Carbon-based direct plating process

Abstract

A method for preparing a non-conductive substrate and a two-component gel coating composition thereon that can be metal plated. The method includes the steps of: a) contacting the non-conductive substrate with a conditioner containing a polymeric conditioning agent; b) applying a carbon-based dispersion to the conditioned substrate, the carbon-based dispersion containing adhesive carbon or graphite particles dispersed in a liquid solution; and c) etching the non-conductive substrate. The adhesive carbon black or graphite particles in the liquid-carbon-based dispersion have a small particle size and a narrow particle size distribution.

Description

[Technical Field]

[0001] The present invention relates generally to a carbon-based direct plating process for use in printed circuit board manufacturing. [Background technology]

[0002] A printed wiring board (also known as a printed circuit board) is generally a laminated material comprising two or more plates of copper foil separated from each other by a layer of non-conductive material. Copper is most typically used as the electroplated metal for printed wiring boards, but other metals, such as nickel, gold, palladium, and silver, may also be electroplated. The non-conductive layer(s) generally comprise an organic material, such as epoxy resin impregnated with glass fibers, but may also comprise thermosetting resins, thermoplastic resins, and mixtures thereof, alone or in combination with reinforcing materials, such as fiberglass and fillers. Multilayer wiring boards may be fabricated by sandwiching additional layers of metal (e.g., copper) between layers of insulating material to accommodate additional circuitry on the printed wiring board.

[0003] In many printed wiring board designs, electrical paths or traces require connections between separate metal layers (i.e., copper plates) at specific points within the trace. This is typically accomplished by drilling holes at desired locations through a laminate of copper plates and non-conductive layer(s) to connect the separate metal layers. Metallizing the through-hole walls is necessary to achieve connections between two metal circuit traces on opposite sides of a printed wiring board and / or between inner-layer circuit traces in a multilayer board.

[0004] Although electroplating is a desirable method for depositing copper and other conductive metals onto surfaces, it cannot be used to coat non-conductive surfaces such as untreated through-holes. Therefore, the through-holes must be treated with a conductive material to make them electroplatable.

[0005] One process for making through-holes conductive involves physically coating them with a conductive film. Thus, while the coated through-holes are sufficiently conductive for electroplating, they typically lack sufficient conductivity and robustness to form permanent electrical connections between circuit layers at either end of the through-hole. Thus, coated through-holes are electroplated to provide the permanent connections. Electroplating reduces the resistance of the through-hole to negligible levels and does not consume significant amounts of power or alter circuit characteristics.

[0006] The through-hole walls may be prepared for electroplating by a carbon-based process that utilizes a liquid carbon dispersion. Typical steps of this process are as follows: 1) Drill and deburr the surface of the through-holes. For multilayer printed circuit boards, the board may be subjected to a desmear or etch-back process to clean the copper interface surface inside the through-holes. 2) The printed wiring board is optionally, but preferably, subjected to a pre-cleaning process which involves applying a pre-cleaner to the surface of the printed wiring board to prepare the printed wiring board to receive the liquid carbon black dispersion thereon. 3) After application of the cleaner, the printed wiring board is rinsed with water to remove excess cleaner and then contacted with a conditioner solution that ensures that substantially all through-hole wall surfaces are prepared to receive a successive layer of the carbon-based dispersion that is subsequently applied. 4) The liquid carbon-based dispersion is applied to or contacted with the cleaned and conditioned printed wiring board. Preferred methods for applying the dispersion to the printed wiring board include dipping and spraying. 5) subjecting the carbon-coated printed wiring board to a process that removes substantially all (i.e., greater than about 95% by weight) of the water in the applied dispersion, leaving a dry carbon-containing deposit on the through-holes and other exposed surfaces of the non-conductive layer. This drying process may be accomplished by a variety of methods, including, for example, evaporation at room temperature, heating the printed wiring board at an elevated temperature for a period of time, an air knife, or other similar means commonly known to those skilled in the art. The drying process may be repeated after immersion of the substrate in the liquid carbon dispersion to ensure complete coverage of the through-hole walls. 6) The metal portion of the substrate is then aggressively etched at a high spray pressure and a high total etching volume to thoroughly remove the dried carbon coating from the metal portion of the substrate. This microetching process simultaneously performs two highly desirable tasks: (1) removing substantially all excess carbon black or graphite material adhering to the exposed surfaces of the outer and inner copper plates or foils of the multilayer printed wiring board, and (2) chemically cleaning and slightly microetching the outer copper surfaces, thereby providing a good base for either a dry film application or electrolytic deposition of copper after mechanically scrubbing the printed wiring board.

[0007] The mechanism by which this microetching process works is not by attacking the carbon material deposited directly on the copper foil, but rather by attacking only the first few atomic layers of the copper immediately below, which provide the adhesion of the coating. A printed wiring board coated with carbon black or graphite is contacted with a microetching solution to shed the carbon black or graphite "flakes" from the copper surface, which are then removed from the microetching bath by filtration or other similar means.

[0008] The basic steps of this process are described in more detail, for example, in US Pat. No. 4,619,741, the subject matter of which is incorporated herein by reference in its entirety. Various modifications and improvements to this process are described in U.S. Pat. Nos. 4,622,107, 4,622,108, 4,631,117, 4,684,560, 4,718,993, 4,724,005, 4,874,477, 4,897,164, 4,964,959, 4,994,153, 5,015,339, 5,106,537, 5,110,355, 5,139,642, 5,143,592, 5,725,807, and 7,128,820, the subject matter of each of which is incorporated herein by reference in its entirety.

[0009] U.S. Patent No. 4,897,164 to Piano et al. describes a process in which, after a drying step, the dried deposit of carbon black in the through-holes is contacted with an aqueous solution of an alkali metal borate prior to microetching to remove loose or easily removable carbon black particles from the through-hole area.

[0010] US Patent No. 4,964,959 to Piano et al. describes the addition of conductive polymers or combinations thereof to carbon black dispersions.

[0011] U.S. Pat. No. 4,994,153 to Piano et al. describes a process for treating tooling holes or slots coated with a carbon black dispersion in a non-conductive material, which process involves removing the carbon black with an aqueous solution containing: (a) an alkanolamine, (b) an anionic surfactant which is the neutralized addition product of maleic acid and / or fumaric acid with a poly(oxylated) alcohol, (c) a nonionic surfactant which is an aliphatic monophosphate ester and / or aliphatic diphosphate ester, and (d) an alkali metal or alkaline earth metal hydroxide.

[0012] US Patent No. 5,015,339 to Pendleton describes an electroplating pretreatment in which a non-conductive material is first contacted with an alkaline permanganate solution, then a neutralizer / conditioner solution, and then a carbon black dispersion.

[0013] In variations on this basic process, the carbon-coated wiring board is subjected to a fixation step prior to drying to remove excess carbon dispersion from the surface of the printed wiring board and make the carbon dispersion more processable, as described, for example, in U.S. Patent Application Publication No. 2010 / 0034965 to Retallick et al., the subject matter of which is incorporated herein by reference in its entirety. Fixation can be achieved by chemical fixation or by mechanical fixation.

