Porous liquid crystal polymer sheet, porous liquid crystal polymer sheet with metal layer, and electronic circuit substrate

Abstract

A porous liquid crystal polymer sheet (1) is a porous liquid crystal polymer sheet including a resin sheet (1s) and having a void (1h) provided in the resin sheet (1s), the resin sheet (1s) including a first component (1e) including a liquid crystal polymer and a second component (1f) having the largest proportion by weight other than the first component (1e), wherein, when an area including the second component (1f) is set as a first area and an area in which the proportion of the second component (1f) is smaller than in the first area is set as a second area, the compressive strength of the first area is higher than the compressive strength of the second area, and the average particle diameter of the second component (1f) is smaller than the average void diameter of the void (1h).

Description

TECHNICAL FIELD

[0001] The present application relates to a porous liquid crystal polymer sheet, a porous liquid crystal polymer sheet with a metal layer, and an electronic circuit substrate. BACKGROUND

[0002] As the porous liquid crystal polymer sheet, a porous composite sheet containing (a) polytetrafluoroethylene and (b) a liquid crystal polymer is disclosed in Patent Literature 1. The porous composite sheet contains polytetrafluoroethylene fine particles and liquid crystal polymer fine particles, and has a continuous porous matrix of polytetrafluoroethylene in which the liquid crystal polymer is contained. The porous composite sheet has a liquid crystal polymer concentration of 2 to 85 vol%.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent No. 3618760 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] However, the porous composite sheet described in Patent Literature 1 has low compressive strength because it contains polytetrafluoroethylene. Therefore, if an electronic circuit substrate used in various electronic devices is manufactured using a porous liquid crystal polymer sheet having low compressive strength like the porous composite sheet described in Patent Literature 1, it is difficult to perform processing such as laminating a metal layer to the porous liquid crystal polymer sheet or forming a via hole that penetrates the porous liquid crystal polymer sheet.

[0008] The present application has been made to solve the above-described problems, and aims to provide a porous liquid crystal polymer sheet having high compressive strength. In addition, the present application aims to provide a porous liquid crystal polymer sheet with a metal layer having the above-described porous liquid crystal polymer sheet. Furthermore, the present application aims to provide an electronic circuit substrate having the above-described porous liquid crystal polymer sheet with a metal layer.

[0009] TECHNICAL SOLUTION FOR SOLVING THE PROBLEMS

[0010] The porous liquid crystal polymer sheet of the present application is a porous liquid crystal polymer sheet comprising a resin sheet and having a void provided in the resin sheet, the resin sheet including a first component comprising a liquid crystal polymer and a second component having the largest weight ratio except for the first component, characterized in that when a region containing the second component is set as a first region and a region containing the second component at a smaller ratio than the first region is set as a second region, the compressive strength of the first region is higher than that of the second region, and the average particle diameter of the second component is smaller than the average void diameter of the void.

[0011] The porous liquid crystal polymer sheet with a metal layer of the present application is characterized by comprising the porous liquid crystal polymer sheet of the present application and a metal layer provided on at least one main surface of the porous liquid crystal polymer sheet.

[0012] The electronic circuit substrate of the present application is characterized by comprising the porous liquid crystal polymer sheet with a metal layer of the present application.

[0013] Effects of the Invention

[0014] According to the present application, a porous liquid crystal polymer sheet having high compressive strength can be provided. Further, according to the present application, a porous liquid crystal polymer sheet with a metal layer having the above porous liquid crystal polymer sheet can be provided. Furthermore, according to the present application, an electronic circuit substrate having the above porous liquid crystal polymer sheet with a metal layer can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a cross-sectional schematic view showing one example of the porous liquid crystal polymer sheet of the present application.

[0016] Figure 2 is a cross-sectional schematic view showing a state in which the average particle diameter of the second component is larger than the average void diameter of the void with respect to the porous liquid crystal polymer sheet.

[0017] Figure 3 is a cross-sectional schematic view showing one example of the porous liquid crystal polymer sheet with a metal layer of the present application.

[0018] Figure 4 is a cross-sectional schematic view showing one example of the electronic circuit substrate of the present application.

[0019] Figure 5 is a cross-sectional schematic view showing a manufacturing process of the porous liquid crystal polymer sheet with a metal layer with respect to one example of the manufacturing method of the electronic circuit substrate of the present application.

[0020] Figure 6is a cross-sectional view schematically showing a manufacturing process of a porous liquid crystalline polymer sheet with a metal layer, which is one example of a method for manufacturing an electronic circuit substrate of the present application.

[0021] Figure 7 is a cross-sectional view schematically showing a manufacturing process of a porous liquid crystalline polymer sheet with a metal layer, which is one example of a method for manufacturing an electronic circuit substrate of the present application.

[0022] Figure 8 is a cross-sectional view schematically showing a manufacturing process of a porous liquid crystalline polymer sheet with a metal layer, which is one example of a method for manufacturing an electronic circuit substrate of the present application.

[0023] Figure 9 is a cross-sectional view schematically showing a manufacturing process of a porous liquid crystalline polymer sheet with a metal layer, which is one example of a method for manufacturing an electronic circuit substrate of the present application.

[0024] Figure 10 is a cross-sectional view schematically showing a manufacturing process of a porous liquid crystalline polymer sheet with a metal layer, which is one example of a method for manufacturing an electronic circuit substrate of the present application.

[0025] Figure 11 is a cross-sectional view schematically showing a manufacturing process of a porous liquid crystalline polymer sheet with a metal layer, which is one example of a method for manufacturing an electronic circuit substrate of the present application.

[0026] Figure 12 is a cross-sectional view schematically showing a manufacturing process of a porous liquid crystalline polymer sheet with a metal layer, which is one example of a method for manufacturing an electronic circuit substrate of the present application. DETAILED DESCRIPTION

[0027] Hereinafter, a porous liquid crystalline polymer sheet of the present application, a porous liquid crystalline polymer sheet with a metal layer of the present application, and an electronic circuit substrate of the present application will be described. In addition, the present application is not limited to the following structures, and can be appropriately changed within a range not departing from the gist of the present application. Furthermore, a product obtained by combining a plurality of each of the preferred structures described below is also the present application.

[0028] The porous liquid crystalline polymer sheet of the present application is a porous liquid crystalline polymer sheet including a resin sheet and having a void provided in the resin sheet, and the resin sheet includes a first component including a liquid crystalline polymer, and a second component having the largest weight ratio excluding the first component.

[0029] In the present specification, "sheet" is synonymous with "film", and the two are not distinguished according to thickness.

[0030] Figure 1 is a cross-sectional view schematically showing a manufacturing process of a porous liquid crystalline polymer sheet with a metal layer, which is one example of a method for manufacturing an electronic circuit substrate of the present application.

[0031] Figure 1The porous liquid crystal polymer sheet 1 shown has a first main surface la and a second main surface lb facing each other in the thickness direction.

[0032] The porous liquid crystal polymer sheet 1 includes a resin sheet Is including a first component le including a liquid crystal polymer, and a second component If having the largest weight ratio other than the first component le. In the porous liquid crystal polymer sheet 1, the voids 1h are provided in the resin sheet Is. More specifically, in the porous liquid crystal polymer sheet 1, the voids 1h are provided in the inside of the resin sheet Is.

[0033] The second component in the porous liquid crystal polymer sheet is determined as follows.

[0034] First, for the porous liquid crystal polymer sheet, the presence or absence of an organic component other than the liquid crystal polymer is evaluated by a Fourier transform infrared spectroscopy method (FT-IR method), a pyrolysis gas chromatography mass spectrometry method (pyrolysis GC-MS method), a differential scanning calorimetry method (DSC method), or the like. In addition, for the porous liquid crystal polymer sheet, the presence or absence of an inorganic component is evaluated by a thermogravimetric differential thermal analysis method (TG-DTA method), a fluorescent X-ray analysis method (XRF method), or the like. Then, based on these evaluation results, it is determined which of the following patterns 1 to 3 the object porous liquid crystal polymer sheet corresponds to.

[0035] Pattern 1: a case where the component other than the liquid crystal polymer is only an organic component

[0036] Pattern 2: a case where the component other than the liquid crystal polymer is only an inorganic component

[0037] Pattern 3: a case where the component other than the liquid crystal polymer is both an organic component and an inorganic component

[0038] Next, for each pattern determined by the above-described method, the weight ratio of each component other than the liquid crystal polymer is measured as follows.

[0039] <Pattern 1>

[0040] For the porous liquid crystal polymer sheet, the identification of each organic component is performed by a pyrolysis gas chromatography mass spectrometry method, and their weight ratios are calculated. In performing the identification of each organic component, a comprehensive judgment is also made in view of the evaluation results when the pattern determination described above is performed. In addition, in a case where the weight ratios of each organic component are not easily calculated by the pyrolysis gas chromatography mass spectrometry method, the volume ratios of each organic component can also be calculated using an X-ray CT device, from which the weight ratios of each organic component are inferred.

[0041] <Pattern 2>

[0042] From porous liquid crystal polymer sheets, the liquid crystal polymer was pyrolyzed and volatilized using thermogravimetric differential thermal analysis (TGA) to extract only the inorganic components. Then, the extracted inorganic components were identified using X-ray diffraction (XRD), fluorescence X-ray diffraction, and inductively coupled plasma optical emission spectrometry (ICP-AES). Finally, the weight proportions of each inorganic component were determined based on the results from fluorescence X-ray diffraction and ICP-AES.

[0043] <Style 3>

[0044] By combining the methods described in <Formula 1> and <Formula 2>, the weight ratios of each organic component and each inorganic component can be determined.

[0045] The component with the largest weight proportion among the components having the weight proportions obtained as described above, excluding the first component (liquid crystal polymer), is determined to be the second component.

[0046] In the porous liquid crystal polymer sheet of the present invention, when the region containing the second component is designated as the first region and the region containing the second component in a smaller proportion than the first region is designated as the second region, the compressive strength of the first region is higher than that of the second region.

