JP2007262481A - Surface metallizing method of polyimide resin material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface metallizing method of a polyimide resin material which is easy for continuous treatment, has high productivity and capable of enhancing the plating deposition consistency by a process mainly consisting of a wet treatment, and capable of consistently ensuring the smoothness and adhesiveness of a boundary surface between a polyimide resin film and a metal irrespective of the kind of the polyimide resin film. <P>SOLUTION: The surface metallizing method of a polyimide resin material includes a pre-treatment step of performing the pre-treatment of a polyimide resin material, an electroless plating step, and a thick copper plating step. The pre-treatment step includes a step of treating the surface of the polyimide resin material by using an organic solvent having carbonyl group in a molecule, a step for oxidizing the surface, and a step of performing the treatment with an alkaline aqueous solution. The electroless plating step is an electroless nickel plating step. The thick copper plating step is at least one plating step to be selected from an alkaline electroless copper plating and an alkaline electrolytic copper plating on the surface of the plating layer obtained by the electroless plating. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for surface metallization of a polyimide resin material. In particular, by a wet method that can simplify the process without performing dry treatment such as plasma treatment or sputtering treatment, a method for producing a copper-clad polyimide resin film having excellent smoothness and adhesion between the metal wiring layer and the film layer. About.

The downsizing and weight reduction of electronic devices has been greatly promoted by innovations in semiconductor mounting technology by increasing the number of semiconductor terminals, reducing the size of packages, and mounting bare chips. Also in TAB and COF mounting semiconductor packages, with the increase in CPU frequency and density, there is a demand for higher accuracy in wiring shape processing. Copper wiring on a copper-clad flexible film is several tens of micrometers or several micrometers. It is necessary to process the line / space (L / S) with high accuracy. For this purpose, the smoothness of the interface between the flexible film and the surface copper foil has become more necessary.
In addition, with high-frequency devices, transmission signals tend to concentrate on the periphery of fine wiring, and if the surface irregularities of the wiring are large, resistance increases and obstructs high-speed transmission. Excellent smoothing is required at the interface.

  In response to these requirements, a two-layer copper-clad FPC (flexible printed wiring board) with high dimensional stability is being used. The two-layer copper-clad FPC manufacturing method includes a laminating method, a casting method, and a plating method. For high-density wiring, a plating method in which the interface between the copper foil and the polyimide resin film is smoothest is suitable. However, the conventional plating method is generally a pretreatment method in which the surface of the polyimide resin film is subjected to plasma treatment, metallization treatment by sputtering or the like is performed in vacuum, and then plating is performed. Therefore, an apparatus becomes large for performing plasma processing or processing in a vacuum. In addition, since dry processing such as plasma processing and sputtering processing is performed and wet processing by plating is performed, it is difficult to continue the process, resulting in low productivity and high process cost.

In order to solve the problems that the continuation of the process is difficult, the productivity is low, and the process cost is high, the polyimide resin film surface is etched with sulfuric acid or diamine and an aqueous solution of quaternary ammonium hydroxide to make it hydrophilic. A method of metallizing the surface of a polyimide resin film by electroless plating after alteration and further imparting a palladium catalyst is disclosed (Patent Document 1).
However, since palladium used as a catalyst for electroless plating is not completely dissolved by etching solutions such as ferric chloride, cupric chloride, sulfuric acid-hydrogen peroxide, ammonium persulfate used for FPC etching, wiring Metal palladium remains on the surface of the polyimide resin film in which copper is dissolved after the circuit pattern is formed. For this reason, when the wiring density is increased, a large problem arises in that a potential is applied between the wirings and moisture absorption causes generation of metal migration and a decrease in insulation resistance. Further, when terminal plating by electroless plating, bonding pad plating, or the like is performed, if metal palladium remains, there is a problem in that plating deposits on unnecessary portions.
Conventionally, many methods for metallizing polyimide resin film surfaces by wet plating have been disclosed (Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5, and Patent Document 6). However, both use palladium as a catalyst for electroless plating and have the same problems as in Patent Document 1.

