Liquid crystal polymer film, metal-clad laminate, and electronic circuit board

Abstract

This liquid crystal polymer film 1 contains 1g of a liquid crystal polymer as a main component, and has a total free volume parameter, found using the positron annihilation lifetime method, of 0.08-0.19, inclusive.

Description

Liquid crystal polymer film, metal-clad laminate, and electronic circuit board

[0001] The present invention relates to a liquid crystal polymer film, a metal-clad laminate, and an electronic circuit board.

[0002] Patent Document 1 discloses an extruded LCP film that contains an aromatic polyester liquid crystal polymer having at least one or more selected from the group consisting of parahydroxybenzoic acid, terephthalic acid, isophthalic acid, 6-naphthalenedicarboxylic acid, 4,4'-biphenol, bisphenol A, hydroquinone, 4,4-dihydroxybiphenol, ethylene terephthalate, and derivatives thereof, and 6-hydroxy-2-naphthoic acid and derivatives thereof as monomer components, and that has a solubility of 25% or more in pentafluorophenol at 60°C.

[0003] Japanese Patent Application Laid-Open No. 2021-4330

[0004] Due to their excellent electrical properties, liquid crystal polymer (LCP) films have been considered for use in various electronic devices. For example, liquid crystal polymer films are sometimes laminated with metal foil to form metal-clad laminates, which are then used in electronic devices. When manufacturing metal-clad laminates, the metal foil is laminated to the liquid crystal polymer film by, for example, pressing the metal foil to the liquid crystal polymer film. However, when the metal foil is pressed onto the liquid crystal polymer film, air can be trapped between the two, resulting in the formation of bubbles at the interface between the liquid crystal polymer film and the metal foil in the resulting metal-clad laminate. The presence of bubbles at the interface between the liquid crystal polymer film and the metal foil in metal-clad laminates can result in defects such as circuit defects when forming circuits on the metal foil.

[0005] In contrast, the LCP extrusion film described in Patent Document 1 is said to be able to increase the process tolerance during the production of flexible laminates without excessively impairing the excellent basic performance of liquid crystal polymers. However, while Patent Document 1 assumes that the process for producing flexible laminates using the LCP extrusion film involves thermocompression bonding of the LCP extrusion film to a metal foil, it does not at all recognize the problem of bubbles forming at the interface between the LCP extrusion film and the metal foil during this thermocompression bonding. Therefore, the LCP extrusion film described in Patent Document 1 has room for improvement in terms of suppressing the formation of bubbles at the interface with the metal foil when laminating the metal foil.

[0006] The present invention has been made to solve the above problems, and aims to provide a liquid crystal polymer film that can suppress the generation of bubbles at the interface with a metal foil when laminating the metal foil. Another aim of the present invention is to provide a metal-clad laminate formed using the liquid crystal polymer film. A further aim of the present invention is to provide an electronic circuit board formed using the metal-clad laminate.

[0007] The liquid crystal polymer film of the present invention is characterized by containing a liquid crystal polymer as a main component and having a total free volume parameter determined by positron annihilation lifetime spectroscopy of 0.08 or more and 0.19 or less.

[0008] The metal-clad laminate of the present invention is characterized by being formed using the liquid crystal polymer film of the present invention and a metal foil.

[0009] The electronic circuit board of the present invention is characterized in that it is formed using the metal-clad laminate of the present invention and has a circuit formed on the metal foil.

[0010] According to the present invention, a liquid crystal polymer film capable of suppressing bubble generation at the interface with a metal foil when laminating the metal foil can be provided. Also, according to the present invention, a metal-clad laminate formed using the liquid crystal polymer film can be provided. Furthermore, according to the present invention, an electronic circuit board formed using the metal-clad laminate can be provided.

[0011] Fig. 1 is a cross-sectional view schematically showing an example of a liquid crystal polymer film of the present invention. Fig. 2 is a cross-sectional view schematically showing an example of a method for producing a liquid crystal polymer film of the present invention. Fig. 3 is a cross-sectional view schematically showing an enlarged view of the die and its periphery in Fig. 2. Fig. 4 is a cross-sectional view schematically showing an example of a metal-clad laminate of the present invention. Fig. 5 is a cross-sectional view schematically showing an example of an electronic circuit board of the present invention. Fig. 6 is a block diagram showing an example of a positron lifetime spectrum measurement device.

[0012] The liquid crystal polymer film of the present invention, the metal-clad laminate of the present invention, and the electronic circuit board of the present invention will be described below. Note that the present invention is not limited to the following configurations and may be modified as appropriate within the scope of the present invention. In addition, a combination of multiple individual preferred configurations described below also constitutes the present invention.

[0013] The drawings shown below are schematic diagrams, and the dimensions, aspect ratio, scale, etc. may differ from those of the actual product.

[0014] In this specification, unless otherwise specified, terms indicating the relationship between elements (e.g., "parallel," "perpendicular," etc.) and terms indicating the shape of elements not only mean the literal strict form, but also mean a range that is substantially equivalent, for example, a range that includes a difference of about a few percent.

[0015] [Liquid Crystal Polymer Film] The liquid crystal polymer film of the present invention is characterized by containing a liquid crystal polymer as a main component and having a total free volume parameter determined by positron annihilation lifetime spectroscopy of 0.08 or more and 0.19 or less.

[0016] In this specification, the term "film" is synonymous with "sheet," and the two are not distinguished by thickness.

[0017] In this specification, the term "major component" means the component with the highest weight percentage, preferably a component with a weight percentage greater than 50% by weight.

[0018] In studying a liquid crystal polymer film capable of suppressing the generation of bubbles at the interface with a metal foil when laminating the metal foil, the present inventors focused on voids in the liquid crystal polymer film, specifically voids present as portions not occupied by the liquid crystal polymer (for example, gaps between liquid crystal polymer molecules). The present inventors then found that by setting the total number of voids in the liquid crystal polymer film within a predetermined range, specifically by setting the total free volume parameter of the liquid crystal polymer film determined by positron annihilation lifetime spectroscopy (PALS) to 0.08 or more and 0.19 or less, it is possible to suppress the generation of bubbles at the interface between the liquid crystal polymer film and the metal foil when laminating the metal foil to the liquid crystal polymer film.

[0019] In this regard, the present inventors have considered that the voids in the liquid crystal polymer film function as a buffer space that facilitates the movement of the liquid crystal polymer when the liquid crystal polymer film is stretched or bent. Therefore, the present inventors have considered that the voids in the liquid crystal polymer film contribute to the flexibility of the liquid crystal polymer film in relation to stretching, bending, etc. On the other hand, the present inventors have further studied and have concluded that if the total number of voids in the liquid crystal polymer film is too small, specifically, if the total free volume parameter of the liquid crystal polymer film determined by positron annihilation lifetime spectroscopy is less than 0.08, the liquid crystal polymer film loses flexibility and becomes rigid. Therefore, when a metal foil is laminated onto the liquid crystal polymer film, the rigid liquid crystal polymer film cannot fully conform to the surface roughness of the metal foil, resulting in the generation of bubbles at the interface between the liquid crystal polymer film and the metal foil. Furthermore, after further investigation, the inventors of the present invention have concluded that if the total number of voids in the liquid crystal polymer film is too large, specifically if the total free volume parameter of the liquid crystal polymer film determined by positron annihilation lifetime spectroscopy is larger than 0.19, the flexibility of the liquid crystal polymer film is ensured, and when a metal foil is laminated onto the liquid crystal polymer film, the flexible liquid crystal polymer film can conform to the surface roughness of the metal foil; however, the voids in the liquid crystal polymer film with a large total number gather together to form large voids, and as a result, these large voids form bubbles at the interface between the liquid crystal polymer film and the metal foil.

