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

Abstract

The porous liquid crystal polymer sheet (1) is a porous liquid crystal polymer sheet comprising a resin sheet (1s) containing a liquid crystal polymer and having pores (1h) formed in the resin sheet (1s). The test temperature is set at a temperature 20°C higher than the melting point of the resin sheet (1s), and the shearing speed is set at 1000 s. ‑1 The melt viscosity under the given conditions is above 20 Pa·s.

Description

Technical Field

[0001] This invention relates to porous liquid crystal polymer sheets, porous liquid crystal polymer sheets with metal layers, and electronic circuit substrates. Background Technology

[0002] As a method for manufacturing porous liquid crystal polymer sheets, Patent Document 1 discloses a method for manufacturing porous liquid crystal polymer sheets comprising an aggregate of protofibrils arranged in a certain direction. In this method, a self-oriented liquid crystal polymer and a non-liquid crystal polymer that is soluble in a solvent are mixed in a weight ratio of 70:30 to 40:60, and then extruded into a sheet shape. Next, the non-liquid crystal polymer is selectively extracted from the molded body to remove it.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 6-98666 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] Liquid crystal polymer sheets are known as components for improving the dielectric properties in high-frequency regions of electronic circuit boards used in various electronic devices due to their low dielectric constant.

[0008] In response, the inventors investigated a conventional porous liquid crystal polymer sheet, as described in Patent Document 1, which contains pores in addition to the liquid crystal polymer that contribute to a further reduction in dielectric constant, thereby further improving the dielectric properties in the high-frequency region of the electronic circuit board.

[0009] However, the inventors conducted research and discovered that when using conventional porous liquid crystal polymer sheets to manufacture electronic circuit boards, if a metal layer is laminated onto the porous liquid crystal polymer sheet, the pores of the porous liquid crystal polymer sheet become easily crushed under the high temperature and pressure during lamination. This problem of the pores of the porous liquid crystal polymer sheet becoming easily crushed under high temperature and pressure was not previously recognized.

[0010] This invention addresses the aforementioned problems and aims to provide a porous liquid crystal polymer sheet that is resistant to damage from pores under high temperature and pressure. Furthermore, this invention aims to provide a porous liquid crystal polymer sheet with a metal layer. Finally, this invention aims to provide an electronic circuit board using the aforementioned porous liquid crystal polymer sheet with a metal layer.

[0011] Technical solutions for solving the problem

[0012] The porous liquid crystal polymer sheet of the present invention comprises a resin sheet containing a liquid crystal polymer, and pores are provided in the resin sheet. The invention is characterized by setting a temperature 20°C higher than the melting point of the resin sheet as the measurement temperature and setting a shearing speed of 1000 s. -1 The melt viscosity under the specified conditions is above 20 Pa·s.

[0013] The porous liquid crystal polymer sheet with a metal layer of the present invention is characterized in that it comprises the porous liquid crystal polymer sheet of the present invention and a metal layer disposed on at least one main surface of the porous liquid crystal polymer sheet.

[0014] The electronic circuit board of the present invention is characterized by having a porous liquid crystal polymer sheet with a metal layer as described in the present invention.

[0015] Invention Effects

[0016] According to the present invention, a porous liquid crystal polymer sheet that is not easily damaged by pressure under high temperature and pressure can be provided. Furthermore, according to the present invention, a porous liquid crystal polymer sheet with a metal layer having the above-mentioned porous liquid crystal polymer sheet can be provided. Moreover, according to the present invention, an electronic circuit board having the above-mentioned porous liquid crystal polymer sheet with a metal layer can be provided. Attached Figure Description

[0017] Figure 1 This is a cross-sectional schematic diagram illustrating an example of a porous liquid crystal polymer sheet according to the present invention.

[0018] Figure 2 This is a cross-sectional schematic diagram illustrating an example of a porous liquid crystal polymer sheet with a metal layer according to the present invention.

[0019] Figure 3 This is a cross-sectional schematic diagram illustrating an example of an electronic circuit board according to the present invention.

[0020] Figure 4 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.

[0021] Figure 5 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.

[0022] Figure 6This 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.

[0023] Figure 7 This is a cross-sectional schematic diagram showing a via formation process as an example of a method for manufacturing an electronic circuit board according to the present invention.

[0024] Figure 8 This is a cross-sectional schematic diagram showing a via formation process as an example of a method for manufacturing an electronic circuit board according to the present invention.

[0025] Figure 9 This is a cross-sectional schematic diagram showing the filling process of conductive paste as an example of a method for manufacturing an electronic circuit board according to the present invention.

[0026] Figure 10 This is a cross-sectional schematic diagram showing the filling process of conductive paste as an example of a method for manufacturing an electronic circuit board according to the present invention.

[0027] Figure 11 This is a cross-sectional schematic diagram showing the formation process of interlayer interconnect conductors as an example of a method for manufacturing an electronic circuit board according to the present invention. Detailed Implementation

[0028] The porous liquid crystal polymer sheet of the present invention, the porous liquid crystal polymer sheet with a metal layer of the present invention, and the electronic circuit board of the present invention will be described below. Furthermore, the present invention is not limited to the structures described below, and appropriate modifications can be made without departing from the spirit of the present invention. Moreover, products obtained by combining multiple preferred structures described below are also part of the present invention.

[0029] The porous liquid crystal polymer sheet of the present invention is a porous liquid crystal polymer sheet comprising a resin sheet containing a liquid crystal polymer and having pores provided in the resin sheet.

[0030] In this specification, "sheet" and "film" are used interchangeably and are not distinguished by thickness.

[0031] Figure 1 This is a cross-sectional schematic diagram illustrating an example of a porous liquid crystal polymer sheet according to the present invention.

[0032] Figure 1 The porous liquid crystal polymer sheet 1 shown has a first main surface 1a and a second main surface 1b facing each other in the thickness direction.

[0033] The porous liquid crystal polymer sheet 1 includes a resin sheet 1s comprising a liquid crystal polymer. In the porous liquid crystal polymer sheet 1, pores 1h are provided in the resin sheet 1s. More specifically, in the porous liquid crystal polymer sheet 1, pores 1h are provided inside the resin sheet 1s.

[0034] In this invention, the porous liquid crystal polymer sheet is tested at a temperature 20°C higher than the melting point of the resin sheet, and the shearing speed is set to 1000 s. -1 The melt viscosity under the specified conditions is above 20 Pa·s.

[0035] Figure 1 The porous liquid crystal polymer sheet 1 shown is measured at a temperature 20°C higher than the melting point of the resin sheet 1s, and the shear rate is set to 1000s. -1 The melt viscosity under the specified conditions is above 20 Pa·s.

[0036] The inventors conducted research and found that when using conventional porous liquid crystal polymer sheets to manufacture electronic circuit boards, if a metal layer is laminated onto the porous liquid crystal polymer sheet, the pores in the sheet become easily crushed under the high temperature and pressure during lamination. Therefore, in electronic circuit boards manufactured using conventional porous liquid crystal polymer sheets, the pores are crushed, making it difficult to achieve the dielectric constant reduction effect generated by the porous liquid crystal polymer sheet. Consequently, the dielectric properties in the high-frequency region are not easily improved.

