Effects Of Gnss And Bi On The Structure And Properties Of Sn-0.7Cu Lead-free Solder

In recent years,the traditional Sn-Pb solder has been unable to meet the needs of miniaturization,green and high integration of electronic packaging materials.Therefore,the development of a lead-free solder which can replace Sn Pb solder has become a hot spot in the field of electronic packaging.Sn-Cu solder is considered as one of the most potential lead-free solders to replace Sn-Pb solder due to its advantages of low cost,high strength,non-toxic and easy production and recovery.However,the Sn-Cu solder has the disadvantages of low hardness,poor mechanical properties and poor corrosion resistance.In order to make up for the shortage of Sn-Cu solder,particle strengthening and alloying methods are used to modify it to improve the structure and properties of Sn Cu solder.In this paper,Sn-0.7Cu-x GNSs composite solders and Sn-0.7Cu-x Bi composite solders were successfully prepared by hot pressing sintering and arc melting.At the same time,the microstructure of the composite solder alloys was investigated by SEM and XRD;The densitometer,conductivity meter and DSC were applied to test physical properties;Also,hardometer and tensile testing machine were used to test the mechanical properties;And the wettability was tested by spreading rate experiment;Potentiodynamic polarization method and XPS were applied to test the electrochemical corrosion.The experimental results show that:(1)In terms of microstructure,GNSs dispersed in the grain boundary of Sn-0.7Cu matrix and refined the grains when a small amount of GNSs was added.However,the excessive GNSs content agglomerated at the grain boundary and coarsened the grain.A small amount of Bi could refine the structure of Sn-0.7Cu matrix and improved its properties.However,the excessive Bi started to aggregate at the grain boundary,and resulting in segregation and coarsening,which reduced the performance.(2)In terms of physical properties,the addition of GNSs had a small effect on the melting point and density of Sn-0.7Cu composite solder.And the electrical conductivity of Sn-0.7Cu composite solder increased first and then decreased with the increase of GNSs content.However,with the increase of Bi content,the density of composite solder increased,while the conductivity and melting point decreased.(3)In terms of mechanical properties,the hardness of Sn-0.7Cu solder was significantly increased when GNSs was added.The tensile properties increase first and then decrease with the increase of GNSs,but it was still higher than that of pure Sn-0.7Cu solder;Meanwhile,the hardness and compression properties of Sn-0.7Cu-x Bi composite soldersboth increased first and then decreased with the increase of Bi.(4)In terms of wettability,with the increase of GNSs content,the spread rate and spread area of Sn-0.7Cu-x GNSs solder decreased and the wetting angle increased.So the wettability became worse.However,with the increase of Bi content,the spreading rate and spreading area of Sn-0.7Cu-x Bi solder increased and the wetting angle decreased,which indicated that the wettability of composite solders improved.(5)In terms of anti-corrosion performance,with the increase of GNSs content,the corrosion potential(Ecorr)increased first and then decreased,while the corrosion current density(Icorr)and corrosion rate were opposite;And,with the increase of Bi content,the composite solder's Ecorr decreased first and then increased,while the change of Icorr and corrosion rate were contrast.At the same time,the corrosion products produced by the addition of a small amount of GNSS and Bi were closely arranged,and almost no holes were formed,then the corrosion resistance was improved.