[0020] Based on the above, the inventors have concluded that if the total number of voids in the liquid crystal polymer film is within an appropriate range, specifically, if the total free volume parameter of the liquid crystal polymer film determined by positron annihilation lifetime spectroscopy is 0.08 or more and 0.19 or less, then this will lead to the suppression of bubble generation at the interface between the liquid crystal polymer film and the metal foil when laminating the metal foil to the liquid crystal polymer film.

[0021] Specific examples of the liquid crystal polymer film of the present invention will be described below.

[0022] FIG. 1 is a cross-sectional view schematically showing an example of the liquid crystal polymer film of the present invention.

[0023] The liquid crystal polymer film 1 shown in FIG. 1 contains a liquid crystal polymer 1g as a main component.

[0024] 1 and the like, liquid crystal polymer 1g is shown to refer to a region in the liquid crystal polymer film (liquid crystal polymer film 1 in FIG. 1), but in reality, the region shown by liquid crystal polymer 1g is a state in which multiple liquid crystal polymers (molecular chains) are aligned. Unless otherwise specified, liquid crystal polymer 1g will hereinafter refer to each individual liquid crystal polymer in the liquid crystal polymer film.

[0025] Since liquid crystal polymer 1g has a low relative permittivity and dielectric loss tangent among thermoplastic resins, the inclusion of liquid crystal polymer 1g as a main component in liquid crystal polymer film 1 facilitates improvement in the electrical properties, particularly the dielectric properties in the high frequency range, of liquid crystal polymer film 1. Furthermore, since liquid crystal polymer 1g has low hygroscopicity, the inclusion of liquid crystal polymer 1g as a main component in liquid crystal polymer film 1 makes it difficult for changes in the electrical properties, particularly the dielectric properties, of liquid crystal polymer film 1 to occur due to moisture absorption.

[0026] The liquid crystal polymer 1g preferably contains a copolymer of p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA).

[0027] When the liquid crystal polymer 1g contains a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, the molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid is preferably 0.20 or more and 5 or less. When the molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid in the liquid crystal polymer 1g is lower than 0.20 or higher than 5, the melting point of the liquid crystal polymer film 1 may become higher than the preferred range (270°C or more and 340°C or less) described below.

[0028] When the liquid crystal polymer 1g contains a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, the liquid crystal polymer 1g preferably contains 10 mol% or more of each of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, when the total amount of monomers is 100 mol%. If the content of each of the p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid monomers in the liquid crystal polymer 1g is less than 10 mol%, it may be difficult for the liquid crystal polymer 1g to exhibit liquid crystallinity, for the liquid crystal polymer 1g to have a low dielectric tangent, and for the liquid crystal polymer film 1 to have a melting point in the preferred range (270°C or higher and 340°C or lower) described below.

[0029] Copolymers of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid are generally referred to as type II wholly aromatic polyesters (also referred to as type 1.5 wholly aromatic polyesters). Type II wholly aromatic polyesters are less susceptible to hydrolysis than type III partially aromatic polyesters, and are therefore preferred as constituent materials for the liquid crystal polymer film 1. Furthermore, type II wholly aromatic polyesters have a low dielectric loss tangent due to the naphthalene ring, and therefore contribute to reducing electrical energy loss in the liquid crystal polymer film 1.

[0030] The liquid crystal polymer 1g may further contain a type I wholly aromatic polyester in addition to the type II wholly aromatic polyester, or may further contain a type III partially aromatic polyester, or may further contain a type I wholly aromatic polyester and a type III partially aromatic polyester.

[0031] The structure (type), ratio, and content of each monomer constituting 1 g of liquid crystal polymer can be analyzed by reactive pyrolysis gas chromatography mass spectrometry (reactive pyrolysis GC-MS method).

[0032] The liquid crystal polymer film 1 may further contain components other than the liquid crystal polymer 1g (for example, a resin material, an inorganic filler, etc.) as long as it contains the liquid crystal polymer 1g as a main component.

[0033] Voids 1h exist inside the liquid crystal polymer film 1. The voids 1h are assumed to be voids that exist as portions not occupied by the liquid crystal polymer 1g (for example, gaps between the liquid crystal polymers 1g). Because such voids 1h are minute (for example, on the sub-nano order), the positron annihilation lifetime method is suitable as a measurement method for the voids 1h.

[0034] The liquid crystal polymer film 1 has a total free volume parameter determined by positron annihilation lifetime spectroscopy of 0.08 or more and 0.19 or less. This makes it possible to suppress the generation of bubbles at the interface between the liquid crystal polymer film 1 and the metal foil when laminating the metal foil onto the liquid crystal polymer film 1 in producing a metal-clad laminate using the liquid crystal polymer film 1 and the metal foil, as will be described later. In other words, the liquid crystal polymer film 1 makes it possible to realize a liquid crystal polymer film that can suppress the generation of bubbles at the interface with the metal foil when laminating the metal foil.

[0035] In the case of the liquid crystal polymer film 1, if the total free volume parameter determined by the positron annihilation lifetime method is smaller than 0.08, the liquid crystal polymer film 1 loses its flexibility and becomes rigid. Therefore, when a metal foil is laminated onto the liquid crystal polymer film 1, the rigid liquid crystal polymer film 1 is unable to conform to the surface roughness of the metal foil, and as a result, bubbles are generated at the interface between the liquid crystal polymer film 1 and the metal foil.

[0036] In the liquid crystal polymer film 1, when the total free volume parameter determined by the positron annihilation lifetime method is greater than 0.19, the flexibility of the liquid crystal polymer film 1 is ensured, so that when a metal foil is laminated onto the liquid crystal polymer film 1, the flexible liquid crystal polymer film 1 can conform to the surface roughness of the metal foil, but the voids 1h in the liquid crystal polymer film 1 gather together to form large voids, and as a result, these large voids form bubbles at the interface between the liquid crystal polymer film 1 and the metal foil.

[0037] The liquid crystal polymer film 1 preferably has a total free volume parameter determined by positron annihilation lifetime spectroscopy of 0.12 to 0.17 inclusive, which significantly suppresses the generation of bubbles at the interface between the liquid crystal polymer film 1 and the metal foil when the metal foil is laminated onto the liquid crystal polymer film 1.

