JP2021105148A - Resin composition, resin film and metal-clad laminate - Google Patents

Abstract

To provide a resin composition that is adaptable to a higher frequency of an electronic apparatus by further improving dielectric characteristics of a resin film using polyimide as a raw material and to provide a resin film.SOLUTION: The resin composition contains a solid component of an organic compound containing polyamic acid or polyimide and silica particles. The content of silica particles is in the range of 10 to 85 wt% based on the sum of the total amount of the solid component and the silica particles, and the silica particles as a whole have a ratio of the total area of peaks derived from a cristobalite crystal phase and a quartz crystal phase to the whole peak area derived from SiO2 in the range of 2θ=10° to 90° of an X-ray diffraction analysis spectrum by a CuKα ray of 20 wt% or more.SELECTED DRAWING: None

Description

The present invention relates to resin compositions, resin films and metal-clad laminates that are useful, for example, as circuit board materials.

In recent years, the use of thin and lightweight flexible printed wiring boards (FPCs) has been increasing along with the miniaturization, weight reduction, and space saving of electronic devices. Since FPC can be mounted three-dimensionally and at high density even in a limited space, its use is expanding to wiring of moving parts of electronic devices and parts such as cables and connectors. In addition to these, the speed of communication equipment and the performance of equipment are increasing, and an FPC compatible with high-frequency transmission signals for achieving a high transmission speed is also required.

An issue in transmitting high-frequency signals is transmission loss in the signal transmission path. If the transmission loss is large, inconveniences such as electrical signal loss and signal delay occur. In order for FPCs to cope with high frequencies, it is important to reduce the dielectric constant of the insulating resin layer and reduce the transmission loss by lowering the dielectric loss tangent. Therefore, in the FPC for high-frequency signals, a liquid crystal polymer or a fluororesin having a low dielectric constant and a low dielectric loss tangent is used as the insulating resin layer. However, although the liquid crystal polymer has excellent dielectric properties, there is room for improvement in heat resistance and adhesiveness to the metal foil, and the fluororesin has a high coefficient of thermal expansion and is not easy to handle.

Polyimide is also used as an insulating resin having excellent heat resistance and adhesiveness to metal foil. However, in general, polyimide is inferior in dielectric properties to liquid crystal polymers and fluororesins. As a method of reducing the dielectric value of the aromatic polyimide, there is a method of incorporating an aliphatic structure into the resin skeleton. However, the merit of incorporating the aliphatic structure into the resin skeleton is often a trade-off relationship with the required characteristics of FPC such as heat resistance and dimensional stability. As another means, such as using a special monomer or an expensive fluorine-based monomer, in order to reduce the dielectric while maintaining the excellent heat resistance and the required characteristics of FPC only with the polyimide skeleton, in terms of cost and productivity. There are various hurdles.

Therefore, a method of improving the characteristics by combining a resin and a different material is known. For example, Patent Document 1 reports a polyimide composition having excellent thermal conductivity by combining a powder of aluminum nitride or silicon nitride with a specific polyimide.
Further, in Patent Document 2, the occurrence of warpage and cracks in the semiconductor package is suppressed by adding cristobalite silica to the epoxy resin.
Composite is also effective in improving the dielectric properties, and in Patent Document 3, a resin having a low dielectric loss tangent and low thermal expansion is a combination of a thermosetting polyimide resin synthesized from amorphous silica and bismaleimide and an elastomer. I am proposing a film. Further, Patent Document 4 presents a method for producing a low-dielectric polyimide film in which polyimide and fluororesin particles are combined.

Japanese Patent No. 3551687 JP-A-2019-1937 Japanese Unexamined Patent Publication No. 2018-12747 Japanese Patent No. 6387181

As described above, it has been desired to develop a polyimide having a low dielectric weight while maintaining characteristics such as high heat resistance and excellent adhesiveness. However, Patent Document 3 is limited to thermosetting resins, and there is a problem in adhesive strength when multilayered. Further, Patent Document 4 is a composite with a relatively expensive fluororesin filler, and has a problem that the coefficient of thermal expansion becomes high.
Furthermore, the composition of the filler is emphasized in the composite of the prior art, and there is almost no mention of its crystal structure.

Therefore, an object of the present invention is to provide a resin composition and a resin film capable of coping with high frequency of electronic devices by further improving the dielectric property of polyimide.

The present inventors have found that in the composite of a polyimide resin and silica particles, the dielectric properties of silica particles having a high proportion of the cristobalite phase are improved as compared with amorphous silica. The heading, the present invention was completed.

That is, the resin composition of the present invention contains a solid content of an organic compound containing polyamic acid or polyimide and silica particles.
The content of the silica particles is in the range of 10 to 85% by weight (however, polyamic acid is converted to imidized polyimide) with respect to the total amount of the solid content and the total of the silica particles.
The ratio of the total area of the peaks derived from the cristobalite crystal phase and the quartz crystal phase to the total peak area derived from _{SiO 2} in the range of 2θ = 10 ° to 90 ° in the X-ray diffraction analysis spectrum using CuKα rays for the entire silica particles. Is 20% by weight or more.

_{The resin composition of the present invention may have a median diameter D 50} in the range of 6 to 20 μm in the frequency distribution curve of the silica particles obtained by volume-based particle size distribution measurement by a laser diffraction / scattering method.

In the resin composition of the present invention, 90% by weight or more of the silica particles having a particle size of 3 μm or more may have a circularity of 0.7 or more.

In the resin composition of the present invention, 90% by weight or more of the silica particles may have a true specific gravity of 2.3 or more.