[0014] In chemical fixation, a fixative solution is applied to the surface wetted with the carbon dispersion to smooth the carbon coating on the recessed surface by removing excess carbon deposits, eliminating clumps, and making the coating more uniform. In physical fixation, the recessed or other surface of the substrate wetted with the carbon dispersion is subjected to a mechanical force, such as with a fluid or air jet, to remove excess carbon coating buildup before drying. For example, a fluid or air jet may be used to contact the carbon dispersion-coated surface to blow away excess buildup of carbon deposits, remove clumps, and smooth the carbon coating on the recessed surface by making the coating more uniform.

[0015] Once the carbon coated printed wiring board has been microetched, the printed wiring board can be electroplated with a suitable conductive metal.

[0016] All of the above-mentioned processes include a step, prior to the microetching step, of subjecting the carbon-coated printed wiring board to removing substantially all of the water (i.e., about 95% by weight or more) in the applied dispersion, such that a dry deposit containing carbon remains in the holes and on other exposed surfaces of the non-conductive layer. That is, in all of these processes described above, the carbon-coated wiring board is dried prior to the microetching step.

[0017] Microetching often causes problems in plating, especially in the region of the copper-dielectric interface. Specifically, copper etching also often strips carbon coatings from the dielectric regions directly adjacent to the copper, thereby creating an insulating barrier for electrical continuity in subsequent electroplating steps. This barrier can then lead to plating failures and defects such as voids, knit lines, and plating creases. To avoid these types of defects, a lower microetching step is desirable.

[0018] To adequately remove carbon black or graphite from copper surfaces, large pumps, high pressures, large etching chambers, and / or harsh etching chemicals must typically be used to achieve acceptable results. Frequent cleaning of the equipment from carbon black or graphite that has flakes off the copper surface is also required to reduce agglomeration during the metal plating process.

[0019] It has also been discovered that carbon-based direct plating colloids / dispersions tend to have poor adhesion to dielectric substrates, due in part to the size of the colloidal particles. A wide distribution of particle sizes can also contribute to poor adhesion due to the presence of larger sized colloidal particles.

[0020] Therefore, it would be desirable to provide a direct plating process that reduces agglomeration and does not require additional processing steps or conditions to achieve good results. It would also be desirable to provide a direct plating process that improves the adhesion of the carbon dispersion to the printed wiring board. Summary of the Invention

[0021] It is an object of the present invention to provide an improved direct plating process for preparing printed wiring boards to receive electroplating thereon.

[0022] Another object of the present invention is to provide an improved direct plating process that can reduce agglomeration in the metal plating process.

[0023] It is yet another object of the present invention to provide a direct plating process that improves electroplating conditions.

[0024] It is yet another object of the present invention to provide a graphite or carbon black dispersion in which the carbon particles exhibit a smaller average particle size to enhance adhesion of the particles to printed wiring boards.

[0025] It is yet another object of the present invention to provide graphite or carbon black dispersions having narrower particle size distributions to enhance particle adhesion to printed wiring boards.

[0026] It is yet another object of the present invention to provide a graphite or carbon black dispersion in which the graphite or carbon black particles are adhesive.

[0027] To that end, in one embodiment, the present invention generally relates to a method for preparing a non-conductive substrate onto which metal can be plated, the method comprising: a) optionally but preferably contacting a non-conductive substrate with a precleaner; b) contacting the non-conductive substrate with a conditioner comprising a polymeric conditioning agent; c) applying a liquid carbon-based dispersion to the conditioned non-conductive substrate to form a carbon / conditioner gel coating on the conditioned non-conductive substrate, the carbon-based dispersion comprising adhesive carbon black particles or adhesive graphite particles dispersed in a liquid solution, the carbon particles solidifying on the conditioned substrate to form the carbon / conditioner gel coating; d) etching the carbon / conditioner gel coated substrate; The adhesive carbon black particles or adhesive graphite particles in the liquid carbon-based dispersion have a small particle size and a narrow particle size distribution. In one embodiment, the present invention also generally relates to a two-component gel coating composition for preparing a non-conductive substrate to allow metal plating thereon, the two-component gel coating comprising: a. A conditioner, i. a polyquaternium compound having a molecular weight greater than 1,000,000 g / mol; ii. a pH buffer; iii. a surface tension reducing agent; a conditioner having a pH in the range of about 8 to about 10; b. A liquid carbon-based dispersion, the liquid carbon-based dispersion comprising: i. adhesive carbon particles or adhesive graphite particles dispersed in a dispersing agent; ii. a pH adjuster; a liquid carbon-based dispersion, wherein the adhesive carbon black particles or adhesive graphite particles have a small particle size and a narrow particle size distribution, and the pH of the liquid carbon dispersion is in the range of about 8 to about 10; When the conditioner and liquid carbon-based dispersion are applied sequentially to the non-conductive substrate, an adherent carbon / conditioner gel coating is formed on the surface of the non-conductive substrate. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention relates generally to a carbon-based direct plating process for printed circuit board or printed wiring board manufacturing.

[0029] As used herein, "a," "an," and "the" refer to both the singular and the plural, unless the context clearly dictates otherwise.

[0030] As used herein, the term "about" refers to a measurable value of a parameter, amount, duration, etc., and is meant to include a variation of no more than + / -15%, preferably no more than + / -10%, more preferably no more than + / -5%, even more preferably no more than + / -1%, and still more preferably no more than + / -0.1% of the specifically recited value, to the extent that such variations are appropriate for practicing the invention described herein. It is also to be understood that the value to which the modifier "about" refers is itself specifically disclosed herein.

[0031] As used herein, spatially relative terms such as "beneath," "below," "lower," "above," "upper," "front," "back," etc. are used for ease of description to describe the relationship of one element or feature to another element or feature. It will be further understood that the terms "front" and "back" are not intended to be limiting and are intended to be interchangeable where appropriate.

[0032] As used herein, the terms "comprises" and / or "comprising" specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0033] In one embodiment, the present invention generally relates to a method for preparing a non-conductive substrate onto which metal can be plated, the method comprising: a) optionally but preferably contacting a non-conductive substrate with a precleaner; b) contacting the pre-cleaned non-conductive substrate with a conditioner comprising a polymeric conditioning agent; c) applying a liquid carbon-based dispersion to the pre-cleaned and conditioned non-conductive substrate to form a carbon / conditioner gel coating on the conditioned non-conductive substrate, the carbon-based dispersion comprising adhesive carbon black particles or adhesive graphite particles dispersed in a liquid solution, the carbon particles coagulating on the conditioned substrate to form the carbon / conditioner gel coating; d) etching the carbon / conditioner gel coated substrate; The adhesive carbon black particles or adhesive graphite particles in the liquid carbon-based dispersion have a small particle size and a narrow particle size distribution.

