JP4632580B2 - Method for forming conductive film on resin substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a conductive film on a resin substrate.
[0002]
[Prior art]
Electrolytic copper plating has long been used as a method for forming a conductive film on a non-conductive resin in plating treatments for plastic resin products and plating treatments for printed wiring boards, such as through-hole plating and semi-additive plating. Yes. However, the environment surrounding the electroless copper plating process is becoming more severe year by year due to the carcinogenic problem of formalin blended in the electroless copper plating solution, the regulation of EDTA, the restriction of discarding the waste liquid into the ocean and the like.
[0003]
In general, since the electroless plating process is composed of many steps, it takes a long time and there are problems such as complicated management of the electroless plating solution. For this reason, there is a strong demand for a new method for forming a conductive film in a resin product that can replace electroless plating.
[0004]
Incidentally, in recent years, with the progress of downsizing, thinning, and weight reduction of electronic devices, the demand for higher density of printed wiring boards is becoming stricter. As methods for increasing the density of printed wiring boards, methods such as fine patterning, fine pitch, and high lamination can be considered. However, in recent years, there has been a strong demand for cost reduction, and without increasing the number of laminations, the conductor It is desired to improve the surface density of the circuit.
[0005]
In order to improve the surface density of the conductor circuit on the printed wiring board, it is necessary to make the circuit width and the circuit interval narrower, that is, to make a fine pattern of the circuit, in order to cope with such a fine pattern of the circuit. Therefore, it is necessary to keep the surface roughness of the surface of the resin base material, which is an insulating layer, to a minimum.
[0006]
In order to improve the adhesion of the conductive film to the surface of the resin base material, there is a method of using a so-called anchor effect by forming irregularities of about several μm on the surface of the resin layer when the circuit width is wide. In a printed wiring board having a high surface density of a conductor circuit, it is necessary to form a conductive film having high adhesion without roughening the resin surface.
[0007]
JP-A-8-209354 discloses a method in which an acidic group is introduced into a resin product, then treated with a metal ion-containing liquid, and then immersed in a solution containing a reducing agent to form a conductive film. Has been.
[0008]
However, in this method, when metal ions are reduced using a reducing agent-containing solution, the metal ions adsorbed and present in the resin surface layer diffuse to the resin surface, and relatively large metal particles are formed on the resin surface. Precipitation tends to lower the nucleation density of the metal fine particles. As a result, when the surface roughness of the resin substrate surface is small, the formed conductive film cannot obtain sufficient adhesion strength.
[0009]
For this reason, in order to cope with the fine patterning of the printed wiring board which is considered to be further developed in the future, development of a method capable of forming a conductive film having high adhesion even on a smooth resin surface is desired.
[0010]
[Problems to be solved by the invention]
The main object of the present invention is to provide a method for forming a novel conductive film that can replace the electroless plating method, and can form a conductive film having high adhesion even on a smooth resin surface. is there.
[0011]
[Means for Solving the Problems]
As a result of intensive research to achieve the above-mentioned problems, the present inventor has introduced an acidic group into a resin base material, then treated with a metal ion-containing liquid, and then treated the metal ions adsorbed or bound to the resin base material with water. According to the method of forming a conductive film by converting to a compound such as oxide, oxide, carbonate, sulfide, etc., surface diffusion, coarsening, etc. of the formed metal particles are suppressed. As a result, it has been found that it is possible to form a conductive film with good adhesion on the surface of a resin substrate having high smoothness, and the present invention has been completed here.
[0012]
That is, the present invention provides the following method for forming a conductive film.
1. A method for forming a conductive film on a resin substrate, which comprises treating the resin substrate by a method comprising the following steps:
(1) a step of introducing an acidic group into the resin base material;
(2) A step of bringing the resin substrate treated in the step (1) into contact with a metal ion-containing liquid,
(3) A step of converting the metal ion adsorbed or bound to the resin base material into the metal compound in the step (2),
(4) A step of reducing the resin substrate treated in the step (3) to form a conductive film on the resin substrate.
2. (1) The method according to item 1, wherein the acidic group introduced in the step is a sulfonic acid group, a carboxyl group or a phenolic hydroxyl group.
