Research On Interface Behavior Of Sn-Bi-In Series Alloys

With the development of the microelectronics industry and the implementation of lead-free,various Sn-Pb solder substitutes have become popular,among which alloy solders such as Sn-Ag-Cu have been commercialized.Among many solders,Sn-Bi solder has caused extensive research due to its higher mechanical strength and lower melting point.However,the problem of Bi segregation in Sn-Bi solder has been plagued by researchers.Moreover,the mechanical instability caused by the hard and brittle nature of the Bi phase has greatly affected its application prospects.In order to solve the problems encountered by the Sn-Bi component solder,we reduced the Bi content near the maximum solid solubility of the Sn-Bi alloy and added a small amount of In to reduce the negative effect of Bi.In this paper,the study of the influence mechanism of the addition of In on the Sn Bi structure,the improvement of the properties of the solder,and the study of the interface behavior of the solder on different substrates are carried out.Combining various material detection methods,the phase composition and phase morphology of the sample are analyzed by X-ray diffractometer(XRD),optical microscope(OM),scanning electron microscope(SEM),energy spectrometer(EDS).Wetting dynamic visualization system,differential scanning calorimetry(DSC),AGS-J10 universal testing machine and HV-1000 A microhardness tester are used to characterize the wetting,thermal and mechanical properties of the material.The research results of Sn-Bi alloys with different contents of In elements found that: when the In content does not exceed 5 wt.%,the Sn-Bi-In solder mainly consists of ?-Sn and Bi phases.With the addition of In,the solid solubility of the solder to Bi increases,and the Bi phase tends to decrease and refine.As the In content increases,although the Bi content as a hard and brittle phase decreases,the hardness of the alloy increases by 41.96%.As the In content increases,the lattice distortion of ?-Sn increases,more Bi is dissolved in the matrix Sn,which increases the strength of the alloy.As the In content increases,the corresponding solder welding strength decreases by 24.78%.This is because as the In content increases,the interface IMC layer(Intermetallic Compounds)has a tendency to thicken,and the internal composition also changes,and the IMC layer has brittleness,resulting in a decrease in welding strength.The interface performance of Sn-Bi-In solder is different on different welding substrates.In terms of wettability,the wettability of different substrates is different.Specifically,the Ag substrate wetting angle is 13.6°?20.7°,the Cu substrate wetting angle is 23.2°?28.5°,and the Ni substrate wetting angle is 34.9°?42.2°.For the same substrate,as the In content increases,the wettability of the solder on the Cu substrate first increases and then decreases.At the position where the In content is 4 wt.%,the wettability reaches the maximum.The wetting on the Ag substrate tends to decrease with the increase of In content.The change trend of wetting on the Ni substrate is not clear,and the overall change regularity is not strong.In the interface reaction of the Cu matrix,as the In content increases,the thickness of the IMC layer increases,and the time constant is 0.57,which is dominated by volume diffusion.In the Ni matrix,the time constant is 0.82,and its IMC growth is initially limited by the reaction and then dominated by volume diffusion.In the Ag matrix,the time constant is 0.39,and its IMC growth is dominated by grain boundary diffusion.In terms of growth rate,the growth rate on the Ag substrate is greater than that on the Cu substrate than on the Ni substrate.