First Principles Study Of The Properties Of Sn-based Interfacial Intermetallics

Due to the adoption of the Electroless Nickel Immersion Gold,the metal atoms of the under bump metallization such as Ni and Au can dissolve and diffuse into the solder matrix to form the Sn-based intermetallic compounds.This work is aimed to compute the Sn-based interfacial intermetallics to derive their intrinsic properties including the structure,mechanical,thermodynamic and electronic properties.The finding will provide a good reference for the future application of these materials.The derived main conclusions are:?1?The properties of a series of Au-Sn binary intermetallics are predicted.Through calculation,AuSn is the most stability one while Au₅Sn is elastically instability among the four intermetallics.They are all ductile,low stiffness and anisotropic.Among them,Au₅Sn possesses the highest anisotropy and hardness mainly due to the strong Au-Au covalent bonds.Based on the quasi-harmonic Debye model,the thermodynamic properties of AuSn from 0 to 20 GPa are obtained.?2?The essence of Au-embrittlement is clarified through calculation of the Ni,Pd single-doped and codoped AuSn₄.The doped phases are more stable than the mother phase.The elastic modulus and hardness are increased but Poisson's ratio is decreased.The brittleness is increased with the Ni concentration for the Ni doped phase,while Au_0.75Pd_0.25Sn₄ is more brittle than Au_0.5Pd_0.5Sn₄.Both of the Debye temperature and the minimum thermal conductivity are higher than the mother phase.And Au_0.5Ni_0.5Sn₄ has the best heat conductivity property among them.The stability of these intermetallics is attributed to the low bonding electrons at the Fermi-level according to the density of states.?3?The effect of substitution of Cu and Au for Ni of two different Ni₃Sn₂ structures is calculated.The stability structures are obtained after substitution.Part of the calculation results are agreed with the reported outcomes.Through comparison,?phase is more stable than?phase but the electric conductivity of?phase is superior to?phase.The degree of anisotropy along Z axis decreases dramatically for?phase,but it increases along Y axis for?phase after substitution based on the three dimensional graphic of the directional Young's modulus.?4?The intermetallics formed by Ni,Sn and P are computed.Through calculation,the three ternary Ni-Sn-P intermetallics are all thermodynamic stable but Ni₃SnP is elastically unstable.The bulk modulus is decreased but the shear modulus,Young's modulus,hardness and brittleness is increased after Sn diffused into Ni₂P.Ni₂SnP has the largest degree of elastic anisotropy and is more brittle than Ni₂P while Ni₁₀SnP₃ is close to be isotropic.The Debye temperature and the both of Cahill's model and Clark's model are used to investigate the thermal conductivity of the compounds.The heat transfer property of Ni₂SnP is lower than Ni₂P when the temperature is higher than Debye temperature.