JP7715313B1 - Multilayer polyimide film and polyimide-metal laminate - Google Patents

Abstract

A multilayer polyimide film is provided that has excellent heat resistance, low dielectric loss tangent, and dimensional stability. This multilayer polyimide film has a heat-resistant polyimide layer and a heat-fusible polyimide layer laminated on one or both sides thereof; the heat-resistant polyimide is obtained from a tetracarboxylic acid component containing 75 mol % or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) and 25 mol % or less of pyromellitic dianhydride (PMDA), and a diamine component containing 70 mol % to 95 mol % of p-phenylenediamine and 5 mol % to 30 mol % of 2,2'-dimethylbenzidine; and the heat-fusible polyimide is obtained from a tetracarboxylic acid component containing 10 mol % to 60 mol % of s-BPDA and 40 mol % to 90 mol % of PMDA, and a diamine component containing 50 mol % or more of 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

Description

The present invention relates to a polyimide film and a polyimide-metal laminate.

Polyimide film has excellent heat resistance and mechanical properties and is widely used as an electronic substrate material such as flexible printed circuit boards (hereinafter also referred to as FPC) and tape automated bonding (hereinafter also referred to as TAB).

In the manufacture of FPCs and TABs, polyimide-metal laminates (e.g., copper-clad laminates) are used, in which a metal foil such as copper foil is bonded to a polyimide film. While adhesives such as epoxy resins and acrylic resins are known to be used to bond metal foil and polyimide film, polyimide-metal laminates using adhesives have poor heat resistance. Therefore, multilayer polyimide films, in which a heat-resistant polyimide layer and a heat-sealable polyimide layer are laminated, have been proposed as polyimide films that can be bonded to metal foil such as copper foil without the use of adhesives (e.g., Patent Document 1).

On the other hand, with the recent use of high-frequency bands in electronic devices, there is an increasing demand for low transmission loss in polyimide, an electronic circuit board material. Transmission loss is correlated with the dielectric constant and dielectric loss tangent, and lowering the dielectric loss tangent is particularly effective in reducing transmission loss.

As a polyimide with a low dielectric dissipation factor, Patent Document 2 proposes "a polymer film (claim 1) comprising one or more dianhydrides selected from the group consisting of crankshaft monomers, flexible monomers, rigid rotational monomers, rigid non-rotational monomers, and rotation-reducing monomers, and one or more diamines selected from the group consisting of crankshaft monomers, flexible monomers, rigid rotational monomers, rigid non-rotational monomers, and rotation-reducing monomers, and having an extinction coefficient Df (synonymous with dielectric dissipation factor) of 0.005 or less, a specific water absorption coefficient, etc."

International Publication No. 2016/055673 Japanese Patent Application Laid-Open No. 2021-11567

FPCs for high-frequency applications require polyimides that not only have a low dielectric dissipation factor but also meet the basic physical properties required for standard FPCs, such as high heat resistance and high dimensional stability. High dimensional stability not only suppresses defects such as circuit misalignment, improving the reliability of circuit boards, but also improving product yield. This problem is generally solved by making the linear thermal expansion coefficient of the polyimide film close to that of the metal foil (copper foil, etc.).

However, no multilayer polyimide film was known that combines excellent heat resistance with a low dielectric loss tangent and high dimensional stability even in highly heated environments. Patent Document 2 describes the use of a polyimide film exhibiting a low dielectric loss tangent as the core layer (heat-resistant polyimide layer) of a multilayer film, but does not provide detailed information about the heat-sealable layer (thermoplastic layer), leaving its performance as a multilayer film or metal laminate unclear.

An object of the present invention is to provide a multilayer polyimide film that has excellent heat resistance and combines a low dielectric loss tangent with high dimensional stability.
Another object of the present invention is to provide a polyimide metal laminate in which a multilayer polyimide film and a metal foil such as a copper foil are laminated together.

The main disclosures of this application can be summarized as follows:

1. A multilayer polyimide film having a heat-resistant polyimide layer made of a heat-resistant polyimide (PIc), and a heat-fusible polyimide layer made of a heat-fusible polyimide (PIb) laminated on one or both sides of the heat-resistant polyimide layer;
The heat-resistant polyimide (PIc) is
a tetracarboxylic acid component (Ac) containing 75 mol% or more and 100 mol% or less of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 0 mol% or more and 25 mol% or less of pyromellitic dianhydride;
a diamine component (Bc) containing 70 mol% or more and 95 mol% or less of p-phenylenediamine and 5 mol% or more and 30 mol% or less of 2,2'-dimethylbenzidine;
The heat-bondable polyimide (PIb) is
a tetracarboxylic acid component (Ab) containing 10 mol% or more and 60 mol% or less of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 40 mol% or more and 90 mol% or less of pyromellitic dianhydride;
and a diamine component (Bb) containing 2,2-bis[4-(4-aminophenoxy)phenyl]propane in an amount of 50 mol % or more,
Multilayer polyimide film.

2. The heat-resistant polyimide (PIc) is
a tetracarboxylic acid component (Ac) containing 80 mol% or more and less than 100 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride and more than 0 mol% and 20 mol% or less of pyromellitic dianhydride;
and a diamine (Bc) containing 75 mol% or more of p-phenylenediamine and 25 mol% or less of 2,2'-dimethylbenzidine,
2. The multilayer polyimide film according to item 1.

3. The heat-bondable polyimide (PIb) is
a tetracarboxylic acid component (Ab) containing 15 mol% or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 85 mol% or less of pyromellitic dianhydride;
and a diamine component (Bb) containing 2,2-bis[4-(4-aminophenoxy)phenyl]propane in an amount of 60 mol % or more,
3. The multilayer polyimide film according to item 1 or 2.

