Resin sheet, circuit board and method for manufacturing the same, and semiconductor device

Abstract

To provide a resin sheet which can suppress swelling of a bleed-out part, while having a resin composition layer containing (A) a liquid resin, (B) an active ester-based resin and (C) an inorganic filler.SOLUTION: A resin sheet includes a support and a resin composition layer formed on the support, wherein the resin composition layer contains (A) a liquid resin, (B) an active ester-based resin, and (C) an inorganic filler, when an evaluation test for heating a test layer obtained by heating the resin composition layer on the support at 130°C for 30 minutes and at 170°C for 30 minutes, at 200°C for 90 minutes is performed, a mass reduction ratio of the test layer by heating at 200°C for 90 minutes is 5.5% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a resin sheet, a circuit board and a manufacturing method thereof, and a semiconductor device. [Background technology]

[0002] Circuit boards such as printed wiring boards are widely used in various electronic devices. A known method for manufacturing circuit boards is a build-up method in which insulating layers and conductor layers are alternately stacked on an inner layer substrate. The insulating layer is formed, for example, by forming a resin composition layer containing a resin composition and curing the resin composition layer. A known method for forming a resin composition layer on an inner layer substrate is to laminate a resin sheet including a support and a resin composition layer onto the inner layer substrate (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-172221 Summary of the Invention [Problem to be solved by the invention]

[0004] The inner layer substrate may have components and a conductor layer on its surface. From the viewpoint of satisfactorily embedding the components and the conductor layer in the resin composition layer during lamination, the resin composition contained in the resin composition layer is required to have high fluidity during lamination.

[0005] On the other hand, from the viewpoint of suppressing warpage of the circuit board, the insulating layer is required to have a low thermal expansion coefficient. To lower the thermal expansion coefficient, it is conceivable to form the insulating layer using a resin composition layer containing (C) an inorganic filler. However, (C) an inorganic filler generally tends to reduce the fluidity of the resin composition layer. Therefore, from the viewpoint of achieving high fluidity while containing (C) an inorganic filler, it is conceivable to combine a low-viscosity (A) liquid resin with (C) an inorganic filler.

[0006] Furthermore, in order to meet the high demands of recent years, the insulating layer of the circuit board is further required to have a low dielectric loss tangent. In order to achieve such a low dielectric loss tangent, the present inventors attempted to combine (A) a liquid resin and (C) an inorganic filler with (B) an activated ester resin.

[0007] However, it has been found that a resin sheet having a resin composition layer containing a combination of (A) a liquid resin, (B) an active ester-based resin, and (C) an inorganic filler may experience swelling in the bleed-out area.

[0008] The details are as follows. In the process of laminating an inner layer substrate and a resin sheet during the manufacturing process of a circuit board, heat and pressure are applied to the resin composition layer, causing the resin composition layer to fluidize. As a result, a portion of the resin composition layer may seep out from the gap between the inner layer substrate and the support. This portion of the resin composition layer or insulating layer that seeps out from the gap between the inner layer substrate and the support is called a "bleed-out portion." When a combination of (A) a liquid resin, (B) an active ester-based resin, and (C) an inorganic filler is used, swelling may occur in the bleed-out portion of the insulating layer. Generally, a conductor layer is formed on the insulating layer, and an annealing treatment is performed after the formation of the conductor layer. This annealing treatment may cause swelling in the bleed-out portion of the insulating layer. Such swelling may hinder the smooth execution of subsequent processes (e.g., processes for forming additional insulating layers and conductor layers).

[0009] The present invention has been made in view of the above-mentioned problems, and aims to provide: a resin sheet that is capable of suppressing swelling of a bleed-out portion while having a resin composition layer that contains (A) a liquid resin, (B) an active ester-based resin, and (C) an inorganic filler; a circuit board that includes a cured layer obtained by curing the resin composition layer of the resin sheet; a method for manufacturing a circuit board using the resin sheet; and a semiconductor device that includes the circuit board. [Means for solving the problem]

[0010] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by a resin sheet having a resin composition layer containing (A) a liquid resin, (B) an active ester-based resin, and (C) an inorganic filler, wherein the resin composition layer has a rate of mass loss due to heating that is measured in a specific range when a specific evaluation test is conducted on the resin composition layer, and have thus completed the present invention. That is, the present invention includes the following.

[0011] <1> A resin sheet comprising a support and a resin composition layer formed on the support; the resin composition layer contains (A) a liquid resin, (B) an active ester-based resin, and (C) an inorganic filler; A resin sheet in which, when a test layer obtained by heating a resin composition layer on a support at 130°C for 30 minutes and 170°C for 30 minutes is heated at 200°C for 90 minutes in an evaluation test, the mass loss rate of the test layer due to heating at 200°C for 90 minutes is 5.5% or less. <2> The evaluation test laminating the resin sheet and the polyimide film so that the resin composition layer and the polyimide film are in contact with each other; The resin composition layer is heated at 130°C for 30 minutes and 170°C for 30 minutes, and the support and the polyimide film are peeled off to obtain a test layer; and Heating the test layer at 200°C for 90 minutes; in this order, <1> The resin sheet according to claim 1. <3> The amount of (A) liquid resin is 1% by mass or more and 25% by mass or less with respect to 100% by mass of the resin component in the resin composition layer. <1> or <2> The resin sheet according to claim 1. <4> (C) The amount of the inorganic filler is 65% by mass or more relative to 100% by mass of the nonvolatile components in the resin composition layer; <1> ~ <3> The resin sheet according to any one of claims 1 to 10. <5> the average linear thermal expansion coefficient of the cured product layer obtained by heating the resin composition layer at 190°C for 90 minutes in the temperature range of 25°C to 150°C is less than 20 ppm / °C; <1> ~ <4> The resin sheet according to any one of claims 1 to 10. <6> the dielectric loss tangent of the cured layer obtained by heating the resin composition layer at 190°C for 90 minutes is less than 0.0030; <1> ~ <5> The resin sheet according to any one of claims 1 to 10. <7> The minimum melt viscosity of the resin composition layer is 3000 poise or less. <1> ~ <6> The resin sheet according to any one of claims 1 to 10. <8> (A) The liquid resin is a liquid curable resin; <1> ~ <7> The resin sheet according to any one of claims 1 to 10. <9> <1> ~ <8> A circuit board comprising a cured layer obtained by curing the resin composition layer of the resin sheet according to any one of claims 1 to 4. <10> Inner layer board and <1> ~ <8> a step of laminating the resin sheet according to any one of the above items 1 to 3 above so that the inner layer substrate and the resin composition layer are in contact with each other; curing the resin composition layer; A method for manufacturing a circuit board, wherein the step of laminating an inner layer substrate and a resin sheet includes allowing a portion of a resin composition layer to seep out from a gap between the inner layer substrate and the support. <11> <9> A semiconductor device comprising the circuit board according to claim 1. [Effects of the Invention]