[0047] exist Figure 1 In the porous liquid crystal polymer sheet 1 shown, when the region containing the second component 1f is designated as the first region, and the region containing a smaller proportion of the second component 1f is designated as the second region, the compressive strength of the first region is higher than that of the second region. For example, in the porous liquid crystal polymer sheet 1, when the region containing both the first component 1e and the second component 1f is designated as the first region, and the region containing the first component 1e is designated as the second region, the compressive strength of the first region is higher than that of the second region. Thus, in the first region where the proportion of the second component 1f is larger, the compressive strength is higher compared to the second region where the proportion of the second component 1f is smaller; therefore, it can be said that the second component 1f contributes to the improvement of the compressive strength of the porous liquid crystal polymer sheet 1.

[0048] The compressive strengths of regions 1 and 2 of the porous liquid crystal polymer sheet are determined as follows: First, multiple 10mm square specimens are cut from region 1 of the porous liquid crystal polymer sheet, and these specimens are stacked until the thickness reaches 1mm. Next, using a compression testing apparatus, the resulting stack is compressed at a speed of 1mm / min, and the compressive stress corresponding to the deformation rate at each time point is obtained. Then, the compressive stress at the time point when the deformation rate reaches 10% is determined as the compressive strength of region 1 of the porous liquid crystal polymer sheet. Furthermore, for the deformation rate, the thickness of the stack before the compression test is set as L1, and the thickness of the stack at a certain time point during the compression test is set as L2, calculated based on the formula: deformation rate (%) = [(L1-L2) / L1] × 100. The compressive strength of region 2 of the porous liquid crystal polymer sheet is determined in the same way as the compressive strength of region 1, except that specimens are cut from region 2 of the porous liquid crystal polymer sheet.

[0049] In the porous liquid crystal polymer sheet of the present invention, the average particle size of the second component is smaller than the average pore size of the pores.

[0050] exist Figure 1 In the porous liquid crystal polymer sheet 1 shown, the average particle size of the second component 1f is smaller than the average pore size of the pores 1h.

[0051] In porous liquid crystal polymer sheets, as mentioned above, although the second component helps to improve the compressive strength of the porous liquid crystal polymer sheet, the effect of improving compressive strength produced by the second component cannot be fully realized if the second component is present alone.

[0052] In contrast, in the porous liquid crystal polymer sheet 1, the average particle size of the second component 1f is smaller than the average pore size of the pores 1h, thus... Figure 1 As shown, the second component 1f becomes less likely to exist in contact with the pore 1h. Therefore, it becomes less likely to form a boundary between the first component 1e, the second component 1f, and the pore 1h, which can be considered to have low compressive strength, so the compressive strength improvement effect produced by the second component 1f can be fully utilized.

[0053] Figure 2 This is a cross-sectional schematic diagram showing a state in which the average particle size of the second component is greater than or equal to the average pore size of the pores in a porous liquid crystal polymer sheet.

[0054] If so Figure 2The average particle diameter of the second component 1f is equal to or greater than the average pore diameter of the pores 1h in the illustrated porous liquid crystal polymer sheet 101. If the average particle diameter of the second component 1f is greater than the average pore diameter of the pores 1h, the second component 1f is likely to exist in contact with the pores 1h. Depending on the case, the second component 1f is likely to exist by penetrating the first component 1e and spanning between the pores 1h. Therefore, in the porous liquid crystal polymer sheet 101, a boundary between the first component 1e, the second component 1f, and the pores 1h, which can be considered to have low compressive strength, is likely to occur, and thus the effect of increasing the compressive strength by the second component 1f cannot be sufficiently exerted.

[0055] The average particle diameter of the second component is determined by the particle diameter at which the cumulative probability becomes 50% in the cumulative particle diameter distribution of the second component on a number basis, that is, the so-called median diameter D 50 .

[0056] More specifically, the average particle diameter of the second component is determined as follows. First, the three-dimensional structure of the second component of the porous liquid crystal polymer sheet is recognized using an X-ray CT device, and thus the maximum diameter is measured for each second component, and the obtained maximum diameter is set as the particle diameter of each second component. Then, the cumulative particle diameter distribution on a number basis is calculated from the particle diameter of each second component, and the median diameter D 50 is determined as the average particle diameter of the second component.

[0057] The average pore diameter of the pores is determined by the pore diameter at which the cumulative probability becomes 50% in the cumulative pore diameter distribution of the pores on a number basis, that is, the so-called median diameter D 50 .

[0058] More specifically, the average pore diameter of the pores is also determined in the same manner as the average particle diameter of the second component.

[0059] As described above, in the porous liquid crystal polymer sheet 1, the second component 1f is present while the average particle diameter of the second component 1f is smaller than the average pore diameter of the pores 1h, and thus the compressive strength is increased. The porous liquid crystal polymer sheet 1 having high compressive strength like this is excellent in processability when a metal layer is compression-bonded or a via hole is formed, for example, in the case of manufacturing an electronic circuit substrate.

[0060] Further, in the porous liquid crystal polymer sheet 1, in addition to the first component 1e containing a liquid crystal polymer having a small dielectric constant, there is a void 1h that contributes to further reduction of the dielectric constant, and thus in an electronic circuit substrate manufactured using the porous liquid crystal polymer sheet 1, it becomes easy to improve the dielectric properties in the high frequency region. Further, the first component 1e containing a liquid crystal polymer is low in hygroscopicity, and thus in an electronic circuit substrate manufactured using the porous liquid crystal polymer sheet 1, it becomes less likely to cause a change in dielectric properties due to hygroscopicity.

[0061] In the porous liquid crystal polymer sheet of the present application, the second component preferably contains an inorganic filler.

[0062] In the porous liquid crystal polymer sheet 1 shown in FIG. 1, the second component 1f preferably contains an inorganic filler. Figure 1

[0063] If the second component 1f contains an inorganic filler, it becomes easy to improve the compressive strength of the porous liquid crystal polymer sheet 1.

[0064] Further, if the second component 1f contains an inorganic filler, it becomes easy to make the linear expansion coefficient of the porous liquid crystal polymer sheet 1 small. Thus, in a porous liquid crystal polymer sheet with a metal layer and an electronic circuit substrate manufactured using the porous liquid crystal polymer sheet 1, it is possible to make the linear expansion coefficient of the porous liquid crystal polymer sheet 1 close to the linear expansion coefficient of the metal layer, such as a copper foil. More specifically, it is possible to make the linear expansion coefficient in the in-plane direction of the porous liquid crystal polymer sheet 1 close to the linear expansion coefficient in the in-plane direction of the metal layer, such as a copper foil. Thus, in the porous liquid crystal polymer sheet with a metal layer and the electronic circuit substrate, it becomes less likely to cause warping and dimensional changes.

[0065] As the inorganic filler, for example, there can be mentioned amorphous silica, zirconium phosphotungstate, crystalline silica, glass, talc, mica, wollastonite, attapulgite, shirasu balloons, montmorillonite, activated clay, zeolite, sepiolite, xonotlite, copper, gold, silver, lead, iron, tungsten, stainless steel, aluminum, nickel, alloys (Fe-Ni system, Fe-Si system, Fe-Si-Al system, Fe-Si-Cr system, Fe-Co system, Fe-Si-B-Cr system, etc.), ferrite, zinc oxide, alumina, calcium oxide, magnesium oxide, titanium oxide, cerium oxide, barium sulfate, potassium titanate, barium titanate, calcium titanate, strontium titanate, calcium carbonate, boron nitride, and the like.

[0066] Various surface treatments can also be applied to the inorganic filler.

[0067] ​In the porous liquid crystal polymer sheet of the present application, in the case where the second component contains an inorganic filler, the linear expansion coefficient of the inorganic filler is preferably negative in the temperature range of 23°C or higher and 300°C or lower.

[0068] In Figure 1 In the porous liquid crystal polymer sheet 1 shown in FIG. 1, in the case where the second component If contains an inorganic filler, the linear expansion coefficient of the inorganic filler is preferably negative in the temperature range of 23°C or higher and 300°C or lower. The linear expansion coefficient of the inorganic filler is more preferably negative in the temperature range of 23°C or higher and 300°C or lower in all directions including the thickness direction and the in-plane direction.

[0069] In the case where the second component If contains an inorganic filler, if the linear expansion coefficient of the inorganic filler is negative in the above temperature range, the linear expansion coefficient of the porous liquid crystal polymer sheet 1 easily becomes smaller.

[0070] The second component If can also contain an organic high polymer.

[0071] If the second component If contains an organic high polymer, the affinity of the first component le and the second component If easily becomes higher, and thus it becomes easy to ensure the flexibility and the stretchability of the porous liquid crystal polymer sheet 1.

[0072] As the organic high polymer, for example, a liquid crystal polymer (LCP), a polyether ether ketone (PEEK), a thermoplastic polyimide (TPI), a polyether imide (PEI), a polyether sulfone (PES), a polyphenylene sulfide (PPS), a polyamide imide (PAI), a polycarbonate (PC), a cyclic olefin copolymer (COC), or the like can be cited.

[0073] Here, in the case where the second component If contains an organic high polymer and the organic high polymer is a liquid crystal polymer, the melting point of the liquid crystal polymer as the second component If is preferably higher than the melting point of the liquid crystal polymer as the first component le.

[0074] In addition, among the organic high polymers, a fluorine-based resin such as polytetrafluoroethylene (PTFE) described in Patent Document 1 is generally contained. However, in the porous liquid crystal polymer sheet of the present application, in the case where the second component contains a fluorine-based resin, in the case where a region containing the second component is set as a first region and a region in which the content ratio of the second component is smaller than the first region is set as a second region, the compressive strength of the first region is not higher than that of the second region. That is, the fluorine-based resin does not contribute to the improvement of the compressive strength of the porous liquid crystal polymer sheet. Therefore, in the porous liquid crystal polymer sheet of the present application, the fluorine-based resin is excluded from the second component.