[0038] As mentioned above, the voids 1h are assumed to be voids that exist as parts not occupied by the liquid crystal polymer 1g (for example, gaps between the liquid crystal polymers 1g). Therefore, unless, for example, the individual liquid crystal polymers 1g are aligned with the same length and no gaps, the voids 1h do not exist, specifically, the total free volume parameter calculated by the positron annihilation lifetime method does not become 0.

[0039] The positron annihilation lifetime method will be outlined below.

[0040] A positron is the antiparticle of an electron and has a positive charge. When a positron binds with an electron, it emits a gamma ray and annihilates. When a positron is incident on a polymeric material (e.g., a liquid crystal polymer) that contains vacancies, i.e., missing atomic nuclei, the incident positron is trapped in the vacancy due to the Coulomb repulsion from the nucleus, and then binds with an electron present in the vacancy wall and annihilates. At this time, the size, quantity, etc. (radius, free volume, etc.) of the vacancy can be evaluated by measuring the time until the positron trapped in the vacancy binds with an electron and annihilates, i.e., the positron lifetime. Specifically, when positrons are incident on a polymeric material that contains vacancies, some of the incident positrons are electrically bound together with electrons to form pairs, forming a state known as positronium (Ps). Positronium exists in two types: ortho-positronium (o-Ps), in which the spin directions are parallel, and para-positronium (p-Ps), in which the spin directions are antiparallel. Of these, ortho-positronium is captured by a vacancy and then annihilates with an electron present on the vacancy wall (pick-off annihilation). At this time, by measuring the lifetime of the ortho-positronium captured in the vacancy until it annihilates with an electron, that is, the lifetime of the ortho-positronium derived from the vacancy in the polymer material, the radius of the vacancy in the polymer material can be evaluated.

[0041] The lifetime of ortho-positronium originating from vacancies in a polymeric material is determined as follows. First, a positron lifetime spectrum is measured when a positron is incident on the polymeric material. Next, the obtained positron lifetime spectrum is fitted with three components to determine the positron lifetimes from the shortest to the longest. １ , τ ２ , and τ ３ Then, the longest life τ ３ is defined as the lifetime of ortho-positronium originating from vacancies in the polymer material.

[0042] Ortho-positronium lifetime τ from vacancies ３ and the radius R of the vacancy are related by the Tao-Eldrup equation shown in the following formula (1). ３By measuring the lifetime τ of the ortho-positronium originating from the vacancy, ３ can be converted to the radius R of the hole. ３ =0.5[1-{R / (R+0.166)}+(1 / 2π) sin{2πR / (R+0.166)}] －１ ...(1)

[0043] Furthermore, according to the above formula (1), the lifetime τ of ortho-positronium originating from vacancies ３ is converted into the radius R of the air hole, and then the diameter D of the air hole can be calculated from the radius R of the air hole by the following formula (2): D = 2R (2)

[0044] In this specification, the pore diameter determined by the positron annihilation lifetime spectroscopy is synonymous with the pore size, free volume diameter, microvoid diameter, pore size, and the like.

[0045] Furthermore, the free volume V of the pore can be calculated from the radius R of the pore using the following formula (3): V = 4πR ３ / 3...(3)

[0046] Furthermore, by fitting the positron lifetime spectrum to three components as described above, the positron lifetime can be calculated from the shortest to the longest τ １ , τ ２ , and τ ３ Then, the relative spectral intensities corresponding to each of these positron lifetimes are defined as I １ , I ２ , and I ３ (I １ +I ２ +I ３ = 100%), the relative spectral intensity I due to ortho-positronium is calculated by the following formula (4): ３ The total free volume parameter VP of a polymer material can be calculated from the free volume V of the pores. The total free volume parameter VP of a polymer material corresponds to the total amount of pores in the polymer material. VP = I ３ ×V... (4)

[0047] In this specification, the total free volume parameter determined by the positron annihilation lifetime spectroscopy is synonymous with the total free volume.

[0048] The melting point of the liquid crystal polymer film 1 is preferably 270° C. or higher. In this case, the heat resistance of the liquid crystal polymer film 1 is sufficient, so that the size, quantity, etc. (radius, free volume, etc.) of the pores 1h are unlikely to change due to heat, even when a metal-clad laminate and an electronic circuit board (described later) formed using the liquid crystal polymer film 1 are incorporated into an electronic device by reflow soldering.

[0049] If the melting point of the liquid crystal polymer film 1 is lower than 270°C, the heat resistance of the liquid crystal polymer film 1 will be insufficient, and when the metal-clad laminate and electronic circuit board described below formed using the liquid crystal polymer film 1 are incorporated into electronic devices by reflow soldering, the size, quantity, etc. (radius, free volume, etc.) of the voids 1h may be easily changed by heat.

[0050] The melting point of the liquid crystal polymer film 1 is more preferably 280° C. or higher.

[0051] The melting point of the liquid crystal polymer film 1 is preferably 340° C. or lower. In this case, the processing temperature when molding the liquid crystal polymer film 1 does not become too high, so that the liquid crystal polymer is less likely to decompose and deteriorate during molding of the liquid crystal polymer film 1.

[0052] If the melting point of the liquid crystal polymer film 1 is higher than 340° C., the processing temperature when molding the liquid crystal polymer film 1 becomes high, which may make the liquid crystal polymer more susceptible to decomposition and deterioration during molding of the liquid crystal polymer film 1 .

[0053] The melting point of the liquid crystal polymer film 1 is more preferably 330° C. or lower.

[0054] The thickness of the liquid crystal polymer film 1 is preferably 10 μm or more and 500 μm or less, in which case the liquid crystal polymer film 1 can be easily used in the production of metal-clad laminates and electronic circuit boards, which will be described later.

[0055] If the thickness of the liquid crystal polymer film 1 is less than 10 μm, the liquid crystal polymer film 1 is prone to wrinkles, warping, etc., which may make it difficult to handle the liquid crystal polymer film 1 when using it to manufacture the metal-clad laminate and electronic circuit board described below.

[0056] If the thickness of the liquid crystal polymer film 1 is greater than 500 μm, when using the liquid crystal polymer film 1 to manufacture an electronic circuit board having an interlayer connection conductor as described below, it may be difficult to form a via hole in which the interlayer connection conductor will be formed so that it penetrates the film portion.

[0057] The liquid crystal polymer film 1 is produced, for example, by the following method.

[0058] In the following, an inflation molding method will be shown as an example of a method for producing the liquid crystal polymer film 1.

[0059] FIG. 2 is a cross-sectional view schematically showing an example of the method for producing a liquid crystal polymer film of the present invention.

[0060] The inflation molding machine 100 shown in FIG. 2 includes an extruder 110 , a die (mold) 120 , an inflation / cooling mechanism 130 , a clamping roll 140 , and a winder 150 .

[0061] First, a resin composition 1s containing a liquid crystal polymer 1g as a main component is melted and then placed in an extruder 110. Then, the melted resin composition 1s placed in the extruder 110 is extruded into a die 120 by the extruder 110.

[0062] Next, the molten resin composition 1s extruded into the die 120 is discharged from the die 120 into the inflation / cooling mechanism 130 so as to become a tubular film.

