US20070269680A1

US20070269680A1 - Electroless Plating Pretreatment Agent and Copper-Clad Laminate for Flexible Substrate

Info

Publication number: US20070269680A1
Application number: US11/662,046
Authority: US
Inventors: Toshifumi Kawamura; Toru Imori
Original assignee: Individual
Current assignee: Nippon Mining Holdings Inc
Priority date: 2004-09-10
Filing date: 2005-08-22
Publication date: 2007-11-22
Also published as: JP2012007244A; WO2006027947A1; JPWO2006027947A1; TW200619418A; TWI305237B; KR20070088611A; JP4859232B2

Abstract

Provided are an electroless plating pretreatment liquid used in a copper-clad laminate for a flexible substrate whose initial adhesive force between the substrate material and copper plating layer in an ordinary state as well as the adhesive force in a peel test after aging (in the atmosphere at 150° C. for 168 hours) are at least 0.4 kgf/cm, and a copper-clad laminate for a flexible substrate produced using same. The electroless plating pretreatment agent used in a substrate material of a copper-clad laminate for a flexible substrate comprising a thermoset resin and a silane coupling agent having a metal capturing capability. The copper-clad laminate for a flexible substrate wherein a substrate material is treated with the electroless plating pretreatment agent, a copper plating layer is then formed by electroless plating, and a copper plating layer is formed thereon by electroplating.

Description

TECHNICAL FIELD

The present invention relates to an electroless plating pretreatment agent used in materials of a copper-clad laminate used as a base material or the like of flexible substrates for printed wiring and to a copper-clad laminate for a flexible substrate produced using same.

BACKGROUND ART

Polyimide substrates are often used as a material of insulating substrates for electronic components. With the recent trend toward smaller, thinner electronics, two-layer copper polyimide substrates in which a metal layer is directly formed on a polyimide film have attracted attention for their greater flexibility. Although the initial adhesive force of these substrates between polyimide films and metal layers in the ordinary state is on a practical level, the characteristics such as adhesive force in an environment requiring heat resistance, or in that of high temperature and high humidity are considered unstable.
A method for producing a metal layer in a flexible copper-clad laminate board of polyimide film by sputtering is disclosed in Patent Document 1, for example. However, that method costs high, and the adhesive force is not adequate in an environment requiring heat resistance, or an environment of high temperature and high humidity.
Methods to improve the adhesion of the polyimide film and metal layer include plasma, UV, and other dry processes as well as alkaline and other wet processes, but in addition to safety and operability issues of the liquid used, these methods can lead to unevenness in the metal layer surface if excessively applied, damaging fine wire formation.
Patent Document 2 describes a method of performing electrolytic copper plating after electroless copper plating comprising the five processes of forming a resin composite coating on a polyimide film, activating the coating, applying a catalyst, activating the catalyst, and electroless metal plating. The main object of this method is to form a resin composite layer as an adhesion imparting layer, but the processes are complex and results in a resin composite layer having a thickness of 1 to 20 μm.

Patent Document 1: Japanese Patent Publication No. H9-136378
Patent Document 2: Japanese Patent Publication No. 2001-168496

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an electroless plating pretreatment liquid used in a copper-clad laminate for a flexible substrate whose initial adhesive force between the substrate material and copper plating layer in an ordinary state, and the adhesive force in a peel test after aging (in the atmosphere at 150° C. for 168 hours) are at least 0.4 kgf/cm, and a copper-clad laminate for a flexible substrate produced using same.
As a result of diligent investigations, the inventors have discovered a solution to the problems described above, that is, an electroless plating pretreatment agent comprising a thermoset resin and a silane coupling agent having a metal capturing capability is used as an electroless plating pretreatment agent for the copper-clad laminate for a flexible substrate. A detailed description of the invention is as follows.
(1) An electroless plating pretreatment agent applied to a substrate material of a copper-clad laminate for a flexible substrate, comprising a thermoset resin and a silane coupling agent having a metal capturing capability.
(2) The electroless plating pretreatment agent according to (1), wherein said thermoset resin is an epoxy resin.
(3) A copper-clad laminate for a flexible substrate, wherein a substrate material is treated with the electroless plating pretreatment agent according to (1) or (2), a copper plating layer is then formed by electroless plating, and a copper plating layer is formed thereon by electroplating.

