The Effects Of Trace Element Addition On Microstructure Evolution Of Solder Joints Undergoing Solid-liquid Electromigration

5G,new energy,semiconductor chips and other fields continue to require micro-packaged electronic devices with stronger functions,smaller sizes,and higher reliability.Driven by the goal of“low-temperature connection and high-temperature service”,full IMC solder joints prepared based on the solid-liquid electromigration mechanism have attracted much attention.However,the traditional Cu-Sn solder joints were relatively brittle,so improving the mechanical properties of the solder joint IMC compound prepared by electromigration has become one of the urgent problems to be solved in the field of electronic packaging technology.This paper was based on the structure of solid-liquid electromigration to increase the diffusion flux,and the evolution law of the interface microstructure of Cu/SAC305/Cu,Cu-Ni/SAC305/Cu-Ni and Cu-Co/SAC305/Cu-Co solder joint systems Analyze and explain the mechanical properties.In the classic Cu/SAC305/Cu system,compared to the solder joints without current load,when the temperature was 260?and the current load of 2.89×10²A/cm² was applied,the interface compound had obvious polar growth phenomenon.Under the action of current,the Cu₆Sn₅[100]crystal orientation tended to be parallel to the direction of the loaded current,and the fracture cracks propagate in the thicker Cu₆Sn₅ IMC layer near the anode interface.With the extension of the bonding time,the tensile strength of the solder joints gradually decreased,and the fracture showed a brittle fracture mode.At the same time,the tensile strength of the solder joints after the current load was applied under the same bonding time decreased.At a temperature of 260°C and a current load of 2.89×10² A/cm²,the incorporation of Ni in the substrate changes the structure and morphology of the interface compound.When 1.5 wt.%Ni was added,the solder joint interface(Cu,Ni)₆Sn₅ compound exhibits a polar growth phenomenon.When 5 wt.%Ni was added,the compound polar growth phenomenon becomes weaker,and when the bonding time is extended to 10 h At this time,the(Cu,Ni)₆Sn₅ grains completely realize the non-interface growth phenomenon,and many(Cu,Ni)₆Sn₅ grain regions are concentrated and distributed in the solder.The[100]direction of(Cu,Ni)₆Sn₅grains has no correlation with the current direction.With the increase of Ni addition,the(Cu,Ni)₆Sn₅ grains are refined.During the stretching process of the solder joint samples,the hindering effect of the refined and homogeneous IMCs and the(Cu,Ni)₆Sn₅ particles dispersed in the solder makes the tensile strength of the solder joints improved.In the solid-liquid electromigration system of the solder joint with a temperature of 260?and a current density of 2.89×10² A/cm² composed of a bidirectional Cu-Co substrate,the addition of Co will cause the solder joint IMCs to be in the area of the solder away from the substrate interface disperse nucleation,and as the bonding time was extended to 10 h,the solder joint interface can form a complete full IMCs solder joint filled with(Cu,Co)₆Sn₅.In the solder joints with 30 wt.%Co addition,the flake(Co,Cu)Sn₂ grains were distributed in(Cu,Co)₆Sn₅ IMC to form many“islands”.After 50 wt.%Co was added,the proportion of(Co,Cu)Sn₂ phase in the solder joint and the area of the concentrated area were further increased and part of the(Co,Cu)Sn₂ phase nucleates around the cobalt-rich phase with the cobalt-rich phase as the center.In addition,the addition of Co increased the hardness and Young's modulus of(Cu,Co)₆Sn₅,and refined the IMCs grains.In addition,the uniform distribution of(Co,Cu)Sn₂ grains throughout the solder joint inhibited crack propagation.The combined effect of the joints improves the tensile strength of the solder joints.