JP2002266076A - Electroless plating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of easily manufacturing an electroless plating base material having an excellent adhesion property of a plating film in an etching process step in the electroless plating method. SOLUTION: This electroless plating method comprises installing a solid dielectric substance to at least one opposite surface of a pair of electrodes facing each other at a pressure near atm. pressure, introducing treating gas between a pair of these opposite electrodes and subjecting the base material to be plated to contact treatment by the plasma obtained by impressing impulsive electric field, to these electrodes in the etching process step for the surface of the base material to be plated in the electroless plating method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless plating method, and more particularly to an electroless plating method using a normal-pressure pulse plasma in an etching surface treatment step for a substrate to be plated.

[0002]

2. Description of the Related Art Electroless plating, which has conventionally been employed as a method of metalizing the surface of a substrate to be insulated such as plastic, glass, and ceramic, is generally made hydrophilic by making the surface rough by various etching methods. By applying a catalyst nucleus of palladium, silver, indium, tin, etc. for electroless plating to the hydrophilic substrate to be plated, then activating the catalyst nucleus, and finally immersing it in an electroless plating solution. I have been.

[0003] One of the important processing steps in electroless plating is pre-treatment etching of the surface of the substrate to be plated in order to increase the adhesion of the plating film. Affects film deposition and adhesion. Conventionally, this etching method is mainly performed by a wet method. For example, first, the base material to be plated is immersed in a solvent to be swollen, washed with water, then immersed in an etching solution such as a NaOH solution, a chromic acid solution, a mixed solution of chromic sulfuric acid, a permanganic acid solution, and then etched, and further washed with water. , Neutralization, washing, drying and the like.

[0004] These wet methods involve a large number of processing steps, such as repeating a solution processing step and a water washing step, and also require bath management of various processing liquids, treatment of waste liquid such as washing water, and further, fine etching. There is a problem that acid or the like, which is a processing liquid, remains in the trace, which becomes a factor that hinders the sensitizing effect and the like in a catalyst activation treatment and the like in a later step.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a method capable of easily producing an electroless plating base material having excellent adhesion of a plating film in an etching step in an electroless plating method. The purpose is to provide.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, by treating the surface of a substrate to be plated with plasma capable of realizing a stable discharge state under atmospheric pressure conditions. It has been found that etching can be performed easily and a high-quality plating film can be obtained, and the present invention has been completed.

[0007] That is, a first invention of the present invention is a method for etching a surface of a substrate to be plated in an electroless plating method, wherein a solid is formed on at least one opposing surface of a pair of opposing electrodes under a pressure near atmospheric pressure. An electroless plating method characterized in that a dielectric material is provided, and a processing gas is introduced between the pair of opposed electrodes and a substrate to be plated is contact-treated with plasma obtained by applying a pulsed electric field. is there.

According to a second aspect of the present invention, in the electroless plating method, the step of etching the surface of the substrate to be plated is performed by the plasma treatment according to the first aspect, followed by a catalyst applying step and a catalyst activating step. And an electroless plating step.

A third aspect of the present invention is the electroless plating method according to the first or second aspect, wherein the processing gas is a gas containing oxygen and / or sulfur dioxide.

In a fourth aspect of the present invention, the pulse-like electric field has a pulse rise and / or fall time of 100 μs or less and an electric field intensity of 0.5 to 250 kV / cm.
The electroless plating method according to any one of the first to third inventions, characterized in that:

According to a fifth aspect of the present invention, the pulsed electric field has a frequency of 0.5 to 100 kHz and a pulse duration of 1 to 1000 μs.
The electroless plating method according to any one of the inventions.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the electroless plating method of the present invention, a solid dielectric is placed on at least one opposing surface of a pair of electrodes facing each other under a pressure near atmospheric pressure, and a solid dielectric is placed between the pair of electrodes. By introducing a processing gas and applying a pulsed electric field between the electrodes, a plasma of the obtained gas is brought into contact with the surface of the substrate to be plated, and a pretreatment for etching the surface is performed. This is a method of performing electroless plating through a step of providing a catalyst nucleus on the surface of a plating base material, a step of activating the catalyst, and a step of immersing it in an electroless plating solution. Hereinafter, the present invention will be described in detail.

(1) Etching Treatment In the plasma treatment of the surface of the substrate to be plated in the electroless plating method of the present invention, the pressure under the atmospheric pressure means that:
It refers to a pressure of 333 × 10 ^{4 to} 10.664 × 10 ⁴ Pa. Among them, pressure adjustment is easy and the apparatus is simple.
The range is preferably 331 × 10 ^{4 to} 10.39 × 10 ⁴ Pa.

