Polyimide film, method for producing the same, metal-clad laminate, circuit board, multilayer circuit board, electronic device, and electronic apparatus

Abstract

This invention provides a polyimide film, a method for manufacturing the same, a metal-clad laminate, a circuit board, a multilayer circuit board, an electronic device, and an electronic device. The single-sided circuit board provided by this invention suppresses adhesion of the insulating resin layer by altering the surface state of the insulating resin layer. The polyimide film (10) has a three-layer laminate structure consisting of a polyimide layer (11), a polyimide layer (12) stacked adjacent to the polyimide layer (11), and a polyimide layer (13) stacked adjacent to the polyimide layer (12). The polyimide layer (11) has a modified layer and an exposed modified surface (MS). The concentration of fluorine atoms in the polyimide film (10) when measured by X-ray photoelectron spectroscopy (XPS) of the modified surface (MS) is in the range of 25–50 atm%.

Description

Technical Field

[0001] This invention relates to polyimide films useful as circuit board materials, methods for manufacturing the same, metal-clad laminates using the polyimide film as an insulating resin layer, circuit boards, multilayer circuit boards, electronic devices and electronic equipment using the same. Background Technology

[0002] With the miniaturization, weight reduction, and space-saving development of electronic devices, the demand for thin, lightweight, flexible, and highly durable flexible printed circuit boards (FPCs) that withstand repeated bending is increasing. FPCs can achieve three-dimensional and high-density mounting even in limited spaces, thus expanding their applications for various electronic components.

[0003] In addition, in recent years, portable electronic devices such as smartphones utilizing touch panels have been used in a wide range of fields. Among them, the market for flexible electronic devices (so-called "foldable devices") that have a hinge portion formed in the display area such as a display screen and thus have a degree of foldability has also expanded in recent years. In the bending section of such foldable devices, a multilayer circuit board with an air-gap structure is used, in which the insulating resin layer sides of a pair of single-sided circuit boards are partially bonded by means of a bonding layer called a bonding sheet. When such a multilayer circuit board with an air-gap structure is bent, the insulating resin layers facing each other across the air-gap come into contact with each other, sometimes resulting in adhesion, requiring countermeasures.

[0004] To suppress adhesion of the insulating resin layer in a circuit board, modification treatments that alter the surface state are considered effective. As a technology related to circuit board materials, Patent Document 1 discloses a metal-clad laminate with moderate adhesion and easy peelability. In Patent Document 1, a balance between adhesion and peelability is achieved by including inorganic fillers in the resin layer forming the bonding surface.

[0005] Patent Document 2 proposes a method to prevent adhesion at bends and maintain bend resistance by ensuring that the average roughness of the polyimide layer surface (which serves as the electrical insulation layer of a flexible printed wiring board) at 10 points is 1.5 μm or more to less than 2.0 μm and the contact angle is 60° or more to less than 120°. In Patent Document 2, the surface roughness and contact angle of the polyimide layer are controlled by adding fillers or by not performing surface treatments such as plasma treatment.

[0006] Although surface modification is not involved, Patent Document 3 discloses treating polyimide films used as interlayer insulating materials and passivation materials in multilayer wiring for semiconductor devices with fluorine-containing plasma to fluorinate them into the interior of the film. However, the purpose of the fluorine-containing plasma treatment in Patent Document 3 is to reduce the relative permittivity.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 6774285 Patent Document 2: Japanese Patent No. 4954111 Patent Document 3: Japanese Patent No. 2626559 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] In patent documents 1 and 2, the surface state of the insulating resin layer is altered by including inorganic fillers. However, in response to the miniaturization of electronic devices, the insulating resin layer of the circuit board is also thinned, thus limiting the high-concentration mixing of inorganic fillers. For example, when inorganic fillers are mixed at high concentrations in an extremely thin insulating resin layer, defects such as breakage are easily caused during bending, significantly reducing the reliability of electronic devices. Furthermore, increasing the amount of inorganic fillers raises concerns about adverse effects such as impaired dimensional stability, reduced processability of openings, and contamination of the production line during the circuit board manufacturing process.

[0010] On the other hand, as other ways to change the surface state of the insulating resin layer, surface treatments such as plasma treatment are also known. However, plasma treatment is generally known to improve adhesion by introducing hydrophilic functional groups such as carboxyl and hydroxyl groups onto the surface of the insulating resin layer (e.g., Patent Document 2, paragraph 0044), but its effect on inhibiting the adhesion of the insulating resin layer has not been verified.

[0011] The purpose of this invention is to provide a circuit board that inhibits the adhesion of the insulating resin layer by changing the surface state of the insulating resin layer.

[0012] means for solving problems

[0013] In order to solve the above-mentioned problems, the inventors conducted in-depth research and found that by treating the surface of the insulating resin layer with plasma containing fluorine atoms, an extremely thin modified layer is formed, which has the effect of inhibiting the adhesion of the insulating resin layer, thus completing the present invention.

[0014] That is, the polyimide film of the present invention is characterized in that it is a polyimide film comprising one or more polyimide layers. The polyimide film has a modified layer containing fluorine atoms. The modified layer has a modified surface exposed to the outside, and the concentration of fluorine atoms on the modified surface, as determined by X-ray photoelectron spectroscopy, is in the range of 25~50 atm%.

[0015] The polyimide film of the present invention may be a polyimide layer comprising the modified layer, wherein the polyimide layer having the modified layer contains inorganic filler particles. In this case, the average particle size of the inorganic filler particles may be in the range of 0.3 to 1.5 μm, and the content of the inorganic filler particles in the polyimide layer having the modified layer may be in the range of 1 to 10% by volume.

[0016] The polyimide film of the present invention may have a structure in which a first thermoplastic polyimide layer, a non-thermoplastic polyimide layer and a second thermoplastic polyimide layer having the modified layer are sequentially stacked.

[0017] The polyimide film of the present invention may have a maximum thickness of less than 30 nm in the depth direction from the surface.

[0018] The method for manufacturing the polyimide film of the present invention is characterized by comprising the following steps i) and ii). Process i) The process of preparing a polyimide film comprising a single or multiple polyimide layers; and Step ii) The process of treating the surface of the polyimide film using plasma containing fluorine gas.

[0019] The metal-clad laminate of the present invention is characterized in that it is a metal-clad laminate having an insulating resin layer and a metal layer laminated on one side of the insulating resin layer. The insulating resin layer comprises the polyimide film of the present invention, and the modified layer in the polyimide film is exposed on the side opposite to the metal layer.