[0063] Next, blow-up air is fed into the tubular resin composition 1s discharged from the die 120 into the inflation / cooling mechanism 130 through the air inlet 121 of the die 120, thereby expanding the resin composition 1s. At the same time, the expanded resin composition 1s is cooled by cooling air that passes through the air ring 131 of the inflation / cooling mechanism 130. The resin composition 1s cooled by the cooling air is then stretched while remaining in its tubular form, and is further cooled by the guide plate 132 of the inflation / cooling mechanism 130. As a result, the resin composition 1s is cooled and hardened (solidified) by the guide plate 132.

[0064] Next, the tubular resin composition 1s cooled and solidified by the guide plate 132 is sandwiched between tightening rolls 140 and pulled, thereby obtaining a liquid crystal polymer film 1.

[0065] Finally, the obtained liquid crystal polymer film 1 is transported via a guide roll 160 as needed, and is wound up by a winder 150 .

[0066] When the liquid crystal polymer film 1 is produced by the inflation molding method, for example, the following molding parameters are appropriately set.

[0067] FIG. 3 is an enlarged cross-sectional view schematically showing the die and its periphery in FIG.

[0068] 3 indicates the width of the outlet 122 of the die 120 from which the molten resin composition 1s is discharged. The die clearance a is determined as a = (b - c) / 2, where b is the inner diameter of the outer lip and c is the outer diameter of the inner lip, which will be described later. Note that the die clearance a can be considered to be equivalent to the thickness of the molten resin composition 1s immediately after being discharged from the outlet 122 of the die 120, but due to the occurrence of die swelling, it may not be strictly equivalent to the thickness of the molten resin composition 1s immediately after being discharged from the outlet 122 of the die 120.

[0069] <Inner Diameter of Outer Lip> The inner diameter b of the outer lip shown in FIG. 3 indicates the inner diameter of the outer portion 123 of the die 120 .

[0070] <Outer Diameter of Inner Lip> The outer diameter c of the inner lip shown in FIG. 3 refers to the outer diameter of the inner portion 124 of the die 120 .

[0071] <Die Land Length> The die land length d shown in FIG. 3 refers to the length of the land portion 125 of the die 120 .

[0072] <Discharge Amount> The discharge amount refers to the weight of the molten resin composition 1s discharged from the die 120 per hour.

[0073] <Draft Ratio> The draft ratio refers to the ratio of the winding speed of the liquid crystal polymer film 1 by the winder 150 to the extrusion speed of the molten resin composition 1s by the die 120 (winding speed / extrusion speed).

[0074] The larger the draft ratio, the more strongly the molten resin composition 1s is stretched in the machine direction (MD) corresponding to the direction in which it is extruded from the die 120, and therefore the thickness of the resulting liquid crystal polymer film 1 becomes smaller.

[0075] <Blow-up ratio> The blow-up ratio refers to the ratio (tube diameter / die diameter) of the tube diameter corresponding to the diameter of the resin composition 1s extruded from the die 120 and formed into a tube to the die diameter corresponding to the diameter of the die 120. The die diameter is often set to be the same as the inner diameter b of the outer lip.

[0076] The larger the blow-up ratio, the stronger the stretching of the molten resin composition 1s in the transverse direction (TD) perpendicular to the flow direction, and therefore the thinner the thickness of the resulting liquid crystal polymer film 1 becomes.

[0077] <Blow-up air temperature> The blow-up air temperature refers to the temperature of the blow-up air that is fed from the air inlet 121 of the die 120 when expanding the resin composition 1s that has been extruded from the die 120 and formed into a tubular shape.

[0078] The higher the blow-up air temperature, the higher the temperature at which the resin composition 1s is heated when inflating the resin composition 1s extruded from the die 120. This makes the liquid crystal polymer 1g in the resin composition 1s more likely to decompose, which in turn makes it more likely for gas to be generated in the resin composition 1s. When gas is more likely to be generated in the resin composition 1s, the resin composition 1s is cooled and solidified in the guide plate 132 or the like used later, with a large amount of gas remaining in the resin composition 1s. As a result, the resulting liquid crystal polymer film 1 contains more voids 1h due to gas, which are assumed to be portions not occupied by the liquid crystal polymer 1g (e.g., gaps between the liquid crystal polymers 1g). From the above, the higher the blow-up air temperature, the larger the total free volume parameter, corresponding to the total amount of voids 1h, in the resulting liquid crystal polymer film 1.

[0079] On the other hand, the lower the blow-up air temperature, the lower the temperature at which the resin composition 1s is heated when inflating the resin composition 1s extruded from the die 120. This reduces the decomposition of the liquid crystal polymer 1g in the resin composition 1s, thereby reducing the generation of gas in the resin composition 1s. When gas generation in the resin composition 1s is reduced, the resin composition 1s is cooled and solidified in the guide plate 132, etc., used later, with less gas remaining in the resin composition 1s. As a result, the resulting liquid crystal polymer film 1 contains fewer voids 1h due to gas, which are assumed to be portions not occupied by the liquid crystal polymer 1g (e.g., gaps between the liquid crystal polymers 1g). From the above, the lower the blow-up air temperature, the smaller the total free volume parameter, corresponding to the total amount of voids 1h, in the resulting liquid crystal polymer film 1.

[0080] In the liquid crystal polymer film 1 produced by the inflation molding method described above, from the viewpoint of setting the total free volume parameter determined by the positron annihilation lifetime method to 0.08 or more and 0.19 or less, the blow-up air temperature is preferably 230°C or more and 290°C or less, more preferably 240°C or more and 280°C or less, and even more preferably 250°C or more and 270°C or less.

[0081] <Guide Plate Temperature> The guide plate temperature refers to the temperature of the guide plate 132 used when cooling and solidifying the resin composition 1s stretched into a tubular shape.

[0082] The method for producing the liquid crystal polymer film 1 may be a molding method other than the inflation molding method described above, as long as it uses a mechanism capable of heating the resin composition 1s at a desired temperature to set the total free volume parameter within a predetermined range (in the example shown in FIG. 2, blow-up air fed from the air inlet 121 of the die 120). For example, the liquid crystal polymer film 1 may be produced by a T-die extrusion molding method. In this case, the total free volume parameter of the resulting liquid crystal polymer film 1 can be set within a predetermined range by controlling the environmental temperature from when the resin composition 1s is extruded through the T-die until it is cooled.

[0083] The liquid crystal polymer film of the present invention is not limited to the above-mentioned form, and various applications and modifications can be made within the scope of the present invention with respect to the structure, production conditions, etc. of the liquid crystal polymer film.

[0084] [Metal-Clad Laminate] The metal-clad laminate of the present invention is characterized by being formed using the liquid crystal polymer film of the present invention and a metal foil.

[0085] FIG. 4 is a cross-sectional view schematically showing an example of the metal-clad laminate of the present invention.

[0086] The metal-clad laminate 10 shown in FIG. 4 includes a liquid crystal polymer film 1 ′ and a metal foil 2 .

