Interface IMC Evolution And Mechanical Properties Of Sn-5Sb-xCuNiAg/Cu Micro Solder Joints Under Temperature Cycling

With the development of electronic power devices in the direction of miniaturization,intelligence and multi-function,the packaging quality of electronic products are required higher and higher.However,in the actual working service environment of electronic products,the components are in the service environment with alternating temperature for a long time,and the stress and strain are generated in the process of temperature change due to the different thermal expansion coefficients among chip,solder joints and substrate,which make the performance of solder joints sharply decrease and reduce the reliability of solder joints.Therefore,it is particularly important to study the influence of temperature cycling on the reliability of micro solder joints.The paper was based on the research basis of our laboratory staffs.The interface intermetallic compounds（IMC）growth and evolution of micro solder joints formed by Sn-5Sb-0.5Cu-0.1Ni-0.5Ag solder on Cu substrate were studied by compared with two kinds of common Sn-5Sb and SAC305 solder,and the action mechanism of adding trace elements Cu,Ni and Ag were analyzed.The shear properties,bulk solder hardness and creep behavior of three kinds of micro solder joints were studied by shear and nano indentation experiments before and after temperature cycling.The results indicated that the interface IMC of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu was formed by stacking fine granular（Cu,Ni）₆Sn₅ before temperature cycling.The morphology of interface IMC of Sn-5Sb/Cu and SAC305/Cu were sawtooth and scallop respectively.The main component of interface IMC was Cu₆Sn₅.After 1000 cycles,the morphology of interface IMC of Sn-5Sb/Cu and SAC305/Cu solder joints became relatively smooth,and the main components of interface IMC changed.The interface IMC near the solder side was composed of Cu₆Sn₅.The interface IMC near the solder side was composed of Cu₃Sn.But the morphology and composition of interface IMC of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu had not changed significantly.The thickness of interface IMC three kinds of micro solder joints increased significantly when the number of temperature cycles increased.However,the growth rates of interface IMC of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu was significantly lower than that of Sn-5Sb/Cu under the same cycles.This was because the concentration difference between solder and substrate was reduced by adding trace element Cu,which hindered the reaction diffusion and bulk diffusion,and inhibited the growth of interface IMC.The bulk solder hardness and the shear strength of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu were higher than those of Sn-5Sb/Cu and SAC305/Cu before and after temperature cycling.The smallest creep displacements and creep rates of bulk solders and the strongest creep resistance of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag bulk solder was compared with those of Sn-5Sb and SAC305 bulk solder after the same number of cycles.Sb was dissolved inβ-Sn and the replacement solid solution was formed in Sn-Sb based solder,which played the role of solid solution strengthening.The addition of trace element Ni formed a large amount of（Cu,Ni）₆Sn₅,which hindered the movement of dislocations and played the role of dispersion strengthening.Ni could refine grains and playde the role of fine grain strengthening.The addition of trace element Ag formed a large amount of Ag₃Sn,which played the role of the second-phase strengthening.The shear strength,bulk hardness and creep resistance of micro solder joints were enhanced by the addition of trace elements.Ductile fracture occurred at the bulk solder of three kinds of micro solder joints before temperature cycling.The fracture mode and fracture position of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu still unchanged after 1000 temperature cycles.Ductile fracture still occured at the bulk solder.On the contrary,the other two kinds of solder joints changed significantly.Sn-5Sb/Cu appeard ductile-brittle mixed fracture at the bulk solder and the junction of bulk solder and interface IMC.SAC305/Cu appeard intergranular brittle fracture at the junction of bulk solder and interface IMC.