[0020] The circuit board of the present invention is characterized in that it is a circuit board having an insulating resin layer and a circuit wiring layer laminated on one side of the insulating resin layer. The insulating resin layer comprises the polyimide film of the present invention, and the modified layer of the polyimide film is exposed on the side opposite to the circuit wiring layer.

[0021] The multilayer circuit board of the present invention is characterized in that it is a multilayer circuit board having multiple circuit boards stacked on top of each other. It has at least a first circuit board, a second circuit board, and a bonding layer partially located between the first circuit board and the second circuit board to bond the two together. Both the first circuit board and the second circuit board are single-sided circuit boards having an insulating resin layer and a circuit wiring layer stacked on one side of the insulating resin layer. In the region where the bonding layer is absent, the insulating resin layer side face of the first circuit board faces the insulating resin layer side face of the second circuit board and are disposed separately from each other. One or both of the first circuit board and the second circuit board are the circuit boards of the present invention.

[0022] In the multilayer circuit board of the present invention, the bonding layer may be used as a spacer, and a gap may be formed between the two insulating resin layers, with the gap serving as the bending portion for repeated bending operations.

[0023] The electronic device of the present invention comprises the multilayer circuit board of the present invention.

[0024] The electronic device of the present invention includes the multilayer circuit board of the present invention.

[0025] Invention Effects

[0026] The polyimide film of the present invention has a modified layer containing a specified concentration of fluorine atoms, thereby suppressing the formation of adhesion in the polyimide film. Therefore, when the polyimide film of the present invention is used in metal-clad laminates and circuit boards with insulating resin layers, improved yield and ensured reliability can be achieved. Therefore, the polyimide film of the present invention is particularly preferred as a circuit board material such as an FPC in electronic devices and electronic equipment. Attached Figure Description

[0027] Figure 1 This is a schematic diagram showing the cross-sectional structure of the polyimide film in the thickness direction according to a preferred embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram showing the cross-sectional structure of the metal-clad laminate in the thickness direction according to a preferred embodiment of the present invention.

[0029] Figure 3 This is a schematic diagram showing the cross-sectional structure of the circuit board in the thickness direction according to a preferred embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram showing the cross-sectional structure in the thickness direction of a multilayer circuit board to which the present invention is applied.

[0031] Explanation of reference numerals in the attached figures 10…Polyimide film, 11, 12, 13…Polyimide layers, 14…Silica particles, 20, 21, 22…Insulating resin layers, 30…Metal layers, 40, 41, 42…Circuit wiring layers, 100…Metal-clad laminate, 200, 201, 202…Circuit substrate, 300…Multilayer circuit substrate, MS…Modified surface, BS…Bond, AG…Voids Detailed Implementation

[0032] Embodiments of the present invention will be described with appropriate reference to the accompanying drawings.

[0033] One embodiment of the present invention provides a polyimide film comprising one or more polyimide layers. The polyimide film can be a film (sheet), or it can be, for example, laminated onto an inorganic substrate or other resin substrate.

[0034] There is no particular limitation on the type of polyimide film, as long as it is a main component of the resin, preferably comprising 70% or more, more preferably 80% or more, and most preferably 90-100% by weight of the resin. Here, "main component of the resin" refers to a component that is contained in more than 50% by weight relative to the total resin component. It should be noted that, when referred to as "polyimide" in this invention, in addition to polyimide, it also refers to resins formed from polymers having imide groups in their molecular structure, such as polyamide imide, polyether imide, polyester imide, polysiloxane imide, and polybenzimidazole imide.

[0035] Figure 1 The cross-sectional configuration of the polyimide film 10 according to a preferred embodiment of the present invention is shown. Figure 1 In a preferred example, a polyimide film 10 is shown to have a three-layer laminated structure comprising a polyimide layer 11, a polyimide layer 12 laminated adjacent to the polyimide layer 11, and a polyimide layer 13 laminated adjacent to the polyimide layer 12. The polyimide layers 11 and 13 can be thermoplastic polyimide layers primarily ensuring adhesion to the metal layer, while the polyimide layer 12 can be a non-thermoplastic polyimide layer primarily serving as a base resin layer ensuring mechanical properties. The polyimide film 10 has a modified layer containing fluorine atoms. The modified layer is extremely thin, therefore... Figure 1 Not shown in the figure, but formed on the exposed side of the polyimide layer 11. The modified layer has a modified surface MS exposed to the outside in the polyimide film 10.

[0036] It should be noted that, Figure 1 This is merely an example; therefore, the polyimide film of the present invention does not necessarily have to be a three-layer structure, and can be one, two, or four or more layers. Furthermore, the polyimide film of the present invention may include a resin layer made of any material other than polyimide, to the extent that it does not impair the effect of the invention. Moreover, a modified layer may be present in the polyimide layer 13, or a modified layer may be present in both the polyimide layer 11 and the polyimide layer 13. Additionally, the polyimide layer with the modified layer does not necessarily have to be a thermoplastic polyimide layer; it may also be a non-thermoplastic polyimide layer.

[0037] The modified layer can be very thin. For example, the maximum thickness of the modified layer is preferably less than 30 nm in the depth direction from the modified surface MS, more preferably less than 25 nm, and further preferably thinner in the order of less than 20 nm, less than 15 nm, less than 10 nm, and less than 5 nm. As will be described later, in this invention, surface treatment is performed by fluorine-containing plasma, so the concentration of fluorine atoms is highest near the surface of the polyimide film 10, and the concentration of fluorine atoms is relatively lower as the depth increases. Therefore, the maximum thickness of the modified layer refers to the maximum depth at which fluorine atoms are detected. In this invention, from the viewpoint of suppressing the adhesion of the polyimide film 10, it is sufficient to modify only the polar surface of the polyimide film 10, and fluorine atoms do not need to diffuse to the depth. From this viewpoint, the lower limit of the thickness of the modified layer is only 1 nm or more in the depth direction from the modified surface MS.

[0038] Furthermore, in the polyimide film 10, in the deeper portions extending beyond the modified layer in the thickness direction, there are substantially no fluorine atoms originating from the modification. Here, "substantially not" means that the concentration of fluorine atoms originating from the modification is below the detection limit.

[0039] The concentration of fluorine atoms in the polyimide film 10 of the present invention, measured by X-ray photoelectron spectroscopy (XPS) on the modified surface, is in the range of 25-50 atm%. When the concentration of fluorine atoms is less than 25 atm%, the modification effect is not achieved, and the effect of suppressing the adhesion of the polyimide film 10 (or the insulating resin layer) cannot be fully obtained. On the other hand, when the concentration of fluorine atoms exceeds 50 atm%, the adhesion is drastically reduced; for example, even when bonding with bonding layers such as bonding sheets is desired, sufficient bonding force may not be obtained.

