A pulse and pulse reverse through mask electrochemical machining (ECM) process is being developed for fabrication of gas flow field channels on metal bipolar plates used in PEM fuel cells. The process involves patterning a photoresist mask on the surface of the bipolar plate to protect specific areas during the ECM process. A pulsed electric field is applied between the bipolar plate and a suitable counter electrode to remove the metal not protected by the photoresist mask. The application of pulsed electric fields, as opposed to constant direct current (DC) electric fields provides an improved level of control through optimization of the pulse parameters. The influence of the through mask pulse and pulse reverse ECM processing parameters, such as electrolyte composition, flow rates, pulsed voltage, pulsed on-times and off-times on material removal rates, surface finish, accuracy and dimensional control for the channel fabrication are examined.

Plating cell geometry and uniform solution flow are the foundation for a uniform plating process for printed circuit board and electronic packaging applications. Currently, the plating cells used for copper metallization for these applications utilize a number of agitation methods to reduce the thickness of the diffusion boundary layer as well as fostering solution movement into and through small features. In order to achieve a uniform diffusion boundary layer, a requirement for uniform plating thickness, a uniform diffusion layer must be established by flow/agitation method within the cell. A novel plating cell geometry that provides a thin uniform diffusion boundary layer and consequently uniform plating thickness is disclosed. Results from cell characterization in terms of diffusion boundary layer thickness and deposit thickness uniformity is also reported.

Faraday Technology, Inc. has developed a number of novel processing cells based on an innovative cell geometry that results in high levels of processing uniformity. This geometry is comprised of a number of unique attributes for the uniform electrodeposition or electroetching of metals across large planar substrates as well as fine features that are utilized for printed circuit board (PCB) and electronic packaging applications. The cell has been characterized with a 457 mm x 610 mm substrate. A coefficient of variation of 5.3% was achieved in FARADAYIC® ElectroCell over a 457 mm x 610 mm substrate; these values were compared to a commercial system. This cell design has been applied to a number of industrial processes, including electroplating of copper, trivalent chromium and platinum and electroetching of copper for interlayer circuit board applications. The current work outlines the importance of various cell components and resulting uniformity.

Limiting currents under mass transport limiting conditions were determined experimentally for two distinct types of electrochemical plating cells using voltammetric and chronoamperometric methods. The average limiting currents were used to estimate the thickness of the diffusion boundary layer that results from the novel cell configurations and agitation schemes. Additionally, the deposit thickness uniformity across the surface of copper plated substrates was experimentally determined and reported as the coefficient of variation (CV). Results show that optimization of the cell configurations and solution agitation within provides a thin uniform diffusion boundary layer thickness and low CVs for the metal thickness distribution indicating a uniform current distribution is achieved across the surface of the substrate.