Study On The Bonding And High Temperature Response Mechanism Of Sn₅Sb-xCuNiAg/Cu?Ni?Micro Solder Joints

With the wide application of the third generation semiconductor power devices,higher requirements are put forward for electronic device packaging technology and mechanical properties of micro solder joints.Among them,the improvement of fatigue resistance and creep resistance of micro solder joints is very important to improve the reliability of micro solder joints.The purpose of this paper is to study the high temperature resistance of the Sn₅Sb-x Cu Ni Ag/Cu?Ni?joints,and to compare with Sn-5Sb solder to study the effect of trace elements Cu,Ni,Ag and analyze the influence mechanism.At the same time,compared with SAC305,the properties of the new solder were evaluated comprehensively from shear strength,plasticity,creep resistance,hardness,elastic modulus and other mechanical properties,providing basis and theoretical support for the research and development of high-performance high-temperature lead-free solder.The solderability of three kinds of Sn₅Sb-x Cu Ni Ag solder was studied,including the influence of different temperature,wetting time and flux on the wettability.Compared with Sn-5Sb solder,the mechanism of trace elements affecting wettability was analyzed.The growth and evolution of interfacial IMC of micro solder joints on Cu and Ni?Cu?substrates during aging at different temperatures were analyzed.The shear experiment of the aged micro solder joints was carried out to obtain the bonding strength of the joints and analyze the action mechanism of trace elements.The hardness and elastic modulus of Sn₅Sb-x Cu Ni Ag/Cu,Sn-5Sb/Cu and SAC305/Cu solder joints after different aging time were studied by nano indentation test.The hardness,elastic modulus and plastic factor of the matrix solder of the micro solder joints at different temperatures were studied.The high temperature creep properties of three kinds of micro solder joints were studied from three aspects:creep stress index,steady-state creep rate and creep activation energy.The wettability of SS1CN0.1A solder with different fluxes on Cu and Ni?Cu?substrates was studied.The results showed that rosin flux had the best wettability.Through the wetting experiments on Cu and Ni?Cu?substrates,it is found that the wettability of solder increases with the increase of temperature.Compared with Sn-5Sb solder,the addition of trace elements Cu and Ni can improve the wettability of solder on Cu and Ni?Cu?substrates.The mechanism of improving wettability by trace elements was analyzed:the radii of Cu and Ni atoms are close,and the crystal structures of Cu and Ni are all face centered cubic.The inherent affinity between Cu and Ni determines that the addition of Cu and Ni in Sn₅Sb-x Cu Ni Ag solder is conducive to the improvement of wettability on Cu and Ni?Cu?substrates.The interface IMC growth model of micro solder joints with the same size under different aging conditions was established.Under the aging conditions of?T=150?,t??0 h?2016 h??and?T=180?,t??0 h?336 h??,the thickness of the interfacial IMC layer was positively related to the square root of aging time.The IMC growth model shows that the diffusion coefficient D of the interface of the micro solder joints on the Cu substrate decreases when aging at 150?and increases when aging at 180?.The addition of trace elements makes the interface diffusion coefficient of micro solder joints on Ni?Cu?substrate decrease when aging at 180?.The effect of trace elements on the evolution of interfacial IMC during aging was clarified:the addition of trace elements Cu and Ni will have a significant effect on the precipitation of new phases in the process of IMC growth.On the Cu substrate,the addition of trace elements makes the phenomenon of IMC precipitation at the interface of micro solder joint restrained significantly.On Ni?Cu?substrate,the interfacial IMC of micro solder joint changes from a kind of?Cu,Ni?₃Sn₄ IMC structure before and after aging to a kind of?Cu,Ni?₃Sn₄structure before and after aging,which is the upper/lower structure of?Cu,Ni?₆Sn₅/?Cu,Ni?₃Sn₄ with two components.The effect of trace elements on the shear resistance after high temperature aging was analyzed.The experimental results show that the shear strength of micro solder joints of Sn₅Sb-x Cu Ni Ag solder on Cu and Ni?Cu?substrates is higher than that of Sn-5Sb solder joints,and trace elements enhance the shear strength of solder joints.In addition,the strength decreased more slowly during high temperature aging.With the addition of trace elements,the fracture mode of micro solder joint changed from brittle fracture in the early stage to ductile fracture in the later stage.Among them,Cu/Sn-5Sb/Cu solder joints are ductile fracture before aging and intergranular brittle fracture after aging.Before aging,the fracture of Cu/SAC305/Cu solder joint is ductile fracture,and after aging,it is transgranular brittle fracture,which can be observed cleavage fracture.After aging,there are second phase?Cu,Ni?₆Sn₅ particles in the fracture dimple of Cu/SS0.5CN0.5A/Cu solder joint,which are uniform in size,deep in dimple and large in dimple,and the solder joints has strong plastic deformation ability.The influence of trace elements on the growth of interfacial IMC makes the strength of solder joint interface increase,and the fracture position will not transfer to the interface after aging.From the comparison of the shear force-displacement curves of Cu/SS0.5CN0.5A/Cu and Cu/Sn-5Sb/Cu solder joints,it was concluded that the trace elements can improve the plasticity of the solder joints.A large number of intermetallic compounds with small size formed in the matrix solder of micro solder joint,which will increase the number of dislocations and provide more obstacles for dislocation accumulation,and hinder the intergranular slip,resulting in the increase of shear strength and plasticity.The in-situ plasticity and creep behavior of micro solder joints at different temperatures and the plasticity after high temperature aging were studied.The mechanism of the influence of trace elements on the creep behavior was analyzed,and the mechanism of the formation of the ring-shaped plastic deformation area around the indentation under a long creep time?120 s?was revealed.The SS0.5CN0.5A/Cu solder joint in Sn₅Sb-x Cu Ni Ag/Cu was taken as a representative and compared with Sn-5Sb/Cu and SAC305/Cu solder joints.Three constitutive models of microjoints hardness with aging time were established.Under the aging test conditions?T=150?,t??0 h?2016 h??,the hardness of matrix solder with aging time presents a linear function.A constitutive model of hardness,modulus of elasticity,plasticity factor and temperature is established.When the temperature is between 25??150?,the hardness,modulus of elasticity and temperature show a linear function,and the plasticity factor decreases exponentially with the temperature.The creep stress index and creep activation energy of SS0.5CN0.5A/Cu solder joints are higher than those of Sn-5Sb/Cu and SAC305/Cu solder joints.That is,SS0.5CN0.5A/Cu solder joints have higher creep resistance at high temperature.By comparing with Sn-5Sb/Cu solder joint,the mechanism of the influence of trace elements on the high temperature creep performance of micro solder joint was revealed,that is,trace elements increase a large number of fine compounds with dispersed distribution in the matrix solder.Under the condition of stress,dislocation accumulation and slip are affected,and a large amount of IMC hinders dislocation climbing.The decrease of dislocation climbing rate determines the decrease of creep rate drop.The high temperature creep resistance of the solder joint was enhanced.The cyclic plastic deformation zone is mainly the crack produced by the creep fracture along the crystal.