| Ni-Sn TLPS（Transient Liquid Phase Sintering）possesses the characteristics of lower bonding temperature/higher temperature resistance,simply equipped process conditions,and low cost,which perfectly meet the requirements of packaging process for the new generation semiconductor devices.The kinetics during the bonding process is the theoretical foundation for controlling the microstructure and optimizing the properties of bonded joints,which are of great significance for the TLPS packing of the new generation of power chips.In this paper,the interdiffusion coefficient of Ni-Sn in Ni3Sn4 was determined by studying the kinetics of Ni-Sn one-dimensional interfacial reaction.The reaction behavior between solid Ni and liquid Sn during the TLPS process was systematically investigated by a physical simulation method,in which Ni-Sn mixed powder compacts were sintered.On this basis,combined with the reaction-diffusion theory,a kinetic unit cell model and corresponding kinetic equations were established to describe the Ni3Sn4 growth during the Ni-Sn TLPS process,and their analytic solutions and regression solutions were obtained.By measuring the melting enthalpy of residual Sn in the samples,and defining the transformed rate of Sn φSn as a characterization parameter of the isothermal solidification kinetics,the Ni3Sn4 growth kinetics and the isothermal solidification kinetics were systematically investigated.Finally,the Ni@Sn core shell powder with high Sn content was prepared for the TLPS bonding on the Ni substrate,and the microstructure,properties and the kinetics of the bonded joints were studied.The main results are as follows:The kinetic model and equations of Ni3Sn4 growth at the Ni-Sn onedimensional solid-liquid interface were established.Under the condition of accurate analysis,that is,with consideration of the volume change caused by phase transitions,the solution of the kinetic equations of Ni3Sn4 growth was derived as lIMG=0.584(（?）t1/2).Combined with the Ni-Sn one-dimensional interfacial reaction experiments,the relationship between temperature and the interdiffusion coefficient of Ni-Sn in Ni3Sn4 was obtained as （?）=3.76 × 10-12exp（-24.76kJ/mol/RT）.Results showed that there was an obvious effect on the determination results of the interdiffusion coefficient.Ni3Sn4 was the main intermetallic compounds formed during the TLPS process.Only Ni3Sn4 formed when liquid Sn remained in the samples,which was distributed around the Ni particles.Only if the liquid Sn was consumed,Ni3Sn began to form from Ni3Sn4.On this basis,combined with the reaction-diffusion theory,the kinetic unit cell model and corresponding kinetic equations of Ni3Sn4 growth were established.Under the condition of accurate analysis,that is,with consideration of the volume change,the implicit solutions of the kinetic equations were obtained as:r12+0.3397（3.9438r03-2.9438r13）2/3=-0.0691Dt+1.3397r02,r2=（3.9438r03-2.9438r13）1/3,and the regression solutions were fitted as:r1=r0-0.06184（（?）t）0.6969,r2=r0+0.5588（（?）t）0.3899.It showed that the theoretical results of Ni3Sn4 growth were confirmed to coincide well with the experimental results.The transformed rate of Sn φSn was defined as the ratio of the Sn mass in the Ni3Sn4 layer to the initial Sn mass.It was proved to be a more proper kinetic parameter to precisely characterize the kinetics of isothermal solidification in the Ni-Sn TLPS bonding.When the isothermally sintered temperature was rised or the initial Ni particle size was decreased,the kinetics of the Ni-Sn TLPS bonding process was quicken.The mass ratio of Ni to Sn had no effect on the growing kinetics of the Ni3Sn4 layer,but had effect on the isothermal solidification kinetics.The larger the mass ratio of Ni to Sn was,the faster the isothermal solidification kinetics would be.For Ni substrates,compared with that of Ni-Sn mixed powder TLPS,the microstructure of Ni@Sn powder TLPS bonding joint was more uniform,and the porosity was lower.At the early stage of the isothermal solidification,there was little difference in the kinetics（including Ni3Sn4 growth kinetics and isothermal solidification kinetics）between Ni@Sn powder TLPS and Ni-Sn mixed powder TLPS.At the later stage of the isothermal solidification,the kinetics of Ni@Sn powder TLPS was significantly faster than the Ni-Sn mixed powder TLPS,and the difference increased with the prolongation of isothermal sintering time,the decrease of the initial Ni particle size and initial Ni-Sn mass ratio,respectively. |