[0087] The metal-clad laminate 10 is formed using a liquid crystal polymer film 1 and a metal foil 2. For example, the metal-clad laminate 10 is produced by laminating, preferably by pressure bonding (e.g., thermocompression bonding), the metal foil 2 to the liquid crystal polymer film 1. After being pressure-bonded to the liquid crystal polymer film 1, the metal foil 2 may be etched to form a pattern such as a circuit. Alternatively, the metal foil 2 may be pressure-bonded to the liquid crystal polymer film 1 in a pre-patterned state.

[0088] As described above, in the metal-clad laminate 10 formed using the liquid crystal polymer film 1 and the metal foil 2, the liquid crystal polymer film 1' is derived from the liquid crystal polymer film 1.

[0089] The liquid crystal polymer film 1' may differ from the liquid crystal polymer film 1 in terms of, for example, the size and quantity (radius, free volume, etc.) of the pores 1h, but may be the same as the liquid crystal polymer film 1.

[0090] Examples of the metal foil 2 include copper foil, aluminum foil, stainless steel foil, nickel foil, tin foil, and alloy foil containing at least one of these metals. Among these, copper foil is preferred as the metal foil 2. In this case, metals other than copper may be present on the surface of the copper foil.

[0091] The thickness of the metal foil 2 is preferably 1 μm or more and 35 μm or less, and more preferably 6 μm or more and 18 μm or less.

[0092] In the example shown in Figure 4, the metal-clad laminate 10 has a metal foil 2 adjacent to one main surface of the liquid crystal polymer film 1', but in addition to the metal foil 2, it may also have another metal foil adjacent to the other main surface of the liquid crystal polymer film 1'.

[0093] The metal-clad laminate 10 is formed using a liquid crystal polymer film 1 that can suppress the generation of bubbles at the interface with the metal foil 2 when laminating the metal foil 2, and therefore can suppress the generation of bubbles at the interface between the liquid crystal polymer film 1 and the metal foil 2 during the manufacturing process of the metal-clad laminate 10. In other words, in the metal-clad laminate 10, the generation of bubbles at the interface between the liquid crystal polymer film 1' and the metal foil 2, which is caused by the liquid crystal polymer film 1, is suppressed.

[0094] The metal-clad laminate of the present invention is not limited to the above-described form, and various applications and modifications can be made within the scope of the present invention with respect to the configuration, manufacturing conditions, etc. of the metal-clad laminate.

[0095] [Electronic Circuit Board] The electronic circuit board of the present invention is characterized in that it is formed using the metal-clad laminate of the present invention and has a circuit formed on the metal foil.

[0096] FIG. 5 is a cross-sectional view schematically showing an example of an electronic circuit board according to the present invention.

[0097] 5 includes a metal-clad laminate 10A, a metal-clad laminate 10B, and a metal-clad laminate 10C, which are stacked in this order in the thickness direction (the vertical direction in FIG. 5). That is, in the electronic circuit board 50, the metal-clad laminate 10A, the metal-clad laminate 10B, and the metal-clad laminate 10C are stacked in this order in the thickness direction.

[0098] The metal-clad laminate 10A includes a liquid crystal polymer film 1A and a metal foil 2A.

[0099] The metal-clad laminate 10B includes a liquid crystal polymer film 1B and a metal foil 2B.

[0100] The metal-clad laminate 10C includes a liquid crystal polymer film 1C and a metal foil 2C.

[0101] The electronic circuit board 50 is formed using a metal-clad laminate 10. For example, the electronic circuit board 50 is manufactured by stacking, preferably by compression bonding (e.g., thermocompression bonding), a plurality of (three in FIG. 5 ) metal-clad laminates including at least one metal-clad laminate 10.

[0102] As described above, in the electronic circuit board 50 formed using at least one metal-clad laminate 10, at least one selected from the group consisting of the metal-clad laminate 10A, the metal-clad laminate 10B, and the metal-clad laminate 10C is derived from the metal-clad laminate 10. In other words, among the metal-clad laminate 10A, the metal-clad laminate 10B, and the metal-clad laminate 10C, all of the metal-clad laminates may be derived from the metal-clad laminate 10, or some of the metal-clad laminates may be derived from the metal-clad laminate 10.

[0103] As described above, in the electronic circuit board 50 formed using at least one metal-clad laminate 10, at least one selected from the group consisting of liquid crystal polymer film 1A, liquid crystal polymer film 1B, and liquid crystal polymer film 1C is derived from liquid crystal polymer film 1'. In other words, among the liquid crystal polymer films 1A, liquid crystal polymer film 1B, and liquid crystal polymer film 1C, all of the liquid crystal polymer films may be derived from liquid crystal polymer film 1', or some of the liquid crystal polymer films may be derived from liquid crystal polymer film 1'. For example, if the metal-clad laminate 10A is derived from the metal-clad laminate 10, the liquid crystal polymer film 1A will be derived from the liquid crystal polymer film 1'.

[0104] Of the liquid crystal polymer films 1A, 1B, and 1C, the liquid crystal polymer film derived from the liquid crystal polymer film 1' may differ from the liquid crystal polymer film 1', for example, in terms of the size, quantity, etc. (radius, free volume, etc.) of the voids 1h, but may be the same as the liquid crystal polymer film 1'.

[0105] The thicknesses of the liquid crystal polymer film 1A, the liquid crystal polymer film 1B, and the liquid crystal polymer film 1C may be the same as one another, may be different from one another, or may be partially different from one another.

[0106] As described above, in the electronic circuit board 50 formed using the metal-clad laminate 10, at least one selected from the group consisting of metal foil 2A, metal foil 2B, and metal foil 2C is derived from metal foil 2. In other words, among the metal foils 2A, metal foil 2B, and metal foil 2C, all of the metal foils may be derived from metal foil 2, or some of the metal foils may be derived from metal foil 2. For example, if the metal-clad laminate 10A is derived from the metal-clad laminate 10, then the metal foil 2A is derived from metal foil 2.

[0107] The metal foil 2A is adjacent to the liquid crystal polymer film 1A on the side of the liquid crystal polymer film 1B. Also, the metal foil 2A is adjacent to the liquid crystal polymer film 1B on the side of the liquid crystal polymer film 1A. In other words, the metal foil 2A is located between the liquid crystal polymer film 1A and the liquid crystal polymer film 1B, and is in contact with both the liquid crystal polymer film 1A and the liquid crystal polymer film 1B.

[0108] The metal foil 2B is adjacent to the liquid crystal polymer film 1B on the side of the liquid crystal polymer film 1C. Also, the metal foil 2B is adjacent to the liquid crystal polymer film 1C on the side of the liquid crystal polymer film 1B. In other words, the metal foil 2B is located between the liquid crystal polymer film 1B and the liquid crystal polymer film 1C, and is in contact with both the liquid crystal polymer film 1B and the liquid crystal polymer film 1C.