The electrodes include, for example, electrodes made of a single metal such as copper and aluminum, alloys such as stainless steel and brass, and intermetallic compounds. The counter electrode is
In order to avoid occurrence of arc discharge due to electric field concentration, it is preferable that the distance between the opposed electrodes is substantially constant. Examples of an electrode structure that satisfies this condition include a parallel plate type, a cylindrical opposed plate type, a spherical opposed plate type, a hyperboloid opposed plate type, and a coaxial cylindrical type structure.

In addition, other than a substantially constant structure, a cylindrically opposed cylindrical type having a large cylindrical curvature can be used as a counter electrode because the degree of electric field concentration that causes arc discharge is small. The curvature is preferably at least 20 mm in radius. Although it depends on the dielectric constant of the solid dielectric, at a curvature smaller than that, arc discharge due to electric field concentration tends to concentrate. If the respective curvatures are greater than this, the curvatures of the opposing electrodes may be different. The larger the curvature, the closer to the flat plate, the more stable the discharge can be obtained. Therefore, the radius is more preferably 40 mm or more.

Further, the electrodes for generating plasma only need to be provided with a solid dielectric on at least one of the pair. Even if the pair of electrodes face each other at an appropriate distance so as not to cause a short circuit. Well, they may be orthogonal.

The solid dielectric is provided on one or both of the opposing surfaces of the electrodes. At this time, it is preferable that the solid dielectric and the electrode on the side to be installed are in close contact with each other and completely cover the opposing surface of the contacting electrode. This is because if there is a portion where the electrodes directly face each other without being covered by the solid dielectric, an arc discharge is likely to occur therefrom.

The solid dielectric may be in the form of a sheet or a film, and preferably has a thickness of 0.01 to 4 mm. If it is too thick, a high voltage may be required to generate discharge plasma, and if it is too thin, dielectric breakdown may occur when a voltage is applied, and arc discharge may occur. As the shape of the solid dielectric, a container type can be used.

Examples of the material of the solid dielectric include plastics such as polytetrafluoroethylene and polyethylene terephthalate, glass, metal oxides such as silicon dioxide, aluminum oxide, zirconium dioxide and titanium dioxide, and double oxides such as barium titanate. And those obtained by layering them.

In particular, the solid dielectric preferably has a relative dielectric constant of 2 or more (the same applies under a 25 ° C. environment). Specific examples of the dielectric having a relative dielectric constant of 2 or more include polytetrafluoroethylene, glass, and a metal oxide film. In order to stably generate a high-density discharge plasma, it is preferable to use a fixed dielectric having a relative dielectric constant of 10 or more. Although the upper limit of the relative permittivity is not particularly limited, about 18,500 of actual materials are known. As a solid dielectric having a relative dielectric constant of 10 or more, for example, a metal oxide film mixed with 5 to 50% by weight of titanium oxide and 50 to 95% by weight of aluminum oxide, or a metal oxide film containing zirconium oxide It is preferable to use one having a thickness of 10 to 1000 μm.

The distance between the electrodes is determined by the thickness of the solid dielectric,
It is appropriately determined in consideration of the magnitude of the applied voltage, the purpose of utilizing the plasma, and the like, and is preferably 1 to 50 mm. If it is less than 1 mm, it may not be sufficient to place the electrodes at intervals. If it exceeds 50 mm, it is difficult to generate uniform discharge plasma.

FIG. 1 shows an example of a pulse voltage waveform of a pulse electric field applied between the electrodes in the present invention. The waveforms (a) and (b) are impulse waveforms, the waveform (c) is a pulse waveform, and the waveform (d) is a modulation waveform. Although FIG. 1 shows an example in which voltage application is repeated positive and negative, a pulse of a type in which a voltage is applied to either the positive or negative polarity side may be used. Also,
A pulse electric field on which a direct current is superimposed may be applied. The waveform of the pulse electric field in the present invention is not limited to the waveforms described above, and may be modulated using pulses having different pulse shapes, rise times, and frequencies. Such modulation is suitable for performing high-speed continuous surface treatment.

The rise and / or fall time of the pulse electric field is preferably 100 μs or less. 100μ
If s exceeds s, the discharge state is likely to shift to an arc and becomes unstable, making it difficult to maintain a high-density plasma state due to a pulsed electric field. Further, the shorter the rise time and the fall time, the more efficiently the gas is ionized at the time of plasma generation, but it is actually difficult to realize a pulse electric field with a rise time of less than 40 ns. More preferably, it is 50 ns to 5 μs. Here, the rise time refers to the time during which the voltage change is continuously positive, and the fall time refers to the time during which the voltage change is continuously negative.