4. A multilayer polyimide film according to any one of items 1 to 3 above, wherein the multilayer polyimide film has a dielectric dissipation factor of 0.0060 or less, and the polyimide metal laminate has a dimensional change rate (absolute value) of 0.10% or less in the machine direction (MD) and the width direction (TD) (wherein the dimensional change rate is calculated according to the following formula, by measuring the initial dimension (X) of a polyimide metal laminate produced using the multilayer polyimide film and the dimension (Y) after etching the metal foil and then heat-treating it at 250°C for 30 minutes:
Dimensional change rate (%) = (Y - X) / X x 100
).

5. A polyimide metal laminate in which a metal foil is laminated on the heat-sealable polyimide layer side of the multilayer polyimide film described in any one of items 1 to 4 above.

6. The polyimide metal laminate described in item 5 above, wherein the multilayer polyimide film has a heat-sealable polyimide layer on both sides of a heat-resistant polyimide layer, and metal foil is laminated on both sides of the multilayer polyimide film.

7. A flexible wiring board manufactured using the polyimide metal laminate described in item 5 above.

The present invention provides a multilayer polyimide film that has a small dielectric loss tangent in the high frequency range, excellent heat resistance, and excellent dimensional stability. Furthermore, according to another aspect of the present invention, a polyimide metal laminate can be provided in which a multilayer polyimide film is laminated with a metal foil such as copper foil. This polyimide metal laminate is suitable for manufacturing high-frequency compatible FPCs.

The multilayer polyimide film of the present invention has a structure in which a heat-sealable polyimide layer (hereinafter also referred to as a core layer) is laminated on one or both sides of a heat-resistant polyimide layer (hereinafter also referred to as a core layer). Hereinafter, the material of the core layer may be represented by the suffix "c" (for core ), and the material of the heat-sealable layer may be represented by the suffix "b" ( for bondable).

<Heat-resistant polyimide layer>
The heat-resistant polyimide layer (core layer) contains a heat-resistant polyimide (PIc) obtained by reacting a tetracarboxylic acid component (Ac) with a diamine component (Bc).
The tetracarboxylic acid component (Ac) for producing a heat-resistant polyimide contains, relative to 100 mol% of the total tetracarboxylic acid component, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) in an amount of 75 mol% or more and 100 mol% or less, preferably 80 mol% or more, more preferably 85 mol% or more, preferably less than 100 mol%, and more preferably 95 mol% or less, and pyromellitic dianhydride (PMDA) in an amount of 0 mol% or more and 25 mol% or less, preferably more than 0 mol%, more preferably 5 mol% or more, preferably 20 mol% or less, and more preferably 15 mol% or less.

Tetracarboxylic acid dianhydrides other than s-BPDA and PMDA may be used as the tetracarboxylic acid component (Ac), but the amount is preferably 10 mol % or less, preferably 5 mol % or less, more preferably 2 mol % or less, and it is highly preferred that they are not included at all.

Tetracarboxylic acid components that can be used in combination include aromatic tetracarboxylic acid dianhydrides and aliphatic (especially alicyclic) tetracarboxylic acid dianhydrides. Specific examples include 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)1,4-phenylene, para-ter-phenyl-3,3',4,4'-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, and 1,2,4,5-cyclohexanetetracarboxylic dianhydride.

The diamine component (Bc) used to produce heat-resistant polyimide contains p-phenylenediamine (PPD) in an amount of 70 mol% or more and 95 mol% or less, preferably 75 mol% or more and preferably 93 mol% or less, and 2,2'-dimethylbenzidine (m-TB) in an amount of 5 mol% or more and 30 mol% or less, preferably 7 mol% or more and preferably 25 mol% or less, based on 100 mol% of all diamine components.

Diamine compounds other than PPD and m-TB may be used as the diamine component (Bc), but the amount is preferably 10 mol % or less, preferably 5 mol % or less, more preferably 2 mol % or less, and it is highly preferred that they are not included at all.

Diamine components that can be used in combination include aromatic diamine compounds and aliphatic (especially alicyclic) diamine compounds. Specific examples include m-phenylenediamine, 4,4''-diamino-p-terphenyl, 2,4-toluenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane bis(aminophenoxy)benzenes such as benzene, 2,2-di(3-aminophenyl)propane, 2,2-di(4-aminophenyl)propane, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 1,4-bis(3-aminophenoxy)benzene; 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-bis(4-aminophenoxy)biphenyl; and 1,4-cyclohexanediamine.

The heat-resistant polyimide layer is primarily composed of the aforementioned heat-resistant polyimide, and the resin component excluding additives preferably consists essentially of the aforementioned heat-resistant polyimide (95% by weight or more, preferably 98% by weight or more), and it is also highly preferred that it consists solely of heat-resistant polyimide (100% by weight).

In addition to the heat-resistant polyimide, the heat-resistant polyimide layer may contain additives as needed. Typical examples include fine inorganic or organic fillers. Examples of inorganic fillers include particulate or flat inorganic fillers. Specific examples include inorganic oxide powders such as fine titanium dioxide powder, silicon dioxide (silica) powder, magnesium oxide powder, aluminum oxide (alumina) powder, and zinc oxide powder; inorganic nitride powders such as fine silicon nitride powder and titanium nitride powder; inorganic carbide powders such as silicon carbide powder; and inorganic salt powders such as fine calcium carbonate powder, calcium sulfate powder, and barium sulfate powder. Examples of organic fillers include polyimide powder, liquid crystal polymer powder, fluororesin powder, and thermosetting resin powder. These additives may be used in combination with two or more types. The amount and shape (size, aspect ratio) of the filler are preferably selected depending on the intended use. Furthermore, known methods can be used to uniformly disperse these fillers.

