Effect Of Silver-coated Multi-walled Carbon Nanotubes On Microstructure And Mechanical Properties Of Sn-58Bi Solder

In the field of microelectronic packaging,the level of miniaturization,high density and multi-function packaging technology is improving day by day.However,the key problem of the interconnection of packaging matrix is still the reliability of solder joints.How to effectively improve the toughness of Sn-58 Bi solder is still a hot topic in the current electronic packaging field.At present,many researchers use the principle of fiber reinforced composites to add carbon nanotubes(CNTs)into the alloy,and take advantage of the high strength and toughness of CNTs to improve the comprehensive mechanical properties of solder.However,CNTs cannot effectively combine with metals.After years of research,it has been discovered that the purpose of wetting with Sn can be achieved by electroless metal plating of CNTs to improve the overall performance of the solder.However,the detailed process and characterization of electroless plating on the surface of CNTs,the way that electroless metal-plated CNTs are effectively added to Sn-58 Bi alloy,the effect of electroless metal-plated CNTs on the overall performance of the alloy after adding Sn-58 Bi alloy,and related simulation experiments are lack of system research.In order to solve the above problems,silver-coated multi-walled carbon nanotubes(AgMWCNTs)were prepared by in-situ co-reduction method.The morphology of AgMWCNTs was characterized by SU8020 field emission scanning electron microscopy(SU8020 FE-SEM)and Tecani G2 F30 S-Twin transmission electron microscopy(Tecani G2 F30 S-Twin TEM),and the phase analysis of Ag-MWCNTs was performed by X-ray diffraction(XRD)The original method of adding Ag-MWCNTs in the process of making flux was used to effectively add the nanocomposite into the solder paste.After that,the morphology of Sn-58 Bi metallographic with different Ag-MWCNTs content was characterized by SEM and the influence of the addition amount on the metallographic structure of Sn-58 Bi was analyzed The mechanical properties of Sn-58 Bi nano-composite solder with different content of Ag-MWCNTs were tested,and the effect of the addition amount of Ag-MWCNTs on the mechanical properties of the alloy was discussed.Use Materials Studio(MS)software to optimize the geometry of the Sn and MWCNT-Sn solid solution models,and analyze the periodic annealing and various performance comparisons.The tensile properties of Sn solid solution and MWCNT-Sn solid solution at temperatures of 298 K,323 K,348 K and 373 K were analyzed with Large-scale Atomic/Molecular Massively Parallel Simulator(LAMMPS)software,and the following conclusions were drawn:Ag nanoparticles prepared by in-situ co-reduction method were uniformly coated on MWCNTs,and most of the Ag nanoparticles were not oxidized during the reaction.By analyzing the microstructure of Sn-58 Bi nano-composite solder with content of 0 wt.%,0.03 wt.%,0.05 wt.%,0.07 wt.% and 0.1 wt.%,it can be seen that the addition of AgMWCNTs can refine the grain to a certain extent.When the addition amount is 0.05 wt.%,the degree of structure refinement reaches the highest.But when the addition amount reaches 0.07 wt.%,the network structure begins to become coarse,the microstructure of the composite solder becomes coarser,and the grain spacing increases.This is because when the content of Ag-MWCNTs increases,an aggregation effect will occur.This situation not only does not effectively inhibit the coarsening of the mesh structure,but also produces certain organizational defects.The tensile test results show that with the increase of the Ag-MWCNTs content,the elongation first increases and then decreases.The elongation of Sn-58 Bi nanocomposite solder containing 0.05 wt.% Ag-MWCNTs is the largest,about 27.4%.The fracture has the most dimples,which can be judged to be ductile fracture.The fracture of Sn-58 Bi alloy and nanocomposite Sn-58 Bi alloy containing 0.1 wt.% Ag-MWCNTs is brittle fracture.The 0.03 wt.% and 0.07 wt.% nanocomposite Sn-58 Bi alloys have fewer dimples and a part of tearing edges.The fracture in this case can be judged as a ductile-brittle mixed fracture.The results of shear test show that the shear strength of Sn-58 Bi composite solder increase from 35.3 MPa to 57.2 MPa after adding 0.05 wt.% Ag-MWCNTs.This shows that the addition of Ag-MWCNTs can not only improve the mechanical properties of the material but also make the material structure more uniform.This is because MWCNTs have excellent elastic modulus and tensile strength.When they are effectively added to the alloy,these excellent mechanical properties of MWCNTs help the stress to be evenly distributed to each Ag-MWCNTs.Moreover,the addition of Ag-MWCNTs plays a role of strengthening the second phase,interacting with dislocations in mechanical tests,hindering the movement of dislocations,and increasing the tensile and shear stress of the alloy.The results of nanoindentation experiments show that the nanocomposite solder with 0.05 wt.% Ag-MWCNTs has the smallest indentation depth,its elastic modulus is about 43.7 GPa,and its hardness is about 182.3 MPa.When the addition amount reaches 0.1 wt.%,the depth of nanoindentation is the largest.The main deformation control mechanism of nano-composite Sn-58 Bi solder and original Sn-58 Bi solder is the dislocation climbing mechanism.In the process of MS geometry optimization,the overall heat changes of Sn solid solution and MWCNT-Sn solid solution system are both exothermic energy reduction processes.In addition,MWCNT-Sn solid solution has a high enthalpy,so the step size and heat released for the optimization process are much higher than that of Sn solid solution,so that the system can be more stable and ideal.Therefore,it can be seen that the geometric optimization process of MS is a process that reduces the energy of the overall system.Through geometric optimization,the crystal structure will be more stable.The Hamiltonian,total potential energy,total kinetic energy and bond energy of Sn and MWCNT-Sn solid solution systems all increase with the number of annealing cycles.The simulation results of LAMMPS software show that the tensile strength of Sn solid solution and MWCNT-Sn solid solution decrease slowly with the increase of temperature,and the elongation increases gradually.The difference is that within 373 K,regardless of the temperature,the tensile strength and elongation of MWCNT-Sn solid solution are greater than Sn solid solution.This is because MWCNT also has excellent elastic modulus,tensile strength and super toughness.When it is added to the alloy,its excellent mechanical properties help to increase the cohesive force between the Sn solid solution molecules,making MWCNT exhibit excellent mechanical properties to avoid the breaking of the metal bond between the Sn solid solution molecules,and improve the alloy performance.