It is preferable that the fall time of the pulse electric field is also steep.
It is preferable that the time scale is less than μs. Although it depends on the pulsed electric field generation technology, it is preferable that the rise time and the fall time can be set to the same time.

The electric field strength of the pulse electric field is 0.5 to 2
It is preferable that the pressure be 50 kV / cm. If the electric field intensity is less than 0.5 kV / cm, it takes too much time for the treatment, and if the electric field intensity exceeds 250 kV / cm, arc discharge tends to occur.

The frequency of the pulse electric field is 0.5 to 10
Preferably, it is 0 kHz. If the frequency is less than 0.5 kHz, the plasma density is low, so that it takes too much time to process,
If it exceeds 100 kHz, arc discharge is likely to occur. More preferably, the frequency is 1 to 100 kHz. By applying such a high-frequency pulsed electric field, the processing speed can be greatly improved.

The duration of one pulse in the pulse electric field is preferably 1 to 1000 μs. If the time is less than 1 μs, the discharge becomes unstable,
If it exceeds 000 μs, it is easy to shift to arc discharge.
More preferably, it is 3 to 200 μs. Here, one pulse duration is shown in FIG. 1 as an example,
In a pulsed electric field composed of ON and OFF repetitions,
It refers to the continuous ON time of one pulse.

The processing gas used in the present invention is
Roughening the surface of the substrate and making the surface hydrophilic at the same time
Oxygen-containing gas, sulfur oxide-based gas, etc.
Is preferred. Oxygen-containing gas has carbonyl groups,
Generates ruboxyl group, hydroxyl group, etc., and produces sulfur oxide based gas, etc.
Generates sulfonic acid groups on the substrate surface,
Imparts properties. Oxygen-containing gas emits oxygen radicals
It is a gas that is produced, and oxygen, ozone, carbon monoxide, and diacid
Carbonized gas, air, steam, and the like can be used. Also,
Examples of the sulfur oxide-based gas include sulfur dioxide gas,
And sulfur oxide gas. Also, the material of the substrate to be plated
Depending on the type of charge, CF _Four, C_TwoF₆, C_Three
F₆And the like can be added.

In the present invention, the above oxygen-containing gas or the like may be used as it is as a processing gas. However, from the viewpoint of economy and safety, the oxygen-containing gas or the like is diluted with a diluent gas and used as a processing gas. You can also. Examples of the diluting gas include rare gases such as neon, argon, and xenon, and nitrogen gas. These may be used alone or in combination of two or more. At a pressure close to the atmospheric pressure, processing has been performed in the presence of helium. However, according to the method of applying a pulsed electric field of the present invention, argon and nitrogen gas, which are less expensive than helium, are used. , Stable processing is possible. In particular, by using argon gas, the treatment can be performed in the presence of a gas having a large molecular weight and a large amount of electrons, and a high-density plasma state can be realized. It is effective for surface roughening.

It is known that under a pressure close to the atmospheric pressure, except for a specific gas such as helium, ketone, etc., the plasma discharge state is not stably maintained, but instantaneously shifts to the arc discharge state. By applying the electric field, it is considered that a cycle of stopping the discharge before starting the arc discharge and restarting the discharge is realized.

According to the method of the present invention, glow discharge plasma can be generated regardless of the type of gas existing in the plasma generation space. In the atmospheric pressure plasma treatment under a specific gas atmosphere as well as the plasma treatment under the known low pressure condition, it is essential to perform the treatment in a closed vessel shielded from the outside air. According to the processing method, the processing can be performed in an open system or a low airtight system that prevents free flow of gas.

Examples of the substrate to be plated according to the present invention include insulating resin substrates such as epoxy resin, acetylcellulose and ABS resin, glass, and ceramics.

Means for bringing the plasma into contact with the substrate to be plated include, for example, (1) a method in which the substrate is placed in a discharge space of plasma generated between opposing electrodes, and the plasma is brought into contact with the substrate. And (2) a method (gun type) in which plasma generated between opposed electrodes is brought into contact with a substrate placed outside a discharge space so as to be guided toward the substrate.

As a specific method of the above (1), a substrate is placed between parallel plate type electrodes coated with a solid dielectric and is brought into contact with plasma, using an upper electrode having a large number of holes. , A method of treating with a shower-like plasma, a method of running a film-like substrate in a discharge space, providing a container-like solid dielectric having an outlet nozzle on one electrode,
A method in which plasma is sprayed from the nozzle onto a substrate disposed on another electrode, and the like.

