JPH0959778A - Pretreatment for electroless plating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct pretreatment for electroless plating good in operability and suitable for mass production by coating the desired place on the surface of the nonconductive substrate with a liq. org. binder wherein a nonconductive powder carrying a metallic catalyst is dispersed. SOLUTION: A metallic catalyst for electroless plating such as palladium is deposited on the nonconductive powder consisting of the ceramic or plastic grains having <=20μm average diameter. The powder is added and dispersed by 5-10vol.% into a liq. org. binder. The org. solvent soln. or aq. emulsion of acrylic, polyurethanic and epoxy paints, etc., is preferably use as the binder. The desired place on the surface of the base consisting of a nonconductive substrate is coated with the liq. dispersion to form a coating film. The ratio of the catalyst to the binder in the coating film is preferably controlled to <=1wt.%. As a result, a coating film wherein a catalyst is uniformly dispersed is formed, dimensional precision and weight-lightening are improved, and a lightweight high-quality electroless plating having high dimensional accuracy is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electroless plating on a non-conductive substance, and more particularly to a pre-treatment method for electroless plating useful for forming a conductive layer for electromagnetic wave shielding.

[0002]

2. Description of the Related Art Electroless plating is widely used as a means for forming a metal layer on the surface of a cabinet of electronic equipment, a printed circuit board, etc., which is made of a non-conductive material such as ceramics or plastics. That is, it is a method in which a catalyst for activating the electroless plating is applied to the surface of the non-conductive substance which is the substrate to be plated and then brought into contact with the electroless plating solution. As these catalysts, various active metal particles such as palladium, platinum, gold, silver, copper, nickel and cobalt are generally used.

By the way, in this type of electroless plating method, in order to firmly adhere and support the plating layer on the substrate, it is necessary to roughen the surface of the substrate to which the catalyst is applied in advance by etching or the like. It was For example, when electrolessly plating copper or nickel on an ABS resin, a catalyst nucleus is usually formed using a stannous chloride solution and a palladium chloride solution. As a previous step, the catalyst core is formed in a heated chromic acid-sulfuric acid solution. A so-called etching operation in which a material is dipped to form fine irregularities on its surface is performed.

According to such an operation, fine cracks are generated on the surface depending on the kind of the material, and in the worst case, it cannot be used as a base material. In addition, it is difficult to plate only on an arbitrary place, in other words, leaving only a part of the material and plating only on a necessary place complicates the process and causes an increase in cost. Therefore, recently, an electroless plating method has been developed which does not require roughening the surface of a material made of a non-conductive material in advance. For example, the method disclosed in Japanese Examined Patent Publication (Kokoku) No. 2-62960 has been proposed in order to improve such a defect, and a relatively large amount of active metal particles having a specific range of dimensions in a liquid organic binder. It is to disperse the powder into the surface of the non-conductive enclosure and to apply the catalytic property to the surface of the non-conductive enclosure.

[0005]

[Patent Document 1] Japanese Patent Publication No. 2-629
The method disclosed in Japanese Patent No. 60 has the convenience that no special surface treatment operation is required other than removing burrs, oil, dust, and other contaminants during manufacturing to clean the surface of the material. On the other hand, since the metal particles used here have a high specific gravity and easily settle in the binder, the ratio of the binder to the metal particles changes without constant stirring, which causes variations in the quality of the coated film. I will end up. In particular, in spray painting, there is a problem that productivity is impaired because it causes workability to be impaired by not evenly ejecting from a nozzle.

Further, since an organic binder layer containing about 50% or more of metal particles is applied to a thickness of 12.5 μm or more when dried, when this method is applied to a mobile phone, a personal computer or the like, However, the weight of the product is large and the dimensional accuracy of the product is poor.

