Effects Of Trace Elements On Properties Of Gold-silver Based Bonding Wire From First-principles Calculations

With the upgrading of semiconductor packaging technology and the development of new electronic industry,traditional Au bonding wire can not meet the bonding needs of high density,narrow spacing,long distance and low cost since gold prices have been raised significantly and limitations of own properties.Cu bonding wire has displaced Au bonding wire a significant percentage owing to low cost of Cu wire in the past few years.However,the high hardness of Cu wires brings concerns over the bonding quality and the long-term reliability of the packages.Ag,a softer material in nature,is a good candidate to displace Au as an alternative low cost bonding wire.While the development of the traditional gold and silver wire bonding generally need through lots of experiments to find effects of alloying elements on the properties of bonding wire,and then determine to meet specific performance of the alloy composition of bonding wire,which will spend high development cost and long research time.Moreover,the evolution of material properties is not very good explanation limited by the experimental conditions.The first-principles calculations are widely used in the evaluation of the mechanical and electronic structure of metal materials and the design of alloy components.Therefore,The first-principles calculations are performed to research effects of elements X?Au,Be,Pd,Y,Ca,Cu,In,Zn,Pt,Ni,Sn,Sb,Mg,Ti,Nb and Al?on crystal structure,thermodynamic,conductivity and mechanical properties of Ag within the density function theory?DFT?,which is helpful to provide essential guidance in identifying materials with desired mechanical and conductivity properties,and also reduce development cycle and research costs of Ag alloys used as boding wire.Firstly,calculation model Ag₁₀₈08 and Ag₁₀₇X alloys consisting of 107 atoms of Ag and one solute atom X are built,then crystal structure of Ag₁₀₈08 and Ag₁₀₇X are optimized and their formation enthalpies and cohesion energy are calculated to investigate thermodynamic property.The results show that the lattice parameter of Ag is 4.1413?,and which will increase with the addition of elements Nb,Mg,In,Sn,Sb,Ca and Y,and decrease with the addition of elements Au,Ti,Pt,Zn,Pd,Al,Cu,Ni and Be.In calculated Ag₁₀₇X alloys,Ag₁₀₇Y has the largest lattice parameter 4.1491?and Ag₁₀₇Be has the smallest lattice parameter 4.1340?.The formation enthalpies of Ag₁₀₇X are negative,except Ag₁₀₇Be and Ag₁₀₇Ni,the value of which are 0.93×10^-22 eV/atom,0.06×10^-22 eV/atom,respectively,meaning that they are formed more difficult than other calculated alloys.The cohesion energy of Ag₁₀₇X are negative,suggesting all of them are stable.Secondly,the band structure,density of state and charge population of Ag₁₀₈08 and Ag₁₀₇X alloys are calculated to investigate the bonding characteristic and the electrical conductivity.The results show that there are many bands go through the Fermi level of Ag₁₀₈08 and Ag₁₀₇X alloys,indicating their metallic behavior.There are more electrons transfer between Sn,Mg,Ca,Sb,Zn,Y and Ag than other atoms,the value of which are0.94e,0.95e,1.21e,1.84e,1.54e and-2.21e,respectively,suggesting there are the strong covalent bonds between Sn,Mg,Ca,Sb,Zn,Y and Ag,wchich are mainly caused by orbital hybridization between Sn-5p,Mg-3s?2p,Ca-3d,Sb-5p,Zn-3d,Y-5p orbitals and Ag-4d,5s and 5p orbitals.The value of electrons transfer between Au,Be,Pd,Cu,Pt,Nb,In,Ni,Ti,Al and Ag are less than 0.3e,indicating there are weak covalent bonds between them.After doping the X elements,the electrical conductivity of Ag are decreased,the order from small to large under 300K as follows:Cu<Au<Pd<Zn<Be<Al<In<Mg<Ca<Ti<Ni<Pt<Sn<Sb<Nb<Y.The electrical conductivity of Ag₁₀₇Cu and Ag₁₀₇Au are larger than other calculated alloys under 300K,the value of which are 0.611×10⁸/??*m?and0.592×10⁸/??*m?.The electrical conductivity of Ag₁₀₇Nb and Ag₁₀₇Y are smaller than than other calculated alloys under 300K,the value of which are 0.289×10⁸/??*m?and0.290×10⁸/??*m?.Finally,the elastic constant,bulk modulus,shear modulus and Young's modulus of Ag₁₀₈08 and Ag₁₀₇X alloys are calculated to investigate the effects of X on Vickers hardness and ductility of Ag.The results show that the order of effect on Vickers hardness of Ag from small to large as follows:Mg>Be>Cu>Au>Al>Ti>Y>Pd>Zn>Ca>Pt>Ni>Sb>Sn>Nb>In.Comparing to other calculated Ag107X alloys,Ag107Mg,Ag107Be and Ag107Cu have the larger Vickers hardness,the value of which are 4.27GPa,3.96GPa and 3.86GPa,respectively.All of Ag107X alloys are ductility since theirs B/G ratio,Poisson's ratios?were larger than 1.75 and 0.33,respectively.