[0012] According to the present invention, there can be provided a resin sheet that is capable of suppressing swelling of a bleed-out portion while having a resin composition layer that includes (A) a liquid resin, (B) an active ester-based resin, and (C) an inorganic filler; a circuit board that includes a cured layer obtained by curing the resin composition layer of the resin sheet; a method for manufacturing a circuit board using the resin sheet; and a semiconductor device that includes the circuit board. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a method for manufacturing a circuit board according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and may be modified and implemented within the scope of the claims and their equivalents.

[0015] In the following description, unless otherwise specified, the "resin component" in the resin composition layer refers to the non-volatile components in the resin composition layer excluding (C) the inorganic filler. Also, unless otherwise specified, the "non-volatile component" in the resin composition layer refers to the components in the resin composition layer excluding (H) the solvent.

[0016] In the following description, unless otherwise specified, the "resin component" in a resin composition refers to the non-volatile components in the resin composition excluding (C) the inorganic filler. Also, unless otherwise specified, the "non-volatile component" in a resin composition refers to the components in the resin composition excluding (H) the solvent.

[0017] <Resin Sheet Overview> A resin sheet according to one embodiment of the present invention includes a support and a resin composition layer formed on the support. The resin composition layer contains a combination of (A) a liquid resin, (B) an active ester resin, and (C) an inorganic filler. The resin sheet satisfies the following requirement (R):

[0018] Requirements(R): When a test layer obtained by heating a resin composition layer on a support at 130°C for 30 minutes and 170°C for 30 minutes is subjected to an evaluation test in which the test layer is heated at 200°C for 90 minutes, the mass loss rate of the test layer due to heating at 200°C for 90 minutes is 5.5% or less.

[0019] The resin sheet according to this embodiment can suppress swelling of the bleed-out portion. Furthermore, the resin composition layer of the resin sheet according to this embodiment can usually have a low minimum melt viscosity. Furthermore, the resin sheet according to this embodiment can usually obtain an insulating layer with a low dielectric tangent. Furthermore, the resin sheet according to this embodiment can usually obtain an insulating layer with a low linear thermal expansion coefficient. The inventors speculate that the mechanism by which these advantages are obtained is as follows. However, the present invention is not limited to the mechanism described below.

[0020] When a circuit board is manufactured using a resin sheet having a resin composition layer, the resin sheet and an inner layer substrate are generally laminated together, and the resin composition layer is cured to form an insulating layer. Since the resin composition layer contains a low-viscosity liquid resin (A), the resin composition layer can have a low minimum melt viscosity.

[0021] Furthermore, since the insulating layer is formed by a cured layer obtained by curing the resin composition layer, it contains an inorganic filler (C). The degree of expansion and contraction of the inorganic filler (C) due to temperature changes is generally smaller than the degree of expansion and contraction of organic materials. Therefore, by using a resin composition layer containing the inorganic filler (C), an insulating layer with a small linear thermal expansion coefficient can be obtained.

[0022] Furthermore, the mechanism of curing of the resin composition layer involves the reaction of the (B) active ester resin contained in the resin composition layer to form a crosslinked structure. The reaction of the (B) active ester resin does not produce polar groups such as hydroxyl groups. Therefore, the polarity of the insulating layer as a cured product layer obtained by curing the resin composition layer can be reduced. Furthermore, the insulating (C) inorganic filler used in the insulating layer generally has a small dielectric loss tangent. Therefore, an insulating layer formed from a cured product layer obtained by curing a resin composition layer containing the (B) active ester resin and the (C) inorganic filler can have a low dielectric loss tangent.

[0023] However, the resin composition layer containing (B) inorganic filler has a relatively small amount of resin component. Generally, the resin component functions as a binder. Therefore, in the resin composition layer containing (B) inorganic filler, the binder tends to have a weaker ability to maintain the shape of the cured layer against the stress generated by the heat of the annealing treatment.

[0024] Furthermore, a portion of the (A) liquid resin may be vaporized by heat. Furthermore, a portion of the (B) active ester resin may also be vaporized by heat. As the vaporization of the (A) liquid resin and the (B) active ester resin progresses, the amount of resin components in the resin composition layer further decreases. Therefore, as the vaporization progresses, the force that attempts to maintain the shape of the cured material layer against the stress generated by the heat of the annealing treatment may further weaken.

