JP2024070321A - Copper-clad laminates, printed wiring boards, and copper-clad laminates - Google Patents

Abstract

[Problem] To provide a copper-clad laminate that exhibits excellent adhesion and is suitable for applications requiring high reliability, and a printed wiring board using said copper-clad laminate. [Solution] The above problem can be solved by providing a copper-clad laminate laminated in the order of heat-resistant insulating substrate layer X/layer A/metal foil, said layer A containing a fumed metal oxide and a thermoplastic polyimide resin, the number of parts by weight of the fumed metal oxide per 100 parts by weight of the thermoplastic polyimide resin being 10 to 60 parts by weight, said metal foil being an electrolytic copper foil or a rolled copper foil, and said heat-resistant insulating substrate layer X being selected from a non-thermoplastic polyimide resin film, a liquid crystal polyester film, a glass epoxy substrate, and a glass substrate. [Selected Figure] None

Description

The present invention relates to a copper-clad laminate, a printed wiring board, and a copper-clad laminate.

Printed wiring boards, which have circuits made of metal conductors on an insulating substrate, are widely used as components that realize the functions of electronic devices, with various electronic components mounted on the printed wiring board. Among them, printed wiring boards with circuits formed on a flexible film portion, specifically (a) flexible printed wiring boards, (b) rigid-flex boards, (c) multilayer flexible boards, and (d) COF (chip-on-film), etc., are widely used in mobile terminal applications, which require small size, weight, and thinness, because they can be folded compactly and stored inside electronic devices. On the other hand, printed wiring such as (a), (b), (c), and (d) are also being used in automotive applications because of their light weight from the perspective of environmental friendliness and their ease of installation in in-vehicle devices. In-vehicle applications are used in harsh environments compared to consumer applications such as mobile terminals, and higher reliability is required. In order to obtain high reliability, high adhesion between the metal conductor and the insulating substrate is required.

As a method for improving the adhesion between a metal conductor and an insulating substrate, Patent Document 1 discloses a method for obtaining a copper-clad laminate by attaching a sheet-like thermoplastic resin to the roughened surface of a roughened copper foil, at least one side of which has a roughened surface with fine irregularities composed of needle-like crystals containing copper oxide and cuprous oxide.

Patent No. 6178035

However, after extensive research, the inventors have found that the above-mentioned conventional techniques have both advantages and disadvantages, and that there is room for improvement or problems as described below.

For example, in Patent Document 1, unevenness is intentionally formed on the copper foil surface to ensure adhesion between the insulating substrate and the copper foil, and good adhesion is achieved. However, in order to prevent loss of electrical signals, the copper foil is required to have smaller unevenness, but if the copper foil has smaller unevenness, adhesion tends to decrease. Therefore, there is a demand for an alternative approach to improve adhesion, which is to improve the insulating substrate material.

The present invention has been made in consideration of the above problems, and its purpose is to provide a copper-clad laminate, a printed wiring board, and a copper-clad laminate that have good adhesion between the metal foil and the insulating substrate.

After extensive research, the inventors discovered that the above problems can be overcome by using the following configuration.

1) A copper-clad laminate laminated in the order of heat-resistant insulating substrate layer X/layer A/metal foil, wherein layer A contains fumed metal oxide and thermoplastic polyimide resin, the number of parts by weight of the fumed metal oxide per 100 parts by weight of the thermoplastic polyimide resin is 10 to 60 parts by weight, the metal foil is electrolytic copper foil or rolled copper foil, and the heat-resistant insulating substrate layer X is selected from a non-thermoplastic polyimide resin film, a liquid crystal polyester film, a glass epoxy substrate, and a glass substrate.

2) The copper-clad laminate described in 1) above, characterized in that it further has one more layer A and is laminated in the following order: layer A/heat-resistant insulating substrate layer X/layer A/metal foil.

3) The copper-clad laminate described in 2) above, characterized in that it further has one more layer of metal foil and is laminated in the following order: metal foil/layer A/heat-resistant insulating substrate layer X/layer A/metal foil.

4) A copper-clad laminate according to any one of 1) to 3), in which the heat-resistant insulating substrate layer X is a non-thermoplastic polyimide resin film.

5) A printed wiring board using the copper-clad laminate described in any one of 1) to 4).

The present invention can provide a copper-clad laminate, a printed wiring board, and a copper-clad laminate that have good adhesion between the metal foil and the insulating substrate.

[Copper-clad laminate]
A copper-clad laminate according to one embodiment of the present invention is characterized in that a heat-resistant insulating substrate layer X/layer A/metal foil are laminated in this order, the layer A contains a fumed metal oxide and a thermoplastic polyimide resin, the number of parts by weight of the fumed metal oxide per 100 parts by weight of the thermoplastic polyimide resin is 10 to 60 parts by weight, the metal foil is an electrolytic copper foil or a rolled copper foil, and the heat-resistant insulating substrate layer X is selected from a non-thermoplastic polyimide resin film, a liquid crystal polyester film, a glass epoxy substrate, and a glass substrate.

The copper-clad laminate according to one embodiment of the present invention has the above-mentioned configuration, and thus exhibits high adhesion. In this specification, adhesion is evaluated by peel strength (N/cm).

The copper-clad laminate of the present invention is formed by laminating a layer A containing a thermoplastic polyimide resin and a fumed metal oxide with a metal foil, i.e., an electrolytic copper foil or a rolled copper foil. This configuration allows for strong adhesion at the layer A/metal foil interface, and the copper-clad laminate of the present invention with excellent adhesion can be obtained.

<Metal foil>
The metal foil will be described. The metal foil refers to electrolytic copper foil or rolled copper foil. Metal foils obtained by physical vapor deposition (dry plating) or electroless plating (wet plating), which are methods for directly depositing metal foil on the surface of an insulating substrate, are not included in the present invention. As the metal foil according to the present invention, electrolytic copper foil or rolled copper foil, which is generally used for printed wiring board applications, can be preferably used. There is no particular restriction on the thickness of the metal foil, and metal foils of various thicknesses can be used in the present invention. For example, metal foils with a thickness of 1 micron to 70 microns are industrially available and can be preferably used. In addition, metal foils whose surfaces have been roughened or rust-proofed can also be preferably used. In addition, as the thickness of the metal foil becomes thinner, the handling becomes poor, and copper foils with carriers that have improved handling can also be preferably used.

<Heat-resistant insulating substrate layer X>
From the viewpoint of dimensional stability when the copper-clad laminate of the present invention is used for printed wiring board applications, the linear expansion coefficient of layer X is preferably 20 ppm/° C. or less. The linear expansion coefficient of any of the non-thermoplastic polyimide resin film, liquid crystal polyester film, glass epoxy substrate, and glass substrate preferably used for layer X of the present invention can be controlled to 20 ppm/° C. or less by controlling the chemical structure, by compounding an inorganic material such as glass fiber with a resin, or by utilizing techniques such as inorganic material technology.

