Impedance Based Characterization of Raw Materials Used in Electrochemical Manufacturing

Manufacturing of precision stainless steel parts by electrochemical methods such as through-mask etching allow for nearly arbitrary shapes and sizes. An example of such precision components include micro-surgical blades where the blade shape and edge are both created in the electrochemical process, (Fig. 1a and c). Surgical blade edges made using this process require no post-manufacturing sharpening process and hold their edge longer than ground blades due to the electrochemical process enabling the steel temper to be properly maintained. Another example is the manufacture of hard disk drive suspension assemblies, where the shape of the stainless steel component is produced by the same etching techniques. Here, modifications to the mass and spring properties in the hard disk suspension assembly can also be made by partially etching away some of the material (Fig. 1b). Through-mask etching allows many components to be made in parallel, greatly reducing costs at high volume, and holding dimensional tolerances to that of the photolithography capability, material thickness, and the fluid mechanics of the etching process. This is often an order of magnitude better than what can be accomplished by mechanical machining. Many of the electrochemical processes used to make advanced components are sensitive to the state of the oxide film on the raw materials used in the manufacturing process. Photo-resist adhesion, etch initiation, and laser welding are examples that would affect product performance and quality. High yield manufacturing requires raw materials (precursors) with consistent surface properties to obtain repeatable results. To be able to understand the extent to which the oxide state (on the surface of the precursor) influences process parameters, appropriate measurement methods are required to probe the relevant properties that would change with oxide coverage. Electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) are excellent methods for this purpose. This article outlines a case study wherein these techniques have been employed to probe the growth of oxide films on a stainless steel sample that represented the precursor, and provides a practical example of how such methods can be beneficially used in practice during electrochemical manufacturing processes.