[0037] In contrast, the porous liquid crystal polymer sheet 1 has a melt viscosity of 20 Pa·s or higher under the aforementioned conditions. Therefore, when manufacturing an electronic circuit board using the porous liquid crystal polymer sheet 1, for example, the pores 1h are less likely to be damaged under the high temperature and pressure during the lamination process when the metal layer is pressed onto the porous liquid crystal polymer sheet 1. Consequently, in electronic circuit boards manufactured using the porous liquid crystal polymer sheet 1, the reduction in dielectric constant caused by the porous liquid crystal polymer sheet 1 becomes more readily apparent, thus improving the dielectric properties in the high-frequency region. Furthermore, since liquid crystal polymers have low hygroscopicity, changes in dielectric properties due to moisture absorption are less likely to occur in electronic circuit boards manufactured using the porous liquid crystal polymer sheet 1.

[0038] If the melt viscosity of the porous liquid crystal polymer sheet 1 under the above conditions is less than 20 Pa·s, the pores become easily crushed under high temperature and high pressure for 1 hour.

[0039] On the other hand, if the melt viscosity of the porous liquid crystal polymer sheet 1 under the above conditions is too high, for example, when pressing a metal layer onto the porous liquid crystal polymer sheet 1, the porous liquid crystal polymer sheet 1 is not easily deformed, and therefore the adhesion between the porous liquid crystal polymer sheet 1 and the metal layer is sometimes difficult to improve. From this point of view, the melt viscosity of the porous liquid crystal polymer sheet 1 under the above conditions is preferably 500 Pa·s or less, more preferably 200 Pa·s or less.

[0040] In the porous liquid crystal polymer sheet of the present invention, the melt viscosity is specified at a measurement temperature 20°C higher than the melting point of the resin sheet in order to accurately measure the melt viscosity while suppressing the deterioration of the liquid crystal polymer.

[0041] At temperatures lower than the aforementioned measurement temperature, porous liquid crystal polymer sheets do not readily reach a fully molten state, making it difficult to accurately measure their melt viscosity. Furthermore, when measuring the melt viscosity of multiple porous liquid crystal polymer sheets, it becomes difficult to accurately compare these results.

[0042] Temperatures higher than those measured above can accelerate the deterioration of liquid crystal polymers, thus introducing significant noise into the melt viscosity measurement results of porous liquid crystal polymer sheets.

[0043] The melting point of the resin sheet is determined as follows. First, for example, using a differential scanning calorimeter such as the Hitachi High-Tech Science Corporation's "DSC7000X," the resin sheet, i.e., the porous liquid crystal polymer sheet, is heated until it is completely melted. 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. This time, 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 temperature corresponding to the endothermic peak observed during this heating process is determined as the melting point of the resin sheet, i.e., the porous liquid crystal polymer sheet. Alternatively, if the endothermic peak is not easily observed using the above method, the melting point of the resin sheet, i.e., the porous liquid crystal polymer sheet, is determined by texture observation under crossed Nicols conditions using a polarizing microscope.

[0044] The melt viscosity of the porous liquid crystal polymer sheet of the present invention under the above conditions is adjusted to 20 Pa·s or more, for example, by performing solid-state polymerization of the liquid crystal polymer during the manufacture of the porous liquid crystal polymer sheet. When solid-state polymerization of the liquid crystal polymer is performed, the molecular chain length of the liquid crystal polymer elongates, and thus the elongated liquid crystal polymer chains entangle with each other, thereby making it easier to increase the melt viscosity of the porous liquid crystal polymer sheet.

[0045] Although the effect is slightly less than that of solid-state polymerization of liquid crystal polymers, as will be described later, the melt viscosity of porous liquid crystal polymer sheets can also be increased by irradiating the liquid crystal polymer with electron beams.

[0046] Furthermore, the melt viscosity of porous liquid crystal polymer sheets can also be adjusted by polymerization conditions such as polymerization temperature and polymerization time of the liquid crystal polymer.

[0047] The melt tension of the porous liquid crystal polymer sheet of the present invention at the above-mentioned measurement temperature is preferably 3 mN or more.

[0048] Figure 1 The melt tension of the porous liquid crystal polymer sheet 1 shown at the above-mentioned measurement temperature is preferably 3 mN or more.

[0049] If the melt viscosity of the porous liquid crystal polymer sheet 1 under the above conditions is 20 Pa·s or more, and the melt tension of the porous liquid crystal polymer sheet 1 at the above measurement temperature is 3 mN or more, then, for example, when a metal layer is pressed onto the porous liquid crystal polymer sheet 1, the pores 1h become less likely to be crushed.

[0050] If the melt tension of the porous liquid crystal polymer sheet 1 at the aforementioned measurement temperature is too high, for example, when pressing a metal layer onto the porous liquid crystal polymer sheet 1, the porous liquid crystal polymer sheet 1 is not easily deformed, and therefore the adhesion between the porous liquid crystal polymer sheet 1 and the metal layer is sometimes difficult to improve. From this point of view, the melt tension of the porous liquid crystal polymer sheet 1 at the aforementioned measurement temperature is preferably 20 mN or less, more preferably 10 mN or less, and even more preferably 7 mN or less.

[0051] In the porous liquid crystal polymer sheet of the present invention, the reason for specifying the melt tension at the above-mentioned measurement temperature is the same as the reason for specifying the melt viscosity at the above-mentioned measurement temperature.

[0052] The melt tension of the porous liquid crystal polymer sheet of the present invention at the aforementioned measurement temperature is adjusted to 3 mN or more, for example, by irradiating the liquid crystal polymer with electron beams during the manufacture of the porous liquid crystal polymer sheet. Irradiating the liquid crystal polymer with electron beams promotes the crosslinking reaction of the liquid crystal polymer, thereby increasing the number of crosslinking points and making it easier to increase the melt tension of the porous liquid crystal polymer sheet.

[0053] Although the effect is slightly less than that of electron beam irradiation of the liquid crystal polymer, the melt tension of porous liquid crystal polymer sheets can still be increased by solid-state polymerization of the liquid crystal polymer.

[0054] Furthermore, the melt tension of porous liquid crystal polymer sheets can also be adjusted by polymerization conditions such as polymerization temperature and polymerization time of the liquid crystal polymer.

[0055] In the porous liquid crystal polymer sheet of the present invention, the melting point of the resin sheet is preferably 275°C or higher and 330°C or lower.

[0056] exist Figure 1 In the porous liquid crystal polymer sheet 1 shown, the melting point of the resin sheet 1s is preferably above 275°C and below 330°C.

[0057] If the melting point of the resin sheet 1s is below 275°C, for example, when assembling an electronic circuit board made of a porous liquid crystal polymer sheet 1 containing the resin sheet 1s into an electronic device by reflow soldering, the heat resistance of the resin sheet 1s may be insufficient.

[0058] If the melting point of the resin sheet 1s is higher than 330°C, then a higher processing temperature is required, for example, when the resin sheet 1s is being film-formed, which sometimes promotes the deterioration of the liquid crystal polymer.