Among these options for the heat-resistant insulating substrate, it is more preferable that the layer X is a non-thermoplastic polyimide resin film from the viewpoints of heat resistance, flexibility, heat resistance, etc. In the present invention, the non-thermoplastic polyimide resin film refers to a polyimide that, when fixed in a film state on a metal fixing frame and heated for 2 minutes under a heating temperature condition of 450° C., does not wrinkle or stretch and maintains a film shape (flat film shape), and a polyimide that does not wrinkle, stretch, or maintain a film shape (flat film shape) is called a thermoplastic polyimide (resin).

<Heat-resistant insulating substrate layer X: non-thermoplastic polyimide film>
Next, a description will be given of the non-thermoplastic polyimide film used in the heat-resistant insulating substrate layer X. The layer X, which is a heat-resistant insulating substrate layer according to one embodiment of the present invention, has the layer A formed on one or both sides thereof, and further has a metal foil laminated on one or both sides thereof.

It is known that the linear expansion coefficient of a polyimide resin film can be controlled by the type of monomer used. In order to reduce the linear expansion coefficient of a polyimide resin film, it is effective to use a monomer having a rigid chemical structure and increase its composition ratio. By using a monomer having a rigid chemical structure and increasing its composition ratio, when the film is molded (processed) into a film, the polyimide molecular chains are oriented in the plane direction, and further, a state in which the molecular chains are accumulated in the thickness direction can be formed. Conversely, in order to increase the linear expansion coefficient of a polyimide resin film, it is effective to use a monomer having a flexible chemical structure and increase its composition ratio. By using a monomer having a flexible chemical structure and increasing its composition ratio, when the film is molded into a film, the polyimide molecular chains are not only oriented in the plane direction, but also in the thickness direction, that is, they tend to show random orientation. When a non-thermoplastic polyimide film is used for layer B, the diamine used in the production of the non-thermoplastic polyimide film is not particularly limited, but it is preferable to make the linear expansion coefficient of the polyimide film finally obtained 20 ppm/°C or less. Therefore, in the production of non-thermoplastic polyimide films, it is preferable to use an appropriate combination of a diamine with a rigid structure and a diamine with a flexible structure in accordance with the structure of the acid dianhydride.

Examples of diamines having a rigid structure that are suitable for use in the production of non-thermoplastic polyimide films include 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-3,3'-dihydroxybiphenyl, 1,4-diaminobenzene, 1,3-diaminobenzene, 4,4'-bis(4-aminophenoxy)biphenyl, and 4,4'-diaminobenzanilide.

Examples of diamines having a flexible structure that are suitable for use in the production of non-thermoplastic polyimide films include 4,4'-diaminodiphenyl ether, 2,2-bis{4-(4-aminophenoxy)phenyl}propane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, and 1,3-bis(3-aminophenoxy)benzene. In the production of non-thermoplastic polyimide films, it is also possible to use the diamines described in the description of the thermoplastic polyimide resin of layer A as appropriate.

When a non-thermoplastic polyimide film is used for the layer X, the acid dianhydride used for the production of the non-thermoplastic polyimide film is not particularly limited, but it is preferable that the linear expansion coefficient of the polyimide finally obtained is 20 ppm/°C or less. Therefore, in the production of the non-thermoplastic polyimide film, it is preferable to use an appropriate combination of an acid dianhydride having a rigid structure and an acid dianhydride having a flexible structure in accordance with the structure of the diamine. Specific examples of acid dianhydrides having a rigid structure that are preferably used in the production of the non-thermoplastic polyimide film include 3,3',4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride. Examples of acid dianhydrides having a flexible structure that are preferably used in the production of the non-thermoplastic polyimide film include 3,3',4,4'-benzophenonetetracarboxylic dianhydride and 4,4'-oxydiphthalic dianhydride. In the production of the non-thermoplastic polyimide film, it is also possible to appropriately use the acid dianhydrides described in the description of the thermoplastic polyimide resin of the layer A.

Polyamic acid, which is a precursor of polyimide, is obtained by mixing the diamine and the acid dianhydride in an organic solvent so that they are substantially equimolar or approximately equimolar, and reacting them. Any organic solvent can be used as long as it can dissolve polyamic acid. As the organic solvent, amide-based solvents, i.e., N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, etc. are preferred, and at least one of N,N-dimethylformamide and N,N-dimethylacetamide is particularly preferred. There are no particular limitations on the solids concentration of polyamic acid, and if it is within the range of 5% by weight to 35% by weight, a polyamic acid having sufficient mechanical strength when made into polyimide can be obtained.

There are no particular limitations on the order in which the diamine and dianhydride raw materials are added. It is possible to control the properties of the resulting polyimide not only by controlling the chemical structures of the diamine and dianhydride raw materials, but also by controlling the order in which they are added.

A filler can be added to the polyamic acid to improve the film's properties, such as sliding properties, thermal conductivity, electrical conductivity, corona resistance, and loop stiffness. Any filler can be used, but preferred examples include silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, and mica.

In addition, thermosetting resins such as epoxy resins and phenoxy resins, and thermoplastic resins such as polyether ketone and polyether ether ketone may be used within a range that does not impair the properties of the resulting resin layer as a whole. As a method for adding these resins, if they are soluble in a solvent, they may be added to the polyamic acid. If the polyimide is also soluble, they may be added to a polyimide solution. If the polyimide is insoluble in a solvent, the polyamic acid may be imidized first, and then the polyimide obtained by imidization and the polyimide insoluble in the solvent to be added are compounded by melt kneading. However, since the solder heat resistance and/or heat shrinkage rate of the resulting flexible metal-clad laminate may be deteriorated, it is preferable not to use a meltable polyimide in one embodiment of the present invention. Therefore, it is preferable to use a soluble resin to be mixed with the polyimide.

A method for obtaining a non-thermoplastic polyimide film preferably used for the layer X in one embodiment of the present invention preferably includes the following steps (i) to (iv).
(i) reacting an aromatic diamine with an aromatic tetracarboxylic dianhydride in an organic solvent to obtain a polyamic acid solution;
(ii) casting a membrane-forming dope containing the polyamic acid solution onto a support;
(iii) heating the film-forming dope on the support and then peeling off the gel film obtained from the support;
(iv) further heating the gel film to imidize the polyamic acid remaining in the gel film and to dry it.

(ii) The methods for the steps after this can be broadly divided into thermal imidization and chemical imidization. Thermal imidization is a method in which a polyamic acid solution is cast onto a support as a film-forming dope without using a dehydrating ring-closing agent, and imidization is promoted by simply heating. On the other hand, chemical imidization is a method in which at least one of a dehydrating ring-closing agent and a catalyst is added to a polyamic acid solution as an imidization promoter, and the resulting solution is used as a film-forming dope to promote imidization. Either method can be used, but chemical imidization is more productive.

