JPS62133099A - Electroplating of conductive metal layer to surface of non-conductive substance - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to the surface of non-conductive materials, particularly printed wiring &
The present invention relates to a method for electroplating a conductive metal layer on the walls of through-holes in WB), a novel dispersion used therefor, and a print arrangement and a mount produced therewith.

Description of Related Art For the past 25 years, the printed wiring board industry has relied on electroless steel adhesion methods to electroplate the walls of through holes in printed wiring boards.

Plating of the through-hole walls is necessary to make connections between metal circuit patterns on both sides of a printed wiring board or additionally on the inner layers of a multilayer board.

Deposition of copper to the through-hole walls by electroless plating is typically accomplished by pre-cleaning the PWB followed by the following process diagram.

Pre-cleaned corners ↓ Circuit boards from these processes may also be photoimaged (photomagθ) before the electroplating process. Typically, the thickness of copper deposited on each through-hole wall is approximately 1±0. .2 mil.

Conventional electroless plating methods have several industrial drawbacks. It requires a relatively long process time.

Multiple processing baths require complex chemistry and separate replenishment of individual components that must be constantly monitored. -Gradium/tin activators require expensive wastewater treatment. Moreover, these electroless plating methods are very sensitive to contamination. Finally, many cleaning baths require large amounts of water.

Prior to coating (plating) the through holes with electroless plating, the page through hole walls for coating (plating) were manufactured using graphite. For example, U.S. Pat. A method of forming hole walls is taught. The patent further discloses that graphite has previously been used as a conductive layer for electroplating (
Column 1, lines 63-70 and column 4, line 72 to column 5, line 1
(see line 1). The patent points out that the use of graphite has several drawbacks, including the lack of control when using graphite, the poor adhesion of the resulting electroplated metal, and the through-hole diameter. , and the low electrical resistance of graphite.

In U.S. Pat. No. 16,588 to Hortt et al.

It is also stated that graphite or its equivalent is used to make the through-hole walls of electrical circuit boards quadrielectric, followed by electroplating metals thereon (column 3, 45).
(See column 4, line 2).

For example, US Pat. Graphite powder (graphite) in a volatile liquid is then evaporated to cover the asbestos with graphite particles, and then the asbestos-coated graphite sheet is immersed in a copper electroplating solution. It teaches passing electrical current through the asbestos sheet to form a thin copper film thereon. The copper-coated sheet is then placed in a molten metal bath of tin, lead or zinc and sputtered from the acid bath to solidify the molten metal.

The resulting metal-coated asbestos sheet is described as relatively flexible, non-thermal conductive, and flame resistant.

U.S. Pat. No. 1,03Z469 to Goldberg and U.S. Pat. No. 1,352,331 to Unno first coat a non-conductive material with wax and then apply the wax to finely divided particles of graphite or other metals. A method of electroplating non-conductive objects by coating with a slurry and then dull plating the particulate coated surface with copper or other metals is disclosed. None of these methods will remove the holes in the circuit board because the holes in the circuit board are usually very small in diameter and dipping in wax will clog the holes and prevent coating the hole walls with electroplating material. Not suitable for wall coating.

Laux, U.S. Pat. No. 2,243,429, discloses a non-conductive method consisting of forming a thin layer of graphite on a non-conductive surface, then applying a layer of copper by electroplating, and finally depositing another metal by electroplating. A method for electroplating conductive materials is described.

Separately, carbon black methods have been used as conductive coatings on non-conductive materials.

For example, U.S. Pat. No. 4,035 by 5unders
, 265 describes an electrically conductive coating composition containing both graphite and carbon black together with an air-curable binder. These paints are suitable for application to walls of buildings used as heating elements.

U.S. Pat. No. 4,090.984 to Lin et al.
A semiconductive coating for glass fibers is disclosed which comprises a polyacrylate emulsion, (b) a 4-conductor-bonblack dispersion, and (C) a thixotropic gelling agent.

The conductive carbon black dispersion used consists of a suitable dispersant and about 6 to about 4 parts of conductive carbon black dispersed therein.

U.S. Pat. No. 4,239,794 to A.11ard discloses dispersing conductive carbon black in a latex binder with a specific dispersant and then impregnating a non-woven fabric with the carbon black dispersion. It is disclosed that a thin coating of dispersed carbon black is formed on the surface of the nonwoven fabric by drying the nonwoven fabric to remove moisture.

There is currently a need for a method of electroplating non-conductive surfaces that is more reliable and less expensive than electroless plating techniques. A better overall electroplating method for obtaining a uniform and continuous metal surface to the through-hole walls of printed wiring boards, especially for obtaining effective electrical connections (especially between conductive layers of printed wiring boards). is necessary.

A primary object of the present invention is to provide an improved method of electroplating non-conductive surfaces.

Another object of the present invention is to provide an improved electroplating method for applying conductive metal layers to the walls of through holes in printed wiring boards.

Still another object of the present invention is to form tetraconducting gold M/f5 on the surface of a non-conductive layer of a printed wiring board in a more convenient and simplified manner than currently known electroless plating methods. The purpose is to provide a method.

Still another object of the present invention is to obtain more reliable electrical connection between copper plates of a printed wiring board.

It is the application of a copper layer to the through-hole walls of a printed wiring board by electroplating.

DETAILED DESCRIPTION OF THE INVENTION The present invention accomplishes these objects by following the steps below: carbon black particles having an average particle diameter of less than about 3.0 microns in a dispersion.

■ An effective dispersion amount of a surfactant compatible with carbon black; and ■ A carbon black dispersion in a liquid dispersion medium (the amount of carbon black in the above dispersion is such that it covers substantially the entire surface of the non-conductive material). and applying the dispersion to the surface of the non-conductive material to obtain Fbl.
C+ separating substantially all of the liquid dispersion medium from said carbon black particles, thereby depositing carbon black particles on said non-conductive surface in a substantially continuous layer; and (dl deposited carbon black layer The present invention provides a method for electroplating a conductive metal layer on a non-conductive material surface, comprising electroplating a substantially continuous conductive metal layer over the surface of the non-conductive material. The method is particularly suitable for applying a more conductive metal surface than copper to non-thick conductive parts of the through-hole walls of printed wiring boards. Printed wiring boards usually consist of two conductive metal layers (e.g. copper or nickel plates or foils) or a number of non-conductive NI (e.g. epoxy resin/glass fiber mixtures) located between some alternating layers of these.
It consists of Applying a conductive metal layer to the non-conductive portion of the through-hole wall causes the conductive metal layer to be electrically connected.