[0109] The metal foil 2B preferably spans the interface between the liquid crystal polymer film 1B and the liquid crystal polymer film 1C. In this case, the interface between the liquid crystal polymer film 1B and the metal foil 2B and the interface between the liquid crystal polymer film 1C and the metal foil 2B are shifted from the interface between the liquid crystal polymer film 1B and the liquid crystal polymer film 1C, making it difficult for peeling to occur at the interface between the liquid crystal polymer film 1B and the metal foil 2B and at the interface between the liquid crystal polymer film 1C and the metal foil 2B.

[0110] 5 shows the interface between the liquid crystal polymer film 1B and the liquid crystal polymer film 1C, but in reality, this interface does not have to be clearly visible. When the interface between the liquid crystal polymer film 1B and the liquid crystal polymer film 1C is not clearly visible, in a cross section along the thickness direction of the electronic circuit board 50 as shown in FIG. 5, a plane passing through the center in the thickness direction of the cross section of the metal foil 2B and running along a plane direction perpendicular to the thickness direction (the left-right direction in FIG. 5) is regarded as the interface between the liquid crystal polymer film 1B and the liquid crystal polymer film 1C.

[0111] The metal foil 2B does not have to extend across the interface between the liquid crystal polymer film 1B and the liquid crystal polymer film 1C.

[0112] The metal foil 2C is adjacent to the liquid crystal polymer film 1C on the opposite side to the liquid crystal polymer film 1B.

[0113] The thicknesses of the metal foil 2A, the metal foil 2B, and the metal foil 2C may be the same as each other, may be different from each other, or may be partially different.

[0114] At least one selected from the group consisting of metal foil 2A, metal foil 2B, and metal foil 2C has a circuit formed thereon.

[0115] Of metal foil 2A, metal foil 2B, and metal foil 2C, the metal foil on which the circuit is formed may be in a planar shape that extends across the entire surface of electronic circuit board 50, or may be in a patterned shape that is patterned along the surface of electronic circuit board 50.

[0116] In the example shown in FIG. 5, the metal foil 2A and the metal foil 2C are planar and extend over the entire surface of the electronic circuit board 50.

[0117] In the example shown in Figure 5, the metal foil 2B has a patterned shape that is patterned along the surface direction of the electronic circuit board 50, and has a first portion 2Ba, a second portion 2Bb, and a third portion 2Bc along the surface direction of the electronic circuit board 50.

[0118] 5, all of the metal-clad laminates constituting the electronic circuit board 50 have a liquid crystal polymer film, but resin films other than liquid crystal polymer films may be present as long as there is at least one liquid crystal polymer film derived from the liquid crystal polymer film 1' constituting the metal-clad laminate 10. For example, when the liquid crystal polymer film 1A is derived from the liquid crystal polymer film 1', the liquid crystal polymer film 1B and the liquid crystal polymer film 1C may be resin films other than the liquid crystal polymer film.

[0119] 5, the number of metal-clad laminates constituting the electronic circuit board 50 is three, but the number of metal-clad laminates constituting the electronic circuit board 50 is not particularly limited as long as it is one or more. In other words, the number of metal-clad laminates used to form the electronic circuit board 50 is not particularly limited as long as it is one or more.

[0120] The electronic circuit board 50 may further include interlayer connection conductors that connect the metal foils together. In the example shown in Fig. 5, the electronic circuit board 50 further includes an interlayer connection conductor 20A, an interlayer connection conductor 20B, an interlayer connection conductor 20C, and an interlayer connection conductor 20D.

[0121] The interlayer connection conductor 20A penetrates the liquid crystal polymer film 1B in the thickness direction, but is connected to the metal foil 2A without penetrating the metal foil 2A in the thickness direction, and is connected to the second portion 2Bb of the metal foil 2B without penetrating the metal foil 2B in the thickness direction. In other words, the metal foil 2A and the second portion 2Bb of the metal foil 2B are electrically connected via the interlayer connection conductor 20A.

[0122] The interlayer connection conductor 20B penetrates the liquid crystal polymer film 1B in the thickness direction at a position spaced apart from the interlayer connection conductor 20A in the surface direction, but is connected to the metal foil 2A without penetrating the metal foil 2A in the thickness direction, and is connected to the third portion 2Bc of the metal foil 2B without penetrating the metal foil 2B in the thickness direction. In other words, the metal foil 2A and the third portion 2Bc of the metal foil 2B are electrically connected via the interlayer connection conductor 20B.

[0123] The interlayer connection conductor 20C penetrates the liquid crystal polymer film 1C in the thickness direction, but is connected to the second portion 2Bb of the metal foil 2B without penetrating the metal foil 2B in the thickness direction, and is connected to the metal foil 2C without penetrating the metal foil 2C in the thickness direction. In other words, the second portion 2Bb of the metal foil 2B and the metal foil 2C are electrically connected via the interlayer connection conductor 20C.

[0124] The interlayer connection conductor 20D penetrates the liquid crystal polymer film 1C in the thickness direction at a position spaced apart from the interlayer connection conductor 20C in the surface direction, but is connected to the third portion 2Bc of the metal foil 2B without penetrating the metal foil 2B in the thickness direction, and is connected to the metal foil 2C without penetrating the metal foil 2C in the thickness direction. In other words, the third portion 2Bc of the metal foil 2B and the metal foil 2C are electrically connected via the interlayer connection conductor 20D.

[0125] As a result of the above, in the electronic circuit board 50, the metal foils 2A and 2C are electrically connected via the interlayer connection conductor 20A, the second portion 2Bb of the metal foil 2B, and the interlayer connection conductor 20C. In addition, in the electronic circuit board 50, the metal foils 2A and 2C are also electrically connected via the interlayer connection conductor 20B, the third portion 2Bc of the metal foil 2B, and the interlayer connection conductor 20D.

[0126] The interlayer connection conductor 20A is formed, for example, by plating a metal material onto the inner wall surface of a via hole that penetrates the liquid crystal polymer film 1B in the thickness direction but does not penetrate the metal foil 2B in the thickness direction so as to reach the second portion 2Bb of the metal foil 2B, or by filling the hole with a conductive paste and then subjecting the hole to heat treatment (for example, heating when thermocompressing a metal-clad laminate).

[0127] The interlayer connection conductors 20B, 20C, and 20D are formed in the same manner as the interlayer connection conductor 20A, except that they are formed at different positions.

[0128] When at least one selected from the group consisting of interlayer connection conductor 20A, interlayer connection conductor 20B, interlayer connection conductor 20C, and interlayer connection conductor 20D is formed by plating a metal material, the interlayer connection conductor formed by plating a metal material preferably contains at least one metal selected from the group consisting of copper, tin, and silver, and more preferably contains copper.

[0129] When at least one selected from the group consisting of interlayer connection conductor 20A, interlayer connection conductor 20B, interlayer connection conductor 20C, and interlayer connection conductor 20D is formed by heat treatment of a conductive paste, the interlayer connection conductor formed by heat treatment of the conductive paste preferably contains at least one metal selected from the group consisting of copper, tin, and silver, more preferably contains copper, and even more preferably contains copper and tin. For example, when interlayer connection conductor 20A contains copper and tin and metal foil 2B is copper foil, interlayer connection conductor 20A undergoes an alloying reaction with metal foil 2B at low temperatures, thereby facilitating electrical conduction between the two. The combinations of interlayer connection conductor 20B and metal foil 2B, interlayer connection conductor 20C and metal foil 2C, and interlayer connection conductor 20D and metal foil 2C are similar to the combination of interlayer connection conductor 20A and metal foil 2B.

