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achieving fine lines and spaces: part 3 continues Figure 2: Structure of ED (electrodeposited foil). electrodeposited foil. The foil type (electrodeposited [ED] versus rolled annealed [RA]) plays a role in how the micro-etching process reacts with the foil. A closer look at the topography of RA foils after micro-etching will be presented in a future column of Trouble in Your Tank. Summary "Making a soil soluble in a solvent." That is a simple but accurate definition of cleaning. In the case of copper foil surfaces, this suggests that organic soils, chromate anti-tarnish coatings and oxides must be removed from the copper prior to micro-etching the foil. The former is accomplished with acid cleaners containing mineral acids, surfactants and other functional materials. 68 The PCB Magazine • January 2014 Figure 3: Structure of ED foil after treatment with hydrogen peroxide sulfuric acid micro-etchant (ED foil). Once a clean virgin copper surface is obtained, the fabricator is then able to increase the surface area of the foil with a chemical micro-etch. PCB References 1. U.S. Patent 3,853,716. 2. U.S. patent 4,387,006. Michael Carano is with OMG Electronic Chemicals, a developer and provider of processes and materials for the electronics industry supply chain. To read past columns, or to contact the author, click here.