The resin film of the present invention is a resin film having a single layer or a plurality of polyimide layers, and at least one of the polyimide layers is a crystalline silica-containing polyimide layer formed of any of the above resin compositions. Yes, the thickness of the crystalline silica-containing polyimide layer is in the range of 15 μm to 200 μm.

In the resin film of the present invention, the ratio of the thickness of the crystalline silica-containing polyimide layer to the total thickness of the resin film may be 50% or more.

The resin film of the present invention may have a relative permittivity of 3.1 or less at a frequency of 3 to 20 GHz as measured by a split post dielectric resonator (SPDR).

The resin film of the present invention may have a dielectric loss tangent of 0.005 or less at a frequency of 3 to 20 GHz as measured by a split post dielectric resonator (SPDR).

The resin film of the present invention may have a coefficient of thermal expansion of 50 ppm / K or less.

The metal-clad laminate of the present invention includes an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer, and at least one layer of the insulating resin layer is any one of the above. It is made of a resin film.

The resin composition of the present invention is excellent in dielectric properties because it contains silica particles having a specific crystal structure in addition to the original heat resistance of polyimide. Therefore, the resin composition and the resin film of the present invention can be particularly preferably used as a circuit board material for FPCs and the like in electronic devices that require high-speed signal transmission. Specifically, it is suitable for applications such as an insulating resin layer for FPCs for mobile devices such as smartphones that handle high-frequency signals, and an insulating resin layer for in-vehicle FPCs that require heat resistance.

Hereinafter, embodiments of the present invention will be described.

[Resin composition]
The resin composition according to the embodiment of the present invention is a resin composition containing a solid content of an organic compound containing polyamic acid or polyimide and silica particles.
The content of the silica particles is in the range of 10 to 85% by weight based on the total amount of the solid content and the total amount of the silica particles.
The ratio of the total area of the peaks derived from the cristobalite crystal phase and the quartz crystal phase to the total peak area derived from _{SiO 2} in the range of 2θ = 10 ° to 90 ° in the X-ray diffraction analysis spectrum using CuKα rays for the entire silica particles. Is 20% by weight or more. The resin composition may be a varnish (resin solution) containing a polyamic acid, or a polyimide solution containing a solvent-soluble polyimide.

[Solid content of organic compounds]
The solid content of the organic compound means the remaining solid content obtained by removing the solvent and the inorganic solid content from the resin composition. That is, the solid content of the organic compound contains polyamic acid or polyimide, and as optional components, resins other than polyimide, cross-linking agents, organic fillers, plasticizers, curing accelerators, coupling agents, organic pigments, organic flame retardants. , Non-volatile organic compounds such as fillers can be contained. Here, examples of the resin other than polyimide include epoxy resin, fluororesin, olefin resin, polyether resin, polyester resin and the like. Examples of the cross-linking agent include amino compounds having at least two primary amino groups as functional groups (amino compounds for cross-linking), which will be described later. Examples of the organic filler include liquid crystal polymer particles, fluorine-based polymer particles, polyether-based resin particles, and olefin-based resin particles.

The content of polyamic acid or polyimide in the solid content of the organic compound is preferably 60% by weight or more, more preferably 70% by weight or more, and most preferably 80% by weight or more. When the content of the polyamic acid or the polyimide is less than 60% by weight, the toughness of the resin is lowered and the film retention when the resin film is formed is lowered. In the case of polyamic acid, the weight ratio shall be calculated by converting to imidized polyimide.

[Polyamic acid or polyimide]
Polyimide is generally represented by the following general formula (1). Such a polyimide can be produced by a known method in which a diamine component and an acid dianhydride component are substantially equimolarized 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 in order to bring the viscosity into a desired range, and the range is, for example, within the range of the molar ratio of 0.98 to 1.03. It is preferable to do so.

Here, Ar ₁ is a tetravalent organic group having one or more aromatic rings, and Ar ₂ is a divalent organic group having one or more aromatic rings. And Ar ₁ can be said to be a residue of acid dianhydride, and Ar ₂ can be said to be a residue of diamine. Further, n represents the number of repetitions of the structural unit of the general formula (1), and is a number of 200 or more, preferably 300 to 1000.

As the acid dianhydride, for example, _{an aromatic tetracarboxylic dianhydride represented by O (OC) 2-} Ar _1- (CO) ₂ O is preferable, and the following aromatic acid anhydride residue is designated as _{Ar 1.} What is given is exemplified.

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

As the diamine, for example, an aromatic diamine represented by _{H 2} N-Ar _2- NH ₂ is preferable, and an aromatic diamine that gives the following aromatic _{diamine residue as Ar 2 is exemplified.}

Among these diamines, diaminodiphenyl ether (DAPE), 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), para-phenylenediamine (p-PDA), 1,3-bis (4-amino) Phenoxy) 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) are exemplified as suitable ones.

Polyimide can be produced by reacting an acid dianhydride with a diamine compound in a solvent to produce a polyamic acid as a precursor, and then heating and ring-closing (imidizing) the polyimide. For example, a polyamic acid can be obtained by dissolving an acid dianhydride and a diamine compound in substantially equimolar amounts in an organic solvent, stirring at a temperature in the range of 0 to 100 ° C. for 30 minutes to 72 hours, and carrying out a polymerization reaction. In the reaction, the reaction components are dissolved in an organic solvent so that the precursor produced is in the range of 5 to 30% by weight, preferably in the range of 10 to 20% by weight. Examples of the organic solvent used in the polymerization reaction include N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N, N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2 -Butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethylsulfate, cyclohexanone, dioxane, tetrahydrofuran, diglime, triglime, cresol and the like can be mentioned. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can be used in combination. The amount of such an organic solvent used is not particularly limited, but it should be adjusted so that the concentration of the polyamic acid solution obtained by the polymerization reaction is about 5 to 30% by weight. Is preferable.