As a method that does not use palladium, after the polyimide resin film is treated with an aqueous potassium hydroxide solution to generate carboxyl groups, copper ions are adsorbed by an ion exchange reaction, and the adsorbed copper ions are reduced by heat treatment in a hydrogen atmosphere. And the method of forming the copper fine particle in the resin film surface part, and using this as an anchor and trying to ensure the adhesiveness to fine wiring is known (nonpatent literature 1).
However, although this method does not require plasma treatment or sputtering treatment, the heat treatment is performed in a hydrogen atmosphere, so the risk of the process is high, and the transition from wet treatment to dry treatment makes it difficult to continue the process. Therefore, there is a problem that it is inferior in productivity. Moreover, since the polyimide resin film is deeply modified in the thickness direction for anchor formation, the metal anchor becomes thick. Therefore, when a wiring circuit pattern necessary for selective etching is formed, there is a problem in that the exposed inner metal of the polyimide portion is not completely removed, and the insulation resistance is deteriorated and migration is promoted.

As another method not using palladium, a polyimide resin is temporarily cured and treated with an aqueous potassium hydroxide solution to adsorb copper (II) ions to a carboxyl group accompanying cleavage of the imide ring, and reduced with an aqueous sodium borohydride solution. After copper is metallized, electrolytic copper plating is performed, and then a method of directly metallizing the surface of the polyimide resin film by performing thermocompression bonding at 260 ° C. or higher and 20 MPa or higher is known (non-patent) Reference 2).
However, in the case of a polyimide resin film, since the curing has progressed too much, it is difficult to adsorb enough copper, and sufficient adhesion of copper to polyimide cannot be obtained, so copper (II) ions are repeatedly adsorbed and reduced many times. There is a need. Therefore, a process becomes complicated and it is inferior to mass productivity. In addition, there is a problem that a heat press or a vacuum press is required for thermocompression bonding after electrolytic copper plating, and a large-scale apparatus is required.

Japanese Patent Laid-Open No. 4-72070 Japanese Patent Laid-Open No. 5-112873 Japanese Patent Laid-Open No. 7-243085 JP-A-7-286277 JP-A-8-167770 JP-A-12-286559 Shingo Ikeda et al., Production of Copper Nanoparticle-Dispersed Polyimide Resin for Microwiring, 11th Microelectronics Symposium, Japan Institute of Electronics Packaging, 18 October 2001 Shingo Ikeda et al., Direct Metallization of copper using surface modification of polyimide resin and thermocompression bonding, Journal of Japan Institute of Electronics Packaging, p603-606, Vol.4, No.7 (November 2001)

In Japanese Patent Application No. 2004-289893, the present inventors treat the surface of a polyimide resin material with an aqueous alkaline solution and treat it with an aqueous solution containing at least one metal ion selected from the group consisting of nickel, cobalt and silver. The present invention proposes a method for surface metallization of a polyimide resin material, comprising a step and a step of treating with an aqueous solution containing a reducing agent capable of reducing the metal ions. In this method, pretreatment for electroless plating can be performed only by wet treatment without using palladium, and in particular, by keeping the treatment water temperature and the treatment temperature of pure water within a predetermined range, stabilization of plating precipitation and peeling There is an excellent effect that strength can be secured.
However, it is necessary to shorten the plating operation time and to further improve the plating deposition stability.
In addition, blisters after electrolytic copper plating and heat treatment (hereinafter also referred to as baking) are likely to occur, and there is a problem that adhesion between polyimide and electroless nickel plating and adhesion between electroless nickel and electrolytic copper plating are partially low. there were.