These inorganic or organic fillers, particularly preferably silica powder, can be contained in the heat-resistant polyimide layer in an amount of preferably 30% by weight or less, more preferably 20% by weight or less, and even more preferably 10% by weight or less (which may be 0% by weight).

<Heat-fusible polyimide layer>
The heat-fusible polyimide layer (heat-fusible layer) contains a heat-fusible polyimide (PIb) obtained by reacting a tetracarboxylic acid component (Ab) with a diamine component (Bb).
The tetracarboxylic acid component (Ab) for producing a heat-fusible polyimide contains, relative to 100 mol % of the total tetracarboxylic acid component, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) in an amount of 10 mol % to 60 mol %, preferably 15 mol % or more, more preferably 20 mol % or more, and also preferably 55 mol % or less, more preferably 50 mol % or less, and pyromellitic dianhydride (PMDA) in an amount of 40 mol % to 90 mol %, preferably 45 mol % or more, more preferably 50 mol % or more, and also preferably 85 mol % or less, more preferably 80 mol % or less.

Tetracarboxylic acid dianhydrides other than s-BPDA and PMDA may be used as the tetracarboxylic acid component (Ab), but the amount is preferably 10 mol % or less, preferably 5 mol % or less, more preferably 2 mol % or less, and it is highly preferred that they are not included at all.

Tetracarboxylic acid components that can be used in combination include aromatic tetracarboxylic acid dianhydrides and aliphatic (especially alicyclic) tetracarboxylic acid dianhydrides. Specific examples include 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, and 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride.

The diamine component (Bb) used to produce heat-bondable polyimide contains 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) in an amount of 50 mol% or more (preferably more than 50 mol%), preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and even more preferably 90 mol% or more, based on 100 mol% of all diamine components, and it is also preferable that it is 100 mol%.

Diamine compounds other than BAPP may be used as the diamine component (Bb). Examples of other diamine components that may be used in combination include m-phenylenediamine, 2,2'-dimethylbenzidine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 3,3'-diaminobenzophenone, 4,4'-bis(3-aminophenoxy)biphenyl, and 4,4'-bis(4-aminophenoxy)biphenyl. bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, bis[4-[4-(4-aminophenoxy)phenoxy]phenyl]ether, and 1,4-cyclohexanediamine.

The glass transition temperature (Tg) of the heat-sealable polyimide is preferably 250°C to 310°C, more preferably 260°C to 300°C, from the viewpoint of improving the peel strength between the heat-sealable layer and the core layer, and between the heat-sealable layer and the metal foil, as well as from the viewpoint of solder heat resistance during FPC manufacturing.

The heat-fusible polyimide layer is primarily composed of the heat-fusible polyimide described above, and the resin composition excluding additives preferably consists essentially of the heat-fusible polyimide described above (95% by weight or more, preferably 98% by weight or more), and it is also highly preferred that it consists solely of heat-fusible polyimide (100% by weight).

The heat-fusible polyimide layer may contain additives as needed in addition to the heat-fusible polyimide. Specific additives and amounts of additives can be those described for the heat-resistant polyimide layer.

<Multilayer polyimide film>
The thickness of the multilayer polyimide film of the present invention is not particularly limited, but the thickness of the heat-resistant polyimide layer is preferably 3 to 70 μm, more preferably 5 to 65 μm. The thickness of the heat-fusible polyimide layer is preferably 0.5 to 15 μm, more preferably 1 to 12.5 μm. The thickness of the entire multilayer polyimide film is preferably 4 to 100 μm, more preferably 7 to 90 μm.

The dielectric dissipation factor (10 GHz) of the multilayer polyimide film is preferably 0.0060 or less, more preferably less than 0.0060, and even more preferably 0.0055 or less.

The dimensional change rate (absolute value) of the multilayer polyimide film is preferably 0.10% or less, preferably less than 0.10%, more preferably 0.09% or less.
The dimensional change rate was calculated according to the following formula, using a polyimide metal laminate produced using a multilayer polyimide film, by measuring the initial dimension (X) and the dimension (Y) after etching the metal foil, heat treating the laminate at 250°C for 30 minutes, and conditioning the humidity.
Dimensional change rate (%) = (Y - X) / X x 100

<Method of manufacturing a multilayer polyimide film>
The method for producing the multilayer polyimide film of the present invention is not particularly limited, and any known method can be used. Representative methods include a coating method and a co-extrusion-casting film-forming method, which will be described below.

(Manufacturing method using coating method)
The multilayer polyimide film of the present invention can be obtained by coating one or both sides of a self-supporting film obtained from a polyimide precursor solution (a) that provides a heat-resistant polyimide with a polyimide precursor solution (b) that provides a heat-fusible polyimide, and then heating and drying the resulting multilayer self-supporting film to carry out imidization.

Polyimide precursor solution (a) that produces heat-resistant polyimides is obtained by reacting a tetracarboxylic acid component and a diamine component in substantially equimolar amounts, or with one component in slight excess relative to the other, in an organic solvent. The structure of polyimide precursor solution (a), which contains multiple tetracarboxylic acid components and diamine components, may be a random structure or a block structure, with a random structure being more preferred. A self-supporting film can be obtained by casting polyimide precursor solution (a) onto a support and drying the cast product by heating.

