Brightening Agents

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Thiourea additions brighten copper deposited from acid sulfate baths. A patent disclosed the use of 0.002 to 0.005 g/l. An appreciable grain-refining and brightening effects of thiourea are attributed to its adsorption in copper deposits and the resulting effect on crystal nucleation.

Sulfide ions created when thiourea decomposeds reduce the ductility of copper deposits. Combined with dextrin, molasses, lignosulfonats, mercaptobenzimdazoles, naphthalene sulfonic acid, or tribenzylamine and other organic agents, small concentrations of thiourea were once employed for brightening purposes, but have been largely superseded by better brighteners that have little or no harmful effect on ductility.

Sulfonated acetylthiourea or sulfanated aryl and alkyl substitution products of acetylthiourea were developed for bright copper plating from acid baths. Another process utilized the sulfonation products of sulfurized aromatic compounds presence of anhydrous aluminum chloride or thionyl chloride in the presence of anhydrous aluminum chloride and sulfuric acid. Acetyl cyanide was proposed as a brightener for either the sulfate or the floroborate bath. Several complex amines was patented as brightening agents in 1958. In 1958, a patent disclosed a combination of thiohydantion (a thiourea derivative) and a multiringed aromatic amine. A substituted amino benzene sulfonic acid was disclosed in another patent for brightening copper deposited from the copper sulfate bath.

Polyacrylamides, the reaction product of aminothiazole, acrylaminates, thiocarboxylic acid amides, tetrahydropyranyl amides, homopolymers of 1-3-dioxolane, and a combination of phenol polyglycols and thiosemicarbozones are also included among the brightening agents patented since 1955.

Some of these brightening agents also induce leveling. For example, a surface finish of 0.46 μm with 12.5 μm of good leveling bright copper or to only 0.1 μm with 25 μm. Such processes deposit copper with a leveling power much higher than typical bright nickel deposits.