The synthesized polyamic acid is usually advantageous to be 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. The method for imidizing the polyamic acid is not particularly limited, and for example, a heat treatment such as heating in the solvent under a temperature condition in the range of 80 to 400 ° C. for 1 to 24 hours is preferably adopted.

The polyimide may be a thermoplastic polyimide or a thermosetting polyimide. The "thermoplastic polyimide" is generally a polyimide whose glass transition temperature (Tg) can be clearly confirmed, but in the present invention, it is measured at 30 ° C. using a dynamic viscoelastic modulus measuring device (DMA). A polyimide having a storage elastic modulus of 1.0 × 10 ⁸ Pa or more and a storage elastic modulus of ^{less than 3.0 × 10 7 Pa at 300 ° C.} The "non-thermoplastic polyimide" is a polyimide that generally does not soften or show adhesiveness even when heated, but in the present invention, it was measured using a dynamic viscoelasticity measuring device (DMA). A polyimide having a storage elastic modulus of 1.0 × 10 ⁹ Pa or more at ° C. and a storage elastic modulus of 3.0 × 10 ⁸ Pa or more at 300 ° C.

[Silica particles]
The silica particles may include crystalline silica particles. It may also contain amorphous silica particles. By blending crystalline silica particles with the resin composition, it is possible to reduce the dielectric loss tangent when the resin film is formed. From the viewpoint of achieving low dielectric loss tangent when the resin film is formed, it is particularly preferable to use silica particles having a cristobalite crystal phase as the crystalline silica particles. Silica particles having a cristobalite crystal phase have extremely excellent dielectric properties as compared with general silica particles (for example, silica particles containing 90% by weight or more of a cristobalite crystal phase alone have a dielectric loss tangent at 10 GHz. (Approximately 0008), which can greatly contribute to the low dielectric loss tangent of the resin film.

_{Further, the silica particles preferably have a median diameter D 50} in the range of 6 to 20 μm and 8 to 15 μm in the frequency distribution curve obtained by the volume-based particle size distribution by the laser diffraction / scattering method. Within this range, a low-dielectric resin film can be obtained without effectively increasing the dielectric properties and deteriorating the surface smoothness when blended in the resin film. When the median diameter D ₅₀ is less than the above range, the surface area of the silica particles increases, and the adsorbed water on the surface of the silica particles may affect the dielectric properties. If the median diameter D ₅₀ exceeds the above range, it may appear as unevenness on the surface of the film and deteriorate the smoothness of the film surface.

Further, as the silica particles, it is preferable to use spherical silica particles. Spherical silica particles are silica particles having a shape close to a true sphere, and the ratio of the average major axis to the average minor axis is close to 1 or 1. Further, in order to enhance the dispersibility and dielectric property improving action of the silica particles, 90% by weight or more of the silica particles having a particle diameter of 3 μm or more preferably have a circularity of 0.7 or more, and preferably 0.9 or more. Is more preferable. The circularity of the silica particles can be determined by the image analysis method, assuming a circle having the same projected area as the photographed particles, and the ratio of the perimeter of the circle to the perimeter of the particles. If the circularity is less than 0.7, the surface area increases, the dielectric properties may be adversely affected, and the viscosity increases when blended in the resin solution, making handling difficult. Further, even in the sphericity obtained three-dimensionally, a value substantially corresponding to the value of the circularity is preferable.

Further, the silica particles preferably have a true specific gravity of 2.3 or more in order to enhance the dispersibility of the silica particles and the effect of improving the dielectric properties. If the true specific gravity is less than 2.3, it is suggested that the crystallinity of the silica particles is small, and the effect of improving the dielectric properties is reduced.

The silica particles may be surface-treated. A known technique can be used for the surface treatment, and for example, modification by corona treatment, plasma treatment, UV treatment or the like, functionalization treatment using a silane coupling agent or the like, or the like is preferable. By surface-treating the silica particles, an alkyl group, an amino group, an alkoxy group, etc. are imparted to the particle surface to improve the affinity with the solvent or polyamic acid, or to improve the repulsive force between the particles. , The dispersibility of silica particles and the long-term stability of varnish are improved.

From the viewpoint of achieving low dielectric normal contact when the resin film is formed, the entire aggregate of silica crystals used is derived from _{SiO 2 in the range of 2θ = 10 ° to 90 ° in the X-ray diffraction analysis spectrum using CuKα rays.} The ratio of the total area of the peaks derived from the cristobalite crystal phase and the quartz crystal phase to the total area of all peaks is preferably 20% by weight or more, more preferably 40% by weight or more, and preferably 80% by weight or more. By increasing the ratio of the cristobalite crystal phase and / or the quartz crystal phase in the entire silica particles, it is possible to further reduce the dielectric loss tangent of the polyimide. If the ratio of the area of the peak derived from the cristobalite crystal phase and the quartz crystal phase to the entire silica particles is less than 20% by weight, the effect of improving the dielectric property becomes unclear. The proportion of the cristobalite crystal phase is measured within the range of 10 ° ≤ 2θ ≤ 90 ° by X-ray diffraction (XRD) using α-radiation for all silica particles in a uniformly mixed state. It is obtained by the ratio of the total area of the diffraction peaks derived from the quartz crystal phase and the total area of the diffraction peaks derived from all the silica particles within the above range. If the target peak in the X-ray diffraction analysis spectrum is difficult to separate from the amorphous broad peak or overlaps with other crystal phase peaks, various known analysis methods such as the internal standard method and PONKCS The law etc. can be used.