However, in the present invention, electroplating of a conductive metal onto the surface of a non-conductive substance having an arbitrary shape or surface area is effective.

Furthermore, the present invention also includes a printed wiring board manufactured by the method described above (i.e., a printed wiring board in which one through-hole wall is coated with carbon black only, or with carbon black and metal plating thereon).

DESCRIPTION OF THE PREFERRED EMBODIMENTS From the foregoing, preferred embodiments of the present invention provide a through-hole wall in a non-conductive layer separating two copper plates or foils) II! It is to apply a metal plating layer of I.

This process requires the application of a specific carbon black dispersion to the non-conductive portions of the through-hole walls prior to electroplating.

Carbon black dispersions completely replace traditional electroless plating copper baths and all associated chemical processes. That is, the carbon black dispersion replaces the preactivation step, the Pa/Sn activator, the accelerator step, and the electroless plating bath itself.

Although steel is commonly used as the electroplating metal in printed wiring boards, other metals such as nickel, gold, and silver can also be used for electroplating by the method of the present invention.

A printed wiring board (also known as a printed circuit board) is typically a laminate consisting of two or more copper plates or foils and a non-conductive layer separating them from each other. The non-conductive layer is preferably an organic material such as glass fiber particles impregnated with Epoquine resin. However, the non-conductive layers may also be thermosetting resins, thermoplastic resins and mixtures thereof, and they may or may not contain reinforcing materials such as glass fibers or fillers. good.

Suitable thermoplastic resins include acetal resin; acrylic resin such as methyl acrylate; ether cellulose;
Cellulose resins such as cellulose acetate, cellulose propionate, cellulose acetate), cellulose nitrate, etc.: Chlorinated polyether: Nylon: Polyethylene; Polypropylene: Boristyrene; Acrylonitrile
Styrenic polymers such as styrene copolymers and acrylonitrile-butadiene-styrene (ABS) copolymers;
Polycarbonate; polychlorotrifluoroethylene; examples include vinyl acetate, vinyl alcohol, vinyl butyral, vinyl chloride-vinyl sulfate co-subpolymers, vinyl monopolymers and copolymers of vinylidene chloride and vinyl formal. .

Preferred thermosetting resins include alkyl heptatalates.

Furan: melamine-formaldehyde; phenol-formaldehyde, phenol-furfural copolymer:
alone or together with butadiene-acrylonitrile copolymer or acrylonitrile-butadiene-styrene (
ABS) copolymer mixture; polyacrylic acid ester: silicone &+ fat: PKIA-formaltehyde: epoxy, FIl tl: polyimide; alkyl press: glyceryl phthalate; polyester, etc.

In many printed wiring board designs, airways or chisels are required to connect between separate copper plates at specific points in the pattern. This is typically accomplished by connecting between the separate metal plates at the desired locations of the design through a laminate of copper plates and non-conductive layers. The diameter of the holes in the printed wiring board generally ranges from about 0.5 to about 10 mm, preferably about 1 to 5 mm.

After drilling the through hole, it is preferred to scrub the hole wall to make it relatively smooth. In the case of multilayer printed wiring boards, it is desirable to perform a dirt dam or etchback (8tchback) process to clean the inner steel interlayer surface of the through hole. Some or all of the conventional treatments currently in use can be used as suitable preliminary steps.

After the surface of the through-hole has been smoothed for plating, the test printed wiring board is preferably pre-cleaned to make it more receptive to the car pump book dispersion of the present invention. One preferred pre-cleaning process is to first place the printed wiring board in a cleaner/conditioner bath at about 60° C. for about 5 minutes to loosen grease and other impurities from the surface of the hole walls. One of the preferred cleaners/conditioners for doing this is:
It mainly consists of monomethanolamine and ethylene glycol added to water. The preferred cleaner/conditioner is 0 Cleaner/Conditioner 102″
The product name is Ph1llip, A, Hunt Chem,
sold by the company.

After applying the cleaner/conditioner, the PWB is then rinsed with deionized water to remove cleaner/conditioner residue from the mounting plate. Next, it is desirable to clean the outer copper surface. This is accomplished by immersing the plate in a sodium persulfate microetching solution or an aqueous sulfuric acid solution or both. A preferred persulfate microetching solution is Ph1llip.
A. MICRO-ET manufactured by Hunt Chem.
C) (601), which contains 2009 parts per β of sodium persulfate and 0.5% by weight of sulfuric acid. Both the sodium persulfate microetching solution and the sulfuric acid solution.

It is known that it does not affect the surface of the Epokin/glass fiber or the through-hole portion of the PWB. It should be recognized that none of the above-described drilling or pre-cleaning is essential to the invention. Similar conventional treatments may be used instead.

For further processing, for example, the circuit board may be immersed in a chromic acid-sulfuric acid etching bath for about 60 seconds at about 60°C, then removed, and then soaked in deionized water to remove excess acid etching bath. This includes methods such as cleaning for 50 seconds with water, and removing dirt using plasma.

The method of the present invention consists of electroplating the pre-cleaned PWB according to the following process diagram.

Preliminary cleaning step 2 ↓ The carbon black dispersion of the present invention is applied to PWB VC which has been first subjected to cleaning treatment. This dispersion has 6
It contains the essential ingredients of yuzu, namely carbon black, one or more surfactants capable of dispersing the carbon black, and a liquid dispersion medium including water. Suitable methods for applying the dispersion to the PWB include dipping, spraying, or
Other application methods of kaji millet employed in industry are included. One treatment bath is sufficient to use this carbon black dispersion, but one treatment bath may be sufficient for reprocessing or other purposes.
More than one bath may be used.

In the preparation of this dispersion, the above six essential ingredients and other optional preferred ingredients are used to form a stable dispersion t1. Mixed thoroughly into a pot. This is accomplished by subjecting the concentrated dispersion to a ball mill, colloidal mill, high shear mill or other high speed mixing means. The thoroughly mixed dispersion can later be diluted with water while stirring until the desired concentration of the treatment bath is obtained. A preferred method of mixing is to ball mill the concentrated dispersion in a container containing glass minerals or plastic beads for about 1 to 24 hours. This thorough mixing ensures that the carbon black particles are intimately coated or wetted with the surfactant. This thick mixture is then diluted with water or other dispersion liquid to the desired concentration. Preferably, the treatment bath is agitated during both the dilution and application steps to maintain stability of the dispersion.