[0025] The majority of the resin composition layer is cured in the gap between the support and the inner layer substrate. In the gap, the resin composition layer is covered by the support and the inner layer substrate. Therefore, loss of the resin component from the resin composition layer due to evaporation can be suppressed. In contrast, the bleed-out portion is the portion that seeps out from the gap between the inner layer substrate and the support. Therefore, at least one side of the bleed-out portion is not covered by the inner layer substrate or the support. Therefore, when the resin composition layer is subjected to heat during curing, some of the resin components, such as (A) the liquid resin and (B) the active ester resin, may be vaporized and lost from the bleed-out portion. Therefore, in the past, the amount of resin component in the bleed-out portion was reduced, resulting in a reduced ability to maintain the shape of the cured material layer against the stress generated by the heat of the annealing treatment. It is believed that this excessively small amount of resin component in the bleed-out portion resulted in "bulging" in the bleed-out portion.

[0026] Therefore, in the resin sheet according to this embodiment, the resin component lost from the resin composition layer when subjected to heat is reduced, thereby suppressing "swelling" in the bleed-out portion. Specifically, the mass loss rate of the test layer in requirement (R) indicates that when the bleed-out portion is subjected to heat equivalent to the heat received during curing of the resin composition layer, the component lost from the bleed-out portion is small. Since the inorganic filler (C) is usually not lost due to heat, it is considered that most or all of the component that may be lost is the resin component. Therefore, by adopting a composition that reduces the resin component loss, suppression of "swelling" in the bleed-out portion is achieved.

[0027] The evaluation test for the above-mentioned requirement (R) is a test conducted to determine whether or not the requirement (R) is satisfied. Therefore, a resin sheet having a resin composition layer that satisfies the requirement (R) when the above-mentioned evaluation test is conducted is included in the scope of the present invention, regardless of whether or not the evaluation test is conducted.

[0028] <Explanation of Requirement (R)> A resin sheet according to one embodiment of the present invention satisfies the above-mentioned requirement (R). Specifically, when a test layer obtained by heating a resin composition layer on a support at 130°C for 30 minutes and 170°C for 30 minutes was subjected to an evaluation test in which the test layer was heated at 200°C for 90 minutes, the mass loss rate of the test layer due to heating at 200°C for 90 minutes falls within a specific range of 5.5% or less. Specifically, the mass loss rate range is typically 5.5% or less, preferably 5.0% or less, more preferably 4.0% or less, and even more preferably 3.0% or less. The lower limit is typically 0% or more, and may be 1.0% or more, 1.5% or more, etc.

[0029] Specifically, the evaluation test is carried out as follows. A resin sheet and a polyimide film are laminated together so that the resin composition layer and the polyimide film are in contact with each other. The resin composition layer is then heated at 130°C for 30 minutes, and then heated at 170°C for 30 minutes. The support and polyimide film are then peeled off to obtain a test layer. Although the curing of the resin composition layer may progress by heating at 130°C for 30 minutes and then at 170°C for 30 minutes, the curing usually does not progress completely. Therefore, the test layer is formed from a resin composition layer in a semi-cured state. In this specification, the term "cured product layer" also refers to a semi-cured resin composition layer.

[0030] The mass loss rate of the test layer thus obtained is measured using a thermogravimetric differential thermal analyzer (TG-DTA) when the temperature is maintained at 200° C. for 90 minutes. Specifically, the mass loss rate can be calculated by the following formula (M1) using the mass W0 of the test layer before the temperature is maintained at 200° C. for 90 minutes and the mass W1 of the test layer after the temperature is maintained at 200° C. for 90 minutes. Mass reduction rate (%)=(W0-W1) / W0×100 (M1)

[0031] As a specific procedure for the evaluation test, the method described in the "Test for evaluating mass reduction rate" in the Examples section described later can be adopted.

[0032] Examples of methods for obtaining a mass loss rate within a range that satisfies requirement (R) include the following methods. Some resin components in the resin composition layer may be partially vaporized by heat. Therefore, for example, by reducing the amount of such vaporizable components, a mass loss rate within a range that satisfies requirement (R) may be obtained. Specific examples include (A) liquid resins that are vaporized by heat. Furthermore, even resins that are solid at room temperature may have some components that can be vaporized by heat, such as (B) active ester resins. Therefore, the amount of resin components lost during heating may be reduced by appropriately adjusting the amount of these resins.

[0033] Furthermore, when a resin composition layer is formed using a resin varnish containing a (H) solvent, the resin composition layer may contain the (H) solvent. Although the amount of the (H) solvent in the resin composition layer is generally small, the (H) solvent evaporates due to heat, which can cause an increase in the mass loss rate. Therefore, when a resin composition layer is formed using a resin varnish, it is preferable to thoroughly dry the resin composition layer during the manufacturing process to reduce the amount of the (H) solvent remaining in the resin composition layer. Since the ease of drying usually varies depending on the type of (H) solvent, it is preferable to set specific drying conditions according to the type of (H) solvent.

[0034] <Description of Composition of Resin Composition Layer> A resin sheet according to one embodiment of the present invention includes a resin composition layer containing (A) a liquid resin, (B) an active ester resin, and (C) an inorganic filler. The resin composition layer typically contains a resin composition containing the liquid resin (A), the active ester resin, and the inorganic filler (C), and preferably contains only the resin composition. A resin composition containing a combination of the liquid resin (A), the active ester resin, and the inorganic filler (C) typically has a low minimum melt viscosity and can produce a cured product with a low dielectric loss tangent and a small linear thermal expansion coefficient. Therefore, a resin composition layer containing the resin composition typically has a low minimum melt viscosity and can produce a cured product with a low dielectric loss tangent and a small linear thermal expansion coefficient.