As the dehydration ring-closing agent, an acid anhydride such as acetic anhydride can be preferably used. As the catalyst, a tertiary amine such as an aliphatic tertiary amine, an aromatic tertiary amine, or a heterocyclic tertiary amine can be preferably used.

As a support for casting the film-forming dope, a glass plate, aluminum foil, an endless stainless steel belt, a stainless steel drum, etc. can be suitably used. The heating conditions are set according to the thickness of the final film to be obtained and/or the production speed, and the film-forming dope is either partially imidized or dried, and then the imidized product is peeled off from the support to obtain a polyamic acid film (hereinafter referred to as a gel film).

The gel film is dried while fixing the ends of the gel film to avoid shrinkage during curing, and water, residual solvent, and imidization accelerator are removed from the gel film. The amide acid remaining in the gel film is then completely imidized to obtain a film containing polyimide. Heating conditions can be set appropriately depending on the thickness of the final film to be obtained and/or the production speed.

In addition, it is preferable to use an industrially available polyimide film as layer B of one embodiment of the present invention. Examples of commercially available polyimide films that can be used as layer B include "Apical" (manufactured by Kaneka), "Kapton" (manufactured by DuPont and Toray DuPont), and "Upilex" (manufactured by Ube Industries).

<Thermoplastic polyimide resin of layer A>
Layer A contains a thermoplastic polyimide resin and a fumed metal oxide, and is characterized by its strong adhesion to the metal foil. The thermoplastic polyimide resin of layer A will be described. When it is assumed that the copper-clad laminate of one embodiment of the present invention is used for a printed wiring board, it is preferable that the thermoplastic polyimide resin of layer A withstands the high temperature process temperature during the processing process and the high temperature when components are mounted. Therefore, the thermoplastic polyimide resin used in layer A preferably has a high glass transition temperature and a high elastic modulus at high temperatures. By having these high, the adhesion between layer A and the metal foil at high temperatures can be maintained high, and it becomes possible to withstand the high temperature process temperature and the component mounting process. In addition, if these are too high, the processing temperature when thermally laminating with the metal foil becomes high, which is industrially disadvantageous. From the above, from the viewpoint of heat resistance, it is preferable that the glass transition temperature of the thermoplastic polyimide resin is as high as possible, for example, preferably 180°C or higher, more preferably 210°C or higher, and particularly preferably 230°C or higher. On the other hand, from the viewpoint of processing temperature, it is preferable that it is 300°C or lower. In order to achieve good solder heat resistance, the thermoplastic polyimide resin used in Layer A preferably has a certain elastic modulus or more even near the melting point of solder. Specifically, the thermoplastic polyimide resin contained in Layer A has a storage elastic modulus at 300° C. of 0.02×10 ⁹ Pa or more, preferably 0.05×10 ⁹ Pa or more, more preferably 0.08×10 ⁹ Pa or more, and even more preferably 0.1×10 ⁹ Pa or more.

<Formulation of Thermoplastic Polyimide Resin for Layer A>
Next, the monomer species and polymerization method used for the polyimide resin used in Layer A will be described. It is preferable that the physical properties of the polyimide resin, such as the glass transition temperature and the storage modulus at high temperatures, are appropriately controlled. As a means for controlling these physical properties within an appropriate range, the selection of the raw material monomers to be used can be mentioned. The raw material monomers for polyimide resin include monomers having a flexible skeleton and monomers having a rigid skeleton, and by appropriately selecting these and further adjusting the compounding ratio, it is possible to realize the desired physical properties.

Diamines with flexible skeletons include 4,4'-oxydianiline, 3,3'-oxydianiline, 3,4'-oxydianiline, bis{4-(4-aminophenoxy)phenyl}sulfone, 2,2'-bis{4-(4-aminophenoxy)phenyl}propane, bis{4-(3-aminophenoxy)phenyl}sulfone, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodi Phenyl thioether, 3,4'-diaminodiphenyl thioether, 3,3'-diaminodiphenyl thioether, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 3,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl Nilsulfone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminobenzophenone, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 2,2-bis[4-( 3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, etc.

On the other hand, examples of diamines with a rigid skeleton include 1,4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene, 1,2-diaminobenzene, benzidine, 3,3'-dichlorobenzidine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 3,3'-dihydroxy-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)benzidine, 1,5-diaminonaphthalene, 4,4'-diaminobenzanilide, 3,4'-diaminobenzanilide, and 3,3'-diaminobenzanilide.

Among these, from the viewpoints of control of thermal properties and ease of industrial availability, one or more diamines having a flexible skeleton selected from the group consisting of 4,4'-oxydianiline, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-oxydianiline, 3,4'-oxydianiline, 1,3-bis(4-aminophenoxy)benzene, bis{4-(4-aminophenoxy)phenyl}sulfone, 2,2'-bis{4-(4-aminophenoxy)phenyl}propane, bis{4-(3-aminophenoxy)phenyl}sulfone, 1,3-bis(3-aminophenoxy)benzene, 3,3'-diaminobenzophenone, and 4,4'-diaminobenzophenone can be preferably used. In particular, one or more selected from the group consisting of 4,4'-oxydianiline, 1,3-bis(4-aminophenoxy)benzene, and 2,2'-bis{4-(4-aminophenoxy)phenyl}propane can be preferably used.

As the diamine having a rigid skeleton, one or more selected from the group consisting of 1,4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene, and 2,2'-dimethylbenzidine can be preferably used because they have the effect of stiffening the polymer chain with a relatively small amount and are easily available industrially. In particular, at least one of 1,4-diaminobenzene (p-phenylenediamine) and 2,2'-dimethylbenzidine can be preferably used. These diamines may be used alone or in a mixture (combination) of two or more.

Tetracarboxylic dianhydrides with a flexible skeleton include 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,4'-oxydiphthalic anhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylidene)phthalic anhydride, 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride, 2,2-bis(3,4-dicarboxyphenyl)propane, and 2,2-bis(3,4-dicarboxyphenyl)propane. Examples include propane dianhydride, bis(3,4-dicarboxyphenyl)propane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, p-phenylene bis(trimellitic acid monoester anhydride), ethylene bis(trimellitic acid monoester anhydride), and bisphenol A bis(trimellitic acid monoester anhydride).

On the other hand, examples of tetracarboxylic dianhydrides with a rigid skeleton include pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, and 3,4,9,10-perylenetetracarboxylic dianhydride.

Among these, from the viewpoints of control of thermal properties and ease of industrial availability, one or more tetracarboxylic dianhydrides having a flexible skeleton selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 4,4'-oxydiphthalic anhydride can be preferably used. Among these, 3,3',4,4'-biphenyltetracarboxylic dianhydride is more preferable, and can be effectively used to achieve a good balance of various physical properties desired in a preferred embodiment of the present invention, i.e., adhesion to metal foil, elastic modulus at high temperatures, glass transition temperature, etc.