In order to cope with the above problem, the present inventors include, in Japanese Patent Application No. 2005-265365, a pretreatment step of pretreating a polyimide resin material, an electroless plating treatment step, and a thickened copper plating treatment step, (1) The pretreatment step includes a step of treating the surface of the polyimide resin material using an organic solvent having a carbonyl group in the molecule, and a step of treating with an alkaline aqueous solution. (2) The electroless plating treatment The process is an electroless nickel plating process, and (3) the thick copper plating process is selected from an alkaline electroless copper plating process and an alkaline electrolytic copper plating process on the plating layer surface obtained by the electroless plating. A surface metallization method characterized by at least one plating process is proposed.
However, even if the above method is used, there is a problem that the adhesion between the polyimide film and the plating layer is likely to fluctuate due to the production lot of polyimide film, aging, and the like.

  The present invention is a wet-process-based process that is easy to process continuously, has high productivity, and promotes reduction in plating work time without promoting deterioration of insulation resistance and migration, thereby improving plating deposition stability. The purpose is to provide a surface metallization method that can be improved and can ensure the smoothness and adhesion of the interface between the polyimide resin film and the metal stably regardless of the type of the polyimide resin film. To do.

A method for surface metallization of a polyimide resin material according to the present invention includes a pretreatment step for pretreating a polyimide resin material, an electroless plating treatment step, and a thick copper plating treatment step. The pretreatment step includes a step of treating the surface of the polyimide resin material using an organic solvent having a carbonyl group in the molecule, a step of surface oxidation treatment, and a step of treatment with an alkaline aqueous solution, The electroless plating treatment step is an electroless nickel plating treatment step, and the thick copper plating treatment step is selected from alkaline electroless copper plating treatment and alkaline electrolytic copper plating treatment on the surface of the plating layer obtained by electroless plating. It is at least one plating process step.
The organic solvent is an aprotic polar solvent.
Further, the surface oxidation treatment step includes an oxidation treatment step with an oxidizing metal ion solution and a reduction removal step of metal oxide ions adhering to the polyimide surface.

By the surface metallization method of the polyimide resin material according to the present invention, stable deposition of electroless nickel plating can be obtained, and processing time with an alkaline aqueous solution can be shortened, so that workability is improved. In addition, since electroless nickel plating is performed without using palladium, a metal film can be formed on the polyimide resin material by a simple process.
It includes a step of treating the surface of the polyimide resin material with an organic solvent having a carbonyl group in the molecule, particularly an aprotic polar solvent such as dimethylformamide, a step of surface oxidation treatment, and a step of treatment with an alkaline aqueous solution. Thus, it was found that cleavage of the imide group easily occurs in the surface portion of the polyimide resin material. The present invention is based on such knowledge, and stable deposition of electroless nickel plating can be obtained by increasing carbonyl groups and the like based on cleavage of imide groups.
Moreover, since the change in the surface state is limited to an extremely thin surface layer, the smoothness and adhesiveness of the interface between the polyimide resin film and the metal can be secured stably.
Furthermore, since the step of surface oxidation treatment is a step of oxidation treatment with an oxidizing metal ion solution, the polyimide resin film surface is uniformly oxidized. As a result, surface metallization can be performed stably regardless of the type of polyimide resin film.

The polyimide resin material that can be used in the present invention is a molded article, sheet, or film of a resin having a repeating unit represented by the formula (1). It is preferable that the polyimide resin which has a repeating unit represented by Formula (1) is an aromatic polyimide resin which can endure manufacture and use of FPC.
In the aromatic polyimide resin, in formula (1), R ¹ is a residue of an aromatic tetracarboxylic acid or a derivative thereof, and R ² is a residue of an aromatic diamine or a derivative thereof. Examples of such R ¹ or R ² include a phenyl group, a naphthyl group, a diphenyl group, and a group derived from an aromatic group in which these are connected by a connecting group such as a methylene group, an ether group, a carbonyl group, or a sulfone group. Can be mentioned. R ¹ and R ² may be the same or different.
Examples of aromatic tetracarboxylic acids or derivatives thereof include pyromellitic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetra Carboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, bis (2,3-dicarboxyphenyl) Examples thereof include methanoic dianhydride, and these are used alone or in combination.
Examples of aromatic diamines or derivatives thereof include aromatic diamines such as 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl sulfone, 4,4′-diaminodiphenylmethane, metaphenylenediamine, paraphenylenediamine, or the like. Aromatic diisocyanates of the amine derivative can be mentioned.