[0034] In one embodiment, the present invention also generally relates to a two-component gel coating composition for preparing a non-conductive substrate to allow metal plating thereon, the two-component gel coating comprising: c. A conditioner, i. a polyquaternium compound having a molecular weight greater than 1,000,000 g / mol; ii. a pH buffer; iii. a surface tension reducing agent; a conditioner having a pH in the range of about 8 to about 10; d. A liquid carbon-based dispersion, the liquid carbon-based dispersion comprising: i. adhesive carbon particles or adhesive graphite particles dispersed in a dispersing agent; ii. a pH adjuster; a liquid carbon-based dispersion, wherein the adhesive carbon black particles or adhesive graphite particles have a small particle size and a narrow particle size distribution, and the pH of the liquid carbon dispersion is in the range of about 8 to about 10; When the conditioner and liquid carbon-based dispersion are applied sequentially to the non-conductive substrate, an adherent carbon / conditioner gel coating is formed on the surface of the non-conductive substrate.

[0035] In one embodiment, the non-conductive substrate is a printed wiring board or a printed circuit board.

[0036] Once the etching step has been performed and the liquid carbon coating has dried on the non-conductive substrate to form a conductive carbon coating on the printed wiring board, the printed wiring board can be electroplated with a suitable metal.

[0037] The inventors have discovered that improved results are obtained if the etching step is performed before the conductive carbon coating has dried on the substrate.

[0038] It was previously believed that the conductive carbon coating on the surface needed to be dried before contacting the substrate with an etching solution. Thus, it was previously understood that drying the conductive carbon coating on the substrate surface was necessary before etching the substrate to ensure sufficient adhesion of the carbon particles to the non-conductive portions of the substrate and facilitate electroplating of metal onto the non-conductive portions of the substrate. However, drying the conductive carbon coating before etching can result in contamination of the equipment with carbon particles.

[0039] Thus, in one preferred embodiment, the etching step is performed before the liquid conductive carbon coating dries on the non-conductive substrate, in other words, the etching step is preferably performed without first drying the conductive carbon coating on the surface prior to the drying step.

[0040] Some of the advantages of performing an etching step prior to drying the conductive carbon coating on the substrate include the following: 1) It is easier to etch away the metal portion of the substrate and remove the overlying conductive carbon coating if an etching step is performed prior to drying the conductive carbon coating. A dried conductive carbon coating layer acts as a barrier to etching the underlying metal, but a wet conductive carbon coating layer does not act as a significant barrier to etching. 2) The total etching volume and spray pressure required to obtain a clean metal portion of the substrate is significantly reduced when the substrate is etched prior to drying the conductive carbon coating compared to after the conductive carbon coating has dried. 3) The cleanliness of the process and equipment used to apply the conductive carbon coating is greatly improved because the carbon particles are etched from the metal portions of the substrate in the chamber or tank immediately after the carbon suspension / colloid is placed in the chamber or tank. Typically, this means that the outer surface of the substrate is completely free of carbon, which typically involves the use of rollers and dryers after the carbon suspension remains at least substantially free of carbon particles.

[0041] Overall, a benefit of the processes described herein is also the reduction in the amount of agglomerates that can occur in subsequent metal plating steps. In contrast, prior art processes left more carbon particles on the metal portion of the substrate due to the difficulty of removing particles in the etching step and carbon contamination from dried carbon remaining on the equipment that can be redeposited on the surface of the substrate.

[0042] In contrast, the present invention provides much less agglomeration during the metal plating process because the wet carbon coating on the substrate is etched from the metal portion of the substrate prior to drying the coating so that the carbon is more completely removed from the metal portion of the substrate. Thus, there is less opportunity for the equipment to redeposit dried carbon particles onto the surface, resulting in significantly less nodule formation during the metal plating process.

[0043] As described herein, in one embodiment, the printed wiring board is optionally, but preferably, contacted with a precleaner prior to the conditioning step. When used, a suitable precleaner includes a standard acid cleaner for printed wiring boards, such as a solution of sulfuric acid and a nonionic surfactant, a commercially available product of which is available from MacDermid Enthone Inc. under the trade name Acid Cleaner 6A. The printed wiring board may be subjected to the precleaner by immersing (or contacting) the printed wiring board in the precleaner for a time suitable to remove debris and / or contaminants from the surface of the board. For example, the printed wiring board may be immersed in the precleaner at a temperature of from about room temperature to about 55°C for 30 seconds to 5 minutes, more preferably 1 minute to 2 minutes.

[0044] The printed wiring board is then subjected to a conditioning step in which the board is contacted with a conditioner comprising a polymeric conditioning agent, for example, as described in U.S. Patent No. 10,986,738, the subject matter of which is incorporated herein by reference in its entirety. In one embodiment, the printed wiring board is contacted with the conditioner by immersing the printed wiring board in the conditioner at a suitable temperature for a suitable period of time.

[0045] In one embodiment, the conditioner comprises a high molecular weight conditioning agent, the molecular weight of which is greater than about 1,000,000 g / mol, more preferably greater than about 2,000,000 g / mol, and even more preferably greater than about 3,000,000 g / mol. The printed wiring board is contacted with the conditioner for at least 20 seconds. In one embodiment, the printed wiring board is contacted with the conditioner for about 20 seconds to about 5 minutes. Furthermore, the pH of the conditioner is generally 1 to 14, more preferably 7 to 14, and more preferably about 8 to about 10. In one embodiment, the conditioner is alkaline, with a pH of about 9 being preferred.

[0046] Examples of high molecular weight conditioning agents for use in the conditioners described herein include, but are not limited to, polyquaternium compounds having a molecular weight of greater than 1,000,000 g / mol, or greater than 2,000,000 g / mol, or greater than 3,000,000 g / mol. Polyquaternium is an international nomenclature for cosmetic ingredients used in the personal care industry and is used to define structures containing quaternary ammonium centers in the polymer. Examples of polyquaternium compounds are listed in Table 1 below. Other polyquaternium compounds having a molecular weight of greater than 1,000,000 g / mol and other similar structures can also be used in the practice of the present invention.

[0047] [Table 1]

[0048] In addition to the polymeric conditioning agent, the conditioner may also include a pH buffer such as borax, and optionally, but preferably, a surface tension reducing agent such as a non-ionic surfactant, an example of which is available under the trade name Tomadol 91-6 from Evonik Industries AG.

[0049] The temperature of the conditioner may be maintained at a temperature of from room temperature to about 150°F, more preferably from about 80 to about 130°F, even more preferably from about 85 to about 110°F, or about 95°F while the printed wiring board is in contact with the conditioner.

[0050] The large molecular weight of the conditioning agent results in the formation of a gel when the carbon dispersion contacts and then coats the surface of the pre-adsorbed conditioner on the substrate surface. The agglomerating graphite (or carbon black) and the conditioner containing the high molecular weight conditioning agent together form a gel-like solid-liquid coating, which allows the gel-like coating to be sprayed strongly without washing off during the subsequent microetching step. The gel-like coating between the conditioner and the graphite (or carbon black) coating is formed due to the very high molecular weight of the conditioner and its inclusion of a polyquaternary compound, as well as the adhesive properties of the carbon black or graphite particles. The polyquaternary compound neutralizes the negative charge on the graphite (or carbon black) colloid, and then the conditioner containing the high molecular weight polyquaternary compound turns the resulting agglomerating agent into a gel-like solid-liquid coating that is not easily washed off and can withstand the microetching step even if the carbon coating is not first dried.