On the other hand, polyimide precursor solution (b) that produces heat-fusible polyimides can also be obtained by reacting a tetracarboxylic acid component and a diamine component in substantially equimolar amounts, or in a slight excess of one component relative to the other, in an organic solvent. The structure of polyimide precursor solution (b), which contains multiple tetracarboxylic acid components and diamine components, may be a random structure or a block structure, with a random structure being more preferred.

The monomer compositions for preparing the polyimide precursor solution (a) that provides the heat-resistant polyimide and the polyimide precursor solution (b) that provides the heat-fusible polyimide are the compositions described in the <Heat-resistant polyimide layer> and <Heat-fusible polyimide layer> sections, respectively.

For the purpose of suppressing gelation, a phosphorus-based stabilizer, such as triphenyl phosphite or triphenyl phosphate, may be added to the polyimide precursor solution (b) and/or the polyimide precursor solution (a) in an amount of 0.01 to 1 mass % based on the solid content (polymer) concentration during polymerization of the polyimide precursor solution.
From the viewpoint of the film surface condition and productivity, it is preferable to add a phosphate ester or a salt of a tertiary amine and a phosphate ester to the polyimide precursor solution. The amount of these added is preferably 0.01 to 5 parts by mass per 100 parts by mass of polyimide or polymer. Specific examples of phosphate esters include distearyl phosphate ester and monostearyl phosphate ester. Furthermore, examples of salts of tertiary amines and phosphate esters include monostearyl phosphate triethanolamine salt. Regarding imidization in the present invention, either thermal imidization (thermal imidization) or chemical imidization (chemical imidization) can be applied. Of these, thermal imidization is preferably applied.

A basic organic compound can be added to polyimide precursor solution (b) and/or polyimide precursor solution (a) to promote imidization. Examples of such compounds include lower alkyl- or aromatic-substituted imidazoles such as 1,2-dimethylimidazole, N-methylimidazole, N-benzyl-2-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, and 2-phenylimidazole; benzimidazoles such as 5-methylbenzimidazole; and substituted pyridines such as isoquinoline, 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, and 4-n-propylpyridine. These compounds can be used in a proportion of 0.05 to 10% by weight, more preferably 0.05 to 7% by weight, and even more preferably 0.1 to 5% by weight, based on the solids (polymer) concentration. When these basic organic compounds are used, the imidization of the polyimide precursor is promoted at a relatively low temperature to form a polyimide film, and therefore these basic organic compounds can be used to avoid insufficient imidization.

Examples of organic solvents used to produce the polyimide precursor solution include amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, and hexamethylsulfonamide; sulfoxides such as dimethyl sulfoxide and diethyl sulfoxide; and sulfones such as dimethyl sulfone and diethyl sulfone. These solvents may be used alone or in combination.

The concentration of all monomers in the organic solvent when carrying out the polymerization reaction between the tetracarboxylic acid component and the diamine component can be selected appropriately depending on the intended use. For example, the solids (polymer) concentration of the polyimide precursor solutions (a) and (b) is preferably 5 to 40% by mass, more preferably 6 to 35% by mass, and particularly preferably 10 to 30% by mass.

The production temperature for polyimide precursor solution (a) and polyimide precursor solution (b) is not particularly limited, but is preferably 25°C to 100°C, more preferably 25°C to 80°C, and even more preferably 30°C to 70°C to prevent the imidization reaction from proceeding too quickly. The production time is approximately 1 to 72 hours, more preferably 2 to 60 hours. The reaction can be carried out in an air atmosphere, but is usually preferably carried out in an inert gas atmosphere, preferably a nitrogen gas atmosphere.

The solution viscosities of polyimide precursor solution (a) and polyimide precursor solution (b) can be appropriately selected depending on the intended use (e.g., coating, casting, etc.). For example, when polyimide precursor solution (a) and polyimide precursor solution (b) are used for casting, from the viewpoint of ease of handling the polyimide precursor solution, the rotational viscosity measured at 30°C is preferably approximately 100 to 5,000 poise, more preferably 500 to 4,000 poise, and particularly preferably approximately 1,000 to 3,000 poise. Furthermore, when polyimide precursor solution (a) and polyimide precursor solution (b) are used for coating, from the viewpoint of ease of handling the polyimide precursor solution, the rotational viscosity measured at 30°C is preferably 1 to 100 centipoise, more preferably 3 to 50 centipoise, and particularly preferably 5 to 20 centipoise. Therefore, it is desirable to carry out the polymerization reaction to such an extent that the resulting polyimide precursor solution exhibits the above-mentioned viscosity. The viscosity of the solution can also be adjusted by adding the organic solvent described above to the produced polyimide precursor solution.

A self-supporting film obtained from polyimide precursor solution (a) that provides a heat-resistant polyimide can be obtained, for example, by casting polyimide precursor solution (a) onto the surface of a suitable support (e.g., a metal, ceramic, or plastic roll, or a metal belt, etc.) to form a film of uniform thickness, and then heating it to preferably 50 to 210°C, more preferably 60 to 200°C, using a heat source such as hot air or infrared rays to gradually remove the solvent and dry it until it becomes self-supporting (e.g., to the point where it can be peeled off from the support).