[0035] ((A) Explanation of liquid resin) The liquid resin (A) used as component (A) is a resin that is liquid at 25°C. Typically, this liquid resin (A) has a low viscosity within a specific range at 25°C. The specific viscosity range of the liquid resin (A) is typically 500 mPa·s or less, preferably 400 mPa·s or less, more preferably 300 mPa·s or less, even more preferably 200 mPa·s or less, and even more preferably 150 mPa·s or less. Because the liquid resin (A) has such a low viscosity, the resin composition layer can have a low minimum melt viscosity. The lower limit is not particularly limited and can be, for example, 1 mPa·s or more, 2 mPa·s or more, or 3 mPa·s or more. Viscosity can be measured at 25°C and 20 rpm using an E-type viscometer (Toki Sangyo RE-25U, using a 1°34' x R24 cone rotor).

[0036] The (A) liquid resin preferably contains a curable resin, and more preferably contains only a curable resin. Therefore, the (A) liquid resin is more preferably a liquid curable resin. The liquid curable resin refers to a (A) liquid resin that has curability. The liquid curable resin can react with heat to form a crosslinked structure. Normally, the molecules of the (A) liquid resin that have formed a crosslinked structure do not vaporize. Therefore, when a liquid curable resin is used, the amount of the (A) liquid resin lost due to heat during curing of the resin composition layer can be reduced. However, since a portion of the liquid curable resin may vaporize before the reaction, it is preferable to appropriately adjust the type and amount of the liquid curable resin to satisfy the above-mentioned requirement (R).

[0037] From the viewpoint of obtaining curability, it is preferable that the (A) liquid resin contains a reactive functional group. Preferred examples of such functional groups include epoxy groups and radically reactive groups. Examples of radically reactive groups include groups containing ethylenically unsaturated bonds. The ethylenically unsaturated bond represents a non-aromatic carbon-carbon unsaturated bond, such as a non-aromatic carbon-carbon double bond and a non-aromatic carbon-carbon triple bond. Specific examples of radically reactive groups include allyl groups, acryloyl groups, and methacryloyl groups. When a resin containing an epoxy group or a radically reactive group is used as the (A) liquid resin, an insulating layer with a particularly low dielectric loss tangent can be obtained. The number of functional groups contained in the (A) liquid resin may be one or two or more.

[0038] Examples of the (A) liquid resin containing an epoxy group include lauryl glycidyl ether type epoxy resins, alicyclic epoxy resins, cyclohexanedimethanol type epoxy resins, trimethylolpropane type epoxy resins, hexanediol type epoxy resins, trimethylolpropane type epoxy resins, polypropylene glycol type epoxy resins, neopentyl glycol type epoxy resins, and o-toluidine type epoxy resins. Specific examples of commercially available liquid resins (A) containing epoxy groups include lauryl glycidyl ether type epoxy resin "Epogosey LA (D)" (viscosity 5 mPa·s at 25°C) manufactured by Yokkaichi Synthetic Co., Ltd.; alicyclic epoxy resin "Celloxide 2021P" (viscosity 240 mPa·s at 25°C) manufactured by Daicel Corporation; cyclohexanedimethanol type epoxy resin "ZX1658GS" (viscosity 34 mPa·s at 25°C) manufactured by Nippon Steel Chemical & Material Co., Ltd.; trimethylolpropane type epoxy resin "ZX1542" (viscosity 109 mPa·s at 25°C) manufactured by Nippon Steel Chemical & Material Co., Ltd.; cyclohexanedimethanol type epoxy resin "Showfree CDMDG" (viscosity 34 mPa·s at 25°C) manufactured by Showa Denko K.K.; and 1,6-hexanediol type epoxy resin "Denacol EX212" manufactured by Nagase ChemteX Corporation. L (viscosity 10 mPa·s at 25°C); ADEKA hexanediol-type epoxy resins "ED-503" (viscosity 25 mPa·s at 25°C) and "ED-503G" (viscosity 15 mPa·s at 25°C); ADEKA trimethylolpropane-type epoxy resin "ED-505" (viscosity 150 mPa·s at 25°C); ADEKA polypropylene glycol-type epoxy resin "ED-506" (viscosity 60 mPa·s at 25°C); ADEKA neopentyl glycol-type epoxy resin "ED-523T" (viscosity 15 mPa·s at 25°C); ADEKA o-toluidine-type epoxy resin "EP-3980S" (viscosity 31 mPa·s at 25°C); and ADEKA dicyclopentadiene dimethanol-type epoxy resin "EP-4088S" (viscosity 213 mPa·s at 25°C).

[0039] Examples of liquid resins (A) containing radical reactive groups include diallyl diphenate, trimethylolpropane triacrylate, and resins represented by the following formula (a-1): Specific examples of commercially available liquid resins (A) containing radical reactive groups include trimethylolpropane triacrylate "A-TMPT" manufactured by Shin-Nakamura Chemical Co., Ltd. (viscosity 105 mPa·s at 25°C); diallyl diphenate "DAD" manufactured by Nisshoku Techno Fine Chemical Co., Ltd. (viscosity 59 mPa·s at 20°C, viscosity 59 mPa·s or less at 25°C); and "A-DOG" manufactured by Shin-Nakamura Chemical Co., Ltd. (resin represented by the following formula (a-1), viscosity 300 mPa·s at 25°C).

[0040] [ka]

[0041] The (A) liquid resin may be used alone or in combination of two or more.

[0042] The functional group equivalent range of the (A) liquid resin is preferably 50 g / eq. or more, more preferably 60 g / eq. or more, even more preferably 80 g / eq. or more, and even more preferably 110 g / eq. or more, and is preferably 5,000 g / eq. or less, more preferably 3,000 g / eq. or less, even more preferably 2,000 g / eq. or less, even more preferably 1,000 g / eq. or less, even more preferably 500 g / eq. or less, even more preferably 300 g / eq. or less, and even more preferably 200 g / eq. or less. Functional group equivalent refers to the mass of resin per equivalent of functional group. The mass of resin per equivalent of epoxy group is sometimes referred to as the "epoxy equivalent," which can be measured according to JIS K7236. The mass of resin per equivalent of radical reactive group is sometimes referred to as the "radical reactive group equivalent."