[0059] In the porous liquid crystal polymer sheet of the present invention, the liquid crystal polymer preferably comprises a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid.

[0060] exist Figure 1 In the porous liquid crystal polymer sheet 1 shown, the liquid crystal polymer preferably comprises a copolymer of p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA).

[0061] Copolymers of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid are generally referred to as type II fully aromatic polyesters (also known as type 1.5 fully aromatic polyesters). Type II fully aromatic polyesters are less prone to hydrolysis compared to type III partially aromatic polyesters, making them a preferred material for electronic circuit boards manufactured using porous liquid crystal polymer sheets 1. Furthermore, type II fully aromatic polyesters, being derived from naphthalene rings, have a small dielectric loss tangent, thus contributing to reduced power loss in the porous liquid crystal polymer sheet 1 within the electronic circuit board.

[0062] In the porous liquid crystal polymer sheet 1, in addition to the type II fully aromatic polyester, the liquid crystal polymer may further include the type I fully aromatic polyester, or a portion of the type III aromatic polyester, or both the type I fully aromatic polyester and a portion of the type III aromatic polyester.

[0063] The structure (type) of each monomer that makes up the liquid crystal polymer can be analyzed by reaction pyrolysis gas chromatography-mass spectrometry (reaction pyrolysis GC-MS).

[0064] In the porous liquid crystal polymer sheet of the present invention, the molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid in the liquid crystal polymer is preferably 0.20 or more and 5 or less.

[0065] exist Figure 1 In the porous liquid crystal polymer sheet 1 shown, the molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid in the liquid crystal polymer is preferably 0.20 or more and 5 or less.

[0066] In liquid crystal polymers, if the molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid is less than 0.20 or greater than 5, the melting point of the resin sheet 1s sometimes becomes higher than the preferred range described above.

[0067] In the porous liquid crystal polymer sheet of the present invention, when the total amount of monomers is set to 100 mol%, the liquid crystal polymer preferably contains 10 mol% or more of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid.

[0068] exist Figure 1 In the porous liquid crystal polymer sheet 1 shown, when the total amount of monomers is set to 100 mol%, the liquid crystal polymer preferably contains 10 mol% or more of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid.

[0069] If the content of each of the monomers of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid in the liquid crystal polymer is less than 10 mol%, it becomes difficult to achieve the liquid crystal properties of the liquid crystal polymer, the preferred range of the melting point of the resin sheet 1s, and the small dielectric loss tangent of the liquid crystal polymer.

[0070] The ratio and content of the various monomers constituting the liquid crystal polymer can be analyzed by reaction pyrolysis gas chromatography-mass spectrometry.

[0071] The thickness of the porous liquid crystal polymer sheet of the present invention is preferably 10 μm or more and 200 μm or less.

[0072] Figure 1 The thickness of the porous liquid crystal polymer sheet 1 shown is preferably 10 μm or more and 200 μm or less.

[0073] If the thickness of the porous liquid crystal polymer sheet 1 is less than 10 μm, the porosity of the voids 1h on at least one of the main surfaces, the first main surface 1a and the second main surface 1b, becomes more likely to increase, and thus the smoothness becomes more likely to decrease. In this case, if a metal layer is laminated onto a main surface with low smoothness, and the metal layer is etched into a pattern shape such as wiring, pattern defects are more likely to occur due to the voids 1h present on that main surface.

[0074] If the thickness of the porous liquid crystal polymer sheet 1 is greater than 200 μm, it may become difficult to form the vias that form the interlayer interconnect conductors through the porous liquid crystal polymer sheet 1 when the porous liquid crystal polymer sheet 1 is used to manufacture an electronic circuit substrate with interlayer interconnect conductors.

[0075] The thickness of the porous liquid crystal polymer sheet is determined as follows: First, a 100mm square sample is cut from the porous liquid crystal polymer sheet. Then, the thickness at nine equally spaced points within a 25mm square region sharing a center with the sample is measured, and the average value of these measurements is taken as the thickness of the porous liquid crystal polymer sheet. Alternatively, if a 100mm square sample cannot be cut from the porous liquid crystal polymer sheet, the thickness is determined using the same method as described above, except that the porous liquid crystal polymer sheet itself is used as the sample. In this case, if the aforementioned 25mm square region cannot be obtained from the porous liquid crystal polymer sheet, the thickness at nine equally spaced points within the porous liquid crystal polymer sheet is measured, and the average value of these measurements is taken as the thickness of the porous liquid crystal polymer sheet.

[0076] The porous liquid crystal polymer sheet 1, more specifically the resin sheet 1s, is configured with pores 1h, preferably having an independent bubble structure.

[0077] The term "porous liquid crystal polymer sheet with independent bubble structure" refers to a structure in which the walls of the pores (bubbles) are completely surrounded by resin. When observing cross-sections of the porous liquid crystal polymer sheet along its thickness direction and along in-plane directions orthogonal to the thickness direction, if the walls of the pores are not connected to each other, it is considered that the porous liquid crystal polymer sheet has an independent bubble structure.

[0078] When the porous liquid crystal polymer sheet 1 has an independent bubble structure, compared with the case of a continuous bubble structure, the path for air in the pore 1h to be released to the outside is reduced, making it easier to ensure compressive strength. Therefore, when the metal layer is pressed onto the porous liquid crystal polymer sheet 1, the porous liquid crystal polymer sheet 1, and more specifically the pore 1h, becomes less prone to crushing.

[0079] Porous liquid crystal polymer sheet 1 is manufactured, for example, by the following method.

[0080] First, the liquid crystal polymer and the foaming agent are mixed in a given ratio to prepare the resin material.

[0081] Next, using resin material, a resin sheet with pores is produced by extrusion molding, that is, a so-called porous resin sheet. Examples of extrusion molding methods include T-die molding and blow molding.

[0082] Then, for porous resin sheets, either solid-state polymerization of the liquid crystal polymer is carried out, or electron beam irradiation of the liquid crystal polymer is carried out, or both are carried out, thereby increasing the melt viscosity under the above conditions to 20 Pa·s or more.

[0083] Through the above methods, a porous liquid crystal polymer sheet 1 comprising a resin sheet 1s with pores 1h is manufactured. The melt viscosity of the porous liquid crystal polymer sheet 1 under the above conditions is 20 Pa·s or higher.

[0084] The porous liquid crystal polymer sheet with a metal layer of the present invention comprises: the porous liquid crystal polymer sheet of the present invention, and a metal layer disposed on at least one main surface of the porous liquid crystal polymer sheet.

[0085] Figure 2 This is a cross-sectional schematic diagram illustrating an example of a porous liquid crystal polymer sheet with a metal layer according to the present invention.

[0086] Figure 2 The porous liquid crystal polymer sheet 10 with a metal layer shown has a porous liquid crystal polymer sheet 1 and a metal layer 2 in the stacking direction.

[0087] The stacking direction corresponds to the direction along the thickness direction of the porous liquid crystal polymer sheet that constitutes the porous liquid crystal polymer sheet with the metal layer.

