Electroless copper plating compositions and methods for electroless plating copper on substrates

Abstract

Stable electroless copper plating baths include imidazolium compounds to improve rate of copper deposition on substrates. The copper from the electroless plating baths can be plated at low temperatures and at high plating rates.

Description

FIELD OF THE INVENTION[0001]The present invention is directed to electroless copper plating compositions and methods for electroless plating copper on substrates, wherein electroless copper plating has a high electroless copper plating rate at low temperatures and the electroless copper plating compositions are stable. More specifically, the present invention is directed to electroless copper plating compositions and methods for electroless plating copper on substrates, wherein electroless copper plating has a high electroless copper plating rate at low temperatures and the electroless copper plating compositions are stable, wherein the electroless copper plating compositions include imidazolium compounds or salts thereof.BACKGROUND OF THE INVENTION[0002]Electroless copper plating baths are in widespread use in metallization industries for depositing copper on various types of substrates. In the manufacture of printed circuit boards, for example, the electroless copper baths are use...

AI Technical Summary

Benefits of technology

The patent describes a new method for electroless copper plating that uses imidazolium compounds to increase the plating speed at low temperatures. The method also results in better coverage of through-holes and reduces the cost of the process by lowering the temperature requirements. The electroless copper plating compositions have a wide range of concentration ranges for the imidazolium compounds, which means that the concentration does not need to be carefully monitored. This provides a more stable and reliable method for plating copper.

Problems solved by technology

Control of the baths to maintain high plating rates with substantially uniform copper deposits over long periods of time is exceedingly difficult.

In general, electroless copper plating rates of greater than 0.6 μm / 5 min. are highly desirable but rarely achieved, especially at low electroless plating temperatures, such as below 40° C. Consumption and replenishment of bath components over several metal turnovers (MTO) can also contribute to bath instability, for example, through the buildup of side products.

Therefore, such baths, and particularly those having a high plating potential, i.e. highly active baths, tend to become unstable and to spontaneously decompose with use.

Such electroless copper bath instability can result in non-uniform or discontinuous copper plating along a surface.

Such discontinuity of the copper deposit can ultimately lead to mal-functioning of any electrical device in which the defective printed circuit board is included.

However, many stabilizers lower electroless copper plating rates, and, also, at high concentrations can be catalyst poisons, thus reducing plating rates or inhibiting plating and compromising the performance of the plating bath.

Low plating rates are detrimental to electroless copper plating performance.

However, increasing the operating temperatures can decrease the stability of the electroless copper bath by increasing the buildup of byproducts as well as reducing bath additives by side reactions, thus negating some of the effects of increasing the stabilizer concentration.

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