As a specific method of the above (2),
The solid dielectric is extended to form a plasma induction nozzle, such as a method of spraying toward a substrate disposed outside the discharge space, a parallel plate electrode and a long nozzle,
A combination of a coaxial cylindrical electrode and a cylindrical nozzle can be used. The material at the tip of the nozzle does not necessarily need to be the above-mentioned solid dielectric, and may be a metal or the like as long as it is insulated from the above-mentioned electrodes.

Among these, in the etching treatment of the present invention, a method in which a base material is arranged between parallel plate electrodes coated with a solid dielectric and brought into contact with plasma is preferred.
Further, in the etching treatment of the present invention, in order to prevent oxidation of the substrate surface, the treatment is performed in an inert gas atmosphere in the sense that the substrate or the film is prevented from coming into contact with humid air or other impurities in the atmosphere. Is preferred. Further, as a means for transporting the substrate, if the substrate is a film-like, using a transport system consisting of a feeding roll and a winding roll,
If it is a single wafer, a transport system such as a transport conveyor or a transport robot can be used.

An example of the apparatus for performing the etching process of the present invention will be described with reference to FIG. FIG. 2 is a diagram schematically showing a method of arranging a substrate to be plated in a plasma gas generated between opposed parallel plate electrodes and treating the surface thereof. 1 is a power supply, 2 is an upper electrode, 3 is a lower electrode, 4 is a solid dielectric, 1
1 is a processing gas inlet, 10 is a gas suction port after processing, 14
Denotes a substrate to be plated, 20 denotes a transfer robot, 21 denotes a substrate cassette, 22 denotes a robot arm, and 23 denotes a suction head. For example, the processing gas is blown into the discharge space, is excited by plasma generated by applying a pulse electric field between the upper and lower electrodes, and is transferred from the cassette 21 by the transfer robot 20 to the robot arm 22 and the suction head attached to the tip thereof. The substrate 23 is brought into contact with the substrate 14 to be plated in and out by using 23, and the surface thereof is roughened and made hydrophilic. In addition, the lower electrode 3 is provided with an XYZ moving mechanism, can be moved so that a required portion can be processed, and can be combined with a heating mechanism and the like.

(2) Catalyst nucleation treatment and activation treatment The substrate after the above-mentioned etching treatment on the surface of the substrate to be plated is:
Next, a catalyst nucleation process and an activation process are performed.
These processes are not particularly limited, and a conventionally known method can be used.

For example, in the sensi-act method, first, S
Immerse the substrate to be plated after etching in nCl ₂ solution,
Adsorb Sn ²⁺ ions on the surface. Next, by immersing in a PdCl ₂ solution, Pd ²⁺ ions can be reduced and the active catalyst nuclei can be attached to the surface by the following reaction. Sn ²⁺ + Pd ²⁺ → Sn ⁴⁺ + Pd

In the colloidal method, the substrate to be plated after etching is immersed in a catalyst solution containing a catalyst core in a colloidal state through a pre-dip solution.
A catalyst nucleus is attached to the surface of the substrate to be plated. Next, by immersing in an activating solution called an accelerator,
The catalyst core is activated.

As a method of activating the catalyst core by applying a dry method after applying the catalyst nucleus to the substrate to be plated, thermally decomposable silver or palladium is applied to the substrate to form a thin electroless plating film. After laminating on a material, there is also a method of performing an activation treatment using heat or plasma. In this case, since the substrate is heated, the substrate to be plated is limited.

Further, a method of activating the catalyst by using plasma can be adopted. The above-described plasma by the pulse electric field of the present invention can be used, or a known plasma processing method can be used. When plasma is used, processing can be performed at a low temperature. However, when using reduced-pressure plasma, large-scale equipment for reducing pressure such as a vacuum pump is required.

Further, a noble metal compound which is decomposed by plasma as a specific catalyst core is wet-processed on the surface of the substrate to be plated, that is, the substrate to be plated is immersed in a solution, or the solution is sprayed onto the substrate to be plated. After applying by the above method, there is also a method in which the solvent is removed from the noble metal compound solution applied to the surface of the substrate to be plated, and then the noble metal compound applied to the surface of the substrate to be plated is activated by plasma. As the activation treatment by the plasma, the substrate to be plated is plasma-treated with an oxidizing gas plasma obtained from an oxidizing reaction gas, and then the plasma treatment is performed with a reducing gas plasma obtained from a reducing reaction gas. It is preferable to perform a treatment or the like.