As a preferred embodiment, an aggregate of silica particles having a cristobalite crystal phase ratio of 50% by weight or more can be used. In a more preferred embodiment, a part of the aggregate of silica particles having a cristobalite crystal phase ratio of 90% by weight or more (for example, 80% by weight or less of the whole) is replaced with amorphous silica particles. Can be done. The alternative use of amorphous silica particles can be performed as needed, which has the advantage of reducing costs, high-density filling and adjusting the solution viscosity, and preparing a resin composition with excellent handleability. There is.

As the silica particles, commercially available products can be appropriately selected and used. As the crystalline silica particles, for example, spherical cristobalite silica powder (manufactured by Nittetsu Chemical & Materials Co., Ltd., trade name; CR10-20) can be preferably used. Further, as amorphous silica particles that can be blended in combination with crystalline silica particles, spherical amorphous silica powder (manufactured by Nittetsu Chemical & Materials Co., Ltd., trade name; SC70-2, trade name: SP40-10) and the like can be used. Can be used. Further, two or more different types of silica particles may be used in combination as the silica particles.

[Composite composition]
The content of the silica particles in the resin composition is 10 to 85% by weight based on the total amount of the solid content of the organic compound and the silica particles in the resin composition (however, the polyamic acid is converted into imidized polyimide). It is within the range, preferably within the range of 10 to 80% by weight, and more preferably within the range of 15 to 75% by weight. If the content ratio of the silica particles is less than 10% by weight, the effect of lowering the dielectric loss tangent cannot be sufficiently obtained. Further, when the content ratio of the silica particles exceeds 85% by weight, the properties such as the adhesiveness of the polyimide deteriorate, and particularly when the content ratio of the silica particles exceeds 80% by weight, the resin film becomes brittle when formed. When the bendability is lowered and the resin film is to be formed, the viscosity of the resin composition is increased and the workability is also lowered.

[Arbitrary component]
The resin composition of the present embodiment can contain an organic solvent. Examples of the organic solvent include N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N, N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, and dimethyl. Examples thereof include sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethylformamide, cyclohexanone, dioxane, tetrahydrofuran, diglime, triglime, cresol and the like. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can be used in combination. The content of the organic solvent is not particularly limited, but it is preferable to adjust the content so that the concentration of polyamic acid or polyimide is about 5 to 30% by weight.

The resin composition of the present invention is appropriately blended with an inorganic filler other than silica, an inorganic pigment, an inorganic flame retardant, an inorganic heat radiating agent and the like as optional components as long as the effects of the invention are not impaired. Can be done. Examples of inorganic fillers other than silica particles include aluminum oxide, magnesium oxide, beryllium oxide, niobium oxide, titanium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, calcium fluoride, magnesium fluoride, and potassium fluoride. , Phosphinate metal salt and the like. These can be used alone or in admixture of two or more.

[viscosity]
The viscosity of the resin composition is preferably in the range of, for example, 3000 cps to 100,000 cps, and is preferably in the range of 5000 cps to 100,000 cps as a viscosity range in which the handleability at the time of coating the resin composition grains is enhanced and a coating film having a uniform thickness is easily formed. It is more preferably within the range of 50,000 cps. If it is out of the above viscosity range, defects such as thickness unevenness and streaks are likely to occur in the film during coating work by a coater or the like.

[Preparation of resin composition]
When preparing the resin composition, for example, silica particles may be directly blended into a resin solution of polyamic acid prepared using an arbitrary solvent. Alternatively, in consideration of the dispersibility of the silica particles, the silica particles are previously mixed in a reaction solvent containing either one of the acid dianhydride component and the diamine component, which are the raw materials of the polyamic acid, and then the other raw material is stirred. May be charged to allow the polymerization to proceed. In either method, the entire amount of silica particles may be added at one time, or may be added little by little in several portions. In addition, the raw materials may be added all at once, or may be divided into several times and mixed little by little.

[Resin film]
The resin film of the present embodiment is a resin film having a single layer or a plurality of polyimide layers, and at least one layer, preferably all of the polyimide layers, is a crystalline silica-containing polyimide formed of the above resin composition. It may be a layer.

In the resin film, the thickness of the crystalline silica-containing polyimide layer formed by the resin composition is preferably in the range of, for example, 15 to 200 μm, and more preferably in the range of 20 to 150 μm. If the thickness of the crystalline silica-containing polyimide layer is less than 15 μm, the silica particles protrude to the surface of the resin film, resulting in poor surface smoothness. On the contrary, if the thickness of the crystalline silica-containing polyimide layer exceeds 200 μm, the bendability of the resin film is lowered, which tends to be disadvantageous.

The thickness of the entire resin film is, for example, in the range of 15 to 200 μm, preferably in the range of 20 to 200 μm, and more preferably in the range of 25 to 200 μm. If the thickness of the resin film is less than 15 μm, problems such as wrinkles in the metal foil and tearing of the resin film are likely to occur in the transport process during the production of the metal-clad laminate. On the contrary, if the thickness of the resin film exceeds 200 μm, the bendability of the resin film is lowered, which tends to be disadvantageous.

The ratio of the thickness of the crystalline silica-containing polyimide layer to the total thickness of the resin film is preferably 50% or more with respect to the total thickness. If the ratio of the thickness of the crystalline silica-containing polyimide layer to the total thickness of the resin film is less than 50%, the effect of improving the dielectric properties cannot be sufficiently obtained.

