JP7518647B2 - Resin composition, its manufacturing method, resin film and metal-clad laminate - Google Patents

Description

The present invention relates to a resin film and a metal-clad laminate useful as, for example, a circuit board material, a resin composition used therein, and a method for producing the same.

Flexible printed circuit boards (FPCs) are capable of three-dimensional, high-density mounting even in limited spaces, so their uses have expanded to include wiring for moving parts of electronic devices, cables, connectors, and other components, and they are now installed in devices in many fields. As a result, the environments in which FPCs are used are becoming more diverse, and the performance required is becoming more sophisticated.

For example, in the field of information processing and information communication, efforts are being made to increase the transmission frequency in order to transmit and process large volumes of information, and there is a demand for reducing transmission loss by improving the dielectric properties of the insulating resin layer of the circuit board. As a technology for improving the dielectric properties of the insulating resin layer of the circuit board, it has been proposed to blend liquid crystalline polymer particles into a thermoplastic resin or a thermosetting resin (Patent Document 1). However, Patent Document 1 does not include any examples other than epoxy resin, which is a thermosetting resin, and no detailed consideration is given to thermoplastic resins.

In addition, with the advancement of miniaturization accompanying high-density mounting, high dimensional stability is also required for the insulating resin layer of the circuit board. As a technique for improving the dimensional stability of the insulating resin layer of the circuit board, the incorporation of organic or inorganic fillers has been proposed (Patent Documents 2 to 4).

Patent No. 6295013 Japanese Patent Application Publication No. 11-273456 Japanese Patent Application Publication No. 10-338809 JP 2006-321853 A

Polyimide is a resin with excellent properties such as heat resistance and chemical resistance, and is widely used as a material for the insulating resin layer of circuit boards. On the other hand, liquid crystal polymers are also used as circuit board materials and have excellent dielectric properties. For this reason, it is thought that the dielectric properties of polyimide films can be improved by blending liquid crystal polymers as a filler in polyimide. However, liquid crystal polymers have a large coefficient of thermal expansion (CTE), and there are concerns that this may impair the dimensional stability of the insulating resin layer.

Therefore, the object of the present invention is to provide a resin film in which a liquid crystal polymer filler is dispersed in a polyimide, achieving both excellent dielectric properties and dimensional stability.

The resin composition of the present invention comprises the following components (A) and (B):
(A) a polyamic acid obtained by reacting a tetracarboxylic acid anhydride component with a diamine component;
and (B) a filler having shape anisotropy made of a liquid crystal polymer;
Contains:

In the resin composition of the present invention, the ratio (L/D) of the average major axis diameter (L) to the average minor axis diameter (D) of the filler of component (B) may be within the range of 3 to 200.

In the resin composition of the present invention, the filler of component (B) may have an average major axis diameter (L) in the range of 50 to 3000 μm, and an average minor axis diameter (D) in the range of 1 to 50 μm.

In the resin composition of the present invention, the content of the filler in the (B) component may be within the range of 1 to 70 volume % relative to the total amount of the (A) component and the (B) component.

In the resin composition of the present invention, the melting point of the liquid crystal polymer may be 280°C or higher.

In the resin composition of the present invention, the liquid crystal polymer may have a polyester structure.

The resin composition of the present invention may have a tensile modulus of elasticity in the major axis direction of the filler of component (B) of 20 GPa or more.

The resin composition of the present invention may have a ratio of the tensile modulus of the filler of the (B) component in the major axis direction to the tensile modulus of the polyimide obtained by curing the polyamic acid of the (A) component of the resin composition of the present invention of 1 or more.

The resin composition of the present invention may have a ratio of the true specific gravity of the filler (B) to the true specific gravity of the polyimide obtained by curing the polyamic acid (A) in the range of 0.5 to 2.0.

In the resin composition of the present invention, the liquid crystal polymer of component (B) may have a relative dielectric constant in the range of 2.0 to 3.5 at 1 GHz, and a dielectric loss tangent of less than 0.003.

The method for producing a resin composition of the present invention is any one of the methods for producing a resin composition described above,
The method is characterized in that a shape-anisotropic filler made of a liquid crystal polymer of the component (B) is added before the reaction of synthesizing the polyamic acid by reacting the tetracarboxylic anhydride component with the diamine component is completed.

In the method for producing the resin composition of the present invention, a shape-anisotropic filler made of a liquid crystal polymer of component (B) may be added and mixed before the viscosity of the reaction solution of the tetracarboxylic anhydride component and the diamine component reaches 1500 cps.

The resin film of the present invention is a resin film including a polyimide layer,
The polyimide layer is characterized in that it contains polyimide and a filler having shape anisotropy and made of a liquid crystal polymer dispersed in the polyimide.

The resin film of the present invention may have a thermal expansion coefficient of the polyimide layer of 30 ppm/K or less.

In the resin film of the present invention, the polyimide layer may have a relative dielectric constant in the range of 2.0 to 3.8 at 10 GHz, and a dielectric loss tangent of 0.004 or less.

The resin film of the present invention may have a content of shape-anisotropic filler made of a liquid crystal polymer in the range of 1 to 70 volume % relative to the total amount of resin components in the polyimide layer.

In the resin film of the present invention, the liquid crystal polymer may be oriented in the longitudinal direction in the polyimide layer.

The metal-clad laminate of the present invention is a metal-clad laminate comprising an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer,
At least one of the insulating resin layers is made of any one of the resin films described above.

According to the present invention, a resin film is provided in which a liquid crystal polymer filler is dispersed in a polyimide, and which combines excellent dielectric properties with dimensional stability. The resin film of the present invention reduces loss in high-frequency signal transmission and maintains dimensional stability, making it suitable for use as a circuit board material for FPCs and other electronic devices.