(3) Plating Treatment The substrate to be plated with the activated noble metal compound is immersed in an electroless plating solution as it is to carry out plating treatment. As the electroless plating solution, a known plating solution such as copper, nickel, and silver can be used, and is not limited. After the electroless plating, if necessary, it may be thickened to a predetermined thickness by electroplating.

[0045]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 Using the apparatus shown in FIG. 2, the substrate to be plated was etched under the following discharge conditions. 200 mm wide x 150 mm long x 20 m thick as upper electrode 2 and lower electrode 3
m SUS304 stainless steel parallel plate type electrode,
Alumina sprayed to a thickness of 1 mm was used as the solid dielectric 4. An epoxy resin substrate of 100 mm × 150 mm was set as a substrate to be plated in a space having a distance of 2 mm between the electrodes.

Plasma processing conditions Processing gas: mixed gas consisting of oxygen gas 20% and argon gas 80% Discharge conditions: waveform a, voltage 7 kV, rising / falling time 5 μs, output 400 W, frequency 10 KHz, processing time 30 seconds; The resulting plasma was a uniform discharge with no arc columns.

Next, the substrate that had been subjected to the plasma treatment described above was placed in a pre-dip solution (Cataprep 40, trade name, manufactured by Cypre).
After immersion in 4), the substrate was immersed in a catalyst solution (Cataprep 404, Cataposit 44, trade name, manufactured by Cypre), washed with water, and a catalyst core in a colloidal state was attached to the substrate surface. Finally, after immersing the substrate in an accelerator solution (manufactured by Cypre: trade name: Accelerator 19),
Rinse with water and use a commercially available electroless copper plating solution (CM3, manufactured by Shipley)
85-2), the substrate is immersed in an electroless copper plating film of about 0.
About 3 μm was precipitated. Then, in order to evaluate the adhesion of the plating film, the total film thickness was about 35 μm by electrolytic copper plating.
m. After thickening, the substrate was washed with water and dried, and the substrate on which the plating film was formed was cut into a width of about 10 mm, the peel strength was measured, and the adhesion of plating was evaluated. The result was 1.0 kg / cm.

Comparative Example 1 Electroless plating was performed on the substrate in the same manner as in Example 1 except that the surface of the substrate to be plated was not subjected to the normal pressure pulse plasma treatment, but no plating film was formed.

Comparative Example 2 The substrate was subjected to electroless plating in the same manner as in Example 1 except that the surface of the substrate to be plated was subjected to corona treatment (in an air atmosphere) using a wire electrode. Although a plating film was partially formed on the surface of the base material, the plating film was swollen and peeled as a whole.

[0051]

According to the electroless plating method of the present invention, in the etching step, the substrate to be etched is processed by the plasma of the processing gas by the pulse electric field near the atmospheric pressure. It is hydrophilized, can effectively provide catalyst nuclei, can contribute to the improvement of the adhesion of the plating film, and can make the plating process a more efficient system. Further, since the method of the present invention can be carried out under atmospheric pressure, it can be easily inlined, and by using the method of the present invention, the speed of the entire plating process can be improved.

[Brief description of the drawings]

FIG. 1 is a voltage waveform diagram showing an example of a pulse electric field according to the present invention.

FIG. 2 is a diagram showing an example of the etching apparatus of the present invention.

[Explanation of symbols]

 Reference Signs List 1 power supply (high-voltage pulse power supply) 2, 3 electrode 4 solid dielectric 10 gas suction port after processing 11 processing gas introduction port 14 base material 20 transfer robot 21 cassette 22 arm 23 suction head

Claims (5)

[Claims] In a step of etching a surface of a substrate to be plated in an electroless plating method, a solid dielectric is placed on at least one of the opposing surfaces of a pair of electrodes facing each other under a pressure near atmospheric pressure. An electroless plating method, wherein a substrate to be plated is contacted with plasma obtained by introducing a processing gas between opposed electrodes and applying a pulsed electric field. 2. The method according to claim 1, wherein the step of etching the surface of the substrate to be plated in the electroless plating method is performed by the plasma treatment according to claim 1, followed by the step of applying a catalyst, the step of activating the catalyst, and the step of electroless plating. Electroless plating method. 3. The electroless plating method according to claim 1, wherein the processing gas is a gas containing oxygen and / or sulfur dioxide. 4. The pulsed electric field according to claim 1, wherein the pulse rise and / or fall time is 100 μs or less, and the electric field intensity is 0.5 to 250 kV / cm. 2. The electroless plating method according to 1. 5. A pulse-like electric field having a frequency of 0.5 to 1
The electroless plating method according to any one of claims 1 to 4, wherein the pulse duration is 00 kHz and the pulse duration is 1 to 1000 µs.