The self-supporting film that provides the heat-resistant polyimide preferably has a heat loss in the range of 20 to 40% by mass and an imidization rate in the range of 8 to 40%. If the heat loss and imidization rate are within the above ranges, the mechanical properties of the self-supporting film will be sufficient, the polyimide precursor solution (b) can be easily and neatly applied to the upper surface of the self-supporting film, the polyimide film obtained after imidization will be less likely to develop bubbles, cracks, crazes, fissures, and the like, and the adhesive strength between the heat-resistant polyimide layer and the heat-fusible polyimide layer will be sufficient.
The heat loss of the self-supporting film is calculated by drying the film to be measured at 400° C. for 30 minutes and then calculating the weight before drying (W1) and the weight after drying (W2) according to the following formula.
Heating loss (mass%) = {(W1-W2)/W1}×100
The imidization ratio of the self-supporting film can be calculated by measuring the IR spectra of the self-supporting film and its fully cured product (polyimide film) using the ATR method and utilizing the ratio of the vibrational band peak areas. Examples of the vibrational band peaks that can be utilized include the asymmetric stretching vibration band of the imide carbonyl group and the benzene ring skeleton stretching vibration band. Another method for measuring the imidization ratio is to use a Karl Fischer moisture meter, as described in JP-A-9-316199.

Next, polyimide precursor solution (b) that provides a heat-fusible polyimide is applied to one or both sides of the self-supporting film. Polyimide precursor solution (b) may be applied to the self-supporting film after it has been peeled from the support, or it may be applied to the self-supporting film on the support before it is peeled from the support. It is preferable to apply polyimide precursor solution (b) uniformly to one or both sides of the self-supporting film. Therefore, it is preferable that the self-supporting film of polyimide precursor solution (a) has a surface that allows polyimide precursor solution (b) to be uniformly applied.

The method for applying polyimide precursor solution (b) to the self-supporting film obtained from polyimide precursor solution (a) is not particularly limited, but examples include known application methods such as gravure coating, spin coating, silk screening, dip coating, spray coating, bar coating, knife coating, roll coating, blade coating, and die coating.

Next, the self-supporting film of polyimide precursor solution (a) coated with polyimide precursor solution (b) is heated and imidized to obtain a multilayer polyimide film. The maximum heating temperature for the heat treatment for imidization is preferably 330°C to 600°C, more preferably 350°C to 550°C, and even more preferably 370°C to 500°C.

The heat treatment for imidization is preferably carried out in stages, with a primary heat treatment being carried out at a temperature of 200°C or higher but lower than 300°C for 1 minute to 60 minutes, followed by a secondary heat treatment at a temperature of 300°C or higher but lower than 330°C for 1 minute to 60 minutes, and then a tertiary heat treatment being carried out at a maximum heating temperature of preferably 330°C to 600°C, more preferably 370 to 550°C, and even more preferably 370 to 500°C for 1 minute to 30 minutes. This heat treatment can be carried out using known equipment such as a hot air oven or infrared heating oven. Furthermore, this heat treatment is preferably carried out by fixing the self-supporting film of polyimide precursor solution (a) coated with polyimide precursor solution (b) using a pin tenter, clips, or the like.

(Manufacturing method by co-extrusion-casting film formation method)
The multilayer polyimide film of the present invention can also be produced by a coextrusion-casting film-forming method (hereinafter simply referred to as the "coextrusion method"), in which a polyimide precursor solution (hereinafter also referred to as a dope solution) that provides a heat-resistant polyimide layer and a dope solution that provides a heat-fusible polyimide layer are laminated, dried, and imidized. This coextrusion method can be, for example, the method described in JP-A-3-180343 (JP-B-7-102661).

More specifically, this co-extrusion method involves first using an extruder having a die for extrusion molding two or more layers. A dope liquid for providing a heat-resistant polyimide layer and a dope liquid for providing a heat-sealable polyimide layer are cast onto a support from the die outlet, thereby forming a laminated thin film. The thin film on the support is then dried to form a multilayer self-supporting film. The multilayer self-supporting film is then peeled from the support, and finally, the multilayer self-supporting film is heat-treated. In this process, the dope liquid in contact with the support can be either the dope liquid for providing a heat-resistant polyimide layer or the dope liquid for providing a heat-sealable polyimide layer.

Both the dope solution that produces the heat-resistant polyimide layer and the dope solution that produces the heat-fusible polyimide layer are prepared by reacting a tetracarboxylic acid component with a diamine component, as explained in the (Coating Production Method) section, to produce polyimide precursor solutions (a) and (b). The dope solution preferably has a solids (polymer) concentration of 5 to 40% by weight, and particularly 10 to 30% by weight, and a solution viscosity (rotational viscosity) of approximately 50 to 10,000 poise, and particularly 100 to 6,000 poise at the temperature at which it is discharged from the multilayer extrusion die during the aforementioned multilayer extrusion molding of two or three layers.

Examples of two-layer extrusion dies include those having dope supply ports, dope passages extending from the supply ports to the manifolds, the manifolds having bottom flow paths that join together at a confluence, and the resulting dope passage (lip) that communicates with a slit-shaped discharge port from which the dope is discharged onto a support in the form of a thin film (multi-manifold two-layer die). The lip spacing can be adjusted by a lip adjustment bolt.
The gaps in the flow paths at the bottom of each manifold (near the confluence) are adjusted by choke bars. Each manifold preferably has a hanger-coat type shape. The two-layer extrusion die has dope supply ports on the left and right sides of the upper part of the die, and the dope paths immediately merge at a confluence point equipped with a partition plate. The dope paths connect to the manifold from the confluence point, and the dope path (lip portion) at the bottom of the manifold connects to a slit-shaped discharge port. The die may also have a structure in which the dope is discharged from the discharge port in the form of a grooved film onto a support (a feedblock-type two-layer die or a single-manifold-type two-layer die).

In addition to the two-layer extrusion described above, by using a die for extrusion molding of three or more layers, it is also possible to produce a multi-layer extruded polyimide film using a molding method similar to two-layer extrusion molding. That is, if the composition is a first dope liquid that provides a heat-sealable polyimide layer, a dope liquid that provides a heat-resistant polyimide layer, and a second dope liquid that provides a heat-sealable polyimide layer, a three-layer polyimide film can also be obtained. The first dope liquid and the second dope liquid that provide the heat-sealable polyimide layer may be the same or different.