The object of the present invention, however, is different from the case of using metal particles, in that the catalyst does not settle in the organic binder during coating, workability is good, and electroless plating suitable for mass production is suitable. It is to provide a processing method. Another object of the present invention is to form a coating film in which the specific gravity is light and a small amount of a catalyst is uniformly dispersed, the quality of the conductive layer does not vary, and dimensional accuracy and weight reduction of the product can be advantageously achieved. It is to provide a pretreatment method for electrolytic plating.

[0008]

In order to achieve the above object, the present invention disperses a non-conductive powder having a metal catalyst for electroless plating previously supported on a surface thereof in a liquid organic binder, and thereafter, The gist of the pretreatment method for electroless plating is characterized in that a coating film is formed by coating the obtained dispersion liquid on a desired place on the surface of a base made of an electrically non-conductive substance.

As the metal catalyst for electroless plating to be carried on the surface of the non-conductive powder, palladium, platinum, gold,
Various metals such as silver, copper, nickel, cobalt, iron,
Of these, palladium is the most preferable.

The non-conductive powder used in the present invention is glass,
It is made of inorganic powder such as ceramics and minerals or plastics powder such as thermoplastic resin and thermosetting resin. Specific examples of the inorganic powder include shirasu balloon, glass balloon, glass flake, alumina, silica, mica, talc, zeolite and the like. Also, examples of plastics powder include ABS, polyester,
Examples thereof include plastics particles such as nylon, polycarbonate, polystyrene, polypropylene and polyethylene. Of these non-conductive powders, foams such as shirasu balloons and glass balloons have a small apparent specific gravity, and the latter various plastics powders also have a smaller specific gravity compared to metals and inorganic substances, so the weight of plated products is light. It is a suitable material that can contribute to realization.

The shape of these non-conductive powders is not particularly limited, and may be any shape such as granular, plate-like, flake-like, needle-like, etc. The average particle diameter of the non-conductive powder having such a shape is 20
It is preferable to select and use those having a size of less than or equal to μm, particularly those in the range of 2 to 10 μm. In addition, many inorganic powders such as glass, ceramics, and minerals are plate-like, flake-like, and acicular, rather than granular, and the powders of this kind also preferably have a longest dimension of 20 μm or less. .

As a method of preliminarily supporting a metal catalyst for electroless plating on the surface of these non-conductive powders, a technique already known as a pretreatment method for electroless plating on various powders, for example, a plating technique, Vol.5, No.5, 1-10, 1992, technology for imparting catalytic property to powder surface disclosed in publications such as Japanese Patent Laid-Open No. 59-182961, and through holes of printed wiring boards It is possible to adopt all the alkaline catalyst application processes which have been recently developed as a technique for catalyzing nonconductors such as plating and plastics.

Specifically, a method of supporting palladium on the surface of the powder using an acidic solution of stannous chloride-palladium chloride, or a neutral solution consisting of a borohydride compound-palladium chloride-surfactant is used. A method of supporting palladium on the surface of the powder by using it, a method of treating with an alkaline aqueous solution containing an organopalladium complex and then reducing with a boron-based reducing agent (alkali-activation method), or using a surface-treating agent having a metal-trapping property It is possible to appropriately use a method of bringing the surface-treated powder into contact with a solution containing palladium ions to carry the palladium ions on the surface thereof, and then performing reduction (organic material coating-catalyst applying method). The powder thus imparted with the catalytic property is washed with water and dried, and then added to an appropriate liquid organic binder in a volume fraction of at least 5 to 10% and stirred to be dispersed. Therefore, the weight fraction increases as the specific gravity of the powder increases.

The liquid organic binder used in the present invention has a sufficient affinity for the powder to which the catalytic property is imparted and the coated surface, allows the powder to be uniformly dispersed, and is non-conductive. Any one can be used as long as it has the ability to form a thin and tough coating film that firmly adheres to the surface of the flexible base, but acrylic paints, polyurethane paints, and epoxy paints are preferred in the present invention. . These paints themselves are relatively easily available as volatile organic solvent type or aqueous emulsion type compositions,
Inorganic materials such as glass and ceramics or ABS resin,
Any material capable of exhibiting an excellent function as a surface coating for organic materials such as polyester resin and polycarbonate resin may be used. It is also possible to use a printing ink in place of these paints, and this can be preferably applied to the formation of a conductive pattern on a printed circuit board or the like.