[0040] Based on the above viewpoints, the lower limit of the concentration of fluorine atoms when measuring the modified surface MS by X-ray photoelectron spectroscopy is preferably 26 atm% or more, more preferably 27 atm% or more, and even more preferably 28 atm% or more. Furthermore, the upper limit of the concentration of fluorine atoms is preferably 45 atm% or less, more preferably 40 atm% or less, and even more preferably 35 atm% or less.

[0041] It should be noted that when a monomer containing fluorine atoms is used in the raw materials of polyimide 10, the fluorine atoms are present in the main chain or side chain of the polyimide, and therefore fluorine atoms can be detected deep within the polyimide beyond the modified layer. In this case, the thickness of the modified layer can be estimated by the difference in fluorine atom concentration between the modified layer and the deeper regions outside the modified layer.

[0042] That is, when using a monomer containing fluorine atoms in the polyimide raw material, the difference (F1-F0) between the fluorine atom concentration (F1) of the modified surface MS and the fluorine atom concentration (F0) of the deeper part of the modified layer (i.e., the unmodified part) is within the above-mentioned concentration range. As shown in the examples and comparative examples described later, the fluorine atoms from the raw material monomer of polyimide are bonded to the main chain or side chain of polyimide, thus confirming that there is almost no effect on inhibiting adhesion of the polyimide film 10 (or the insulating resin layer). Therefore, in order to inhibit adhesion, it is considered important to diffuse fluorine atoms only to the polar surface of the polyimide film 10 by fluorine-containing plasma treatment.

[0043] Regarding the contact angle of the modified surface MS, there is no particular limitation. For example, the contact angle relative to pure water is preferably 90 degrees or more, more preferably 100 degrees or more, and even more preferably in the range of 100 to 120 degrees. It is believed that when the contact angle relative to pure water is 90 degrees or more, the surface free energy of the polyimide film is generally reduced, resulting in reduced adhesion, which is effective in suppressing adhesion. However, as shown in the examples described later, it is believed that the fluorine atom concentration of the modified surface MS is the dominant factor in suppressing adhesion, and the contact angle is only a secondary factor.

[0044] Furthermore, similar to the contact angle, the surface roughness of the modified surface MS is only a secondary factor from the viewpoint of suppressing the adhesion of the polyimide film 10 (or insulating resin layer), and the fluorine atom concentration of the modified surface MS is considered to have a dominant effect on the suppression of adhesion.

[0045] In the polyimide film 10, the polyimide layer 11 having the modified layer preferably contains silica particles 14 as an inorganic filler. The silica particles 14 are generally uniformly dispersed in the polyimide layer 11. By containing silica particles 14, the coefficient of thermal expansion of the polyimide layer 11 can be easily controlled within a desired range. In addition, the silica particles 14 also have the function of reducing the adhesion of the polyimide layer 11.

[0046] The preferred average particle size of the silica particles 14 is closely related to the thickness of the polyimide layer 11 with the modified layer. For example, when the thickness of the polyimide layer 11 is in the range of 0.5 to 2.5 μm, the average particle size of the silica particles 14 is preferably in the range of 0.3 to 1.5 μm, more preferably in the range of 0.7 to 1.5 μm, and even more preferably in the range of 0.9 to 1.3 μm. If the average particle size is less than 0.3 μm, the effects of improved adhesion and control of the coefficient of thermal expansion cannot be sufficiently obtained. When it exceeds 1.5 μm, the film is prone to brittleness, especially when the thickness of the polyimide layer 11 is reduced to the above-mentioned range, this tendency becomes significant.

[0047] It should be noted that the average particle size of silica particles can be measured, for example, by laser diffraction, or analyzed by scanning electron microscopy of cross-sectional images of polyimide films.

[0048] The preferred content of silica particles 14 is closely related to the thickness of the polyimide layer 11 with the modified layer. For example, when the thickness of the polyimide layer 11 is in the range of 0.5 to 2.5 μm, the content of silica particles 14 in the polyimide layer 11 is preferably in the range of 1 to 10 vol%. If the content of silica particles 14 is less than 1 vol%, the effects of improved adhesion and control of the coefficient of thermal expansion cannot be fully obtained. If it exceeds 10 vol%, it is easy to cause disadvantages such as brittleness of the polyimide film 10, reduced dimensional stability, reduced processability, and production line contamination caused by the shedding of silica particles 14 during the circuit processing.

[0049] In the polyimide film 10, the adhesion of the modified surface MS is controlled not only by the diffusion of fluorine atoms but also by the dispersed silica particles 14. Thus, the advantages of pre-dispersing the silica particles 14 as fluorine atoms diffuse into the polyimide layer 11 are as follows.

[0050] With the advancement of thin-film technology, the high-concentration blending of inorganic fillers has become limited. As in existing technologies, it is difficult to control the surface state of polyimide films (insulating resin layers) solely through the dispersion of inorganic fillers. Specifically, high-concentration blending of inorganic fillers in the film can easily lead to drawbacks such as brittleness, reduced dimensional stability, decreased processability, and production line contamination. On the other hand, regarding the introduction of fluorine atoms into the polyimide film, environmental constraints necessitate minimizing the concentration. In a preferred embodiment of the present invention, by treating the polyimide layer 11 with dispersed silica particles 14 using fluorine-containing plasma, the concentration of fluorine atoms can be suppressed compared to the case where the silica particles 14 are not dispersed. Specifically, when the silica particles 14 are dispersed, the upper limit of the fluorine atom concentration in the polyimide layer 11 when measured by X-ray photoelectron spectroscopy (XPS) of the modified surface is preferably 40 atm% or less, more preferably 35 atm% or less. Thus, in the preferred embodiment of the present invention, by performing both the diffusion of fluorine atoms based on plasma treatment and the dispersion of silica particles 14, the amount of fluorine atom diffusion is suppressed on the one hand, and the content of silica particles 14 is reduced on the other hand, while the adhesion of the modified surface MS is appropriately controlled.

[0051] It should be noted that the polyimide layer 13 can also be incorporating silica particles 14 in the same manner as the polyimide layer 11. This is because the silica particles 14 affect the coefficient of thermal expansion, and therefore, a significant difference in the content of silica particles 14 between the polyimide layer 11 and the polyimide layer 13 can cause warping of the polyimide film 10. Therefore, the average particle size and content of the silica particles 14 in the polyimide layer 13 are preferably the same as those in the polyimide layer 11.

