Coating processes – With pretreatment of the base – Preapplied reactant or reaction promoter or hardener
Reexamination Certificate
2001-10-17
2003-11-11
Barr, Michael (Department: 1762)
Coating processes
With pretreatment of the base
Preapplied reactant or reaction promoter or hardener
C427S305000, C427S306000, C427S307000, C427S322000, C427S443100
Reexamination Certificate
active
06645557
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to processes for applying a metal to a non-conductive surface.
BACKGROUND OF THE INVENTION
During the last three decades, the plating of non-conductive or dielectric substrates has evolved into a big business, covering a wide spectrum of commercial applications. Typical applications range from decorative plating of plastics to automotive parts and printed wiring board fabrication.
A variety of processes have been directed to the problem of applying a metal to non-conductive surfaces, for example, to polymers, glass or other dielectric material. Although a number of such processes are known, none have proven completely satisfactory for various economic and/or environmental reasons. Thus, there exists a need for a further improved process for applying a metal to a non-conductive surface.
In general, the known methods apply a first metal, usually tin, to provide a tie between the surface and a subsequently applied metal, then apply a second, “catalyst” metal, usually palladium, and then apply a third metal layer by an electroless plating process. The third metal is the metal of primary interest, i.e., the metal which is desired to be applied to provide a conductive layer on the non-conductive surface or substrate.
Many conventional methods include the use of palladium as the catalyst metal for subsequent electroless deposition of a metal such as copper. However, palladium is quite expensive, the price at times exceeding the price of gold by a factor of two or more. Other less expensive metals have been suggested as the catalyst, such as silver. However, silver has presented difficulties in that it may not provide sufficient catalytic strength, or may result in a poor deposition of the subsequently applied electroless metal. For these reasons, silver has been disfavored.
Thus, a need remains for a catalytic metal in such applications which is both economical and provides excellent electroless plating results on the non-conductive surface of interest.
SUMMARY OF THE INVENTION
The present invention relates to a method of forming a conductive metal layer on a non-conductive surface, including providing a non-conductive surface; contacting the non-conductive surface with an aqueous solution or mixture containing a stannous salt to form a sensitized surface; contacting the sensitized surface with an aqueous solution or mixture containing a silver salt having a pH in the range from about 5 to about 10 to form a catalyzed surface; and electroless plating the catalyzed surface by applying an electroless plating solution to the catalyzed surface.
In one embodiment the aqueous silver salt solution is at a pH in the range from about 6 to about 9. In one embodiment, the non-conductive surface is contacted with a conditioner prior to contacting with the stannous salt. In one embodiment, the non-conductive surface is modified prior to contacting with the stannous salt, or prior to the conditioning treatment.
The method of the present invention provides an electroless-deposited metal layer which is economical and of excellent quality. Thus, the present invention provides a solution to the problems remaining in the prior art.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a process for metallization of non-conductive materials, and includes steps of surface modification, sensitizing, catalyzing and chemical plating. The method is not limited to, but should include the following steps:
(i) Sensitizing the surface to prepare for application of the catalyst;
(ii) Applying a catalyst to the surface to provide catalytic sites for the initiation of electroless plating;
(iii) Electroless plating the surface to provide a layer of conductive metal, which may be followed by electrolytic plating steps.
The method may further include a step of conditioning to improve sensitizer and catalyst adsorption on difficult to plate plastics.
As noted below, in one embodiment, prior to the conditioning step, the surface is modified initially to activate the surface towards the subsequent treatment steps. Such surface modification may include, for example, treatment with chromic acid, chromic/sulfuric acid, plasma etching and solvent swelling. Such methods are known in the art, and any such method may be bused as appropriate to the non-conductive material.
Non-Conductive Substrates
The process is applicable for the metallization of non-conductor polymer substrates including, for example, ABS, ABS/PC, polyamide (PA), polypropylene (PP), thermoplastic olefins (TPO's), polyphenyleneoxide (PPO), polyphenylene ether, polyimides, polyether imide (PEI), polyether ether ketone (PEEK), polyphenylene sulfide, polyphthalamide, polyurethane (PU) and its blends as well as composites such as epoxy-glass laminates.
Additional non-conductive substrates include a wide variety of non-conductive materials, including synthetic resins such as thermoplastic, thermosetting and elastomeric polymers, and glass. In one embodiment, the substrate is a composite material, e.g., epoxy-glass, phenolic-paper, or polyester-glass; and typical composites used in circuit board manufacturing include polyimides for flexible circuitry or high-temperature applications; paper/phenolic which can be readily punched: NEMA grade FR-2; paper/epoxy which has better mechanical properties than the paper/phenolic: NEMA grade FR-3; glass/epoxy and woven glass fabric which have good mechanical properties: NEMA grade FR-4, FR-5; and random glass/polyester which is suitable for some applications: NEMA grade FR-6.
Typical thermosetting polymeric materials which are suitable include polyepoxides; phenolic resins; aminoplastics; unsaturated polyesters; polyimides; and polyamides. Specific thermosetting polymeric materials include the epoxy resins; phenolic resins, e.g., copolymers of phenol, resorcinol and cresol; and polyimides. The non-conductive substrates can be molded from such polymeric materials additionally containing fillers and/or reinforcing agents, such as glass filled epoxy or phenolic base materials. Other additives which may be present in the polymer include natural fibers such as cotton, paper and cellulose; synthetic fibers; carbon black; powdered alumina; fine silica particles; wax and so forth, used as fillers, pigments, reinforcing agents, mold release agents, and so forth.
In one embodiment, the non-conductive surface is a thermoplastic polymer. The thermoplastic olefins include, among others, polyethylenes and poly(&agr;-olefins) such as poly(1-butene) and poly(1-hexene), wherein the olefin may comprise from 3 to 20 carbon atoms, and may be branched or straight chain compounds. Suitable thermoplastic polymeric materials include polyolefins, such as high and low density polyethylene, polypropylene, polyfluoroethylene, ethylene-propylene copolymers and the like; polyacetals; polyvinyl chloride and copolymers thereof; polyvinyl acetate; polysulfones; polysulfides including polyalkylene sulfides and polyarylene sulfides; polystyrenes and acrylonitrile-butadiene-styrene (ABS) copolymers; polyamides such as poly(hexamethylene adipamide), polycaprolactam, poly(hexamethylene sebacamide), and poly(undecamide); polyimides; polyesterimides; polyetherimides; polycarbonates; polyestercarbonates; polyphenylene oxide; polyacrylics such as poly(methacrylate), polyacrylic acid, and polyacrylonitrile; cellulose esters; polyurethanes; and polyamideimides. In one embodiment, the thermoplastic polymeric material is a polyolefin, e.g., polypropylene; a polysulfone or a polycarbonate. In one embodiment, the polymer is an ABS copolymer. Examples of useful elastomers are natural and synthetic rubbers; silicone rubbers; polyurethane elastomers; and nitrile rubbers.
The foregoing list of non-conductive substrates is intended to be exemplary and is non-limiting. Other suitable non-conducting substrates may be suitably selected by those of skill in the art.
Throughout the present specification and claims, the limits of the ranges and ratios may be combined.
Non-Conductive Surface Modification
In one
Atotech Deutschland GmbH
Barr Michael
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