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Calculations are performed for the purpose of determining the steady-state behavior of plated through-holes with various aspect ratios during the dc electrodeposition of copper over a wide range of operating conditions. The results indicate that when electrolyte flow is restricted the maximum average current density possible within the through-holes is much less than 1 mA/cm ~ and the current distribution is considerably nonuniform for the high aspect ratio through-holes. Higher average current densities within the through-holes are possible only when flow of electrolyte is induced. However, the current distribution remains nonuniform for the high aspect ratio holes. While periodic flow reversal has been shown to improve the current distribution under mass-transfer limiting situations, the results indicated that the effect on the current distribution will not be significant when operating well below the limiting current density for deposition.The electrodeposition of metals and alloys is a major processing step during the manufacture of electronic components. An area of major interest to the industry is the plating of printed circuit boards (PCB's) of the multilayered type.

Electrodeposited coatings of tin-lead alloys are widely used throughout the electronics industry for interconnections and masking. Other applications include protective coatings for steel as well as surface layers on bearings.There have been many process improvements which have lead to increased productivity, improved quality, and better control of alloy composition. In many cases, characterization of the important process parameters has been realized with the aid of a rotating disk electrode (1, 2). Recently, Cheng and Cheh (3) developed a model to describe the behavior of a rotating disk electrode during the deposition of tin-lead alloys by periodic electrolysis. They assumed a uniform current distribution over the electrode surface and demonstrated that the average current-voltage relationship and the average composition of the electrodeposited alloy can be predicted reasonably well by using single component tin and lead kinetic parameters in the alloy plating model. In addition, migration effects and solid phase activities were not considered.With the aim of enhancing the usefulness of the rotating disk electrode as a tool for investigating the effects of process parameters on the properties of electrodeposited alloys, we have performed an experimental investigation for the purpose of demonstrating whether or not the approach used by Cheng and Cheh (3) can be used to study the effect of process parameters on the current and composition distributions during the deposition of tin-lead alloys.A model which describes the behavior of a rotating disk electrode, based on earlier modeling work presented by White and Newman (4), will be discussed for the deposition of tin-lead including the effects of mass transfer, charge transfer, and ohmic resistance. Using the kinetic parameters for each species obtained from single component tin and lead systems, calculated results for the polarization curves as well as the current and composition distributions at various fractions of the limiting current density are presented. Finally, these calculated results are compared to experimental results obtained from a fluoborate plating system with and without organic additives. TheoreticalThe problem of current distribution on a rotating disk electrode for a single electrode reaction was first studied by Newman (5) and subsequently verified experimentally by Marathe and Newman (6) for a disk of radius ro embedded in a large insulating plane with a counterelectrode placed far away. Caban and Chapman (7) demonstrated how the incorporation of orthogonal collocation concepts in the solution of this problem resulted in a faster and more stable computational algorithm. Later, White and Newman (4) extended the theory to accommodate multiple simultaneous electrode reactions.Mass transfer in the diffusion layer.--The local partial current densities can be expressed by an integral equation relating the reactant concentration distribution at the electrode surface to the current density (6,8) where ij, illmj, and Cso are the local partial curren...

A diffusion model was used to obtain an analytical solution for the mass transport to a rotating disk electrode under superimposed sinusoidal and triangular alternating current conditions for the case where the polarity of the applied current does not change. The analytical solution was compared to a numerical solution which resulted from a convective‐diffusion model. Using the analytical solution, an expression for the instantaneous diffusion limiting current density was derived and verified experimentally using a ferri‐ferrocyanide reaction system. Further, a quantitative comparison was made between the maximum rate of electrolysis under superimposed sinusoidal, triangular, and rectangular alternating current conditions with equal cycle times.

A model is presented for the purpose of determining the transient behavior of a plated through-hole system during electrolysis with a periodic applied potential, including the effects of mass transfer, charge transfer, and ohmic resistance. Calculations are performed for through-holes of various aspect ratios during the periodic electrodeposition of copper. The results indicate that electrolysis with a rectangular-pulse applied potential causes the current distribution to be less uniform than dc electrolysis at the same average rate of plating. The results also indicate that electrolysis with a periodicreverse applied potential appears to be a promising technique for obtaining a more uniform current distribution in this particular system.In part I of this series (1), calculations were performed for the purpose of determining the steady-state behavior of plated through-holes with various aspect ratios during the dc electrodeposition of copper over a wide range of operating conditions. The results indicated that when electrolyte flow was restricted the maximum average current density possible within the through-holes was much less than 1 mA/cm 2 and the current distribution was considerably nonuniform for the high aspect ratio through-holes. Higher average current densities within the through-holes were possible only when flow of electrolyte was induced. However, the current distribution remained nonuniform for the high aspect ratio holes. While periodic flow reversal was shown to improve the current distribution under mass-transfer limiting situations (2), the results indicated that the effect on the current distribution would not be significant when operating well below the limiting current density for deposition.In this paper, a model is presented for the purpose of determining the transient behavior of a plated through-hole system, including the effects of mass transfer, charge transfer, and ohmic resistance when electrolyte is forced to flow through the system in a fully developed laminar flow.Calculations based on the theoretical model are performed for the deposition of copper by a periodic applied potential within through-holes of various aspect ratios at situations below mass-transfer limiting conditions. The effects of periodic electrolysis on the current distribution within through-holes of various aspect ratios during copper deposition are discussed.