Effect Of CNT Surface Modification On Microstructure And Shear Properties Of Lead-free Solder Joints

With the development of electronic products towards functional integration and volume miniaturization,the interconnection solder joints inside electronic equipment will inevitably face more severe challenges.The preparation of high-quality solder joints can effectively ensure the service of high-reliability electronic products.Carbon nanotubes(CNT)have excellent mechanical properties and high thermal conductivity.Adding them as a reinforcing phase to solder joints is an effective method to enhance solder joint reliability.In order to reduce the agglomeration effect of carbon nanotubes and improve its enhancement effect on the reliability of solder joints,this paper prepared surface-modified CNTs by electroless plating,and explored the influence of the addition of surface-modified CNTs on the thermal and mechanical properties of the SAC305 solder matrix.Prepare surface-modified CNT composite solder and surface-modified CNT composite flux at the same time,apply the two materials to reflow soldering experiments to prepare lead-free solder joints,and explore the growth kinetics of interface IMC and morphology evolution under the action of surface-modified CNT.In addition,the shear strength of the solder joint was tested through the solder joint shear experiment,and the effect of surface modification CNT on the reliability of the solder joint was studied.The experiment uses electroless plating to prepare nickel-modified carbon nanotubes(Ni-CNT)and copper-modified carbon nanotubes(Cu-CNT).Transmission electron microscopy shows that the surface of CNT has dark nanoparticles.According to the results of EDX and XPS,It was confirmed that Ni and Cu were used as the plating layer to successfully modify the CNT.DSC results show that the addition of surface-modified CNTs can increase the melting point of lead-free solders,the mass fraction of surface-modified CNTs increases,and the melting point of composite solders also increases.Nanoindentation experiments show that the hardness and modulus of surface-modified CNT composite solders increase with the increase of surface-modified CNT content,indicating that the addition of surface-modified CNTs can significantly improve the mechanical properties of SAC305 solders.In order to study the interface reaction between the surface-modified CNT composite solder and the Cu substrate,a reflow soldering experiment was carried out at 250 ? for 5minutes,and SAC-x Ni-CNT/Cu(x=0.1 and 0.2 wt.%)was prepared.And SAC-x Cu-CNT/Cu(x=0.1 and 0.2 wt.%)composite solder joints,and solid-state aging at 150 ? to simulate the service state of the solder joints.The results show that the surface-modified CNT as the reinforcement phase of SAC305 solder can inhibit the growth of IMC at the solder joint interface and the coarsening of IMC grains.As the mass fraction of surface-modified CNT increases,the inhibitory effect increases.Among them,the growth rate of the IMC layer of the composite solder joint with a surface modified CNT mass fraction of 0.2 wt.% is the lowest,and the IMC grain refinement effect is the most obvious.Shear tests show that adding the mass fraction of surface-modified CNTs can improve the shear strength of solder joints.When the mass fraction of surface-modified CNT reaches 0.2 wt.%,the fracture mode of the solder joint changes from mixed fracture to ductile fracture.In order to explore the reliability of SAC305/Cu solder joints treated with surface-modified CNT composite flux,reflow soldering experiments were carried out,and aging experiments were carried out at 150 ? for 0,24,120,240,and 360 hours.The results show that the use of composite flux to treat solder joints can inhibit the growth of interface IMC.As the mass fraction of surface modified CNT in the composite flux increases,its inhibitory effect on the growth of the interface IMC layer increases first and then decreases.The use of 0.1 wt.% surface modified CNT composite flux to treat the solder joints has the most obvious inhibitory effect on the growth of the interface IMC layer.In addition,in order to study the effect of ultrasonic vibration on composite flux solder joints,ultrasonic assisted welding was used in the preparation of composite flux solder joints.Experimental results show that ultrasonic vibration can reduce the thickness of the interface IMC layer,refine the IMC grains,and significantly improve the shear strength of the solder joints.After applying ultrasound in the reflow soldering process,the fracture mode of the solder joint changes from mixed fracture to ductile fracture.