[0075] As described above, from the viewpoint of improving the compressive strength of the porous liquid crystal polymer sheet 1 or reducing the coefficient of linear expansion, the second component 1f preferably contains an inorganic filler. Furthermore, from the viewpoint of improving the affinity between the first component 1e and the second component 1f, the second component 1f preferably contains an organic polymer.

[0076] In the porous liquid crystal polymer sheet of the present invention, when a temperature 50°C lower than the melting point of the liquid crystal polymer is set as a reference temperature, the melting point of the second component is preferably higher than the reference temperature. Here, "melting point of the liquid crystal polymer" refers to the melting point of the liquid crystal polymer that is the first component.

[0077] exist Figure 1 In the porous liquid crystal polymer sheet 1 shown, when a temperature 50°C lower than the melting point of the liquid crystal polymer as the first component 1e is set as the reference temperature, the melting point of the second component 1f is preferably higher than the reference temperature.

[0078] If the melting point of the second component 1f is below the aforementioned reference temperature, then during the film formation of the porous liquid crystal polymer sheet 1 (resin sheet 1s), the second component 1f may sometimes deteriorate or decompose due to insufficient heat resistance.

[0079] When the second component 1f contains inorganic fillers, the melting point of the inorganic fillers is preferably higher than the reference temperature when a temperature 50°C lower than the melting point of the liquid crystal polymer as the first component 1e is set as the reference temperature.

[0080] The melting points of the liquid crystal polymer as the first component and the melting point of the second component in a porous liquid crystal polymer sheet are determined as follows: First, the porous liquid crystal polymer sheet is heated and completely melted, for example, using a differential scanning calorimeter such as the Hitachi High-Tech Science Corporation DSC7000X. During this heating process, the heating rate is set to, for example, 20°C / min. Next, the resulting melt is cooled and then heated again. During the cooling process, for example, it is cooled to 175°C at a cooling rate of 20°C / min, and during the heating process, for example, it is heated at a heating rate of 20°C / min. Then, the melting points of the liquid crystal polymer as the first component and the melting points of the second component are determined based on the temperatures corresponding to the endothermic peaks observed during this heating process. Furthermore, when the endothermic peak originating from the liquid crystal polymer is not easily determined using the methods described above, texture observation under crossed Nicols conditions using a polarizing microscope is performed in addition to the methods described above to determine the melting point of the liquid crystal polymer. In addition, for liquid crystal polymers, when the endothermic peak is not easily observed using the methods described above, the melting point of the liquid crystal polymer is determined by texture observation under crossed Nicols conditions using a polarizing microscope.

[0081] In the porous liquid crystal polymer sheet of the present invention, the weight percentage of the second component in the resin sheet is preferably 10% by weight or more and 70% by weight or less. Furthermore, in the porous liquid crystal polymer sheet of the present invention, the weight percentage of the second component in the resin sheet is more preferably 20% by weight or more and 50% by weight or less.

[0082] exist Figure 1 In the porous liquid crystal polymer sheet 1 shown, the weight percentage of the second component 1f in the resin sheet 1s is preferably 10% by weight or more and 70% by weight or less, more preferably 20% by weight or more and 50% by weight or less.

[0083] If the weight percentage of the second component 1f in the resin sheet 1s is less than 10% by weight, then sometimes only a slight increase in compressive strength can be obtained from the second component 1f.

[0084] If the weight percentage of the second component 1f in the resin sheet 1s is greater than 70% by weight, the weight percentage of the first component 1e containing the liquid crystal polymer becomes relatively smaller, so sometimes only a small amount of the hygroscopicity reduction effect produced by the first component 1e can be obtained.

[0085] In the case where the 2nd component 1f contains the inorganic filler, the weight proportion of the inorganic filler in the resin sheet Is is preferably 10% by weight or more and 70% by weight or less, more preferably 20% by weight or more and 50% by weight or less.

[0086] In the porous liquid crystal polymer sheet of the present application, the melting point of the liquid crystal polymer is preferably 275°C or higher and 330°C or lower. The "melting point of the liquid crystal polymer" referred to here means the melting point of the liquid crystal polymer as the 1st component.

[0087] In the case where the 2nd component 1f contains the inorganic filler, the weight proportion of the inorganic filler in the resin sheet Is is preferably 10% by weight or more and 70% by weight or less, more preferably 20% by weight or more and 50% by weight or less. Figure 1 In the porous liquid crystal polymer sheet 1 shown in FIG. 1, the melting point of the liquid crystal polymer as the 1st component le is preferably 275°C or higher and 330°C or lower.

[0088] If the melting point of the liquid crystal polymer as the 1st component le is lower than 275°C, the liquid crystal polymer is sometimes deteriorated or decomposed due to the lack of heat resistance, for example, when an electronic circuit substrate manufactured using the porous liquid crystal polymer sheet 1 is assembled to an electronic device by reflow soldering.

[0089] If the melting point of the liquid crystal polymer as the 1st component le is higher than 330°C, a higher processing temperature is required, for example, at the time of film formation of the porous liquid crystal polymer sheet 1 (resin sheet Is), and thus the deterioration of the liquid crystal polymer is sometimes promoted.

[0090] In the porous liquid crystal polymer sheet of the present application, the liquid crystal polymer preferably contains a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. The "liquid crystal polymer" referred to here means the liquid crystal polymer as the 1st component.

[0091] In the case where the 2nd component 1f contains the inorganic filler, the weight proportion of the inorganic filler in the resin sheet Is is preferably 10% by weight or more and 70% by weight or less, more preferably 20% by weight or more and 50% by weight or less. Figure 1 In the porous liquid crystal polymer sheet 1 shown in FIG. 1, the liquid crystal polymer as the 1st component le preferably contains a copolymer of p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA).

[0092] The copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid is generally referred to as a wholly aromatic polyester of Type II (also referred to as a wholly aromatic polyester of Type 1.5). The wholly aromatic polyester of Type II is less likely to cause hydrolysis than the partially aromatic polyester of Type III, and thus is preferable as a constituent material of an electronic circuit substrate manufactured using the porous liquid crystal polymer sheet 1. In addition, the wholly aromatic polyester of Type II has a small dielectric loss tangent due to the naphthalene ring, and thus contributes to the reduction of electric energy loss in the porous liquid crystal polymer sheet 1 in an electronic circuit substrate.

[0093] In the porous liquid crystalline polymer sheet 1, the liquid crystalline polymer as the first component le can further contain, in addition to the wholly aromatic polyester of Type II, a wholly aromatic polyester of Type I, a partially aromatic polyester of Type III, or a combination of a wholly aromatic polyester of Type I and a partially aromatic polyester of Type III.

[0094] The kind (structure) of each monomer constituting the liquid crystalline polymer can be analyzed by a reaction pyrolysis gas chromatography mass spectrometry (reaction pyrolysis GC-MS method).

[0095] In the porous liquid crystalline polymer sheet of the present application, the molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid in the liquid crystalline polymer is preferably 0.20 or more and 5 or less. The "liquid crystalline polymer" referred to here means the liquid crystalline polymer as the first component.

[0096] In the porous liquid crystalline polymer sheet 1 shown in Figure 1 In the porous liquid crystalline polymer sheet 1 shown in

[0097] In the liquid crystalline polymer as the first component le, if the molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid is less than 0.20 or more than 5, the melting point of the liquid crystalline polymer sometimes becomes higher than the above-mentioned preferable range.

[0098] In the porous liquid crystalline polymer sheet of the present application, the liquid crystalline polymer preferably contains each of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid in an amount of 10 mol% or more, when the total amount of monomers is taken as 100 mol%. The "liquid crystalline polymer" referred to here means the liquid crystalline polymer as the first component.

[0099] In the porous liquid crystalline polymer sheet 1 shown in Figure 1 In the porous liquid crystalline polymer sheet 1 shown in

[0100] If the content ratio of each of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid in the liquid crystalline polymer as the first component le is less than 10 mol%, it is sometimes difficult to achieve all of the liquid crystallinity as a liquid crystalline polymer, the melting point of the liquid crystalline polymer to be in the above-mentioned preferable range, and the decrease in the dielectric loss tangent of the liquid crystalline polymer.

[0101] The ratio and content ratio of each monomer constituting the liquid crystalline polymer can be analyzed by a reaction pyrolysis gas chromatography mass spectrometry (reaction pyrolysis GC-MS method).

[0102] The thickness of the porous liquid crystal polymer sheet of the present application is preferably 10 μm or more and 200 μm or less.

[0103] Figure 3 The thickness of the porous liquid crystal polymer sheet 1 is preferably 10 μm or more and 200 μm or less.

[0104] If the thickness of the porous liquid crystal polymer sheet 1 is less than 10 μm, the void ratio of the voids 1h tends to increase in at least one of the first main surface la and the second main surface lb, and thus the smoothness tends to decrease. In this case, after the metal layer is pressed against the main surface in which the smoothness is low with respect to the porous liquid crystal polymer sheet 1, if the metal layer is etched into a pattern shape of a wiring or the like, a pattern defect tends to occur due to the voids 1h present in the main surface.

[0105] If the thickness of the porous liquid crystal polymer sheet 1 is more than 200 μm, in the case where the porous liquid crystal polymer sheet 1 is used to manufacture an electronic circuit substrate having an interlayer connection conductor, it sometimes becomes difficult to form a via hole that forms the interlayer connection conductor so as to penetrate the porous liquid crystal polymer sheet 1.

[0106] The thickness of the porous liquid crystal polymer sheet is determined as follows. First, a 100 mm square sample is cut out from the porous liquid crystal polymer sheet. Then, the thickness at nine points at equally spaced positions in a 25 mm square region having a center in common with the sample is measured, and the average thereof is determined as the thickness of the porous liquid crystal polymer sheet. In addition, in the case where a 100 mm square sample cannot be cut out from the porous liquid crystal polymer sheet, the thickness of the porous liquid crystal polymer sheet is determined in the same manner as the above method, except that the porous liquid crystal polymer sheet itself is used as the above sample. At this time, in the case where the above 25 mm square region cannot be obtained in the porous liquid crystal polymer sheet, the thickness at nine points at equally spaced positions in the porous liquid crystal polymer sheet is measured, and the average thereof is determined as the thickness of the porous liquid crystal polymer sheet.