1 is a photograph showing the appearance of a resin layer of a copper-clad laminate produced in Example 7.

The following describes an embodiment of the present invention.

[Resin composition]
The resin composition of the present embodiment comprises the following components (A) and (B):
(A) a polyamic acid obtained by reacting a tetracarboxylic acid anhydride component with a diamine component;
and (B) a shape-anisotropic filler made of a liquid crystal polymer (hereinafter sometimes referred to as "LCP filler");
Contains:

[Component A: Polyamic acid]
The polyamic acid of component A is a precursor of polyimide, and is obtained by reacting a tetracarboxylic anhydride component with a diamine component. Polyimide is a polymer having an imide group represented by the following general formula (1). When it further has an amide group or an ether bond, it may be called polyamideimide or polyetherimide, but in this specification, these are collectively described as polyimide. Polyimide can be produced by a known method in which substantially equimolar amounts of a diamine component and an acid dianhydride component are used and polymerized in an organic polar solvent. In this case, the molar ratio of the acid dianhydride component to the diamine component may be adjusted to set the viscosity in the desired range, and the range is preferably within a molar ratio of, for example, 0.98 to 1.03.

In general formula (1), _Ar1 represents a tetravalent group derived from an acid anhydride containing a tetracarboxylic dianhydride residue, _R2 represents a divalent diamine residue derived from a diamine, and n is an integer of 1 or more.

As the acid dianhydride, for example, an aromatic tetracarboxylic acid dianhydride represented by O(OC) ₂ --Ar ₁ --(CO) ₂ O is preferable, and examples thereof include those which give the following aromatic acid anhydride residue as Ar ₁ .

The acid dianhydrides can be used alone or in combination of two or more. Among these, it is preferable to use one selected from pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), and 4,4'-oxydiphthalic dianhydride (ODPA).

As the diamine, for example, a diamine represented by H ₂ N—R ₂ —NH ₂ is preferable, and examples thereof include diamines giving the following diamine residue as R ₂ .

Among these diamines, preferred examples include diaminodiphenyl ether (DAPE), 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), paraphenylenediamine (p-PDA), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,3-bis(3-aminophenoxy)benzene (APB), 1,4-bis(4-aminophenoxy)benzene (TPE-Q), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), and 2,2-bis(trifluoromethyl)benzidine (TFMB).

The synthesized polyamic acid is usually advantageously used as a reaction solvent solution, but if necessary, it can be concentrated, diluted, or replaced with another organic solvent to form a resin composition. There are no particular limitations on the method for imidizing the polyamic acid, and a suitable method is, for example, heat treatment in the solvent at a temperature within the range of 80 to 400°C for 1 to 24 hours.

[Component (B): LCP filler]
The LCP filler is made of a liquid crystal polymer. The liquid crystal polymer has almost no frequency dependence of the dielectric properties, has very excellent dielectric properties, and also contributes to improving flame retardancy, so by blending it as a filler, the dielectric properties and flame retardancy of the resin film can be improved. When blending for the purpose of improving the dielectric properties of the resin film, the LCP filler to be used alone has a relative dielectric constant at 1 GHz of preferably 2.0 to 3.5, more preferably 2.7 to 3.2, and a dielectric loss tangent of preferably less than 0.003, more preferably 0.002 or less.

The melting point of a liquid crystal polymer is sometimes called the liquid crystal transition temperature or liquid crystallization temperature, and is preferably 280°C or higher. More preferably, it is 295°C or higher, and even more preferably, it is 310°C or higher. If the melting point is below 280°C, the polymer may melt during the manufacturing process of electronic devices, etc., causing changes in the properties.

The liquid crystal polymer is not particularly limited, but is preferably one having a polyester structure such as known thermotropic liquid crystal polyesters and polyester amides derived from compounds classified into the following (1) to (4) and their derivatives.
(1) Aromatic or aliphatic dihydroxy compounds (2) Aromatic or aliphatic dicarboxylic acids (3) Aromatic hydroxycarboxylic acids (4) Aromatic diamines, aromatic hydroxyamines or aromatic aminocarboxylic acids

Representative examples of liquid crystal polymers obtained from these raw material compounds include copolymers having a combination of two or more structural units selected from the structural units shown in the following formulas (a) to (j), and preferably copolymers containing either the structural unit shown in formula (a) or the structural unit shown in formula (e), and more preferably copolymers containing the structural unit shown in formula (a) and the structural unit shown in formula (e). In addition, the more aromatic rings there are in the liquid crystal polymer, the more effective it is to improve dielectric properties and flame retardancy, so it is preferable to use an aromatic dihydroxy compound as the above (1) and an aromatic dicarboxylic acid as the above (2).

The LCP filler has shape anisotropy. Shape anisotropy means that the ratio (L/D) of the average major axis diameter (L) to the average minor axis diameter (D) of the LCP filler is 3 or more, and is preferably in the range of 3 to 200. Here, when imaginary rectangular parallelepipeds circumscribing the LCP filler in a linearly stretched state are assumed, the length of the shortest side of the three mutually perpendicular sides of the rectangular parallelepiped is defined as the minor axis diameter, and the length of the longest side is defined as the major axis diameter.

The average major axis diameter (L) of the LCP filler is preferably, for example, within the range of 50 to 3000 μm, and more preferably within the range of 100 to 1000 μm. The average minor axis diameter (D) of the LCP filler is preferably, for example, within the range of 1 to 50 μm, and more preferably within the range of 3 to 30 μm. If the average major axis diameter (L) and the average minor axis diameter (D) are within the above ranges, the surface smoothness of the resin film formed from the resin composition is not deteriorated, and a resin film with good appearance can be obtained.

