Research On Interface Evolution And Properties Of Ag Coated Graphene Nanosheets/Sn-Ag-Cu Composite Solder Joints

With the improvement of packaging density in electronic packaging field and the rapid development of nanotechnology,solder joints tend to be miniaturized and high-density development,which puts forward higher requirements for the service conditions of solder joints.In this paper,in order to improve the reliability of solder joints,Ag coated graphene nanosheets（Ag-GNSs）were used as the reinforcement,and different contents of Sn-3.0Ag-0.5Cu-x（Ag-GNSs）new composite lead-free solder were prepared by mechanical mixing method,the microstructures and properties of solder joints with different components at three different aging temperatures for six different aging times as well as mechanism of Ag-GNSs were studied.The analysis of intermetallic compound（IMC）growth behavior of Sn-3.0Ag-0.5Cu-x（Ag-GNSs）composite solder shows that the addition of Ag-GNSs can inhibit the growth of IMC layer and Cu₆Sn₅ particles.The IMC layer thickness and Cu₆Sn₅ particles of the composite solder first decrease and then increase with the increase of Ag GNSS content,but they are still less than those of Sn-3.0Ag-0.5Cu solder.With the same Ag-GNSs content,the IMC layer and Cu₆Sn₅ particles increases gradually with the extension of aging time and the increase of aging temperature.It is revealed that the longitudinal growth of IMC layer is controlled by bulk diffusion,whereas,the transverse growth of Cu₆Sn₅ particles is controlled by grain boundary diffusion.It also concluded that as the addition amount of Ag-GNSs reaches 0.05wt%,the IMC layer thickness of the composite solder is the smallest,and the diffusion coefficient reaches the minimum value of 2.356×10^-18 m²/s,the maximum diffusion activation energy of composite solder is 27.559 k J/mol.It is proved that Ag-GNSs hinders the growth of IMC layer and Cu₆Sn₅ particles of composite lead-free solder by impeding the inter-diffusion of atoms.The research of properties of Sn-3.0Ag-0.5Cu-x（Ag-GNSs）composite solder displays that the addition of Ag-GNSs can improve the wettability of composite solder,the wettability increases first and then decreases with the increase of Ag-GNSs content,but it is still better than that of Sn-3.0Ag-0.5Cu solder.The melting point of the composite solder decreases slightly.It also shows the variation rules of microhardness and shear strength of composite solder are the same as those of wettability,when the content of Ag-GNSs is 0.05wt%,the performance is better.However,as the content of Ag-GNSs is constant,Cu₆Sn₅ grain coarsens inducing grain boundaries decrease,which leads to the inhibition of dislocation decreases,thereby microhardness decreases slightly,and the shear strength of composite solder decreases with the increase of aging time and aging temperature.It is revealed that Ag-GNSs play the role of second phase particle strengthening and fine grain strengthening.Ag₃Sn particles and reinforced phase Ag-GNSs hinder the dislocation movement inducing the enhancement about deformation resistance of solder and improvement of microhardness;Moreover,the shear strength of the composite solder increases with the increase of the number and depth of parabolic or semi elliptical dimples.As the content of Ag-GNSs is in the range of 0 wt%to 0.2wt%,combined with the comprehensive analysis of IMC structure,wettability,melting characteristics,microhardness and shear properties of Sn-3.0Ag-0.5Cu-x（Ag-GNSs）composite solder,the performance of the composite solder is better when the content of Ag-GNSs is 0.05wt%.