[0088] A metal layer 2 is disposed on at least one main surface of the porous liquid crystal polymer sheet 1, here disposed on the first main surface 1a. More specifically, the metal layer 2 is adjacent to the first main surface 1a side of the porous liquid crystal polymer sheet 1.

[0089] The metal layer 2 can be patterned into a shape such as wiring, or it can be a surface covering the entire surface.

[0090] Materials that form the metal layer 2 include, for example, copper, silver, aluminum, stainless steel, nickel, gold, and alloys containing at least one of these metals.

[0091] In the porous liquid crystal polymer sheet with a metal layer of the present invention, the metal layer preferably comprises copper foil.

[0092] exist Figure 2 In the porous liquid crystal polymer sheet 10 with a metal layer shown, the metal layer 2 preferably comprises copper foil. In this case, a metal other than copper may also be plated on the surface of the copper foil.

[0093] The thickness of the metal layer 2 is preferably 1 μm or more and 35 μm or less, more preferably 6 μm or more and 18 μm or less.

[0094] The porous liquid crystal polymer sheet 10 with a metal layer may also have other metal layers disposed on the second main surface 1b of the porous liquid crystal polymer sheet 1 in addition to the metal layer 2.

[0095] The porous liquid crystal polymer sheet 10 with a metal layer is manufactured, for example, by pressing the metal layer 2 onto the first main surface 1a of the porous liquid crystal polymer sheet 1. The metal layer 2 may also be etched into a patterned shape after being pressed onto the first main surface 1a of the porous liquid crystal polymer sheet 1.

[0096] The porous liquid crystal polymer sheet 10 with a metal layer can also be manufactured by pressing a pre-patterned metal layer 2 onto the first main surface 1a of the porous liquid crystal polymer sheet 1.

[0097] The electronic circuit board of the present invention comprises the porous liquid crystal polymer sheet with a metal layer of the present invention.

[0098] Figure 3 This is a cross-sectional schematic diagram illustrating an example of an electronic circuit board according to the present invention.

[0099] Figure 3The electronic circuit board 50 shown has, in the stacking direction, a porous liquid crystal polymer sheet 10A with a metal layer, a porous liquid crystal polymer sheet 10B with a metal layer, and a porous liquid crystal polymer sheet 10C with a metal layer. That is, in the electronic circuit board 50, the porous liquid crystal polymer sheet 10A with a metal layer, the porous liquid crystal polymer sheet 10B with a metal layer, and the porous liquid crystal polymer sheet 10C with a metal layer are stacked sequentially in the stacking direction.

[0100] The porous liquid crystal polymer sheet 10A with a metal layer has a porous liquid crystal polymer sheet 1A and a metal layer 2A.

[0101] The porous liquid crystal polymer sheet 1A has a first main surface 1Aa and a second main surface 1Ab that are opposed in the thickness direction.

[0102] The porous liquid crystal polymer sheet 1A includes a resin sheet 1As comprising a liquid crystal polymer. In the porous liquid crystal polymer sheet 1A, pores 1Ah are provided in the resin sheet 1As.

[0103] A metal layer 2A is disposed on the first main surface 1Aa of the porous liquid crystal polymer sheet 1A. Furthermore, the metal layer 2A is adjacent to the second main surface 1Bb of the porous liquid crystal polymer sheet 1B, which will be described later.

[0104] The porous liquid crystal polymer sheet 10B with a metal layer has a porous liquid crystal polymer sheet 1B, a metal layer 2B, a metal layer 2B' and a metal layer 2B.

[0105] The porous liquid crystal polymer sheet 1B has a first main surface 1Ba and a second main surface 1Bb facing each other in the thickness direction.

[0106] The porous liquid crystal polymer sheet 1B includes a resin sheet 1Bs comprising a liquid crystal polymer. In the porous liquid crystal polymer sheet 1B, pores 1Bh are provided in the resin sheet 1Bs.

[0107] Metal layers 2B, 2B', and 2B" are disposed on the first main surface 1Ba of the porous liquid crystal polymer sheet 1B. Furthermore, metal layers 2B, 2B', and 2B" are adjacent to the second main surface 1Cb of the porous liquid crystal polymer sheet 1C, which will be described later.

[0108] The porous liquid crystal polymer sheet 10C with a metal layer has a porous liquid crystal polymer sheet 1C and a metal layer 2C.

[0109] 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.

[0110] The porous liquid crystal polymer sheet 1C includes a resin sheet 1Cs comprising a liquid crystal polymer. In the porous liquid crystal polymer sheet 1C, pores 1Ch are provided in the resin sheet 1Cs.

[0111] The metal layer 2C is disposed on the first main surface 1Ca of the porous liquid crystal polymer sheet 1C.

[0112] like Figure 3 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.

[0113] 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.

[0114] In addition, Figure 3 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 3 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.

[0115] Porous liquid crystal polymer sheet 1A, porous liquid crystal polymer sheet 1B, and porous liquid crystal polymer sheet 1C, like porous liquid crystal polymer sheet 1, are measured at a temperature 20°C higher than the melting point of the resin sheet constituting each of them, and the shearing speed is set to 1000 s. -1 The melt viscosity under the specified conditions is above 20 Pa·s. Therefore, in porous liquid crystal polymer sheets 1A, 1B, and 1C, similar to porous liquid crystal polymer sheet 1, the pores are not easily damaged under high temperature and high pressure.

[0116] Furthermore, since the electronic circuit board 50 has porous liquid crystal polymer sheets 1A, 1B, and 1C, the dielectric properties in the high-frequency region of the electronic circuit board 50 are easily improved. In addition, changes in dielectric properties due to moisture absorption become less likely to occur in the electronic circuit board 50.

[0117] Preferably, in all of the porous liquid crystal polymer sheets 1A, 1B, and 1C, the melt viscosity under the above conditions is 20 Pa·s or higher. However, in some of the porous liquid crystal polymer sheets, the melt viscosity under the above conditions may also be 20 Pa·s or higher.

[0118] The preferred features of porous liquid crystal polymer sheet 1A, porous liquid crystal polymer sheet 1B, and porous liquid crystal polymer sheet 1C are the same as the preferred features of porous liquid crystal polymer sheet 1 described above.

[0119] The thicknesses of porous liquid crystal polymer sheets 1A, 1B, and 1C can be the same, different, or as follows: Figure 3 The part shown is different.

[0120] As constituent materials of metal layers 2A, 2B, 2B', 2B'', and 2C, similar to the constituent materials of metal layer 2, examples include copper, silver, aluminum, stainless steel, nickel, gold, and alloys containing at least one of these metals.

[0121] Metal layers 2A, 2B, 2B', 2B'', and 2C, like metal layer 2, preferably contain copper foil. In this case, a metal other than copper may also be plated onto the surface of the copper foil.

[0122] While the constituent materials of metal layers 2A, 2B, 2B', 2B'', and 2C are preferably the same, they may be different from each other or partially different.

[0123] The thicknesses of metal layers 2A, 2B, 2B', 2B'', and 2C can be as follows: Figure 3 The images shown may be the same as each other, or they may be different from each other, or they may be partially different.

