Theoretical Calculation On Cu₆Sn₅ Intermetallics And Experimental Investigation On Properties Of Sn58Bi-Cu₆Sn₅ Lead-free Solder

With progress of science and technology,the electronic equipment follows a tendency of miniaturization.In the solder joint of integrated circuits,the intermetallic compound formed through reaction between solder and substrate has received much attention because of the increasing volume fraction.Since Cu₆Sn₅ is one of the most common intermetallic compounds,in this work,we do both experiment and theoretical calculation on it to investigate its properties and effects in lead-free solder.In the experiment,Cu₆Sn₅ nanoparticles in dimension of 10 nm are synthesized and first applied to improve the Sn58Bi solder alloys.The microstructure,tensile properties,creep behavior and corrosion resistance of the composite solder are mainly investigated in this work.Addition of Cu₆Sn₅ nanoparticles not only refines the microstructure of Sn58Bi solder but also triggers a brittle to ductile change of the tensile properties.The nanoindentation test reveals that the creep resistance of SnBi-Cu₆Sn₅ samples is enhanced through the creep mechanism transformation.In corrosion experiments,samples with nanoparticles exhibit a lower corrosion rate.Furthermore,solder with 0.05 wt%nanoparticles presents the best performance among all the samples.According to the calculation,the structural,elastic and electronic properties of quaternary intermetallic compound?-?Cu,Ni,Au?₆Sn₅ are investigated by a first-principles method.Also,the effect of different Ni,Au concentrations is carefully analyzed.The preferential substitution sites and formation heats are calculated and they suggest that Ni atom is more effective in stabilizing the quaternary intermetallic structure than Au atoms.The change of cell volume reveals that the formation heat in this work is mainly affected by the atomic bonding.The single-crystal elastic stiffness illustrates that Ni atoms are effective in enhancing the polycrystalline moduli while Au atoms trigger an inverse effect.Although the anisotropy of Young's modulus and shear modulus is weakened after concurrent addition of Ni and Au,it grows continuously with the increasing ratio of incorporated elements.The density of states and gives an interpretation that the change of all the properties above is due to the variation of atomic bonding between Ni-Cu and Au-Sn.