Anand Parameters Determination for SnAgCu Solder Bearing Micro-amounts Rare Earth Ce

摘要

SnAgCu solder system with the addition of rare earth Ce,which has better thermo-mechanical properties compared to those of SnPb solder,is regarded as one of the promising candidates for electronic assembly.Moreover,the SnAgCuCe solder alloys can provide good quality joints with Cu substrates.However,there is few report of the constitutive model for SnAgCu solder bearing micro-amounts rare earth Ce.In this paper,the unified viscoplastic constitutive model,Anand equations,is used to represent the inelastic deformation behavior for SnAgCu and SnAgCuCe solders.In order to obtain the acquired data for the fitting of the material parameters of this unified model,a series of experiments of constant strain rate test were conducted under isothermal conditions at different temperatures.The Anand parameters of the constitutive equations for SnAgCu and SnAgCuCe solder were determined from separated constitutive relations and experimental results.Nonlinear least-square fitting was selected to determine the model constants.And the simulated results were then compared with experimental measurements of the stress-inelastic strain curves:excellent agreement was found.The model accurately predicted the overall trend of steady-state stress-strain behavior of SnAgCu and SnAgCuCe solders for the temperature ranges from 25 ℃ to 150 ℃,and the strain rate ranges from 0.01 s-1 to 0.001 s-1.It is concluded that the Anand model can be applied for representing the inelastic deformation behavior of solders at high homologous temperature and can be recommended for finite element simulation of the stress-strain response of lead free soldered joints.Based on the Anand model,the investigations of thermo-mechanical of SnAgCu and SnAgCuCe soldered joints in fine pitch quad flat package by finite element code were done under thermal cyclic loading,it is found that the reliability of SnAgCu soldered joints can be improved remarkably with addition of rare earth Ce.The results may provide a theory guide for developing constitutive model for lead-free solders.