As stated above, the carbon black particles should have an average particle size in the dispersion of less than about 3 microns. It is desirable that the average particle size of the carbon black particles be as small as possible in order to achieve substantially flat plating and to prevent peeling of the plating layer. Preferably, the average particle size of the carbon black particles in the dispersion is from about 0.1 to about 60 microns, more preferably from 0.2 to about 2.0 microns.

"Average particle size" as used in this specification and claims
The term refers to the average diameter (number average) of the particles. The average diameter in the dispersion is Ni comp! V4od
e 1270 submicron particle size analyzer (V'ersio
nro, 0) or H Engineering ACPA-720 Automatic Particle Size Analyzer (
Both are available from Pacific 5 Scientific Inc.).

All types of carbon black can be used in the present invention;
It also includes commonly available furnace carbon. However, when slurried with water, it is initially acidic or neutral, i.e. from about 1 to about 75..., particularly preferably from about 2 to about 4
It is preferable to use carbon black.

The bite type carbon black particles are about 1 to about 10
% by weight of volatile components and has an amorphous structure. In contrast, the graphite particles used to plate the through holes described in U.S. Pat. Nos. 6,099,608 and 3,163,588 are relatively pure carbon in crystalline form; It does not affect - of aqueous solution.

It has been noted that when graphite particles are used in place of the carbon black particles of the present invention, the adhesion of copper to non-conductive materials after subsequent electroplating is weak. See Comparative Examples 1 and 2 below.

Preferred carbon black particles are also highly porous and typically have a surface area of between about 45 and about 1100 m2/9, preferably between about 300 and about 600 m2/9 (according to the BKT method (Brunauer4mmett-Teller method)). are doing.

Examples of carbon blacks suitable for use in the present invention include Cabot XC-72R Conductive
.

cabot MQnarc! h800.0abot
There is Monarch 1300 (all manufactured by Cabot). Other suitable carbon blacks include Columbi
an T-10189, Columbian COna
uct8X 975 conauctlve, Ool
umbian CO-n o-220, and Column
bian Raven3500 (all Columbi
available from anCorbon). Monar
ch 800 and Raven 3500 are the two most preferred due to their ease of dispersion and low voice.

As used herein and in the claims, the term "liquid dispersion medium" includes water and polar solvents (both protic and aprotic). Suitable protic polar organic solvents include methanol, ethanol, impropatol, isobutanol and pentanol.
Lower alcohols of 5; polyalcohols such as glycols (e.g. triethylene glycol); ether alcohols such as cellosolve; organic acids such as formic acid and acetic acid; derivatives of trichloroacetic acid; methane More sulfonic acids are included. Suitable aprotic polar organic solvents include aldehydes such as acetaldehyde; ketones such as acetone; aprotic aromatic solvents such as toluene and mineral spirits: chlorofluoromethane and dichlorodifluoromethane (F' lON
) is a more aprotic halogenated hydrocarbon dimethylformamide (DMF); dimethyl sulfoxide (
DMSO); and more carboxylic acid esters of methyl formate, ethyl acetate and cellosolve acetate. Water is the preferred liquid dispersion medium due to its cost and ease of use. It is preferable to use deionized water that is free of lime, fluorine, iodine and other impurities commonly found in drinking water, which minimizes the contamination of other ions during the subsequent electroplating process. It's for a reason.

In addition to water and carbon black, a third component may be needed in the dispersion, which is a surfactant that is capable of dispersing the carbon black in the liquid dispersion medium (i.e., making the carbon black and the liquid dispersion medium miscible). ).

One or more surfactants are added to the dispersion to enhance the wettability and stability of the carbon black, thereby maximizing its penetration into the pores and interfibers of the non-conductive layer.

Suitable wetting agents include anionic, nonionic and cationic surfactants (or mixtures thereof, including amphoteric surfactants). The surfactant should be soluble and stable in the carbon black dispersion, and should preferably be antifoaming. In general, surfactants with high HLB numbers (8-1
8) is preferred. The preferred type of surfactant depends primarily on the nature of the dispersion. If the dispersion is alkaline (ie the overall pH is in the basic range), it is preferable to use an anionic or nonionic surfactant. DARVA is an anionic surfactant that can be used.
N ra 1 (R, T, manufactured by 'VancLerbilt), gccowrr LF (F, astern Co.
10r and Chemica1), Pff
i'IROAA, PETR0TJIJ” (Petro
Chemica1) and -SQL O8 (Amer
The sodium or potassium salts of naphthalene sulfonic acid (manufactured by Cyanamid, Inc.) are included.

Preferred anionic surfactants include Takuda HO855,5
6,8135,6OA, L6 (Mazer Che
There is a more neutral phosphate ester type product (manufactured by mica1). The most suitable for carbon black dispersions is MAPHO856.

A suitable nonionic surfactant is POLY-TKE.
More ethoxylation of Oke B-series (manufactured by O1in): #7 Engineering/-/L/Father is POLY-TJ
! : RGENT SL-series (manufactured by 01in) is a more alkoxylated chain alcohol.

If the entire dispersion is acidic, it is preferred to use a cationic surfactant in place of the particular anionic surfactant. Among the cationic surfactants that can be used are the sodium or potassium salts of naphthalenesulfonic acid mentioned above. Cationic surfactants that can be used include AMM
ONYXT (manufactured by 0nyx Chemica 1) Yorina dimethel benzyl ammonium chloride; AJffiO8OLC-61 (American
Ribocol (1xpoca1)
; DOWFAX 2AI (Dow Chemica
Dodecyl diphenyl oxide disulfonic acid (DDODA): 5TRODEX (Dexter
The sodium salt of DODA (manufactured by Chemica'1); and salts of organic phosphate ester complexes are included. Preferred surfactants include) amphoteric potassium salts of complex amino acids based on more fatty amines of aPo 15 and MAZEEN S-5 or MAZTRFliAT
(Mazer Chemical.

Company! A) more cationic ethoxylated soybean (soybean)
) amines. Mixtures of surfactants can also be used.

The amount of carbon black in the dispersion is approximately 4 times the weight of the dispersion.
%, preferably less than about 2 parts by weight. It has been found that the use of carbon black at high concentrations results in undesirable plating properties. For the same reason.

The solids concentration (i.e., all components other than the liquid dispersion medium) is
Preferably less than about 10% by weight of the dispersion, and about 5.
It is preferable to have less than 6 weight factors.

A dispersion may be formed using only the above three essential components of the present invention, namely carbon black, liquid dispersion medium and surfactant. In some cases it may be desirable to add other preferred ingredients to the dispersion.