[0052] The above description uses silica particles 14 as a representative example of inorganic filler. However, the polyimide film 10 of the present invention may use other inorganic fillers instead of silica particles 14, or may use other inorganic fillers together with silica particles 14, without impairing the effect of the invention. There are no particular limitations on the types of inorganic fillers other than silica particles; preferred examples include alumina, magnesium oxide, beryllium oxide, niobium oxide, titanium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, calcium fluoride, magnesium fluoride, potassium fluorosilicate, talc, glass, barium titanate, etc. Two or more of these can be used in combination. The average particle size and total mixing amount when using inorganic fillers other than silica particles are the same as in the case of silica particles 14.

[0053] Polyimide layers 11 and 13 preferably contain thermoplastic polyimide as the main component of the resin composition, and polyimide layer 12 preferably contains non-thermoplastic polyimide as the main component of the resin composition. Here, "main component of the resin composition" refers to a component containing more than 50% by weight of the resin composition, preferably 70% by weight or more, more preferably 80% by weight or more, and most preferably 90-100% by weight of the resin composition. Furthermore, in this invention, "thermoplastic polyimide" refers to a polyimide whose glass transition temperature (Tg) can generally be clearly determined; in this invention, it refers to a storage modulus of 1.0 × 10⁻⁶ at 30°C, as measured using a dynamic viscoelasticity measuring device (DMA). 8 The energy storage modulus above Pa and at 300℃ is less than 3.0 × 10⁻⁶. 7 Pa of polyimide. Furthermore, "non-thermoplastic polyimide" refers to polyimide that does not exhibit softening or bonding even with normal heating; in this invention, it refers to polyimide with a storage modulus of 1.0 × 10⁻⁶ at 30°C, as measured using a dynamic viscoelasticity measuring device (DMA). 9 The energy storage modulus above Pa and at 300℃ is 3.0 × 10⁻⁶. 8 Polyimide with a strength of Pa or higher.

[0054] exist Figure 1In the illustrated configuration, polyimide layers 11 and 13 may also be composed of the same or different types of thermoplastic polyimides. The thermoplastic polyimide used in polyimide layers 11 and 13 is a thermoplastic polyimide obtained by reacting a tetracarboxylic anhydride component with a diamine component. The tetracarboxylic anhydride component and the diamine component, which are raw materials for the thermoplastic polyimide, can be monomers commonly used in the synthesis of thermoplastic polyimides.

[0055] The average coefficient of thermal expansion in the in-plane direction of the polyimide layers 11 and 13 can be in the range of more than 30 ppm / K, preferably more than 30 ppm / K and less than 100 ppm / K, and more preferably more than 30 ppm / K and less than 80 ppm / K. Flame retardants can be appropriately blended into the polyimide layers 11 and 13 as any component.

[0056] The non-thermoplastic polyimide used in the polyimide layer 12 is a non-thermoplastic polyimide obtained by reacting a tetracarboxylic anhydride component with a diamine component. The tetracarboxylic anhydride component and the diamine component, which are raw materials for the non-thermoplastic polyimide, can be monomers commonly used in the synthesis of non-thermoplastic polyimides.

[0057] The average coefficient of thermal expansion in the in-plane direction of the polyimide layer 12 can be in the range of 1 ppm / K or more and 30 ppm / K or less, preferably in the range of 1 ppm / K or more and 25 ppm / K or less, and more preferably in the range of 15 ppm / K or more and 25 ppm / K or less. As an arbitrary component, fillers, flame retardants, etc., can be appropriately blended into the polyimide layer 12.

[0058] <Layer Thickness> The overall thickness of the polyimide film 10 is not particularly limited. However, from the viewpoint of addressing miniaturization while ensuring electrical insulation, the upper limit of the thickness is preferably 20 μm or less, more preferably 16 μm or less, and even more preferably 12 μm or less. The lower limit of the thickness is preferably 3 μm or more, more preferably 4 μm or more, and even more preferably 5 μm or more. When the overall thickness of the polyimide film 10 exceeds the upper limit, it becomes difficult to address miniaturization. If it is less than the lower limit, the electrical insulation of the insulating resin layer may become insufficient, or the operability may deteriorate.

[0059] The thickness of polyimide layers 11 and 13 is not particularly limited, but the upper limit of the thickness is preferably 2.5 μm or less, more preferably 2 μm or less, and even more preferably 1.5 μm or less. The lower limit of the thickness is preferably 0.5 μm or more, more preferably 0.75 μm or more, and even more preferably 1 μm or more. When the thickness of polyimide layers 11 and 13 exceeds the upper limit, it is difficult to cope with miniaturization and there is a tendency for dimensional stability to deteriorate. When it is less than the lower limit, adhesion cannot always be adequately ensured. It should be noted that the thicknesses of polyimide layer 11 and polyimide layer 13 can be the same or different.

[0060] In the polyimide film 10, the thickness of the polyimide layer 12 is not particularly limited. From the viewpoint of addressing miniaturization while ensuring the function of the base resin layer and, consequently, the transportability during film manufacturing, the upper limit of the thickness is preferably 15 μm or less, more preferably 12 μm or less, and even more preferably 9 μm or less. The lower limit of the thickness is preferably 2 μm or more, more preferably 2.5 μm or more, and even more preferably 3 μm or more. When the thickness of the polyimide layer 12 exceeds the upper limit, it becomes difficult to address miniaturization; if it is less than the lower limit, electrical insulation and operability become insufficient. Furthermore, ensuring the mechanical properties of the polyimide film 10 becomes difficult.

[0061] [Manufacturing of polyimide films] The polyimide film of the present invention can be manufactured by performing a method comprising the following steps i) and ii): Process i) The process of preparing a polyimide film comprising a single or multiple polyimide layers; and Step ii) The process of treating the surface of the polyimide film using plasma containing fluorine gas.

[0062] The polyimide film prepared in step i) can be manufactured, for example, by the following methods: (1) A method of coating a polyamic acid solution onto any support substrate and drying it, repeating the process as needed, performing heat treatment to imidize the mixture, and then peeling it off from the support substrate to form a film. (2) A method of coating a polyamic acid solution onto any support substrate and drying it, repeating the process as needed, peeling the polyamic acid gel film off the support substrate, and imidizing it by heat treatment to form a film. (3) A method of preparing a film by coating a polyamic acid solution or a soluble polyimide solution onto any support substrate by multilayer extrusion and drying, and then imidizing it as needed and peeling it off from the support substrate. (4) A method of coating a solution of soluble polyimide onto any support substrate and drying it, and then peeling it off from the support substrate to form a film.

[0063] It should be noted that, as described above, by using metal foil as a supporting substrate, the metal-clad laminate described later can be manufactured without peeling off and maintaining its original shape.

