Study On Interfacial IMC Growth Mechanism Of High P Content Co-P/SAC/Co-P Solder Joint Induced By Temperature Gradient

The miniaturization and high integration of electronic components have become an important trend in the development of the present age.The reduction of solder joint size leads to a large increase in the ratio of Intermetallic Compound(IMC)in micro solder joint,which may eventually form the full IMC solder joint.It is difficult to solve the brittleness and hardness of traditional full IMC solder joints such as Cu-Sn and Ni-Sn interconnection,so it can not be applied to production practice.It is found that Co-based UBM with excellent performance is expected to replace Cu as the interlayer,but the full IMC solder joint of the Co-Sn interconnection system has not been studied yet.Some scholars have proposed that IMC growth at the Co-P/SAC105 interface can be induced by accelerating interatomic diffusion migration by temperature gradient.However,the solder joint size effect under thermal migration and the change of P content in Co-P UBM are both important factors affecting the induction of temperature gradient,which will greatly affect the growth behavior of IMC.Therefore,it is a key problem to study the mechanism of IMC growth of Co-P/SAC105/Co-P solder joint interface induced by temperature gradient to prepare full Co Sn₃micro solder joint.In this paper,Co-P/SAC105/Co-P flip chip solder joints with P content of 13at.%and20at.%were stressed at the temperature gradients of 2215?/cm and 3260?/cm,respectively.The effect of Co-P UBM structure change caused by P content change on the growth of Co Sn₃at the interface induced by temperature gradient was studied.Finally,amorphous Co-P UBM with P content of 20at.%was selected as the follow-up experiment object.Flip chip solder joints of 0.4 mm,0.5 mm and 0.6 mm were prepared and stressed at the temperature gradient of 2215?/cm and 3260?/cm to study the size effect of Co-P/SAC105/Co-P solder joints under thermal migration.In this paper,the morphology evolution and thickness change of the interfacial IMC were observed,the growth evolution law and mechanism of the interface microstructure were analyzed,and the performance change of solder joints under temperature gradient loading was tested.The most suitable way for interfacial Co Sn₃growth induced by temperature gradient was explored,and it provides the theoretical basis for the subsequent preparation of full Co Sn₃solder joints.Co-P/SAC105/Co-P solder joint under the continuous loading of the temperature gradient,the Co-20%P/SAC105 interfacial reaction was more intense,the Co-13%P/SAC105 interfacial Co Sn₃always presented fine needle-like and a small amount of tile-like.At the Co-20%P/SAC105 interface,needle-like Co Sn₃evolved into continuous dense layered Co Sn₃.The morphology evolution process could accelerate with the temperature gradient increased.Co Sn₃at the hot and cold interfaces of the solder joints showed asymmetric growth,and the asymmetric growth was more significant with the increase of temperature gradient.Co-13%P UBM has relatively good diffusion resistance.Sn diffusion rate in Co-13%P was slow during thermal migration,but with the increase of temperature gradient,the diffusion resistance of Co-13%P will be weakened to some extent.In Co-20%P UBM,Sn diffusion rate was the fastest,and Co and Sn have the most intense mutual diffusion reaction at the interface,which is more conducive to the growth of IMC.The results of Co Sn₃growth kinetics calculation showed that the diffusion flux of Co atoms in Co-20%P/SAC105/Co-20%P solder joints is larger.It meaned that the presence of amorphous Co-P UBM strengthens the induction effect of temperature gradient on the growth of the interfacial Co Sn₃IMC.The growth mechanism of interfacial IMC of 0.4 mm,0.5 mm and 0.6 mm Co-20%P/SAC105/Co-20%P solder joints under different temperature gradients was investigated.The results showed that the size effect was still applicable to the Co-P/SAC105/Co-P micro solder joint at the temperature gradients of 2215?/cm and3260?/cm,and the interfacial IMC growth rate increased as the size of the solder joint decreases,and the slow growth zone is delayed.The thickness of the IMC at the hot and cold ends increased sharply under 3260?/cm,and the total IMC increment of the 0.4 mm solder joint reached 133.41?m after 400 h,accounting for half of the solder joint height.Co Sn₃at the hot and cold end interface of solder joints with different sizes still showed asymmetric rapid growth under temperature gradient,but the decrease in solder joint size would enhance the asymmetry of IMC growth.Small-sized Co-P/SAC105/Co-P solder joints had a large concentration of Co atoms in the solder,and the concentration gradient of Co at the Co Sn₃/SAC105 interface was small.When the temperature gradient increased,more Co atoms migrated from the hot end to the cold end.The growth rate of IMC intensified the interfacial reaction and induced the rapid growth of Co Sn₃at the interface,which proved that the smaller the size of the solder joint,the stronger the induction effect of the temperature gradient on the growth of the interfacial IMC.Finally,the mechanical properties of different size solder joints under temperature gradient were studied.Small-sized solder joints have thicker IMC,but with the release of internal stress caused by the layer-by-layer peeling of Co-Sn-P IMC,the tensile strength of solder joints increases to a certain extent.The tensile strength test results showed that the tensile mechanical properties of the 0.4 mm solder joint were the best after 400 h at the temperature gradient.The use of amorphous UBM as an intermediate layer on small-sized solder joints is beneficial to maximize the induction of temperature gradients on the growth of interfacial IMCs on the premise of maintaining excellent mechanical properties.It has great guiding significance for the systematic preparation of full Co Sn₃flip-chip solder joints.