[0124] Although the electronic circuit substrate 50 has three porous liquid crystal polymer sheets with metal layers in the stacking direction, it may have only one, two, or more than four.

[0125] That is, the electronic circuit board 50 only needs to have at least one porous liquid crystal polymer sheet with a melt viscosity of 20 Pa·s or more under the above conditions. The electronic circuit board 50 only needs to have at least one porous liquid crystal polymer sheet with a melt viscosity of 20 Pa·s or more under the above conditions, and it can have either a porous liquid crystal polymer sheet with a melt viscosity of less than 20 Pa·s under the above conditions, or a liquid crystal polymer sheet that is not porous.

[0126] like Figure 3 As shown, the electronic circuit board 50 preferably further includes an interlayer connection conductor configured to penetrate the porous liquid crystal polymer sheet in the stacking direction but not penetrate the metal layer in the stacking direction, and connected to the metal layer. Figure 3 In the example shown, the electronic circuit board 50 also has interlayer connection conductors 20A, 20B, 20C, and 20D.

[0127] The interlayer connection conductor 20A is configured to penetrate the porous liquid crystal polymer sheet 1B in the stacking direction but not penetrate the metal layer 2B' in the stacking direction, yet is connected to the metal layer 2B'. More specifically, while penetrating the porous liquid crystal polymer sheet 1B in the stacking direction, the interlayer connection conductor 20A is connected to the metal layer 2B' on the first main surface 1Ba side of the porous liquid crystal polymer sheet 1B. Furthermore, the interlayer connection conductor 20A is connected to the metal layer 2A on the second main surface 1Bb side of the porous liquid crystal polymer sheet 1B. That is, the metal layer 2A and the metal layer 2B' are electrically connected via the interlayer connection conductor 20A.

[0128] At a position separate from the interlayer connecting conductor 20A, the interlayer connecting conductor 20B is configured to penetrate the porous liquid crystal polymer sheet 1B in the lamination direction but not penetrate the metal layer 2B” in the lamination direction, and is connected to the metal layer 2B”. More specifically, at a position separate from the interlayer connecting conductor 20A, the interlayer connecting conductor 20B penetrates the porous liquid crystal polymer sheet 1B in the lamination direction and is connected to the metal layer 2B” on the first main surface 1Ba side of the porous liquid crystal polymer sheet 1B. Furthermore, at a position separate from the interlayer connecting conductor 20A, the interlayer connecting conductor 20B is connected to the metal layer 2A on the second main surface 1Bb side of the porous liquid crystal polymer sheet 1B. That is, the metal layer 2A and the metal layer 2B” are electrically connected via the interlayer connecting conductor 20B.

[0129] The interlayer connection conductor 20C is configured to penetrate the porous liquid crystal polymer sheet 1C in the stacking direction but not penetrate the metal layer 2C in the stacking direction, and is connected to the metal layer 2C. More specifically, while penetrating the porous liquid crystal polymer sheet 1C in the stacking direction, the interlayer connection conductor 20C is connected to the metal layer 2C on the first main surface 1Ca side of the porous liquid crystal polymer sheet 1C. Furthermore, the interlayer connection conductor 20C is connected to the metal layer 2B' on the second main surface 1Cb side 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.

[0130] At a position separate from the interlayer connecting conductor 20C, the interlayer connecting conductor 20D is configured to penetrate the porous liquid crystal polymer sheet 1C in the lamination direction but not penetrate the metal layer 2C in the lamination direction, and is connected to the metal layer 2C. More specifically, at a position separate from the interlayer connecting conductor 20C, the interlayer connecting conductor 20D penetrates the porous liquid crystal polymer sheet 1C in the lamination direction and is connected to the metal layer 2C on the first main surface 1Ca side of the porous liquid crystal polymer sheet 1C. Furthermore, at a position separate from the interlayer connecting conductor 20C, the interlayer connecting conductor 20D is connected to the metal layer 2B” on the second main surface 1Cb side 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 connecting conductor 20D.

[0131] In this way, in the electronic circuit board 50, metal layer 2A and metal layer 2C are electrically connected via interlayer connection conductor 20A, metal layer 2B', and interlayer connection conductor 20C. Furthermore, in the electronic circuit board 50, metal layer 2A and metal layer 2C are also electrically connected via interlayer connection conductor 20B, metal layer 2B'', and interlayer connection conductor 20D.

[0132] The interlayer connecting conductor 20A is formed, for example, by plating the inner wall of a via that is configured to penetrate the porous liquid crystal polymer sheet 1B in the thickness direction but not penetrate the metal layer 2B' in the thickness direction, and then heat-treating it after filling it with conductive paste.

[0133] Interlayer connecting conductors 20B, 20C, and 20D are formed in the same way as interlayer connecting conductor 20A, except that they are formed in different locations.

[0134] When the interlayer connecting conductors 20A, 20B, 20C, and 20D are formed by plating, the metals constituting each interlayer connecting conductor can be, for example, copper, tin, silver, etc., with copper being preferred.

[0135] When interlayer connecting conductors 20A, 20B, 20C, and 20D are formed by heat treatment of conductive paste, the metals included in each interlayer connecting conductor can be, for example, copper, tin, or silver. Preferably, each interlayer connecting conductor includes copper, and more preferably, both copper and tin. For example, when interlayer connecting conductor 20A includes both copper and tin and metal layer 2B' includes copper foil, an alloying reaction occurs between interlayer connecting conductor 20A and metal layer 2B' at low temperature, thus making them easily conductive. The same applies to other combinations of interlayer connecting conductors and metal layers.

[0136] When interlayer connecting conductors 20A, 20B, 20C, and 20D are formed by heat treatment of conductive paste, the resin contained in each interlayer connecting conductor preferably includes: at least one thermosetting resin selected from the group consisting of epoxy resin, phenolic resin, polyimide resin, silicone resin or modified resin thereof, and acrylic resin; or at least one thermoplastic resin selected from the group consisting of polyamide resin, polystyrene resin, polymethacrylic resin, polycarbonate resin, and cellulose resin.

[0137] The electronic circuit board 50 may also have a metal layer 2B as a signal line for transmitting signals. In this case, the electronic circuit board 50 constitutes a transmission line.

[0138] The electronic circuit board 50 may also have a metal layer 2B as a signal line for transmitting signals, and metal layers 2A and 2C as ground electrodes. In this case, the electronic circuit board 50 constitutes a stripline transmission line.

[0139] 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.

[0140] 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.

[0141] The electronic circuit board 50 is manufactured, for example, by the following method.

[0142] <Fabrication process of porous liquid crystal polymer sheets with metal layers>

[0143] Figure 4 , Figure 5 ,as well as Figure 6This 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.

[0144] like Figure 4 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.

[0145] like Figure 5 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'' are prepared in advance, and each metal layer is pressed onto the first main surface 1Ba of the porous liquid crystal polymer sheet 1B.

[0146] like Figure 6 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.

[0147] <Through hole formation process>

[0148] Figure 7 as well as Figure 8 This is a cross-sectional schematic diagram showing a via formation process as an example of a method for manufacturing an electronic circuit board according to the present invention.