3. (3) The method according to item 1 or 2, wherein the metal compound formed in the step is a hydroxide, oxide, carbonate or sulfide.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereafter, each process of the formation method of the electrically conductive film of this invention is demonstrated in detail.
Step (1):
In the method of the present invention, an acidic group is first introduced into a resin substrate to be treated.
[0014]
There are no particular limitations on the type of resin base material that can be used in the present invention, as long as it is made of a resin having appropriate physical properties according to the purpose of use and can introduce acidic groups into the resin. Good. For example, when a sulfonic acid group is introduced by sulfonation, it is preferable to use a resin material made of a resin having a group that is relatively easy to sulfonate, such as an aromatic ring such as a benzene ring or a hydroxyl group. Of the resins having these groups, epoxy resins, polyimide resins, polyphenylene ether resins, vinyl resins, phenol resins, and the like are preferably used. Moreover, when introduce | transducing a carboxyl group, a polyimide resin etc. are used suitably, for example.
[0015]
The resin substrate may be composed of a single resin, or may be a mixture of a plurality of resins. For example, an epoxy resin can be used by mixing with a polyimide resin or a polyamide resin.
[0016]
Further, in the present invention, the resin base material to be processed is not limited to a molded article made only of a resin, and may be a composite in which a reinforcing material such as a glass fiber reinforcing material is interposed between resins, Or what formed the film | membrane by resin on the base material which consists of various raw materials, such as ceramics, glass, and a metal, may be used.
[0017]
A printed wiring board can be mentioned as an example of the resin base material.
[0018]
The acidic group introduced into the resin base material can be used without limitation as long as it can be introduced into the resin base material used as the object to be treated and can chemically adsorb or bond metal ions. In particular, examples of acidic groups that can be effectively used in the method of the present invention include sulfonic acid groups, carboxyl groups, phenolic hydroxyl groups, and the like, and preferred acidic groups include sulfonic acid groups, carboxyl groups, and the like. A particularly preferred acidic group is a sulfonic acid group.
[0019]
The method for introducing an acidic group is not particularly limited, and various methods are possible, and a known introduction method may be adopted as appropriate according to the type of the resin to be used and the acidic group.
[0020]
Below, an example of the method of introduce | transducing a sulfonic acid group as an acidic group is shown.
[0021]
The sulfonic acid group can be introduced into the resin base material by a known sulfonation reaction. As the sulfonating agent used in this case, various known sulfonating agents can be used, and examples thereof include sulfuric acid, fuming sulfuric acid, sulfur trioxide, chlorosulfuric acid, and sulfuryl chloride.
[0022]
Among these sulfonating agents, a production method in the case of using sulfuric acid will be specifically described. The sulfonation reaction can be usually performed by immersing the resin base material in a sulfuric acid aqueous solution. The sulfuric acid concentration used in the sulfonation reaction is generally about 70 to 90% by weight, preferably about 75 to 85% by weight. When the sulfuric acid concentration is less than 70% by weight, sulfonation takes time, which is not preferable. On the other hand, when it exceeds 90% by weight, the resin is easily dissolved and deteriorated. The treatment temperature for sulfonation is generally about 50 to 100 ° C., preferably about 60 to 80 ° C., although it depends on the type of resin to be sulfonated. The treatment time may vary depending on the degree of sulfonation, but generally may be about 1 to 60 minutes.
[0023]
The introduction amount of the sulfonic acid group can be adjusted by changing the concentration of the sulfonating agent, the treatment temperature, the treatment time, etc., and the treatment step with the metal ion-containing solution described later as the introduction amount of the sulfonic acid group increases. In this case, the amount of the metal adsorbed or bonded increases. Therefore, specific treatment conditions for sulfonation may be determined according to the required thickness of the conductive film.
[0024]
In the case of introducing a carboxyl group, a phenolic hydroxyl group, etc. as an acidic group, it can be carried out using a known reaction for introducing these groups, and is introduced appropriately depending on the type of resin used. You just have to decide the conditions. For example, when a carboxyl group is introduced, the carboxylation reaction may be carried out using acetic acid at a concentration of about 70 to 100% by weight, preferably about 80 to 90% by weight as a carboxylating agent. About reaction temperature, what is necessary is just to make it a temperature comparable as the case of sulfonation.