Specific shapes of the LCP filler include, for example, fibrous (including needle-like) and plate-like. Examples of fibrous shapes include milled fibers, chopped fibers, cut fibers, etc. Examples of plate-like shapes include disk-like, flat, plate-like, flake-like, scale-like, and strip-like. The cross-sectional shape of the LCP filler is not limited to a circle, and may be a star-like, flower-like, cross-like, or hollow shape. By changing the cross-sectional shape of the LCP filler, it is possible to adjust the surface area of the LCP filler to control the adhesion to polyimide and to control the viscosity of the resin solution. From the viewpoint of ease of control of the CTE of the resin film, a short fiber-like LCP filler is particularly preferred.

It is preferable that the LCP filler is oriented so that its long axis direction and the longitudinal direction of the liquid crystal polymer molecules are roughly aligned. In order to orient the liquid crystal polymer molecules, it is important to go through a molding process by a melting step and an extrusion step, and in particular, it is preferable that the maximum shear rate u during extrusion calculated by the following formula is 10 ³ sec ^-1 or more, more preferably 10 ⁴ sec ^-1 or more.
u= 4Q/{π×(d/2) ³ }
[where Q is the polymer discharge amount ( ^cm3 /sec) passing through the cross section of the extrusion nozzle per unit time, and d is the length (cm) of the shortest diameter of the cross section of the extrusion nozzle, but in the case of a circular extrusion nozzle such as a tubular nozzle or a fine hole, for example, it is the diameter (cm).]
At such a maximum shear rate, the liquid crystal molecules are sufficiently oriented, and it becomes easier to obtain controllability of the CTE when used as an LCP filler.

If the orientation of the LCP filler is insufficient, the orientation can be controlled by stretching after the casting or extrusion process. The stretching process can be omitted by ejecting the resin from a small hole. To achieve this, the hole size (diameter) of the spinneret is preferably, for example, 1.0 mm or less, and more preferably 0.5 mm or less.

The LCP filler can be produced by bundling the long fibers produced by the above method and cutting them to a specified length or by crushing them. LCP filler can also be produced by crushing a molded product that has a high degree of orientation of the liquid crystal polymer molecules, without making it into fibers.

In order to reduce the CTE of the resin film, the tensile modulus of elasticity of the LCP filler in the major axis direction is preferably, for example, 20 GPa or more, and more preferably in the range of 40 to 200 GPa. In particular, it is preferable that the ratio (E _L /E _P ) of the tensile modulus of elasticity E _L of the LCP filler in the major axis direction to the tensile modulus of elasticity E P of the _polyimide obtained by curing the polyamic acid of component (A) is 1 or more. When the relationship between the tensile modulus of elasticity E _P of the polyimide that forms the matrix in the resin film and the tensile modulus of elasticity E _L of the LCP filler is E _L ≧E _P , the effect of reducing the CTE is large.

It is also preferable that the ratio (S _L /S _P ) of the true specific gravity S _L of the LCP filler to the true specific gravity S _P of the polyimide obtained by curing the polyamic acid of component (A) is within the range of, for example, 0.5 to 2.0. When the relationship between the true specific gravity S _P of the polyimide that forms the matrix in the resin film and the true specific gravity S _L of the LCP filler is within the above range, the dispersibility of the LCP filler is improved and the weight of the entire resin film can be reduced.

The LCP filler may be surface-modified to improve dispersibility and adhesion to polyimide. Examples of surface-modifying treatments include plasma treatment and coating treatment. The LCP filler may also have a core-sheath structure. A core-sheath structure in which the core is a liquid crystal polymer and the sheath is a resin that is highly adhesive to polyimide is preferred. Examples of resins that are highly adhesive to polyimide include thermoplastic resins such as polyimide, polyamide, perfluoroalkoxy fluororesin (PFA), and polyolefin.

The LCP filler can be selected from commercially available products as appropriate. For example, fibrous fillers such as Vectran (product name) and Beckley (product name) manufactured by Kuraray Co., Ltd., Sciberas (product name) manufactured by Toray Industries, Inc., and Zexion (product name) manufactured by KB Seiren Co., Ltd. can be preferably used. Two or more different types of LCP fillers may be used in combination.

[solvent]
The resin composition preferably further contains a solvent. Examples of the solvent include organic solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethylsulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, cresol, acetone, and methyl isobutyl ketone. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used in combination. The content of the solvent is not particularly limited, but it is preferable to adjust the amount of use so that the solid content concentration in the resin composition is about 5 to 50% by weight.

[Optional ingredients]
The resin composition may contain, as necessary, optional components such as resin components other than polyamic acid, flame retardants, crosslinking agents, curing accelerators, chemical catalysts, organic fillers other than LCP fillers, inorganic fillers, plasticizers, coupling agents, and pigments.

[composition]
The content of the LCP filler of component (B) in the resin composition can be appropriately set depending on the intended use of the resin film, but is preferably within the range of 1 to 70 volume % relative to the total amount of components (A) and (B), and more preferably within the range of 5 to 65 volume %. If the amount of LCP filler is less than the lower limit, the effect of improving the dielectric properties and the effect of reducing the CTE may not be sufficiently obtained, and if it exceeds the upper limit, the viscosity of the resin solution may increase, resulting in a decrease in handleability and a weakening of the resin film.
The solvent is preferably blended in an amount capable of dissolving the polyamic acid of component (A) and turning it into a solution.

[viscosity]
The viscosity of the resin composition is preferably within a range of, for example, 3000 cps to 100000 cps, more preferably 5000 cps to 50000 cps, which is a viscosity range that improves the handling properties when the resin composition is applied and makes it easy to form a coating film of uniform thickness. If the viscosity is outside the above range, defects such as uneven thickness and streaks are likely to occur in the film during coating work using a coater or the like.