[0043] The weight-average molecular weight of the (A) liquid resin is preferably small. The specific range of the weight-average molecular weight of the (A) liquid resin is preferably 1,000 or less, more preferably 500 or less, and even more preferably 300 or less. There is no particular restriction on the lower limit, and it can be, for example, 50 or more, 80 or more, or 100 or more. The weight-average molecular weight of the resin can be measured as a polystyrene-equivalent value by gel permeation chromatography (GPC).

[0044] The amount of the (A) liquid resin in the resin composition layer is preferably 0.1% by mass or more, more preferably 1.0% by mass or more, even more preferably 2.0% by mass or more, and preferably 6.0% by mass or less, more preferably 5.0% by mass or less, and even more preferably 4.0% by mass or less, relative to 100% by mass of the nonvolatile components in the resin composition layer. Furthermore, the amount of the (A) liquid resin in the resin composition relative to 100% by mass of the nonvolatile components in the resin composition is preferably the same as the aforementioned range of the amount of the (A) liquid resin in the resin composition layer relative to 100% by mass of the nonvolatile components in the resin composition layer. In a resin sheet satisfying requirement (R), when the amount of the (A) liquid resin is equal to or greater than the aforementioned lower limit, the minimum melt viscosity of the resin composition layer can be effectively reduced. Furthermore, when the amount is equal to or less than the upper limit, swelling in the bleed-out area can be effectively suppressed.

[0045] The range of the amount of the (A) liquid resin in the resin composition layer is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 25% by mass or less, more preferably 22% by mass or less, and even more preferably 18% by mass or less, relative to 100% by mass of the resin components in the resin composition layer. Furthermore, the range of the amount of the (A) liquid resin in the resin composition relative to 100% by mass of the resin components in the resin composition is preferably the same as the aforementioned range of the amount of the (A) liquid resin in the resin composition layer relative to 100% by mass of the resin components in the resin composition layer. In a resin sheet satisfying requirement (R), when the amount of the (A) liquid resin is equal to or greater than the aforementioned lower limit, the minimum melt viscosity of the resin composition layer can be effectively reduced. Furthermore, when the amount is equal to or less than the upper limit, swelling in the bleed-out area can be effectively suppressed.

[0046] The mass ratio of the (A) liquid resin to the (B) active ester resin {(A) liquid resin / (B) active ester resin} is preferably 0.05 or more, more preferably 0.1 or more, even more preferably 0.2 or more, and preferably 0.8 or less, more preferably 0.7 or less, even more preferably 0.6 or less. In a resin sheet satisfying requirement (R), when the mass ratio {(A) liquid resin / (B) active ester resin} is equal to or greater than the lower limit, the minimum melt viscosity of the resin composition layer can be effectively reduced. Furthermore, when the mass ratio is equal to or less than the upper limit, swelling of the bleed-out portion can be effectively suppressed.

[0047] The mass ratio of the (A) liquid resin to the (C) inorganic filler {(A) liquid resin / (C) inorganic filler} is preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.03 or more, and preferably 0.08 or less, more preferably 0.07 or less, even more preferably 0.06 or less. In a resin sheet satisfying requirement (R), when the mass ratio {(A) liquid resin / (C) inorganic filler} is equal to or greater than the lower limit, the minimum melt viscosity of the resin composition layer can be effectively reduced. Furthermore, when the mass ratio is equal to or less than the upper limit, swelling of the bleed-out portion can be effectively suppressed.

[0048] The range of the total amount of the (A) liquid resin, (B) active ester resin, and (C) inorganic filler in the resin composition layer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on 100% by mass of the nonvolatile components in the resin composition layer. The upper limit is usually 100% by mass or less, and may be 95% by mass or less, 90% by mass or less, etc. Furthermore, the range of the total amount of the (A) liquid resin, (B) active ester resin, and (C) inorganic filler in the resin composition based on 100% by mass of the nonvolatile components in the resin composition is preferably the same as the above-mentioned range of the total amount of the (A) liquid resin, (B) active ester resin, and (C) inorganic filler in the resin composition layer based on 100% by mass of the nonvolatile components in the resin composition layer.

[0049] (B) Explanation of active ester resin The active ester resin (B) as the component (B) has an active ester group in the molecule. The active ester group can react with functional groups such as epoxy groups that may be contained in the liquid resin (A) and any curable resin (D) to form a crosslinked structure. The crosslinked structure can then be cured to form an insulating layer as a cured product layer.

[0050] The (B) active ester resin may be a compound having one or more active ester groups per molecule. Among these, the (B) active ester resin is preferably a compound having two or more highly reactive ester groups per molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds. The (B) active ester resin may be used singly or in combination of two or more.

[0051] The (B) active ester resin is preferably one obtained by a condensation reaction between a carboxylic acid compound and / or a thiocarboxylic acid compound and a hydroxy compound and / or a thiol compound. From the viewpoint of improving heat resistance in particular, an active ester resin obtained from a carboxylic acid compound and a hydroxy compound is preferred, and an active ester resin obtained from a carboxylic acid compound and a phenol compound and / or a naphthol compound is more preferred. Examples of the carboxylic acid compound include benzoic acid, acetic acid, succinic acid, maleic acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and pyromellitic acid. Examples of phenol compounds or naphthol compounds include hydroquinone, resorcinol, bisphenol A, bisphenol F, bisphenol S, phenolphthalene, methylated bisphenol A, methylated bisphenol F, methylated bisphenol S, phenol, o-cresol, m-cresol, p-cresol, catechol, α-naphthol, β-naphthol, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, dihydroxybenzophenone, trihydroxybenzophenone, tetrahydroxybenzophenone, phloroglucin, benzenetriol, dicyclopentadiene-type diphenol compounds, and phenol novolak. Here, "dicyclopentadiene-type diphenol compounds" refers to diphenol compounds obtained by condensing one dicyclopentadiene molecule with two phenol molecules.

