Study On The Properties Of Al₂O₃ Nanoparticles And Cr Reinforced Sn58Bi Lead-free Solder

Based on the demand for low temperature soldering in photovoltaic power generation and high performance computer packaging,Sn58Bi lead-free solder has been widely used in the package of temperature sensitive devices due to its low melting point,high mechanical strength and good creep resistance.However,the Bi-rich phases formed by the Sn58Bi solder during the soldering process are extremely brittle,and the interface intermetallic compound layers of the Sn58Bi solder joints are too thick and form elongated intermetallic compounds.These problems can degrade the mechanical properties of the Sn58Bi solder and adversely affect the final package.Al₂O₃ nanoparticles have the advantages of high hardness,stable chemical properties,high surface energy,etc.,and the addition of chromium can greatly enhance the ductility of the solder alloy,inhibit the growth of intermetallic compounds at the interface of the solder joint,and improve the morphology of the intermetallic compound layer.In order to solve the above problems of Sn58Bi solder,different mass fractions of alumina nanoparticles and chromium were separately added into Sn58Bi solder by powder metallurgy method to compositely strengthen it.The results show that the addition of Al₂O₃ nanoparticles refines the microstructure of Sn58Bi solder while reducing the peak temperature and paste range of the solder.When the addition amount of Al₂O₃ nanoparticles is 0.5 wt.%,the ultimate tensile strength and hardness of the composite Sn58Bi solder are increased by 22%and 19%compared with no added solder.The microstructures of the cross section indicate that the fracture mode of the solder changes from brittle fracture to ductile fracture with the addition of Al₂O₃ nanoparticles.In the corrosion experiments,the corrosion resistances of the Sn58Bi-Al₂O₃ nanoparticle composite solders are significantly stronger than that of the non-added solder.The results of nanoindentation tests show that the addition of Al₂O₃ nanoparticles transforms the creep mechanism of the Sn58Bi solder,which in turn enhances the creep resistance of the solder.The CrSn₂ intermetallic compounds were formed in the Sn58Bi-Cr composite solder.The average phase spacings of the composite solders are smaller than that of the non-added Sn58Bi solder,and the addition of Cr also improves the tensile strength and creep resistance of the solder.The ductility of the 0.2 wt.%Cr composite solder is31%whose fracture surface of the solder slab sample shows a sign of ductile fracture,the dimple.The micrographs of the solder joints show that the addition of Cr improves the morphology of the Cu₆Sn₅ intermetallic compound and inhibits the growth of intermetallic compounds.In addition,the tensile strengths of the composite Sn58Bi solder joint are higher than that of the non-added Sn58Bi solder joint.