[0051] Once the conditioning step is complete, the printed wiring board is contacted with a carbon-based dispersion, as further described herein.

[0052] The carbon-based dispersion includes a source of conductive adhesive carbon particles and one or more binders and / or dispersants capable of dispersing the conductive adhesive carbon particles. Preferred methods for applying the liquid carbon dispersion to printed wiring boards include dipping and spraying, as well as other methods of applying chemicals used in the printed circuit board industry. In preparing the liquid carbon-based dispersion, the components, and any other preferred ingredients, are mixed together to form a stable dispersion. This may be achieved by subjecting the concentrated dispersion to wet-grinding or wet-milling to thoroughly mix the components. Suitable wet-grinding and wet-milling processes include, for example, ball milling, colloid milling, high-shear milling, ultrasonic techniques, or other similar procedures. Importantly, wet-grinding or wet-milling techniques can produce carbon dispersions with small particle sizes and narrow particle size distributions, and can produce adhesive carbon particles. While there are several methods for reducing the particle size of carbon-based dispersions, controlling the particle size distribution is also important. The dispersion can then be subsequently diluted with water or other dispersants to the desired concentration for the working bath.

[0053] An important factor is particle size consistency, and it is desirable that the dispersions do not contain large particles, such as particles having diameters greater than 800 nm for carbon black and greater than 3,500 nm for graphite. Additionally, it is also desirable that the milling method produce a consistent particle size for the dispersions of the present invention without requiring waste or centrifugation.

[0054] Thus, this combination of dispersant and / or binder selection and milling process together creates a much improved product that is easier to manufacture, more efficient, cheaper, more stable, produces less waste, and adheres much better to the surface of the PCB, allowing for a microetching solution to be sprayed heavily before drying and still not wash away. It should be noted that while graphite and carbon black particles are generally considered to be lubricating, the milling process of the present invention surprisingly produces carbon black particles or graphite particles that are themselves adhesive / adhesive. Thus, the adhesive carbon particles of the present invention, when dispersed in a dispersant, can adhere more firmly to the substrate and therefore are not easily washed away.

[0055] Unlike prior art processes in which the carbon dispersion is dried prior to the microetching step, the gel-like solid-liquid coating formed by the carbon dispersion containing adhesive carbon black and / or adhesive graphite particles and the conditioner agent described herein is able to withstand high pressure spraying before drying, allowing the adhesive carbon particles to better adhere to the through-hole walls and withstand the spray etching step even before the coating dries.

[0056] Controlling and / or reducing the particle size and particle size distribution of carbon-based colloids / dispersions has surprisingly been shown to affect the adhesion of carbon particles to the dielectric substrate of printed circuit boards. Creating colloids or dispersions with smaller particle sizes and narrower particle size distributions than those currently available in the art surprisingly aids in the subsequent adhesion of particles to the substrate in direct plating processes that make printed circuit boards conductive. This adhesion is particularly good when processing circuit boards in direct plating processes in which an etching step is performed before the coating is dried. Typically, when such wet carbon-containing coatings are spray-etched before drying, the particles spray off the substrate and do not have sufficient adhesion.

[0057] The carbon-based colloid or dispersion contains adhesive graphite or carbon black particles, which are reduced to less than a specified size. For carbon black-containing colloids / dispersions, the particles are reduced to a D50 of less than 120 nm, preferably less than 110 nm, more preferably less than 100 nm, and a D99 of less than 400 nm, preferably less than 300 nm, and more preferably less than 250 nm. For graphite-containing colloids / dispersions, the particles are reduced to a D50 of less than 350 nm, preferably less than 325 nm, more preferably less than 300 nm, and a D99 of less than 2500 nm, preferably less than 2,000 nm, and more preferably less than 1,800 nm. The particle sizes were measured using a BLUEWAVE particle size analyzer available from Microtrac MRB. The BLUEWAVE uses a laser diffraction analyzer to measure particle volume, number, and area distributions, as well as percentiles.

[0058] Typically, small graphite particles exhibit a D50 of about 1,000 nm. However, the D50 of the graphite particles of the present invention is significantly smaller, on the order of less than 350 nm, or less than 325 nm, or less than 300 nm. This is due in part to the means by which the graphite is milled into smaller particles, as well as the dispersants used therein.

[0059] Examples of conductive carbon that can be used in the carbon dispersion include carbon black and graphite. Many types of carbon can be used, such as carbon black, furnace black, and graphite.

[0060] In the case of carbon black, it is preferred to utilize carbon black that is initially acidic or neutral, i.e., that when slurried with water has a pH of from about 1 to about 7.5, more preferably from about 2 to about 4. Preferred carbon black particles are also highly porous, having a surface area, as measured by the BET (Brunauer-Emmert-Teller) method, of from about 45 to about 1100, preferably from about 300 to about 600 square meters per gram.

[0061] Examples of some commercially available carbon blacks suitable for use in the present invention include Cabot XC-72 R Conductive, Cabot Monarch 800, and Cabot Monarch 1300 (all available from Cabot Corporation, Boston, Massachusetts). Other suitable carbon blacks include Columbian T-10189, Columbian Conductiex 975 Conductive, Columbian CC-40,220, and Columbian Raven 3500 (all available from Columbian Carbon Company, New York, NY). Suitable graphites include Showa-Denko UFG (available from Showa-Denko KK, 1-13-9 Shibadaimon, Minato-ku, Tokyo, Japan, Postal Code 105), Nippon Graphite AUP (available from Nippon Graphite Industries, Ishiyama, Japan), and Asbury Micro 850 (available from Asbury Graphite Mills, Asbury, New Jersey).

[0062] The conductive carbon particles should be present in an amount effective to provide a conductive coating when the coating composition is applied to a substrate. The carbon may be present in a concentration ranging from about 0.1 to about 20% by weight of the composition, alternatively from about 0.5 to about 10% by weight, alternatively from about 1% to about 7% by weight, or alternatively from greater than about 4% to about 6.5% by weight.

[0063] In one embodiment, the lower limit for the total solids concentration in the coating composition is about 1.5% to about 5% by weight solids, more preferably about 2.0% to about 4.5% by weight solids, which includes the graphite and / or carbon black particles themselves, along with dispersants and / or one or more binders, and optional buffers and / or pH adjusters, to produce a total solids concentration in solution. The upper limit for the total solids concentration in the coating composition is based in part on cost. Typically, the upper limit for the total solids concentration is about 10% by weight solids, more preferably 5% by weight or less solids. In one embodiment, the total solids concentration in the coating composition is in the range of 3% by weight or less solids, or in the range of about 2.0 to about 2.5% by weight solids.

[0064] A typical percentage of graphite to other ingredients is about 50-60% by weight, so 1.5% by weight total solids is, as an example, 0.75% by weight graphite particles. This ratio of graphite / carbon to other ingredients such as dispersants, binders, buffers, pH adjusters, etc. can range from about 33% to 80% by weight of total solids as graphite / carbon black.

