Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Organic compound containing
Reexamination Certificate
2001-10-24
2004-01-20
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Organic compound containing
C438S678000
Reexamination Certificate
active
06680273
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of plating catalysts, particularly new catalysts for electroless metallization deposition. Preferred catalysts of the invention can be selectively activated (e.g. thermally) and may be free of tin. Catalysts of the invention are preferably employed for electroless copper deposition.
2. Background
Electroless metallization can require multiple processing steps. See, for example, reviews of electroless plating in C. R. Shipley Jr.,
Plating and Surface Finishing
, vol. 71, pp. 92-99; and
Metal Finishing Guidebook and Directory
, vol. 86, published by Metals and Plastics Publications, Inc. (1988). On typical sequence for metallization, such as providing a copper deposit, of polymeric substrates employs a colloidal palladium-tin catalyst in the following sequence: (1) pre-cleaning the substrate surface; (2) microetching, e.g. with a chromic-based solution; (3) conditioning the etched substrate surface; (4) adsorption of the palladium-tin catalyst onto the conditioned surface; (5) treatment with an accelerator to modify and activate the absorbed catalyst; and (6) treatment with an electroless plating solution, such as an electroless copper solution. See, for example, U.S. Pat. Nos. 4,061,588 and 3,011,920.
Electroless metal deposition has a wide range of applications, including for use in the manufacture of electronic printed circuit boards and non conductors such as decorative and engineering plastic substrates which can be used in electronic, communication, computer, plumbing parts and automotive parts among other applications of the plated products. More particularly, an electroless copper deposit plated over the walls of through-holes, vias, interconnects, etc. provides conductivity between surfaces of the substrate renders the substrate conductive and suitably prepared for electrolytically deposited topcoats or other metal or oragnic layers which confer functionality or decorative effect to the object being treated of a board and/or between circuit layers. In additive circuit manufacture, in addition to providing conductivity between surfaces and/or circuit layer, the deposit also serves as the conductor lines.
SUMMARY OF THE INVENTION
We have now found new electroless metallization catalysts compositions that can provide significantly improved capabilities and properties.
Catalysts of the invention in general comprise a copper source (e.g. copper salt) and an organic binder compound. Preferably, the catalyst's composition has an acidic component, such as provided by an organic acid, and preferably further contains a reducing agent. The catalyst composition can be formulated as a fluid, preferably as an aqueous composition.
Catalyst compositions of the invention are preferably neutral or alkaline. It is believed that maintaining a substantially neutral or Alkaline pH promoted formation of a complex of composition components, which in turn promotes enhanced properties of the composition. A pH of from about 5 to about 12 or 13 is generally suitable, more preferably a pH of about 5, 6, 7, 8, 9, 10 or 11, even more preferably a pH of about 7, 8, 9 or 10. Such a neutral or alkaline pH can be provided by addition of a suitable base to the catalyst composition. e.g. a hydroxide such as potassium hydroxide or sodium hydroxide, and the like.
Significantly, the catalyst composition can be selectively activated, e.g. thermally, via radiation, or other activation. Thus, the catalyst's composition of the invention can be applied to a substrate to provide an inactive catalyst coating layer. Upon activation of that coating layer, the coating becomes catalytic and is able to initiate metal deposition from standard electroless plating baths. Copper is a preferred metal to electrolessly plate via a catalyst of the invention.
Activation of the catalysts coating layer also can be performed to provide a catalytic image pattern. For instance, the inactive catalyst coating layer can be exposed through a photomask to activating radiation, e.g. excimer laser operating in the infrared, ultraviolet radiation e.g. having a wavelength of from 250 to 450 nm, etc. An image pattern then will be transferred to the copper catalyst layer and copper deposition will occur only in those areas activated by the transmitted radiation. The transferred image can provide e.g. a copper circuit pattern, selectively plate a via in the substrate surface, etc.
It also should be appreciated that catalysts of the invention are substantially, essentially or more preferably completely free of tin and/or palladium, in contrast to prior catalysts.
The invention also includes methods for manufacturing plating printed circuit board substrates, and other electronic packaging plated substrates, comprising use of a catalyst composition of the invention. Such methods in general comprise deposition of a catalyst composition of the invention onto an electronic packaging substrate, such as polymeric through-hole walls of a printed circuit board, and contact of the catalyst substrate surface with an electroless plating composition, particularly an electroless copper composition. The catalyst composition can be applied by a variety of methods, e.g. dip coating, spin coating, etc. The catalyst composition is preferably dried before the plating step. The deposited catalyst layer also is activated prior to the plating step, e.g. thermally or other activating radiation as discussed above.
The invention also includes articles coated with a catalyst composition of the invention, including printed circuit board substrates and other electronic packaging substrates and other non conductive substrates having a catalyst composition thereon, which may be overcoated with an electroless metal deposit, particularly an electroless copper deposit.
Other aspects of the invention are disclosed infra.
DETAILED DESCRIPTION OF THE INVENTION
As discussed above, the present invention provides compositions suitable for depositing an electroless plating catalyst on a substrate, particularly electronic packaging substrates such as a printed circuit board. Preferred catalysts compositions comprise one or more metal ions, one or more organic acids, one or more organic binders, and one or more reducing agents. The catalyst composition also preferably is substantially neutral or alkaline. Any metal salt suitable for use as an electroless plating catalyst may be used in the present invention. Such metal salts include, but are not limited to: cobalt salts, copper salts, platinum salts, palladium salts, and the like. Copper and palladium salts are the preferred catalysts. Such salts are typically at least partially soluble in the solvent used, typically water. Thus any solvent soluble metal salt is suitable. Exemplary metal salts include metal hydroxides, metal halides, metal gluconates, metal acetates, metal sulfates, metal nitrates, metal sulfonates, metal alkylsulfonates, metal arylsulfonates, metal fluoroborates and the like. The choice of such catalysts is within the ability of one skilled in the art.
The one or more metal salts are typically present in the compositions of the invention in an amount of from about 0.1 to about 15 g/L, preferably from 0.5 to 10 g/L, more preferably 1 to 8 g/L. A particularly useful range is from 2 to 5 g/L. Such metal salts are generally commercially available and may be used without further purification. Copper salts are preferred such as a Cu (II) salt e.g. cupric chloride.
As discussed above, the catalyst composition is preferably formulated with an acid component. Preferably, an organic acid is employed. A wide variety of organic acids may be advantageously used in the present invention. Suitable organic acids include, but are not limited to: (C
1
-C
12
)alkylcarboxylic acids, (C
2
-C
12
)alkyldicarboxylic acids, (C
1
-C
12
)alkyltricarboxylic acids, substituted (C
1
-C
12
)alkylcarboxylic acids, substituted (C
2
-C
12
)alkyldicarboxylic acids, substituted (C
1
-C
12
)alkyltricarboxylic acids, (C
2
-C
12
)alkenylcarbo
Bains Narinder Singh
Goosey Martin T.
Bell Mark L.
Brown Jennine
Cairns S. Matthew
Shipley Company L.L.C.
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