FEM Modeling And Simulation Of The Electrodeposition In Micro Via And Micro-galvanic Corrosion

Local electrochemical processes are always extremely complicated by involving multi phases and multi dynamic processes.The complexity of the phenomenon and their small geometric size often severely restrict the basic understanding of the undelying mechanism through experimental methods.In recent decades,modeling and simulation methods have been developed as an alternative.One example is the Finite Element Method(FEM),which has been successfully used to solve partial differential equations in technically complex issues,including heating transfer,solid mechanism and so on.Compared to experimental methods,modeling and numerical simulation based on FEM enable complicated systems to be systematically investigated.In the current Doctral thesis,advanced calculation methodology has been used to study two typical local electrochemcial processes,electrodeposition of copper in micro via and localized corrosion of aluminum alloy with geometric resolution at micrometer level.By combining with the experimental methods,the common key problems,for instance,the continuality at the interface between different phases,coupling between different dynamic processes,and the geometry changing caused by generation of new phase or dissolving of old phase,etc.,are solved.Based on this,a relatively comprehensive and universal mathematic model for analyzing kinetics of local electrochemical processes has been established,enabling quantitative interpretation of the widely used empirical conclusions.Specifically,considering the complexity of copper electrodeposition in the micro via,as a start point,a model investigating the copper plating process on the flat electrode was built first.By doing self-programing with Matlab,the model was able to consider the electrochemical reduction of Cu2+ ion and ad/desorption of different additives on the electrode surface,mass transport of species in the electrolyte,also able to interpret the coupling between these dynamic processes.As a result,the key dynamic parameters were obtained by fitting the model with experimental data.Furthermore,effect of the micro via geometry was assembled based on a commercial FEM software,COMSOL Multiphysics,which enables the real-time tracing of the moving electrode surface caused by copper deposition.Particular efforts were done to investigate the effect of additives concentration,geometric factors(depth and radius of micro via)on the via filling result.By adjusting the concentration of different additives,an appropriate electrolyte composition was suggested to get a bottom up superfilling,somehow guide the additives selection.Meanwhile the model illustrated the underlying mechanism of the synergistic effect between the inhibitor PEG and accelerator SPS in the via filling process.In the investigation of localized corrosion in Al alloys,the model considered not only the local electrochemical reactions purely driven by micro-galvanic coupling effect,the mass transport in the electrolyte,but also the deposition of corrosion product and its concomitant blocking effect on the surface activity.Moreover,the real time tracing of the moving dissolution front made it possible to take into account the evolution of the local environment with corrosion proceeding.By individually varying the geometric parameters,the effect of the radius of the cathode particle and the effect of the width of the anodic ring has been studied in depth.Thus,the effect of the area relationship between cathode and anode on the kinetics of the micro-galvanic corrosion could be given a more detailed explanation.In addition,according to the simualtion results,the stablization of localized corrosion requires both a relatively high dissolution rate to release sufficient metal ions,thus through hydrolysis generate sufficient H+ ions,providing a severe corrosion environment;and also a small enough open width of the dissolving volume,which isolates effectively the local environemnt from the bulk suloution.The interpretion is consistent with the widely accepted empirical experience.As a further complement,the model can examine the effect of generated heterogeneous chemical environment during corrosion by using a chemical(primarily pH and O2 concentration)dependent electrochemical kinetics as the input parameters.And the relevant simulation results may provide deep insight in the initiation mechanism of the investigated micro-galvanic corrosion.Generally,FEM modeling and simulation shows obvious advantages in the real-time investigation of local electrochemical processes.As complementary of experimental methods,it is becoming more and more important.Owing to the commonness of different models and the flexibility in parameter setting,the model presented in the current work can be easily extended and fitted to other systems,providing valuable guilds and directions for industrial manufacture,also establishing a substantial platform for further modeling work.