[0065] Common binders and / or dispersants used in prior art carbon dispersions are starches or polysaccharides, such as cornstarch, potato starch, dextrin, and gum acacia. However, starch does not produce foam or low surface tension in the solution, and it has also been found to be a poor dispersant for producing small particles, narrow particle size distributions, and stable colloids, as described herein. While starches and polysaccharides are believed to help dry particles adhere more effectively to the surface of a non-conductive substrate, the present inventors have discovered that such starches and polysaccharides do not aid in producing small particles and stable colloids in the processes described herein. Furthermore, compositions containing starch or other polysaccharides are more susceptible to bacterial or fungal growth than the compositions of the present invention. Thus, in one embodiment, the carbon dispersions described herein contain no starch or polysaccharides, or only trace amounts of starch or polysaccharides.

[0066] The selection of dispersant and / or binder is an important feature of the present invention. In one embodiment, the dispersant has a negative charge that imparts a negative charge to the particles that aids in stability. Note that the carbon dispersion must also exhibit desirable properties, including dispersant and / or binder materials that allow the carbon particles to solidify on the conditioned wall surface and form a gel-like carbon / conditioner coating.

[0067] In one embodiment, the dispersing agent comprises a wetting agent such as an anionic surfactant, a nonionic surfactant, or a cationic surfactant (or a combination thereof, such as an amphoteric surfactant). The dispersing agent should be soluble, stable, and preferably non-foaming in the liquid carbon black dispersion. Generally, for a polar continuous phase such as water, the surfactant should preferably have a high HLB number (8-18). The preferred type of surfactant depends primarily on the pH of the dispersion.

[0068] When the entire dispersion is alkaline (i.e., has an overall pH within the basic range), anionic or nonionic surfactants are preferably used. Anionic surfactants include, for example, sodium or potassium salts of naphthalene sulfonic acid, such as DARVAN No. 1 (Vanderbilt Chemicals), ECCOWET LF (Eastern Color and Chemical), PETRO AA, PETRO ULF (Petro Chemical Co., Inc.), and AEROSOL OT (American Cyanamid). Other anionic surfactants include neutralized phosphate ester surfactants, such as MAPHOS 55, 56, 8135, 60A, and L6 (Mazer Chemicals Inc.). One preferred anionic surfactant for liquid carbon black dispersions is MAPHOS 56. Suitable nonionic surfactants include ethoxylated nonylphenols, such as the POLY-TERGENT B series (Olin Corporation), or alkoxylated linear alcohols, such as the POLY-TERGENT SL series (Olin Corporation).

[0069] When the entire dispersion is acidic (i.e., has a pH in the acidic range), it is preferable to use a selected anionic or cationic surfactant. Examples of such anionic surfactants include, for example, the sodium or potassium salts of naphthalenesulfonic acid mentioned above. Examples of suitable cationic surfactants include cetyldimethylbenzylammonium chloride, such as AMMONYX T (Onyx Chemical Corporation), ethanolic alkylguanidine amine complexes, such as AEROSOL C-61 (American Cyanamid), lipocals, dodecyldiphenyloxide disulfonic acid (DDODA), such as sodium salts of DDODA, e.g., DOWFAX 2Al (Dow Chemical) and STRODEX (Dexter Chemical Corporation), and salts of complex organic phosphate esters. Examples of preferred surfactants include potassium amphoteric salts of complex amino acids based on fatty amines such as MAFO 13 and cationic ethoxylated soy amines such as MAZEEN S-5 or MAZTREAT (Maazel Chemicals, Inc.). Combinations of surfactants may also be used.

[0070] If used, the binder may be any natural or synthetic polymer, polymerizable monomer, or other viscous or solid material (or precursor thereof) that can adhere to the carbon particles and accept the anionic dispersing agent. Alternatively, the binder may be one that allows the carbon particles to which it is attached to be dispersed in the aqueous medium of the dispersion. For example, the binder may be a water-soluble or water-dispersible material selected from the group consisting of monosaccharides and polysaccharides (or more broadly, carbohydrates) and anionic polymers.

[0071] Polysaccharide (for purposes of this invention, including disaccharides and higher sugars) binders contemplated for use herein include cornstarch, other starches, and polysaccharide gums. Polysaccharide gums contemplated for use herein include agar, arabic, xanthan (e.g., KELZAN Industrial Grade Xanthan Gum, available from Kelco Div. of Merck & Co., Inc., Rahway, New Jersey), pectin, alginate, tragacanth, dextran, and other gums. Derived polysaccharides contemplated for use herein include cellulose acetate, cellulose nitrate, methylcellulose, and carboxymethylcellulose. Hemicellulosic polysaccharides contemplated for use herein include d-gluco-d-mannan, d-galacto-d-gluco-d-mannan, and the like. As noted above, in one embodiment, the carbon dispersion contains no starch or polysaccharides, or only trace amounts of starch or polysaccharides.

[0072] Anionic polymers contemplated herein include alkyl celluloses or carboxyalkyl celluloses, their low- and medium-viscosity alkali metal salts (e.g., sodium carboxymethylcellulose, or "CMC"), cellulose ethers, and nitrocellulose. Examples of such anionic polymers include KLUCEL hydroxypropyl cellulose, AQUALON CMC 7L sodium carboxymethyl cellulose, and NATROSOL hydroxyethyl cellulose (all commercially available from Aqualon Company, Hopewell, Virginia), ethyl cellulose (available from Hercules, Wilmington, Delaware), METHOCEL cellulose ethers available from Dow Chemical Company, Midland, Michigan, and nitrocellulose (also available from Hercules).

[0073] In one embodiment, the dispersant comprises an anionic surfactant such as ethoxylated phosphate esters, ethoxylated and propoxylated phosphate esters, ethoxylated tristyrylphenol phosphate esters, and combinations of one or more of the foregoing. Commercially available products include, for example, POLYSTEP® TSP-16PE30 available from Stepan Company and Soprophor® FLK available from Solvay SA. Other examples of acceptable anionic surfactants include sodium or potassium salts of naphthalene sulfonic acid, such as DARVAN No. 1 (available from Eastern Color & Chemical Company), PETRO AA and PETRO ULE (available from Petro Chemical Company), and AEROSOL OT (available from American Cyanamid Company). Preferred anionic surfactants include neutralized phosphate ester surfactants such as MAPHOS 55, 56, 8135, 60A, and L6, commercially available from BASF Chemical Co. The surfactant should be soluble, stable, and preferably non-foaming in the liquid carbon dispersion.

[0074] The dispersant is selected to reduce surface tension, resulting in much more stable and smaller suspended particles. The inventors of the present invention believe that a suitable dispersant is one that can adhere to the carbon particles through the milling process, with additional dispersant in solution. The dispersant also allows the graphite (or carbon black) particles to adhere to the printed wiring board.