[0052] Specifically, the (B) active ester resin is preferably a dicyclopentadiene-type active ester resin, a naphthalene-type active ester resin containing a naphthalene structure, an active ester resin containing an acetylated product of phenol novolac, or an active ester resin containing a benzoylated product of phenol novolac, and among these, a naphthalene-type active ester resin is more preferred. The dicyclopentadiene-type active ester resin is preferably an active ester resin containing a dicyclopentadiene-type diphenol structure.

[0053] (B) Commercially available active ester resins include, for example, "EXB9451", "EXB9460", "EXB9460S", "EXB-8000L", "EXB-8000L-65M", "EXB-8000L-65TM", "HPC-8000L-65TM", "HPC-8000", "HPC-8000-65T", "HPC-8000H", and "HPC-8000H-65TM" (manufactured by DIC Corporation) as active ester resins containing a dicyclopentadiene-type diphenol structure; and "HP-B-8151-62T", "EXB-8100L-65T", "EXB-8150-60T", and "EXB-81 Examples of such active ester resins include "EXB-9416-70BK", "HPC-8150-60T", "HPC-8150-62T", and "EXB-8" (manufactured by DIC Corporation); an active ester resin containing phosphorus, such as "EXB9401" (manufactured by DIC Corporation); an active ester resin which is an acetylated product of phenol novolac, such as "DC808" (manufactured by Mitsubishi Chemical Corporation); active ester resins which are benzoylated products of phenol novolac, such as "YLH1026", "YLH1030", and "YLH1048" (manufactured by Mitsubishi Chemical Corporation); and an active ester resin containing a styryl group and a naphthalene structure, such as "PC1300-02-65MA" (manufactured by Air Water Inc.).

[0054] The active ester group equivalent of the (B) active ester resin is preferably 50 g / eq. to 3000 g / eq., more preferably 100 g / eq. to 1000 g / eq., even more preferably 100 g / eq. to 500 g / eq., and particularly preferably 100 g / eq. to 300 g / eq. The active ester group equivalent represents the mass of the resin per equivalent of the active ester group.

[0055] In one example, the weight-average molecular weight (Mw) of the (B) active ester resin is preferably in the range of 100 to 5,000, more preferably 250 to 3,000, and even more preferably 400 to 1,500. The weight-average molecular weight can be measured by gel permeation chromatography (GPC) as a polystyrene-equivalent value.

[0056] The amount of the (B) active ester resin in the resin composition layer is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, relative to 100% by mass of the nonvolatile components in the resin composition layer, and is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. Furthermore, the amount of the (B) active ester resin in the resin composition relative to 100% by mass of the nonvolatile components in the resin composition is preferably the same as the aforementioned range of the amount of the (B) active ester resin in the resin composition layer relative to 100% by mass of the nonvolatile components in the resin composition layer. Such an amount of the (B) active ester resin effectively reduces the dielectric tangent of the insulating layer. Furthermore, while conventional resin composition layers containing such an amount of the (B) active ester resin tended to cause swelling in the bleed-out area, the resin sheet according to this embodiment can suppress such swelling.

[0057] The amount of the (B) active ester resin in the resin composition layer is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, relative to 100% by mass of the resin components in the resin composition layer, and is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. Furthermore, the amount of the (B) active ester resin in the resin composition relative to 100% by mass of the resin components in the resin composition is preferably the same as the aforementioned range of the amount of the (B) active ester resin in the resin composition layer relative to 100% by mass of the resin components in the resin composition layer. Such an amount of the (B) active ester resin effectively reduces the dielectric tangent of the insulating layer. Furthermore, while conventional resin composition layers containing such an amount of the (B) active ester resin tended to cause swelling in the bleed-out area, the resin sheet according to the present embodiment can suppress such swelling.

[0058] When the resin composition layer contains an epoxy resin, the (B) active ester resin can react with the epoxy resin to cure the resin composition layer. Therefore, the amount of the (B) active ester resin is preferably set so that the ratio of the number of active ester groups in the (B) active ester resin to the number of epoxy groups in all epoxy resins in the resin composition layer falls within a specific range. Specifically, when the number of epoxy groups in all epoxy resins in the resin composition layer is set to 1, the number of active ester groups in the (B) active ester resin is preferably 0.46 or more, more preferably 0.47 or more, even more preferably 0.48 or more, and preferably 2.00 or less, more preferably 1.50 or less, and even more preferably 1.20 or less. The "number of active ester groups in the (B) active ester resin" refers to the sum of all values ​​obtained by dividing the mass of the non-volatile components of the (B) active ester resin present in the resin composition layer by its active ester group equivalent. The "number of epoxy groups in the epoxy resin" refers to the total value obtained by dividing the mass of the non-volatile components of the epoxy resin present in the resin composition layer by its epoxy equivalent.

[0059] ((C) Explanation of inorganic filler) The inorganic filler (C) as the component (C) is in the form of particles of an inorganic material. Therefore, the inorganic filler (C) is contained in the resin composition layer in the form of particles, and is usually contained in the cured product layer while maintaining this particulate state.

[0060] Inorganic compounds are typically used as the inorganic material forming the (C) inorganic filler. Examples of materials for the (C) inorganic filler include silica, alumina, glass, cordierite, silicon oxide, barium sulfate, barium carbonate, talc, clay, mica powder, zinc oxide, hydrotalcite, boehmite, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, magnesium oxide, boron nitride, aluminum nitride, manganese nitride, aluminum borate, strontium carbonate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, titanium oxide, zirconium oxide, barium titanate, barium titanate zirconate, barium zirconate, calcium zirconate, zirconium phosphate, and zirconium tungstate phosphate. Among these, silica and alumina are preferred, with silica being particularly preferred. Therefore, the (C) inorganic filler preferably contains silica, or may contain only silica. Examples of silica include amorphous silica, fused silica, crystalline silica, synthetic silica, and hollow silica. Moreover, the silica is preferably spherical silica.The inorganic filler (C) may be used alone or in combination of two or more kinds.

