Study On Mechanical Properties Of Sn-Bi-xIMC(Sn-Cu-Ni) Low Temperature Solder For Electronic Packaging

The birth of space integration equipment,the rise of multi-chip integration technology and the application of various thermal-sensitive electronic components all put forward the demand for low temperature welding technology of electronic packaging.The low temperature welding technology can effectively reduce the carbon dioxide emission in the production process,greatly improve the reliability defects caused by thermal stress in the welding process,and reduce the production cost.Sn-Bi alloy is the representative solder for low temperature packaging,but its brittle fracture and but its brittle fracture property and within easily creeping characteristic at room temperature bring challenges to the reliability of low temperature packaging system.In this paper,Sn58Bi eutectic alloy solder was used as matrix,and by adding(Sn-Cu-Ni)intermetallic compound(IMC)micro-nano particles,micro-nano particles enhanced Sn-Bi-xIMC low-temperature composite solder was obtained.The effects of different IMC particles contents on the wettability,thermal behavior,microstructure and mechanical properties of Sn58Bi solder were studied,in order to provide a new idea for the design of new low temperature solder alloys.This paper mainly covers the following four parts:(1)Near-amorphous multiphase IMC particles were prepared from Cu,Sn and Ni powders by powder metallurgy.After that,the prepared IMC particles were doped into Sn58Bi solder by mechanical mixing method,and Sn-Bi-xIMC composite solder and solder balls with different IMC particles contents(x=0,0.25,0.5 and 1wt.%)were obtained.Then the wettability and thermal behavior of Sn-Bi-xIMC composite solder and solder balls were studied.The experimental results showed that the addition of IMC particles further improved the wettability of the original Sn58Bi solder,and reduced its melting point,melting range and subcooling degree.It was confirmed that the prepared Sn-Bi-xIMC has a good technological basis as a new low temperature solder.(2)Single-interface Cu/Sn-Bi-xIMC micro-solder joints and dual-interface Cu/Sn-Bi-xIMC/Cu linear micro-solder joints were prepared.The shear and tensile tests were conducted on four kinds of IMC particles contents micro-solder joints.It was found that the addition of IMC particles improved the shear and tensile properties of micro-solder joints to different degrees,among which Sn-Bi-0.5IMC micro-solder joints had the highest strength and Sn-Bi-1IMC micro-solder joints had the best plasticity.The microstructure and fracture morphology of different micro-solder joints were analyzed by SEM and EDS,and the fracture modes and differences of micro-solder joints with different IMC particles contents were further described.(3)The load-displacement(P-h)curve,elastic modulus(E)and hardness(h)of Sn-Bi-xIMC micro-solder were obtained by nanoindentation test.Based on the Norton creep power law model,the load holding stage of P-h curve obtained by displacement control mode and load control mode were studied,and the influence of different IMC particles contents and control methods on the creep performance index(creep stress index n and creep sensitivity index m)of Sn-Bi-xIMC composite solder was analyzed.Furthermore,the difference of creep mechanical mechanism of composite solder with different IMC particles contents was discussed.(4)Using ABAQUS finite element software,finite element inversion analysis was carried out for the loading stage of nano-indentation P-h curve,and a series of nonlinear fitting equations were obtained.Then,the elastoplastic constitutive models of Sn-Bi-xIMC composite solders were obtained by calculating the corresponding dimensionless equation.The inversion analysis shows that the contents of IMC particles impact on the strain strengthening index n and yield strengthσ_y of the composite solders,and the stress-strain relationships of the composite solders in the plastic stage are not same.