Study On Microstructure And Properties Of A New Type Of Highly Conductive Silver-Gold Alloy

As electronic devices become more versatile and miniaturized,electronic packaging is developing toward to high integration and high density,and higher requirements are placed on the conductivity of bonding wire materials for electronic packaging.Silver bonding wire has considerable application potential in the field of electronic packaging due to its advantages such as lower cost and better thermal conductivity.As the most conductive metal,silver has been used as a high-end new type bonding wire material in recent years.Foreign research started earlier,but its detailed preparation parameters are not disclosed to the public.In order to break the foreign monopolies,China carried out the national key research and development plan-key technology research and industrialization(2016YFB0402602)research on high-performance bonding wire and micro-material processing.The research group studied Ag-Au,Ag-Au-Cu,Ag-Au-Ce,Ag-Au-Cu-Ce and Ag-Au-X series of silver alloys according to the project requirements,and investigated their possibility as a new type of bonding wire.As one of the project tasks,this article mainly studies the microstructure,mechanics,and corrosion properties of the above-mentioned silver alloys during the preparation and application process,and obtains the changes in the structure and performance of the silver alloys in the process.The design and application of wire are provided for reference.The microstructure and properties of Ag-Au,Ag-Au-Cu,Ag-Au-Ce and Ag-Au-Cu-Ce continuous casting alloys were studied through analysis techniques such as metallographic observation,differential calorimetry(DSC),X-ray diffraction(XRD),electrochemical workstation,and hardness testing.The effects of alloy elements Au,Cu,Ce on the metallographic structure,melting point,phase structure,hardness,corrosion resistance of silver alloys and the existence in the alloy and mechanism of action are investigated.The texture evolution of Ag-Au-X alloy during deformation was analyzed by electron backscatter diffraction(EBSD)technique,and the method of scanning electron microscope(SEM),push-pull test,high and low temperature cycle and other means was used to study the burning ball parameters on the morphology of Ag-Au-X alloy bonding wire free-air ball(FAB),the bonding strength of the Ag-Au-X alloy wire component and the reliability of the bonding component were analyzed.Microstructure and properties of as-cast alloys show that Ag-Au,Ag-Au-Cu,Ag-Au-Ce,Ag-Au-Cu-Ce continuous casting alloys have little change in melting point during heating,and there is no phase structure transition.Combined with XRD and Thephase diagram analysis shows that the alloying elements Au,Cu,and Ce are mainly present in the alloy in a solid solution manner.The solid solution strengthening effect Ag-Au-Cu alloy> Ag-Au alloy >Ag-Au-Ce alloy> Ag-Au-Cu-Ce alloy,the lattice constants are respectively: 4.10028,4.09656,4.09219,and 4.09094 nm.In terms of structure,the Ag-Au continuous casting alloy has continuous coarse columnar crystals parallel to the axis of the sample,and the structure is unevenly distributed perpendicular to the axis.There is no obvious rule.The grain size is large,and the average grain size is 1.20 mm.After adding the alloying elements Cu and Ce separately,the Ag-Au alloy structure is improved,the grains are refined and the distribution become more uniform.The average grain sizes of the cross-sections of Ag-Au-Cu and Ag-Au-Ce are 0.77 mm and 0.66 mm,respectively.Ag-Au-Cu-Ce alloy compounded with Cu and Ce has extremely uneven microstructure distribution and large grain size differences.The grain share of 0.2 ~ 0.4mm accounts for more than 55%,but the area occupied is about A quarter of the entire cross section.Ag-Au-Cu alloy has the highest self-corrosion potential of-77.3mV,which improves the corrosion resistance of Ag-Au alloy;Ag-Au-Cu alloy has the better hardness value,which is considered to be due to the fine grain strengthening mechanism dominating.Drawing deformation research shows that the hardness of Ag-Au-X alloy gradually increases,and the hardness of alloys with true strain of 0,0.82,1.20,1.83 and 2.41 are62.3Hv,86.2Hv,93.6Hv,97.2Hv,and 100.3Hv,respectively.With the progress of drawing,the grains of Ag-Au-X alloy gradually turned toward the cold drawing direction,and finally distributed in a fibrous shape parallel to the drawing direction;the center area of the alloy finally formed the <110> + <111> + <100> texture;during this process,the alloy mainly has two deformation mechanisms: slip and twinning.The low-angle interface mainly dominated by the slip is mainly at the center of the specimen,with twins as the main The angle interface mainly exists in the sample areas Ⅰ and Ⅱ.Ag-Au-X alloy bonding wire application performance research shows that 25μm Ag-Au-X alloy bonding wire has good morphology and stable ball forming performance under 55 mA,1.0ms preferred parameters.The average FAB diameter is 46.06μm,and the average eccentricity The angle is 2.7 °.The bonding wire components have high push-pull strength with the average breaking force value of 13.62 g and the shear force of 30.02 g.The tensile fracture is mainly concentrated on the neck of the solder ball,the highest point of the arc,and the second welding point.The position of the neck is an effective bond.There are a large number of grains existing along the axial direction of the bonding wire.which possess low-resistance characteristics.After the bonding,the alloy elements at the solderjoints diffuse sufficiently and a good metallurgical bond is formed;the failure reason of the high and low temperature cycle samples of the bonding wire bonding is mainly Insufficient welding at the second positive electrode of the positive electrode.