[0107] The porous liquid crystal polymer sheet 1, more specifically the resin sheet Is, preferably has an independent bubble structure as a configuration of the voids 1h.

[0108] The porous liquid crystal polymer sheet is said to have an independent bubble structure, meaning that the porous liquid crystal polymer sheet has a configuration in which the walls of the voids (bubbles) are all surrounded by the resin. When observing a cross section of the porous liquid crystal polymer sheet along the thickness direction and a cross section of the porous liquid crystal polymer sheet along a direction in the plane orthogonal to the thickness direction, as long as the walls of the voids are in a state in which they are not connected to each other, the porous liquid crystal polymer sheet is determined to have an independent bubble structure.

[0109] In the case where the porous liquid crystal polymer sheet 1 has an independent bubble structure, as compared with the case where it has a continuous bubble structure, the path of the air in the voids 1h to the outside is easily made less, and the compressive strength is easily ensured, so when a metal layer is laminated to the porous liquid crystal polymer sheet 1, the porous liquid crystal polymer sheet 1 becomes less likely to be crushed.

[0110] The porous liquid crystal polymer sheet 1 is manufactured, for example, by the following method.

[0111] First, the first component 1e, the second component 1f, and the blowing agent, which contain a liquid crystal polymer, are mixed at a given ratio, whereby a resin material is prepared. At this time, the weight ratio of the second component 1f is made largest except for the first component 1e.

[0112] Next, using the resin material, a resin sheet 1s provided with the voids 1h is produced by an extrusion molding method. As the extrusion molding method, for example, a T-die molding method, a blow molding method, or the like can be cited.

[0113] By the above, the porous liquid crystal polymer sheet 1 including the resin sheet 1s provided with the voids 1h can be manufactured. In the porous liquid crystal polymer sheet 1, the average particle diameter of the second component 1f is smaller than the average void diameter of the voids 1h. As a method of making the average particle diameter of the second component 1f smaller than the average void diameter of the voids 1h like this, for example, a method in which, at the time of preparing the resin material, a material having a small average particle diameter is used as the second component 1f or a material having a large average particle diameter is used as the blowing agent can be cited.

[0114] The metal-layer-equipped porous liquid crystal polymer sheet of the present application has: the porous liquid crystal polymer sheet of the present application, and a metal layer provided on at least one main face of the porous liquid crystal polymer sheet.

[0115] Figure 3 is a cross-sectional schematic view showing one example of the metal-layer-equipped porous liquid crystal polymer sheet of the present application.

[0116] Figure 3 The metal-layer-equipped porous liquid crystal polymer sheet 10 shown has the porous liquid crystal polymer sheet 1 and the metal layer 2 in the stacking direction.

[0117] The stacking direction corresponds to a direction along the thickness direction of the porous liquid crystal polymer sheet constituting the metal-layer-equipped porous liquid crystal polymer sheet.

[0118] The metal layer 2 is provided on at least one main face of the porous liquid crystal polymer sheet 1, here on the first main face la. More specifically, the metal layer 2 is adjacent to the first main face la side of the porous liquid crystal polymer sheet 1.

[0119] The metal layer 2 can be in a pattern shape patterned as a wiring or the like, or can be a planar shape covering the entire surface.

[0120] As a material constituting the metal layer 2, for example, copper, silver, aluminum, stainless steel, nickel, gold, an alloy containing at least one of these metals, or the like can be listed.

[0121] In the porous liquid crystal polymer sheet with a metal layer of the present application, the metal layer preferably contains a copper foil.

[0122] In Figure 4 In the porous liquid crystal polymer sheet with a metal layer 10 shown in FIG. 1, the metal layer 2 preferably contains a copper foil. In this case, a metal other than copper can also be plated on the surface of the copper foil.

[0123] The thickness of the metal layer 2 is preferably 1 μm or more and 35 μm or less, and more preferably 6 μm or more and 18 μm or less.

[0124] The porous liquid crystal polymer sheet with a metal layer 10 can also have another metal layer provided on the other of the second main surface lb of the porous liquid crystal polymer sheet 1 in addition to the metal layer 2.

[0125] The porous liquid crystal polymer sheet with a metal layer 10 is manufactured, for example, by pressure bonding the metal layer 2 to the first main surface la of the porous liquid crystal polymer sheet 1. The metal layer 2 can also be etched into a pattern shape after being pressure bonded to the first main surface la of the porous liquid crystal polymer sheet 1.

[0126] The porous liquid crystal polymer sheet with a metal layer 10 can also be manufactured by pressure bonding a metal layer 2 that has been patterned in advance to the first main surface la of the porous liquid crystal polymer sheet 1.

[0127] The electronic circuit substrate of the present application is provided with the porous liquid crystal polymer sheet with a metal layer of the present application.

[0128] Figure 4 is a cross-sectional schematic view showing one example of the electronic circuit substrate of the present application.

[0129] Figure 4 The electronic circuit substrate 50 shown in FIG. 2 has, in the stacking direction, in order, the porous liquid crystal polymer sheet with a metal layer 10A, the porous liquid crystal polymer sheet with a metal layer 10B, and the porous liquid crystal polymer sheet with a metal layer IOC. That is, in the electronic circuit substrate 50, the porous liquid crystal polymer sheet with a metal layer 10A, the porous liquid crystal polymer sheet with a metal layer 10B, and the porous liquid crystal polymer sheet with a metal layer IOC are stacked in order in the stacking direction.

[0130] The porous liquid crystal polymer sheet 10A with a metal layer has the porous liquid crystal polymer sheet 1A and the metal layer 2A.

[0131] The porous liquid crystal polymer sheet 1A has a first main surface 1Aa and a second main surface 1Ab which are opposed in the thickness direction.

[0132] The porous liquid crystal polymer sheet 1A includes a resin sheet 1As which includes a first component 1Ae including a liquid crystal polymer, and a second component 1Af which is the largest in proportion by weight except for the first component 1Ae. In the porous liquid crystal polymer sheet 1A, a void 1Ah is provided in the resin sheet 1As.

[0133] In the porous liquid crystal polymer sheet 1A, when a region including the second component 1Af is set as a first region, and a region in which the proportion by weight of the second component 1Af is smaller than that of the first region is set as a second region, the compressive strength of the first region is higher than that of the second region.

[0134] The metal layer 2A is provided on the first main surface 1Aa of the porous liquid crystal polymer sheet 1A. Further, the metal layer 2A is adjacent to the second main surface 1Bb side of the porous liquid crystal polymer sheet 1B described later.

[0135] The porous liquid crystal polymer sheet 10B with a metal layer has the porous liquid crystal polymer sheet 1B, the metal layer 2B, the metal layer 2B', and the metal layer 2B".

[0136] The porous liquid crystal polymer sheet 1B has a first main surface 1Ba and a second main surface 1Bb which are opposed in the thickness direction.

[0137] The porous liquid crystal polymer sheet 1B includes a resin sheet 1Bs which includes a first component 1Be including a liquid crystal polymer, and a second component 1Bf which is the largest in proportion by weight except for the first component 1Be. In the porous liquid crystal polymer sheet 1B, a void 1Bh is provided in the resin sheet 1Bs.

[0138] In the porous liquid crystal polymer sheet 1B, when a region including the second component 1Bf is set as a first region, and a region in which the proportion by weight of the second component 1Bf is smaller than that of the first region is set as a second region, the compressive strength of the first region is higher than that of the second region.

[0139] The metal layer 2B, the metal layer 2B', and the metal layer 2B" are provided on the first main surface 1Ba of the porous liquid crystal polymer sheet 1B. Further, the metal layer 2B, the metal layer 2B', and the metal layer 2B" are adjacent to the second main surface 1Cb side of the porous liquid crystal polymer sheet 1C described later.

[0140] The porous liquid crystal polymer sheet 10C with a metal layer has a porous liquid crystal polymer sheet 1C and a metal layer 2C.

[0141] The porous liquid crystal polymer sheet 1C has a first main surface 1Ca and a second main surface 1Cb that are opposed in the thickness direction.

[0142] The porous liquid crystal polymer sheet 1C includes a resin sheet 1Cs, which comprises a first component 1Ce containing a liquid crystal polymer and a second component 1Cf having the largest weight proportion other than the first component 1Ce. In the porous liquid crystal polymer sheet 1C, pores 1Ch are provided in the resin sheet 1Cs.

[0143] In the porous liquid crystal polymer sheet 1C, when the region containing the second component 1Cf is designated as the first region, and the region containing a smaller proportion of the second component 1Cf than the first region is designated as the second region, the compressive strength of the first region is higher than that of the second region.

[0144] The metal layer 2C is disposed on the first main surface 1Ca of the porous liquid crystal polymer sheet 1C.

[0145] like Figure 4 As shown, the metal layer 2B is preferably disposed across the interface between the porous liquid crystal polymer sheet 1B and the porous liquid crystal polymer sheet 1C. Therefore, the interface between the metal layer 2B and the porous liquid crystal polymer sheet 1B, and the interface between the metal layer 2B and the porous liquid crystal polymer sheet 1C, are offset in the lamination direction from the interface between the porous liquid crystal polymer sheet 1B and the porous liquid crystal polymer sheet 1C, thereby suppressing peeling at the interface between the metal layer 2B and the porous liquid crystal polymer sheet 1B, and peeling at the interface between the metal layer 2B and the porous liquid crystal polymer sheet 1C.

[0146] The metal layer 2B' and the metal layer 2B" are also preferably disposed across the interface between the porous liquid crystal polymer sheet 1B and the porous liquid crystal polymer sheet 1C, just like the metal layer 2B.