The method for forming the crystalline silica-containing polyimide layer is not particularly limited, and a known method can be adopted. Here, the most typical example is shown.
First, the resin composition is cast and applied directly onto an arbitrary supporting base material to form a coating film. Next, the solvent is dried and removed from the coating film at a temperature of 150 ° C. or lower to some extent. When the resin composition contains a polyamic acid, the coating film is then further heat-treated for imidization in a temperature range of 100 to 400 ° C., preferably 130 to 360 ° C. for about 5 to 30 minutes. In this way, the crystalline silica-containing polyimide layer can be formed on the supporting base material.
When forming two or more polyimide layers, a resin solution of the first polyamic acid is applied and dried, and then a resin solution of the second polyamic acid is applied and dried. After that, in the same manner, the resin solution of the third polyamic acid, then the resin solution of the fourth polyamic acid, and so on, the resin solution of the polyamic acid is sequentially applied as many times as necessary. ,dry. After that, it is preferable to carry out imidization by collectively performing heat treatment in a temperature range of 100 to 400 ° C. for about 5 to 30 minutes. If the imidization temperature is lower than 100 ° C., the dehydration ring closure reaction of the polyimide does not proceed sufficiently, and conversely, if it exceeds 400 ° C., the polyimide layer may be deteriorated.
Further, by appropriately performing an appropriate surface treatment or the like on the imidized arbitrary polyimide layer, a new layer can be layered through the steps of coating, drying and imidizing the resin solution. In that case, it is not necessary to complete the imidization in the intermediate step, and the imidization can be completed collectively in the final step.
Further, any imidized polyimide layer can be heat-bonded to a separately formed resin film.
The resin film may be in a state of having a supporting base material.

Another example of forming the crystalline silica-containing polyimide layer will be given.
First, the resin composition is cast-coated on an arbitrary supporting base material and molded into a film. This film-like molded product is heat-dried on a supporting base material to obtain a gel film having self-supporting properties. After the gel film is peeled off from the supporting base material, if the resin composition contains a polyamic acid, it is further heat-treated at a high temperature and imidized to obtain a polyimide resin film.

The supporting base material used for forming the crystalline silica-containing polyimide layer is not particularly limited, and a base material of any material can be used. Further, in forming the resin film, it is not necessary to form the resin film that has been completely imidized on the base material. For example, the resin film in the semi-cured polyimide precursor state can be separated from the supporting base material by means such as peeling, and imidization is completed after the separation to obtain a resin film.

The resin film may consist of only a polyimide layer containing an inorganic filler (including the above-mentioned crystalline silica-containing polyimide layer), or may have a polyimide layer containing no inorganic filler. When the resin film has a laminated structure of a plurality of layers, it is preferable that all the layers contain an inorganic filler in consideration of improvement in dielectric properties. However, by setting the adjacent layer of the polyimide layer containing the inorganic filler to a layer not containing the inorganic filler or a layer having a low content thereof, it is advantageous that the inorganic filler can be prevented from slipping off during processing or the like. Can have a positive effect. When the polyimide layer containing no inorganic filler is provided, the thickness thereof is, for example, within the range of 1/100 to 1/2, preferably 1/20 to 1/3 of the polyimide layer containing the inorganic filler. That is good. When the polyimide layer containing no inorganic filler is provided, if the polyimide layer is brought into contact with the metal layer, the adhesiveness between the metal layer and the insulating layer is improved.

The coefficient of thermal expansion (CTE) of the resin film is not particularly limited ^{, but is preferably in the range of, for example, 10 × 10 -6} to 50 × 10 ^-6 / K (10 to 50 ppm / K), and is preferably 15 × 10 ^−. More preferably, it is in the range of ⁶ to 40 × ^{10-6 / K (15 to 40 ppm / K).} If the coefficient of thermal expansion of the resin film is ^{smaller than 10 × 10 -6} / K, curling is likely to occur after the metal-clad laminate is formed, and the handleability is poor. On the other hand, when the coefficient of thermal expansion of the resin film ^{exceeds 50 × 10 -6} / K, the dimensional stability as an electronic material such as a flexible substrate is inferior, and the heat resistance tends to be lowered.

[Dissipation factor]
When the resin film is applied as an insulating resin layer of a circuit board, for example, when the film as a whole is measured by a split post dielectric resonator (SPDR) in order to reduce the dielectric loss during transmission of a high frequency signal. The dielectric loss tangent (Tanδ) at 3 to 20 GHz is preferably 0.005 or less, and more preferably 0.004 or less. In order to improve the transmission loss of the circuit board, it is particularly important to control the dielectric loss tangent of the insulating resin layer, and by setting the dielectric loss tangent within the above range, the effect of reducing the transmission loss is increased. Therefore, when the resin film is applied as, for example, an insulating resin layer of a high-frequency circuit board, the transmission loss can be efficiently reduced. If the dielectric loss tangent at 3 to 20 GHz exceeds 0.005, when the resin film is applied as the insulating resin layer of the circuit board, inconveniences such as a large loss of electric signals on the high frequency signal transmission path are likely to occur. .. The lower limit of the dielectric loss tangent at 3 to 20 GHz is not particularly limited, but it is necessary to consider the physical property control when the resin film is applied as the insulating resin layer of the circuit board.

[Relative permittivity]
When the resin film is applied as an insulating resin layer of a circuit board, for example, in order to ensure impedance matching, the resin film as a whole has a relative permittivity at 3 to 20 GHz as measured by a split post dielectric resonator (SPDR). The rate is preferably 3.1 or less. If the relative permittivity at 3 to 20 GHz exceeds 3.1, when the resin film is applied as the insulating resin layer of the circuit board, the dielectric loss is deteriorated, and the loss of the electric signal is large on the transmission path of the high frequency signal. Inconveniences such as

[Metal-clad laminate]
The metal-clad laminate of the present embodiment 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, and is at least one layer of the insulating resin layer. Is made of the above resin film. The metal-clad laminate may be a single-sided metal-clad laminate having a metal layer only on one side of the insulating resin layer, or a double-sided metal-clad laminate having metal layers on both sides of the insulating resin layer. ..