[0075] In one embodiment, the conductive carbon black dispersion of the present invention consists essentially of (a) anionic surfactant or dispersing agent, (b) adhesive carbon black and / or adhesive graphite particles, (c) a pH adjuster, the pH adjuster being a hydroxide, (d) a binder, the binder being free of starch or polysaccharides, and (e) balance water, where the adhesive carbon black and / or adhesive graphite particles are milled using a milling process capable of producing small particle sizes and narrow particle size distributions of carbon particles. In one embodiment, the conductive carbon black dispersion of the present invention consists essentially of (a) anionic surfactant or dispersing agent, (b) adhesive carbon black and / or adhesive graphite particles, (c) a pH adjuster, the pH adjuster being a hydroxide, and (d) balance water, where the adhesive carbon black and / or adhesive graphite particles are milled using a milling process capable of producing small particle sizes and narrow particle size distributions of carbon particles. By "consisting essentially of" it is meant that the conductive carbon dispersion does not contain any additional elements that impair the ability of the carbon dispersion to adhere to a printed wiring board. In one preferred embodiment, the conductive carbon dispersion of the present invention consists of the recited components.

[0076] It is also important to have an alkaline pH, preferably in the range of about 8 to about 13, more preferably in the range of about 8 to about 10. Higher pHs cause more carbonate to be absorbed into solution from carbon dioxide in the air, so excessively high pHs are avoided for this reason. In preferred embodiments, a pH adjuster may be used; suitable pH adjusters include hydroxides such as potassium hydroxide and sodium hydroxide. In contrast, certain prior art products use ammonia as a pH adjuster, which is undesirable because it is a volatile pH adjuster that evaporates, making control more difficult. Thus, in one embodiment, the carbon dispersion is at least substantially free of ammonia.

[0077] The liquid carbon dispersion is typically placed in a container and the printed circuit board is immersed, sprayed, or otherwise contacted with the liquid carbon dispersion. The temperature of the liquid dispersion in the immersion bath should be maintained between about 60°F and about 95°F, preferably between about 70°F and about 80°F, during immersion. Immersion times advantageously range from about 15 seconds to about 10 minutes, more preferably from about 30 seconds to 5 minutes.

[0078] The desired thickness of the carbon coating is sufficient to allow for electroplating of copper or other metal films onto the printed circuit board in a direct plating process. The upper thickness limit is determined by the ability to remove the carbon coating from the copper surface. If the carbon is not removed from the copper surface, circuit board defects such as poor copper-to-copper contact within the inner layers of the circuit board can occur, also referred to as "interconnect defects." In one embodiment, the thickness may range from about 0.05 to about 0.25 micrometers.

[0079] However, as mentioned above, what is important is that the thickness is sufficient to allow metal plating in a direct plating process without any defects.

[0080] The problem of carbon particle deposition on the surface of a printed wiring board can occur particularly when a microetching spray etching step is performed prior to drying the coating. In many prior art processes, after coating a printed wiring board with a carbon-containing dispersion, the coating is dried before using a spray etch to clean the copper surface. However, the inventors of the present invention have found that this order of steps may be changed and that good results can be achieved if the microetching step is performed prior to the drying step.

[0081] On the other hand, typical systems used to perform direct plating processes are horizontal processing machines, and the order of steps in horizontal processing systems cannot be easily changed or modified. Therefore, it may not be possible to change the order of steps in the process, in which case a drying step may necessarily need to be performed after the drying step. However, the adhesion of the carbon coating composition to the substrate can be optimized, in part, through careful selection of the high molecular weight conditioning agent and the properties of the carbon dispersion, including small particle size and close particle size distribution.

[0082] In one embodiment, the printed wiring board is further contacted with compressed air to void any through-holes that may hold a plug of dispersion.

[0083] Carbon black or graphite dispersions on printed wiring boards not only coat the drilled through-hole surfaces (which is desirable), but also completely coat the metal (i.e., copper) plate or copper foil surface (which is undesirable). Therefore, all carbon black or graphite must be removed from the copper (or other metal) plate and / or copper foil surface prior to subsequent operations.

[0084] Removal of carbon black or graphite from copper (or other metal) surfaces, particularly including the rims of drill holes, while leaving the coating on the fiberglass and epoxy surfaces of the hole walls intact, is achieved using a microetching process.

[0085] The processes described herein also reduce the tendency for hole wall delamination, in which electroplated copper plated on a direct plating coating pulls away from the walls of a hole, slot, or microvia after soldering or thermal cycling. The increased adhesion of the carbon particles as a result of using the processes described herein reduces or eliminates this problem.

[0086] Microetching solutions used to remove excess graphite and / or carbon black are typically based on an oxidizing agent, e.g., hydrogen peroxide or a persulfate, such as sodium persulfate. For example, one suitable microetching solution is a sodium persulfate-based microetching solution that combines 100-300 grams of sodium persulfate per liter of deionized water with sufficient sulfuric acid to produce a microetching bath containing about 1-10% sulfuric acid by weight.

[0087] However, any etchant suitable for the metal being plated may be used in the practice of the present invention. For example, for copper plating, sodium persulfate-based etchants, hydrogen peroxide sulfuric acid-based etchants, copper chloride-based etchants, and ferric trioxide-based etchants are all suitable for use. However, any oxidizing agent capable of oxidizing copper metal to copper ions is suitable and can be used in the processes described herein.

[0088] In one embodiment, the printed circuit board is contacted with the microetchant by spraying the microetchant, which may be sprayed at a pressure in the range of about 20 to about 50 psi, more preferably about 30 to about 40 psi, and at a temperature in the range of about 20 to about 45°C, more preferably about 30 to about 35°C.

[0089] As described herein, the steps of the direct plating process can be performed in various orders. For example, the printed wiring board panel can be dried before or after the spray etching step. While it is generally preferred that the drying step occurs after the spray etching step, there is still an advantage achieved in increased adhesion if the spray etching step is performed after the drying step.

[0090] After the microetching step and subsequent water rinse, the printed wiring board may proceed to a photoimaging process followed by electroplating, or may be directly panel electroplated. After the microetching step, the printed wiring board may be further cleaned, for example, with a citric acid or benzotriazole anti-tarnish solution or other acid cleaner solution, or both. The thus-treated printed wiring board is then ready for the electroplating operation, which involves immersing the printed wiring board in a suitable electroplating bath to plate a copper (or other metal) coating onto the through-hole walls of the non-conductive layer.

[0091] As described herein, in a preferred embodiment, the carbon coating is not dried prior to etching, although it is possible to perform the metal plating step without first drying the carbon coating.

[0092] After the etching step (or etching and plating step), the printed circuit board is dried for a period of time to remove water. In one embodiment, the printed circuit board is dried at an elevated temperature for a period of about 20 seconds to about 90 seconds, more preferably about 30 seconds to about 60 seconds. The elevated temperature may be about 125°F to about 200°F, more preferably about 150°F to about 175°F.

[0093] The plating metal is typically copper. However, the invention is not limited to copper plating, and the plating metal may be, for example, nickel, rhodium, platinum, cobalt, gold, tin, lead, and alloys of any of the foregoing. Other metals are known to those skilled in the art and may be plated using the processes described herein.

[0094] The invention will now be discussed with reference to the following non-limiting examples.