EFFECT OF THE INVENTION

The copper-clad laminate for a flexible substrate, which is obtained by treating a substrate material with an electroless plating pretreatment agent of the present invention and then laminating an electroless copper plating layer and an electroplated copper layer, is a copper-clad laminate for a flexible substrate having two copper layers excellent in adhesion such that the initial adhesive force between the substrate material and copper plating layer in an ordinary state, and the adhesive force in a peel test after aging (in the atmosphere at 150° C. for 168 hours) are at least 0.4 kgf/cm. An adhesive force is provided to the surface of the substrate material without any wet or dry pretreatment whatsoever.

BEST MODE FOR CARRYING OUT THE INVENTION

The electroless plating pretreatment agent of the present invention comprises a thermoset resin and a silane coupling agent having a metal capturing capability.
By adding the silane coupling agent having a metal capturing capability, a noble metal catalyst can be adhered to the surface to be plated more uniformly and reliably via the silane coupling agent.
A preferred silane coupling agent is obtained by reacting an azole compound or an amine compound with an epoxy compound.
Examples of the azole compound include imidazole, oxazole, thiazole, selenazole, pyrazol, isoxazole, isothiazole, triazole, oxadiazole, thiadiazole, tetrazole, oxatriazole, thiatriazole, bendazole, indazole, benzimidazole, and benzotriazole. While the azole compound is not limited thereto, imidazole is especially preferred.
Examples of the amine compound include saturated hydrocarbon amines such as propylamine, unsaturated hydrocarbon amines such as vinylamine, and aromatic amines such as phenylamine.
The silane coupling agent is a compound having an —SiX₁X₂X₃group in addition to having a noble metal capturing group derived from the above-mentioned azole compound or amine compound, where X₁, X₂, and X₃represent an alkyl, halogen, alkoxide group or the like and may be a functional group capable of being attached to an article to be plated. X₁, X₂, and X₃may be identical or different.
The above-mentioned silane coupling agent may be obtained by reacting the above-mentioned azole or amine compound with the epoxy silane compound.
Such an epoxy silane compound is preferably an epoxy coupling agent expressed as

(In the formula, R¹and R²are hydrogen or alkyl groups having 1 to 3 carbons, and n is a number from 0 to 3).
A reaction between the above-mentioned azole compound and the above-mentioned epoxy group-containing silane compound is carried out under the conditions described in Japanese Patent Publication No. H6-256358, for example.
For example, the above-mentioned silane coupling agent is obtained by dripping 0.1 to 10 mol of an epoxy group-containing silane compound in 1 mol of an azole compound at 80 to 200° C. for between 5 minutes and 2 hours. In that process, a solvent is not particularly needed, though chloroform, dioxane, methanol, ethanol, or some other organic solvent may be used.
An example of a particularly favorable reaction of an imidazole compound with an epoxy silane compound is shown below.