[Insulating resin layer]
The insulating resin layer is composed of a single layer or a plurality of layers, and includes a layer made of the above resin film. For example, the resin film may form a non-thermoplastic polyimide layer as a main layer of an insulating resin layer for ensuring mechanical properties and thermophysical characteristics. Further, the resin film may form a thermoplastic polyimide layer as an adhesive layer that bears an adhesive strength with a metal layer such as a copper foil. The "main layer" means a layer that occupies 50% or more of the total thickness of the insulating resin layer.
Further, the metal-clad laminate of the present embodiment does not exclude the use of an adhesive for adhering the polyimide layer containing the inorganic filler and the metal foil. However, when the adhesive layer is interposed in the double-sided metal-clad laminate having metal layers on both sides of the insulating resin layer, the thickness of the adhesive layer is 30% of the thickness of the total insulating resin layer so as not to impair the dielectric properties. It is preferably less than, more preferably less than 20%. Further, when the adhesive layer is interposed in the single-sided metal-clad laminate having the metal layer on only one side of the insulating resin layer, the thickness of the adhesive layer is 15 of the thickness of the total insulating resin layer so as not to impair the dielectric properties. It is preferably less than%, and more preferably less than 10%. Further, since the adhesive layer constitutes a part of the insulating resin layer, it is preferably a polyimide layer. When the crystalline silica-containing polyimide layer constitutes the main layer of the insulating resin layer, the glass transition temperature of the crystalline silica-containing polyimide layer is preferably 300 ° C. or higher from the viewpoint of imparting heat resistance. The glass transition temperature can be set to 300 ° C. or higher by appropriately selecting the above-mentioned acid dianhydride and diamine components constituting the polyimide.

As a method for producing a metal-clad laminate having a resin film as an insulating resin layer, for example, a method of heat-pressing a metal foil directly on the resin film or via an arbitrary adhesive, a method of heat-pressing a metal foil, or a method such as metal deposition Examples thereof include a method of forming a metal layer on a film. The double-sided metal-clad laminate can be formed, for example, by forming a single-sided metal-clad laminate and then pressing the polyimide layers facing each other by heat pressing, or by applying a metal foil to the polyimide layer of the single-sided metal-clad laminate. It can be obtained by a method of crimping and forming.

[Metal layer]
The material of the metal layer is not particularly limited, but for example, copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese and these. Alloys and the like. Among these, copper or a copper alloy is particularly preferable. The metal layer may be made of a metal foil, may be metal-deposited on a film, or may be printed with a paste or the like. Further, since the resin composition can be directly applied, either a metal foil or a metal plate can be used, and a copper foil or a copper plate is preferable.

The thickness of the metal layer is not particularly limited because it is appropriately set according to the purpose of use of the metal-clad laminate, but is preferably in the range of, for example, 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 metal-clad laminates. On the contrary, if the thickness of the metal layer exceeds 3 mm, it is hard and the workability is deteriorated. As for the thickness of the metal layer, a thick one is generally suitable for applications such as an in-vehicle circuit board, and a thin metal layer is suitable for an application such as an LED circuit board.

Examples will be shown below, and the features of the present invention will be described in more detail. However, the scope of the present invention is not limited to the examples. In the following examples, various measurements and evaluations are as follows unless otherwise specified.

[Measurement of viscosity]
The viscosity of the resin solution was measured at 25 ° C. using an E-type viscometer (manufactured by Brookfield, trade name; DV-II + Pro). The rotation speed was set so that the torque was 10% to 90%, and one minute after the start of the measurement, the value when the viscosity became stable was read.

[Measurement of relative permittivity and dielectric loss tangent]
<Silica particles>
Using a vector network analyzer (manufactured by KeySight Technology Co., Ltd., trade name; vector network analyzer E8633C) and a relative permittivity measuring device manufactured by Kanto Denshi Applied Development Co., Ltd. by the cavity resonator perturbation method, set the relative permittivity measurement mode to TM020. , The relative permittivity (ε1) and the dielectric constant tangent (Tanδ1) of the silica particles at a frequency of 10 GHz were measured. The silica particles were in the form of powder and were filled in a sample tube (inner diameter: 1.68 mm, outer diameter: 2.28 mm, height: 8 cm) for measurement.
<Resin film>
The relative permittivity (ε1) and dielectric loss tangent (Tanδ1) of the resin film at a frequency of 10 GHz were measured using a vector network analyzer (manufactured by Keysight Technology Co., Ltd., trade name; vector network analyzer E8633C) and an SPDR resonator. The resin film used for the measurement was left to stand for 24 hours under the conditions of temperature: 24-26 ° C. and humidity: 45-55%.

[Measurement of coefficient of thermal expansion (CTE)]
A resin film having a size of 3 mm × 20 mm was heated from 30 ° C. to 265 ° C. at a constant heating rate while applying a load of 5.0 g using a thermomechanical analyzer (manufactured by Bruker, trade name; 4000SA). Further, after holding at that temperature for 10 minutes, the film was cooled at a rate of 5 ° C./min to determine the average coefficient of thermal expansion (coefficient of thermal expansion, CTE) from 200 ° C. to 100 ° C.

[Measurement of particle size]
Using a laser diffraction type particle size distribution measuring device (manufactured by Malvern, trade name; Master Sizer 3000), the particles of silica particles are measured by a laser diffraction / scattering type measurement method under the condition of using water as a dispersion medium and having a particle refractive index of 1.54. The diameter was measured.

[Measurement of true density]
The true specific gravity of silica particles was measured by a pycnometer method (liquid phase substitution method) using a continuous automatic powder truth density measuring device (manufactured by Seishin Enterprise Co., Ltd., trade name; AUTO TRUE DENSERMAT-7000).

