Research On Interfacial Reaction Of (111) Nanotwin Copper

Micro-interconnect technology is one of the cores of advanced packaging manufacturing,which essentially melts Sn-based solder and occurs liquid/solid interface reaction with Cu substrate to form Intermetallic Compound（IMC）layer by soldering technology.At present,the size of the advanced package interconnection structure has been reduced from hundreds of microns to tens of microns and developed to several microns,which puts forward new requirements for the properties of the interconnect materials.（111）nanotwinned Cu（nt-Cu）with preferred orientation has unique interfacial reaction characteristics and is considered as an ideal new substrate material.Using（111）nt-Cu as substrate,the effects of soldering temperature,soldering time,solder composition on the nucleation,growth,micro-structure and shear properties of IMC at solder joint interface were investigated.At the same time,electroplated polycrystalline Cu and rolled Cu were selected for comparative study.The isothermal soldering interfacial reaction of（111）nt-Cu/Sn（25μm）/electroplated polycrystalline Cu micro-joint was studied.The main research results of this thesis are as follows:（1）The effects of soldering temperature and soldering time on the interfacial reaction of（111）nt-Cu micro-joint:When the brazing temperature was 260℃,the initial grain morphology of Cu₆Sn₅ on（111）nt-Cu substrate was scallop-type.As the reaction time prolongs,the Cu-Sn bond bonding at the interface increases,and Sn atoms fall on the（21 1 3）surface of Cu₆Sn₅.Cu₆Sn₅ gradually shifts from[0001]to near the[2113]orientation.At300℃,the Cu₆Sn₅ grains on（111）nt-Cu substrate exhibit a prismatic shape of[2110],and the prism type of Cu₆Sn₅ maintains the preferred orientation of[2110]for a longer time,which also proves that the growth and orientation transition of Cu₆Sn₅ can be effectively inhibited by the prismatic shape of Cu₆Sn₅.（2）The effect of Cu concentration in the solder on the interfacial reaction of（111）nt-Cu micro-joints:The scallop-type Cu₆Sn₅ grains show preferential growth near the direction of[21 1 3]at 260℃,any Cu concentration or at 300℃,higher Cu concentrations（1.5 and 3.0wt.%）.However,the prism-type Cu₆Sn₅ grains had high[21 1 0]preferred orientation at 300℃and low Cu concentration（0 and 0.7 wt.%）.This is due to the small Cu₆Sn₅ clusters in the solder,which nucleate directly on（111）nt-Cu substrate,following the minimum lattice mismatch rule.However,the growth of IMC on rolled Cu substrate and electroplated polycrystalline Cu substrate was only affected by the size of Cu₆Sn₅ clusters with the change of Cu concentration.（3）Isothermal soldering interface reaction of（111）nt-Cu/Sn/electroplated polycrystalline Cu micro-joint:The concentration gradient of Cu atoms from（111）nt-Cu substrate to electroplated polycrystalline Cu substrate was established in the micro-joint,which driven Cu atoms to diffuse and migrate from electroplated polycrystalline Cu to（111）nt-Cu.Since（111）nt-Cu substrate has the lowest surface energy,a large number of twin boundaries,and a considerable number of triple junctions,The diffusion rate of Cu atoms and the vacancy concentration in the substrate were reduced,which inhibited the growth of intermetallic compounds and the formation of Kirkendal voids.