As a method for coating the powder dispersion of these coating materials on the surface of the base, a conventional coating means such as a spray method, a brush coating method or a dipping method can be appropriately used. Also,
In that case, it is also possible to add a volatile diluent such as benzine or thinner to adjust the viscosity suitable for each coating method. In any case, the coating film obtained after drying is 1
It is important to form a continuous film having a thickness of 10 μm. By doing this, the average particle size is 10 μm
For the following non-conductive powder, preferably 20 to 50
%, A powder layer occupying two-dimensionally is arranged in a two-dimensional array to form a catalyst layer consisting of at least one layer. In other words, the thickness of the coating film according to the present invention does not need to be 10 μ or more.

The non-conductive substance forming the base is A
BS resin, polyester resin, polycarbonate resin,
Plastics such as polyurethane resin and polypropylene resin or fiber reinforced plastics obtained by reinforcing these resins with fibers are used. By the way, since the liquid organic binder used in the present invention has a sufficient affinity with these plastics as described above, as long as the surface is clean, no extra surface treatment such as etching is required for coating. Not necessary.

In the present invention, as described above, in forming the catalyst layer for electroless plating on the surface of the non-conductive base through the liquid organic binder, the catalyst metal is a non-conductive powder having a specific gravity lighter than that. Supported on the surface and dispersed in a liquid organic binder, and then the dispersion was coated on the surface of the base, so unlike the conventional metal particles, a stable dispersion in which the catalyst does not settle during coating. A liquid is obtained, which has good workability even during spray coating and improves productivity. In particular, since the plastics powder has a specific gravity almost equal to that of the synthetic resin constituting the organic binder and has a high affinity with the organic binder, a uniform floating state can be maintained for a long time.

Further, in the present invention, the metal catalyst supported on the powder surface is colloidal particles having a particle size of 1 to 100 mμ, which is 1/100 or less as compared with the plastic powder having an average particle size of 10 μm. And small. Therefore, compared with the case of using metal particles of the same size, the amount of catalyst is small, and since it is uniformly supported on the surface of the powder having a large surface area, a catalyst layer advantageous in terms of both cost and performance is formed. To be done.

Further, according to the present invention, the particle size of the powder and the volume of the powder in the binder are adjusted so that the powder carrying the catalyst continuously forms at least one catalyst layer in the coating film. Since the ratio is adjusted, electroless plating can be directly performed, and a conductive layer having uniform quality can be formed.
However, depending on the material of the coating film, such as acrylic paint, it may be possible to obtain a more preferable result by subjecting the surface to hydrophilic treatment. Also, a coating film with a small specific gravity is 10 μm thick.
Since it is formed as thin as the following, the weight of the product can be advantageously reduced.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, for electroless plating on the surface of a non-conductive powder consisting of ceramic particles or plastics particles having an average particle size of 20 μm or less, preferably in the range of 2 to 10 μm. A metal catalyst is supported, this is dispersed in a liquid organic binder, and the resulting dispersion is applied to a desired place on the surface of a base molded article such as an electronic component made of a non-conductive substance, and the surface has a catalytic property. A coating film was formed. Then, after rinsing with a caustic soda solution to make the surface hydrophilic, it was successively immersed in an electroless plating bath of copper and nickel to obtain an electroless plated product having excellent performance.

[0021]

EXAMPLES Next, the features of the present invention will be described in more detail based on examples.

