electroforming, rotogravure, and printed circuit board and semiconductor fabrication. Acid sulfate baths contain cupric sulfate as the source of copper(II) ions; sulfuric acid to increase bath conductivity, ensure copper salt solubility, decrease anode and cathode polarization, and increase throwing power; and a source of chloride ions such as hydrochloric acid or sodium chloride, which helps reduce anode polarization and prevents striated deposits from forming. Most baths also contain a variety of organic additives to help refine the grain structure, improve ductility, and brighten the deposit. Variations of the acid copper electrolyte include general-purpose baths, high-throw baths, and high-speed baths. The high-throw and high-speed baths are used when greater throwing power and faster plating rates are required, including for printed circuit board fabrication where high throw is required to plate the low-current-density areas in the through holes. Bath composition Operating conditions Temperature: Usually ambient, although some baths may operate as high as 43 °C Cathode current density: 2–20 A/dm2 (general purpose); 1.5–5 A/dm2 (high throw); 5–20 A/dm2 (high speed) Current efficiency: 100% Additives Various common and proprietary additives have been developed for acid copper electrolytes to help improve throwing and leveling power, brighten the finish, control hardness and ductility, and impart other desired properties to the deposit. Historical formulations dating to the mid-20th century often used thiourea and molasses, while other formulations used various gums, carbohydrates, and sulfonic acids. Acid fluoroborate Copper fluoroborate baths are similar to acid sulfate baths, but they use fluoroborate as the anion rather than sulfate. Copper fluoroborate is much more soluble than copper sulfate, which allows one to dissolve larger quantities of copper salt into the bath, enabling much higher current densities than what is possible in copper sulfate baths. Their main use is for high-speed plating where high current densities are required. Drawbacks to the fluoroborate chemistry include lower throwing power than acid sulfate baths, higher cost to operate, and greater safety hazards and waste treatment concerns. Acid fluoroborate baths contain cupric tetrafluoroborate and fluoroboric acid. Boric acid is typically added to the bath to prevent hydrolysis of the fluoroborate ions, which generates free fluoride in the bath. Unlike acid sulfate baths, fluoroborate baths usually do not contain organic additives. Bath composition Operating conditions Temperature: 18-66 °C Cathode current density: 13-38 A/dm2 (high concentration); 8-13 A/dm2 (low concentration) pH: 0.2-0.6 (high concentration); 1.0-1.7 (low concentration) Pyrophosphate Pyrophosphate copper plating baths possess gentler chemistry compared to