Growth Behavior And Mechanism Of Intermetallic Compounds In Co-P/Solder Interface Under Temperature Gradient

With the development of the Internet of Things and artificial intelligence,in order to satisfy the needs of light weight,portability,fast computing and multi-function,electronic products require smaller and higher integration density of devices while miniaturizing.Due to the development of integrated circuit silicon chip technology,packaging technology has transitioned from 2D packaging to 3D packaging.The 3D packaging will cause higher Joule heating effect than the 2D packaging structure,making the intermetallic compound?IMC?nucleation and growth in the micro solder joints more sensitive.In particular,when high-power devices such as IGBTs are in service,the huge temperature difference between the hot end and the heat sink end of the micro-interconnect causes the solder joint to withstand a large temperature gradient,resulting in the rapid failure of traditional Cu-Sn solder joints under the coupling of thermal aging and thermal migration.The study found that Co and Co-P are expected to be used as substitutes for traditional Cu UBM,which can greatly improve the performance of solder joints.However,the growth law of the interfacial IMC under large temperature gradients has not be studied.Therefore,studying and controlling the growth of the Co-P?Co?/lead-free solder joint interfacial IMC under extreme temperature gradients is an important way to improve the reliability of solder joints and select new micro solder joints,which is of great significance to solve the rapid failure of small solder joints of power devices under large temperature gradients.Primarily,Co/Sn and Co-P/Sn couples were used as experimental research objects.The interfacial reaction under 220?and 320?was investigated,the growth and evolution of the interfacial IMC was analyzed,and the Co-P UBM with optimal P content?5at.%?was selected for subsequent experiments.Then Co-P/Sn/Co-P,Co-P/Sn0.5Cu/Co-P,Co-P/SAC105/Co-P were prepared by Co-5at.%P UBM,which were stressed at the temperature gradients of 1110?/cm and 1620?/cm.Then analyze the growth and evolution rules and mechanism of interfacial IMC,establish the growth mode of interfacial IMC under extreme temperature gradient,and evaluate the reliability and application prospect of new Co-P/lead-free solder joints.Firstly,the interfacial reactions of Co/Sn and Co-P/Sn under isothermal aging were studied.The results show that when the P content is 13at.%and 20at.%,a thick continuous sheet of CoSn₃ is formed at the Co-P/Sn interface,which leads to the deformability of the plastic phase Sn cannot be exerted,which embrittle the micro solder joints.Co/Sn and Co-5at.%P/Sn couples react to form a thin,dense layered IMC.Among them,Co-5at.%P/Sn couple form diffusely distributed CoP₂ and SnP_0.94,and[100]preferred growth orientation CoSn₃ grains,which greatly enhances the stability of the interfacial IMC and the diffusion barrier performance.This has important research value for improving the impact resistance,drop resistance,long-term reliability,and reliability at high temperature of micro solder joints.Therefore,Co-5at.%P UBM is used as the research object for temperature gradient stressing experiments.Then,the growth behavior and mechanism of interfacial IMC of Co-P/Sn/Co-P,Co-P/Sn0.5Cu/Co-P and Co-P/SAC105/Co-P under large temperature gradient were studied.The results show that under the temperature gradient,the thermal migration effect of all three solder joints occurs,and as the temperature gradient increases,the thermal migration effect is stronger,the asymmetric growth of the interface IMC is more significant,and the thickness increase of the interfacial IMC in the three solder joints above is mainly due to the growth of CoSn₃.In Co-P/Sn/Co-P,only the single crystal?-Sn hinders thermal migration,the thermal migration effect is strongest;in Co-P/Sn0.5Cu/Co-P,except?Cu,Co?Sn₃ covers the surface of the interfacial CoSn₃ hindering thermal migration,?-Sn in the solder also hinders thermal migration to a certain extent,the thermal migration effect is weak;in Co-P/SAC105/Co-P,the network distribution of Ag₃Sn in the solder greatly weakened the thermal migration,and the thermal migration effect was the weakest.Therefore,in terms of thermal migration effect in solder joint:Co-P/Sn/Co-P>Co-P/Sn0.5Cu/Co-P>Co-P/SAC105/Co-P.However,?Cu,Co?Sn₃ in Co-P/Sn0.5Cu/Co-P is continuously distributed on the surface of interfacial CoSn₃,which reduces the direct contact between CoSn₃ and solder,greatly reduces the growth rate of the interfacial CoSn₃.Therefore,in terms of the interfacial IMC growth rate:Co-P/Sn/Co-P>Co-P/SAC105/Co-P>Co-P/Sn0.5Cu/Co-P.In addition,Cu segregation may occur in Co-P/Sn0.5Cu/Co-P micro interconnects to generate coarse Cu₆Sn₅/CoSn₃ structures,but experiments have proven that the structure is stable under the effect of temperature gradients,which has little effect on the reliability of solder joints.