[0130] When at least one selected from the group consisting of interlayer connection conductor 20A, interlayer connection conductor 20B, interlayer connection conductor 20C, and interlayer connection conductor 20D is formed by heat treatment of a conductive paste, it is preferable that the interlayer connection conductor formed by heat treatment of the conductive paste contains at least one thermosetting resin selected from the group consisting of epoxy resin, phenolic resin, polyimide resin, silicone resin or modified resin thereof, and acrylic resin, or at least one thermoplastic resin selected from the group consisting of polyamide resin, polystyrene resin, polymethacrylic resin, polycarbonate resin, and cellulose-based resin.

[0131] The conductive paste used to form the interlayer connection conductor may further contain a vehicle, a solvent, a thixotropic agent, an activator, and the like in addition to the metal and resin described above.

[0132] When manufacturing an electronic circuit board 50 having interlayer connection conductors, for example, a plurality of metal-clad laminates including the metal-clad laminate 10 filled with conductive paste as described above are pressure-bonded together. At this time, the conductive paste filled in the metal-clad laminates becomes the interlayer connection conductors by being solidified by the heat generated when the metal-clad laminates are thermocompression-bonded.

[0133] The above describes an example of forming an interlayer connection conductor by plating a metal material on the inner wall surface of a via hole that penetrates the liquid crystal polymer film in the thickness direction but does not penetrate the metal foil in the thickness direction so as to reach the metal foil, or by filling it with a conductive paste and then heat treating it.However, an interlayer connection conductor may also be formed by plating a metal material on the inner wall surface of a via hole that is formed so as to penetrate both the liquid crystal polymer film and the metal foil in the thickness direction, or by filling it with a conductive paste and then heat treating it.

[0134] The electronic circuit board 50 may form a transmission line. For example, the electronic circuit board 50 may have the first portion 2Ba of the metal foil 2B as a signal line for transmitting a signal, forming the transmission line. In this case, the first portion 2Ba of the metal foil 2B may be a signal line for transmitting a high-frequency signal.

[0135] The electronic circuit board 50 may have the first portion 2Ba of the metal foil 2B as a signal line for transmitting signals, and may have the metal foil 2A and the metal foil 2C as ground electrodes. In this case, the electronic circuit board 50 constitutes a stripline-type transmission line.

[0136] When the electronic circuit board 50 constitutes the above-mentioned transmission line, the liquid crystal polymer film 1B containing a liquid crystal polymer 1g with a low dielectric constant and the liquid crystal polymer film 1C containing a liquid crystal polymer 1g with a low dielectric constant are in contact with the first part 2Ba of the metal foil 2B, i.e., the signal line, and therefore the transmission characteristics of the electronic circuit board 50 are likely to be improved.

[0137] The electronic circuit board 50 may be configured with a transmission line other than a stripline type, such as a microstrip type transmission line or a coplanar type transmission line.

[0138] The electronic circuit board 50 can be used in various electronic devices. For example, the electronic circuit board 50 can be used in electronic devices for communication for 5G / 6G.

[0139] The electronic circuit board 50 may be in a bent state or in an unbent state when it is incorporated into an electronic device.

[0140] The electronic circuit board of the present invention is not limited to the above-described embodiment, and various applications and modifications can be made within the scope of the present invention with respect to the configuration, manufacturing conditions, etc. of the electronic circuit board.

[0141] EXAMPLES Hereinafter, examples will be shown that more specifically disclose the liquid crystal polymer film and the metal-clad laminate of the present invention, but the present invention is not limited to the following examples.

[0142] [Examples 1 to 8 and Comparative Examples 1 to 6] The liquid crystal polymer films (biaxially oriented liquid crystal polymer films) of Examples 1 to 8 and Comparative Examples 1 to 6 were produced by the inflation molding method described above (see FIGS. 2 and 3). The production conditions were as follows:

[0143] <Materials> Liquid crystal polymer A or liquid crystal polymer B was used as shown in Tables 1 and 2. Liquid crystal polymer A: A copolymer of 73 mol % of p-hydroxybenzoic acid and 27 mol % of 6-hydroxy-2-naphthoic acid. Liquid crystal polymer B: A copolymer of 80 mol % of p-hydroxybenzoic acid and 20 mol % of 6-hydroxy-2-naphthoic acid.

[0144] <Molding parameters> Die clearance: 500 μm Outer lip inner diameter: 60 mm Inner lip outer diameter: 59 mm Die land length: 30 mm Discharge rate: 12 kg / hour Draft ratio: As shown in Tables 1 and 2 Blow-up ratio: As shown in Tables 1 and 2 (where die diameter = outer lip inner diameter) Blow-up air temperature: As shown in Tables 1 and 2

[0145] [Evaluation] The liquid crystal polymer films of Examples 1 to 8 and Comparative Examples 1 to 6 were evaluated as follows. The evaluation results are shown in Tables 1 and 2.

[0146] <Thickness> First, a 100 mm square liquid crystal polymer film sample was cut out from the liquid crystal polymer film. Then, in a 25 mm square region sharing the center with this liquid crystal polymer film sample, the thicknesses were measured at nine equally spaced points using a dial gauge, and the average value of these measurements was determined to be the thickness of the liquid crystal polymer film.

[0147] <Melting Point> First, using a differential scanning calorimeter "DSC7000X" manufactured by Hitachi High-Tech Science Corporation, the liquid crystal polymer film was heated at a heating rate of 20°C / min to completely melt it. The resulting melt was then cooled to 175°C at a heating rate of 20°C / min, and then heated again at a heating rate of 20°C / min. The temperature corresponding to the endothermic peak observed during this heating process was determined as the melting point of the liquid crystal polymer film. When an endothermic peak was difficult to observe using the above-mentioned method, the melting point of the liquid crystal polymer film was determined by texture observation under crossed Nicols conditions using a polarizing microscope.

[0148] <Total Free Volume Parameter> FIG. 6 is a block diagram showing an example of a positron lifetime spectrum measurement apparatus.