[0147] In addition, Figure 4 Although the interface between porous liquid crystal polymer sheet 1B and porous liquid crystal polymer sheet 1C is shown in the diagram, this interface can actually be unclear. In cases where the interface between porous liquid crystal polymer sheet 1B and porous liquid crystal polymer sheet 1C is unclear, as in... Figure 4 In the cross-section shown along the stacking direction, the surface at the center of the cross-section passing through the metal layer 2B in the stacking direction and along the direction orthogonal to the stacking direction is regarded as the interface between the porous liquid crystal polymer sheet 1B and the porous liquid crystal polymer sheet 1C.

[0148] In the porous liquid crystalline polymer sheet 1A, the porous liquid crystalline polymer sheet 1B, and the porous liquid crystalline polymer sheet 1C, as with the porous liquid crystalline polymer sheet 1, the average particle diameter of the second component is smaller than the average void diameter of the voids. Therefore, as with the porous liquid crystalline polymer sheet 1, the compressive strength is high. The porous liquid crystalline polymer sheet 1A, the porous liquid crystalline polymer sheet 1B, and the porous liquid crystalline polymer sheet 1C, which are high in compressive strength, are excellent in processability at the time of compression bonding of a metal layer or formation of a via hole in the case of manufacturing an electronic circuit substrate 50.

[0149] Further, since the electronic circuit substrate 50 has the porous liquid crystalline polymer sheet 1A, the porous liquid crystalline polymer sheet 1B, and the porous liquid crystalline polymer sheet 1C, the dielectric properties in the high frequency region of the electronic circuit substrate 50 are easily improved. In addition, in the electronic circuit substrate 50, a change in dielectric properties caused by moisture absorption is less likely to occur.

[0150] Preferably, in all of the porous liquid crystalline polymer sheets 1A, 1B, and 1C, the average particle diameter of the second component is smaller than the average void diameter of the voids, but the average particle diameter of the second component can be smaller than the average void diameter of the voids in some of the porous liquid crystalline polymer sheets.

[0151] The preferable features of the porous liquid crystalline polymer sheet 1A, the porous liquid crystalline polymer sheet 1B, and the porous liquid crystalline polymer sheet 1C are the same as those of the above-described porous liquid crystalline polymer sheet 1.

[0152] The thicknesses of the porous liquid crystalline polymer sheet 1A, the porous liquid crystalline polymer sheet 1B, and the porous liquid crystalline polymer sheet 1C can be the same as each other, can be different from each other, or can be partially different as shown in Figure 4

[0153] As the constituent material of the metal layer 2A, the metal layer 2B, the metal layer 2B', the metal layer 2B", and the metal layer 2C, as with the constituent material of the metal layer 2, for example, copper, silver, aluminum, stainless steel, nickel, gold, an alloy containing at least one of these metals, or the like can be exemplified.

[0154] The metal layer 2A, the metal layer 2B, the metal layer 2B', the metal layer 2B", and the metal layer 2C, as with the metal layer 2, preferably contain a copper foil. In this case, a metal other than copper can be plated on the surface of the copper foil.

[0155] ​The constituent materials of the metal layer 2A, the metal layer 2B, the metal layer 2B', the metal layer 2B", and the metal layer 2C are preferably the same as each other, but can be different from each other, or some of them can be different.

[0156] The thicknesses of the metal layer 2A, the metal layer 2B, the metal layer 2B', the metal layer 2B", and the metal layer 2C can be the same as each other as shown in Figure 4

[0157] The electronic circuit substrate 50 has three porous liquid crystalline polymer sheet materials with metal layers in the stacking direction, but can have only one, two, or four or more.

[0158] That is, the electronic circuit substrate 50 can have at least one porous liquid crystalline polymer sheet material in which the average particle diameter of the second component is smaller than the average pore diameter of the pores. The electronic circuit substrate 50 can have a porous liquid crystalline polymer sheet material that does not contain the second component, a porous liquid crystalline polymer sheet material in which the average particle diameter of the second component is equal to or larger than the average pore diameter of the pores, or a non-porous liquid crystalline polymer sheet material, as long as it has at least one porous liquid crystalline polymer sheet material in which the average particle diameter of the second component is smaller than the average pore diameter of the pores.

[0159] As shown in Figure 5 The electronic circuit substrate 50 preferably further has an interlayer connection conductor that is provided so as to penetrate the porous liquid crystalline polymer sheet material in the stacking direction but is not connected to the metal layer in the stacking direction. In Figure 6 the example shown, the electronic circuit substrate 50 further has an interlayer connection conductor 20A, an interlayer connection conductor 20B, an interlayer connection conductor 20C, and an interlayer connection conductor 20D.

[0160] The interlayer connection conductor 20A is provided so as to penetrate the porous liquid crystalline polymer sheet material IB in the stacking direction but is not connected to the metal layer 2B' in the stacking direction. More specifically, the interlayer connection conductor 20A is connected to the metal layer 2B' on the first main surface IBa side of the porous liquid crystalline polymer sheet material IB while penetrating the porous liquid crystalline polymer sheet material IB in the stacking direction. In addition, the interlayer connection conductor 20A is connected to the metal layer 2A on the second main surface IIBb side of the porous liquid crystalline polymer sheet material IB. That is, the metal layer 2A and the metal layer 2B' are electrically connected via the interlayer connection conductor 20A.

[0161] ​The interlayer connection conductor 20B is provided so as to penetrate the porous liquid crystal polymer sheet 1B in the stacking direction but not to penetrate the metal layer 2B" in the stacking direction, at a position separate from the interlayer connection conductor 20A, and is connected to the metal layer 2B". More specifically, the interlayer connection conductor 20B is connected to the metal layer 2B" on the side of the first main surface 1Ba of the porous liquid crystal polymer sheet 1B while penetrating the porous liquid crystal polymer sheet 1B in the stacking direction, at a position separate from the interlayer connection conductor 20A. Further, the interlayer connection conductor 20B is connected to the metal layer 2A on the side of the second main surface 1Bb of the porous liquid crystal polymer sheet 1B, at a position separate from the interlayer connection conductor 20A. That is, the metal layer 2A and the metal layer 2B" are electrically connected via the interlayer connection conductor 20B.

[0162] The interlayer connection conductor 20C is provided so as to penetrate the porous liquid crystal polymer sheet 1C in the stacking direction but not to penetrate the metal layer 2C in the stacking direction, and is connected to the metal layer 2C. More specifically, the interlayer connection conductor 20C is connected to the metal layer 2C on the side of the first main surface 1Ca of the porous liquid crystal polymer sheet 1C while penetrating the porous liquid crystal polymer sheet 1C in the stacking direction. Further, the interlayer connection conductor 20C is connected to the metal layer 2B' on the side of the second main surface 1Cb of the porous liquid crystal polymer sheet 1C. That is, the metal layer 2B' and the metal layer 2C are electrically connected via the interlayer connection conductor 20C.

[0163] The interlayer connection conductor 20D is provided so as to penetrate the porous liquid crystal polymer sheet 1C in the stacking direction but not to penetrate the metal layer 2C in the stacking direction, at a position separate from the interlayer connection conductor 20C, and is connected to the metal layer 2C. More specifically, the interlayer connection conductor 20D is connected to the metal layer 2C on the side of the first main surface 1Ca of the porous liquid crystal polymer sheet 1C while penetrating the porous liquid crystal polymer sheet 1C in the stacking direction, at a position separate from the interlayer connection conductor 20C. Further, the interlayer connection conductor 20D is connected to the metal layer 2B" on the side of the second main surface 1Cb of the porous liquid crystal polymer sheet 1C, at a position separate from the interlayer connection conductor 20C. That is, the metal layer 2B" and the metal layer 2C are electrically connected via the interlayer connection conductor 20D.

[0164] As such, in the electronic circuit substrate 50, the metal layer 2A and the metal layer 2C are electrically connected via the interlayer connection conductor 20A, the metal layer 2B', and the interlayer connection conductor 20C. Further, in the electronic circuit substrate 50, the metal layer 2A and the metal layer 2C are also electrically connected via the interlayer connection conductor 20B, the metal layer 2B", and the interlayer connection conductor 20D.

[0165] The interlayer connection conductor 20A is formed, for example, by a via hole reaching the metal layer 2B' provided to penetrate the porous liquid crystal polymer sheet 1B in the thickness direction but not to penetrate the metal layer 2B' in the thickness direction, plating treatment on the inner wall, or heat treatment after filling of a conductive paste.

[0166] The interlayer connection conductor 20B, the interlayer connection conductor 20C, and the interlayer connection conductor 20D are formed in the same manner as the interlayer connection conductor 20A except that the formation positions are different.

[0167] In the case where the interlayer connection conductor 20A, the interlayer connection conductor 20B, the interlayer connection conductor 20C, and the interlayer connection conductor 20D are formed by plating treatment, as the metal constituting each of the interlayer connection conductors, for example, copper, tin, silver, or the like can be listed, with copper being preferred.

[0168] In the case where the interlayer connection conductor 20A, the interlayer connection conductor 20B, the interlayer connection conductor 20C, and the interlayer connection conductor 20D are formed by heat treatment of a conductive paste, as the metal contained in each of the interlayer connection conductors, for example, copper, tin, silver, or the like can be listed. Of these, each of the interlayer connection conductors preferably contains copper, and more preferably contains copper and tin. For example, in the case where the interlayer connection conductor 20A contains copper and tin and the metal layer 2B' includes a copper foil, the interlayer connection conductor 20A and the metal layer 2B' cause an alloying reaction at low temperatures, and thus the two become easily conductive. The same applies to other combinations of the interlayer connection conductors and the metal layer.