In addition, with regard to the drying conditions, heating conditions, etc. after the operation of continuously extruding onto the support in the co-extrusion-casting film production method, the contents described above in the "Manufacturing method by coating method" can be applied as is.

In either the coating method or the co-extrusion method, when the self-supporting film is heated to produce the polyimide film, a stretching operation may be carried out, if necessary.
By the above-mentioned operations, it is possible to continuously produce a long polyimide film.
When a thick multilayer polyimide film is required, it can be produced by laminating together the multilayer polyimide films produced by the above-mentioned production method. The lamination operation can also be carried out continuously.

<Polyimide metal laminate>
A polyimide-metal laminate can be produced by laminating a multilayer polyimide film (or layer) and a metal foil (or layer) using the polyimide precursor solution or multilayer polyimide film of the present invention. The polyimide-metal laminate has a structure in which a metal foil (or layer) is laminated on one or both sides of a multilayer polyimide film. Examples of methods for producing a polyimide-metal laminate include the following methods.
(i) A method in which a multilayer polyimide film and a metal foil are directly bonded without an adhesive and laminated by applying pressure or heat and pressure; (ii) A method in which a polyimide precursor solution is applied to a metal foil and then dried and imidized; (iii) A method in which a metal layer is directly formed on a multilayer polyimide film by a dry method (metallizing such as vacuum deposition or sputtering) and/or a wet method (plating).

The metal foils (i) and (ii) above can be made of various metals, such as copper, aluminum, gold, or alloys thereof. Among these, copper foil is preferred. Those using copper foil as the metal foil are also called "copper-clad laminates." Furthermore, when metal layers are laminated on both sides of a multilayer polyimide film, the same or different metals can be used. Specific examples of copper foil include rolled copper foil and electrolytic copper foil. While not particularly limited, the thickness of the copper foil is preferably 2 to 35 μm, with 5 to 18 μm being particularly preferred. Regarding the Ra and Rz, which indicate surface roughness, it is preferable that Ra be 0.01 μm to 0.4 μm and Rz be 0.2 μm to 2.0 μm.

The multilayer polyimide film and copper foil are preferably continuously thermocompression bonded under heat using at least one pair of pressure members. The temperature of the pressure members is preferably at least 50°C higher than the glass transition temperature of the heat-sealable polyimide, more preferably at least 60°C higher, and even more preferably at least 70°C higher. Using such a heating temperature advantageously results in a strong laminate between the multilayer polyimide film and copper foil. Furthermore, a heating temperature of 420°C or lower is preferred to prevent thermal degradation of the multilayer polyimide film and copper foil. As mentioned above, the glass transition temperature of the heat-sealable polyimide is preferably 250°C or higher. Specifically, thermocompression bonding is preferably performed at a temperature range of 300°C to 420°C, more preferably at a temperature range of 310°C to 410°C, and even more preferably at a temperature range of 320°C to 400°C.

The thermocompression bonding device can be a known device such as a double belt press or a roll laminator using a pressure-bonding metal roll. For example, rolled multilayer polyimide film and copper foil can be continuously supplied to the thermocompression bonding device, and a copper-clad laminate (polyimide-metal laminate) can be produced in a rolled state.

The dry process (metallizing method) used in (iii) above can be a known method such as vacuum deposition, sputtering, ion plating, or electron beam deposition. Metals used in the metallizing method include, but are not limited to, copper, nickel, chromium, manganese, aluminum, iron, molybdenum, cobalt, tungsten, vanadium, titanium, tantalum, and other metals, as well as alloys thereof, oxides of these metals, and carbides of these metals. The metal layer formed has a thickness of, for example, 1 nm to 500 nm, and a metal plating layer of copper, tin, or the like can be formed on this surface by electroplating or electroless plating to a thickness of, for example, 1 μm to 40 μm.

The wet method (plating method) used in (iii) above can be any known plating method, including electrolytic plating and electroless plating, or a combination of these. There are no limitations on the metal used in the wet plating method, as long as it can be wet-plated.

The thickness of the metal layer formed by wet plating can be selected appropriately depending on the intended use, and is preferably in the range of 0.1 μm to 50 μm, and more preferably 1 μm to 30 μm for practical use. The number of layers of the metal layer formed by wet plating can be selected appropriately depending on the intended use, and may be one layer, two layers, or three or more layers.

Examples of wet plating methods include conventional methods such as the Elfseed process manufactured by Ebara-Udylite Co., Ltd., or the Catalyst Bond process, a surface treatment process manufactured by Nippon Mining & Metals Co., Ltd., followed by electroless copper plating.

The polyimide metal laminate of the present invention has good moldability and can be directly subjected to processes such as drilling, bending, drawing, and metal wiring formation. Furthermore, the multilayer polyimide film of the present invention can be used for thermocompression bonding of electronic circuits onto wiring.

The multilayer polyimide film and polyimide-metal laminate of the present invention can be suitably used as electronic substrate materials such as FPCs and TABs, coverlays, and adhesive sheets that require reliability at high temperatures.

The present invention will now be described in more detail based on examples. However, the present invention is not limited to these examples.

