solder joint also increases.Its fracture mode gradually changes from a ductile fracture that occurs in the Au layer to a brittle fracture mode which is a mixture of transgranular fracture and intergranular fracture that occurs between the Au-Ni-Sn intermetallic compound layer and the Au layer.Within the thickness range of AuSn20 solder layer of 3μm ～ 12μm,AuSn20 welded joints show a dimensional effect of shear strength increasing with the thickness of the welded layer.The thickness of the solder film has no obvious mechanical restraint strengthening effect on the shear strength of the welded joint.The main factor which affects the shear strength of joints is the morphology of the microstructure inside the welding layer.Excessive voids and pores will also degrade the mechanical properties of the joint.