As a tetracarboxylic dianhydride having a rigid skeleton, pyromellitic dianhydride is preferably used because it exerts the effect of stiffening the polymer chain with a relatively small amount and is easily available industrially. Two or more of these tetracarboxylic dianhydrides may be mixed and used.

By appropriately selecting the above-mentioned raw material monomers, adjusting the compounding ratio, and further combining the appropriate type and amount of fumed metal oxide, it is possible to improve the adhesion to the metal foil of one embodiment of the present invention, which is preferable. In order to achieve a good balance between the elastic modulus at high temperatures and the glass transition temperature, it is also possible to preferably use other diamines and acid dianhydrides in combination with the above-mentioned preferable diamines and acid dianhydrides.

The polyamic acid, which is the precursor of the polyimide of layer A, is obtained by mixing the diamine and the acid dianhydride in an organic solvent in a substantially equimolar or nearly equimolar amount and reacting them. Any organic solvent can be used as long as it can dissolve the polyamic acid. As the organic solvent, amide-based solvents, i.e., N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, etc., are preferred, and at least one of N,N-dimethylformamide and N,N-dimethylacetamide is particularly preferred. The solids concentration of the polyamic acid is not particularly limited, and if it is within the range of 5% by weight to 35% by weight, a polyamic acid having sufficient mechanical strength when made into a polyimide can be obtained.

There are no particular limitations on the order in which the diamine and dianhydride raw materials are added. It is possible to control the properties of the resulting polyimide not only by controlling the chemical structures of the diamine and dianhydride raw materials, but also by controlling the order in which they are added.

When 1,4-diaminobenzene and pyromellitic dianhydride are used as raw materials, the polyimide structure obtained by combining the two has low durability against the desmear solution, so it is preferable to adjust the order of addition of 1,4-diaminobenzene and pyromellitic dianhydride so as not to form a structure in which the two are directly combined.

Layer A may contain a resin other than the polyimide resin described above as a resin component. The content ratio of polyimide resin in the resin component contained in layer A is preferably high. For example, of 100% by weight of the resin component contained in layer A, the polyimide resin is preferably 50% by weight or more, more preferably 60% by weight or more, more preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and even more preferably 95% by weight or more. Of 100% by weight of the resin component contained in layer A, the polyimide resin is most preferably 100% by weight. In other words, it is most preferable that layer A contains only polyimide resin as a resin component.

As a combination of diamines and acid dianhydrides, a combination including 1,3-bis(4-aminophenoxy)benzene and 3,3',4,4'-biphenyltetracarboxylic dianhydride is preferred, and further, a combination in which a part of the monomer species is replaced with another monomer is also preferred. Specifically, a combination in which a part of 1,3-bis(4-aminophenoxy)benzene is replaced with 4,4'-oxydianiline, 2,2'-bis{4-(4-aminophenoxy)phenyl}propane, 1,4-diaminobenzene (p-phenylenediamine), or 2,2'-dimethylbenzidine is also preferred. Furthermore, a combination in which a part of 3,3',4,4'-biphenyltetracarboxylic dianhydride is replaced with 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, or pyromellitic dianhydride is also preferred. In addition to these combinations, a combination of 2,2'-bis{4-(4-aminophenoxy)phenyl}propane and pyromellitic dianhydride is also preferred, and further combinations in which a part of the monomer species is replaced with another monomer are also preferred. Specifically, combinations in which a part of 2,2'-bis{4-(4-aminophenoxy)phenyl}propane is replaced with 4,4'-oxydianiline, 1,3-bis(4-aminophenoxy)benzene, 1,4-diaminobenzene (p-phenylenediamine), or 2,2'-dimethylbenzidine are also preferred. Furthermore, combinations in which a part of pyromellitic dianhydride is replaced with 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, or 4,4'-oxydiphthalic anhydride are also preferred.

<Layer A Fumed Metal Oxide>
Layer A contains a thermoplastic polyimide resin and a fumed metal oxide, and is characterized by its strong adhesion to the metal foil. The fumed metal oxide of Layer A will be described. The fumed metal oxide of the present invention is a metal oxide mainly composed of silica, alumina, titania, copper, iron, zirconia, magnesium, barium, etc.

The fumed metal oxide of the present invention is obtained by gas phase synthesis. Due to the characteristics of the gas phase synthesis process, the obtained fumed metal oxide has a feature that the structural unit is a structure in which primary particles are aggregated. In other words, it is preferable that the structural unit of the fumed metal oxide is a structure in which primary particles are aggregated (for example, it has an aggregate structure like a bunch of grapes). The fumed metal oxide is mixed with a thermoplastic polyimide resin to form layer A of the present invention. As a result of various studies by the inventor, it is preferable that layer A is in a state in which (i) the structural unit of the fumed metal oxide is embedded in the thermoplastic polyimide resin with low voids, (ii) the structural unit is present on the surface and/or near the surface of layer A in the bulk direction, and (iii) the structural unit is evenly present and dispersed in layer A, and it is believed that such a state is effective in expressing adhesion to metal foil, which is the object of the present invention.

In the blending of thermoplastic polyimide resin and fumed metal oxide, increasing the blending ratio of fumed metal oxide tends to increase the porosity in layer A. If the porosity in layer A is not too high, the binding strength between the thermoplastic polyimide resin and the fumed metal oxide does not decrease, and the strength of layer A itself tends to be good, and as a result, the adhesion to the metal foil tends to be good. Therefore, in the blending of thermoplastic polyimide resin and fumed metal oxide, it is preferable that the blending ratio of fumed metal oxide is not too high. Conversely, in the blending of thermoplastic polyimide resin and fumed metal oxide, if the blending ratio of fumed metal oxide is low, the porosity tends to be low. If the porosity in layer A is not too low, it is preferable because it is easy to exhibit sufficient adhesion to the metal foil.

In view of the above, in order to achieve good adhesion, it is preferable to control the blending ratio of thermoplastic polyimide resin to fumed metal oxide within an appropriate range. On the other hand, there are various grades of fumed metal oxide that differ in primary particle size, structure of the structure formed by agglomeration of primary particles, and type of surface treatment, and it is believed that there is an appropriate blending ratio that is influenced by these factors.

<Primary particle size and specific surface area of fumed metal oxide>
The primary particle size of the fumed metal oxide is not particularly limited, and is preferably 5 nanometers to 1,000 nanometers, more preferably 5 nanometers to 100 nanometers, even more preferably 5 nanometers to 50 nanometers, and even more preferably 10 nanometers to 20 nanometers. The specific surface area of the fumed metal oxide is also a physical property value that expresses the primary particle size, and the larger the primary particle size, the smaller the specific surface area. The specific surface area of the fumed metal oxide is preferably 30 square meters/gram to 400 square meters/gram, more preferably 100 square meters/gram to 250 square meters/gram.

