Effective Characterization Of Mechanical Parameters Of Lead-Free Solder Using Nano-Indentation

The rapid development of science and technology has continuously promoted the birth of various new materials.The mechanical properties of materials characterized by tension,compression,torsion and other traditional testing methods are no longer applicable to some specific new materials/structures,such as thin film,tiny solder joints etc.,in the field of micro-nano manufacturing.The nano-indentation can obtain the relevant mechanical properties parameters of the material through the local in-situ indentation test of the surface micro-region of the material,which has a strong universality.However,the accuracy and effectiveness of nano-indentation in characterizing the mechanical properties of engineering materials are still in question.Taking lead-free solder alloy?SnAg3.5?as the research object,this paper presents an effective method based on nano-indentation method to characterize elastic-plastic mechanical parameters and strain rate sensitivity of metals.The main contents and results are as follows:The elastoplastic mechanical parameters of lead-free solder SnAg3.5were extracted by nano-indentation method combined with finite element numerical simulation.Using a cylindrical indenter and two pyramid indenters to conduct nano-indentation test of lead-free solder,based on the cylindrical indenter testing for the modulus of solder alloys.The strain gradient plasticity theory is used to modify the test results of two pyramid indenters and the corresponding representative stress and representative plastic strain values are obtained by inversion analysis.The initial yield stress and strain hardening index of solder alloy are obtained by solving the equations,and then the power law elastoplastic constitutive relation of lead-free solder is obtained.An effective method for characterizing the elastoplastic mechanical parameters of metal materials by nano-indentation is also presented.The strain rate sensitivity of lead-free solder SnAg3.5 was investigated by nano-indentation technique.The nano-indentation test of solder SnAg3.5 was carried out under four different strain rates????/P?(0.005s^-1,0.01s^-1,0.05s^-1 and 0.1s^-1)in combination with the continuous stiffness Measurement.The strain rate sensitivity index value m of different depth zones was calculated.Based on the strain gradient plasticity theory,the influence of the size effect on the four strain rate loading processes is eliminated,and the strain rate sensitivity index m₀after removing the size effect is obtained.Comparing with the strain rate sensitivity index of different depth zones affected by the size effect,the results show that the strain rate sensitivity index value after removing the indentation size effect is larger,and the strain rate sensitivity index increases with the indentation depth.It shows the necessity of eliminating the size effect of indentation when analyzing the sensitivity of the indentation strain rate.