When the polyimide resin having a repeating unit represented by the formula (1) is treated with an alkaline aqueous solution, as represented by the formula (2), a part of the surface is hydrolyzed and a part of the imide ring is cleaved. Generates an amide bond and a carboxyl group. The generated amide bond is easily coordinated with a metal ion to form a complex, and the carboxyl group is easy to exchange cation ions, so that the metal ion can be adsorbed.

The surface metallization method of the polyimide resin material according to the present invention is characterized in that the treatment is performed with an organic solvent having a carbonyl group in the molecule before the treatment with the alkaline aqueous solution, followed by the oxidation treatment. As a result, the plating deposition can be stabilized, and the treatment time with the alkaline aqueous solution can be greatly shortened.
The organic solvent having a carbonyl group in the molecule is preferably an aprotic polar solvent or a ketone organic solvent.
Examples of the aprotic polar solvent include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and the like. Examples of the ketone organic solvent include acetone and methyl ethyl ketone.
Among these, an aprotic polar solvent, particularly N, N-dimethylformamide, is preferable, the plating deposition property is stable, and it is effective for shortening the treatment time of the alkaline aqueous solution.

As a polyimide resin film, Kapton 200-H (trade name of DuPont) was prepared. This film was immersed in N, N-dimethylformamide at 40 ° C. for 5 minutes, and the surface state before and after the solvent treatment was observed. The results are shown in FIG. 1 and FIG. FIG. 1 shows the results of surface analysis with an ESCA (X-ray photoelectron analyzer), and FIG. 2 is a photograph of the surface state observed with an AFM (atomic force microscope).
An aromatic polyimide resin having a repeating unit represented by the formula (1) in which R ¹ and R ² are each an aromatic group, such as poly (4,4′-oxydiphenylenepyromellitimide), is N, N— Does not dissolve in aprotic polar solvents such as dimethylformamide. Only the precursor of the aromatic polyimide resin dissolves. This relationship is shown below.
The polyamic acid (1 ′), which is the precursor of the aromatic polyimide resin represented by the formula (1 ′), dissolves in the aprotic polar solvent, but is dehydrated and ring-closed aromatic polyimide resin represented by the formula (1) Does not dissolve. For this reason, even if a polyimide resin film is immersed in N, N-dimethylformamide at 40 ° C. for 5 minutes, the surface thereof is not dissolved, and hydrolysis does not generate a carboxyl group.

However, in the nano-level surface layer measured by ESCA (X-ray photoelectron analyzer), a slight peak of carboxyl groups is observed. The reason for this is considered to be detected in the swollen surface layer because it is not 100% converted to the dehydrated ring-closed aromatic polyimide resin represented by the formula (1) even in the polyimide resin film. This is also inferred from the fact that the surface is rough at the nano level when observed with an AFM (atomic force microscope).
Thus, it is thought that it becomes easy to hydrolyze a part of surface of a polyimide resin material by processing the surface of a polyimide resin material using the organic solvent which has a carbonyl group in a molecule | numerator.

The step of surface oxidation treatment may be any method that can oxidize the surface of the polyimide resin material. For example, a method of oxidizing with an oxidizing metal ion solution, a photocatalyst such as titanium oxide or zinc oxide is brought into contact with the light, and light is irradiated. Methods can be used. In the present invention, a method of oxidizing with an oxidizing metal ion solution that is easy to adopt a continuous process is preferable.
As the oxidizing metal ion solution, a chromic acid-sulfuric acid oxidant solution, a potassium permanganate aqueous solution, or the like can be used. A potassium permanganate aqueous solution containing manganese ions having excellent safety compared to chromium ions is preferred.
Examples of the potassium permanganate aqueous solution include potassium permanganate-potassium monohydrogen phosphate-potassium hydroxide aqueous solution, potassium permanganate-potassium perchlorate-sodium diphosphate aqueous solution, potassium permanganate-perchloric acid. -Sodium pyrophosphate aqueous solution, potassium permanganate-perchloric acid aqueous solution, potassium permanganate-halogenate aqueous solution and the like can be used.

