Significance of Modeling the Current Distribution

The current distribution can be analyzed on different scales. The macroscopic current distribution, where the distribution is resolved on length scale on the order of centimeters, is important in characterizing the deposit thickness uniformity on a plated part, or in selective plating, where a nonuniform current distribution is sought. The microscale distribution, on the other hand, where the current density is resolved on submillimeter length scales, affects primarily parameters such as the deposit texture and roughness, nucleation, and deposition within micron-scale and nanoscale features. 

For many applications, numerical simulation capability which provides the current distribution in a given configuration and plating conditions, or for a given set of such parameters, is sufficient. However, for predictive process design and for scale-up of cells and 

Electroplating processes, where a solid deposit is formed and its thickness can be directly measured, provide a relatively convenient means for determination of the current distribution. The deposit thickness can be measured by a number of commercially available devices, based on, e.g.. X-ray fluorescence, beta backscatter, magnetic properties, or controlled dissolution. A direct probe based on the induced field associated with the current flow has recently been introduced. Optical and electron microscopy of cross-sectioned deposits provide a common means for measuring the deposit thickness. Once the deposit thickness, d, has been measured, it can be related to the current density, i, through Faraday s law  

t is the plating time, F is Faraday s constant, M, p, and n are the plated metal atomic weight, its density, and the number of electrons transferred in the deposition reaction, respectively, and p is the faradaic efficiency, accounting for side ( parasitic ) reactions. Metals noble to hydrogen are typically plated from aqueous solutions at p 1 corresponding to close to 100% faradaic efficiency (unless driven to the limiting current). When the faradaic efficiency is less than 100%, (1) can be used to determine the ffadaic cmrent efficiency once the current density has been evaluated. 

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