[0064] The plasma treatment in step ii) is not particularly limited as long as it allows fluorine atoms to diffuse within the desired range on the modified surface MS, and can be carried out using conventional methods. For example, there are no particular limitations on the fluorine-containing gas; for instance, CF4, CH2F2, CH3F, etc., can be used. Additionally, inert gases can be used as needed. The plasma treatment pressure can be atmospheric pressure or vacuum. The electromagnetic waves used to generate the plasma can be high-frequency or microwave.

[0065] The plasma treatment in step ii) allows for adjustment of the depth of fluorine atom diffusion into the polyimide film in the thickness direction (depth of the modified layer) and the concentration of fluorine atoms in the modified surface MS by adjusting the plasma treatment conditions. In particular, with other plasma treatment conditions fixed, the depth of the modified layer and the concentration of fluorine atoms in the polyimide film can be easily controlled within an appropriate range by changing one or more conditions selected from treatment time, power, or plasma velocity; therefore, these are preferred as variation factors.

[0066] Specifically, based on a plasma treatment method, by changing one or more conditions selected from treatment time, power, or plasma velocity, the depth of the modified layer and the fluorine atom concentration in the polyimide film under each changing condition can be confirmed through preliminary experiments. Therefore, the treatment time, power, or plasma velocity can be adjusted to achieve the desired values. Thus, there are no particular restrictions regarding whether atmospheric pressure plasma or vacuum plasma is used, whether high-frequency plasma or microwave plasma is used, what type of fluorine-containing gas is used, what method of plasma treatment device is adopted, or the device configuration.

[0067] [Metal-clad laminate] Figure 2 The diagram shows a cross-sectional configuration of a metal-clad laminate 100 according to a preferred embodiment of the present invention. The metal-clad laminate 100 is a single-sided metal-clad laminate in which a metal layer 30 is laminated on one side of an insulating resin layer 20. The metal-clad laminate 100 includes an insulating resin layer 20 and a metal layer 30 laminated on one side of the insulating resin layer 20. The insulating resin layer 20 contains the polyimide film of the present invention, and the modified surface MS of the polyimide film is exposed on the side opposite to the metal layer 30.

[0068] There are no particular limitations on the material of the metal layer 30, and examples include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and their alloys. Among these, copper or copper alloys are particularly preferred. The copper foil can be rolled copper foil or electrolytic copper foil, and commercially available copper foil can be used. It should be noted that the material of the circuit wiring layer in the circuit board of the present invention, described later, is also the same as that of the metal layer 30.

[0069] In addition, for purposes such as rust prevention and improved adhesion, metal foils can be subjected to surface treatments based on siding, aluminum alkoxides, aluminum chelates, silane coupling agents, etc.

[0070] The thickness of the metal layer 30 is not particularly limited. For example, when using copper foil, to accommodate miniaturization, the upper limit of the thickness is preferably 18 μm or less, more preferably 15 μm or less, and even more preferably 12 μm or less. From the viewpoint of production stability and operability, the lower limit of the copper foil thickness is preferably 3 μm or more, more preferably 6 μm or more, and even more preferably 9 μm or more. It should be noted that for extremely thin copper foil with a thickness of about 3 μm, it is preferable to use copper foil with a carrier. In this case, the peelable carrier is made of metal or resin, and its thickness can be in the range of 5 to 100 μm. A release layer can also be present between the carrier and the copper foil. Regarding copper foil with a carrier, for example, it is described in Japanese Patent No. 4762742, the description of which is incorporated herein by reference.

[0071] In the metal-clad laminate 100, the insulating resin layer 20 has the same composition as the polyimide film 10.

[0072] [Manufacturing of metal-clad laminates] Although the illustrations are omitted, the metal-clad laminate 100 can be manufactured, for example, by methods such as coating a metal foil with a polyamic acid solution or a soluble polyimide solution as needed and drying it, and then imidizing it as needed; or by hot-pressing the polyimide film of the present invention to the metal foil, etc.

[0073] The metal-clad laminate 100 obtained in this embodiment, as described above, can be used to manufacture circuit boards such as single-sided FPCs by etching the metal layer 30 to perform wiring circuit processing.

[0074] [Circuit board] In one embodiment of the present invention, the circuit board can be manufactured by patterning the metal layer 30 of the metal-clad laminate 100 using conventional methods to form a circuit wiring layer. For example, see... Figure 3As described above, the circuit board 200 of this embodiment includes: an insulating resin layer 20; and a circuit wiring layer 40, which is stacked on one side of the insulating resin layer 20 and formed by circuit processing of the metal layer 30. The insulating resin layer 20 contains the polyimide film of the present invention, and the modified surface MS of the polyimide film is exposed on the side opposite to the circuit wiring layer 40. The circuit board 200 of this embodiment can preferably be used as an FPC, a rigid-flexible circuit board, etc.

[0075] The circuit board of the present invention can also be applied to multilayer circuit boards. Figure 4 This section illustrates a cross-sectional configuration example of a multilayer circuit board 300 to which the present invention is applied. In the multilayer circuit board 300, multiple circuit boards, including a circuit board 201 having a wiring layer 41 and a circuit board 202 having a wiring layer 42, are stacked together by means of bonding tabs BS. The bonding tabs BS are partially interposed between the circuit board 201 and the circuit board 202, thus bonding them together. Both the circuit board 201 and the circuit board 202 are single-sided circuit boards. In areas where the bonding tabs BS are not present, the side of the circuit board 201 facing the side of the insulating resin layer 21 faces the side of the circuit board 202 facing the insulating resin layer 22, and are disposed separately from each other. Using the bonding tabs BS as spacers, an air-gap AG is formed between the insulating resin layer 21 of the circuit board 201 and the insulating resin layer 22 of the circuit board 202.

[0076] The multilayer circuit board 300 can also use the gap AG as a bending part, in Figure 4 Near the BB line in the stacking direction ( Figure 4 The bending action is repeatedly performed in the up-down direction. In the multilayer circuit board 300, the circuit board 201 and the circuit board 202 can have the same structure or different structures, but either or both of the circuit board 201 and the circuit board 202 can be the circuit board of the present invention. Figure 4 In the example shown, both the insulating resin layer 21 of circuit board 201 and the insulating resin layer 22 of circuit board 202 have modified surfaces MS. That is, both circuit board 201 and circuit board 202 are the circuit boards of the present invention. In the multilayer circuit board 300, even when repeatedly bent, the opposing insulating resin layers 21 and 22 have modified surfaces MS, thus effectively suppressing the formation of adhesion.

