Coating processes – Electrical product produced – Carbon coating
Reexamination Certificate
2000-03-17
2001-10-16
Wong, Edna (Department: 1741)
Coating processes
Electrical product produced
Carbon coating
C427S096400, C427S097100, C427S322000, C205S159000, C205S166000, C205S169000, C205S125000, C205S220000, C205S224000
Reexamination Certificate
active
06303181
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to printed wiring boards having recesses, or other non-conductive surfaces, made electrically conductive by applying a coating containing carbon, preferably graphite, to an initially nonconductive through hole or other surface.
The prior art, for example U.S. Pat. No. 3,224,986, discloses water-insoluble, water-insensitive polymers made by (1) forming a polyamide, (2) reacting the polyamide with epichlorohydrin to make a cationic, water-soluble, thermosetting resin; and (3) reacting the resin with a water-soluble polymer, such as carboxymethylcellulose or others, in water at a low pH. Related disclosure may be found in U.S. Pat. Nos. 3,658,873; 3,049,469; 3,962,159; 3,917,894; 4,037,017; 4,152,199; 2,926,116; 2,926,154; 3,332,834; 3,592,731; and 3,763,060. All the patents listed in this paragraph are hereby incorporated by reference. These patents assert that various polysaccharides, such as starches and carboxymethylcellulose, react with polyamide-epichlorohydrin resins to form water-resistant coatings.
Additional background information about conductive coatings for through holes may be found in U.S. Pat. No. 5,690,805. That patent is hereby incorporated by reference in the present disclosure.
SUMMARY OF THE INVENTION
The present invention is a method of applying an electrically conductive carbon coating to a non-conductive surface.
A substrate is provided having at least one non-conductive surface. An example of such a substrate is the wall of a through hole or via drilled or otherwise formed in the non-conductive substrate for a printed wiring board.
A conditioning agent is provided. The preferred conditioning agent contains a substantive cationic conditioner, for example, a polyamide, more preferably a polyamide epichlorohydrin resin in one embodiment of the invention.
A liquid dispersion of electrically conductive carbon including a water-dispersible binding agent is also provided. The carbon dispersion has a mean particle size no greater than about 50 microns. The carbon particles in the dispersion preferably have a mean particle size of not greater than about 1 micron, particularly for a graphite coating.
The nonconductive surface to be made electrically conductive is first contacted with the conditioning agent to apply a film of a cationic substantive conditioner on the nonconductive surface. The carbon dispersion is applied to the conditioned surface in an amount and under conditions effective to form a substantially continuous, electrically conductive carbon coating.
Next, the conductive carbon coating is optionally fixed on the (formerly) nonconductive surface. (“Fixing” is defined below in the detailed description.) Typically, fixing is carried out after the carbon dispersion is applied, without drying the carbon coating first. The fixing process removes excessive carbon composition deposits, and thus smooths the carbon coating on the recess surfaces by eliminating lumps and by making the coating more uniform and adherent.
As used herein, a “uniform” coating is one essentially free of excess conductive coating composition build-up, particularly at the opening or openings of a recess, so the coating has a substantially uniform thickness at the mouth and in the interior of the recess, as viewed under a 50×magnification of a cross-section of a recess after plating. Graphite or carbon black are referred to in this specification either together or separately as “carbon.” A nonconductive surface can be any surface that does not conduct electricity at all, or to the necessary or desired degree for some practical application.
DETAILED DESCRIPTION OF THE INVENTION
While the invention will be described in connection with one or more preferred embodiments, it will be understood that the invention is not limited to those embodiments. On the contrary, the invention includes all alternatives, modifications, and equivalents as may be included within the spirit and scope of the appended claims.
In one embodiment of the method according to the present invention, an originally non-conductive surface is cleaned, conditioned, treated with a conductive carbon composition, the carbon composition is optionally fixed, and the carbon composition is dried to form an electrically conductive coating. The materials and steps used in this preferred embodiment are set out below in more detail.
Nonconductive Surface
The nonconductive surface can be any material which does not conduct electricity well, or at all. An example of a suitable nonconductive surface is a resin-glass fiber composite board of the type conventionally used as a printed wiring board. Further examples of suitable nonconductive surfaces are the walls of a through hole or via that has been drilled, ablated by application of laser energy, or built up by an additive process. Another example of a suitable nonconductive surface is a glass surface, such as the glass envelope of a television tube, video monitor, or similar device, or a sheet of window glass. Still another example of a suitable nonconductive surface is a polymer or glass/polymer composite surface, such as the face of a printed wiring board. Many other suitable nonconductive substrates are well known to those skilled in the art.
Cleaner/Conditioner
Commonly, the first step of the present process is cleaning the substrate that is to be plated. In the cleaning step, the substrate is thoroughly wetted and contaminants such as grease, oil, or dirt are removed from the substrate that is to receive plating.
Commonly, the next step is a conditioning step, during which the substrate is contacted with a conditioning agent. The contemplated conditioning agent is a substantive material, commonly a cationic material such as a polyamidoamine, a cationic polymer, a cationic surfactant, or the like. The conditioning agent is applied as an adhesion promoter so the substrate will be attractive to the anionic particles of carbon which are later applied by contacting the substrate with a carbon dispersion.
The conditioner can be an alkaline aqueous solution or dispersion of a base and a conditioning agent. The useful conditioning agents include those selected from the group consisting of:
SANDOLEC CF
SANDOLEC CU
SANDOLEC CS
SANDOLEC CL
SANDOLEC CT
CALLAWAY 6818
CYASTAT SP
CYASTAT LS
CYASTAT SN
CYANAMER A-370
MAGNIFLOC 496
DAXAD CP2
PRIMAFLO C C3
CAT-FLOC
CAT-FLOC T
RETEN 210
POLYTEC 7M
PERCOL 727
PERCOL 763
OCTOPOL SDE-25
OCTOPOL SDM-40
GLO-CLEAR 2202
GLO-CLEAR 2220
GLO-CLEAR 2283
PRIFRAC 2990
ALUBRAFSOFT GSS
FIBRABON 35
DENSEFLOC 30
CALLAWAY 6817
CALLAWAY 6831
and combinations of those conditioners. A preferred conditioning agent is made from any of the CALLAWAY or SANDOLEC materials, used alone or in combination to provide polyamide epichlorohydrin resins. Examples of these materials are CALLAWAY 6818 polyamide epichlorohydrin resin, available from Callaway Chemical Co., Columbus, Ga., or SANDOLEC CF, available from Clariant Corp., Charlotte, N.C.
The bases contemplated here include lower alkanol amines (lower alkanol being defined as 1- to 4-carbon alcohol moieties), such as ethanolamines, for example mono-, di- or triethanolamine; alkaline materials generally, such as alkali metal hydroxides, carbonates, and bicarbonates, for example potassium hydroxide, carbonate, or bicarbonate; other materials capable of raising the pH of the composition, preferably to at least about 9; and mixtures of such materials.
A representative formulation for a conditioner is from about 5-30 parts by weight of a base as previously defined, from about 5 to about 90 parts by weight of a conditioning agent selected from the preceding list, and sufficient deionized water to make 1,000 parts by weight of the complete conditioner.
Optionally, 0.5 to about 5 parts by weight of an alkylene glycol can be added to the conditioner composition. The alkylene glycols contemplated herein include 1- to 4-carbon alkylene glycols and their dimers and oligomers. Specific alkylene glycols contemplated herein include ethylene glycol, propylene glycol, butylene
Mosolf Charles A.
Polakovic Frank
Thorn Charles Edwin
Electrochemicals Inc.
McAndrews Held & Malloy Ltd.
Wong Edna
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