(In the formula, R¹and R²indicate hydrogen or alkyl groups having 1 to 3 carbons, R³indicates hydrogen or an alkyl group having 1 to 20 carbons, R⁴indicates either an alkyl group having 1 to 5 carbons or a vinyl group, and n indicates a number from 0 to 3.)
γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane are other examples of silane coupling agents having a functional group with a metal capturing capability used in the present invention.
As the thermoset resin used in the electroless plating pretreatment agent of the present invention, epoxy resin, urea resin, phenol resin, melamine resin, and urethane resin are exemplified. By adding the thermoset resin, the adhesive force is improved. Using an epoxy resin as the thermoset resin is preferable because it has a particularly remarkable effect in improving the adhesive force.
It is not essential for the present invention that the electroless plating pretreatment agent contains a noble metal compound. Plating activity can be obtained by immersion in the plating pretreatment agent of the present invention and then in a palladium chloride aqueous solution. Nevertheless, it is more preferable that the plating pretreatment agent contains a catalyst such as a noble metal compound. Examples of the catalyst include a compound of a noble metal such as palladium, silver, platinum, or gold, for example a halide, a hydroxide, a sulfate and a carbonate thereof, and a noble metal soap thereof, of which a palladium compound is particularly preferable. A conventional catalyst such as tin chloride may be contained in the plating pretreatment agent within the scope of the object of the present invention.
The noble metal soap can be obtained through a reaction of a fatty acid, a resin acid, or a naphthenic acid with a noble metal compound, and is preferably used in the present invention.
For the fatty acid, the number of carbon atoms is preferably 5 to 25 and even more preferably 8 to 16. If the number of carbons is 4 or less, the fatty acid does not dissolve readily in the organic solvent, causing instability. With 26 or more carbon atoms, the portion soluble in the organic solvent is limited and the noble metal content decreases, thereby the amount added is required to increase, which is not practical.
Examples of the fatty acid include octylic acid, neodecanoic acid, dodecanoic acid, pentadecanoic acid, octadecanoic acid, and other saturated fatty acids; oleic acid, linolic acid, and other unsaturated fatty acids; hydroxytetradecanoic acid, carboxydecanoic acid, and other oxygen-containing fatty acids; and mixtures thereof.
Preferable exemplifications of the fatty acids, resin acids, and naphthenic acids include naphthenic acid, octylic acid, neodecanoic acid, and pentadecanoic acid.
Also, examples of the above-mentioned noble metal compound include compounds that can form a soap with a fatty acid or the like, and that can be halides, hydroxides, sulfates, and carbonates of palladium, silver, platinum, and gold showing a catalytic effect when precipitating copper, nickel or the like on a surface of the material to be plated from an electroless plating solution, and palladium compounds are particularly preferable among those compounds.
The noble metal soap used in the present invention can be obtained by ordinary metal soap manufacturing method such as a direct method or double decomposition method with the above-mentioned fatty acid or the like and the above-mentioned noble metal compound.
The palladium naphthenate preferred as the noble metal soap used in the present invention is shown below.
Mixture where n is from 9 to 13

Structural Formula of Palladium Naphthenate

The above-mentioned noble metal soap used in the present invention is soluble in organic solvents and stable as solution. Butanol, 2-ethylhexanol, octyl alcohol, and other alcohols; xylene and other aromatic hydrocarbons; hexane and other aliphatic hydrocarbons; chloroform; dioxane; and the like are examples of such an organic solvent.
The electroless plating pretreatment agent of the present invention is used by dissolving the silane coupling agent having a metal capturing capability, thermoset resin, noble metal soap and the like in an organic solvent such as butanol, 2-ethylhexanol, octyl alcohol, or another such alcohol; xylene or another such aromatic hydrocarbon; hexane or another such aliphatic hydrocarbon; chloroform; or dioxane; for example.
Although the concentration of the silane coupling agent having a metal capturing capability in the electroless plating pretreatment agent is preferably 0.001 to 10 wt % and more preferably 0.05 to 3 wt %, it is not limited thereto. If the concentration is less than 0.001 wt %, the quantity of the compound that attaches to the surface of the substrate material is too low, and the effects are difficult to achieve. If it exceeds 10 wt %, too much compound attaches, thereby drying is difficult and powder readily aggregates.
The concentration of thermoset resin in the electroless plating pretreatment agent is preferably 0.001 to 30 wt %, and more preferably 0.05 to 10 wt %. If it is less than 0.001 wt %, there is little effect, and if it exceeds 30 wt %, the liquid viscosity is too high, resulting in unevenness in the plating.
The noble metal soap may be used in the solution of the electroless plating pretreatment agent at a noble metal concentration of 1 to 30,000 mg/L or preferably 50 to 10,000 mg/L.
Various types of polyimide films, PET, and the like are preferably used as the substrate material of the copper-clad laminate for a flexible substrate of the present invention. Kapton (manufactured by Toray-DuPont) and UPILEX (manufactured by Ube Industries) are examples of the polyimide film, and Lumirror (manufactured by Toray Industries) is an example of the PET.
Although a method such as immersion, brushing, or spin coating is typically used to treat the substrate material with the electroless plating pretreatment agent, the treatment method is not limited thereto, and any method resulting in a pretreatment agent applying to the surface is fine.
In order to volatize the used solvent after surface treatment, heating the solvent to at least the volatilization temperature thereof and then drying the surface are enough, but it is preferable to further heat for 3 to 60 minutes at 60 to 120° C.
The thickness of an electroless plating pretreatment agent layer of the present invention is preferably 1 to 200 nm.
The copper-clad laminate for a flexible substrate of the present invention is made by forming a copper plating layer by ordinary electroless plating on a substrate material pretreated as described above, and then further forming a copper plating layer by ordinary electroplating. In this manner, a copper-clad laminate for a flexible substrate that is uniform and is excellent in adhesion is obtained.
The present invention is described in detail with reference to examples.