[0169] In the case where the interlayer connection conductor 20A, the interlayer connection conductor 20B, the interlayer connection conductor 20C, and the interlayer connection conductor 20D are formed by heat treatment of a conductive paste, the resin contained in each of the interlayer connection conductors preferably contains at least one thermosetting resin selected from the group consisting of an epoxy resin, a phenol resin, a polyimide resin, a silicone resin or a modified resin thereof, and an acrylic resin, or at least one thermoplastic resin selected from the group consisting of a polyamide resin, a polystyrene resin, a polymethacrylic acid resin, a polycarbonate resin, and a cellulose-based resin.

[0170] The electronic circuit substrate 50 can also have the metal layer 2B as a signal line that transmits a signal. In this case, the electronic circuit substrate 50 constitutes a transmission line.

[0171] The electronic circuit substrate 50 can also have the metal layer 2B as a signal line that transmits a signal, and have the metal layer 2A and the metal layer 2C as ground electrodes. In this case, the electronic circuit substrate 50 constitutes a strip line type transmission line.

[0172] When the electronic circuit board 50 constitutes the above-mentioned transmission line, the metal layer 2B can also be a signal line for transmitting high-frequency signals.

[0173] When the electronic circuit board 50 forms a transmission line, the porous liquid crystal polymer sheet 1B and the porous liquid crystal polymer sheet 1C with small dielectric constant are connected to the metal layer 2B, i.e., the signal line, so the transmission characteristics of the electronic circuit board 50 can be easily improved.

[0174] The electronic circuit board 50 is manufactured, for example, by the following method.

[0175] <Fabrication process of porous liquid crystal polymer sheets with metal layers>

[0176] Figure 7 , Figure 5 ,as well as Figure 6 This is a cross-sectional schematic diagram showing the fabrication process of a porous liquid crystal polymer sheet with a metal layer, as an example of a method for manufacturing an electronic circuit board according to the present invention.

[0177] like Figure 7 As shown, a porous liquid crystal polymer sheet 10A with a metal layer 2A is formed on the first main surface 1Aa of the porous liquid crystal polymer sheet 1A. For example, the metal layer 2A is pressed onto the first main surface 1Aa of the porous liquid crystal polymer sheet 1A.

[0178] like Figure 8 As shown, a porous liquid crystal polymer sheet 10B with metal layers 2B, 2B', and 2B'' is fabricated on the first main surface 1Ba of the porous liquid crystal polymer sheet 1B. For example, after the metal layers are pressed onto the first main surface 1Ba of the porous liquid crystal polymer sheet 1B, the metal layers are etched to pattern them as metal layers 2B, 2B', and 2B''. Alternatively, metal layers 2B, 2B', and 2B'' can be prepared in advance, and each metal layer can be pressed onto the first main surface 1Ba of the porous liquid crystal polymer sheet 1B.

[0179] like Figure 9 As shown, a porous liquid crystal polymer sheet 10C with a metal layer 2C is formed on the first main surface 1Ca of the porous liquid crystal polymer sheet 1C. For example, the metal layer 2C is pressed onto the first main surface 1Ca of the porous liquid crystal polymer sheet 1C.

[0180] <Through hole formation process>

[0181] Figure 8 as well as Figure 9is a cross-sectional schematic view showing a via hole formation step of an example of a manufacturing method of an electronic circuit substrate of the present application.

[0182] As shown in Figure 10 , for the porous liquid crystal polymer sheet 10B with a metal layer, a via hole 21A is formed so as to reach the metal layer 2B' through the porous liquid crystal polymer sheet 1B in the thickness direction but not through the metal layer 2B' in the thickness direction. Thereby, a part of the metal layer 2B' is exposed from the via hole 21A.

[0183] Further, for the porous liquid crystal polymer sheet 10B with a metal layer, a via hole 21B is formed so as to reach the metal layer 2B" through the porous liquid crystal polymer sheet 1B in the thickness direction but not through the metal layer 2B" in the thickness direction at a position separate from the position where the via hole 21A is intended to be formed. Thereby, a part of the metal layer 2B" is exposed from the via hole 21B.

[0184] By the above, for the porous liquid crystal polymer sheet 10B with a metal layer, the via hole 21A and the via hole 21B are formed. At this time, the via hole 21A and the via hole 21B can be formed at the same timing or at different timings.

[0185] As shown in Figure 11 , for the porous liquid crystal polymer sheet 10C with a metal layer, a via hole 21C is formed so as to reach the metal layer 2C through the porous liquid crystal polymer sheet 1C in the thickness direction but not through the metal layer 2C in the thickness direction. Thereby, a part of the metal layer 2C is exposed from the via hole 21C.

[0186] Further, for the porous liquid crystal polymer sheet 10C with a metal layer, a via hole 21D is formed so as to reach the metal layer 2C through the porous liquid crystal polymer sheet 1C in the thickness direction but not through the metal layer 2C in the thickness direction at a position separate from the position where the via hole 21C is intended to be formed. Thereby, a part of the metal layer 2C is exposed from the via hole 21D.

[0187] By the above, for the porous liquid crystal polymer sheet 10C with a metal layer, the via hole 21C and the via hole 21D are formed. At this time, the via hole 21C and the via hole 21D can be formed at the same timing or at different timings.

[0188] When the via hole 21A, the via hole 21B, the via hole 21C, and the via hole 21D are formed, it is preferable to irradiate laser light from the porous liquid crystal polymer sheet side for the porous liquid crystal polymer sheet with a metal layer.

[0189] <Conductive paste filling step>

[0190] Figure 10 and Figure 11 is a cross-sectional view schematically showing a filling step of the conductive paste with respect to one example of the manufacturing method of the electronic circuit substrate of the present application.

[0191] As shown in Figure 12 , the conductive paste 22A is filled in the via 21A with respect to the porous liquid crystal polymer sheet with a metal layer 10B. Further, the conductive paste 22B is filled in the via 21B with respect to the porous liquid crystal polymer sheet with a metal layer 10B. At this time, the conductive paste 22A and the conductive paste 22B can be filled at the same timing or at different timings.

[0192] As shown in Figure 12 , the conductive paste 22C is filled in the via 21C with respect to the porous liquid crystal polymer sheet with a metal layer 10C. Further, the conductive paste 22D is filled in the via 21D with respect to the porous liquid crystal polymer sheet with a metal layer 10C. At this time, the conductive paste 22C and the conductive paste 22D can be filled at the same timing or at different timings.

[0193] As the method of filling the conductive paste 22A, the conductive paste 22B, the conductive paste 22C, and the conductive paste 22D, for example, a screen printing method, a vacuum filling method, or the like can be cited.

[0194] The conductive paste 22A, the conductive paste 22B, the conductive paste 22C, and the conductive paste 22D each, for example, contain a metal and a resin.

[0195] As the metal contained in each of the conductive paste 22A, the conductive paste 22B, the conductive paste 22C, and the conductive paste 22D, for example, copper, tin, silver, or the like can be cited. Among them, each of the conductive pastes preferably contains copper, and more preferably contains copper and tin.

[0196] The resin contained in each of the conductive paste 22A, the conductive paste 22B, the conductive paste 22C, and the conductive paste 22D preferably contains at least one thermosetting resin selected from the group consisting of an epoxy resin, a phenol resin, a polyimide resin, a silicone resin or a modified resin thereof, and an acrylic resin, or at least one thermoplastic resin selected from the group consisting of a polyamide resin, a polystyrene resin, a polymethacrylic acid resin, a polycarbonate resin, and a cellulose-based resin.

[0197] Each of the conductive paste 22A, the conductive paste 22B, the conductive paste 22C, and the conductive paste 22D can further contain a carrier, a solvent, a thixotropic agent, an active agent, or the like.

[0198] As the carrier, for example, rosin-based resins including rosin and derivatives thereof such as modified rosin obtained by modifying rosin, synthetic resins including rosin and derivatives thereof such as modified rosin obtained by modifying rosin, or mixtures of these resins, and the like can be exemplified.

[0199] As the rosin-based resins including rosin and derivatives thereof such as modified rosin obtained by modifying rosin, for example, gum rosin, tall rosin, wood rosin, polymerized rosin, hydrogenated rosin, formylated rosin, rosin ester, rosin-modified maleic acid resin, rosin-modified phenol resin, rosin-modified alkyd resin, other various rosin derivatives, and the like can be exemplified.

[0200] As the synthetic resins including rosin and derivatives thereof such as modified rosin obtained by modifying rosin, for example, polyester resins, polyamide resins, phenoxy resins, terpene resins, and the like can be exemplified.

[0201] As the solvent, for example, alcohols, ketones, esters, ethers, aromatic solvents, hydrocarbons, and the like can be exemplified. As specific examples thereof, benzyl alcohol, ethanol, isopropyl alcohol, butyl alcohol, diethylene glycol, ethylene glycol, glycerin, ethyl cellosolve, butyl cellosolve, ethyl acetate, butyl acetate, butyl benzoate, diethyl adipate, dodecane, tetradecene, a-terpineol, terpineol, 2-methyl-2,4-pentanediol, 2-ethylhexanediol, toluene, xylene, propylene glycol monophenyl ether, diethylene glycol monohexyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diisobutyl adipate, hexylene glycol, cyclohexane dimethanol, 2-terpinyl alcohol, 2-dihydroterpinyl alcohol, mixtures thereof, and the like can be exemplified. Among them, terpineol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, or diethylene glycol monoethyl ether is preferred.

[0202] As the thixotropic agent, for example, hardened castor oil, carnauba wax, amides, hydroxy fatty acids, dibenzylidene sorbitol, bis(p-methylbenzylidene) sorbitol, beeswax, stearyl amide, ethylene bis-hydroxy stearic amide, and the like can be exemplified. In addition, if necessary, fatty acids such as caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, hydroxy fatty acids such as 1,2-hydroxy stearic acid, antioxidants, surfactants, amines, and the like can be added to these thixotropic agents.

[0203] As the active agent, for example, halogenated hydrogen acid salts of amines, organic halides, organic acids, organic amines, polyhydric alcohols, and the like can be exemplified.