<Apparent density of fumed metal oxides>
Fumed metal oxides are structures in which the primary particle size is aggregated, and the apparent density can be used as an index of the state of the structure of the fumed metal oxide. If the apparent density of the fumed metal oxide is low, the fumed metal oxide structure has a bulky structure and has large voids. Conversely, if the apparent density of the fumed metal oxide is high, the fumed metal oxide structure has a less bulky structure and has small voids.

By filling the voids in the structure formed by agglomeration of the primary particle diameter of the fumed metal oxide with a thermoplastic polyimide resin component, a layer A having a low porosity can be produced. The smaller the apparent specific gravity of the fumed metal oxide, the more voids there are in the fumed metal oxide structure, and the more thermoplastic polyimide resin components can be used to fill the voids. The larger the apparent specific gravity of the fumed metal oxide, the more the voids in the fumed metal oxide structure can be filled with a small amount of thermoplastic polyimide resin components. In other words, when a certain amount of thermoplastic polyimide resin is mixed with a fumed metal oxide to produce a layer A having a low porosity, (i) in the case of a fumed metal oxide having a small apparent specific gravity, the upper limit of the amount of the fumed metal oxide to be mixed is low, and conversely, (ii) in the case of a fumed metal oxide having a large apparent specific gravity, a large amount of the fumed metal oxide can be mixed, that is, the upper limit of the amount of the fumed metal oxide to be mixed is high. As mentioned above, if the amount of fumed metal oxide is not too large, there is no risk of excessive voids occurring in layer A. As a result, the binding strength between the thermoplastic polyimide resin and the fumed metal oxide is not reduced, and the strength of layer A itself tends to be good, and as a result, the adhesion to the metal foil also tends to be good. Therefore, in the blending of the thermoplastic polyimide resin and the fumed metal oxide, it is preferable that the blending ratio of the fumed metal oxide is not too high. Conversely, if the ratio of the fumed metal oxide is not too low, sufficient adhesion to the metal foil is likely to be exhibited. In other words, in the blending of the thermoplastic polyimide resin and the fumed metal oxide, blending the fumed metal oxide near the upper limit of the blending amount is effective in exhibiting good adhesion.

The upper limit of the amount of fumed metal oxide to be mixed with a certain amount of thermoplastic polyimide resin to produce a layer A with a small porosity varies depending on the apparent specific gravity of the fumed metal oxide and the type of surface treatment. In other words, the adhesion can be further improved by adjusting the amount of fumed metal oxide to be mixed with a certain amount of thermoplastic polyimide resin according to the apparent specific gravity and surface treatment type of the fumed metal oxide. In one embodiment of the present invention, the apparent specific gravity of the fumed metal oxide is preferably 20 g/L or more and 250 g/L or less, and more preferably 20 g/L or more and 220 g/L or less. In addition, the higher the apparent specific gravity of the fumed metal oxide, the higher the upper limit of the amount of fumed metal oxide to be mixed with, and the adhesion tends to be improved. Therefore, the apparent density of the fumed metal oxide is preferably greater than 50 g/L and less than 250 g/L, more preferably greater than 60 g/L and less than 250 g/L, even more preferably greater than 70 g/L and less than 250 g/L, and even more preferably greater than 70 g/L and less than 220 g/L. The apparent density of the fumed metal oxide can also be changed by modifying the structure of the fumed metal oxide by mechanically applying a stress such as shear to the fumed metal oxide.

Various surface treatments are possible for fumed metal oxides. Surface states of fumed metal oxides include silanol (untreated), dimethylsilyl, octylsilyl, trimethylsilyl, dimethylsiloxane, dimethylpolysiloxane, aminoalkylsilyl, methacrylsilyl, etc., all of which are commercially available. When the polarity of the surface treatment type of the fumed metal oxide is similar to that of the polyimide resin component, the upper limit of the amount of fumed metal oxide to be blended tends to be high. It is preferable to make an appropriate selection, taking into consideration the compatibility with the thermoplastic polyimide resin of layer A. The apparent specific gravity of the fumed metal oxide can be measured according to ISO 787/XI.

<Specific examples of fumed metal oxides>
Specific examples of fumed metal oxides that can be preferably used in one embodiment of the present invention are shown below, but are not limited to these. Fumed metal oxides that satisfy the requirements of various properties including apparent specific gravity can be more preferably used in one embodiment of the present invention. Various grades of fumed metal oxides with different primary particle size, specific surface area, surface treatment type, apparent specific gravity, and metal oxide type are available from Nippon Aerosil Co., Ltd., Wacker Asahi Kasei Silicone Co., Ltd., and Cabot Corporation, and can be preferably used. The following is a specific explanation using fumed metal oxides produced by Nippon Aerosil Co., Ltd. as an example. Aerosil R972, R972CF, R972V, etc., which are approximately the same except for the apparent specific gravity, can be preferably used, and among these, R972 (50 grams/liter) with a high apparent specific gravity can be more preferably used. Similarly, Aerosil R974, R9200, VP RS920, etc., which are equivalent except for the apparent density, can be preferably used, and among these, Aerosil R9200 (200 g/L) and Aerosil VP RS920 (80 g/L or more and 120 g/L or less), which have a high apparent density, can be more preferably used. In addition to these, Aerosil NX130, RY200S, R976, NAX50, NX90G, NX90S, RX200, RX300, R812, R812S, etc. can be preferably used as fumed metal oxides manufactured by Nippon Aerosil Co., Ltd., which have a relatively low apparent density of 70 g/L or less, which is one of the preferred physical properties of one embodiment of the present invention. In addition, as fumed metal oxides manufactured by Nippon Aerosil Co., Ltd. having a relatively high apparent specific gravity of 70 grams / liter or more, Aerosil 200V, AEROIDE TiO2 P90, AEROIDE TiO2 NKT90, OX50, RY50, RY51, AEROIDE TiO2 P25, R8200, RM50, RX50, AEROIDE TiO2 T805, R7200, etc. can also be preferably used. In addition, Aerosil VP RS920 has been sold under the name "Aerosil E9200" since November 2021.

"Aerosil" or "AEROSIL" is a registered trademark of Evonik Operations GmbH. As the fumed metal oxide, a fumed metal oxide that is synthesized by gas phase synthesis and has a structure in which the primary particle size is aggregated can be preferably used.

Among these fumed metal oxides, fumed silica such as Aerosil R972, 972V, NX130, R9200, VP RS920, R974, R976, and R8200 are preferred because the surface shape of layer A formed by dissolution in an alkaline environment is good and the surface roughness is within an appropriate range.