The following abbreviations will be used hereinafter:
<Tetracarboxylic acids>
s-BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride PMDA: pyromellitic dianhydride <Diamines>
PPD: p-phenylenediamine m-TB: 2,2'-dimethylbenzidine BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane TPE-R: 1,3-bis(4-aminophenoxy)benzene Bisaniline P: α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene <Others>
DMAc: N,N-dimethylacetamide

<Evaluation of (multilayer) polyimide films>
Coefficient of linear thermal expansion (CTE)
Using an EXSTAR6100 manufactured by SII Corporation, polyimide film samples of 15 mm in length and 3 mm in width were measured in tensile mode under a load of 4 gf at a heating rate of 20°C/min, and the samples were first heated to 300°C to remove thermal shrinkage during film formation. After cooling to room temperature, the samples were secondarily heated to 300°C at 20°C/min, and the linear expansion coefficient was calculated from the TMA curve from 50°C to 200°C.

<Measurement of dielectric loss tangent>
The dielectric loss tangent of the polyimide film was measured under the following conditions using a split cylinder resonator 10 GHz CR-710 (manufactured by EM Lab Co., Ltd.) as the measuring device.
Measurement frequency: 10GHz
Measurement conditions: temperature 25±2℃, humidity 50±3%RH
Measurement sample: A sample that had been left to stand for 24 hours under the above measurement conditions was used.

[MIT folding endurance test]
A test piece for MIT folding endurance test having a width of 15 mm across the entire width was cut out. In accordance with ASTM D2176, the number of times until the polyimide film broke was measured under a curvature radius of 0.38 mm, a load of 9.8 N, a folding speed of 175 times/min, and a left-right folding angle of 135°.

[Evaluation of Polyimide Metal Laminate (Copper Clad Laminate)]
(Production of copper clad laminate)
Using a roll laminator, copper foil was superimposed on both sides of the multilayer polyimide film and thermocompression bonded to produce a copper clad laminate in which copper foil was laminated on both sides of the multilayer polyimide film.

[Dimensional Change Rate] A copper clad laminate was punched using a press puncher, and the initial dimension (X) was measured. Subsequently, the copper foil was removed by double-sided etching, and the laminate was then heat-treated at 250°C for 30 minutes. After heating, the laminate was conditioned at 25°C and 60% RH for 24 hours, and then the dimension (Y) was measured. The dimensional change rate (%) was calculated according to the following formula.
Dimensional change rate (%) = (Y - X) / X x 100

[Appearance evaluation]
The copper clad laminate was etched on both sides to remove the copper foil, and the film surface was observed using an optical microscope and evaluated as follows.
○: No defects (foaming) on the surface ×: Defects (foaming) on the surface

Example 1
[Preparation of polyimide precursor solution]
(Polyimide precursor solution for core layer)
DMAc was added to a reaction vessel equipped with a stirrer and a nitrogen inlet tube, followed by the addition of PPD and m-TB as diamine components. Subsequently, s-BPDA and PMDA as tetracarboxylic dianhydride components were added in equimolar amounts to the diamine components and reacted to obtain polyimide precursor solution A with a monomer concentration of 18% by mass and a solution viscosity of 2,000 poise at 30°C. The molar ratio of PPD to m-TB was 80:20, and the molar ratio of s-BPDA to PMDA was 90:10.

(Polyimide precursor solution for heat-sealing layer)
DMAc was added to a reaction vessel equipped with a stirrer and a nitrogen inlet tube, followed by the addition of BAPP as a diamine component. Subsequently, s-BPDA and PMDA as tetracarboxylic dianhydride components were added in equimolar amounts to the diamine component, and the mixture was allowed to react to obtain a polyimide precursor solution B having a monomer concentration of 18% by mass and a solution viscosity of 800 poise at 30°C. The molar ratio of s-BPDA to PMDA was 30:70.

[Production of Core Single-Layer Polyimide Film]
Polyimide precursor solution A was cast onto a glass plate in the form of a thin film, heated in an oven at 120°C for 12 minutes, and peeled off from the glass plate to obtain a self-supporting film. The four sides of this self-supporting film were fixed with pin tenters and gradually heated in a heating furnace from 150°C to 400°C to remove the solvent and perform imidization, thereby obtaining a single-layer polyimide film with a thickness of 25 μm.

[Production of multilayer polyimide film]
Polyimide precursor solution A and polyimide precursor solution B were continuously extruded and cast onto the upper surface of a smooth metal support from a three-layer extrusion die so as to form a thin film in the following order: polyimide precursor solution B (thermal adhesive layer) - polyimide precursor solution A (core layer) - polyimide precursor solution B (thermal adhesive layer). The thin-film cast was continuously dried with hot air at 140°C to form a self-supporting film. After peeling the self-supporting film from the support, it was conveyed while gripping both ends of the self-supporting film in the width direction using a tenter device and gradually heated from 200°C to 490°C in a heating furnace to remove the solvent and imidize, resulting in a long multilayer film with a thickness of 50 μm. The thicknesses of the two thermal adhesive layers were each 5 μm, and the thickness of the core layer was 40 μm. Note that with respect to the resulting multilayer polyimide film, MD (machine direction) refers to the longitudinal direction (conveyance direction), and TD (transverse direction) refers to the width direction.

The obtained polyimide film was subjected to measurements of the coefficient of linear thermal expansion (CTE), dielectric loss tangent, and MIT folding endurance test. The results are shown in Table 1.

[Polyimide metal laminate (copper-clad laminate)]
Using a roll laminator, copper foil (manufactured by JX Nippon Mining Corporation, BHM-C102F-HA-V2, thickness 12 μm) was superimposed on both sides of the multilayer polyimide film, and thermocompression bonding was performed at a lamination temperature of 360°C, a lamination pressure of 1.5 MPa, and a lamination speed of 0.5 m/min, thereby producing a copper-clad laminate in which copper foil was laminated on both sides of the multilayer polyimide film.