[0077] [Electronic Components & Electronic Devices] The electronic devices and electronic equipment according to embodiments of the present invention include the circuit board of the present invention. Examples of electronic devices according to the present invention include liquid crystal displays, organic EL displays, electronic paper and other display devices, organic EL lighting, solar cells, touch panels, camera modules, inverters, converters, and their constituent components. Examples of electronic devices include HDDs, DVDs, mobile phones, smartphones, tablet terminals, electronic control units (ECUs) and power control units (PCUs) in automobiles. In these electronic devices and electronic equipment, the circuit board is preferably used as a component such as wiring, cables, and connectors for movable parts.

[0078] Example

[0079] The present invention will now be specifically described through embodiments, but the present invention is not limited to these embodiments in any way. It should be noted that, unless otherwise specified, various measurements and evaluations are described in the following embodiments.

[0080] [Determination of Fluorine Atom Concentration] Measurements were performed using an X-ray photoelectron spectroscopy analyzer (KRATOS ULTRA2; manufactured by Shimadzu Corporation) under the following conditions, and the results were analyzed using the included analysis software (ESCApe).

[0081] (XPS measurement conditions)

[0082] (1) Width measurement • X-ray source: AlKa rays, X-ray intensity 300W • Measurement range: 300μm × 700μm • Charge neutralization mechanism: On (Filament Current: 0.45A, Filament Bias: 1V, ChargeBalance: 4V) • Charge correction: Correction is performed with a CH / CC ratio of 284.8~285.0 eV. Number of scans: 2 • Obtained spectra with binding energies of 1200~0 eV Analyze what elements are present at a depth of 2-4 nm from the surface.

[0083] (2) Narrowness measurement Based on the qualitative analysis results of elements obtained through wide-range determination, the energy range in which specific elements appear is analyzed at high resolution, thereby enabling quantitative analysis and chemical structure determination of each element. Peak areas are calculated by applying background correction to the peaks of each element, and the relative sensitivity coefficient of each element is applied to the obtained peak areas to calculate the content of each element in the measured region as atomic concentration (atm%).

[0084] • X-ray source: AlKa rays, X-ray intensity 300W • Measurement range: 300μm × 700μm • Charge neutralization mechanism: On (Filament Current: 0.45A, Filament Bias: 1V, ChargeBalance: 4V) • Charge correction: Correction is performed with a CH / CC ratio of 284.8~285.0 eV. • Scanned peaks: F1s, O1s, N1s, C1s • Scanning conditions: F1s…695~675eV, 4 scans, background correction 692~684eV O1s…543~523eV, 4 scans, background correction 537~529eV N1s…410~390eV, 4 scans, background correction 404~397eV C1s…297~275eV, 4 scans, background correction 296~281eV *The background correction range is approximately ±0.5 eV, depending on the peak position.

[0085] (3) Determination of fluorine atom concentration in the depth direction The concentration of fluorine atoms in the depth direction was quantitatively analyzed by XPS measurement while etching the modified surface of a polyimide film along the depth direction using GCIB (Gas Cluster Ion Beam). GCIB etching was performed on a 1 mm diameter area of ​​the modified surface under accelerating voltage of 5 keV and Ar flow rate of 3000 mL / min. Under these etching conditions, an etching depth of approximately 3.3 nm was achieved in 1 minute.

[0086] [Determination of average particle size and volume fraction of silica particles] The average particle size of the silica particles before blending was determined using a laser diffraction particle size distribution analyzer (Malvern, trade name: Master Sizer 3000) with water as the dispersion medium and a particle refractive index of 1.54. The volumetric content was calculated based on the average volume derived from the average particle size of the silica particles and the amount of silica particles added to the polyamic acid resin solution.

[0087] [Evaluation methods for adhesions] Prepare two metal-clad laminates of the evaluation object, cut to 125mm × 175mm, with each insulating resin layer overlapping the others. Then, heat-press them together at 150℃ and 3MPa for 45 minutes. After heat-pressing, samples with seamless bonding without peeling are designated as "adhesive," while those with naturally peeling bonding without joining are designated as "non-adhesive."

[0088] [Determination of contact angle] The contact angle was determined using the following method.

[0089] 1. Sample preparation: Clean the surface of the solid to be measured and dry it as needed.

[0090] 2. Droplet formation: Using a syringe or similar device, a certain amount of water droplets are placed on a solid surface.

[0091] 3. Image acquisition: Observe the solid surface with water droplets placed on it from the side and take an image with a camera.

[0092] 4. Image analysis: The image obtained is analyzed using the θ / 2 method, and the contact angle is calculated based on the outline of the water droplet.

[0093] [Arithmetic mean height (Sa), unfolded area ratio (Sdr)] The surface roughness of the sample was measured using a Keyence VK-X3000 laser microscope in white microscope mode (10x objective). The surface roughness of the entire measurement area was measured. Based on the ISO 25178 standard (surface roughness), the arithmetic mean height (Sa) and the unfolded area ratio (Sdr) of the entire measurement field of view were calculated. (Filter type: Gaussian, S-filter: 2, F-operation: undulation removal, L-filter: 0.025) [Determination of energy storage modulus] Regarding the storage modulus, the resin film was cut into 5mm × 20mm pieces and heated in an oven at 120°C for 2 hours, followed by heating at 170°C for 3 hours. Using a dynamic viscoelastic apparatus (DMA: UBM, trade name: E4000F), the samples were heated in stages from 30°C to 400°C at a heating rate of 4°C / min, and the measurement was performed at a frequency of 11Hz. The storage modulus at 30°C, thus measured, was 1.0 × 10⁻⁶. 9 The energy storage modulus above Pa and at 300℃ is 3.0 × 10⁻⁶. 8 For materials with a strength above Pa, the storage modulus at 30°C is considered to be 1.0 × 10⁻⁶, which is treated as a non-thermoplastic polyimide. 8 The energy storage modulus above Pa and at 300℃ is less than 3.0 × 10⁻⁶. 7 Pa's polyimide is a thermoplastic polyimide.

[0094] [Determination of glass transition temperature] The glass transition temperature Tg (tanδ maximum) was determined by measuring the dynamic viscoelasticity of a polyimide film (10 mm × 22.6 mm) obtained by etching away copper foil using DMA, when the temperature was increased from 20 °C to 500 °C at a rate of 5 °C / min.

[0095] [Determination of the coefficient of thermal expansion] Using a thermomechanical analyzer manufactured by Seiko Instruments, the polyimide film obtained by etching copper foil was heated to 250°C, held at this temperature for 10 minutes, and then cooled at a rate of 5°C / min to determine the average coefficient of thermal expansion (linear thermal expansion coefficient) from 240°C to 100°C.