[Method of producing resin composition]
It is preferable to add the LCP filler (B) to the resin composition before the reaction of synthesizing polyamic acid by reacting the tetracarboxylic anhydride component and the diamine component, which are the raw materials of the component (A), is completed. Even if the LCP filler is added after the synthesis reaction of polyamic acid is completed, the LCP filler is likely to aggregate, and the dispersion process after the aggregation is likely to become complicated. As a preferable guideline for the timing of adding the LCP filler, for example, it is preferable to add and mix the LCP filler before the viscosity of the reaction liquid of the tetracarboxylic anhydride component and the diamine component reaches 1500 cps. Even if the LCP filler is added after the viscosity of the reaction liquid reaches 1500 cps, a uniform mixed state cannot be obtained.

From the above viewpoints, it is more preferable to add the LCP filler to the tetracarboxylic anhydride component and/or the diamine component at a stage prior to reacting the tetracarboxylic anhydride component with the diamine component.
Specifically, after the tetracarboxylic anhydride component, the diamine component and the LCP filler are simultaneously mixed, the tetracarboxylic anhydride component and the diamine component are reacted with each other to promote the synthesis reaction of the polyamic acid.
Alternatively, the synthesis reaction of polyamic acid may be initiated by adding a diamine component to a mixture of a tetracarboxylic anhydride component and an LCP filler, and mixing the mixture.
Alternatively, the synthesis reaction of polyamic acid may be initiated by adding a tetracarboxylic anhydride component to a mixture of a diamine component and an LCP filler, and mixing the components together.
In either case, the raw materials, tetracarboxylic anhydride component, diamine component, and LCP filler, may be added all at once, or may be added little by little in several portions. Also, a solvent in which the LCP filler has been dispersed beforehand may be used.

[Resin film]
The resin film of the present embodiment includes a polyimide layer (hereinafter, sometimes referred to as an "LCP filler-containing polyimide layer") containing polyimide and LCP filler dispersed in the polyimide. The matrix resin of the LCP filler-containing polyimide layer is an imidized polyimide, in which the LCP filler is dispersed. The resin film may be a single layer or may be composed of multiple layers. That is, the entire resin film may be an LCP filler-containing polyimide layer, or may include a resin layer other than the LCP filler-containing polyimide layer. However, it is preferable that the LCP filler-containing polyimide layer is the main layer of the resin film. Here, the "main layer" means a layer having a thickness of more than 50% of the total thickness of the resin film.

The thermal expansion coefficient of the LCP filler-containing polyimide layer in the resin film is preferably 30 ppm/K or less, and more preferably within the range of 1 to 25 ppm/K, taking into consideration the dimensional stability as a circuit board material.

The dielectric constant of the LCP filler-containing polyimide layer at 10 GHz is preferably within the range of 2.0 to 3.8, and more preferably within the range of 2.5 to 3.5, in order to accommodate high-frequency signal transmission. The dielectric tangent of the LCP filler-containing polyimide layer at 10 GHz is preferably 0.004 or less, and more preferably 0.003 or less, in order to accommodate high-frequency signal transmission.

The content of the LCP filler relative to the total amount of resin components in the LCP filler-containing polyimide layer can be set appropriately depending on the purpose of use, but for example, it is preferably in the range of 1 to 70 volume %, and more preferably in the range of 5 to 65 volume %. If the content of the LCP filler is less than the lower limit, the effect of improving the dielectric properties and the effect of reducing the CTE may not be sufficiently obtained, and if it exceeds the upper limit, the viscosity of the resin solution may increase, resulting in a decrease in handleability and a weakening of the resin film. The volume ratio of the LCP filler in the LCP filler-containing polyimide layer can be calculated from an image obtained by a three-dimensional transmission electron microscope (TEM), or can be calculated from the weight ratio obtained by decomposition analysis by strong alkali dissolution or thermal decomposition analysis. It can also be calculated from the phase volume ratio measurement by X-ray diffraction and the area ratio of a cross-sectional SEM image.

In the LCP filler-containing polyimide layer, it is preferable that the liquid crystal polymer molecules are oriented in the longitudinal direction. In particular, from the viewpoint of improving dimensional stability, it is preferable that the longitudinal direction (MD direction) of the LCP filler-containing polyimide layer and the longitudinal direction of the liquid crystal polymer molecules are approximately the same direction. To achieve this, as described above, it is preferable to orient the LCP filler so that the long axis direction and the longitudinal direction of the liquid crystal polymer molecules are approximately aligned.

<Thickness>
The thickness of the resin film can be appropriately set depending on the purpose of use, but is preferably in the range of 2 to 150 μm, and more preferably in the range of 10 to 120 μm. If the thickness of the resin film is less than 2 μm, problems such as wrinkles may occur during transportation in the production of the resin film, while if the thickness of the resin film exceeds 150 μm, productivity of the resin film may decrease.

The resin film may be in the form of a film (sheet) and may be laminated to any substrate, such as copper foil, glass plate, polyimide film, polyamide film, or polyester film.

[Method of manufacturing resin film]
The resin film can be produced by heat-treating the resin composition and imidizing the polyamic acid to form an LCP filler-containing polyimide layer. The method of heat-treating the resin composition to obtain the LCP filler-containing polyimide layer is not particularly limited, and any known method can be used.

First, the resin composition is cast directly onto any supporting substrate to form a coating film. Next, the coating film is dried to remove a certain amount of the solvent at a temperature of 150°C or less. The coating film is then heat-treated for about 5 to 30 minutes at a temperature range of, for example, 100 to 400°C, preferably 130 to 380°C, to imidize the polyamic acid. In this way, an LCP filler-containing polyimide layer can be formed on the supporting substrate. If the heat treatment temperature for imidization is lower than 100°C, the dehydration ring-closing reaction of the polyimide does not proceed sufficiently, and conversely, if it exceeds 400°C, the polyimide layer may deteriorate.