[0149] like Figure 7 As shown, for the porous liquid crystal polymer sheet 10B with a metal layer, a via 21A is formed, which penetrates the porous liquid crystal polymer sheet 1B in the thickness direction but does not penetrate the metal layer 2B' in the thickness direction, thus reaching the metal layer 2B'. As a result, a portion of the metal layer 2B' is exposed from the via 21A.

[0150] Furthermore, for the porous liquid crystal polymer sheet 10B with a metal layer, a via 21B is formed at a position separate from the position where the via 21A is to be formed, such that it penetrates the porous liquid crystal polymer sheet 1B in the thickness direction but does not penetrate the metal layer 2B" in the thickness direction, thus reaching the metal layer 2B". As a result, a portion of the metal layer 2B" is exposed from the via 21B.

[0151] Through the above, vias 21A and 21B are formed on the porous liquid crystal polymer sheet 10B with a metal layer. At this time, vias 21A and 21B can be formed at the same timing or at different timings.

[0152] like Figure 8 As shown, for the porous liquid crystal polymer sheet 10C with a metal layer, a via 21C is formed, which penetrates the porous liquid crystal polymer sheet 1C in the thickness direction but does not penetrate the metal layer 2C in the thickness direction, thus reaching the metal layer 2C. As a result, a portion of the metal layer 2C is exposed from the via 21C.

[0153] Furthermore, for the porous liquid crystal polymer sheet 10C with a metal layer, a via 21D is formed at a location separate from where the via 21C is to be formed, such that it penetrates the porous liquid crystal polymer sheet 1C in the thickness direction but does not penetrate the metal layer 2C in the thickness direction, thus reaching the metal layer 2C. As a result, a portion of the metal layer 2C is exposed from the via 21D.

[0154] Through the above, vias 21C and 21D are formed on the porous liquid crystal polymer sheet 10C with a metal layer. At this time, vias 21C and 21D can be formed at the same timing or at different timings.

[0155] When forming vias 21A, 21B, 21C and 21D, it is preferable to irradiate the porous liquid crystal polymer sheet with a metal layer from the porous liquid crystal polymer sheet side.

[0156] <Conductive paste filling process>

[0157] Figure 9 as well as Figure 10 This is a cross-sectional schematic diagram showing the filling process of conductive paste as an example of a method for manufacturing an electronic circuit board according to the present invention.

[0158] like Figure 9 As shown, for the porous liquid crystal polymer sheet 10B with a metal layer, conductive paste 22A is filled into the via 21A. Furthermore, for the porous liquid crystal polymer sheet 10B with a metal layer, conductive paste 22B is filled into the via 21B. In this case, conductive paste 22A and conductive paste 22B can be filled at the same time or at different times.

[0159] like Figure 10As shown, for the porous liquid crystal polymer sheet 10C with a metal layer, conductive paste 22C is filled into the via 21C. Furthermore, for the porous liquid crystal polymer sheet 10C with a metal layer, conductive paste 22D is filled into the via 21D. In this case, conductive paste 22C and conductive paste 22D can be filled at the same time or at different times.

[0160] Methods for filling conductive pastes 22A, 22B, 22C, and 22D include, for example, screen printing and vacuum filling.

[0161] Conductive paste 22A, conductive paste 22B, conductive paste 22C and conductive paste 22D each contain, for example, metal and resin.

[0162] The metals contained in each of the conductive pastes 22A, 22B, 22C, and 22D may include, for example, copper, tin, and silver. Preferably, each conductive paste contains copper, and more preferably, it contains both copper and tin.

[0163] The resin contained in each of the conductive pastes 22A, 22B, 22C, and 22D preferably comprises: at least one thermosetting resin selected from the group consisting of epoxy resin, phenolic resin, polyimide resin, silicone resin or modified resin thereof, and acrylic resin; or at least one thermoplastic resin selected from the group consisting of polyamide resin, polystyrene resin, polymethyl methacrylate resin, polycarbonate resin, and cellulose resin.

[0164] Each of the conductive pastes 22A, 22B, 22C, and 22D may also contain a carrier, solvent, thixotropic agent, activator, etc.

[0165] Examples of carriers include rosin-based resins containing rosin and derivatives such as modified rosin, synthetic resins containing rosin and derivatives such as modified rosin, or mixtures of these resins.

[0166] Rosin-based resins, including rosin and its modified derivatives, include, for example, rosin resin, tall rosin, wood rosin, polymerized rosin, hydrogenated rosin, formylated rosin, rosin esters, rosin-modified maleic acid resin, rosin-modified phenolic resin, rosin-modified alkyd resin, and various other rosin derivatives.

[0167] Synthetic resins that include rosin and its modified derivatives, such as polyester resins, polyamide resins, phenoxy resins, and terpene resins, are examples of such resins.

[0168] Examples of solvents include, for example, alcohols, ketones, esters, ethers, aromatic compounds, and hydrocarbons. Specific examples include benzyl alcohol, ethanol, isopropanol, butanol, diethylene glycol, ethylene glycol, glycerol, ethyl cellosolve, butyl cellosolve, ethyl acetate, butyl acetate, butyl benzoate, diethyl adipate, dodecane, tetradecene, α-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 monoethyl ether, diethylene glycol monoethyl ether, diisobutyl adipate, hexanediol, cyclohexanediol, 2-terpinenoxyethanol, 2-dihydroterpinenoxyethanol, and mixtures thereof. Among these, terpineol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, or diethylene glycol monoethyl ether are preferred.

[0169] Examples of thixotropic agents include, for instance, hardened castor oil, carnauba wax, amides, hydroxy fatty acids, dibenzyl sorbitol, bis(p-methylbenzyl)sorbitol, beeswax, stearamide, and hydroxystearic acid ethylenediamide. Furthermore, depending on the requirements, fatty acids such as caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and docosanoic acid, hydroxy fatty acids such as 1,2-hydroxystearic acid, antioxidants, surfactants, and amines can also be added to these thixotropic agents.

[0170] Examples of active agents include, for example, amine hydrohalides, organohalides, organic acids, organic amines, and polyols.

[0171] Examples of amine hydrohalides include diphenylguanidine hydrobromide, diphenylguanidine hydrochloride, cyclohexylamine hydrobromide, ethylamine hydrochloride, ethylamine hydrobromide, diethylaniline hydrobromide, diethylaniline hydrochloride, triethanolamine hydrobromide, monoethanolamine hydrobromide, etc.

[0172] Examples of organohalides include, for example, chloroalkanes, tetrabromoethane, dibromopropanol, 2,3-dibromo-1,4-butanediol, 2,3-dibromo-2-butene-1,4-diol, tris(2,3-dibromopropyl)isocyanurate, etc.

[0173] Examples of organic acids include malonic acid, fumaric acid, glycolic acid, citric acid, malic acid, succinic acid, phenylsuccinic acid, maleic acid, salicylic acid, anthranilic acid, glutaric acid, octanoic acid, adipic acid, sebacic acid, stearic acid, rosin acid, benzoic acid, trimellitic acid, pyromellitic acid, and dodecanoic acid.