[0061] (C) Examples of commercially available inorganic fillers include "SP60-05" and "SP507-05" manufactured by Nippon Steel Chemical & Material Co., Ltd.; "YC100C," "YA050C," "YA050C-MJE," "YA010C," "SC2500SQ," "SO-C4," "SO-C2," and "SO-C1" manufactured by Admatechs Co., Ltd.; "UFP-30," "DAW-03," and "FB-105FD" manufactured by Denka Company, Limited; "Silfil NSS-3N," "Silfil NSS-4N," and "Silfil NSS-5N" manufactured by Tokuyama Corporation; and "CellSpheres" and "MGH-005" manufactured by Taiheiyo Cement Corporation.

[0062] The average particle size of the (C) inorganic filler is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.1 μm or more, and is preferably 10 μm or less, more preferably 5 μm or less, even more preferably 3 μm or less.

[0063] (C) The average particle size of an inorganic filler can be measured by a laser diffraction / scattering method based on Mie scattering theory. Specifically, a volumetric particle size distribution of the inorganic filler is created using a laser diffraction / scattering particle size distribution analyzer, and the median diameter is used as the average particle size. A measurement sample can be prepared by weighing 100 mg of inorganic filler and 10 g of methyl ethyl ketone into a vial and dispersing the mixture ultrasonically for 10 minutes. The volumetric particle size distribution of the inorganic filler is measured using a laser diffraction particle size distribution analyzer with blue and red light source wavelengths using a flow cell system, and the average particle size can be calculated as the median diameter from the particle size distribution obtained. Examples of laser diffraction particle size distribution analyzers include the LA-960 manufactured by Horiba, Ltd.

[0064] (C) The specific surface area of ​​the inorganic filler is preferably 0.1 m 2 / g or more, more preferably 0.5m 2 / g or more, more preferably 1m 2 / g or more, particularly preferably 3m 2 / g or more, preferably 100m 2 / g or less, more preferably 70m 2 / g or less, more preferably 50m 2 / g or less, particularly preferably 40m 2 The specific surface area of ​​the inorganic filler can be measured in accordance with the BET method by adsorbing nitrogen gas onto the surface of a sample using a specific surface area measuring device (Macsorb HM-1210 manufactured by Mountech Co., Ltd.) and calculating the specific surface area using the BET multipoint method.

[0065] The (C) inorganic filler is preferably treated with a surface treatment agent from the viewpoint of improving moisture resistance and dispersibility. Examples of the surface treatment agent include a fluorine-containing silane coupling agent, an aminosilane coupling agent, an epoxysilane coupling agent, a mercaptosilane coupling agent, a silane coupling agent, an alkoxysilane, an organosilazane compound, and a titanate coupling agent. One type of surface treatment agent may be used alone, or two or more types may be used in any combination.

[0066] Examples of commercially available surface treatment agents include Shin-Etsu Chemical Co., Ltd.'s "KBM403" (3-glycidoxypropyltrimethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBM803" (3-mercaptopropyltrimethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBE903" (3-aminopropyltriethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBM573" (N-phenyl-3-aminopropyltrimethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "SZ-31" (hexamethyldisilazane), Shin-Etsu Chemical Co., Ltd.'s "KBM103" (phenyltrimethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBM-4803" (long-chain epoxy-type silane coupling agent), and Shin-Etsu Chemical Co., Ltd.'s "KBM-7103" (3,3,3-trifluoropropyltrimethoxysilane).

[0067] The degree of surface treatment with the surface treatment agent preferably falls within a specific range from the viewpoint of improving the dispersibility of the inorganic filler. Specifically, 100% by mass of the inorganic filler is preferably surface-treated with 0.2% to 5% by mass of the surface treatment agent, more preferably with 0.2% to 3% by mass of the surface treatment agent, and even more preferably with 0.3% to 2% by mass of the surface treatment agent.

[0068] The degree of surface treatment with the surface treatment agent can be evaluated by the amount of carbon per unit surface area of ​​the inorganic filler. From the viewpoint of improving the dispersibility of the inorganic filler, the amount of carbon per unit surface area of ​​the inorganic filler is set to 0.02 mg / m 2 More than 0.1 mg / m is preferable. 2More preferably, 0.2 mg / m or more 2 On the other hand, from the viewpoint of preventing an increase in the melt viscosity of the resin composition layer, it is more preferable that the amount of the resin composition layer is 1.0 mg / m 2 Less than 0.8 mg / m is preferred 2 Less than 0.5 mg / m is more preferable. 2 The following is even more preferred:

[0069] (C) The amount of carbon per unit surface area of ​​the inorganic filler can be measured after the surface-treated inorganic filler is washed with a solvent (e.g., methyl ethyl ketone (MEK)). Specifically, a sufficient amount of MEK as a solvent is added to the inorganic filler that has been surface-treated with a surface treatment agent, and ultrasonic cleaning is performed at 25°C for 5 minutes. After removing the supernatant and drying the solid content, the amount of carbon per unit surface area of ​​the inorganic filler can be measured using a carbon analyzer. An "EMIA-320V" manufactured by Horiba, Ltd., or the like can be used as the carbon analyzer.