[0025]
In addition, in order to perform a subsequent process efficiently, it is preferable to perform a water washing process after the said process.
Step (2):
After introducing an acidic group into the resin substrate in the step (1) described above, the resin substrate is brought into contact with a solution containing metal ions. By this treatment, metal ions are adsorbed or bonded to the acidic groups introduced into the resin base material.
[0026]
The metal ion-containing liquid can be used without particular limitation as long as it is a solution containing metal ions in which the metal layer formed by the vapor phase reduction process in the subsequent step exhibits conductivity. Preferred examples of such metal ions include copper, nickel, cobalt, iron, palladium, gold, silver, and mixtures thereof.
[0027]
Metal ions are generally blended in a metal ion-containing liquid as a metal salt. The type of metal salt to be used is not particularly limited, and an appropriate soluble metal salt may be used depending on the type of metal. For example, in the case of copper ions, it can be blended in the form of copper sulfate, copper chloride, copper nitrate, copper acetate, basic copper carbonate and the like.
[0028]
The concentration of metal ions in the metal ion-containing liquid is usually suitably about 0.01 to 1 mol / liter, and preferably about 0.03 to 0.1 mol / liter.
[0029]
The metal ion-containing liquid is generally used as an aqueous solution. However, an organic medium such as methanol may be used depending on the metal ion used.
[0030]
If necessary, the metal ion-containing liquid may contain a buffering agent for maintaining pH, a complexing agent for preventing precipitation of metal ions, and the like.
[0031]
Since the pH of the metal ion-containing liquid gradually decreases due to the reaction between acidic groups and metal ions, the pH of the metal ion-containing liquid is weakly acidic when the metal ions are replenished in the form of hydroxide. It is appropriate to adjust the pH to about neutral, specifically about pH 2-6, preferably about 3-4.
[0032]
The method of bringing the solution containing metal ions into contact with the resin substrate is not particularly limited, but usually, the resin substrate into which acidic groups have been introduced in step (1) may be immersed in the metal ion-containing liquid. By this treatment, metal ions are adsorbed or bonded to the acidic groups introduced into the resin base material. The immersion treatment may be performed, for example, at a temperature of about 20 to 80 ° C., preferably about 25 to 80 ° C., for example, for about 1 to 10 minutes, preferably about 3 to 5 minutes.
[0033]
In addition, in order to perform a subsequent process efficiently, it is preferable to perform a water washing process after the said process.
Step (3):
After the treatment with the metal ion-containing liquid in the step (2), the metal ions adsorbed or bonded to the resin base material are converted into a metal compound. Although it does not specifically limit about the kind of metal compound to convert, For example, a hydroxide, an oxide, carbonate, sulfide etc. can be illustrated.
[0034]
The method for converting into these compounds is not particularly limited, and a known method capable of forming each metal compound described above may be appropriately employed depending on the type of metal ion.
[0035]
The following method can be illustrated as an example of the method for forming a metal compound.
[0036]
For example, when forming a hydroxide, the resin base material brought into contact with the metal ion-containing liquid in the step (2) may be immersed in an aqueous solution containing a hydroxide. As the hydroxide, any compound that can form hydroxide ions in an aqueous solution can be used without particular limitation. Examples of such hydroxides include alkali metal hydroxides such as NaOH and KOH, NH ₄ OH and the like. Specific treatment conditions may be appropriately determined according to the type of metal ion, the type of hydroxide, etc. Usually, the hydroxide concentration is about 1 to 500 g / l, preferably about 1 to 50 g / l. It is sufficient to immerse in the aqueous solution at about 10 to 80 ° C., preferably about 20 to 40 ° C. for about 1 to 10 minutes, preferably about 3 to 5 minutes.
[0037]
In the case of forming an oxide, for example, after the hydroxide is formed by the above-described method, heat treatment may be performed. Although the heating temperature required for oxide formation changes with kinds of metal ion, what is necessary is just to usually set it as the heating temperature of about 100-200 degreeC.