Example 1 Kaolin powder having a mean particle size of 5 μm (specific gravity
3.0) is immersed in a catalyst-providing agent (made by Atotech Japan KK, trade name: Activator Neogant) of an alkaline aqueous solution containing a palladium-amine complex, and then reduced with sodium borohydride to give a surface of the kaolin powder. A palladium catalyst was supported. in this case,
The concentration of catalyst supported on kaolin is 3.5 mg / g (0.35%)
Met. Then, the above kaolin powder is added at a ratio of 30% by weight to a solution in which a small amount of a curing agent and an acrylic resin are dissolved in a thinner containing toluene, xylene, methyl isobutyl ketone (MIBK) or the like at a ratio of 30% by weight and stirred. And made into paint.

This paint is applied to a part or the whole of the surface of the article to be coated (base) made of ABS resin by an air spray method to form a coating film so that the average thickness after drying is 5 μm. And dried at about 60 ° C. for 30 minutes. Then 1
After rinsing with 0% caustic soda solution for 3 minutes at 50 ° C. to make the surface hydrophilic and thoroughly washing with water, the molded product is immersed in electroless copper plating solution at 45 ° C. for 30 minutes, and washed with water. A plating product was obtained by immersing in electroless nickel melt at 55 ° C. for 10 minutes, washing with water and drying.

The performance of the obtained plated product is as follows. Coating thickness: Average 5μm Copper plating thickness: 1μm Nickel plating thickness: 0.5μm Surface resistance (Measuring instrument: Mitsubishi Yuka KK, Laresta MPC tester): 5mΩ RFI shielding property (Measuring method: Advantest Frequency (MHz) 30 100 200 300 300 Attenuation (dB) 58 68 74 75 Heat shock test (80 ° C and -30 ° C for 1 hour each, 3
Repeatedly leave it alone and observe the condition before and after that ...
No abnormality Moisture resistance (Leave in an atmosphere of 60 ° C, 95% humidity for 168 hours,
Observe the condition before and after that)
… No abnormality

Example 2 Silica grain powder having an average particle diameter of 6 μm (specific gravity 2.6) was immersed in a methanol solution containing γ-aminopropyltriethoxysilane at room temperature, and heated and dried at 110 ° C. for 2 hours with sufficient stirring. The surface was coated with an organic compound containing an amino group as a metal scavenger. Then, it was treated with an alkaline catalyst-imparting agent in the same manner as in Example 1, and the resulting powder was added at a ratio of 40 parts by weight per 100 parts by weight of the acrylic copolymer resin content in the thinner solution, and stirred to form a paint. did. This paint was applied to a molded product made of a polycarbonate resin to form a surface coating film, and electroless plating was performed.

The performance of the obtained plated product measured by the same method as in Example 1 is as follows. Thickness of coating film: average 7 μm Copper plating thickness: 2 μm Nickel plating thickness: 0.5 μm Surface resistance: 5 mΩ RFI shielding property Frequency (MHz) 30 100 200 200 300 Attenuation rate (dB) 60 70 77 77 76

Example 3 Barium sulfate (specific gravity: 4.5) having an average particle diameter of 4 μm was immersed in a methanol solution containing γ-aminopropyltriethoxysilane at room temperature, and heated and dried at 110 ° C. for 2 hours with sufficient stirring, The surface was coated with an organic compound containing an amino group as a metal scavenger. Then, it was treated with an alkaline catalyst-imparting agent in the same manner as in Example 1, and 40 parts by weight of 100 parts by weight of the resin component was added to the resulting acrylic aqueous emulsion paint and stirred to disperse it. This dispersion was sprayed on the surface of a molded product made of a polycarbonate resin to form a coating film, and the surface was electroless plated.

For the obtained plated product, the thickness of the coating film and the plated layer and the surface resistance value were measured in the same manner as in Example 1. The results are as follows. Thickness of coating film: average 5 μm Copper plating thickness: 1 μm Nickel plating thickness: 0.5 μm Surface resistance: 7 mΩ

Example 4 Hydrophilized nylon powder having an average particle size of 6 μm (specific gravity 1.1) was dispersed in an aqueous solution containing a surfactant such as polyethylene glycol mono-P-nonylphenyl ether, and then the example. In the same manner as in 2, a palladium catalyst was supported on the surface of the nylon powder. Then, the nylon powder was added to a 10% thinner solution of an acrylic copolymer resin at a ratio of 10 parts by weight per 100 parts by weight of the acrylic copolymer resin content, and stirred to form a coating material. This paint, AB
After spraying on the surface of the S resin molded product to form a coating film, electroless plating was applied to the surface.