One of the preferred ingredients added to the carbon black-containing dispersion is a strongly basic substance such as an alkali hydroxide.

Suitable strong basic materials include the alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, and lithium hydroxide. If desired, alkaline earth metal hydroxides such as ammonium hydroxide or calcium hydroxide may be used. Potassium hydroxide is the most preferred strong basic material. In this specification and claims, the term "alkali hydroxide" refers to these strongly basic substances.

Sufficient alkali hydroxide is added to the carbon black dispersion to bring the pH of the carbon black dispersion to about 10 to about 14, preferably about 10 to about 12.

The alkali hydroxide may be added to the dispersion alone or together with the silica. A preferred silica is fumed silica. The preferred fumed silica is in the form of dense particles and is available from CabOt as CAB-0-8I.
It is commercially available under the trade name LMS-7SD. However, other fumed silicas of suitable bulk density and particle size can also be used.

Suitable densities for fumed silica generally range from about 5 to 10 bonds/cubic foot. Suitable particle diameters for fumed silica generally range from about 0.005 to about 0.025.
in the range of microns, more preferably about 0.01 to 0
．． In the range of 0.015 microns.

- When used together, the alkali hydroxide reacts with the fumed silica particles in situ to form the corresponding soluble alkali silicate. If excess alkali hydroxide is present, the dispersion will contain hydroxide and silicate. Alkaline earth metal hydroxides, such as lithium hydroxide and calcium hydroxide, should not be used with silica because they produce silicate precipitates.

The porosity of the carbon black particles enhances the adsorption of alkali silicate from the dispersion. As a result, the concentration of alkali silicate in the pores of the carbon black particles is relatively high after drying. The presence of alkali silicates in the pores enhances the conductivity of the carbon black particles during the subsequent electroplating step.

In other embodiments of the invention, the alkali hydroxide and silica may be replaced with mineral acids. H(4, H2SO4, H3P
The carbon black dispersion may be acidified with a suitable mineral acid such as O3. HNO3 produces undesirable reactions with copper and should be removed. Generally, a suitable concentration of acid is about 1 Normal.

Below, a suitable typical formulation of an aqueous alkaline dispersion of carbon black is given, both typical and preferred proportion ranges for the various components.

Component General range Preferred range Carbon black 0.1 to 4 weight 1°% 0.2
~2wt% surfactant 0.01~4wt% cL05~
2% by weight alkali hydroxide 0-1% by weight 0.
4-0.8wt% humid silica 0-1wt i%
0.2-0.8 wt. 4 Water Residual Residual The carbon black dispersion is typically placed in a stirred vessel and the printed wiring board is dipped into it, sprayed with the dispersion, or otherwise. the dispersion liquid. The temperature of the dispersion in the immersion bath ranges from about 15 to about 35°C;
Preferably, the temperature is maintained in the range of about 20-30°C, into which the pretreated printed wiring board is immersed. Soaking times generally range from about 1 to about 10 minutes, preferably from about 6 to about 5 minutes. During immersion, the carbon black-containing dispersion penetrates the pores of the printed wiring board and wets and contacts the glass fibers and epoxy resin forming the components of the non-conducting 1G. The immersed board is then removed from the bath of the carbon black-containing dispersion and then preferably exposed to compressed air to clear any holes in the printed wiring board that are still filled with the dispersion. . At the same time, excess carbon black-containing basic dispersion is removed from the surface of the copper plate.

The carbon black coated wiring board is then cleaned by removing substantially all of the water (i.e., more than about 95 cm) in the dispersion used and freeing the dry deposits containing the carbon black. A processing step leaves holes and other exposed surfaces in the conductive layer.

This is done by evaporation at room temperature, vacuum, short heating of the circuit board at elevated temperature or other similar methods. Heating at elevated temperatures is the preferred method. Heating is usually about 5°C to about 120°C, preferably about 80°C to 98°C.
, for about 5 to about 45 minutes. In order to complete the coverage of the pore walls, the step of dipping the plate in the carbon black dispersion and the subsequent drying step can be repeated one or more times.

This drying step results in a plate completely coated with the carbon black dispersion.

This dispersion not only coats the surfaces of the desired drilled holes, but also the undesired surfaces of the copper plate or foil. Therefore, all carbon black must be removed from the surface of the 2111 plate or copper foil before the photoimaging process. Preferably, this is done by mechanical scrubbing or microetching, leaving the fibers and epoxy resin optical surface coating intact.

Microetching is preferred because of ease of use. A suitable sodium persulfate micro-etching agent is 2M Engineering C.
RO-KTOFI 601', Ph1lip
A.

It is available from Hunt Chemica and is as described above. The mechanism of this microetching action is not to directly attack the carbon black deposited on the copper foil, but rather to attack the first few atomic layers of copper that provide adhesion to the coating. Therefore, the fully coated plate is immersed in a micro-etching solution to separate the carbon black from the copper surface in a 6" brake and transfer it into the solution in the form of a micro-foil. is filtered from the micro-etching bath using a pump or PW
It is removed by a weir-type p-filter commonly used in the B industry. Dispersion of carbon black, optional micro-etching and subsequent optional washing with deionized water prepare the PWB from polypropylene or polyvinyl chloride (PVC).
Immersion in the bath prepared in step C) is carried out with stirring using a recirculating Hp 4 pump or an air pump.

This microetching step is particularly preferred in the case of multilayer plates. This is because, after the drying step 8, not only the outer copper plate or foil but also the inner copper plate or foil protruding into the hole is coated with carbon black. Therefore,
This cross-etching process accomplishes six very desirable scratches simultaneously.

A. Microetching removes any excess carbon black material adhering to the copper plate or foil or the copper inner plate or foil in the multilayer hole.

B. Microetching chemically cleans and slightly microetches the copper surface to provide an excellent base for applying a dry film or for depositing copper by electroplating.

C. Microetching chemically cleans the edges of the copper plate or foil around the drilled holes. This ensures that the interface between the electrolytically deposited copper on the hole wall surface and the outer copper foil is not contaminated with carbon black material.

After an optional microetching step and subsequent water rinsing step, the PWB is sent to a photoimaging step and subsequent electroplating or direct plate electroplating step.

This treated printed wiring board is then immersed in a suitable electroplating bath to coat the buttons on the non-quaternary hole walls.

The present invention contemplates the use of all conventional electroplating processes to apply metal layers to the through-hole walls of PWBs. Therefore, the invention is not limited to Hessian electroplating baths.

