Microstructure And Properties Of Laser Sealing Interface Of High Silicon Aluminum Alloy Electronic Packaging Materials

As a new type of electronic packaging material that has been rapidly developed in recent years,high silicon aluminum alloy has high specific strength,low thermal expansion coefficient,high thermal conductivity and excellent mechanical processing performance,and is widely used in the field of electronic packaging.At the same time,laser welding has the advantages of fast welding speed,large depth-to-width ratio of the molten pool,and small deformation after welding,and has become the main connecting means of the high-silicon aluminum alloy electronic packaging box.However,there are weld defects such as pores and hot cracks,and there will be residual stresses in the weld,when the package is in a vacuum environment,these factors will affect the airtightness of the case and the strength of the weld.Laser welding experiment was carried out on the lid Al-27 wt.%Si and the shell Al-50 wt.%Si high silicon aluminum alloy by pulse laser welding machine,and different defocus amount,welding current and welding frequency process parameters were set,and each welding was analyzed.It is found that the defocusing amount-1mm and the welding frequency of 25 Hz are superior welding parameters,and the welding current should continue to increase.Although good surface forming and large penetration,melting width and aspect ratio can be obtained under the welding process parameters,the weld strength of the sample after welding is low and easy to break,and the weld seam is fractured using a scanning electron microscope.Observations revealed that the fracture of the material is a mixed fracture in which brittle fracture and ductile fracture coexist.Laser welding was performed after the welding current was increased,and the phase change temperature,silicon-aluminum content and mechanical properties of the solidification structure in different areas of the weld were tested.It is found that the different positions of the welded joints cause segregation of silicon-aluminum elements during crystallization due to different heating and cooling rates,and there are differences in silicon-aluminum content and microstructure between different weld zones.The fusion zone close to the base metal is not completely melted,and ?-Al adheres to the surface of the unmelted primary silicon particles in the form of continuous crystal growth to form columnar crystals;as the solidification progresses,the center of the weld is redistributed due to solute redistribution and constitutional undercooling the silicon particles are remarkably refined and the aluminum-silicon eutectic is distributed between the primary silicon;the microhardness of different areas of the weld is different,the microhardness of the weld center is the highest,followed by the fusion zone and the matrix.The pores and hot crack distribution of the laser sealing box,the residual stress distribution of the box,the weld joint interface and performance under the optimized process were analyzed.The pores in the weld are divided into precipitated pores and process pores.The generation of precipitated pores is mainly caused by the difference in solubility of hydrogen in the solid phase and liquid phase of aluminum;the main reason for the production of process pores is the collapse of the keyhole during the laser welding of aluminum alloy.A small amount of hot cracks exist in addition to the pores,and the width is very small and distributed in strips at the boundaries of the primary silicon grains.There are compressive stresses at different positions of the box welds.The stress values are distributed between-10 and-70 MPa and the distribution is uneven.The stress values at the midpoints of the four sides of the box are higher than the four corners.