[0038]
In the case of forming a sulfide, the resin base material brought into contact with the metal ion-containing liquid in the step (2) may be immersed in an aqueous solution containing sulfide. Any sulfide that can form sulfide ions in an aqueous solution can be used without particular limitation. Examples of such sulfides include sodium sulfide, potassium sulfide, ammonium sulfide and the like. Specific treatment conditions may be appropriately determined according to the type of metal ion, the type of sulfide, and the like. Usually, an aqueous solution having a sulfide concentration of about 1 to 100 g / l, preferably about 1 to 50 g / l. What is necessary is just to immerse in about 10-80 degreeC in the inside at a liquid temperature of about 20-40 degreeC for about 1 to 10 minutes, Preferably about 3 to 5 minutes.
[0039]
In addition, in order to perform a subsequent process efficiently, it is preferable to perform a water washing process after the said process.
[0040]
After the metal compound is formed by the various methods described above, a reduction treatment is performed in step (4) to be described later, so that the resin substrate surface is adsorbed to a thickness of about several μm by the treatment in step (2). The diffusion of metal ions present in the bond to the surface of the resin substrate is suppressed, and very fine metal particles with a particle size of several nanometers are formed inside the resin substrate, resulting in a very high nuclear density of the metal particles. To be high. For this reason, the conductive film to be formed has good conductivity and also exhibits high adhesion to a resin substrate having a smooth surface.
Step (4):
In the above-described step (3), after converting metal ions to metal compounds, a reduction treatment is performed to form a conductive film on the resin substrate.
[0041]
The method of the reduction treatment is not particularly limited, and any method may be used as long as the metal compound formed by the treatment in the step (3) can be reduced and metallized. For example, a method in which the resin substrate treated in step (3) is immersed in a solution containing a reducing agent, a method in which the resin substrate treated in step (3) is contacted with a reducing gas, and gas phase reduction is performed. Can be adopted.
[0042]
When reducing using a solution containing a reducing agent, the reducing agent can be used without particular limitation as long as it can reduce the metal compound to precipitate the metal. Usually, the solution containing a reducing agent is used as an aqueous solution. Examples of the reducing agent used in this case include sodium borohydride, potassium borohydride, dimethylamine borane (DMAB), trimethylamine borane (TMAB), hydrazine, formaldehyde, derivatives of these compounds, and sulfurous acid such as sodium sulfite. Examples thereof include salts and hypophosphites such as sodium hypophosphite. The reducing agent concentration in the aqueous solution is usually about 0.003 to 0.02 mol / liter, preferably about 0.005 to 0.009 mol / liter. If the reducing agent concentration is too low, the rate of the reduction reaction tends to be too slow. On the other hand, if the reducing agent concentration is too high, the deposited metal may drop off, which is not preferable. The reduction temperature may normally be about 20 to 90 ° C, and preferably about 25 to 80 ° C. The treatment time may be about 1 to 10 minutes, preferably about 3 to 5 minutes.
[0043]
The specific method of the gas phase reduction treatment is not particularly limited, and the metal substrate bonded or adsorbed to the resin substrate is reduced by bringing the resin substrate to be treated into contact with the reducing gas. Any method that can be metallized is acceptable. As the reducing gas, any gas having a reducing property may be used. For example, hydrogen gas, diborane gas, or the like can be used. Specific treatment conditions such as reaction temperature and reaction time may be appropriately determined according to the type of reducing gas used, the type of metal compound, and the like.
[0044]
For example, when hydrogen gas is used as the reducing gas, the resin base material to be treated may be placed in a hydrogen gas stream and contacted with hydrogen gas at a temperature of about 30 to 300 ° C. for about 5 to 60 minutes. . A specific treatment temperature may be appropriately determined in consideration of the heat resistance of the resin base material, the ease of reduction of the metal compound, and the like.
[0045]
By performing the reduction treatment by the above method, a conductive film excellent in adhesion, conductivity and the like can be formed.