[0204] As the halogenated hydrogen acid salts of amines, for example, diphenyl guanidine hydrobromide, diphenyl guanidine hydrochloride, cyclohexylamine hydrobromide, ethylamine hydrochloride, ethylamine hydrobromide, diethylphenylamine hydrobromide, diethylphenylamine hydrochloride, triethanolamine hydrobromide, monoethanolamine hydrobromide, and the like can be exemplified.

[0205] As the organic halide, for example, chloroalkane, tetra- bromoethane, dibromopropanol, 2,3-dibromo-l,4-butanediol, 2,3- dibromo-2-butene-l,4-diol, tris(2,3-dibromopropyl) isocyanurate, and the like can be exemplified.

[0206] As the organic acid, for example, malonic acid, fumaric acid, glycolic acid, citric acid, malic acid, succinic acid, phenylsuccinic acid, maleic acid, salicylic acid, anthranilic acid, glutaric acid, suberic acid, adipic acid, sebacic acid, stearic acid, abietic acid, benzoic acid, trimellitic acid, pyromellitic acid, dodecanoic acid, and the like can be exemplified.

[0207] As the organic amine, for example, monoethanolamine, diethanolamine, triethanolamine, tributylamine, aniline, diethyl aniline, and the like can be exemplified.

[0208] As the polyhydric alcohol, for example, erythritol, pyrogallol, ribitol, and the like can be exemplified.

[0209] <Formation process of interlayer connection conductor>

[0210] Figure 12 is a cross-sectional schematic view showing the formation process of the interlayer connection conductor, which is one example of the method for manufacturing the electronic circuit substrate of the present application.

[0211] As shown in Figure 4 , the metal layer-equipped porous liquid crystal polymer sheet 10A, the metal layer-equipped porous liquid crystal polymer sheet 10B filled with the conductive paste 22A and the conductive paste 22B, and the metal layer-equipped porous liquid crystal polymer sheet 10C filled with the conductive paste 22C and the conductive paste 22D are sequentially stacked in the stacking direction. At this time, the surface (upper surface) of the metal layer 2A side of the metal layer-equipped porous liquid crystal polymer sheet 10A and the surface (lower surface) of the porous liquid crystal polymer sheet IB side of the metal layer-equipped porous liquid crystal polymer sheet 10B are in contact, and the surface (upper surface) of the metal layer 2B side (metal layer 2B' side, metal layer 2B" side) of the metal layer-equipped porous liquid crystal polymer sheet 10B and the surface (lower surface) of the porous liquid crystal polymer sheet IC side of the metal layer-equipped porous liquid crystal polymer sheet 10C are in contact. In addition, in ​ , each of the metal layer-equipped porous liquid crystal polymer sheets is shown separately from each other for convenience of explanation.

[0212] Then, for the obtained laminate, pressure is applied in the stacking direction while heating, whereby heat pressing is performed. By this, the porous liquid crystal polymer sheet 10A with a metal layer and the porous liquid crystal polymer sheet 10B with a metal layer are pressure-bonded, and the porous liquid crystal polymer sheet 10B with a metal layer and the porous liquid crystal polymer sheet 10C with a metal layer are pressure-bonded. Further, the conductive paste 22A, the conductive paste 22B, the conductive paste 22C, and the conductive paste 22D are cured at the time of heat pressing, whereby they become the interlayer connection conductor 20A, the interlayer connection conductor 20B, the interlayer connection conductor 20C, and the interlayer connection conductor 20D, respectively. In this way, the interlayer connection conductor 20A, the interlayer connection conductor 20B, the interlayer connection conductor 20C, and the interlayer connection conductor 20D are formed in the via 21A, the via 21B, the via 21C, and the via 21D, respectively.

[0213] At the time of forming the interlayer connection conductor 20A, the interlayer connection conductor 20B, the interlayer connection conductor 20C, and the interlayer connection conductor 20D, instead of filling the conductive paste into the via, plating treatment of the inner wall of the via with a metal such as copper, tin, silver, or the like can also be performed.

[0214] By the above, it is possible to manufacture ​ the electronic circuit substrate 50 shown in FIG. 1.

[0215] [Embodiment]

[0216] Hereinafter, an embodiment of the porous liquid crystal polymer sheet of the present application will be described in more detail. In addition, the present application is not limited to the following embodiment.

[0217] [Embodiment 1]

[0218] First, as the first component, a liquid crystal polymer A was prepared, wherein the liquid crystal polymer A was a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, the molar ratio of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid was 80:20, and the melting point was 325°C. Further, as the second component, an amorphous silica A was prepared, wherein the average particle diameter of the amorphous silica A was 3 μm, the melting point was more than 500°C, and the linear expansion coefficient in all directions in the temperature range of 23°C or more and 300°C or less was positive. Next, 70 parts by weight of the liquid crystal polymer A, 30 parts by weight of the amorphous silica A, and 0.4 parts by weight of a foaming agent "VINYFOR AC#6-K6" (main component: azodicarbonamide) manufactured by Nippon Shokubai Co., Ltd. were mixed, whereby a resin material was prepared. Then, using the obtained resin material, a porous liquid crystal polymer sheet of Embodiment 1 was manufactured by a T-die molding method. The thickness of the porous liquid crystal polymer sheet of Embodiment 1 was measured by the above-described method, and the result was 50 μm.

[0219] [Example 2]

[0220] Example 2 was produced in the same manner as the porous liquid crystalline polymer sheet of Example 1 except that, as the second component, amorphous silica B having an average particle diameter of 6 μm, a melting point exceeding 500°C, and a linear expansion coefficient positive in all directions in the temperature range of 23°C or higher and 300°C or lower was used.

[0221] [Example 3]

[0222] Example 3 was produced in the same manner as the porous liquid crystalline polymer sheet of Example 1 except that, as the second component, zirconium phosphotungstate having an average particle diameter of 1.3 μm, a melting point exceeding 500°C, and a linear expansion coefficient negative in all directions in the temperature range of 23°C or higher and 300°C or lower was used.

[0223] [Example 4]

[0224] Example 4 was produced in the same manner as the porous liquid crystalline polymer sheet of Example 1 except that, as the first component, liquid crystalline polymer B, which is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, and has a molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid of 73:27 and a melting point of 280°C, was used, and further the blending amount of the foaming agent was set to 0.2 parts by weight.

[0225] [Example 5]

[0226] Example 5 was produced in the same manner as the porous liquid crystalline polymer sheet of Example 1 except that, as the first component, liquid crystalline polymer B was used, as the second component, zirconium phosphotungstate described in Example 3 was used, and further the blending amount of the foaming agent was set to 0.2 parts by weight.

[0227] [Example 6]

[0228] Example 6 was produced in the same manner as the porous liquid crystalline polymer sheet of Example 1 except that, as the second component, liquid crystalline polymer having an average particle diameter of 5 μm, a melting point of 370°C, and a linear expansion coefficient positive in all directions in the temperature range of 23°C or higher and 300°C or lower was used.

[0229] [Comparative Example 1]

[0230] A porous liquid crystalline polymer sheet of Comparative Example 1 was produced in the same manner as the porous liquid crystalline polymer sheet of Example 1, except that, as the second component, polytetrafluoroethylene having an average particle diameter of 3.5 μm, a melting point of 327°C, and a linear expansion coefficient of positive in all directions in the temperature range of 23°C or higher and 300°C or lower was used.

[0231] [Comparative Example 2]

[0232] A porous liquid crystalline polymer sheet of Comparative Example 2 was produced in the same manner as the porous liquid crystalline polymer sheet of Example 1, except that the blending amount of the first component was set to 100 parts by weight, and further, the second component was not blended.

[0233] [Comparative Example 3]

[0234] A porous liquid crystalline polymer sheet of Comparative Example 3 was produced in the same manner as the porous liquid crystalline polymer sheet of Example 1, except that, as the first component, liquid crystalline polymer B was used, as the second component, polytetrafluoroethylene described in Comparative Example 1 was used, and further, the blending amount of the foaming agent was set to 0.2 parts by weight.

[0235] [Comparative Example 4]

[0236] A porous liquid crystalline polymer sheet of Comparative Example 4 was produced in the same manner as the porous liquid crystalline polymer sheet of Example 1, except that, as the first component, liquid crystalline polymer B was used, the blending amount thereof was set to 100 parts by weight, the second component was not blended, and further, the blending amount of the foaming agent was set to 0.2 parts by weight.

[0237] [Comparative Example 5]

[0238] A porous liquid crystalline polymer sheet of Comparative Example 5 was produced in the same manner as the porous liquid crystalline polymer sheet of Example 1, except that, as the first component, liquid crystalline polymer B was used, as the second component, amorphous silica B was used, and further, the blending amount of the foaming agent was set to 0.2 parts by weight.

[0239] [Comparative Example 6]

[0240] A porous liquid crystalline polymer sheet of Comparative Example 6 was produced in the same manner as the porous liquid crystalline polymer sheet of Example 1, except that, as the first component, liquid crystalline polymer B was used, as the second component, liquid crystalline polymer described in Example 6 was used, and further, the blending amount of the foaming agent was set to 0.2 parts by weight.

[0241] [Evaluation]

[0242] The following measurements were performed on the porous liquid crystalline polymer sheets of Examples 1 to 6 and Comparative Examples 1 to 6. The results are shown in Table 1.

[0243] <Average pore diameter>

[0244] First, the 3-dimensional configuration of the voids of the porous liquid crystal polymer sheet was identified using an X-ray CT device, whereby the maximum diameter of each void was determined, and the obtained maximum diameter was set as the void diameter of each void. Then, the cumulative void diameter distribution based on the number of voids was obtained, and the median diameter D50 was determined from the cumulative void diameter distribution. 50 Let D50 be the average void diameter of the voids.

[0245] <Void ratio>

[0246] First, a 100 mm square sample was cut out from the porous liquid crystal polymer sheet, and the area s, thickness t, and weight m of the sample were measured. In addition, the specific gravity σ of the resin component of the porous liquid crystal polymer sheet was measured in accordance with JIS Z 8807-2012. Then, the void ratio of the porous liquid crystal polymer sheet was calculated based on the formula: Void ratio (vol%) = [1 - (m / (s x t x σ))] x 100.