EXAMPLE 1

An electroless plating pretreatment agent with an organic solvent (butanol) including 1 g/L of imidazole silane (an equimolar reaction product of imidazole and 3-glycidoxypropyltrimethoxysilane), 0.5 g/L (100 mg/L of palladium) of palladium soap (palladium naphthenate, manufactured by Nikko Materials), and 1 g/L of epoxy resin (Epicoat EP828, manufactured by Japan Epoxy Resins) was applied to the surface of the commercially available polyimide film Kapton (200H, manufactured by Toray-DuPont). After removing the solvent at 150° C. and forming a pretreatment agent layer having a thickness of 70 nm, a copper plating layer having a thickness of 0.5 μm was formed by electroless copper plating (plating solution: NKM554, manufactured by Nikko Metal Plating), and electric copper plating (plating solution: copper sulfate base, manufactured by Nikko Metal Plating) was carried out with a current density of 2 A/dm²to form a copper plating layer having a thickness of 35 μm. The peeling strengths were measured in an ordinary state and then after aging for 168 hours at 150° C. in the air. The peeling strengths were measured by a 90-degree peeling test according to JIS C-6481. The same testing method was used in the below examples and comparative examples. The results showed a high post-aging strength of 0.7 kgf/cm as in Table 1.

EXAMPLE 2

An electroless plating pretreatment agent with an organic solvent (butanol) including 1 g/L of imidazole silane (an equimolar reaction product of imidazole and 3-glycidoxypropyltrimethoxysilane), 0.5 g/L (100 mg/L of palladium) of palladium soap (palladium naphthenate, manufactured by Nikko Materials), and 2 g/L of phenol resin (XLC-4L, manufactured by Mitsui Chemicals) was applied to the surface of the commercially available polyimide film Kapton (200H, manufactured by Toray-DuPont). After removing the solvent at 150° C. and forming a pretreatment agent layer having a thickness of 70 nm, a copper plating layer having a thickness of 0.5 μm was formed by electroless copper plating (plating solution: NKM554, manufactured by Nikko Metal Plating), and electric copper plating (plating solution: copper sulfate base, manufactured by Nikko Metal Plating) was carried out to form a copper plating layer having a thickness of 35 μm. The peeling strengths in an ordinary state and after aging for 168 hours at 150° C. in the air were measured.

EXAMPLE 3

Treatment and testing were carried out in the same manner as in Example 1 except that aminosilane (γ-aminopropyltriethoxysilane, manufactured by Shin-Etsu Chemical) was used in place of the imidazole silane in Example 1. The results showed a high post-aging strength of 0.4 kgf/cm as in Table 1.

COMPARATIVE EXAMPLE 1

Treatment and testing were carried out in the same manner as in Example 1 except that no epoxy resin was used. As shown in Table 1, the results showed a high initial peeling strength of 0.9 kgf/cm, but a low post-aging peeling strength of 0.1 kgf/cm.

COMPARATIVE EXAMPLE 2

After forming a copper seed layer having a thickness of 0.5 μm by sputtering, 35 μm of copper plating layer was formed by electric copper plating in the same manner as Example 1, and testing was carried out as in Example 1. The results are shown in Table 1, with the initial peeling strength high at 0.9 kgf/cm, though low after aging.

TABLE 1

Peeling strength in

Initial peeling peel test after

strength (kgf/cm) aging (kgf/cm)

Example 1 0.9 0.7

Example 2 0.8 0.6

Example 3 0.6 0.4

Comparative 0.9 0.1

Example 1

Comparative 0.9 0.1

Example 2

Claims

1. An electroless plating pretreatment agent applied to a substrate material of a copper-clad laminate for a flexible substrate, comprising a thermoset resin and a silane coupling agent having a metal capturing capability.

2. An electroless plating pretreatment agent according to claim 1, wherein said thermoset resin is an epoxy resin.

3. A copper-clad laminate for a flexible substrate, wherein a substrate material is treated with the electroless plating pretreatment agent according to claim 1, a copper plating layer is then formed by electroless plating, and a copper plating layer is formed thereon by electroplating.