<Parts of fumed metal oxide>
The amount of the fumed metal oxide blended is 10 to 60 parts by weight, preferably 15 to 55 parts by weight, and more preferably 20 to 50 parts by weight, per 100 parts by weight of the thermoplastic polyimide resin in Layer A. (Here, 10 to 60 parts by weight means 10 to 60 parts by weight.) This amount is a preferred amount range that the present inventors arrived at through their studies, and it is possible to achieve an improvement of 20% or more compared to the case where the fumed metal oxide is not added.

<Method of mixing thermoplastic polyimide resin and fumed metal oxide, and method of producing layer A>
As the method for producing the layer A, an appropriate method can be selected depending on the characteristics of the thermoplastic polyimide resin.
i) It is also possible to preferably obtain Layer A by mixing and dispersing a solution of polyamic acid, which is a precursor of the thermoplastic polyimide resin of Layer A, with a fumed metal oxide to obtain a Layer A dispersion, which is then applied to a support and heated to imidize the polyamic acid into a polyimide resin, thereby obtaining Layer A.
ii) When the thermoplastic polyimide resin is soluble in a solvent, it is also possible to preferably disperse a fumed metal oxide in an organic solvent, add the dispersion to a solution of a thermoplastic polyimide resin to obtain a layer A dispersion, and then coat the layer A dispersion on a suitable support and dry it to obtain layer A.
iii) A method in which a fumed metal oxide is kneaded at a temperature equal to or higher than the melting point of a thermoplastic polyimide to obtain a layer A resin bulk, and then molded into a film while being heated and pressurized or using a melt extruder, with or without the use of a support, to obtain layer A.

To achieve high adhesion strength, it is preferable that the fumed metal oxide is uniformly dispersed, and it is preferable to disperse it down to the structural unit of the structure in which the primary particles are aggregated. It is preferable to select an appropriate dispersion method according to the type and properties of the thermoplastic polyimide resin and fumed metal oxide used.

In the case of methods i) and ii), examples of the dispersion method include a disperser, homogenizer, planetary mixer, bead mill, centrifugal mixer, roll, kneader, high-pressure disperser, ultrasonic wave, resolver, etc. In the case of method iii), examples of the device include a screw extruder, melt kneader, etc.

As long as the effects of the present invention can be obtained, the fumed metal oxide does not have to be dispersed to the structural unit. It is also possible to disperse and pulverize the fumed metal oxide under conditions that make the structural unit of the fumed metal oxide even smaller. The organic solvent may be a solvent used in the polymerization of polyamic acid, and amide-based solvents, such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone, are preferably used, but are not limited to these.

The copper-clad laminate of the present invention must be in contact with another heat-resistant insulating substrate layer X, with the layer A containing a thermoplastic polyimide resin and a fumed metal oxide, the metal foil formed on the surface of the layer A, and the other surface of the layer A. A layer X/layer A structure or a layer A/layer X/layer A structure in which the layers A and X are laminated in advance may be prepared, and then a metal foil may be laminated to obtain a layer X/layer A/metal foil structure, a layer A/layer X/layer A/metal foil structure, or a metal foil/layer A/layer X/layer A/metal foil structure, i.e., a copper-clad laminate. For the heat-resistant insulating substrate layer X, a polyimide resin film, a liquid crystal polyester film, a glass epoxy substrate, a glass substrate, or the like can be preferably used. Assuming that the copper-clad laminate of the present invention is used for a double-sided flexible printed wiring board, it is preferable that the copper-clad laminate is configured in the order of metal foil/layer A/layer X/layer A/metal foil. In addition, when a glass substrate is used for the heat-resistant insulating substrate layer X, the copper-clad laminate of the present invention can be preferably used for printed wiring boards and glass interposers for semiconductor mounting due to the advantages of the glass substrate, such as low surface roughness and high dimensional stability.

It is also possible to obtain a structure of Layer X/Layer A or a structure of Layer A/Layer X/Layer A by using Layer X as the support described in i), ii), and iii) of the method for producing Layer A above, and to obtain the copper-clad laminate of the present invention by further laminating it with a metal foil.

In addition, when Layer X is a non-thermoplastic polyimide resin film, it is also possible to co-extrude a dispersion of Layer A in which a polyamic acid resin solution of Layer X, which is a precursor of the polyimide resin of Layer X, and a solution of polyamic acid, which is a precursor of the thermoplastic polyimide resin of Layer A described in i) of the method for producing Layer A, are mixed and dispersed with a fumed metal oxide, and the resulting extrudate is dried to imidize the precursors of both the polyimide resins of Layer X and Layer A, thereby obtaining a structure of Layer X/Layer A in which Layer A and Layer X are laminated, or a structure of Layer A/Layer X/Layer A.

There are no particular restrictions on the thickness of Layer A, but when layering with a metal foil with a roughened surface, it is preferable for the thickness to be equal to or greater than the surface roughness Rz, which will ensure the effects of the present invention.

<Lamination>
The copper-clad laminate of the present invention is a laminate of layer A, layer X, and metal foil. As described above, the metal foil is electrolytic copper foil or rolled copper foil, and the copper-clad laminate of the present invention can be obtained by laminating layer A and the metal foil in a facing state. The lamination method is not particularly limited, and is preferably carried out by continuous processing using a hot roll laminating device having one or more pairs of metal rolls or a double belt press (DBP). Lamination using a hot press device is also preferably carried out.

For lamination with a metal layer, it is preferable to use a hot roll laminating device having one or more pairs of metal rolls, because the device configuration is simple and has advantages in terms of maintenance costs. The "hot roll laminating device having one or more pairs of metal rolls" referred to here is any device that has metal rolls for heating and pressurizing the material, and the specific device configuration is not particularly limited.

The specific configuration of the means for carrying out the above-mentioned hot roll lamination is not particularly limited, but in order to improve the appearance of the obtained copper-clad laminate, it is preferable to place a protective material between the pressure surface and the metal foil. The protective material is not particularly limited as long as it can withstand the heating temperature of the hot lamination process, and heat-resistant plastics such as non-thermoplastic polyimide films, and metal foils such as copper foil, aluminum foil, and SUS foil can be suitably used. Among them, non-thermoplastic polyimide films are more preferably used because they have an excellent balance of heat resistance, reusability, and the like. In addition, if the thickness is too thin, it will not be able to fully perform the role of cushioning and protection during lamination, so the thickness of the non-thermoplastic polyimide film is preferably 75 μm or more.

In addition, this protective material does not necessarily have to be a single layer, but may be a multi-layer structure of two or more layers with different properties.

In the above thermal lamination means, the heating method for the layer X/layer A structure or the layer A/layer X/layer A structure and the metal foil (hereinafter sometimes referred to as the laminated material) is not particularly limited, and for example, a heating means employing a conventionally known method capable of heating at a predetermined temperature, such as a heat circulation method, a hot air heating method, or an induction heating method, can be used. Similarly, the pressurization method for the laminated material in the above thermal lamination means is not particularly limited, and for example, a pressurization means employing a conventionally known method capable of applying a predetermined pressure, such as a hydraulic method, an air pressure method, or a gap pressure method, can be used.

