| In recent years,wafer bonding has been seemed as an important bonding method in the manufacture of micro-electro-mechanical systems(MEMS)because it enables the fabrication of silicon-on-insulator(SOI)substrates and allows the three-dimensional(3D)packaging of micro-components.Among the intermediate-layer bonding methods,transient-liquid-phase(TLP)bonding,is an especially attractive bonding method for the packaging of the MEMS devices which operate at high temperatures.In the field of integrated circuit packaging,an interconnection is often composed of two different base metals or metallizations,as an example,the asymmetrical Ni/Sn/Cu system has been widely utilized in the current flip-chip assembly structures.In this work,the interfacial metallurgical reaction of the intermetallic joints formed in the Ni/Sn/Cu system with a variety of transient liquid phase soldering temperatures was investigated,the evolution of grain morphology was characterized,the influence mechanism of soldering temperature and Ni concentration on the grain morphology evolution of Intermetallic Compounds(IMC)was revealed,the effect of particle morphology on the mechanical properties of the joint was evaluated.Then,on the basis of Ni/Sn/Cu interconnect,the influence of Ni particle addition on the nucleating pattern of intermetallic grains during the bonding process was investigated,the addition of Ni particles and the soldering temperature were explained from the theoretical and experimental perspective.The main conclusions are summarized as follows:The grain morphologies and mechanical strengths of the intermetallic joints formed in a Ni/Sn/Cu system by the TLP soldering at 260 ?,300 ? and 340 ? were investigated.The grain morphology evolution of the(Cu,Ni)6Sn5 intermetallic compounds(IMCs)was highly correlated with the Ni concentration gradient across the joints and strongly affected by the soldering temperatures,which was analyzed in detail from the aspect of thermodynamics.The shear strengths of the three types of intermetallic joints were 49.8 MPa,50.3 MPa and 42.7 MPa,respectively.The results of nanoindentation test show that the greater the mechanical strength of the region with higher Ni content,the highest Young's modulus and indentation hardness in the fine rounded grain area in the 260 ? joint were 157.44GPa/7.98 GPa.The intermetallic joints formed in Cu/Sn-x wt%Ni/Cu system with different Ni particles by the TLP soldering at 260 ?,then,the intermetallic joints formed in a Cu/Sn-4 wt%Ni/Cu system by the TLP soldering at 260 ?,300 ? and 340 ?.Ni particle was validated as an effective grain refiner for the Cu-Sn TLP wafer bonding joints,which could induce a dispersive non-interfacial nucleation of intermetallic grains during the bonding process,effectively preventing the grain mergence phenomenon,leading the(Cu,Ni)6Sn5 grain refinement of the formed intermetallic joints.With increasing the Ni particle addition,there were significant reductions in both the(Cu,Ni)6Sn5 grain size and the Cu3 Sn layer thickness,6 wt% addition of Ni particles even led a formation of the homogeneous(Cu,Ni)6Sn5 joints with an average grain size of 1.3 ?m.However,the magnitude of grain refinement induced by Ni particle addition exhibited an inverse relationship with the bonding temperature.With the bonding temperature subsequently increased to 340 ?,the average grain size of(Cu,Ni)6Sn5 grains regained to 3.7 ?m,meanwhile,the average layer thickness of Cu3 Sn grains also regained to 2.5 ?m.The shear test results show that the fracture position of the joint occurs in the(Cu,Ni)6Sn5 grain area,with the increase of the content of the Ni particles,the greater the mechanical strength of the joint,the maximum of the shear strength,the young's modulus and the indentation hardness when the content of Ni is 6 wt%,respectively,65.7MPa,159.502 GPa,7.89 GPa.With the increase of the bonding temperature,the shear is cut,The shear strength of 340 ? joint is 52.7 MPa. |
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