[0174] Examples of organic amines include monoethanolamine, diethanolamine, triethanolamine, tributylamine, aniline, and diethylaniline.

[0175] Examples of polyols include erythritol, pyrogallol, and ribitol.

[0176] <Forming process of interlayer conductor>

[0177] Figure 11 This is a cross-sectional schematic diagram showing the formation process of interlayer interconnect conductors as an example of a method for manufacturing an electronic circuit board according to the present invention.

[0178] like Figure 11 As shown, a porous liquid crystal polymer sheet 10A with a metal layer, a porous liquid crystal polymer sheet 10B with a metal layer filled with conductive paste 22A and conductive paste 22B, and a porous liquid crystal polymer sheet 10C with a metal layer filled with conductive paste 22C and conductive paste 22D are sequentially stacked in the stacking direction. At this time, the surface (upper surface) of the porous liquid crystal polymer sheet 10A with a metal layer on the side of metal layer 2A is in contact with the surface (lower surface) of the porous liquid crystal polymer sheet 10B with a metal layer on the side of porous liquid crystal polymer sheet 1B with a metal layer, and the surface (upper surface) of the porous liquid crystal polymer sheet 10B with a metal layer on the side of metal layer 2B (metal layer 2B' side, metal layer 2B" side) is in contact with the surface (lower surface) of the porous liquid crystal polymer sheet 10C with a metal layer on the side of porous liquid crystal polymer sheet 1C with a metal layer. In addition, in Figure 11 In the illustration, the porous liquid crystal polymer sheets with metal layers are shown separately from each other.

[0179] Then, the resulting laminate is heated while pressure is applied in the lamination direction, thereby performing heat pressing. As a result, porous liquid crystal polymer sheets 10A and 10B with metal layers are pressed together, and porous liquid crystal polymer sheets 10B and 10C with metal layers are pressed together. Furthermore, conductive pastes 22A, 22B, 22C, and 22D are cured during heat pressing, thereby becoming interlayer connecting conductors 20A, 20B, 20C, and 20D, respectively. In this way, interlayer connecting conductors 20A, 20B, 20C, and 20D are formed in vias 21A, 21B, 21C, and 21D, respectively.

[0180] When forming interlayer connection conductors 20A, 20B, 20C, and 20D, instead of filling the vias with conductive paste, the inner walls of the vias can be plated with metals such as copper, tin, or silver.

[0181] Through the above, it is possible to manufacture Figure 3 The electronic circuit board 50 shown.

[0182] [Example]

[0183] The following provides more specific embodiments of the porous liquid crystal polymer sheet of the present invention. However, the present invention is not limited to the following embodiments.

[0184] Porous resin sheet A and porous resin sheet B were prepared using the following method.

[0185] <Porous Resin Sheet A>

[0186] First, liquid crystal polymer A was prepared, wherein liquid crystal polymer A is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, with a molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid of 80:20. Next, 99.6 parts by weight of liquid crystal polymer A were mixed, and 0.4 parts by weight of a foaming agent "VINYFOR AC#6-K6" (main component: azodicarbonamide) manufactured by Yonghe Chemical Industry Co., Ltd. was mixed to prepare resin material A. Then, using resin material A, porous resin sheet A with the properties shown in Table 1 was produced by T-die molding.

[0187] <Porous Resin Sheet B>

[0188] First, liquid crystal polymer B was prepared, wherein liquid crystal polymer B is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, with a molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid of 73:27. Next, 99.8 parts by weight of liquid crystal polymer B were mixed with 0.2 parts by weight of "VINYFOR AC#6-K6" foaming agent manufactured by Yonghe Chemical Industry Co., Ltd., thereby preparing resin material B. Then, using resin material B, porous resin sheet B with the properties shown in Table 1 was produced by T-die molding.

[0189] The methods for determining the properties shown in Table 1 will be described later.

[0190] [Table 1]

[0191]

[0192] [Example 1]

[0193] First, porous resin sheet A was heated from 23°C to 250°C in a nitrogen atmosphere for 1 hour, then heated from 250°C to 310°C for 10 hours, and then held at 310°C for 6 hours, thereby performing solid-state polymerization of the liquid crystal polymer. Then, the solid-state polymerized porous resin sheet A was repeatedly irradiated with an electron beam at an accelerating voltage of 200 kV at 250 kGy intervals in a nitrogen atmosphere until the total irradiation dose reached 1000 kGy, thereby performing electron beam irradiation of the liquid crystal polymer. Through the above methods, the porous liquid crystal polymer sheet of Example 1 was manufactured.

[0194] [Example 2]

[0195] Except that electron beam irradiation of the liquid crystal polymer was not performed, the porous liquid crystal polymer sheet of Example 2 was manufactured in the same manner as the porous liquid crystal polymer sheet of Example 1.

[0196] [Example 3]

[0197] Except that solid-state polymerization of the liquid crystal polymer was not performed, the porous liquid crystal polymer sheet of Example 3 was manufactured in the same manner as the porous liquid crystal polymer sheet of Example 1.

[0198] [Example 4]

[0199] First, porous resin sheet B was heated from 23°C to 250°C in a nitrogen atmosphere for 1 hour, then heated from 250°C to 270°C for 10 hours, and then held at 270°C for 6 hours, thereby performing solid-state polymerization of the liquid crystal polymer. Then, the solid-state polymerized porous resin sheet B was repeatedly irradiated with an electron beam at an accelerating voltage of 200 kV at 250 kGy intervals in a nitrogen atmosphere until the total irradiation dose reached 1000 kGy, thereby performing electron beam irradiation of the liquid crystal polymer. Through the above methods, the porous liquid crystal polymer sheet of Example 4 was manufactured.

[0200] [Example 5]

[0201] Except that electron beam irradiation of the liquid crystal polymer was not performed, the porous liquid crystal polymer sheet of Example 5 was manufactured in the same manner as the porous liquid crystal polymer sheet of Example 4.

[0202] [Example 6]

[0203] Except that solid-state polymerization of the liquid crystal polymer was not performed, the porous liquid crystal polymer sheet of Example 6 was manufactured in the same manner as the porous liquid crystal polymer sheet of Example 4.

[0204] [Comparative Example 1]

[0205] Porous resin sheet A was used as the porous liquid crystal polymer sheet in Comparative Example 1.

[0206] [Comparative Example 2]

[0207] Porous resin sheet B was used as the porous liquid crystal polymer sheet in Comparative Example 2.

[0208] [evaluate]

[0209] The porous liquid crystal polymer sheets of Examples 1-6, Comparative Example 1, and Comparative Example 2 were subjected to the following measurements. The results are shown in Table 2.

[0210] Melting point

[0211] First, using a differential scanning calorimeter (DSC7000X) manufactured by Hitachi High-Tech Co., Ltd., the porous liquid crystal polymer sheet was heated to a rate of 20°C / min until it was completely melted. Then, the melt was cooled to 175°C at a rate of 20°C / min, and then heated again at a rate of 20°C / min. The temperature corresponding to the endothermic peak observed at this point was determined as the melting point of the porous liquid crystal polymer sheet. Alternatively, when the endothermic peak was difficult to observe using the above method, the melting point of the porous liquid crystal polymer sheet was determined by texture observation under orthogonal Nicol conditions using a polarizing microscope.