[0149] First, a positron lifetime spectrum was measured using the positron lifetime spectrum measurement apparatus shown in FIG. 6 as follows. First, two samples were prepared by laminating multiple liquid crystal polymer films to a total thickness of 1 mm or more. Then, as shown in FIG. 6, these two samples were placed on either side of a positron source. Next, the start-side scintillator detected nuclear decay gamma rays generated from the positron source upon positron generation and converted the detected nuclear decay gamma rays into light. The stop-side scintillator detected positron annihilation gamma rays generated from the sample upon positron annihilation and converted the detected positron annihilation gamma rays into light. Next, the start-side photomultiplier tube (PMT) converted the light generated by the start-side scintillator into an electrical signal. The stop-side photomultiplier tube (PMT) also converted the light generated by the stop-side scintillator into an electrical signal. Next, a start signal indicating the time point of positron generation was extracted from the electrical signal generated by the start-side photomultiplier tube (PMT) by the start-side pulse-height discriminator (CFD). Furthermore, a stop signal indicating the time point of positron annihilation was extracted from the electrical signal generated by the stop-side photomultiplier tube (PMT) by the stop-side pulse-height discriminator (CFD). The stop signal output from the stop-side pulse-height discriminator (CFD) was then delayed by a predetermined time by a delay circuit (DELAY). This was done to ensure that the time difference between the stop signal output from the stop-side pulse-height discriminator (CFD) and the start signal output from the start-side pulse-height discriminator (CFD) could be reliably measured even if there was variation in the time resolution of the positron lifetime spectrum measurement device. Next, a time-voltage converter (TAC) was used to measure the time difference between the start signal output from the pulse height discriminator (CFD) on the start side and the stop signal output from the pulse height discriminator (CFD) on the stop side. Finally, a multi-channel analyzer (MCA) and a personal computer (PC) connected thereto were used to perform data analysis based on the time difference between the two signals measured by the time-voltage converter (TAC), thereby obtaining a positron lifetime spectrum. The measurement conditions for the positron lifetime spectrum were as follows. (Measurement conditions for the positron lifetime spectrum) Positron source:２２ Na sealed radiation source Detector: Fast response photomultiplier tube (BaF ２ Scintillator) Total counts: Approximately 4 million counts Measurement time: 24 hours Counts per unit time: Approximately 46 counts / second Analysis software: PALSfit 3.171

[0150] Next, by fitting the obtained positron lifetime spectrum to three components, the lifetime τ of ortho-positronium originating from the voids in the liquid crystal polymer film was calculated. ３ Then, the lifetime τ of the ortho-positronium originating from the vacancy was calculated by the above formula (1) (Tao-Eldrup formula). ３ was converted into the pore radius R. Then, the free volume V of the pore was calculated from the pore radius R using the above formula (3).

[0151] Furthermore, in the positron lifetime spectrum fitted with three components as described above, the relative spectral intensity I due to ortho-positronium is ３ Then, the relative spectral intensity I due to ortho-positronium was calculated using the above equation (4). ３ The total free volume parameter VP of the liquid crystal polymer film was calculated from the free volume V of the pores.

[0152] <Bubble Generation> First, a 100 mm square liquid crystal polymer film sample was cut out from the liquid crystal polymer film. Then, a copper foil (thickness: 12 μm) was thermocompression bonded (laminated) to this liquid crystal polymer film sample to produce a copper-clad laminate. The thermocompression bonding conditions were as follows. (Thermocompression Bonding Conditions) Temperature: Melting point of liquid crystal polymer film Pressure: 1 MPa Time: 10 seconds

[0153] Next, a 10 mm square copper-clad laminate sample was cut out from the copper-clad laminate, sharing the same center as the copper-clad laminate. Then, the copper-clad laminate sample was subjected to ion milling to expose the cross section of the copper-clad laminate sample. The cross section of the copper-clad laminate sample was then observed with a scanning electron microscope (SEM) (magnification: 1000x) to confirm the occurrence of bubbles at the interface between the liquid crystal polymer film and the copper foil. The evaluation criteria for the occurrence of bubbles were as follows: ◎ (Excellent): No bubbles were observed. ○ (Good): Bubbles were observed, but could be removed under the following conditions (no bubbles remained). × (Poor): Bubbles were observed, but could not be removed even under the following conditions (bubbles remained). (Bubble removal treatment conditions: Heat treatment conditions) Apparatus: Vacuum oven Temperature: 200°C Atmosphere: Vacuum Time: 1 hour

[0154]

[0155]

[0156] As shown in Tables 1 and 2, for the liquid crystal polymer films of Examples 1 to 8, in which the total free volume parameters determined by the positron annihilation lifetime spectroscopy were 0.08 or more and 0.19 or less, it was possible to suppress the generation of bubbles at the interface with the copper foil when thermocompression bonding (lamination) the copper foil, compared to the liquid crystal polymer films of Comparative Examples 1 to 6, in which the total free volume parameters determined by the positron annihilation lifetime spectroscopy were less than 0.08 or more and greater than 0.19. In particular, for the liquid crystal polymer films of Examples 2, 3, 4, and 7, in which the total free volume parameters determined by the positron annihilation lifetime spectroscopy were 0.12 or more and 0.17 or less, it was possible to significantly suppress the generation of bubbles at the interface with the copper foil when thermocompression bonding (lamination) the copper foil.

[0157] The present specification discloses the following:

[0158] <1> A liquid crystal polymer film comprising a liquid crystal polymer as a main component, characterized in that the total free volume parameter determined by positron annihilation lifetime spectroscopy is 0.08 or more and 0.19 or less.

[0159] <2> The liquid crystal polymer film according to <1>, wherein the total free volume parameter is 0.12 or more and 0.17 or less.

[0160] <3> The liquid crystal polymer film according to <1> or <2>, having a melting point of 270°C or higher.

[0161] <4> The liquid crystal polymer film according to any one of <1> to <3>, having a thickness of 10 μm or more and 500 μm or less.

[0162] <5> A metal-clad laminate, characterized by being formed using the liquid crystal polymer film according to any one of <1> to <4> and a metal foil.

[0163] <6> An electronic circuit board, which is formed using the metal-clad laminate according to <5>, and in which a circuit is formed on the metal foil.

[0164] DESCRIPTION OF SYMBOLS 1, 1', 1A, 1B, 1C Liquid crystal polymer film 1g Liquid crystal polymer 1h Hole 1s Resin composition 2, 2A, 2B, 2C Metal foil 2Ba First portion 2Bb Second portion 2Bc Third portion 10, 10A, 10B, 10C Metal-clad laminate 20A, 20B, 20C, 20D Interlayer connection conductor 50 Electronic circuit board 100 Inflation molding machine 110 Extruder 120 Die (mold) 121 Air inlet 122 Outlet 123 Outer portion 124 Inner portion 125 Land portion 130 Inflation / cooling mechanism 131 Air ring 132 Guide plate 140 Clamping roll 150 Winder 160 Guide roll

Claims

1. A liquid crystal polymer film containing a liquid crystal polymer as a main component, characterized in that the total free volume parameter determined by positron annihilation lifetime spectroscopy is 0.08 or more and 0.19 or less.

2. The liquid crystal polymer film of claim 1, wherein the total free volume parameter is 0.12 or more and 0.17 or less.

3. The liquid crystal polymer film according to claim 1 or 2, having a melting point of 270°C or higher.

4. The liquid crystal polymer film according to any one of claims 1 to 3, having a thickness of 10 μm or more and 500 μm or less.

5. A metal-clad laminate, characterized in that it is formed using the liquid crystal polymer film according to any one of claims 1 to 4 and a metal foil.

6. An electronic circuit board formed using the metal-clad laminate according to claim 5, wherein a circuit is formed on the metal foil.

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