the toxic alkaline cyanide baths and the corrosive acid copper baths, operating at mildly alkaline pH and utilizing relatively non-toxic pyrophosphate compounds. While pyrophosphate electrolytes are easier to waste treat than alkaline cyanide and acid plating baths, they are more difficult to maintain and control. Pyrophosphate baths offer high throwing power and produce bright, ductile deposits, making them particularly useful for printed circuit board fabrication where high throw is required for plating high-aspect-ratio through holes. Pyrophosphate baths contain cupric pyrophosphate as a source of copper(II) ions, potassium pyrophosphate as a source of free pyrophosphate that increases bath conductivity and helps with anode dissolution, ammonia for increased anode dissolution and deposit grain refinement, and a source of nitrate ions such as potassium or ammonium nitrate to decrease cathode polarization and increase the maximum allowed current density. When the bath is made up, the copper pyrophosphate and potassium pyrophosphate react to form a complex, [K6Cu(P2O7)2], which dissociates to form the Cu(P2O7)26− anion from which copper deposits. Variations of the pyrophosphate electrolyte include general-purpose baths, strike baths, and printed circuit baths. Printed circuit baths typically contain organic additives to improve ductility and throwing power. In pyrophosphate baths, orthophosphate ions are formed from the hydrolysis of pyrophosphate and tend to build up in the electrolyte over time, which presents maintenance challenges. Orthophosphate ions decrease bath throwing power and deposit ductility at concentrations above 40–60 g/L, and they lead to lower solution conductivity, banded deposits, and lower bright current density range at concentrations beyond 100 g/L. Orthophosphate is removed from the bath by either doing partial bails and dilutions or by completely dumping and remaking the bath. Current control It is important to control the current to produce the smoothest copper surface possible. With a higher current, hydrogen bubbles will form on the item to be plated, leaving surface imperfections. Often various other chemicals are added to improve plating uniformity and brightness. These additives can be anything from dish soap to proprietary compounds. Without some form of additive, it is almost impossible to obtain a smooth plated surface. The surface formed always needs to be polished to achieve a shine. As formed it has a matte luster. Applications Excluding the continuous strip plating industry, copper is the second most commonly-plated metal after nickel. Copper electroplating offers a number of advantages over other plating processes, including low metal cost, high-conductivity and high-ductility bright finish, and high