Study On The Characteristics And Kinetics Of Ni-Sn TLPS Bonding Process

Transient liquid-phase sintering?TLPS?bonding is a process for high temperature packaging,which has been considered to be promising for packaging of the new generation power chip.In this dissertation,the Ni-Sn system was employed as TLPS reactive system to bond Ni plates.The microstructural evolution of the bonding layer was studied systematically.Embarking from the characterization of dynamics,the kinetics of TLPS bonding was studied from three levels—experiment,physical simulation and established theoretical model.Furthermore,the mechanical property and high temperature aging characteristics of the joints were investigated in depth.The Cu/Ni-Sn/Cu TLPS bonding was discussed in the last chapter as well.The microstructural evolution of Ni/Ni-Sn/Ni TLPS bonding layer shows that after holding for 240 min at 300 ? and 180 min at 340 ?,Sn was completely transformed into Ni-Sn intermetallic compounds and the bonding layer was mainly composed of N3Sn4 and residual Ni particles.The physical model of the microstructural evolution in the bonding layer was established.The voids were formed within the bonding layer,which is because of the formation of rigid skeleton structure of Ni3Sn4 and a large shrinkage of volume?14.70¹4.94%?during the Ni-Sn isothermal solidification.When Sn was completely transformed into Ni-Sn intermetallic compounds,the porosity reached the maximum.And then the voids began to decrease and shrink with the increasing of holding time.Finally,the bonding layer underwent sintering densification and the voids disappeared completely.The essence of Ni/Ni-Sn/Ni TLPS bonding is a process of compound transformation,in which liquid Sn reacts with solid Ni to form Ni-Sn intermetallic compounds.Therefore,the kinetics can be characterized by the residual rate of Sn in the bonding layer.The melting enthalpy of actual bonding layer was measured by differential scanning calorimetry?DSC?analysis.The residual rate of Sn and the thickness of Ni3Sn4 layer at different holding time were calculated to study the kinetics.Go a step further,the bonding process was simulated by physical method.It revealed that the thickness of Ni3Sn4 layer is linear with t0.308 The kinetics model for the compound transformation in Ni/Ni-Sn/Ni TLPS bonding process was established and the kinetic equations were deduced.It is consistent with the variation of Ni3Sn4 thickness in actual and simulative bonding layer.The study of bonding characteristics shows that the shear strength of joint was increased with the prolonging of holding time and when Sn was completely transformed into Ni-Sn intermetallic compounds,the high-temperature shear strength was not clearly reduced and up to 28.2 MPa.It was also found that whether at room temperature or high temperature,the fracture surfaces were very similar,which indicated that the joints had good mechanical properties at high temperature.The aging tests show that when aged at 350 ?.the microstructure of the bonding layer was stable.When the aging temperature was increased to 500?.however,the residual Ni particles were gradually dissolved and a stable structure with dominated Ni₃Sn₂ was formed after aging for 100 h.Compared with the untreated joint,the strength of the joint was increased slightly.The study of Cu/Ni-Sn/Cu TLPS bonding process shows that after holding for 240 min at 300 ? and for 180 min at 340 ?,Sn was completely transformed into intermetallic compounds and the bonding layer was mainly composed of?Ni1-yCuy?3Sn4 layer,?Cu1-xNix?6Sn5 layer.Cu3Sn layer and residual Ni particle.In the bonding process,the amount of voids was increased in a period of time,but with the holding time prolonging,these voids disappeared.The kinetic research shows that the thickness of?Cu1-xNix?6Sn5 was linear with t1/2,so did Cu3Sn.As the holding time extended,the shear strength of the joints was increased firstly and then decreased.When holding for 90 min at 340 ?,the shear strength reached the maximum 27.0 MPa.