  After the treatment with the aqueous potassium permanganate solution, oxidizing metal ions remain as oxidation treatment residues on the surface of the polyimide resin material, and therefore it is desirable to carry out a reduction neutralization treatment. As the reduction neutralization treatment solution, an aqueous oxalic acid solution, an aqueous stannic chloride solution, or the like can be used.

  By performing the surface oxidation treatment, for example, even if the surface state fluctuates due to a change in the production lot of the polyimide resin film, there is an effect of stabilizing and improving the plating adhesion. Although the effect of stabilizing the plating adhesion is not clear, it is thought that the surface thin film generated in the manufacturing process of the polyimide resin film may be removed. Moreover, it is considered that the plating adhesion is improved because the surface is roughened by the surface oxidation treatment and the anchor effect is obtained. Furthermore, by performing the surface oxidation treatment, there is an effect that the treatment time with an alkaline aqueous solution described later can be shortened.

The alkaline aqueous solution used in the step of treating with the alkaline aqueous solution is preferably a strong alkaline aqueous solution, and examples thereof include aqueous solutions of potassium hydroxide and sodium hydroxide.
The surface modification treatment of the polyimide resin material with an alkaline aqueous solution depends on the concentration of the aqueous solution, the treatment temperature, and the treatment time. As the alkaline aqueous solution concentration increases, the processing temperature increases, and the processing time increases, the surface modification of the polyimide resin material proceeds. As a result, the subsequent plated surface changes from a mirror surface to a glossy surface and further to a matte surface. That is, as the surface modification proceeds, the surface roughness increases and the smoothness of the interface is impaired.
As the concentration of the alkaline aqueous solution, for example, the concentration of the potassium hydroxide aqueous solution is 0.5 to 5 mol / l, preferably 0.5 to 2 mol / l. If it is less than 0.5 mol / l, the hydrolysis of the surface does not proceed sufficiently, and if it exceeds 5 mol / l, the hydrolysis proceeds from the surface to the inside of the polyimide, resulting in reduced smoothness and complex formation and cation ion exchange. The fine metal particles adsorbed and formed by the subsequent reduction are formed up to the inside. In addition, when using a polyimide resin film as FPC, the range of 0.5-2 mol / l is especially preferable. If the amount exceeds 2 mol / l, the polyimide resin film is improved in the thickness direction, and the metal tends to remain in the thickness direction, and metal fine particles remain as a footstep when the wiring circuit pattern is formed by etching. Become. Therefore, when FPC is used, there are problems that the insulation resistance is lowered and metal migration is likely to occur.
The treatment temperature of the alkaline aqueous solution is preferably in the range of 35 to 45 ° C., and the treatment time can be treated in 2 to 20 minutes. However, when an organic solvent is used as a pretreatment for the alkaline aqueous solution treatment, the treatment can be conducted in 2 to 7 minutes. It becomes. Within this range, an FPC can be obtained in which the concentration range of the alkaline aqueous solution, for example, in the range of 0.5 to 2 mol / l, is excellent in plating depositability, excellent adhesion, low insulation resistance, and no metal migration. It is done.
Specifically, when 5 mol / l potassium hydroxide aqueous solution was used and treated at 50 ° C. for 5 minutes, metal fine particles entered through a reduction treatment described later up to about 1.5 to 2 μm in the thickness direction of the polyimide resin film. On the other hand, when treated at 40 ° C. for 5 minutes using a 1 mol / l aqueous potassium hydroxide solution, the surface roughness (Ra) of the polyimide resin film was 10 to 30 nm, but no metal fine particles in the thickness direction were observed. .

