Effect Of The Addition Of Zn And Ni On The Properties Of Cu₆Sn₅ Intermetallic

With the lead-free and miniaturization of solder joints in microelectronic packaging, intermetallic compounds?IMCs? usually form at the Pb-free solder joints/interconnects, which are the basic premise to realize the metal interconnection. The structures and properties of intermetallic compounds have a vital influence for the integrity and reliability of lead-free solder joints. In this paper, the easiest form of Cu₆Sn₅ intermetallic compound was selected as the research object, combined with the microstructure and nano indentation experiment, and the first principles calculation, we have systematically investigated and analyzed the effects of different elements on the structural, mechanical and thermodymanic properties of Cu₆Sn₅ compounds. More details were given as follows:?1? The influences of Zn additions on the properties of Cu₆Sn₅ intermetallic compounds are investigated. Results show that after the Sn–Cu–?Zn? alloys were smelted under the high temperature, mainly formed Cu₆Sn₅ and Cu₆?Zn,Sn?₅ compounds, respectively, and most Zn diffused into the Cu₆Sn₅ to form the more stable ternary phase compound Cu₆Zn_0.5Sn_4.5. X-ray diffraction analyses show that Zn could enhance the stability of hexagonal ?-Cu₆Sn₅ phase at room temperature by inhibiting the transformation from ? to ??. Meanwhile, the results of nanoindentation experiment show that the presence of Zn in the crystal compound increases the elastic modulus and hardness of the high-temperature ?-Cu₆Sn₅ compound, which has the good consistency with the results of first principles calculation. By calculating the electronic structure and charge density distribution find that the covalent bonding of the neighbor Sn and Zn atoms to Cu atoms are stronger than the previous Cu-Sn bonding, which can yield an energy gain when bonding states are created.?2? The effects of various Ni concentrations on the properties of hexagonal ?-Cu₆Sn₅ compound have been systematically investigated. Results show that higher Ni concentration in the ?-Cu6-xNixSn5?x=0, 0.5, 1, 1.5 and 2? leads to thermodynamically stable compounds, and Ni atoms preferentially occupy Cu2+Cu1c sites forming the ?-Cu₄Ni₂Sn₅ compound. It is also found that the unit cell volume and lattice parameter of the ?a‘ axis decrease with increasing Ni concentration, which are consistent with the other experimental results of K.Nogita and D. Mu et al. An efficient stress–strain approach at the optimized structure is used to calculate elastic stiffness, which indicates that the addition of Ni enhances the brittleness, modulus, Debye temperatures, and mechanical stability of ?-Cu₆Sn₅ compound. Therefore, Ni can improve the strength and mechanical properties of the solder joints to increase the reliability of solder joints. Combining the results from the calculations of the electronic structure and charge density distribution, the hybridizations between Cu d, Sn s and Ni d states are expected to account for the better stability and larger modulus of ?-Cu₆Sn₅ compound.