The Effect Of Self-propagating Exothermic Reaction On Microstructure Of Composite Solder

Doping reinforcement in lead-free solder is an excellent way to improve the microstructure and the mechanical properties of composite solder joints.However,in the traditional reflow soldering process,the reinforcement is easily precipitated in the composite solder.It makes the reinforcement have a very low residual rate in the composite solder,which affects the enhancement of the relative composite solder joint.The Al/Ni foil self-propagating exothermic reaction can be used as the reaction heat,makes the composite solder in rapid melting and solidification process.So that a large proportion can be retained in the composite solder after solidification.In thin-film self-propagating and exothermic environments,the compound solder has a very rapid rate of temperature rise and fall,a large temperature gradient is formed inside the solder,and the melting and solidification process of the solder is highly non-equilibrium under the self-propagating reaction heat source of the thin foil.Therefore,the thin foil is studied.It is of great significance to propagate the microstructure of the composite solder under reactive heat source conditions.The composite solders doped different proportions of non-reactive reinforcement nanoparticles,reactive reinforcement nano Ni powder and composite reinforcement Ni-CNTs were prepared by mechanical mixing and SPS vacuum sintering.The composite solder sheet obtained after cold rolling of the composite solder melts and solidified rapidly under the Al/Ni foil self-exothermic reaction heat source,and the microstructure of the composite solder after final solidification was studied.Based on the self-propagating reaction heat source of Al/Ni thin foil,the effects of different types and proportions of reinforcement on the solidification structure of the composite solder were investigated.According to the microstructure analysis,the unmelted area of the composite soldersheet showed the original solder particle morphology,and the crystal grains in the melted area were significantly refined.The closer the distance to the heat source,the finer the grains.Compared with the rapid solidification structure of the undoped solder under the self-propagation reaction heat source of Al/Ni thin foil,the grains in the melt zone of the composite solder sheet doped with different reinforcements are all refined.After the non-reactive ZnO nanoparticle reinforcement was added,the ductility of the composite solder was reduced because ZnO did not react with the solder matrix and the ZnO nanoparticle had its own hardness.A large amount of microcracks inside the rolled solder sheet affected the composite solder.Heat is transferred in the composite solder during melting and cracks form at the boundary of the melting zone.In addition,no aggregation of ZnO nanoparticles was found at the boundary and in the interior of the melting zone.After doping reactive Ni nano-reinforcement,the grain size of the composite solder melting zone will become larger with the increase of the addition amount.When the doping amount is 0.2wt.%,the grain growth is most obvious.When doped composite Ni-CNTs were doped,the addition ratio increased from 0.06 wt.% to 0.2 wt.%,and no grain growth occurred in the melt zone of the composite solder.