[0046]
After the conductive film is formed by the method of the present invention, various treatments can be performed according to ordinary methods. For example, the formed conductive film can be used as a base film for various plating treatments. When conducting circuit formation by panel plating using the conductive film forming method of the present invention, for example, after forming a conductive film by the method of the present invention, an electrolytic copper plating process such as copper sulfate plating is performed. Just do it. In the semi-additive method, after the formation of the conductive film, each of the conventionally known methods such as electroless copper plating, resist pattern formation, electrolytic copper plating, solder plating, resist removal, and solder stripping as necessary. Processing may be performed sequentially.
[0047]
In addition, you may add well-known processes, such as a degreasing process, a water washing process, an etching process, and a rust prevention process, as needed.
[0048]
【The invention's effect】
The method of the present invention is a novel method for forming a conductive film that can be used in place of electroless plating. According to this method, a conductive film having excellent adhesion and conductivity can be formed on a smooth resin surface. . For this reason, the method of the present invention is a highly useful method as a method for forming a conductive film on a printed wiring board that is compatible with high density fine patterning such as a narrow circuit width and circuit interval.
[0049]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[0050]
Example 1
Epoxy resin (FR-4 type) solution is completely cured on the circuit surface of a 50 x 100 x 1.6 mm circuit board made of compressed epoxy resin (FR-4 type) with 8 layers of glass cloth as reinforcement. The coating was applied so that the subsequent thickness was 100 μm, dried, and then completely cured at 150 ° C. to prepare a test sample. The resin surface of the test sample was highly smooth with an average surface roughness (Ra) of 100 nm or less.
[0051]
This test sample was immersed in a sulfuric acid solution having a concentration of 85% by weight at 70 ° C. for 5 minutes to introduce sulfonic acid groups on the resin surface.
[0052]
Then, after washing with water at room temperature for 1 minute, the test sample was immersed in a copper sulfate aqueous solution (pH 4.0) having a concentration of 0.05 mol / l at 50 ° C. for 3 minutes.
[0053]
Next, it was washed with water at room temperature for 1 minute, and immersed in an aqueous sodium sulfide solution having a concentration of 5 g / l at 25 ° C. for 10 minutes to convert copper ions adsorbed or bonded to the resin surface into copper sulfide.
[0054]
Thereafter, the test sample was immersed in an aqueous solution of NaBH _{4 having} a concentration of 0.03 mol / l for 1 minute at room temperature to perform a reduction treatment to form a conductive film.
[0055]
The sample formed with the conductive film by the above-described method was immersed in a 10% sulfuric acid aqueous solution at room temperature for 1 minute to activate the sample surface, and then the cathode current density was 2 A / dm ² using an acidic copper sulfate plating bath. An electrolytic copper plating film having a thickness of 30 μm was formed under the conditions.
[0056]
A slit reaching a substrate having a width of 1 cm was inserted into the obtained copper plating film, and the 90 ° peel (peel) strength was measured.
[0057]
As a result, the peel strength was 0.6 kgf / cm or more, which was a practically sufficient value.
[0058]
From the above results, it was confirmed that according to the method of the present invention, a conductive film having high adhesion strength can be formed even on a resin surface having a high smoothness with an average surface roughness (Ra) of 100 nm or less.
[0059]
Comparative Example 1
A test film similar to that in Example 1 was used, and a conductive film was formed in the same manner as in Example 1 without performing the treatment of immersing in an aqueous sodium sulfide solution.
[0060]
Thereafter, the conductive film was activated using a 10% sulfuric acid aqueous solution in the same manner as in Example 1, and an electrolytic copper plating film having a thickness of 30 μm was formed using an acidic copper sulfate plating bath. Since the adhesion between the films was insufficient, peeling of the conductive film occurred when the electroplated film was formed, and peel strength measurement was impossible.

Claims (2)

A method for forming a conductive film on a resin substrate, which comprises treating the resin substrate by a method comprising the following steps:
(1) a step of introducing an acidic group into the resin base material;
(2) A step of bringing the resin substrate treated in the step (1) into contact with a metal ion-containing liquid,
(3) A step of converting metal ions adsorbed or bonded to the resin base material into a metal sulfide in the step (2).
(4) A step of reducing the resin substrate treated in the step (3) to form a conductive film on the resin substrate. (1) The method according to claim 1, wherein the acidic group introduced in the step is a sulfonic acid group, a carboxyl group or a phenolic hydroxyl group.