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Development and evaluation of industrial electrochemical reactors

Deliverables

A new reactor for magnetic materials electro-deposition on 100 mm silicon wafers has been developed. This reactor has been designed from simulation results and a new geometry has been achieved. This reactor has been conceived in order to have a great versatility and a lot of parameters can be changed. Especially, the anode parameters and the fluid flow conditions can be monitored in order to optimize the process. This new reactor solves the problem of the deposit and alloy composition uniformity for magnetic materials. The deposit uniformity for CoFe was typically around 20 % (1 sigma) with the former system. With the new reactor, an improved uniformity at 2 % (1 sigma) has been obtained and we believe that we will able to improve that in a very near future. For the moment, this reactor is still a prototype but the conception of an optimized version is already in progress and we envisage industrializing it with a partner.
The ELSY3D prototype software is a simulation tool based on the ''potential model'' enabling to compute current density distributions in electrochemical reactors. The software is based on Boundary Element Techniques with fast iterative solvers. ELSY3D enables: CAD import and CAD reconstruction for electrode change. The software has an integrated high quality hybrid mesh generator as well as an integrated visualization of results using MasterSuite/Open Inventor libraries. The ELSY3D modelling technique creates a cost effective ''on screen virtual test environment'' that avoids long and expensive ''trial and error'' testing.
Numerical simulation methods like finite element or finite volume methods require a mesh, which provides the discretization of the geometry of the domain as well as the internal points, and elements in which the solution variables (velocities, electrical potential, ion concentrations...) will be computed. The present result concerns a software package, which generates such grids suitable for computations of mass and heat transfer with electrochemically reacting flow solvers. Typical in these applications is the presence of extremely thin diffusion layers near reacting electrodes, which require anisotropic cells with aspect ratios of several thousands. This means that the spacing of the cells normal to the wall needs to be 3 to 4 orders of magnitude smaller than the spacings tangential to the wall. No commercial package exists which is able to achieve these specifications for the kind of complex geometries encountered in electro-deposition processes. The method followed is a hybrid grid generation approach which combines the strengths of structured grid generators to produce stretched anisotropic layers of elements near the boundary with the capacities of unstructured grid methods to cope with complex geometries. The procedure is hierarchic, beginning with the construction of the edge grids, which constitute the boundaries of the faces. In a second step the face grids are generated starting from the bounding edge grids, and finally in a third step the volume grids are generated starting from the bounding face grids. A strong emphasis is given to efficient interfacing with the CAD system. The geometry and topology of the configuration can be taken directly from the output of the CAD system, provided that the CAD definition is exported under the form of a STEP file. The STEP format is a recently developed ISO standard for the electronic exchange of product data, supported by most CAD packages. Extremely flexible user control of the mesh spacing is possible, allowing to construct either isotropic or boundary layer grids adjacent to each topological entity. The spacing parameters (e.g. stretching, growth rate) can be controlled by the user for each topological entity separately (vertex, edge, surface or brep). For the isotropic volume meshing, two different point placement algorithms have been implemented, while a Delaunay triangulation method is used to generate the tetrahedra from a given point cloud. For the anisotropic boundary layer part, semi-structured layers of prismatic elements are created normal to the surface, starting from the triangular surface mesh. When the prismatic elements become isotropic the layer generation is stopped and the remaining domain is filled with isotropic tetrahedra (eventually after the creation of some intermediate pyramidal elements). To simplify the specification of input parameters for the user a novel method was developed allowing the generation of high quality surface meshes using only a few user parameters. The method is based on the surface curvature to accurately resolve the geometry features and uses the topological model provided in the STEP format to create smooth surface grids on complex CAD models with hundreds of surfaces. The grid generation package has been developed in close collaboration with the software company ElSyCa, who was responsible for Graphical User Interfacing (GUI), CAD interfacing, visualization and interfacing with solvers. Therefore the present grid generator is part of the prototype of the CAD integrated software developed by ELSYCA (see separate result). Apart from the applications within the context of this project on electrochemical modelling, VKI also intends to exploit the grid generation software for aeronautical applications at high Reynolds number, for which similar though less severe requirements exist, e.g. for the computation of drag around a wing or aircraft body.
SCIENTIFIC RESULT It is possible now to simulate electrode shape change algorithms where the topology of the geometry changes. This occurs for example when two growing electrodes merge or when parts of geometry are included in the growth. COMMERCIAL RESULT The obtained results are needed for proper simulation of all electrochemical processes where the electrode shape changes are relevant with respect to the cell dimensions. Applications are found in electroforming of moulds, micro-components, aerospace. CURRENT STATUS The feasability of the algorithms are proved. EXPECTED BENEFITS These algorithms will be coupled with the electrochemical models and will enable to provide software that reduces considerably the production of moulds having complex parts e.g. dashboards or microdevices.
A high precision reactor for electrodeposition on wafers has been developed. The features that make the reactor unique are the fluid flow and the rotation mechanism of the wafer. The design is such that the fluid flow is very reproducible and homogeneous. One of the major issues in the microsystem technology is mastering the deposited layer thickness. The variation of the thickness is typically less than 5% in standard reactors for copper plating. In the new reactor it is possible to achieve a variation of only 2.5 %. Moreover, the reactor is suited for production and industrial applications.
The PIRODE software is a simulation tool designed to investigate electrochemical reaction mechanisms in aqueous solutions at a Rotating Disc Electrode. The numerical solver uses Finite Element (and related) techniques. PIRODE enables you to construct any desired multi-ion reaction model in an entirely versatile way. PIRODE supports electrode types such as RDE, RHE and RCE. The software is based on the Multi Ion Transport Model and involves any possible species that is present in the bulk of the electrolyte solutions, or that is formed at the electrode surface by some electrode charge transfer reaction. Phenomena such as: redox reactions, co-deposition and side-reactions can easily be modelled.
Two reactors for electroplating of Chromium on automotive parts have been developed by applying the software tools. Both reactors, a parallel-plate and a jet reactor, allow the integration of electroplating in production lines. Due to the single-piece treatment, it was possible to achieve a homogeneous layer distribution on the critical surfaces. The plating speed could be increased by a factor 10 compared to traditional plating equipment. Furthermore, a prototype reactor for NiP-electroplating was established. Through various experiments an improved knowledge about the relationship between plating conditions and layer properties could be gained.
MIoTraS is a simulation tool based on the calculation of the mass -and charge transport in diluted electrochemical systems to obtain the ionic current density distribution in 2D and AX-symmetrical cross sections of electrochemical reactors. MIoTraS includes an automatic grid generator, fluid flow solver, and a solver for the mass -and charge transport equations based on the Finite Element Method. The benefits of this advanced state-of-the-art software package is that it enables the electrochemical engineer to: evaluate the current process, easily remove bottlenecks, reduce value-added engineering time, improve the overall quality of designs and processes.
SCIENTIFIC RESULT Totally new solvers are developed that can be applied to the design of electrochemical reactors 1) Multi-Ion Transport Model (MITM) in presence of turbulent flow (k-omega model) 2) MITM in presence of magnetic field 3) MITM in presence of gas evolution COMMERCIAL RESULT These results will be licensed to others. CURRENT STATUS 1) Multi-Ion Transport Model (MITM) in presence of turbulent flow (k-omega model) Different models for the turbulent mass transfer are implemented and validated using measurements and correlations. EXPECTED BENEFITS 1) Multi-Ion Transport Model (MITM) in presence of turbulent flow (k-omega model) Increased range of applicability of the models to calculate potential, concentration and current density distributions in electrochemical reactors.

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