After the treatment with the alkaline aqueous solution, it is washed with water in order to remove the excessive alkaline aqueous solution. The water that can be used is preferably pure water such as distilled water or ion-exchanged water with less unnecessary ions, and washing is performed a plurality of times in order to sufficiently remove the alkaline aqueous solution.
In addition, before the metal ions are adsorbed on the polyimide resin material surface in the next step, treatment with 1 to 5% by weight of hydrogen peroxide aqueous solution at room temperature completely removes potassium ions remaining on the surface, such as nickel ions. Can be improved.

  After the alkaline aqueous solution treatment and washing with water, or after further treatment with a hydrogen peroxide solution, the treatment is carried out with an aqueous solution containing an aqueous solution containing nickel ions.

The treatment liquid concentration is preferably 0.05 to 0.5 mol / l as the nickel metal ion concentration. What is necessary is just to immerse the process liquid temperature at 0-30 degreeC for several minutes. A temperature of 15 to 25 ° C. is preferable. As a result of the experiment, it was observed that the adsorption amount increased as the temperature of the metal salt solution decreased. For this reason, the adsorption of metal ions is considered to be physical adsorption rather than chemical adsorption.
As the salt, inorganic salts that are easily ionized are preferable, and specific examples thereof include sulfates, chlorides, and nitrates. However, silver is preferably nitrate.

  Wash with water after treatment with aqueous solution containing metal ions. This washing with water does not cause the adsorbed metal ions to flow out, so it is preferable to use pure water such as distilled water or ion-exchanged water, and cold water is used. Here, cold water refers to a temperature of 20 ° C. or lower, preferably 10 ° C. or lower. This is because when the washing temperature exceeds 20 ° C., the adsorbed metal ions easily flow out. Again, since ions are considered to be physical adsorption, the lower the washing temperature, the greater the amount of adsorption.

By treating with an aqueous solution containing a reducing agent capable of reducing metal ions adsorbed on the surface, the metal ions are reduced to metal particles in a wet manner.
As the reducing agent, a hydrogenated compound that easily generates active hydrogen in an aqueous solution is preferable. As the hydride compound, borohydride borohydride, potassium borohydride, sodium borohydride and the like are preferable. These borohydride reducing agents are easily decomposed spontaneously in an aqueous solution, but are preferably used because they are relatively stable compared to other reducing agents.
If the concentration of the reducing agent is, for example, potassium borohydride, 0.1 to 5 g / l, it is preferable to use an alkaline solution having a pH of 8 to 12 in order to obtain stability of the solution.
The reduction reaction temperature is preferably maintained at 20 to 40 ° C. If it is less than 20 ° C., uneven plating is likely to occur and uniform metallization becomes difficult. On the other hand, if the temperature exceeds 40 ° C., the hydrogenated compound is likely to be decomposed, the reduction of the reducing ability is accelerated, and the liquid management becomes difficult. The reduction reaction is performed under conditions that allow visual confirmation of the formation of the metal layer.

Wash with water after reduction with hydrogenated compound. This water washing is performed with cold water of 20 ° C. or lower, preferably 10 ° C. or lower, similarly to the water washing after metal ion treatment. By this water washing treatment, the pretreatment for the electroless plating of the polyimide resin material is completed.
After the electroless nickel plating pretreatment is completed, active hydrogen is present on the surface of the metal particles generated by the reduction treatment. This active hydrogen can start the reduction reaction of electroless nickel plating in the next step. For this reason, electroless nickel plating can progress rapidly and the thickness of a nickel metal layer can be increased.

The polyimide resin material after completion of the electroless plating pretreatment is immersed in an electroless plating solution before the surface after washing with water is not dried. This is because the hydrogen activity is deactivated when dried, and electroless plating becomes difficult unless a catalytic metal such as palladium is applied.
As the electroless plating that can be used in the present invention, it is preferable to use electroless nickel plating because the plating precipitate particles are relatively small, such as several tens of nm, and adhesion strength is easily obtained.