When the resin film is formed by two or more polyimide layers, a first polyamic acid resin composition is applied and dried, and then a second polyamic acid resin composition is applied and dried. Thereafter, a third polyamic acid resin composition, a fourth polyamic acid resin composition, and so on are applied and dried in the same manner as many times as necessary. It is preferable to then collectively perform a heat treatment to perform imidization. It is sufficient that at least one of these layers is an LCP filler-containing polyimide layer.
In addition, by subjecting any imidized polyimide layer to an appropriate surface treatment, etc., it is possible to further overlay a new layer through the steps of coating a resin composition, drying and imidization. In this case, it is not necessary to complete the imidization in the middle steps, and the imidization can be completed all at once in the final step.
Furthermore, any imidized polyimide layer can be bonded by heating and pressing to a separately formed resin film.
The resin film may be attached to a supporting substrate.

Another example of forming a resin film will be given.
First, the resin composition is cast onto an arbitrary support substrate to form a film. This film-shaped molded product is heated and dried on the support substrate to form a gel film having self-supporting properties. After peeling the gel film from the support substrate, it is heat-treated for example at a temperature range of 100 to 400° C., preferably 130 to 380° C., for about 5 to 30 minutes to imidize the polyamic acid, thereby obtaining a resin film including an LCP filler-containing polyimide layer. The resin film may be stretched as necessary.

[Metal-clad laminate]
The metal-clad laminate of the present embodiment is a metal-clad laminate including an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer, and at least one of the insulating resin layers is made of a resin film produced by the above-mentioned method. The metal-clad laminate may be a single-sided metal-clad laminate having a metal layer on only one surface of the insulating resin layer, or a double-sided metal-clad laminate having metal layers on both surfaces of the insulating resin layer.

<Insulating resin layer>
The insulating resin layer is composed of a single layer or multiple layers, and includes a layer made of the resin film. For example, the resin film may form a non-thermoplastic polyimide layer as a main layer of the insulating resin layer to ensure mechanical properties and thermal properties. The resin film may also form a thermoplastic polyimide layer as an adhesive layer that provides adhesive strength to a metal layer such as a copper foil. The "main layer" refers to a layer that occupies more than 50% of the total thickness of the insulating resin layer.

Methods for manufacturing a metal-clad laminate with a resin film as an insulating resin layer include, for example, a method of heat-pressing a metal foil directly or via an arbitrary adhesive to a resin film, and a method of forming a metal layer on a resin film by a technique such as metal vapor deposition. Note that a double-sided metal-clad laminate can be obtained, for example, by forming a single-sided metal-clad laminate, and then arranging the polyimide layers to face each other and pressing them together by a heat press, or by pressing a metal foil onto the polyimide layer of a single-sided metal-clad laminate.

<Metal Layer>
The material of the metal layer is not particularly limited, and examples thereof include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and alloys thereof. Among these, copper or a copper alloy is particularly preferred. The metal layer may be made of a metal foil, or may be a film on which metal has been vapor-deposited or a paste or the like has been printed. Either a metal foil or a metal plate can be used, and copper foil or a copper plate is preferred.

The thickness of the metal layer is not particularly limited as it is set appropriately depending on the intended use of the metal-clad laminate, but is preferably in the range of 5 μm to 3 mm, and more preferably in the range of 12 μm to 1 mm. If the thickness of the metal layer is less than 5 μm, problems such as wrinkles may occur during transportation in the manufacture of the metal-clad laminate. Conversely, if the thickness of the metal layer exceeds 3 mm, it becomes hard and difficult to process.

The resin film and metal-clad laminate obtained in the above manner have excellent dielectric properties and dimensional stability due to the LCP filler dispersed in the polyimide. Therefore, the resin film and metal-clad laminate have reduced loss in high-frequency signal transmission and can maintain dimensional stability, making them suitable for use as circuit board materials such as FPCs in various electronic devices.

The following examples are provided to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to the examples. In the following examples, the various measurements and evaluations are as follows, unless otherwise noted.

[Viscosity measurement]
The viscosity was measured at 25° C. using an E-type viscometer (manufactured by Brookfield, product name: DV-II+Pro). The rotation speed was set so that the torque was 10% to 90%, and the value was read when the viscosity stabilized 1 minute after the start of the measurement.

[Measurement of coefficient of thermal expansion (CTE)]
The polyimide film was cut into a size of 3 mm in the TD direction × 20 mm in the MD direction, and using a thermomechanical analyzer (manufactured by Bruker, product name: 4000SA), the temperature was raised from 30°C to 260°C at a constant heating rate while applying a load of 5.0 g in the MD direction, and then the temperature was held for 10 minutes and then cooled at a rate of 5°C/min to determine the average thermal expansion coefficient (thermal expansion coefficient) from 250°C to 100°C.

[Melt point measurement]
The melting point was measured by increasing the temperature from room temperature to 450° C. at a rate of 1.5° C./min in an inert gas atmosphere using a differential scanning calorimeter (DSC, manufactured by SII, product name: DSC-6200).

[Measurement of tensile modulus]
(Resin film)
A test piece (width 12.7 mm × length 127 mm) was prepared from the resin film using a tension tester (manufactured by Orientec, product name: Tensilon). A tensile test was performed at 50 mm/min using this test piece to determine the tensile modulus at 25°C.
(Filler)
Ten long fibers before filler processing were randomly selected, and each was processed to a length of 200 mm. In accordance with the standard test of JIS L 1013 (2010), the tensile modulus of each long fiber was determined at a tensile speed of 200 mm/min using a tensile tester (manufactured by Shimadzu Corporation, product name: AGS-500NX) and expressed as an average value.