[Measurement of cristobalite crystal phase]
All diffraction patterns (peak position, peak) derived from _{SiO 2} in the range of diffraction angle (Cu, Kα) 2θ = 10 ° to 90 ° using an X-ray diffraction measuring device (manufactured by Bruker, trade name; D2PHASER). Width and peak intensity), the total area of all peaks derived _{from SiO 2 is calculated.} Next, the peak position derived from the cristobalite crystal phase was specified, the total area of all peaks of the cristobalite crystal phase was calculated, and the ratio (% by weight) to the total area of all peaks derived from _{SiO 2 was obtained.} For the attribution of each peak, the database of International Center for Diffraction Data (ICDD) was referred to.

[Measurement of circularity]
The average circularity of silica particles was measured by dynamic flow particle image analysis using a wet flow type particle size / shape analyzer (manufactured by Sysmex, trade name; FPIA-3000).

[Evaluation of bendability]
In accordance with JIS K5600-5-1, the center of the long side of a 5 cm x 10 cm size resin film is evenly bent over 1 to 2 seconds so as to be wrapped around a 5 mmφ metal rod, even if the resin film is bent at 180 ° C. Those that did not break or crack were rated as "good", and those that did break or crack were rated as "impossible".

The abbreviations used in Synthesis Examples, Comparative Examples, and Examples indicate the following compounds.
PMDA: pyromellitic dianhydride BPDA: 3,3', 4,4'-biphenyltetracarboxylic dianhydride BAPP: 2,2-bis [4- (4-aminophenoxy) phenyl] propane m-TB: 2,2'-dimethyl-4,4'-diaminobiphenylDMAc: N, N-dimethylacetamide
Filler 1: Made by Nittetsu Chemical & Materials Co., Ltd. Trade name; CR10-20 (spherical cristobalite silica powder, circularity; 0.98, cristobalite crystal phase; 98% by weight, true density; 2.33, D ₅₀ ; 10.8 μm; relative permittivity at 10 GHz; 3.16 Dielectric loss tangent at 10 GHz; 0.0008)
Filler 2: Made by Nittetsu Chemical & Materials Co., Ltd. Trade name; SC70-2 (spherical amorphous silica powder, circularity; 0.98, true specific gravity; 2.21, D ₅₀ ; 11.7 μm, relative permittivity at 10 GHz; 3.08, dielectric loss tangent at 10 GHz; 0.0015)
Filler 3: manufactured by Nittetsu Chemical & Materials Co., Ltd., trade name; SP40-10 (spherical amorphous silica powder, true sphere, true specific gravity; 2.21, D ₅₀ ; 2.5 μm, relative permittivity at 10 GHz; 2. 78, Dielectric Dissipation Factor at 10 GHz; 0.0030)

(Synthesis Example 1)
24 g of BAPP (60 mmol) and 230 g of DMAc were put into a 300 ml separable flask, and the mixture was stirred at room temperature under a nitrogen stream. After complete dissolution, 6.5 g of PMDA (30 mmol) and 8.7 g of BPDA (30 mmol) were added, and the mixture was stirred at room temperature for 18 hours to obtain a polyamic acid solution A. The viscosity of the obtained polyamic acid solution A was 21,074 cps.

(Synthesis Example 2)
19 g of m-TB (90 mmol) and 230 g of DMAc were placed in a 300 ml separable flask, and the mixture was stirred at room temperature under a nitrogen stream. After complete dissolution, 16 g of PMDA (72 mmol) and 5.3 g of BPDA (18 mmol) were added, and the mixture was stirred at room temperature for 18 hours to obtain a polyamic acid solution B. The viscosity of the obtained polyamic acid solution B was 22,400 cps.

[Example 1]
58.7 g of polyamic acid solution A and 6.1 g of filler 1 were mixed and visually stirred until a uniform solution was obtained to prepare a polyamic acid composition 1a (viscosity; 23,000 cps).
The polyamic acid composition 1a was applied onto the copper foil 1 (electrolytic copper foil, thickness; 12 μm) and dried at 130 ° C. for 3 minutes. Then, a stepwise heat treatment was performed from 155 ° C. to 360 ° C. to imidize the metal-clad laminate 1b. The copper foil of the metal-clad laminate 1b was removed by etching to prepare a resin film 1c. The resin film 1c (thickness; 51.6 μm) had a relative permittivity of 3.04, a dielectric loss tangent of 0.0044, and a bendability of “good”.

[Example 2]
70.0 g of polyamic acid solution B and 7.8 g of filler 1 were mixed and visually stirred until a uniform solution was obtained to prepare a polyamic acid composition 2a (viscosity; 24,800 cps).
A metal-clad laminate 2b and a resin film 2c were prepared in the same manner as in Example 1. The resin film 2c (thickness; 46.1 μm) had a relative permittivity of 2.78, a dielectric loss tangent of 0.0037, a CTE of 34 ppm / K, and a bendability of “good”.

[Example 3]
60.0 g of polyamic acid solution B and 20.0 g of filler 1 were mixed and visually stirred until a uniform solution was obtained to prepare a polyamic acid composition 3a (viscosity; 28,400 cps).
A metal-clad laminate 3b and a resin film 3c were prepared in the same manner as in Example 1. The resin film 3c (thickness; 78.1 μm) had a relative permittivity of 2.71, a dielectric loss tangent of 0.0028, a CTE of 34 ppm / K, and a bendability of “good”.

[Example 4]
55.0 g of polyamic acid solution B and 36.6 g of filler 1 were mixed and visually stirred until a uniform solution was obtained to prepare a polyamic acid composition 4a (viscosity; 29,900 cps).
In the same manner as in Example 1, a metal-clad laminate 4b was prepared, and then a resin film 4c was prepared. The resin film 4c (thickness; 117.8 μm) had a relative permittivity of 2.56, a dielectric loss tangent of 0.0015, a CTE of 31 ppm / K, and a bendability of “impossible”.

