Research On Welding Characteristics And Electrical Stability Of Sn-In-Zn-Bi Solder

With the development of 3D packaging technology and functional device packaging industry,In-Sn-based solder has broad application prospects.However,this type of solder has poor electrical resistance,and in long-term applications,there is a phenomenon of climbing indium.In order to improve the overall performance of the solder,alloying methods are usually used to improve the performance of the material.This paper studies the Sn-In-Zn-Bi quaternary alloy,analyzes the structure,electromigration mechanism and welding mechanism of the material,and evaluates the electrical resistance characteristics of the material.X-ray diffractometer（XRD）,optical microscope（OM）,and scanning electron microscope（SEM）were used to analyze the structure and welding characteristics of the sample.The result shows:Sn-In-Zn-Bi solder is mainly composed of matrix phaseβ（Sn）and precipitation phaseγ（InSn₄）,while Bi and Zn elements are dissolved in the matrix.In the Sn-In-Zn-Bi/Cu reaction couple,the composition of the IMC layer is Cu（SnZn）.With the increase of Bi content,the IMC layer becomes thinner,and the shape gradually tends to be flat.On the side of the solder,there are fewer bumps and free interface reactants,which indicates that the diffusion of Cu to the solder is suppressed.The mechanical properties and thermophysical properties of the materials were analyzed by HV-1000A microhardness tester and differential scanning calorimetry（DSC）.The result shows:Solid solution strengthening caused by the solid dissolution of Bi in the matrix.This causes the microhardness of the solder to gradually increase with the increase of Bi content.The addition of Bi reduces the solidus temperature of the solder,but does not have a significant effect on the liquidus temperature,which expands the melting range of the material.The electrical resistance of the material was systematically analyzed.Analysis shows that after 72 h of electromigration of the solder:The content ofγ（InSn₄）phase on the anode side decreases,and the content ofγ（InSn₄）phase on the cathode side increases.And with the increase of current density,the phase separation tends to intensify.Due to the presence of component segregation and dislocations,there are varying degrees of lattice distortion and grain refinement at the anode and cathode poles of the solder,which are most obvious on the anode side.The microhardness of the solder on both sides of the anode and cathode also changes.The microhardness on the anode side increases,and the microhardness on the cathode side decreases.At the same time,the cathode side of the solder also has agglomerated pores and intercrystalline cracks.On one side,there are dispersed nano-scale micropores around the precipitation phase.Finally,analyze the XRD data and according to the degree of phase separation of the solder under different current densities.The phase separation rate of the solder under different current densities is calculated,and the current density threshold value is 9.2 A/mm².