[0096] [Viscosity Measurement] The viscosity at 25°C was measured using an E-type viscometer (Brookfield, trade name: DV-II+Pro). The rotation speed was set to 10%~90% torque, and the viscosity was read after 2 minutes from the start of the measurement when it stabilized.

[0097] Synthesis Example 1 (without filler): In a reaction vessel equipped with a thermocouple and a stirrer, and capable of introducing nitrogen, N,N-dimethylacetamide was added to achieve a final solids concentration of 20% by weight. While stirring, 100 moles of 4,4'-diaminodiphenyl ether were dissolved in the reaction vessel. Next, 100 moles of 3,3',4,4'-benzophenone tetracarboxylic dianhydride were added. Stirring was then continued for 3 hours to obtain a polyamic acid resin solution a with a viscosity of 2960 mPa·s. It should be noted that the solution viscosity is the apparent viscosity value obtained at 25°C using an E-type viscometer (the same applies below). The polyimide obtained from this polyamic acid resin solution a is a thermoplastic polyimide with a glass transition temperature of 312°C and a coefficient of thermal expansion of 45 ppm / K.

[0098] Synthesis Example 2 (filler content 1% by volume): In a reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen, N,N-dimethylacetamide was added to achieve a final solids concentration of 20% by weight. 0.60 g of spherical packing material (silica, average particle size 1.0 μm, manufactured by Admatechs, “SE4050”; hereinafter the same) was added to the reaction vessel and dispersed using an ultrasonic disperser for 3 hours. While stirring, 100 moles of 4,4'-diaminodiphenyl ether were dissolved in the solution. Next, 100 moles of 3,3',4,4'-benzophenone tetracarboxylic dianhydride were added. Stirring was then continued for 3 hours to obtain a polyamic acid resin solution b with a solution viscosity of 3160 mPa·s.

[0099] Synthesis Example 3 (filler content 10 vol%): The spherical filler was set to 6.60 g, and otherwise, a polyamic acid resin solution c was obtained in the same manner as in Synthesis Example 2. The viscosity of the polyamic acid resin solution c was 3500 mPa·s.

[0100] Synthesis example 4 In a reaction vessel equipped with a thermocouple and a stirrer, and capable of introducing nitrogen, N,N-dimethylacetamide was added to achieve a final solids concentration of 20% by weight. While stirring, 100 moles of 4,4'-diamino-2,2'-dimethylbiphenyl were dissolved in the reaction vessel. Next, 20 moles of 3,3'-4,4'-biphenyltetracarboxylic dianhydride and 80 moles of pyromellitic dianhydride were added. Stirring was then continued for 3 hours to obtain a polyamic acid resin solution d with a solution viscosity of 21000 mPa·s. The polyimide obtained from this polyamic acid resin solution d was a non-thermoplastic polyimide with a glass transition temperature of 360 °C and a coefficient of thermal expansion of 15 ppm / K.

[0101] Synthesis example 5: In a reaction vessel equipped with a thermocouple and a stirrer, and capable of introducing nitrogen, N,N-dimethylacetamide was added to achieve a final solids concentration of 15% by weight. Then, 60 moles of 1,3-bis(3-aminophenoxy)benzene and 40 moles of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl were added to the reaction vessel and dissolved while stirring. Next, with an acid / amine ratio of 1.010, 100 moles of 4,4'-oxophthalic anhydride were added. The mixture was then heated at 40°C for 2 hours to dissolve. Subsequently, the solution was stirred at room temperature for 1 day to allow for polymerization, yielding a polyamic acid resin solution e with a solution viscosity of 5500 mPa·s. The polyimide obtained from this polyamic acid resin solution e is a thermoplastic polyimide with a glass transition temperature of 270°C and a coefficient of thermal expansion of 59 ppm / K.

[0102] (Example 1) A polyamic acid resin solution a prepared in Synthesis Example 1 was uniformly coated on one side of a 12 μm thick, elongated strip of electrolytic copper foil to a cured thickness of 2 μm (first layer), and then dried at 130°C to remove the solvent. Next, a polyamic acid resin solution d prepared in Synthesis Example 4 was uniformly coated on the same coated side to a cured thickness of 8 μm (second layer), and then dried at 130°C to remove the solvent. Then, a polyamic acid resin solution b prepared in Synthesis Example 2 was uniformly coated on the same coated side to a cured thickness of 2 μm (third layer), and then dried at 130°C to remove the solvent. This elongated laminate was then heat-treated in a continuous curing oven with the temperature progressively increasing from 130°C to 300°C for a total of approximately 10 minutes to obtain a single-sided flexible copper-clad laminate E1 with a total polyimide layer thickness of 12 μm.

[0103] The exposed surface of the third layer in the polyimide layer of the single-sided flexible copper-clad laminate E1 is irradiated with plasma containing fluorine gas under the conditions described later to perform modification treatment, thereby obtaining a single-sided flexible copper-clad laminate E1P with a modified surface.

[0104] For the modified surface of the single-sided flexible copper clad laminate E1P, the fluorine atom concentration, contact angle, Sa, and Sdr were measured. Additionally, the modified surfaces of two single-sided flexible copper clad laminates E1P were bonded together to evaluate for adhesion. The results are shown in Table 1.

[0105] (Example 2) The third layer was formed from the polyamic acid resin solution c prepared in Synthesis Example 3. Otherwise, single-sided flexible copper clad laminate E2 and single-sided flexible copper clad laminate E2P were prepared in the same manner as in Example 1. The fluorine atom concentration, contact angle, Sa and Sdr of the modified surface were measured, and the presence or absence of adhesion was evaluated. The results are shown in Table 1.

[0106] (Example 3) For the single-sided flexible copper-clad laminate E1 fabricated in Example 1, the plasma treatment conditions were changed. Otherwise, the single-sided flexible copper-clad laminate E3P was fabricated in the same manner as in Example 1. The fluorine atom concentration, contact angle, Sa and Sdr of the modified surface were measured, and the presence or absence of adhesion was evaluated. The results are shown in Table 1.

[0107] (Comparative Example 1) As shown in Table 1, the plasma treatment conditions were modified, but otherwise, a single-sided flexible copper-clad laminate C1P was obtained in the same manner as in Example 1. The fluorine atom concentration, contact angle, Sa, and Sdr of the modified surface of the single-sided flexible copper-clad laminate C1P were measured, and the presence or absence of adhesion was evaluated. The results are shown in Table 1.