[Example 5]
50.0 g of polyamic acid solution B, 6.6 g of filler 1 and 25.3 g of filler 2 are mixed and visually stirred until a uniform solution is obtained, and the polyamic acid composition 5a (viscosity; 31,000 cps) is stirred. ) Was prepared.
In the same manner as in Example 1, a metal-clad laminate 5b was prepared, and then a resin film 5c was prepared. The resin film 5c (thickness; 115.5 μm) had a relative permittivity of 2.71, a dielectric loss tangent of 0.0017, a CTE of 27 ppm / K, and a bendability of “impossible”.

(Comparative Example 1)
The polyamic acid solution A was applied onto the copper foil 1 and dried at 90 ° C. for 1 minute and at 130 ° C. for 5 minutes. Then, a stepwise heat treatment was performed from 155 ° C. to 360 ° C. to imidize the metal-clad laminate A1.
In the same manner as in Example 1, the copper foil of the metal-clad laminate A1 was removed by etching to prepare a resin film A1. The resin film A1 (thickness; 41.4 μm) had a relative permittivity of 3.16, a dielectric loss tangent of 0.0062, a CTE of 51 ppm / K, and a bendability of “good”.

(Comparative Example 2)
56.2 g of polyamic acid solution A and 5.5 g of filler 2 were mixed and visually stirred until a uniform solution was obtained to prepare a polyamic acid composition A2 (viscosity; 23,600 cps).
A metal-clad laminate A2 and a resin film A2 were prepared in the same manner as in Example 1. The resin film A2 (thickness; 50.7 μm) had a relative permittivity of 3.04, a dielectric loss tangent of 0.0047, and a bendability of “good”.

(Comparative Example 3)
56.2 g of polyamic acid solution A and 5.5 g of filler 3 were mixed and stirred visually until a uniform solution was obtained to prepare a polyamic acid composition A3 (viscosity; 30,000 cps).
A resin film A3 was prepared after preparing the metal-clad laminate A3 in the same manner as in Example 1. The resin film A3 (thickness; 45.6 μm) had a relative permittivity of 3.25, a dielectric loss tangent of 0.0052, a CTE of 41, and a bendability of “good”.

The above results are summarized in Tables 1 and 2.
The crystal phase in Table 1 means the ratio of the cristobalite crystal phase, and the filler ratio is the ratio (weight) of the filler to the entire polyimide solution (crocodile) or the solid content of the organic compound and the total of the silica particles. (Ratio) (however, the weight of polyamic acid was calculated by converting it to polyimide after imidization). The filler content in Table 2 means the ratio (weight ratio) of the filler to the resin film.

It was confirmed that the polyamic acid composition 1a of Example 1 had a lower viscosity than the polyamic acid compositions A2 and A3 of Comparative Examples 2 and 3, respectively. Further, the resin film 1c of Example 1 has a lower relative permittivity and dielectric loss tangent than the resin films A2 to A3 of Comparative Examples 2 and 3, and the higher the proportion of the Christobalite crystal phase, the lower the dielectric constant. The effect of was confirmed.

From the above results, it was confirmed that the resin film according to the present embodiment can be suitably used as a material for a flexible printed circuit board compatible with high frequencies.

Although the embodiments of the present invention have been described in detail for the purpose of exemplification, the present invention is not limited to the above embodiments and can be modified in various ways.

Claims (10)

A resin composition containing a solid content of an organic compound containing polyamic acid or polyimide and silica particles.
The content of the silica particles is in the range of 10 to 85% by weight (however, polyamic acid is converted to imidized polyimide) with respect to the total amount of the solid content and the total of the silica particles.
The ratio of the total area of the peaks derived from the cristobalite crystal phase and the quartz crystal phase to the total peak area derived from _{SiO 2} in the range of 2θ = 10 ° to 90 ° in the X-ray diffraction analysis spectrum using CuKα rays for the entire silica particles. Is a resin composition having a content of 20% by weight or more. _{The resin composition according to claim 1, wherein the median diameter D 50} in the frequency distribution curve of the silica particles obtained by volume-based particle size distribution measurement by a laser diffraction / scattering method is in the range of 6 to 20 μm. The resin composition according to claim 1 or 2, wherein 90% by weight or more of the silica particles having a particle size of 3 μm or more has a circularity of 0.7 or more. The resin composition according to any one of claims 1 to 3, wherein 90% by weight or more of the silica particles have a true specific gravity of 2.3 or more. A resin film having a single layer or a plurality of polyimide layers.
At least one layer of the polyimide layer is a crystalline silica-containing polyimide layer formed by the resin composition according to any one of claims 1 to 4, and the thickness of the crystalline silica-containing polyimide layer is from 15 μm to 15 μm. A resin film within the range of 200 μm. The resin film according to claim 5, wherein the ratio of the thickness of the crystalline silica-containing polyimide layer to the total thickness of the resin film is 50% or more. The resin film according to claim 5 or 6, wherein the relative permittivity at a frequency of 3 to 20 GHz as measured by a split post dielectric resonator (SPDR) is 3.1 or less. The resin film according to any one of claims 5 to 7, wherein the dielectric loss tangent at a frequency of 3 to 20 GHz as measured by a split post dielectric resonator (SPDR) is 0.005 or less. The resin film according to any one of claims 5 to 8, wherein the coefficient of thermal expansion is 50 ppm / K or less. 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 characterized in that at least one of the insulating resin layers is made of the resin film according to any one of claims 5 to 9.