Compositions: coating or plastic – Coating or plastic compositions – Metal-depositing composition or substrate-sensitizing...
Reexamination Certificate
1998-12-01
2001-02-27
Beck, Shrive (Department: 1762)
Compositions: coating or plastic
Coating or plastic compositions
Metal-depositing composition or substrate-sensitizing...
C106S001260
Reexamination Certificate
active
06193789
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electroless copper plating solution and a method of electroless copper plating utilizing this solution, and more specifically, to an electroless copper plating solution and a method of electroless copper plating, which together can have a uniform and acicular copper film deposited on the surface of a plating object, and therefore can be used for improving the strength of adhesion between various metals and resins including bonding of a copper foil to a resin as applied in a conductive circuit such as a multi-layer printed circuit board or in a copper-plated laminate; as well as to plated products which can be obtained by said method.
BACKGROUND ART
A multi-layer printed circuit board is conventionally manufactured by first preparing a copper-plated laminate for the inner layer by processing a copper foil on the copper-plated laminate to form a printed circuit; then providing the above copper foil with a surface roughening treatment (generally comprising degreasing, followed by a soft etching process as exemplified by treatment with ammonium persulfate, sodium persulfate, cupric chloride, sulfuric acid-hydrogen peroxide system and the like, as well as an activating treatment); subsequently building an acicular film of copper oxide or cuprous oxide on top of the foil by a process such as blackening or browning; and bonding a copper-plated laminate for the outer layer or copper foils in multiple layers with a material impregnated with a thermosetting resin (i.e. a “prepreg”) to fabricate a multi-layer laminated board having a high adhesion strength.
Since an electric continuity has to be established to each layer of the multi-layer laminated board manufactured in the above process, a through-hole plating on holes drilled through the board is required. However, the conventional method has had a drawback where penetration of the acid solution used in the catalyst treatment process for plating through-holes or penetration of the plating solution in the electroless copper plating process tends to dissolve the film made up from copper oxide or cuprous oxide, thereby causing a phenomenon called “pink ring” (i.e. “haloing”).
On the other hand, there has been an alternative method of manufacturing a multi-layer printed circuit board whereby a printed circuit is formed on a copper-plated laminate using a copper foil that is pre-processed by surface roughening to eliminate the need for surface roughening as well as the oxide film forming processes required in the method described above. This method, however, has shortcomings such as inferior pattern resolution for the printed etching resist or the etching resist for ultra-violet exposure, which are associated with the surface roughness on the copper foil.
In recent years, methods have been developed to correct the above mentioned shortcomings on copper-plated laminates and to enhance the adhesion strength by utilizing certain particular types of electroless copper plating processing (Japanese Patent Application Laid-Open Nos. 15980/1986, 15981/1986, and 41775/1986).
The above electroless copper plating process, however, in practice requires formalin as an essential reducing agent and presents problems such as (a) abnormal copper deposition on the substrate resin, (b) unstable plating bath, or (c) an obnoxious odor as well as a potential carcinogenicity.
The present inventors have recently developed a method for forming a uniform and acicular copper film with excellent adhesion strength using electroless copper plating (Japanese Patent Application Laid-Open No. 116176/1992). While this technology enables manufacturing of a copper-plated laminate having a high adhesion strength and without the aforementioned shortcomings, surfactants that can be used in the process are limited and the benefit of the invention has not always been available.
Accordingly, it has been necessary to improve the above technology to present a technology which is able to provide better adhesion strength and is more versatile.
DISCLOSURE OF INVENTION
While earnestly making research efforts to improve on the technology based on the Japanese Patent Application Laid-Open No. 116176/1992 as described above, the present inventors have discovered the unique fact that a lithium ion is extremely effective in facilitating a copper film with a uniform and acicular structure This and other findings, specifically that by having a lithium ion present in the electroless copper plating solution as prescribed in said technology, a uniform and acicular copper film with excellent adhesive strength can be obtained, either singly or with a polyoxyethylene type surfactant other than the polyoxyethylene type surfactants containing acetylene residue employed in said technology have consummated the invention as hereunder stated.
Accordingly, an object of the present invention is to provide an electroless copper plating solution which is based on an electroless copper plating solution comprising a copper ion, a complexing agent, a hypophosphorous acid compound as a reducing agent, and a metallic catalyst for initiating the reductive reaction, characterized by further comprising a lithium ion.
Another object of the present invention is to provide an electroless copper plating solution which is based on an electroless copper plating solution comprising a copper ion, a complexing agent, a hypophosphorous acid compound as a reducing agent, and a metallic catalyst for initiating the reductive reaction, characterized by further comprising a polyoxyethylene type surfactant and a lithium ion.
Yet another object of the present invention is to provide a method for electroless copper plating which deposits a uniform and acicular copper film on the surface of a plating object by using the above mentioned electroless copper plating solution, and also to provide plated products using said method.
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“Oils and Fats and a Surface Active Agent as Known Chemical Substances and Related Substances Thereof”, Tokyo: Japan Soap and Detergent Assoc., Japan Surface-Active Agents Assoc., pp. 90-91, Apr. 1974.
Tomoyuki Fujinami, The Journal Of The Surface Finishing Society Of Japan, vol. 42, No. 11, pp. 1068-1076, “The Present and Future Trends in the Electroless Copper Plating”, 1991.
M. Matsuoka, et al., J. Electrochem. Soc., vol. 139, No. 9, pp. 2466-2470, “Kinetics of Electroless Copper Plating and Mechanical Properties of deposits”, Sep., 1992.
Fujinami Tomoyuki
Hayashi Shinji
Honma Hideo
Shimizu Satoru
Terashima Yoshitaka
Barr Michael
Beck Shrive
Honma Hideo
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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