[0212] <Porosity>

[0213] First, 100 mm square samples were cut from the porous liquid crystal polymer sheet, and the sample area s, thickness t, and weight m were measured. Furthermore, the specific gravity σ of the resin component of the porous liquid crystal polymer sheet was determined according to JIS Z 8807-2012. Then, the porosity of the porous liquid crystal polymer sheet was calculated based on the formula: porosity (volume%) = [1 - (m / (s×t×σ))]×100.

[0214] Melt viscosity

[0215] Using a capillary rheometer "F-1" manufactured by Toyo Seiki Co., Ltd., the melt viscosity of the porous liquid crystal polymer sheet was measured at a temperature 20°C higher than the melting point of the porous liquid crystal polymer sheet determined by the above method, and at a shear rate of 1000 s⁻¹. The cylinder diameter was set to 9.55 mm, and the capillary diameter to 1 mm.

[0216] Melt tension

[0217] The melt tension of the porous liquid crystal polymer sheet at the above-mentioned measurement temperature was measured using a capillary rheometer "F-1" manufactured by Toyo Seiki Co., Ltd. The cylinder diameter was set to 9.55 mm, the capillary diameter to 1 mm, and the strand winding speed to 150 m / min.

[0218] <Thickness Reduction Rate>

[0219] First, a 100mm square sample was cut from the porous liquid crystal polymer sheet, and the thickness of the sample was set as the thickness A before pressing. Next, a 12μm thick copper foil was laminated onto one main surface of the sample. The resulting laminate was then heated and pressed at the aforementioned measurement temperature for 10 seconds with a pressure of 0.5MPa, thereby pressing the copper foil onto the sample. Then, the copper foil was etched using ferric chloride, and the remaining sample thickness was set as the thickness B after pressing. Here, the thicknesses A before pressing and B after pressing were measured in the same manner as the thickness measurement method for the porous liquid crystal polymer sheet described above. Then, the thickness reduction rate of the porous liquid crystal polymer sheet before and after pressing was calculated based on the formula: thickness reduction rate (%) = (1 - "thickness B after pressing" / "thickness A before pressing") × 100. The criteria for determining the thickness reduction rate of the porous liquid crystal polymer sheet before and after pressing are as follows.

[0220] ◎(Excellent): Thickness reduction rate is less than 1%.

[0221] ○(Good): Thickness reduction rate is 1% or more and less than 5%.

[0222] × (Defective): Thickness reduction rate is higher than 5%.

[0223] [Table 2]

[0224]

[0225] As shown in Table 2, in the porous liquid crystal polymer sheets of Examples 1 to 6 with a melt viscosity of 20 Pa·s or higher, the thickness reduction rate is low, below 5%. Thus, in the porous liquid crystal polymer sheets of Examples 1 to 6, due to the low thickness reduction rate, it can be said that when copper foil is pressed onto the porous liquid crystal polymer sheet, the pores are less likely to be damaged under the high temperature and pressure during pressing. Therefore, it can be considered that in electronic circuit boards manufactured using the porous liquid crystal polymer sheets of Examples 1 to 6, the dielectric constant reduction effect generated by the porous liquid crystal polymer sheets becomes easier to achieve, and thus the dielectric properties in the high-frequency region become easier to improve.

[0226] Furthermore, in the porous liquid crystal polymer sheets of Examples 1-6, the thickness reduction rate is less than 1% in the porous liquid crystal polymer sheets of Examples 1, 3, 4, and 6, where the melt tension is 3 mN or more. Thus, in the porous liquid crystal polymer sheets of Examples 1, 3, 4, and 6, because the thickness reduction rate is very low, it can be said that when copper foil is pressed onto the porous liquid crystal polymer sheet, the pores are very difficult to be damaged under the high temperature and pressure during pressing.

[0227] On the other hand, in the porous liquid crystal polymer sheets of Comparative Examples 1 and 2, where the melt viscosity was less than 20 Pa·s, the thickness reduction rate was greater than 5%. Thus, in the porous liquid crystal polymer sheets of Comparative Examples 1 and 2, due to the high thickness reduction rate, it can be said that when copper foil is pressed onto the porous liquid crystal polymer sheet, the pores are easily damaged under the high temperature and pressure during pressing.

[0228] Explanation of reference numerals in the attached figures

[0229] 1, 1A, 1B, 1C: Porous liquid crystal polymer sheets;

[0230] 1a, 1Aa, 1Ba, 1Ca: The first principal surface of the porous liquid crystal polymer sheet;

[0231] 1b, 1Ab, 1Bb, 1Cb: The second principal surface of the porous liquid crystal polymer sheet;

[0232] 1h, 1Ah, 1Bh, 1Ch: Hollow holes;

[0233] 1s, 1As, 1Bs, 1Cs: Resin sheets;

[0234] 2, 2A, 2B, 2B', 2B”, 2C: Metal layers;

[0235] 10, 10A, 10B, 10C: Porous liquid crystal polymer sheets with metal layers;

[0236] 20A, 20B, 20C, 20D: Interlayer connection conductors;

[0237] 21A, 21B, 21C, 21D: Vias;

[0238] 22A, 22B, 22C, 22D: Conductive paste;

[0239] 50: Electronic circuit board.

Claims

1. A porous liquid crystal polymer sheet, comprising a resin sheet containing a liquid crystal polymer, wherein pores are provided in the resin sheet, characterized in that, The test temperature was set at a temperature 20°C higher than the melting point of the resin sheet, and the shearing speed was set to 1000 s. -1 Under these conditions, the melt viscosity is above 20 Pa·s. The resin sheet has a melting point above 275°C and below 330°C. The porous liquid crystal polymer sheet has an independent bubble structure.

2. The porous liquid crystal polymer sheet according to claim 1, characterized in that, The melt tension at the measured temperature is above 3 mN.

3. The porous liquid crystal polymer sheet according to claim 1 or 2, characterized in that, The liquid crystal polymer comprises a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid.

4. The porous liquid crystal polymer sheet according to claim 3, characterized in that, In the liquid crystal polymer, the molar ratio of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid is 0.20 or more and 5 or less.

5. The porous liquid crystal polymer sheet according to claim 3, characterized in that, When the total amount of monomers is set to 100 mol%, the liquid crystal polymer contains at least 10 mol% of each of the p-hydroxybenzoic acid and the 6-hydroxy-2-naphthoic acid.

6. The porous liquid crystal polymer sheet according to claim 1 or 2, characterized in that, The thickness is greater than 10μm and less than 200μm.

7. A porous liquid crystal polymer sheet with a metal layer, characterized in that, have: The porous liquid crystal polymer sheet according to any one of claims 1 to 6; and A metal layer is disposed on at least one main surface of the porous liquid crystal polymer sheet.

8. The porous liquid crystal polymer sheet with a metal layer according to claim 7, characterized in that, The metal layer comprises copper foil.

9. An electronic circuit board, characterized in that, A porous liquid crystal polymer sheet with a metal layer as described in claim 7 or 8.

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