A typical copper electroplating bath contains the following components in the following proportions:

(Approximately 60-75f/fD (approximately 37.5 fl required)
Electroplating baths are generally stirred and preferably maintained at approximately 0°C.
A temperature of ~25°C is maintained. The electroplating bath is equipped with an anode, usually made of steel, and the printed circuit board to be plated is connected as a cathode to the electroplating circuit.

For example, a current of about 15 amperes per square foot would produce a copper plating up to about 1 mil ± 0.2 mil thick on the hole walls of a non-conducting layer located between two copper plates. is passed through the electroplating circuit for approximately 60 to 90 minutes. This copper plating of the hole walls creates a current path between the copper layers of the printed wiring board.

Other suitable electroplating conditions may be used if desired. If desired, electroplating baths containing other copper salts or other metal salts such as nickel, gold, silver, etc. salts are used.

The printed wiring board is removed from the copper plating bath, rinsed and dried, and subjected to further processing with the application of a photoresist compound as is known in the art of manufacturing printed wiring boards.

Even if the immersion time in the carbon black liquid bath is excessive,
It was found that the thickness of the carbon black coating did not increase appreciably. This seems to imply that this is a surface adsorption process and once the entire surface of the pore contour is υ, no deposition of material occurs anymore.

The method of the present invention in which a copper layer is electroplated onto a non-conductive surface provides a number of unexpected benefits, including the following.

1° The use of preactivators, Pd/Sn activators, and accelerators required in conventional N-free copper-deposited plating technology is unnecessary.

2. Compared to the conventional electroless method, the method of the present invention requires fewer processing steps and shorter processing time to obtain a PWB for electroplating. Also, there are significantly fewer problems with contamination than with electroless plating.

5. There are no stability problems or side reaction problems associated with the use of electroless plating baths. The common traces of ionic impurities in the cleaning bath have little effect on the carbon black dispersion.

Moreover, temperature changes during processing have also been shown to have no effect.

4. A more uniform thickness of the electroplated copper on the through-hole wall is achieved, and shape defects and voids in the electroplated area are minimized or eliminated. The thermal properties of the bond within the pores and the physical properties of the bond are excellent.

5. An electroplated copper layer is deposited uniformly on the epoxy and glass fibers on the non-conductive surface, and the standard bond (s
o/dθr) In the impact test, 'pullaway'
There is no T.

6. No highly conductive graphite or powder metal needed to perform electroplating, a known drawback in the prior art. The porous carbon black particles of the method of the invention apparently adsorb a large amount of copper-containing electrolyte to achieve electrical conductance and electroplating onto the non-conductive layer surface.

7. The carbon black coating in the K hole is
It is not damaged in subsequent photoimaging steps performed before the electroplating process. Also, physical scrubbing prior to photoimaging does not have a deleterious effect on the pore coating. Although the method of the present invention is particularly suitable for use in electroplating the walls of holes in non-conductive parts of printed wiring boards, it has been found that the method of the present invention can be used to make the surfaces of other non-conductive materials conductive. You will notice scales coated with metal.

a The method of the present invention does not require special copper electroplating bath chemicals or special brightening additives.

It is compatible with all electroplating baths currently commercially available in the United States,
Compatible with both types, matte and glossy finishes.

9 The carbon black liquid bath of the present invention has wide latitude in the practical concentrations of its components. Also, determining whether the bath still contains workable amounts of the ingredients is readily accomplished by pH titration of basicity and determination of solids content by H. The simplicity of maintaining this bath contrasts with the extensive chemical monitoring required for many steps in electroless plating.

The following examples are intended to explain the invention more fully and are not intended to be limited thereby. All parts and percentages are by weight unless otherwise specified.

Circuit Board Description Several laminated circuit boards were processed by the method of the present invention. Each circuit board consists of two 55 micron thick thin copper plates bonded by pressure welding to opposite sides of an epoxy/glass fiber layer. ? ! #The thickness of the layer was approximately 155 m. These circuit boards are approximately 20cm wide and 28L long.
:rn. About 50 to about 100 holes, about 1.0 knot in diameter, were drilled through the copper plate and the epoxy resin/glass fiber layer.

Example 1 One of these perforated circuit boards was prepared by first mechanically scrubbing the surface of the cedar board and then placing it in a predetermined volume in an aqueous bath (approximately 4,02 volumes each) in the following order: The through holes were prepared for copper electroplating by soaking for a time.

1. Cleaner/conditioner (5 minutes) 2. Cleaning with deionized water (2 minutes) 3. Sodium persulfate micro-etching (1 minute) 4.
Washing with deionized water (2 minutes) 5.10 T H2SO4 (2 minutes) 6. Washing with deionized water (2 minutes) Z Carbon black pre-plating (coating) dispersion (4 minutes) [Drying at 110°C (10 8. Sodium Persulfate Microetch (1 min) 9. & Cleaning with Ionized Water (1 min) Bath 1 contains a cleaner/conditioner formulation where primarily monomethanolamine and ethylene glycol are present in the water. It was an aqueous solution that was used to remove oil and impurities from the surface of the pore walls of the plate. The bath was heated to approximately 10°C to facilitate this cleaning. Cleaner/conditioner formulations include Ph1lip A, H
It is sold under the trade name Cleaner/Conditioner 102 by the company Unt Chemica 1.

Bath 3 is an aqueous bath at room temperature, containing 20 ml of deionized water/liter.
0% persulfuric acid) l) Contained 0.5% by weight of rum and concentrated sulfuric acid. The purpose was to laminate the copper surface of the plate. This sodium persulfate microetch is called Ph1lip A.

'M engineering C that can be done manually by Hunt Chemica 1 company
It was RO-KTCH601'.

Bath 5 was a room temperature deionized water bath containing 10% by weight H2BO3. This bath was to remove copper oxide from the surface of the cedar board.

Bath 7 was room temperature deionized water containing the carbon black preplating components of the present invention.

The treatment components in this bath were as follows.

0.06wt% A-on surfactant ■0.46wt% KOH' 0, 31 9H% wt Humid silica ■0, 21
The residue of the carbon black bath was deionized water.

■ MAPHO856 anionic surfactant-Maze
rOhemica'1 (surfactant with 90 layers of
10 layers! -H2O).

■ Solid potassium hydroxide (R) (86M-J%KO)
(, 14% water by weight).

■ CAB-0-8 Engineering L ME! -7SD fumed silica (manufactured by Cabot).

■! 'jAVEN 3500 car F van black (C
manufactured by abot).

