Copper electroplating
[1] The copper layer can be decorative, provide corrosion resistance, increase electrical and thermal conductivity, or improve the adhesion of additional deposits to the substrate.
The copper cations form a coordination complex with salts present in the electrolyte, after which they are transported from the anode to the cathode.
[5][8] Cyanide copper baths typically provide high covering and throwing power, allowing uniform and complete coverage of the substrate, but often plate at lower current efficiency.
[2] Additionally, they cannot be used to plate directly onto less-noble metals such as steel or zinc without first applying a cyanide-based strike or other barrier layer, otherwise the acid in the bath will cause an immersion coating to form that will compromise adhesion.
[6][11] 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.
[6] Most baths also contain a variety of organic additives to help refine the grain structure, improve ductility, and brighten the deposit.
[2] 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.
[13][8] For semiconductor and printed circuit board applications, acid copper baths use additives that facilitate plating in high-aspect-ratio vias and through holes.
The leveler helps prevent buildup at the via opening and creates a smoother surface finish.
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.
While pyrophosphate electrolytes are easier to waste treat than alkaline cyanide and acid plating baths, they are more difficult to maintain and control.
Printed circuit baths typically contain organic additives to improve ductility and throwing power.
With a higher current, hydrogen bubbles will form on the item to be plated, leaving surface imperfections.
[5] Products that utilize decorative copper plating include automotive trim, furniture, door and cabinet handles, light fixtures, kitchen utensils, other household goods, and apparel.
[12] The semiconductor industry uses the damascene process to pattern-plate copper into vias and trenches of interconnects for metallization.
[22] As a soft metal, copper is also malleable and so has the inherent flexibility to maintain adhesion even if a substrate is subject to being bent and manipulated post plating.