[Method for measuring average major axis diameter and average minor axis diameter]
Ten fillers were randomly selected and observed independently using a stereomicroscope. The major axis diameter and minor axis diameter of each of the selected fillers were measured and calculated as an average value.

[Measurement of true specific gravity]
The true specific gravity was measured by the pycnometer method (liquid phase displacement method) using a continuous automatic powder true density measuring device (manufactured by Seishin Enterprise Co., Ltd., product name: AUTO TRUE DENSERMAT-7000).

[Agglomeration Evaluation]
When applying the varnish to the support, 500 mL of the varnish was passed through a 500 μm gap coater, and the presence or absence of any solid matter that did not pass through was confirmed.

[Measurement of relative dielectric constant and dielectric loss tangent]
(Resin film)
Using a vector network analyzer (manufactured by Agilent, product name: Vector Network Analyzer E8363C) and an SPDR resonator, the relative dielectric constant (ε1) and dielectric loss tangent (Tan δ1) of the resin film (resin film after curing) at a frequency of 10 GHz were measured. The resin film used for the measurement was left for 24 hours under the conditions of temperature: 24 to 26°C and humidity: 45 to 55%.
(Liquid Crystal Polymer)
Using a vector network analyzer (manufactured by Agilent, product name: Vector Network Analyzer E8363C) and an SPDR resonator, the relative dielectric constant (ε1) and dielectric loss tangent (Tan δ1) at a frequency of 1 GHz of a sample obtained by melt-molding a liquid crystal polymer into a plate shape were measured. The sample used for the measurement was left for 24 hours under the conditions of temperature: 24 to 26°C and humidity: 45 to 55%.

[Cross-section observation]
1) Preparation of a measurement sample A copper-clad laminate (TD; 10 mm x MD; 10 mm) was embedded in epoxy resin so that the observation surface (cross section in the thickness direction) of the sample was in the MD direction, and then a rotating plate type polisher was used to polish the sample with multiple pieces of emery paper (up to #1200) and buff (diamond particle paste up to 1 μm), as well as chemical polishing with a chemical solution, to prepare a measurement sample.
2) Observation of Measurement Sample The observation surface of the measurement sample was observed at a magnification of 200 to 3000 times using a scanning electron microscope (SEM).

The abbreviations used in the examples and comparative examples represent the following compounds.
PMDA: pyromellitic dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl DMAc: N,N-dimethylacetamide Filler 1: Liquid crystal polymer having a polyester structure, short fiber shape, average minor axis diameter: 28 μm, average major axis diameter: 1000 μm, melting point (Tm): 350° C., true specific gravity: 1.4, tensile modulus: 85 GPa, relative dielectric constant: 3.1, dielectric dissipation factor: 0.0010
Filler 2: Liquid crystal polymer having a polyester structure, short fiber form, average minor axis diameter: 28 μm, average major axis diameter: 500 μm, melting point (Tm): 350° C., true specific gravity: 1.4, tensile modulus: 85 GPa, relative dielectric constant: 3.1, dielectric tangent: 0.0010
Filler 3: Liquid crystal polymer having a polyester structure, short fiber form, average minor axis diameter: 28 μm, average major axis diameter: 1000 μm, melting point (Tm): 330° C., true specific gravity: 1.4, tensile modulus: 160 GPa, relative dielectric constant: 3.4, dielectric loss tangent: 0.0020
Filler 4: Liquid crystal polymer having a polyester structure, short fiber form, average minor axis diameter: 14 μm, average major axis diameter: 1000 μm, melting point (Tm): 330° C., true specific gravity: 1.4, tensile modulus: 140 GPa, relative dielectric constant: 3.4, dielectric loss tangent: 0.0020
Filler 5: Liquid crystal polymer particles having a polyester structure, irregular shape, average minor axis diameter: 8 μm, average major axis diameter: 14 μm, melting point (Tm): 320° C., true specific gravity: 1.4, relative dielectric constant: 3.4, dielectric dissipation factor: 0.0010

[Example 1]
17 g of m-TB (82 mmol) and 230 g of DMAc were added to a 300 ml separable flask and stirred at room temperature under a nitrogen stream. After complete dissolution, 4.5 g of PMDA (20 mmol), 18 g of BPDA (62 mmol), and 4.2 g of filler 1 were added and stirred at room temperature for 18 hours to prepare resin solution 1 (viscosity: 30,000 cps, content of filler 1 relative to non-volatile components: 10% by volume).

Resin solution 1 was applied to a thickness of about 350 μm on copper foil (electrolytic copper foil, thickness: 12 μm) and dried for 5 minutes at 130° C. to form a resin layer. Then, heat treatment was carried out stepwise from 150° C. to 380° C. over 20 minutes to complete imidization, and copper-clad laminate 1 was prepared.
The copper foil of the copper-clad laminate 1 was removed by etching to prepare a resin film 1 (thickness: 48 μm). The resin film 1 had a CTE of 13 ppm/K, a relative dielectric constant of 3.1, and a dielectric loss tangent of 0.0039.

[Example 2]
Resin solution 2 (viscosity: 34,000 cps, content of filler 1 relative to non-volatile components: 30% by volume) was prepared in the same manner as in Example 1, except that the amount of filler 1 added in Example 1 was changed to 17 g, and 94 g of DMAc was further added after the addition of filler 1.

Resin solution 2 was applied to a thickness of about 350 μm on copper foil (electrolytic copper foil, thickness: 12 μm) and dried for 5 minutes at 130° C. to form a resin layer. Then, heat treatment was carried out stepwise from 150° C. to 380° C. over 20 minutes to complete imidization, and a copper-clad laminate 2 was prepared.
The copper foil of the copper-clad laminate 2 was removed by etching to prepare a resin film 2 (thickness: 37 μm). The resin film 1 had a CTE of 3 ppm/K, a relative dielectric constant of 2.3, and a dielectric loss tangent of 0.0035.