This carbon black dispersion in bath +7 was prepared by ball milling a concentrate of this dispersion in a wide mouth bottle containing stone beads to approximately Δ of the bottle volume. A continuous phase is obtained when the surfactant is deionized water/KOH
/7 Dissolved in Rika. Carbon black was then added. Milling time was 6 hours. After milling, the concentrate was diluted with sufficient deionized water to prepare a dispersion of the proportions described above.

Bath 8 had the same microetching formula as Bath 5. The purpose is to micro-etch the copper surface of the plate to remove deposited carbon black from that surface. Carbon black deposited on the glass fiber/epoxy was unaffected by this microetching.

Washing baths 2.4, 6 and 9 were used to prevent carryover of chemical components from one processing bath to the next.

After processing according to this bath sequence, the circuit board was then placed in an electroplating bath having agitation means and heating means, the bath having the following composition:

A chloride ion 24.3η/2β circuit board was connected as a cathode in an electroplating vessel having a volume of approximately 42 cm. Two copper rods were placed in the electrolyte and connected to the battery circuit as anodes. The copper rod was about 8 crn long, about 3.2 m wide and about 0.6 cm thick.

The surface of each was approximately 25 cm2. 15 amps per square foot is 85 amps of direct current applied to the electrodes of the electroplating bath.
It ran for a minute. The bath was maintained at a temperature of about 25°C across the time;
Then, stirring was performed by air spray. At the end of that time, the circuit board was removed from the electrolyte and separated from the electroplating circuit, rinsed with deionized water, and dried.

Testing of the resulting electroplated plates revealed that the pore walls were coated with a relatively uniform layer (1.0 mils ± 0
．． 2mil) set'dog honing (dog bon
ing)' was not observed (i.e., this latter effect is an undesirable condition where the plated layer has a thickness close to that of the PWBO steel laminate). A standard adhesion test ■ showed no delamination of the plated copper from the hole walls of the epoxy/fiberglass Id component.

■ Engineering PC test N112.3.8B Thermal stress theory by solder float test (Thermal 5tres
s MethodologyVia 5older F
Ploat Te5t)', here and hereafter the standard solder impact test (atannerd sol+j
ershock test).

Examples 2-8 The process of Example 1 was repeated to further illustrate the invention using different types of carbon blacks other than RAVEN 3500. Carbon black plating bath 7
Several different types of carbon black were tested with slight modifications. The treatment components of these baths were as follows.

0.37% by weight MAPHO856 (90% in water) 0
．． 79% by weight KOH (86% in water) 0.58% by weight
CAB-0-8 Engineering L Me-7SD0.42% by weight
Carbon black (see Table 1) 1.16% by weight total solids The remainder of each bath was deionized water. The most important feature was the adhesion of the plated copper to the hole walls.

All boards of Examples 2-8 were tested in the standard Norder hammer test (PC) of copper plated with epoxy/fiberglass through-holes.
Test l-Nu 2.3.2B) showed good adhesion. Tests of the resulting electroplated plates showed that the hole walls were in each case covered with a relatively uniform layer of copper (1 mil by 0.2 mil) and two dog bannings were applied.
)' was not observed.

In some plates, about 5 to about 10% of the plating in the holes is 2,
3 voids were observed, which is due to the surfactant MAP
This is believed to be due to the slight incompatibility of HO856 with certain carbon blacks. This slight incompatibility means that these particular carbon blacks are preferred
t Monarch 1300 and Columbian
This is thought to be due to the higher PTI than Raven 3500. The specific carbon blacks tested and their physical properties and resulting voiding effects are shown in Table 1 below.

Examples g-15 To demonstrate the production capabilities of the present invention, the process of Example 1 was repeated without the inclusion of silica in the carbon black dispersion. Carbon black pre-coating (plating) of Examples 2-8
Bath +7 was made without silica, so the proportions of ingredients in each dispersion were as follows:

MAPHO856 (90 parts in water) - [1,37% by weight KOH (86% in water), - 0,79% carbon black (see Table 2) - 0,42% total solids
-1.5% by weight The remainder of the above ingredients was deionized water. All coated plates had good adhesion when tested by the standard solder impact test. They exhibited no 'dog honing' and had a flat copper plating. Other results for copper plated circuit boards pretreated with these carbon black dispersions are shown in Table 2 below. Comparing these results in Table 2 with the results in Table 1 shows that the absence of silica in the composition does not adversely affect the plating of through holes in circuit boards.

In related experiments, acrylonitrile butadiene styrene (ABS) copolymer coupons were tested in Example 3 (5i02
) or treated with a carbon black dispersion as in Example i 5 (without Si02) and then electroplated. In the plating step, a dispersion similar to Example 8 (containing 5i02) was plated about twice, as was the dispersion of Example 15. Both had good mesogi contact when tested by the standard tape peel test (IPC!Test N112.4.1).

Examples 16-19 To demonstrate the effectiveness of the present invention, Example 1 was prepared by varying the amount of KOH in the carbon black dispersion without containing silica.
The operation was repeated again. Carbon black precoating (plating) dispersion bath +7 had the following proportions of each component.

MAPHO856 (90% J Kui) 0.37chi 0.
37% 0.37% 0.37%Koa (86%2 咋) 0.36% 0.18chi 0.09chi 0R
AVKN 3500 0.42% 0.42%
0.42% O, a2% total solids 1.15
CH 0.97 CH 0.88 Section 0.79 Table 3 shows the characteristics of the obtained fields and dispersions. Example 19 (zero concentration) was a poor dispersion because the MAPF (O856 surfactant) was not stable in the acidic region and was therefore ineffective in dispersing the acidic RAVKN 3500. The best dispersion properties were observed when the resulting dispersion concentration was high. All of these experiments, with the exception of Example 19, showed that there were only a few voids in the solder (about 5 to about 10 holes in the plate). It showed good uniform plating (1 mil ± 0.2 mil) with 1% voided) and good adhesion when subjected to the standard Norder impact test.

Examples 20-25 The procedure of Example 1 was repeated again to demonstrate the effectiveness of the present invention without the inclusion of either silica or KOH in the carbon black dispersion. Instead, an acidic carbon black precoat was used. (Plating) Dispersion bath +7 was used. The proportion of selected surfactant and carbon black in each dispersion was 2.5% by weight each. Prior to preparing the dispersion, the deionized water making up the remainder of the dispersion was acidified with HCE to a 1.0N solution.

The carbon black particles and surfactants used are shown in Table 4 along with the dispersion and void properties.