The heating temperature in the above thermal lamination process, i.e., the lamination temperature, is preferably a temperature equal to or higher than the glass transition temperature (Tg) of the thermoplastic polyimide resin used in layer A + 50°C, and more preferably equal to or higher than Tg + 100°C. A temperature of Tg + 50°C or higher allows for good thermal lamination of layer A and the metal foil. Furthermore, a temperature of Tg + 100°C or higher allows for increased lamination speed, further improving productivity.

The lamination speed in the above thermal lamination process is preferably 0.5 m/min or more, and more preferably 1.0 m/min or more. A speed of 0.5 m/min or more allows for sufficient thermal lamination, and a speed of 1.0 m/min or more can further improve productivity.

The higher the pressure in the above thermal lamination process, i.e., the lamination pressure, the lower the lamination temperature and the faster the lamination speed can be. However, generally, if the lamination pressure is too high, the dimensional change of the resulting laminate tends to worsen. Conversely, if the lamination pressure is too low, the adhesive strength of the metal foil in the resulting laminate decreases. For this reason, the lamination pressure is preferably within the range of 49 to 490 N/cm (5 to 50 kgf/cm), and more preferably within the range of 98 to 294 N/cm (10 to 30 kgf/cm). Within this range, the three conditions of lamination temperature, lamination speed, and lamination pressure can be improved, and productivity can be further improved.

The tension of the adhesive film in the lamination process is preferably 0.01 to 4 N/cm, more preferably 0.02 to 2.5 N/cm, and particularly preferably 0.05 to 1.5 N/cm. If the tension is below this range, sagging or meandering may occur during transport of the laminate, and it may not be fed uniformly to the heating rolls, making it difficult to obtain a copper-clad laminate with a good appearance. Conversely, if the tension is above this range, the effect of the tension becomes so strong that it cannot be alleviated by controlling the Tg and storage modulus of the adhesive layer, and dimensional stability may be poor.

In order to obtain the copper-clad laminate of the present invention, it is preferable to use a thermal lamination device that continuously heats and presses the laminated material. In this thermal lamination device, a laminated material unwinding means for unwinding the laminated material may be provided in the stage before the thermal lamination means, and a laminated material winding means for winding the laminated material may be provided in the stage after the thermal lamination means. By providing these means, the productivity of the thermal lamination device can be further improved. The specific configurations of the laminated material unwinding means and laminated material winding means are not particularly limited, and examples include known roll-shaped winders that can wind up adhesive films, metal foils, or the resulting laminated board.

As another preferred lamination method, the layer A dispersion liquid described in the method for preparing layer A above is applied to the surface of the metal foil [in the cases of i) and ii)], or in the case of iii), the layer A resin bulk is applied in a molten state to the metal foil.

<Printed Wiring Board>
A printed wiring board using the copper-clad laminate of the present invention is also one embodiment of the present invention. The copper-clad laminate of the present invention is characterized in that Layer A and the metal foil are firmly attached to each other, and is suitable for use in applications requiring strict reliability, such as in-vehicle applications.

From the viewpoint of reliability required for printed wiring board applications, it is preferable that the peel strength is as high as possible. Specifically, it is preferably 4 N/cm or more, more preferably 6 N/cm or more, and even more preferably 9 N/cm or more. The present invention is characterized by strong adhesion between layer A containing fumed metal oxide and thermoplastic polyimide resin and metal foil, and when the number of parts by weight of fumed metal oxide per 100 parts by weight of thermoplastic polyimide resin is 102 to 60 parts, it is possible to improve by 20% or more compared to the case where no fumed metal oxide is added.

Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the following examples.
<Preparation of Monolayer Film of Thermoplastic Polyimide Resin for Layer A>
The polyamic acid solution obtained in the synthesis example was applied to an aluminum foil, and the polyamic acid solution was heated at 120° C. for 360 seconds, at 200° C. for 60 seconds, at 350° C. for 200 seconds, and at 450° C. for 30 seconds, successively, to carry out imidization. The aluminum foil was then dissolved and removed using an etching solution, to obtain a monolayer film of polyimide resin of Layer A. The monolayer film was used to evaluate the storage modulus and glass transition temperature.

<Measurement of storage modulus and glass transition temperature of thermoplastic polyimide resin of layer A>
The monolayer film obtained in the above section <Preparation of monolayer film of polyimide resin of layer A> was used as a sample, and the storage modulus and glass transition temperature were measured using a DMS6100 manufactured by Seiko Electronics Co., Ltd. The sample size was 9 mm in width and 50 mm in length. The measurement was performed at frequencies of 1, 5 and 10 Hz, at a temperature rise rate of 3°C/min in the temperature range from 20°C to 400°C, and the value of the storage modulus at 300°C was read. The glass transition temperature (hereinafter referred to as "Tg") was determined from the value of the inflection point of the storage modulus.

<Preparation of copper-clad laminate>
A 12 μm electrolytic copper foil (3EC-HTE, manufactured by Mitsui Mining & Smelting Co., Ltd.) was attached to both sides of the resin film obtained in the Examples and Comparative Examples, and a protective material (Apical 125NPI, manufactured by Kaneka Corporation) was attached to both sides of the copper foil. Thermal lamination was performed under the conditions of a polyimide film tension of 0.4 N/cm, a lamination temperature of 380° C., a lamination pressure of 196 N/cm (20 kgf/cm), and a lamination speed of 1.5 m/min to produce a double-sided copper-clad laminate according to the present invention.

<Peel strength>
In one embodiment of the present invention, sufficient adhesion between the resin film and the metal foil in the copper-clad laminate can be achieved. This makes it possible to avoid problems of reduced reliability, such as the circuit peeling off from the resin film substrate during the circuit formation process, and to obtain a highly reliable printed wiring board. In view of the above, in order to evaluate the adhesion, the peel strength was measured according to the following procedure.

(Preparation of samples for measuring peel strength)
A 1 mm wide copper pattern was made on the copper layer on one side of the double-sided copper-clad laminate made from the resin film obtained in the Examples and Comparative Examples by etching using masking tape, and an evaluation pattern was made on the back side of the copper layer covering the entire surface. The peel strength was measured according to the following procedure.

(Peel strength measurement)
The peel strength of one double-sided copper-clad laminate was measured by peeling at a crosshead speed of 50 mm/min and a peel angle of 180°, and the load was measured.

