The Reliability Research Of In-Sn-Zn Near-Eutectic Alloy Solder With Low Melting Point

With the development of lead-free in the microelectronics industry,In-Sn-Zn near-eutectic solder is highly regarded for its good wetting properties,low melting point and great thermal conductivity.However,with the improvement of the integration of electronic components and the continuous development of diversified application scenarios,the reliability of solder joints has been challenged a lot,especially in the face of Electromigration?EM?and the fast-growth of Intermetallic Compounds?IMC?between the substrate and solder.To solve the problem that the solder faced in its development,the relevant work was carried out,which focused on the following three issues:The evolution mechanism of the alloys'micro-structure,Electromigration mechanism of the alloy and The IMC evolution process.The X-ray diffraction?XRD?,optical microscope?OM?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,and Energy Dispersive Spectrometer?EDS?were used to analyze the phase composition and phase morphology of the sample.The wetting dynamic visualization system,differential thermal scanning calorimeter?DSC?,AGS-J10universal testing machine and HV-1000A micro-hardness tester were used to characterize the wetting,thermal and mechanical properties of the alloy.Studies on the evolution mechanism of near-eutectic In-Sn-Zn alloys'micro-structure showed that the alloy consists of?,?and Zn phases.The plasticity of the alloy was greatly affected by the soft?phases,and the strength of the alloy was greatly affected by the hard?and Zn phases.When In content was constant and the Zn content was in the range of 6wt.%?9wt.%,with the increase of the Zn phase,the micro-hardness of the alloy gradually increased,the tensile strength increased first and then decreased,the elongation decreased first and then increased.And When Zn content was constant and the Sn content was in the range of 46wt.%?52wt.%,as the?phase increased,the micro-hardness and tensile strength of the alloy were improved,and the elongation was reduced.Electromigration studies of near-eutectic In-Sn-Zn alloys showed that under its influence,the In-rich?phases?In₃Sn?and the Sn-rich?phases?In Sn₄?were segregated at the cathode and anode side,respectively.The phase separation was affected by the combination of electron wind force and back stress.The different degree of lattice distortion between different regions was one of the causes of the back stress.The mutual transformation between?and?phases was carried out in a manner,which was similar to the spinodal decomposition and the process of transformation accompanied with the solid solution or precipitation of Zn.The electron wind force of Zn was much small.Zn atoms migrated to the two poles slightly.The primary Zn phase tended to diffuse along the phase boundary and its size decreased with the process of diffusion.The effect of EM on the micro-structure and morphology changed the properties of the alloy further.After EM,the melting point and melting range of the alloy at cathode side were larger than those of the anode side,while the thermal enthalpy at cathode side was smaller than that of the anode side.And compared with the state before EM,the microhardness of the alloy at the both cathode/anode side were improved to some extent.Research on the evolution of IMC between near-eutectic In-Sn-Zn solder and Cu substrate showed that the Zn addition reduced the tensile strength and wetting performance of the solder,and suppressed the growth of IMC effectively.IMC in diffusion couples had a two-layer structure:Cu₃?In,Sn?adjacent to the Cu substrate and Cu₂?In,Sn?adjacent to the solder,which were formed though a solid-solid diffusion reaction and solid-liquid reaction,respectively.With the addition of Zn in50In-50Sn/Cu couple,the diffusion of Cu was alleviated.Zn exhibited high activity and moderated the dissipation of main atoms?In/Sn?in the solder.So the growth of Cu₃?In,Sn?was suppressed significantly.And the growth of?-Cu₃?In,Sn?was at the expense of?-Cu₂?In,Sn?.In the In-44Sn-6Zn/Cu diffusion couple,the growth of?-Cu₃?In,Sn?was grain-boundary controlled and the time constant n was 0.31.In the50In-50Sn/Cu diffusion couple,due to the slow growth of?-Cu₂?In,Sn?,the time constant of Cu₃?In,Sn?was down to 0.19.