[0095] Example 1: A printed wiring board containing through-holes was treated as follows. 1) The printed wiring board was immersed for 30 seconds in a conditioner bath containing a high molecular weight polyquaternium compound having an average molecular weight of about 3,200,000, a pH buffer and a surfactant at 95°F and pH 9.0. 2) The circuit board was rinsed with tap water for 30 seconds. 3) The circuit board was immersed in a carbon black dispersion according to the present invention. The particles were adhesive carbon black particles with a D-50 of 80 nm and a D-99 of 377 nm. The dispersant used was an ethoxylated phosphate ester. The colloid was prepared at 20% solids and then diluted to 3% solids for use, and had a pH of 9.2. 4) The circuit board was spray etched using 50 g / L sodium persulfate etchant at 40 psi for 30 seconds. 15 microinches of copper was etched away from the copper surface. 5) The substrate was spray rinsed with tap water at 40 psi. 6) The substrate was immersed in a bath containing 80 g / L copper sulfate pentahydrate, 200 g / L sulfuric acid, 60 ppm chloride ion, and 1% PC606 additive (available from MacDermid Enthone Inc., Waterbury, CT) at 20 A / ft 2 The plate was directly electroplated with copper at 4000 kJ / min for 5 minutes.

[0096] Inspection of the copper plated printed circuit board revealed that there were no pinholes in the plated copper deposit.

[0097] Comparative Example 1: A printed wiring board containing through-holes was treated as follows. 1) The printed wiring board was immersed for 30 seconds in a conditioner bath containing a high molecular weight polyquaternium compound having an average molecular weight of about 3,200,000, a pH buffer and a surfactant at 95°F and pH 9.0. 2) The circuit board was rinsed with tap water for 30 seconds. 3) The circuit board was immersed in a carbon black dispersion prepared by mixing carbon black powder with a surfactant having a particle size of D-50 equal to 180 nm and D-99 equal to 743 nm. The dispersion was prepared at 16.7% solids and then diluted to 3% solids for use, and had a pH of 9.2. 4) The circuit board was spray etched using 50 g / L sodium persulfate etchant at 40 psi for 30 seconds. 15 microinches of copper was etched away from the copper surface. 5) The substrate was spray rinsed with tap water at 40 psi. 6) The substrate was immersed in a bath containing 80 g / L copper sulfate pentahydrate, 200 g / L sulfuric acid, 60 ppm chloride ion, and 1% PC606 additive (available from MacDermid Enthone Inc., Waterbury, CT) at 20 A / ft 2 The plate was directly electroplated with copper at 4000 kJ / min for 5 minutes.

[0098] Inspection of the copper plated printed circuit board revealed that the carbon coating had washed away during steps 4 and 5, leaving the holes in the circuit board substantially free of plating.

[0099] Example 2: A printed wiring board containing through-holes was treated as follows. 1) The printed wiring board was immersed for 30 seconds in a conditioner bath containing a high molecular weight polyquaternium compound having an average molecular weight of about 3,200,000, a pH buffer and a surfactant at 95°F and pH 9.0. 2) The circuit board was rinsed with tap water for 30 seconds. 3) The circuit board was immersed in a graphite dispersion according to the present invention, prepared to have a particle size of 237 nm D-50 and 1853 nm D-99. The dispersant used was an ethoxylated phosphate ester. The colloid was prepared at 21% solids and then diluted to 3% solids for use, and had a pH of 9.2. 4) The circuit board was spray etched using 50 g / L sodium persulfate etchant at 40 psi for 30 seconds. 15 microinches of copper was etched away from the copper surface. 5) The substrate was spray rinsed with tap water at 40 psi. 6) The substrate was immersed in a bath containing 80 g / L copper sulfate pentahydrate, 200 g / L sulfuric acid, 60 ppm chloride ion, and 1% PC606 additive (available from MacDermid Enthone Inc., Waterbury, CT) at 20 A / ft 2 The plate was directly electroplated with copper at 4000 kJ / min for 5 minutes.

[0100] Inspection of the copper plated printed circuit board revealed that there were no pinholes in the plated copper deposit.

[0101] Comparative Example 2: A printed wiring board containing through-holes was treated as follows. 1) The printed wiring board was immersed for 30 seconds in a conditioner bath containing a high molecular weight polyquaternium compound having an average molecular weight of about 3,200,000, a pH buffer and a surfactant at 95°F and pH 9.0. 2) The circuit board was rinsed with tap water for 30 seconds. 3) The circuit board was dipped into a graphite dispersion prepared by mixing graphite powder with a surfactant having a particle size of D-50 equal to 1050 nm and D-99 equal to 4288 nm. The dispersion was prepared at 22% solids and then diluted to 3% solids for use, and had a pH of 9.5. 4) The circuit board was spray etched using 50 g / L sodium persulfate etchant at 40 psi for 30 seconds. 15 microinches of copper was etched away from the copper surface. 5) The substrate was spray rinsed with tap water at 40 psi. 6) The substrate was immersed in a bath containing 80 g / L copper sulfate pentahydrate, 200 g / L sulfuric acid, 60 ppm chloride ion, and 1% PC606 additive (available from MacDermid Enthone Inc., Waterbury, CT) at 20 A / ft 2 The plate was directly electroplated with copper at 4000 kJ / min for 5 minutes.

[0102] Inspection of the copper plated printed circuit board revealed that the holes in the circuit board were substantially free of plating because the graphite coating had washed away during steps 4 and 5.

[0103] Example 3: A printed wiring board containing through-holes was treated as follows. 1) The printed wiring board was immersed for 30 seconds in a conditioner bath containing a high molecular weight polyquaternium compound having an average molecular weight of about 3,200,000, a pH buffer and a surfactant at 95°F and pH 9.0. 2) The circuit board was rinsed with tap water for 30 seconds. 3) The circuit board was immersed in a graphite dispersion according to the present invention, prepared to have a particle size of 297 nm D-50 and 1968 nm D-99. The dispersant used was an ethoxylated tristyrylphenol phosphate ester. The colloid was prepared at 19% solids and then diluted to 3% solids for use, and had a pH of 9.3. 4) The circuit board was spray etched using 50 g / L sodium persulfate etchant at 40 psi for 30 seconds. 15 microinches of copper was etched away from the copper surface. 5) The substrate was spray rinsed with tap water at 40 psi. 6) The substrate was immersed in a bath containing 80 g / L copper sulfate pentahydrate, 200 g / L sulfuric acid, 60 ppm chloride ion, and 1% PC606 additive (available from MacDermid Enthone Inc., Waterbury, CT) at 20 A / ft 2 The plate was directly electroplated with copper at 4000 kJ / min for 5 minutes.

[0104] Inspection of the copper plated printed circuit board revealed that there were no pinholes in the plated copper deposit.

