Effect of external static magnetic field on the particle distribution, the metallurgical process and the microhardness of Sn3.5Ag solder with magnetic Ni particles

Purpose This paper aims to investigate the mechanism of Ni particles distribution in the liquid Sn3.5Ag melt under the external static magnetic field. The control steps of Ni particles and the Sn3.5Ag melt metallurgical process were studied. After aging, the microhardness of pure Sn3.5Ag, Sn3.5Ag containing randomly distributed Ni particles and Sn3.5Ag containing columnar Ni particles were compared. Design/methodology/approach Place the sample in a crucible for heating. After the sample melts, place a magnet directly above and below the sample to provide a magnetic field. Sn3.5Ag with the different morphological distribution of Ni particles was obtained by holding for different times under different magnetic field intensities. Finally, pure Sn3.5Ag, Sn3.5Ag with random distributed Ni particles and Sn3.5Ag with columnar Ni particles were aged and their microhardness was tested after aging. Findings The experimental results show that with the increase of magnetic field strength, the time for Ni particle distribution in Sn3.5Ag melt to reach equilibrium is shortened. After aging, the microhardness of Sn3.5Ag containing columnar nickel particles is higher than that of pure Sn3.5Ag and Sn3.5Ag containing randomly distributed nickel particles. A chemical reaction is the control step in the metallurgical process of nickel particles and molten Sn3.5Ag. Originality/value Under the action of the magnetic field, Ni particles in Sn3.5Ag melt will be arranged into columns. With the increase of magnetic field strength, the shorter the time for Ni particles in Sn3.5Ag melt to arrange in a column. With the extension of the service time of the solder joint, if Sn3.5Ag with columnar nickel particles is used as the solder joint material, its microhardness is better than Sn3.5Ag with arbitrarily distributed nickel particles and pure Sn3.5Ag.