As can be seen from Table 4, the void characteristics were less voided in Examples 20, 23 and 25 (only about 1 to
2% had voids). All examples showed good adhesion in the standard Nruder impact test.

Example 26 Employing a Commercial Patterned Metallic Process A multilayer, double-sided copper epoxy/fiberglass circuit board was processed in a commercial process by the method of the present invention. At least 50 holes, about 1.0 rtas in diameter, were drilled and burred through the copper plate and epoxy resin/glass fiber layer.

These perforated and deburred circuit boards are prepared for imaging and copper plating by first mechanically scrubbing the surface of the board and then immersing it in an aqueous bath for a predetermined period of time in the following order: Created.

Bath 1. Cleaner/conditioner solution (4 minutes)
Bath 2. Washing (2 minutes) Bath 3. Sodium persulfate microetching (1 minute) Bath 4 Washing (2 minutes) Bath 5.10 Section H2
SO4 solution (2 minutes) bath 3. Washing
(2 minutes) Bath 7 Carbon black pre-plating dispersion (4 minutes) [Dry at 185-190°C for 10 minutes] Bath a Thorium microetching (2 minutes) Bath 9. Washing (2 minutes) Bath 1
was an aqueous solution containing a cleaner/conditioner component consisting essentially of monomethanolamine and ethylene glycol in water that removed grease and other impurities from the pore wall surfaces of the plate. The bath was heated to about 148 ℃ below to facilitate this cleaning. Cleaner/conditioner: Ph1lip A, Hunt Chemi
Cleaner/conditioner 102 by ca1 company
One item is being sold temporarily under the product name.

Bath 6 is an aqueous bath at room temperature and 0' 5 T! 'j
: gJl of Rφ (together with 2804 contained 200 f sodium persulfate per liter of deionized water).

The purpose was to micro-etch the copper surface of the plate. Microetching is Ph1lipA, Hu
MICRO- available from nt Chemica1.
]11iTCH601.

Bath 5 was a room temperature deionized water bath containing 10% by weight H2SO4. The purpose of this bath was to remove copper oxide from the surface of the board.

Bath 7 was a room temperature bath of deionized water containing the carbon black pre-plating (pre-coating) components of the present invention. The treatment components in this bath were as follows.

0.06 weight (A% anionic surfactant ■0.46
Weight % 0.31% by weight of potassium hydroxide 1.32% by weight of fumed silica The remainder of the total solids bath was deionized water.

Bath 8 had the same microetching composition as Bath 3. Its action is to micro-etch the copper surfaces of the plates to remove deposited carbon black from those surfaces.

Wash baths 2.4.6 and 9 were used to prevent chemical carryover from one processing bath to the next.

After being processed through the above bath sequence, the circuit board was then mechanically scrubbed and sent to an imaging process followed by a copper electroplating process.

Testing of the resulting electroplated board revealed that the pore walls were covered with a relatively uniform layer of copper (i.e., about 1 mil ± (12 mil) and
It turned out that there was no dog honing. Standard solder impact tests show that copper electroplated on the hole walls of the epoxy/fiberglass layer component has good adhesion (i.e., no delamination).
It had These plated circuit boards are also xp
c test l-2, 4, 21'thermal adhesive strength' and IPC
- Passed the 2 mil (M Engineering L) Specification 851100 'long-term thermal shock test and thermal cycle test' described in TR-578.

■ Anionic surfactant MAPHO856-Maze
rOh (manufactured by 1mica'1 (90% by weight surfactant, 1% by weight water).

■ Solid potassium hydroxide is lett (86% by weight KOH).
114% water).

■ CAB-0-B engineering L MS-7SD fumed silica (manufactured by Cabot) ■ RAM1nN 3500 carbon black (Cab
COMPARATIVE EXAMPLES 1 AND 2 The procedure of Example 1 was repeated except that the carbon black pre-plating bath 7 was modified to contain graphite. Two graphite formulations were prepared as follows.

Comparative Example 1 5.6% KOH (86%)! , 7% by weight CAB-0-8IL MS-7SD2
．． 5-layer i-chi MAPHO856 (9o-chi) Comparative Example 2 1.1 weight 4 KOH (86-chi) 0.7 weight% C'AB-0-8 engineering L ME-7BD0
．． 5% by weight MAPRO856 (9ochi) 2.3% by weight
The remainder of each total solids formulation was deionized water. The average particle size of the solids was measured on a HOE particle sizer, and both formulations had a diameter of 3.1 microns and an average volume of 10.7 microns. After plating, the through holes in the circuit board were inspected for defects. The board pre-plated with the formulation of Comparative Example 1 failed the solder impact test, although only a few voids were observed. The copper plating in the holes had delaminated from the epoxy/glass fiber layer. A layer of dried graphite dispersion was visibly observed between the epoxy/glass fiber layer and the peeled steel plating. The thick layer appeared to be due to poor adhesion of the copper. The plates treated with the formulation of Comparative Example 2 had no or very few void-free pores.

This latter graphite formulation could not be subjected to standard impact tests due to the lack of void-free pores. In short, both graphite formulations were quite inferior for copper electroplating compared to the carbon black formulations of the examples described above.

Example 27 C) Commercialized by AF Company with an average molecular weight of about 10.
Example 1 was repeated using 000 polyvinylpyrrolidone (pvp) as the surfactant. The properties of the resulting circuit board were essentially the same as those of the circuit board made in Example 1.

Example 28 The procedure of Example 1 was repeated using methanol, impropyl alcohol, t-butyl alcohol, or polyethylene glycol instead of water as the liquid dispersion medium. In both cases, the resulting circuit boards had some voids in the copper covering the hole walls, but passed the standard bond impact test.