[Example 3]
Resin solution 3 (viscosity: 28,000 cps, content of filler 2 relative to non-volatile components: 10% by volume) was prepared in the same manner as in Example 1, except that 4.3 g of filler 2 was added instead of 4.2 g of filler 1 in Example 1, and 25 g of DMAc was further added after the addition of filler 2.

Resin solution 3 was applied to a thickness of about 350 μm on copper foil (electrolytic copper foil, thickness: 12 μm) and dried for 5 minutes at 130° C. to form a resin layer. Then, heat treatment was carried out stepwise from 150° C. to 380° C. over 20 minutes to complete imidization, and a copper-clad laminate 3 was prepared.
The copper foil of the copper-clad laminate 3 was removed by etching to prepare a resin film 3 (thickness: 55 μm). The resin film 3 had a CTE of 15 ppm/K, a relative dielectric constant of 2.8, and a dielectric loss tangent of 0.0037.

[Example 4]
Resin solution 4 (viscosity: 30,000 cps, content of filler 2 relative to non-volatile components: 30% by volume) was prepared in the same manner as in Example 2, except that filler 2 was used instead of filler 1 in Example 2.

Resin solution 4 was applied to a thickness of about 350 μm on copper foil (electrolytic copper foil, thickness: 12 μm) and dried for 5 minutes at 130° C. to form a resin layer. Then, heat treatment was carried out stepwise from 150° C. to 380° C. over 20 minutes to complete imidization, and copper-clad laminate 4 was prepared.
The copper foil of the copper-clad laminate 4 was removed by etching to prepare a resin film 4 (thickness: 67 μm). The resin film 4 had a CTE of 8 ppm/K, a relative dielectric constant of 2.5, and a dielectric loss tangent of 0.0034.

[Example 5]
Resin solution 5 (viscosity: 45,000 cps, content of filler 2 relative to non-volatile components: 60% by volume) was prepared in the same manner as in Example 1, except that 34 g of filler 2 was added instead of 4.2 g of filler 1 in Example 1, and that 180 g of DMAc was further added after the addition of filler 2.

Resin solution 5 was applied to a thickness of about 350 μm on copper foil (electrolytic copper foil, thickness: 12 μm) and dried for 5 minutes at 130° C. to form a resin layer. Then, heat treatment was carried out stepwise from 150° C. to 380° C. over 20 minutes to complete imidization, and copper-clad laminate 5 was prepared.
The copper foil of the copper-clad laminate 5 was removed by etching to prepare a resin film 5 (thickness: 67 μm). The resin film 5 had a CTE of 2 ppm/K, a relative dielectric constant of 3.0, and a dielectric loss tangent of 0.0029.

[Example 6]
A resin solution 6 (viscosity: 30,000 cps, content of filler 3 relative to non-volatile components: 10% by volume) was prepared in the same manner as in Example 1, except that filler 3 was used instead of filler 1 in Example 1.

Resin solution 6 was applied to a thickness of about 350 μm on copper foil (electrolytic copper foil, thickness: 12 μm) and dried for 5 minutes at 130° C. to form a resin layer. Then, heat treatment was carried out stepwise from 150° C. to 380° C. over 20 minutes to complete imidization, and a copper-clad laminate 6 was prepared.
The copper foil of the copper-clad laminate 6 was removed by etching to prepare a resin film 6 (thickness: 50 μm). The resin film 6 had a CTE of 18 ppm/K, a relative dielectric constant of 3.1, and a dielectric loss tangent of 0.0039.

[Example 7]
Resin solution 7 (viscosity: 28,000 cps, content of filler 4 relative to non-volatile components: 10% by volume) was prepared in the same manner as in Example 1, except that filler 4 was used instead of filler 1 in Example 1.

Resin solution 7 was applied to a thickness of about 350 μm on copper foil (electrolytic copper foil, thickness: 12 μm) and dried at 130° C. for 5 minutes to form a resin layer. Then, heat treatment was performed stepwise from 150° C. to 380° C. over 20 minutes to complete imidization, and copper-clad laminate 7 was prepared. The cross-sectional structure of the obtained copper-clad laminate 7 is shown in FIG. 1. A cross section in the minor axis direction of filler 4 oriented in polyimide was confirmed.
The copper foil of the copper-clad laminate 7 was removed by etching to prepare a resin film 7 (thickness: 45 μm). The resin film 7 had a CTE of 16 ppm/K, a relative dielectric constant of 3.0, and a dielectric loss tangent of 0.0040.

(Comparative Example 1)
Polyamic acid solution 1 was applied to a thickness of about 500 μm on copper foil (electrolytic copper foil, thickness: 12 μm) and dried for 5 minutes at 130° C. to form a resin layer. Then, heat treatment was carried out stepwise from 150° C. to 380° C. over 20 minutes to complete imidization, and a copper-clad laminate 8 was prepared.
The copper foil of the copper-clad laminate 8 was removed by etching to prepare a resin film 8 (thickness: 41 μm). The resin film 8 had a CTE of 19 ppm/K, a relative dielectric constant of 3.4, a dielectric loss tangent of 0.0041, a true specific gravity of 1.4, and a tensile modulus of elasticity of 8 GPa.

(Comparative Example 2)
140 g of the polyamic acid solution 1 and 8.3 g of the filler 3 were mixed and stirred to prepare a resin solution 9 (content of the filler 3 relative to the non-volatile components: 30% by volume).