The resulting copper-clad laminate was etched and the dimensional change rate and appearance were evaluated.

<Examples 2 to 7, Comparative Examples 1 to 10>
A polyimide precursor solution for the core layer and a polyimide precursor solution for the heat-sealing layer were prepared in the same manner as in Example 1. The compositions are as shown in Tables 1 to 3. Furthermore, a core single-layer polyimide film, a multilayer polyimide film, and a copper-clad laminate were produced and evaluated in the same manner as in Example 1. The results are shown in Table 1 (Example), Table 2 (Comparative Example, multilayer film thickness 50 μm), and Table 3 (Comparative Example, multilayer film thickness 75 μm).
In the 75 μm thick multilayer polyimide films (Examples 6 and 7, Comparative Examples 7 to 10), the thickness of each of the two heat-sealing layers was 7 μm, and the thickness of the core layer was 61 μm.

As shown in Tables 1 to 3, the multilayer polyimide films of all Examples exhibited a low dielectric loss tangent of 0.0060 or less. The multilayer polyimide films of Comparative Examples 3, 5, and 9 exhibited a low dielectric loss tangent, but had a large dimensional change rate, which was problematic for practical use. The other Comparative Examples all had large dielectric loss tangents.
Regarding the dimensional change rate, all of the Examples showed small values, while all of the Comparative Examples showed large values. In Comparative Examples 7 and 10, attempts were made to produce copper-clad laminates using a 75 μm multilayer film, but foaming occurred, making evaluation impossible.
Furthermore, this experiment revealed that the dimensional change rate is strongly dependent not only on the CTE of the multilayer film but also on the combination of the core layer and the heat-sealing layer. When examining 50 μm-thick multilayer polyimide films, the multilayer polyimide film of Comparative Example 6 had a CTE (MD and TD) that matched the CTE of 18 ppm/K of the copper foil, and the multilayer polyimide films of Examples 1 to 5 and Comparative Example 1 also had CTEs roughly close to that of the copper foil. However, when comparing the dimensional change rates, the multilayer polyimide films of the Examples had extremely small dimensional change rates, while Comparative Examples 6 and 1 had large dimensional change rates. Similarly, when examining 75 μm-thick multilayer films, the multilayer polyimide film of Example 6 and the multilayer polyimide film of Comparative Example 9 had the same CTE, but Comparative Example 9 showed a large dimensional change rate.
The reason for this is thought to be the optimization of the heat-resistant polyimide layer (core layer), which has a large effect on the dielectric loss tangent, and the optimization of the heat-sealable polyimide layer (heat-sealable layer) to match the core layer, and this result cannot be predicted from the conventional CTE-based approach.

Polyimide films produced from the polyimide precursor solution of the present invention can be suitably used for high-frequency compatible FPC applications.

Claims (7)

A multilayer polyimide film having a heat-resistant polyimide layer made of a heat-resistant polyimide (PIc), and a heat-fusible polyimide layer made of a heat-fusible polyimide (PIb) laminated on one or both sides of the heat-resistant polyimide layer;
The heat-resistant polyimide (PIc) is
a tetracarboxylic acid component (Ac) containing 75 mol% or more and 100 mol% or less of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 0 mol% or more and 25 mol% or less of pyromellitic dianhydride;
a diamine component (Bc) containing 70 mol% or more and 95 mol% or less of p-phenylenediamine and 5 mol% or more and 30 mol% or less of 2,2'-dimethylbenzidine;
The heat-bondable polyimide (PIb) is
a tetracarboxylic acid component (Ab) containing 10 mol% or more and 60 mol% or less of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 40 mol% or more and 90 mol% or less of pyromellitic dianhydride;
and a diamine component (Bb) containing 2,2-bis[4-(4-aminophenoxy)phenyl]propane in an amount of 50 mol % or more,
Multilayer polyimide film. The heat-resistant polyimide (PIc) is
a tetracarboxylic acid component (Ac) containing 80 mol% or more and less than 100 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride and more than 0 mol% and 20 mol% or less of pyromellitic dianhydride;
and a diamine (Bc) containing 75 mol% or more of p-phenylenediamine and 25 mol% or less of 2,2'-dimethylbenzidine,
The multilayer polyimide film according to claim 1 . The heat-bondable polyimide (PIb) is
a tetracarboxylic acid component (Ab) containing 15 mol% or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 85 mol% or less of pyromellitic dianhydride;
and a diamine component (Bb) containing 2,2-bis[4-(4-aminophenoxy)phenyl]propane in an amount of 60 mol % or more,
The multilayer polyimide film according to claim 1 . 2. The multilayer polyimide film according to claim 1, wherein the multilayer polyimide film has a dielectric loss tangent of 0.0060 or less, and the polyimide metal laminate has a dimensional change rate (absolute value) of 0.10% or less in the machine direction (MD) and the width direction (TD). (The dimensional change rate is calculated according to the following formula, by measuring the initial dimension (X) of a polyimide metal laminate produced using the multilayer polyimide film and the dimension (Y) after etching the metal foil and then heat-treating it at 250°C for 30 minutes.)
Dimensional change rate (%) = (Y - X) / X x 100
). A polyimide metal laminate in which a metal foil is laminated on the heat-sealable polyimide layer side of the multilayer polyimide film described in claim 1. The polyimide metal laminate described in claim 5, wherein the multilayer polyimide film has a heat-sealable polyimide layer on both sides of a heat-resistant polyimide layer, and metal foil is laminated on both sides of the multilayer polyimide film. A flexible wiring board manufactured using the polyimide metal laminate described in claim 5.