[0247] <Compression strength>

[0248] First, a plurality of 10 mm square samples were cut out from the porous liquid crystal polymer sheet, and these samples were stacked until the thickness became about 1 mm. Next, using a compression test device, the obtained stack was compressed at a speed of 1 mm / min while the compression stress corresponding to the strain rate at each time point was obtained. Then, the compression stress at the time point at which the strain rate became 10% was set as the compression strength of the porous liquid crystal polymer sheet. In addition, for the strain rate, the thickness of the stack immediately before the start of the compression test was set as L1, and the thickness of the stack at a certain time point during the compression test was set as L2, and the strain rate (%) was calculated based on the formula: Strain rate (%) = [(L1 - L2) / L1] x 100. For the judgment criteria for the compression strength of the porous liquid crystal polymer sheet, the following was set.

[0249] ◎ (Excellent): The compression strength is 100 MPa or more.

[0250] O (Good): The compression strength is 50 MPa or more but less than 100 MPa.

[0251] X (Poor): The compression strength is less than 50 MPa.

[0252] <Linear expansion coefficient>

[0253] First, a 20 mm x 4 mm test piece was cut from the porous liquid crystalline polymer sheet, and set on a probe of a thermal mechanical analysis device manufactured by Seiko Instruments Inc. with a distance between chucks of 10 mm. Next, the test piece was heated at a temperature increase rate of 40°C / min to 170°C while applying a load of 5 g, and then cooled at a temperature decrease rate of 10°C / min to 30°C. Then, the amount of change in the distance between chucks in the temperature range from 100°C to 50°C was measured during the cooling, and thus the linear expansion coefficient of the porous liquid crystalline polymer sheet was calculated. In this evaluation, the linear expansion coefficients in the longitudinal direction (also referred to as the flow direction (MD)) and the width direction (also referred to as the perpendicular direction (TD)) of the test piece of the porous liquid crystalline polymer sheet were calculated by the above-described method, and the average of these was taken as the linear expansion coefficient of the porous liquid crystalline polymer sheet. The criteria for the linear expansion coefficient of the porous liquid crystalline polymer sheet were as follows.

[0254] ◎ (Good): The linear expansion coefficient was 20 ppm / K or more and less than 25 ppm / K.

[0255] ○ (Good): The linear expansion coefficient was 20 ppm / K or more and less than 25 ppm / K.

[0256] x (Poor): The linear expansion coefficient was 25 ppm / K or more.

[0257] [Table 1]

[0258]

[0259] As shown in Table 1, the porous liquid crystalline polymer sheets of Examples 1 to 6, which contained the second component and in which the average particle diameter of the second component was smaller than the average void diameter of the voids, had high compressive strengths.

[0260] More specifically, the porous liquid crystalline polymer sheets of Examples 1 to 6, which contained the second component, had higher compressive strengths than the porous liquid crystalline polymer sheets of Comparative Example 2 and Comparative Example 4, which did not contain the second component.

[0261] In this case, in the porous liquid crystalline polymer sheet of Examples 1 to 6, when the region containing the second component is set as the first region and the region in which the content ratio of the second component is smaller than that of the first region is set as the second region, it can be considered that the relationship between the compressive strengths of the first region and the second region is the same as the relationship between the compressive strengths of the porous liquid crystalline polymer sheet of Examples 1 to 6 containing the second component and the porous liquid crystalline polymer sheet of Comparative Example 2 and Comparative Example 4 not containing the second component. That is, it can be said that in the porous liquid crystalline polymer sheet of Examples 1 to 6, the compressive strength of the first region is higher than that of the second region. As such, it can be said that the second component contained in the porous liquid crystalline polymer sheet of Examples 1 to 6 contributes to the improvement of the compressive strength.

[0262] Further, the porous liquid crystalline polymer sheet of Examples 1 to 6 in which the second component is not polytetrafluoroethylene has a higher compressive strength than the porous liquid crystalline polymer sheet of Comparative Example 1 and Comparative Example 3 in which the second component is polytetrafluoroethylene. That is, it can be said that polytetrafluoroethylene does not contribute to the improvement of the compressive strength of the porous liquid crystalline polymer sheet. It can be considered that this is the same in the case where the second component is a fluorine-based resin other than polytetrafluoroethylene.

[0263] Further, the porous liquid crystalline polymer sheet of Examples 1 to 6 in which the average particle diameter of the second component is smaller than the average pore diameter of the pores has a higher compressive strength than the porous liquid crystalline polymer sheet of Comparative Example 5 and Comparative Example 6 in which the average particle diameter of the second component is larger than the average pore diameter of the pores.

[0264] In view of the above, it can be said that in order to realize a porous liquid crystalline polymer sheet having a high compressive strength, it is important that the porous liquid crystalline polymer sheet contains a second component that contributes to the improvement of the compressive strength, as in the porous liquid crystalline polymer sheet of Examples 1 to 6, and that the average particle diameter of the second component is smaller than the average pore diameter of the pores.

[0265] Further, the porous liquid crystalline polymer sheet of Examples 1 to 6 in which the second component contains an inorganic filler, the porous liquid crystalline polymer sheet of Example 1, the porous liquid crystalline polymer sheet of Example 2, the porous liquid crystalline polymer sheet of Example 3, the porous liquid crystalline polymer sheet of Example 4, and the porous liquid crystalline polymer sheet of Example 5 have a smaller linear expansion coefficient, and the porous liquid crystalline polymer sheet of Example 3 and the porous liquid crystalline polymer sheet of Example 5 in which the linear expansion coefficient in all directions of the inorganic filler is negative in the temperature range of 23°C or higher and 300°C or lower have a further smaller linear expansion coefficient.

[0266] Explanation of Reference Signs

[0267] 1, 1A, 1B, 1C, 101: porous liquid crystalline polymer sheet;

[0268] 1a, 1Aa, 1Ba, 1Ca: first main surface of porous liquid crystalline polymer sheet;

[0269] 1b, 1Ab, 1Bb, 1Cb: second main surface of porous liquid crystal polymer sheet;

[0270] 1e, 1Ae, 1Be, 1Ce: first component;

[0271] 1f, 1Af, 1Bf, 1Cf: second component

[0272] 1h, 1Ah, 1Bh, 1Ch: void;

[0273] 1s, 1As, 1Bs, 1Cs: resin sheet;

[0274] 2, 2A, 2B, 2B', 2B", 2C: metal layer;

[0275] 10, 10A, 10B, 10C: porous liquid crystal polymer sheet with metal layer;

[0276] 20A, 20B, 20C, 20D: interlayer connection conductor;

[0277] 21A, 21B, 21C, 21D: via hole;

[0278] 22A, 22B, 22C, 22D: conductive paste;

[0279] 50: electronic circuit substrate.

Claims

1. A porous liquid crystalline polymer sheet comprising a resin sheet, and, in which a void is provided in the resin sheet, the resin sheet including a first component comprising a liquid crystalline polymer and a second component which is the largest in weight ratio except for the first component, characterized in that, when a region containing the second component is set as a first region, and a region in which the content ratio of the second component is smaller than the first region is set as a second region, the compressive strength of the first region is higher than that of the second region, the average particle diameter of the second component is smaller than the average void diameter of the void, and the second component exists independently of the void or forms a part of a wall surface of the void.

2. The porous liquid crystalline polymer sheet according to claim 1, characterized in that, the second component contains an inorganic filler.

3. The porous liquid crystalline polymer sheet according to claim 2, characterized in that, the inorganic filler has a negative coefficient of linear expansion in a temperature range of 23°C or higher and 300°C or lower.

4. The porous liquid crystalline polymer sheet according to any one of claims 1 to 3, characterized in that, when a temperature 50°C lower than the melting point of the liquid crystalline polymer is set as a reference temperature, the melting point of the second component is higher than the reference temperature.

5. The porous liquid crystalline polymer sheet according to any one of claims 1 to 3, characterized in that, the weight ratio of the second component in the resin sheet is 10% by weight or more and 70% by weight or less.

6. The porous liquid crystalline polymer sheet according to claim 5, characterized in that, the weight ratio of the second component in the resin sheet is 20% by weight or more and 50% by weight or less.

7. The porous liquid crystalline polymer sheet according to any one of claims 1 to 3, characterized in that, the melting point of the liquid crystalline polymer is 275°C or higher and 330°C or lower.

8. The porous liquid crystalline polymer sheet according to any one of claims 1 to 3, characterized in that, the liquid crystalline polymer contains a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid.

9. The porous liquid crystalline polymer sheet according to claim 8, characterized in that, in the liquid crystalline polymer, the molar ratio of the p-hydroxybenzoic acid with respect to the 6-hydroxy-2-naphthoic acid is 0.20 or more and 5 or less.

10. The porous liquid crystalline polymer sheet according to claim 8, characterized in that, when the total amount of monomers is set as 100 mol%, the liquid crystalline polymer contains 10 mol% or more of each of the p-hydroxybenzoic acid and the 6-hydroxy-2-naphthoic acid.

11. The porous liquid crystalline polymer sheet according to any one of claims 1 to 3, characterized in that, the thickness is 10 μm or more and 200 μm or less.

12. A metal-layer-equipped porous liquid crystalline polymer sheet comprising: the porous liquid crystalline polymer sheet according to any one of claims 1 to 11; and a metal layer provided on at least one main surface of the porous liquid crystalline polymer sheet.

13. The metal-layer-equipped porous liquid crystalline polymer sheet according to claim 12, characterized in that, the metal layer contains a copper foil. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 12. A porous liquid crystal polymer sheet with a metal layer, characterized by ​ ​ ​ ​ ​ 14. An electronic circuit substrate, characterized by comprising: The porous liquid crystal polymer sheet with a metal layer according to claim 12 or 13.

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