As described above, the present invention does not use palladium as a catalyst for the first electroless plating in contact with the polyimide resin, but uses an active state metal obtained by reducing metal ions adsorbed on the polyimide resin. Initiate an initiating reaction. If the electroless plating is autocatalytic, the plating reaction starts on the metal surface, and then the plating metal continues to be deposited by the autocatalytic reaction, so that the plating metal layer can be deposited.
As the electroless plating solution, a known electroless nickel plating containing a reducing metal ion, a reducing agent such as sodium hypophosphite, a PH buffering agent, or the like can be used.
Moreover, as temperature conditions of electroless plating, it is 20-40 degreeC. By performing electroless plating at a low temperature, it is possible to prevent a decrease in adhesion between the polyimide resin material and the plating layer due to a difference in thermal shrinkage.

  When electroless nickel plating is applied to the surface of the polyimide resin material to such an extent that the metallic luster is exhibited, the nickel plating thickness is preferably several tens to 100 nm. That is, nickel plating particles 1 to several layers may be deposited. After the electroless nickel plating or copper plating, the surface of the polyimide resin material can be metallized by thick copper plating.

In the method for surface metallization of the polyimide resin material according to the present invention, the thick copper plating step performed after the electroless plating step is preferably an alkaline thick electroless copper plating or an alkaline or weak alkaline electrolytic copper plating. A copper cyanide bath, a copper pyrophosphate bath, or the like can be used. It is also possible to use copper cyanide plating or copper pyrophosphate plating as strike plating, and further use copper sulfate plating or copper borofluoride plating as thick plating.
The deposited electroless nickel metal has a higher ionization tendency than copper, and when immersed in an acidic plating solution such as a copper sulfate plating solution, the nickel ions are eluted and at the same time the sulfuric acid solution penetrates into the coating. For this reason, the adhesion between the electroless nickel plating layer and the electrolytic copper plating deposition layer cannot be obtained, and the blistering immediately after plating or the blister is likely to occur when heated, and the strong adhesion cannot be obtained. Will occur. Therefore, apply thick plating with alkaline electroless copper plating to the electroless nickel plating surface, or apply a copper sulfate plating after providing a barrier layer with electroless copper plating on the electroless nickel plating surface, or electroless It is necessary to perform thick plating by copper sulfate plating after performing strike plating on the nickel plating surface using electrolytic copper plating such as alkaline copper cyanide and copper pyrophosphate as a barrier layer.

  In the present invention, after the electrolytic copper plating step and thick copper plating, it is preferable to perform preliminary drying at 60 to 100 ° C. for 1 to 100 hours and to perform heat treatment (baking) at 150 to 300 ° C. for 30 to 300 minutes. By performing baking, moisture absorbed in the polyimide resin material is removed, and the adhesion strength of the plated metal can be improved by modifying the polyimide resin material.

  The FPC produced using the metallized polyimide material according to the present invention is metallized by modifying only the surface layer of the polyimide layer, and since the metal can be completely removed in the etching process, there is no residue and insulation reliability is improved. High FPC is obtained. Pre-drying and baking after thick copper plating may be performed after the wiring circuit is formed by etching.

Example 1
A polyimide resin film (manufactured by DuPont, product name: production lot A and production lot B of Kapton 200-H) was immersed in N, N-dimethylformamide for 1 minute, and then sufficiently washed with pure water. Then, after being immersed in a potassium permanganate aqueous solution having the following composition at 55 ° C. for 1 minute, it was sufficiently washed with pure water. Furthermore, after being immersed in a neutralizing solution having the following composition at room temperature for 3 minutes, it was sufficiently washed with pure water.
Composition of aqueous potassium permanganate solution:
Potassium permanganate 40g / l
Disodium hydrogen phosphate 30g / l
The pH is adjusted to 12.0 to 12.5 with potassium hydroxide.
Composition of neutralizing solution:
Stannic chloride 30g / l
Concentrated hydrochloric acid 300ml / l