Procedure 111i1T, written July 1, 1986

Claims (1)

[Claims] 1) The steps of: (a) (1) carbon black particles having an average particle size of less than about 3.0 microns in a dispersion; (2) an interface having compatibility with said carbon black; an effective dispersion amount of the activator; and (3) a carbon black dispersion comprising a liquid dispersion medium (in the above dispersion, the amount of carbon black is sufficient to cover substantially the entire surface of the non-conductive material); (b) applying said dispersion to the surface of a non-conductive material; and (c) removing substantially all of the liquid dispersion from said carbon black particles. (d) separating the carbon black particles thereby depositing the carbon black particles on the non-conductive surface in a substantially continuous layer; A method of electroplating a conductive metal layer on a non-conductive material surface, comprising electroplating a conductive metal layer on a non-conductive material. 2) The above dispersion further adjusts the pH of the dispersion to about 10 to about 14.
2. The method of claim 1, further comprising at least one alkali hydroxide in an amount sufficient to raise the temperature within the range of . 3) The method according to claim 2, wherein the alkali hydroxide is selected from the group consisting of potassium hydroxide, sodium hydroxide, lithium hydroxide, ammonium hydroxide and calcium hydroxide. 4) The method of claim 2, wherein the dispersion further contains an alkali silicate formed by the reaction of fumed silica particles with an alkali hydroxide. 5) The method of claim 4, wherein the dispersion further contains an alkali silicate formed by the reaction of about 50 to about 250 grams of fumed silica with about 100 to about 350 grams of alkali hydroxide. 6) The method according to claim 1, wherein the liquid dispersion medium is water. 7) The method according to claim 1, wherein the liquid dispersion medium is an alkyl alcohol having 1 to 15 carbon atoms. 8) The method of claim 1, wherein the dispersion contains less than about 10% solids by weight. 9) The initial pH of the carbon black particles is about 1 to about 7.
5. The method according to claim 1, which is 10) The initial pH of carbon black particles is about 2 to about 4.
The method according to claim 9. 11) The method according to claim 1, wherein the carbon black particles are porous particles. 12) Carbon black particles are about 45 to about 1100 m^
12. The method of claim 11, having a surface area of 2/g. 13) The method of claim 1, wherein the carbon black particles contain from about 1 to about 10% by weight volatile components. 14) The method according to claim 1, wherein the surfactant is a phosphate ester anionic surfactant. 15) The method of claim 1, wherein the conductive metal is selected from the group consisting of copper, nickel, gold and silver. 16) The method according to claim 15, wherein the conductive metal is copper. 17) The method according to claim 1, wherein step (b) is carried out by immersing a non-conductive substance in a dispersion. 18) A method according to claim 1, wherein said separation step (c) is carried out by heating the applied dispersion. 19) The following steps include (a) dispersing the printed wiring board with said through holes in a dispersion with (1) carbon black particles having an average particle size of less than about 3.0 microns; and (3) a bath of a dispersion of carbon black comprising a liquid dispersion medium, in which the amount of carbon black covers substantially all of the non-conductive surface. (b) separating substantially all of the liquid dispersion medium from the dispersion;
thereby depositing carbon black particles in a substantially continuous layer on the non-conductive portion of the pore walls; and (c) depositing a substantially continuous layer of carbon black on the non-conductive portion of the pore walls; at least one non-conductive layer is laminated to at least two separate metal layers comprising electroplating metal layers, thereby providing an electrical connection between said metal layers of the printed wiring board; A method of electroplating the walls of through holes in laminated printed wiring boards. 20) The method of claim 19, wherein the dispersion further contains at least one alkali hydroxide in an amount sufficient to raise the pH of the dispersion to a range of about 10 to about 14. 21) Claim 2, wherein the alkali hydroxide is selected from the group consisting of potassium hydroxide, sodium hydroxide, lithium hydroxide, ammonium hydroxide, and calcium hydroxide.
The method described in item 0. 22) The method of claim 20, wherein the dispersion further contains an alkali silicate formed by the reaction of fumed silica particles with an alkali hydroxide. 23) The method of claim 22, wherein the dispersion further contains an alkali silicate formed by the reaction of about 50 g to about 250 g of fumed silica with about 100 to about 350 g of alkali hydroxide. 24) The method according to claim 19, wherein the liquid dispersion medium is water. 25) The method according to claim 19, wherein the liquid dispersion medium is an alkyl alcohol having 1 to 15 carbon atoms. 26) The method of claim 19, wherein the dispersion contains less than about 10% solids by weight. 27) The initial pH of the carbon black particles is about 1 to about 7.
．． 19. The method according to claim 19, wherein the method is: 28) The initial pH of the carbon black particles is about 2 to about 4.
28. The method according to claim 27. 29) The method according to claim 19, wherein the carbon black particles are porous particles. 30) The method of claim 19, wherein the conductive metal is selected from the group consisting of copper, nickel, gold and silver. 31) The method according to claim 30, wherein the conductive metal is copper. 32) The method according to claim 19, wherein the surfactant is a phosphate ester anionic surfactant. 33) Claim 19 further includes the step of micro-etching the metal layer of the printed wiring board to remove carbon black deposited on the metal layer between step (b) and step (c). Method described. 34) The method according to claim 33, further comprising a water washing step after the microetching step. 35) (1) carbon black particles having an average particle size of less than about 3.0 microns in the dispersion; (2) an effective dispersion amount of a surfactant compatible with the carbon black; and (3) a liquid dispersion. a dispersion suitable for enhancing metal plating of a non-conductive surface consisting of a medium in which the amount of carbon black is sufficient to coat substantially all of the surface of the non-conductive material; less than about 4% by weight of the dispersion). 36) The dispersion of claim 35 further comprising at least one alkali hydroxide in the dispersion in an amount sufficient to raise the pH of the dispersion to a range of about 10 to about 14. liquid. 37) Claim 3, wherein the alkali hydroxide is selected from the group consisting of potassium hydroxide, sodium hydroxide, lithium hydroxide, ammonium hydroxide, and calcium hydroxide.
Dispersion liquid according to item 6. 38) The dispersion according to claim 36, further comprising an alkali silicate formed by a reaction between fumed silica particles and an alkali hydroxide. 39) The dispersion according to claim 35, wherein the liquid dispersion medium is water. 40) The dispersion liquid according to claim 35, wherein the liquid dispersion medium is an alkyl alcohol having 1 to 15 carbon atoms. 41) The dispersion of claim 35 containing less than about 10% solids by weight. 42) The initial pH of carbon black particles is about 1 to about 7.
．． 35. The dispersion according to claim 35, which is No. 5. 43) The initial pH of carbon black particles is about 2 to about 4.
The dispersion according to claim 42. 44) The dispersion according to claim 35, wherein the carbon black particles are porous particles. 45) The dispersion according to claim 35, wherein the surfactant is a phosphate ester anionic surfactant. 46) A printed wiring board in which a substantially continuous layer of carbon black is deposited on the non-conductive portion of the wall of the through hole. 47) The printed wiring board according to claim 46, wherein an alkali silicate is mixed in the continuous layer of carbon black. 48) A printed wiring board in which a substantially continuous layer of carbon black is deposited on the non-conductive portion of the wall of the through hole and metal plating is applied thereon. 49) The printed wiring board according to claim 48, wherein the metal is copper.