[0108] (Comparative Example 2) As shown in Table 1, the plasma treatment conditions were modified, but otherwise, a single-sided flexible copper-clad laminate C2P was obtained in the same manner as in Example 1. The fluorine atom concentration, contact angle, Sa, and Sdr of the modified surface of the single-sided flexible copper-clad laminate C2P were measured, and the presence or absence of adhesion was evaluated. The results are shown in Table 1.

[0109] (Comparative Example 3) For the exposed surface of the third layer in the single-sided flexible copper-clad laminate E1 fabricated in Example 1, the fluorine atom concentration, contact angle, Sa and Sdr were measured, and the presence or absence of adhesion was evaluated. The results are shown in Table 1.

[0110] (Comparative Example 4) Except for forming the third layer using the polyamic acid resin solution e prepared in Synthesis Example 5, the single-sided flexible copper-clad laminate C4 was fabricated in the same manner as in Example 1. It should be noted that the single-sided flexible copper-clad laminate C4 was not subjected to plasma treatment. The fluorine atom concentration, contact angle, Sa, and Sdr were measured on the exposed surface of the third layer of the single-sided flexible copper-clad laminate C4, and the presence or absence of adhesion was evaluated; the results are shown in Table 1.

[0111] <Plasma Processing Conditions> The sample is placed on the sample stage (lower electrode) of a plasma treatment apparatus having a pair of parallel flat plate electrodes within the chamber, in contact with the copper layer side of a single-sided flexible copper-clad laminate. Next, fluorine-containing gas is introduced into the discharge space within the chamber, and a predetermined voltage is applied between the electrodes to generate fluorine-containing plasma in the discharge space, thereby performing plasma treatment on the surface of the insulating resin layer. Based on Example 2, the conditions were varied such that the power of Example 1 was -30%, the power of Example 3 was +30%, the plasma velocity of Comparative Example 1 was 10 times higher and the power was +30%, and the plasma velocity of Comparative Example 2 was 15 times higher.

[0112]

[0113] According to Table 1, in Examples 1-3 where plasma treatment was performed with a fluorine atom concentration in the modified surface ranging from 25 to 50 atm%, adhesion between the insulating resin layers was suppressed. On the other hand, adhesion was observed in Comparative Examples 1 and 2, where plasma treatment was performed but the fluorine atom concentration was too low, and in Comparative Example 3, where no plasma treatment was performed. Furthermore, Comparative Example 4 confirmed that adhesion occurred even when fluorine atoms derived from monomers were present. It should be noted that no correlation was found between contact angle, surface roughness, and the presence or absence of adhesion.

[0114] (Experimental example) Fluorine atom concentration in the depth direction: Except for changing the plasma treatment conditions, test samples T1 to T5 with different fluorine atom concentrations on the modified surface were prepared in the same manner as in Example 1. For each test sample, the fluorine atom concentration in the depth direction was quantitatively analyzed by XPS narrow measurement while etching using GCIB. The results are shown in Table 2. In Table 2, the values ​​in the upper paragraph represent the fluorine atom concentration, and the values ​​in parentheses in the lower paragraph represent the ratio when the fluorine atom concentration of the modified surface is set to 100%.

[0115]

[0116] Table 2 confirms that when the fluorine atom concentration on the modified surface is below 30 atm%, a majority of fluorine atoms exist within a depth range of 3 nm from the modified surface. Based on this result, when the fluorine atom concentration on the modified surface is below 30 atm%, the maximum estimated thickness of the modified layer is only 10 nm, suggesting that there are essentially no fluorine atoms originating from the modification beyond the depth of the modified layer.

[0117] The embodiments of the present invention have been described in detail above for illustrative purposes, but the present invention is not limited to the above embodiments and can be modified in various ways.

Claims

1. A polyimide film, characterized in that, It is a polyimide film containing one or more polyimide layers. The polyimide film has a modified layer containing fluorine atoms. The modified layer has a modified surface exposed to the outside, and the concentration of fluorine atoms on the modified surface, as determined by X-ray photoelectron spectroscopy, is in the range of 25~50 atm%.

2. The polyimide film according to claim 1, wherein, The polyimide film comprises a polyimide layer having the modified layer, the polyimide layer having the modified layer containing inorganic filler particles.

3. The polyimide film according to claim 2, wherein, The average particle size of the inorganic filler particles is in the range of 0.3 to 1.5 μm, and the content of the inorganic filler particles in the polyimide layer having the modified layer is in the range of 1 to 10% by volume.

4. The polyimide film according to claim 2, wherein, The polyimide film has a structure in which a first thermoplastic polyimide layer, a non-thermoplastic polyimide layer, and a second thermoplastic polyimide layer are sequentially stacked, each having the modified layer.

5. The polyimide film according to claim 1, wherein, The maximum thickness of the modified layer is less than 30 nm in the depth direction from the surface.

6. A method for manufacturing a polyimide film, characterized in that, The method for manufacturing the polyimide film according to any one of claims 1 to 5 includes the following steps i) and ii): Process i) The process of preparing a polyimide film comprising a single or multiple polyimide layers; and Step ii) The process of treating the surface of the polyimide film using plasma containing fluorine gas.

7. A metal-clad laminate, characterized in that, It is a metal-clad laminate having an insulating resin layer and a metal layer laminated on one side of the insulating resin layer. The insulating resin layer comprises a polyimide film according to any one of claims 1 to 5, and the modified layer in the polyimide film is exposed on the side opposite to the metal layer.

8. A circuit board, characterized in that, It is a circuit board having an insulating resin layer and a circuit wiring layer stacked on one side of the insulating resin layer. The insulating resin layer comprises a polyimide film according to any one of claims 1 to 5, and the modified layer of the polyimide film is exposed on the side opposite to the circuit wiring layer.

9. A multilayer circuit board, characterized in that, It is a multilayer circuit board with multiple circuit substrates stacked on top of each other. It has at least a first circuit board, a second circuit board, and a bonding layer partially located between the first circuit board and the second circuit board to bond the two together. Both the first circuit board and the second circuit board are single-sided circuit boards having an insulating resin layer and a circuit wiring layer stacked on one side of the insulating resin layer. In the region where the bonding layer is absent, the insulating resin layer side face of the first circuit board faces the insulating resin layer side face of the second circuit board and are disposed separately from each other. One or both of the first circuit board and the second circuit board are the circuit boards described in claim 8.

10. The multilayer circuit board according to claim 9, wherein, Using the bonding layer as a spacer, a gap is formed between the two insulating resin layers, and the gap is used as a bending point to repeatedly perform bending operations.

11. An electronic device, characterized in that, It has the circuit board as described in claim 8.

12. An electronic device, characterized in that, It has the circuit board as described in claim 8.

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