[0105] Comparative Example 3: A printed wiring board containing through-holes was treated as follows. 1. The printed wiring board was immersed for 30 seconds in a conditioner bath containing a high molecular weight polyquaternium compound having an average molecular weight of about 3,200,000, a pH buffer and a surfactant at 95°F and pH 9.0. 2. Rinse the circuit board with tap water for 30 seconds. 3. The circuit board was immersed in a carbon black dispersion prepared by mixing carbon black powder with an oleyl hydroxyethyl imidazoline surfactant having a particle size of D-50 equal to 385 nm and D-99 equal to 1503 nm. The dispersion was prepared at 14% solids and then diluted to 3% solids for use, and had a pH of 9.2. 4. The circuit board was spray etched using 50 g / L sodium persulfate etch at 40 psi for 30 seconds. 15 microinches of copper was etched away from the copper surface. 5. The substrate was spray rinsed with tap water at 40 psi. The substrates were immersed in a bath containing 6.80 g / L copper sulfate pentahydrate, 200 g / L sulfuric acid, 60 ppm chloride ion, and 1% PC606 additive (available from MacDermid Enthone Inc., Waterbury, CT) at 20 A / ft 2 The plate was directly electroplated with copper at 4000 kJ / min for 5 minutes.

[0106] Inspection of the copper plated printed circuit board revealed that the carbon black coating had washed away during steps 4 and 5, so there was essentially no plating on the holes in the circuit board.

[0107] Thus, it can be seen that the process described herein produces a carbon dispersion that adheres more tightly to the printed wiring board, which in turn produces an adherent copper deposit that does not have pinholes or other defects in the deposit.

[0108] Finally, it is also to be understood that the following claims are intended to cover all of the general and specific features of the invention described herein, as well as all statements of the scope of the invention that may lie therebetween as a matter of language.

Claims

1. 1. A method for preparing a non-conductive substrate onto which metal can be plated, comprising: a) optionally but preferably contacting the non-conductive substrate with a precleaner; b) contacting the non-conductive substrate with a conditioner comprising a polymeric conditioning agent; c) applying a liquid carbon-based dispersion to the conditioned non-conductive substrate to form a carbon / conditioner gel coating on the conditioned non-conductive substrate, the carbon-based dispersion comprising adherent carbon particles or adherent graphite particles dispersed in a liquid solution, the carbon particles solidifying on the conditioned substrate to form a carbon / conditioner gel coating; d) etching the carbon / conditioner gel coated substrate; The method of claim 1, wherein the adhesive carbon black particles or the adhesive graphite particles in the liquid carbon-based dispersion have a small particle size and a narrow particle size distribution.

2. 10. The method of claim 1, wherein the etching step is performed before the liquid carbon-based dispersion dries on the non-conductive substrate, and the method further comprises drying the substrate and the carbon-based dispersion after step d) to form a conductive carbon coating on the substrate.

3. The method of claim 2 further comprising the step of electroplating a conductive metal onto the substrate after step d).

4. The method of claim 1 , wherein the conditioning agent is a polyquaternium compound.

5. 5. The method of claim 4, wherein the polyquaternium compound has a molecular weight of at least 1,000,000 g / mol.

6. 6. The method of claim 5, wherein the polyquaternium compound has a molecular weight of at least 2,000,000 g / mol.

7. 7. The method of claim 6, wherein the polyquaternium compound has a molecular weight of at least 3,000,000 g / mol.

8. The method of claim 1 , wherein the substrate comprises a printed circuit board or a printed wiring board.

9. The method of claim 1 , wherein the substrate is contacted with the conditioner by immersing the substrate in the conditioner for at least about 20 seconds.

10. 4. The method of claim 3, wherein the carbon-based dispersion is dried after the etching step and before the electroplating step.

11. 4. The method of claim 3, wherein the carbon-based dispersion is not dried prior to the etching step or the plating step.

12. 4. The method of claim 3, wherein the carbon-based dispersion is dried after the etching step and after the electroplating step.

13. The carbon-based dispersion comprises: a. a dispersant; b. optionally a binder; c. a conductive carbon source selected from carbon black particles and / or graphite particles; d. a pH adjuster, wherein the pH adjuster is a hydroxide; e. the balance water, 10. The method of claim 1, wherein the carbon black particles and / or the graphite particles are pulverized in a milling process capable of producing adhesive carbon black particles and / or adhesive graphite particles exhibiting small particle size and narrow particle size distribution.

14. 14. The method of claim 13, wherein the conductive carbon is graphite and the graphite particles exhibit a D50 of less than 350 nm and a D99 of less than 2500 nm.

15. 15. The method of claim 14, wherein the graphite particles exhibit a D50 of less than 300 nm.

16. 14. The method of claim 13, wherein the conductive carbon is carbon and the graphite particles exhibit a D50 of less than 100 nm and a D99 of less than 400 nm.

17. 14. The method of claim 13, wherein the dispersing agent is an anionic surfactant selected from the group consisting of ethoxylated phosphate esters, ethoxylated and propoxylated phosphate esters, ethoxylated tristyrylphenol phosphate esters, and combinations of one or more of the foregoing.

18. The method of claim 1, wherein the concentration of the carbon particles or the graphite particles in the carbon-based dispersion is from about 2% to about 5% by weight.

19. The method of claim 1, wherein the substrate is dried at a temperature of about 125°F to about 200°F for about 20 seconds to about 90 seconds.

20. The method of claim 19, wherein the substrate is dried for about 30 seconds to about 60 seconds.

21. The method of claim 19, wherein the substrate is dried at a temperature of about 150°F to about 175°F.

22. 10. The method of claim 1, wherein the metal portion of the substrate is etched with an etchant, the etchant being selected from the group consisting of sodium persulfate-based etchants, hydrogen peroxide sulfuric acid-based etchants, copper chloride-based etchants, and ferric trioxide-based etchants.

23. 1. A two-component gel coating composition for preparing a non-conductive substrate that allows metal plating thereon, said two-component gel coating comprising: a. a conditioner, i. a polyquaternium compound having a molecular weight greater than 1,000,000 g / mol; ii. a pH buffer; iii. a surface tension reducing agent; a conditioner, wherein the conditioner has a pH in the range of about 8 to about 10; b. A liquid carbon-based dispersion, said liquid carbon-based dispersion comprising: i. adhesive carbon particles or adhesive graphite particles dispersed in a dispersing agent; ii. a pH adjuster; a liquid carbon-based dispersion, wherein the adhesive carbon black particles or the adhesive graphite particles have a small particle size and a narrow particle size distribution, and the pH of the liquid carbon dispersion is in the range of about 8 to about 10; A two-component gel coating composition wherein, when the conditioner and the liquid carbon-based dispersion are applied sequentially to the non-conductive substrate, an adherent carbon / conditioner gel coating is formed on the surface of the non-conductive substrate.

24. 24. The two-component gel coating composition of claim 23, wherein the conductive carbon is graphite and the graphite particles exhibit a D50 of less than 350 nm and a D99 of less than 2500 nm.

25. 25. The two-component gel coating composition of claim 24, wherein the graphite particles exhibit a D50 of less than 300 nm.

26. 24. The two-component gel coating composition of claim 23, wherein the conductive carbon is carbon and the graphite particles exhibit a D50 of less than 100 nm and a D99 of less than 400 nm.

27. 24. The two-component gel coating composition of claim 23, wherein the pH adjuster of the liquid carbon-based dispersion is a hydroxide.

28. A printed circuit board coating comprising a plurality of through holes; 24. A printed circuit board coating wherein the through-holes are prepared for electroplating by applying the two-component gel coating composition of claim 23 to form an adherent carbon / conditioner gel coating on the surfaces of the through-holes.

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