The performances measured in the same manner for this plated product are as follows. Thickness of coating film: average 7 μm Copper plating thickness: 1 μm Nickel plating thickness: 0.5 μm Surface resistance: 6 mΩ

Example 5 A palladium catalyst was applied in the same manner as in Example 2 except that nylon powder whose surface was coated with titanium oxide having an average particle size of 0.3 μm (average particle size 6 μm, specific gravity 1.2) was used. Then, a coating film was formed on the surface of the polycarbonate resin molded article using this coating material, and electroless plating was performed.

In this case, the performance of the obtained plated product is as follows. Thickness of coating film: average 7μm Copper plating thickness: 1μm Nickel plating thickness: 0.5μm Surface resistance: 5mΩ

Example 6 In the same manner as in Example 4, the surface of nylon powder having an average particle diameter of 6 μm dispersed in a nonionic surfactant was coated with γ-aminopropyltriethoxysilane, and then this was palladium chloride. And polyethylene glycol mono-P-
A palladium catalyst was adsorbed and supported on the surface of the nylon powder by dispersing it in an almost neutral colloidal aqueous solution containing nonylphenyl ether (surfactant) and sodium borohydride (reducing agent). Then, the nylon powder was added to a 10% thinner solution of an acrylic copolymer resin at a ratio of 10 parts by weight per 100 parts by weight of the acrylic copolymer resin content, and stirred to form a coating material. This paint was sprayed on the surface of an ABS resin molded product to form a coating film, and the surface was electroless plated.

In this case, the performance of the obtained plated product is as follows. Thickness of coating ・ ・ ・ Average 7μm Thickness of copper plating ・ ・ ・ 1μm Thickness of nickel plating ・ ・ ・ 0.5μm Surface resistance ・ ・ ・ 4 mΩ

[0035]

As described above, in the pretreatment step of the electroless plating according to the present invention, a stable dispersion liquid in which the metal catalyst is unlikely to settle during coating is obtained, and the operation of etching the substrate surface is unnecessary. The workability of the applying step is good and the productivity is improved, and the product with high dimensional accuracy and uniform quality of the coating film can be obtained. Also, the particle size is several
Since a metal catalyst of mμ is supported on the surface of the powder to form a catalyst layer having a substantially powder thickness, material cost reduction and product weight reduction can be achieved at the same time.

Claims (6)

[Claims] 1. A non-conductive powder having a metal catalyst for electroless plating previously supported on the surface is dispersed in a liquid organic binder, and the resulting dispersion is then formed on the surface of the base of the non-conductive material in a desired amount. A pretreatment method for electroless plating, which comprises applying a coating film to a place to form a coating film. 2. The pretreatment method for electroless plating according to claim 1, wherein the metal catalyst for electroless plating is palladium. 3. The pretreatment method for electroless plating according to claim 2, wherein the ratio of the palladium catalyst to the organic binder in the coating film is 1% by weight or less. 4. The pretreatment method for electroless plating according to claim 1, 2 or 3, wherein the non-conductive powder is ceramic particles or plastic particles having an average particle diameter of 20 μm or less. 5. A pretreatment method for electroless plating, wherein the liquid organic binder according to claim 1 is an organic solvent solution type or aqueous emulsion type acrylic paint, polyurethane paint or epoxy paint. 6. A non-electroconductive material constituting the base according to claim 1, which is made of plastic such as ABS resin, polyester resin, polycarbonate resin, polystyrene resin, polypropylene resin or the like, or electroless plating made of these fiber reinforced plastics. Pretreatment method.