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Additive Composition for Acid Copper Plating

IP.com Disclosure Number: IPCOM000039952D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Bindra, P: AUTHOR [+6]

Abstract

This article relates to a composition for the electrodeposition of copper from aqueous acidic copper plating baths, and, more particularly, to additive compositions for through hole plating in printed circuit boards. Additives are necessary in acid copper plating partly to provide bright and smooth copper films, and partly because additives in general impart more desirable metallurgical characteristics, e.g., ductility, to such film deposits. In the case of printed circuit boards with high aspect ratios (hole length/hole diameter) throwing power is an additional requirement. Throwing power is the ability of a plating solution to plate uniformly (or evenly) on the surface of a board and inside a through-hole.

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Additive Composition for Acid Copper Plating

This article relates to a composition for the electrodeposition of copper from aqueous acidic copper plating baths, and, more particularly, to additive compositions for through hole plating in printed circuit boards. Additives are necessary in acid copper plating partly to provide bright and smooth copper films, and partly because additives in general impart more desirable metallurgical characteristics, e.g., ductility, to such film deposits. In the case of printed circuit boards with high aspect ratios (hole length/hole diameter) throwing power is an additional requirement. Throwing power is the ability of a plating solution to plate uniformly (or evenly) on the surface of a board and inside a through-hole. As illustrated in the drawing, a typical plating rate on the surface, R1, can be as high as one hundred times R2, the plating rate inside the through-hole, for boards with aspect ratios of about 10. These differences in plating rates are associated with differences in the rate of mass transfer of metal ions from the bulk of the plating bath to the surface of the board and inside long and narrow through-holes.

The function of good throwing power additives is to decrease R1 and to increase R2 such that R1 equals R2 . In prior-art acid copper plating baths a sufficiently bright or brilliant finish of the plated metal has been obtained by adding vari ous brightening agents to the bath. A described process relates to an acid copper plating bath containing copper sulfate, free sulfuric acid, chloride ions and a combination of organic additives to improve the throwing power of the bath without impairing the brightening and levelling effects. This is accomplished when surface-active organic additives, in conjunction with chloride ions in the acid copper plating bath, change the rate of one of the steps of the electrode reaction, or introduce a new step into the reaction mechanism. The total overvoltage (h) during the galvanostatic deposition of a metal may be divided into its various components by ...