When resin solution 9 was applied to a thickness of approximately 350 μm on copper foil (electrolytic copper foil, thickness: 12 μm), the agglomerated solids of the filler clogged the gap between the coaters. Even when the gap was expanded to 500 μm, the same clogging of solids occurred.

(Reference Example 1)
A resin solution 10 (viscosity: 28,000 cps, content of filler 5 relative to non-volatile components: 30% by volume) was prepared in the same manner as in Example 1, except that 7 g of filler 5 was used instead of filler 1 in Example 1.

The resin solution 10 was applied to a thickness of about 350 μm on a copper foil (electrolytic copper foil, thickness: 12 μm) and dried for 5 minutes at 130° C. to form a resin layer. Then, heat treatment was carried out stepwise from 150° C. to 380° C. over 20 minutes to complete the imidization, and a copper-clad laminate 10 was prepared.
The copper foil of the copper-clad laminate 10 was removed by etching to prepare a resin film 10 (thickness: 45 μm). The resin film 10 had a CTE of 33 ppm/K, a relative dielectric constant of 3.3, and a dielectric loss tangent of 0.0030.

The above results are summarized in Table 1.

The results of Examples 1 to 7 and Comparative Example 1 confirmed that the addition of Fillers 1 to 4 could reduce the dielectric constant and dielectric tangent while suppressing the increase in CTE. In Comparative Example 2 (blending method), the fillers became entangled in the resin liquid, causing aggregation and making coating impossible. In Reference Example 1, the dielectric tangent decreased, but the CTE increased significantly.

The above describes in detail an embodiment of the present invention for illustrative purposes, but the present invention is not limited to the above embodiment and various modifications are possible.

Claims (17)

The following components (A) and (B):
(A) a polyamic acid which is a precursor of a non-thermoplastic polyimide obtained by reacting a tetracarboxylic anhydride component with a diamine component;
and (B) a filler having shape anisotropy made of a liquid crystal polymer;
A resin composition comprising:
the ratio (L/D) of the average major axis diameter (L) to the average minor axis diameter (D) of the filler of component (B) is within the range of 3 to 200;
A resin composition in which no solid matter is present that does not pass through when 500 mL of the resin composition is passed through a 500 μm gap coater . 2. The resin composition according to claim 1 , wherein the filler of component (B) has an average major axis diameter (L) in the range of 50 to 3000 μm and an average minor axis diameter (D) in the range of 1 to 50 μm. 3. The resin composition according to claim 1 , wherein the content of the filler in the component (B) is within a range of 1 to 70 volume % relative to the total amount of the components (A) and (B). The resin composition according to claim 1 , wherein the liquid crystal polymer has a melting point of 280° C. or higher . The resin composition according to claim 1 , wherein the liquid crystal polymer has a polyester structure. The resin composition according to claim 1 , wherein the filler of component (B) has a tensile modulus of elasticity in the major axis direction of 20 GPa or more. 7. The resin composition according to claim 1, wherein the ratio of the tensile modulus of the filler of component (B) in the major axis direction to the tensile modulus of the non-thermoplastic polyimide obtained by curing the polyamic acid of component (A) is 1 or more. The resin composition according to any one of claims 1 to 7 , wherein the ratio of the true specific gravity of the filler of component (B) to the true specific gravity of the non-thermoplastic polyimide obtained by curing the polyamic acid of component (A) is within the range of 0.5 to 2.0. The resin composition according to any one of claims 1 to 8 , wherein the liquid crystal polymer of component (B) has a relative dielectric constant in the range of 2.0 to 3.5 at 1 GHz and a dielectric loss tangent of less than 0.003. The following components (A) and (B):
(A) a polyamic acid obtained by reacting a tetracarboxylic acid anhydride component with a diamine component;
as well as
(B) a filler having shape anisotropy made of a liquid crystal polymer;
A method for producing a resin composition comprising the steps of:
the ratio (L/D) of the average major axis diameter (L) to the average minor axis diameter (D) of the filler of component (B) is within the range of 3 to 200;
A method for producing a resin composition, comprising adding a shape-anisotropic filler made of a liquid crystal polymer of the component (B) before completion of a reaction in which the tetracarboxylic anhydride component and the diamine component are reacted to synthesize the polyamic acid. The method for producing a resin composition according to claim 10, wherein a filler having shape anisotropy made of a liquid crystal polymer of the component (B) is added and mixed before the viscosity of the reaction liquid of the tetracarboxylic anhydride component and the diamine component reaches 1500 cps. A resin film including a polyimide layer,
the polyimide layer contains a non-thermoplastic polyimide and a filler having shape anisotropy and made of a liquid crystal polymer dispersed in the non-thermoplastic polyimide ,
the ratio (L/D) of the average major axis diameter (L) to the average minor axis diameter (D) of the filler is within a range of 3 to 200;
A resin film, wherein a ratio (E _L /E _P ) of a tensile modulus of elasticity E _L in the major axis direction of said filler to a tensile modulus of elasticity E _P of said non-thermoplastic polyimide is 1 or more . The resin film according to claim 12 , wherein the polyimide layer has a thermal expansion coefficient of 30 ppm/K or less. 14. The resin film according to claim 12 , wherein the polyimide layer has a relative dielectric constant in the range of 2.0 to 3.8 at 10 GHz and a dielectric loss tangent of 0.004 or less. The resin film according to any one of claims 12 to 14 , wherein the content of the shape-anisotropic filler made of a liquid crystal polymer relative to the total amount of resin components in the polyimide layer is within the range of 1 to 70 volume %. The resin film according to claim 12 , wherein the liquid crystal polymer is oriented in the longitudinal direction in the polyimide layer. A metal-clad laminate comprising an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer,
A metal-clad laminate, wherein at least one of the insulating resin layers is the resin film according to any one of claims 12 to 16 .