(Synthesis Example 1: Synthesis of polyimide resin precursor of layer A)
322.3 g of N,N-dimethylformamide (hereinafter also referred to as DMF) and 33.9 g of 1,3-bis(4-aminophenoxy)benzene (hereinafter also referred to as TPE-R) were added to a glass flask with a capacity of 2000 ml. Next, while stirring the solution in the flask under a nitrogen atmosphere, 33.6 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (hereinafter also referred to as BPDA) was added to the flask, and the solution in the flask was stirred at 25°C for 1 hour. A solution in which 0.51 g of BPDA was dissolved in 9.7 g of DMF (hereinafter also referred to as BPDA solution (1)) was separately prepared. The BPDA solution (1) was gradually added to the reaction solution while paying attention to the viscosity, and the reaction solution in the flask was stirred. When the viscosity of the reaction solution reached 1000 poise, the addition of the BPDA solution (1) and the stirring of the reaction solution were stopped. By this operation, a polyamic acid solution, which is a polyimide precursor, was obtained.

Formulation Example 1: Dispersion of Fumed Metal Oxide for Layer A
20 g of Aerosil E9200 manufactured by Nippon Aerosil Co., Ltd. was mixed with 80 g of DMF. The resulting mixture was stirred for 5 minutes at 10,000 rpm using a rotary blade homogenizer (rotary blade diameter: 20 mm) to obtain a dispersion of fumed metal oxide.

Formulation Example 2: Dispersion of Fumed Metal Oxide for Layer A
20 g of Aerosil R9200 manufactured by Nippon Aerosil Co., Ltd. was mixed with 80 g of DMF. The resulting mixture was stirred for 5 minutes at 10,000 rpm with a rotary blade homogenizer (rotary blade diameter: 20 mm) to obtain a dispersion of fumed metal oxide.

Formulation Example 3: Dispersion of Fumed Metal Oxide for Layer A
20 g of Aerosil NX130 manufactured by Nippon Aerosil Co., Ltd. was mixed with 80 g of DMF. The resulting mixture was stirred for 5 minutes at 10,000 rpm with a rotary blade homogenizer (rotary blade diameter: 20 mm) to obtain a dispersion of fumed metal oxide.

Example 1
40.0g of the polyamic acid solution of Synthesis Example 1 and 3.4g of the dispersion of Preparation Example 1 were mixed, and 40g of DMF and 2.0g of lutidine were further mixed into the resulting mixture to obtain a layer A dispersion. The layer A dispersion was applied to one side of a non-thermoplastic polyimide film (Apical FP, thickness 17 microns, manufactured by Kaneka Corporation) so that the thickness of the final layer A on one side was 4 microns, and the layer A dispersion was dried under conditions of 120°C x 2 minutes, and then the layer A dispersion was applied and dried on the remaining side in the same manner. Subsequently, the non-thermoplastic polyimide film to which the layer A dispersion was applied was heated at 450°C for 12 seconds to imidize the polyamic acid of layer A, and a resin film having a configuration in which layer A (containing thermoplastic polyimide resin and fumed metal oxide)/layer X (non-thermoplastic polyimide film)/layer A were laminated in this order was obtained. The non-thermoplastic polyimide film (Apical FP) corresponds to layer X. That is, in Example 1, the layer X is made of a polyimide resin, specifically, made of only a non-thermoplastic polyimide film. The linear expansion coefficient of the Apical FP was 12 ppm/°C.

The resin film was thermally laminated to copper foil under the conditions described above in <Preparation of copper-clad laminate> to prepare a double-sided copper-clad laminate, and the peel strength was evaluated. The composition and results are shown in Table 1.

Example 2
A copper-clad laminate was obtained in the same manner as in Example 1, except that the amount of the dispersion liquid of Preparation Example 1 used in Example 1 was changed to 8.5 g, and the same evaluation was performed. The composition and results are shown in Table 1.

Example 3
A copper-clad laminate was obtained in the same manner as in Example 1, except that the amount of the dispersion liquid of Preparation Example 1 used in Example 1 was changed to 17 g, and the same evaluation was performed. The composition and results are shown in Table 1.

Example 4
A copper-clad laminate was obtained in the same manner as in Example 1, except that the amount of the dispersion liquid of Preparation Example 1 used in Example 1 was changed to 20.4 g, and the same evaluation was performed. The composition and results are shown in Table 1.

Example 5
A copper-clad laminate was obtained and evaluated in the same manner as in Example 3, except that the dispersion of Preparation Example 1 used in Example 3 was changed to the dispersion of Preparation Example 2. The composition and results are shown in Table 1.

Example 6
A copper-clad laminate was obtained and evaluated in the same manner as in Example 3, except that the dispersion of Preparation Example 1 used in Example 3 was changed to the dispersion of Preparation Example 3. The composition and results are shown in Table 1.

(Comparative Example 1)
The same procedure as in Example 1 was carried out except that the dispersion liquid of Preparation Example 1 used in Example 1 was not used, to obtain a copper-clad laminate, which was then similarly evaluated. The composition and results are shown in Table 1.

(Comparative Example 2)
A copper-clad laminate was obtained and evaluated in the same manner as in Example 1, except that the amount of the dispersion of Preparation Example 1 used in Example 1 was changed to 1.7 g. The composition and results are shown in Table 1. Although fumed metal oxide was added, a sufficient effect of improving the peel strength was not observed.

(Comparative Example 3)
A copper-clad laminate was obtained and evaluated in the same manner as in Example 1, except that the amount of the dispersion of Preparation Example 1 used in Example 1 was changed to 23.8 g. The composition and results are shown in Table 1. No effect of adding the fumed metal oxide was observed, and instead the peel strength was lower than that of the additive-free system (Comparative Example 1).

(Comparative Example 4)
A copper-clad laminate was obtained and evaluated in the same manner as in Example 1, except that the amount of the dispersion of Preparation Example 1 used in Example 1 was changed to 34.0 g. The composition and results are shown in Table 1. No effect of adding the fumed metal oxide was observed, and instead the peel strength was lower than that of the additive-free system (Comparative Example 1).

Claims (5)

A copper-clad laminate laminated in the order of heat-resistant insulating substrate layer X/layer A/metal foil, wherein layer A contains fumed metal oxide and thermoplastic polyimide resin, the weight ratio of the fumed metal oxide to 100 parts by weight of thermoplastic polyimide resin is 10 to 60 parts by weight, the metal foil is electrolytic copper foil or rolled copper foil, and the heat-resistant insulating substrate layer X is selected from a non-thermoplastic polyimide resin film, a liquid crystal polyester film, a glass epoxy substrate, and a glass substrate. The copper-clad laminate according to claim 1, characterized in that it further comprises one more layer A, and is laminated in the following order: layer A/heat-resistant insulating substrate layer X/layer A/metal foil. The copper-clad laminate according to claim 2, characterized in that it further has one more layer of metal foil and is laminated in the following order: metal foil/layer A/heat-resistant insulating substrate layer X/layer A/metal foil. The copper-clad laminate according to any one of claims 1 to 3, wherein the heat-resistant insulating substrate layer X is a non-thermoplastic polyimide resin film. A printed wiring board using the copper-clad laminate according to any one of claims 1 to 3.