Research On Creep Behavior Of Ag Nanoparticle-modified Graphene Sn-Ag-Cu Solder Joints Based On Nanoindentation

With the rapid development of the electronics industry,higher requirements have been placed on the thermal,electrical and mechanical properties of existing lead-free solders.The composite solder alloys formed by adding Ag nanoparticle-modified graphene(Ag-GNSs)to the conventional Sn-Ag-Cu solder alloys has better mechanical properties than the Sn-Ag-Cu solder alloys.Solder joints are subjected to heat and stress during use which can cause creep failure.The traditional creep constitutive model is an empirical formula with no physical meaning,which cannot reflect the actual mechanical behavior of the material creep process.Therefore,the existing model needs to be modified according to the physical properties of the material.In this paper,0.1wt.% Ag-graphene was added to 96.5Sn-3.5Ag-0.5Cu(SAC)by mechanical mixing method(H)and ball milling method(Q)to prepare composite solder joints.The traditional creep constitutive model was modified based on the microstructure characteristics of solder joints,and the accuracy of the constitutive model was verified by the results of nanoindentation tests at different temperatures.The maximum penetration depth of solder joints formed by H/0.1Ag-GNSs and Q/0.1Ag-GNSs were reduced by 2.55% and 5.24%,respectively,by the loaddisplacement curve of the nanoindentation test at room temperature.The displacementtime curve shows that the indentation depth variation of solder joints formed by H/0.1Ag-GNSs and Q/0.1Ag-GNSs during the load-bearing period is reduced by 2.03%and 5.62%,respectively,compared with solder joints formed by SAC.The solder joint formed by Q/0.1Ag-GNSs has the strongest resistance to deformation,the solder joint formed by H/0.1Ag-GNSs is the second,and the solder joint formed by SAC is the weakest.Based on the Shear-lag model and Gao model,the load transfer effect of graphene in composites is considered,and the azimuth angle of the olefin is introduced.A method for calculating the stress of Ag-graphene is proposed.At the same time,dislocation strengthening,grain refinement and Orowan effect in Ag-graphene Sn-Ag-Cu solder joints are considered.The Clyne method is used to synthesize the strengthening stress to form effective stress.Finally,the effective stress is brought into the Norton model to obtain modified creep constitutive model.Comparing the creep data of the Ag-graphene Sn-Ag-Cu solder joint calculated by the nanoindentation data with the modified creep constitutive model,it is found to be in good agreement.The results reflect that the model has feasibility in predicting and quantifying the creep behavior of solder joints formed by Ag-graphene Sn-Ag-Cu solder alloys.According to the nanoindentation data at high temperature,the creep activation energy of solder joints formed by SAC was calculated to be 36.12 k J/mol,and the creep activation energy of solder joints formed by H/0.1 Ag-GNSs was 45.42 k J/mol.