Subsequently, after being immersed in a 1 mol / l potassium hydroxide aqueous solution at 40 ° C. for 2 minutes, it was sufficiently washed with pure water.
Next, a 0.05 mol / l nickel sulfate aqueous solution was prepared, and polyimide resin films treated with the aqueous potassium hydroxide solution were immersed in this aqueous solution at 20 ° C. for 3 minutes, respectively, and washed with pure water at 20 ° C.
Next, each film was immersed in a 1 g / l potassium borohydride aqueous solution at 30 ° C. for 5 minutes, washed with pure water at 20 ° C., and immediately subjected to the following electroless nickel plating for 5 minutes. The results are shown in Table 1.
Electroless nickel plating bath composition and plating conditions Bath composition: nickel sulfate 0.1 mol / l
Cobalt sulfate 0.0015 mol / l
Sodium hypophosphite 0.2 mol / l
Sodium citrate 0.05 mol / l
Ammonia water 0.25 mol / l
Stabilizer Small amount Plating condition: Bath temperature 35 ℃
PH 9.0-9.5

After performing electroless nickel plating, about 1 μm of copper was deposited using the following alkaline copper pyrophosphate plating as strike plating. Subsequently, the copper sulfate plating described below was performed, a copper plating of 34 μm was applied, and washed with water and dried.
The peel strength (unit: KN / m) of the obtained plating layer was measured by B method of JISC6471. The results are shown in Table 1.
Copper pyrophosphate plating composition and conditions Bath composition: Copper pyrophosphate (trihydrate) 90 g / l
Potassium pyrophosphate 375 g / l
PH 7.5
Ammonia water 3ml / l
Pyrobright PY-61 0.3ml / l
(Made by Uemura Kogyo)
PH 8.6
Plating conditions: Bath temperature 55 ° C
Current density 2A / dm ²
Copper sulfate plating composition and conditions Bath composition: sulfuric acid 190g / l
Copper sulfate pentahydrate 75g / l
Chloride ion 50mg / l
Copper Gream ST-901AM 2ml / l
Copper Gream ST-901BM 20ml / l
(Capper Grimes are made by Nihon Leronal)
Plating conditions: bath temperature 23 ° C
Current density 2A / dm ²

Comparative Example 1
The polyimide resin film used in Example 1 (DuPont brand name: production lot A and production lot B of Kapton 200-H) was not subjected to immersion treatment with a potassium permanganate aqueous solution and subsequent neutralization solution treatment. Then, copper sulfate plating was performed under the same conditions as in Example 1. The peel strength was measured in the same manner as in Example 1. The results are shown in Table 1.

From the results shown in Table 1, it can be seen that the treatment with a potassium permanganate aqueous solution improves the peel strength even if the production lot of the polyimide resin film changes.

  According to the present invention, since a metal film can be formed on a polyimide resin by a simple process without using palladium as a catalyst for electroless plating as in the prior art, it is possible to prevent the influence of palladium residue after selective etching. The surface of the polyimide resin material suitable for high-speed transmission with a smooth adhesive interface can be obtained. Further, the adhesive strength of the plated metal is high, and it can be used as a highly reliable flexible printed wiring board.

It is a figure of the result of having surface-analyzed with ESCA (X-ray photoelectron analyzer). It is the photograph of the surface state observed with AFM (atomic force microscope).

Claims (3)

A pretreatment process for pretreating a polyimide resin material, an electroless plating treatment process, and a surface metallization method for a polyimide resin material including a thickened copper plating treatment process,
The pretreatment step includes a step of treating the surface of the polyimide resin material using an organic solvent having a carbonyl group in the molecule, a step of surface oxidation treatment, and a step of treatment with an alkaline aqueous solution,
The electroless plating process is an electroless nickel plating process,
The thick copper plating treatment step is at least one plating treatment step selected from alkaline electroless copper plating treatment and alkaline electrolytic copper plating treatment on the surface of the plating layer obtained by the electroless plating. Material metallization method.   2. The method for surface metallizing a polyimide resin material according to claim 1, wherein the organic solvent is an aprotic polar solvent. 2. The surface of a polyimide resin material according to claim 1, wherein the step of oxidizing the surface includes a step of oxidizing with an oxidizing metal ion solution and a step of reducing and removing metal oxide ions adhering to the polyimide surface. Metallization method.