Study Of Ni-modified Graphene On The Micromorphology And Properties Of Sn-58Bi Solder

Under the guidance of the low-carbon environmental protection concept,electronic devices are developing rapidly towards being lead-free.To cope with the trend of high integration and precision,the requirements of reliability of interconnection solder joints are increasing.Sn-58Bi low-temperature lead-free solder is expected to become an alternative to traditional Sn-Pb solder due to its low cost,low energy consumption,and high overall performance.However,the problem of degradation of solder joint reliability needs to be addressed because of inhomogeneous brittle Bi-phase distribution during service.In this study,nickel-modified reduced graphene oxide(r GO@Ni)was prepared by the in-situ co-reduction method,and r GO@Ni-reinforced Sn-58Bi composite solder paste was prepared by the mechanical stirring method.The microstructural composition of r GO@Ni is discussed.The reflow process matching the Sn-58Bi-r GO@Ni solder paste is designed.The morphology of the intermetallic compound(IMC)layer at the interface of Sn-58Bi-r GO@Ni solder and Cu substrate is studied under reflow and thermal aging.The effects of r GO@Ni on the microstructure,crystal structure and shear fracture behavior of Cu/Sn-58Bi-r GO@Ni/Cu solder joints are analyzed,as well as the evolution of the tissue morphology of the solder joints under the electric field.The following main conclusions were obtained.(1)Graphene oxide(GO)and Ni ions were reduced by sodium hypophosphite to reduced graphene oxide(r GO)and nickel particles.Defects on the GO surface provided good adsorption sites for Ni atoms.Structural analysis of r GO@Ni inferred that C-Ni bonds might be formed,which could strengthen the bond between graphene and the solder.(2)After reflowing,the thickness of the IMC layer decreases with increasing r GO@Ni content.When the r GO@Ni content is 0.15 wt.%,the reduction is up to 28%relative to the Sn-58Bi solder.Shear tests showed that the Sn-58Bi-0.01r GO@Ni solder had the best shear performance,with a 15%improvement over that of the Sn-58Bi solder.And the cracks formed inside the solder,which reducing the likelihood of brittle fracture of solder joints.(3)After 120 h of aging at 100°C,the solder joint coarsens,and without significant changes during continues aging,becoming to a sub-equilibrium state.Sn-58Bi-0.01 r GO@Ni solder has the slowest IMC growth rate and 0.01 wt.%r GO@Ni optimizes the crystal slip system to hold the best toughness.(4)The results of the electrical loading experiments showed that after a current density of 2.5×10~3 A/cm~2 for more than 240 h,the phases of the Sn-58Bi and Sn-58Bi-0.15r GO@Ni solders started to coarsen,while the coarsening of the Sn-58Bi-0.01r GO@Ni solder occurred after 360 h.It indicates that the addition of 0.01 wt.%r GO@Ni can slow down the migration of atoms inside the solder joint under the electrical loading.