[0070] The range of the amount of (C) inorganic filler in the resin composition layer is preferably 65% ​​by mass or more, more preferably 68% by mass or more, even more preferably 70% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less, relative to 100% by mass of the nonvolatile components in the resin composition layer. Furthermore, the range of the amount of (C) inorganic filler in the resin composition relative to 100% by mass of the nonvolatile components in the resin composition is preferably the same as the range of the amount of (C) inorganic filler in the resin composition layer relative to 100% by mass of the nonvolatile components in the resin composition layer. When the amount of (C) inorganic filler is within the above range, the dielectric loss tangent and linear thermal expansion coefficient of the cured product layer obtained by curing the resin composition layer can be effectively improved. Furthermore, resin composition layers containing (C) inorganic filler in such an amount have traditionally tended to cause swelling in the bleed-out area. In contrast, the resin sheet of the present embodiment can suppress swelling in the bleed-out area despite containing such an amount of (B) inorganic filler.

[0071] ((D) Description of optional curable resin) The resin composition layer and the resin composition contained in the resin composition layer may contain an optional curable resin (D) as an optional component. The optional curable resin (D) as component (D) does not include components corresponding to the above-mentioned components (A) to (C). The optional curable resin (D) may be used alone or in combination of two or more.

[0072] As the optional curable resin (D), a thermosetting resin is usually used. Examples of the optional curable resin (D) include epoxy resins, phenolic resins, carbodiimide resins, cyanate ester resins, acid anhydride resins, amine resins, benzoxazine resins, and thiol resins. Among these, it is preferable to use a combination of an epoxy resin and a resin capable of reacting with and bonding to the epoxy resin to cure the resin composition layer. Hereinafter, a resin capable of reacting with and bonding to the epoxy resin to cure the resin composition layer may be referred to as a "curing agent." Examples of curing agents include phenolic resins, carbodiimide resins, cyanate ester resins, acid anhydride resins, amine resins, benzoxazine resins, and thiol resins, with phenolic resins and carbodiimide resins being preferred. Hereinafter, a curable resin classified as component (D) may be referred to with the term "optional," such as "optional epoxy resin."

[0073] The optional epoxy resin is (D) any curable resin having epoxy groups. Examples of the optional epoxy resin include bixylenol type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, bisphenol AF type epoxy resins, dicyclopentadiene type epoxy resins, trisphenol type epoxy resins, naphthol novolac type epoxy resins, phenol novolac type epoxy resins, tert-butyl-catechol type epoxy resins, naphthalene type epoxy resins, naphthol type epoxy resins, anthracene type epoxy resins, glycidylamine type epoxy resins, glycidyl ester type epoxy resins, cresol novolac type epoxy resins, phenol aralkyl type epoxy resins, biphenyl type epoxy resins, linear aliphatic epoxy resins, epoxy resins having a butadiene structure, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, cyclohexane type epoxy resins, cyclohexane dimethanol type epoxy resins, naphthylene ether type epoxy resins, trimethylol type epoxy resins, tetraphenylethane type epoxy resins, isocyanurate type epoxy resins, and phenolphthalimidine type epoxy resins.

[0074] From the viewpoint of obtaining an insulating layer having excellent heat resistance, the optional epoxy resin preferably contains an epoxy resin having an aromatic structure. An aromatic structure is a chemical structure generally defined as aromatic, and also includes polycyclic aromatics and aromatic heterocycles. Examples of epoxy resins having an aromatic structure include bixylenol-type epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol S-type epoxy resins, bisphenol AF-type epoxy resins, dicyclopentadiene-type epoxy resins, trisphenol-type epoxy resins, naphthol novolac-type epoxy resins, phenol novolac-type epoxy resins, tert-butyl-catechol-type epoxy resins, naphthalene-type epoxy resins, naphthol-type epoxy resins, anthracene-type epoxy resins, bixylenol-type epoxy resins, and glycidylamines having an aromatic structure. type epoxy resins, glycidyl ester type epoxy resins having an aromatic structure, cresol novolac type epoxy resins, biphenyl type epoxy resins, linear aliphatic epoxy resins having an aromatic structure, epoxy resins having a butadiene structure having an aromatic structure, alicyclic epoxy resins having an aromatic structure, heterocyclic epoxy resins, spiro ring-containing epoxy resins having an aromatic structure, cyclohexanedimethanol type epoxy resins having an aromatic structure, naphthylene ether type epoxy resins, trimethylol type epoxy resins having an aromatic structure, and tetraphenylethane type epoxy resins having an aromatic structure.

[0075] The (D) optional curable resin preferably contains, as the optional epoxy resin, an epoxy resin having two or more epoxy groups in one molecule. The proportion of the epoxy resin having two or more epoxy groups in one molecule relative to 100% by mass of the non-volatile components of the epoxy resin contained in the (D) optional curable resin is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

[0076] Specific examples of the optional epoxy resin include "HP-4032" and "HP4032H" (naphthalene type epoxy resins) manufactured by DIC Corporation; "HP-4700" and "HP-4710" (naphthalene type tetrafunctional epoxy resins) manufactured by DIC Corporation; "N-690" (cresol novolac type epoxy resin) manufactured by DIC Corporation; "N-695" (cresol novolac type epoxy resin) manufactured by DIC Corporation; "HP-7200", "HP-7200HH", "HP-7200H", and "HP-7200L" (dicyclopentadiene type epoxy resins) manufactured by DIC Corporation; and "EX" manufactured by DIC Corporation. A-7311, "EXA-7311-G3", "EXA-7311-G4", "EXA-7311-G4S", "HP6000" (naphthylene ether type epoxy resin); "EPPN-502H" (trisphenol type epoxy resin) manufactured by Nippon Kayaku Co., Ltd.; "NC7000L" (naphthol novolac type epoxy resin) manufactured by Nippon Kayaku Co., Ltd.; "NC3000H", "NC3000", "NC3000L", "NC3000FH", "NC3100" (biphenyl type epoxy resin) manufactured by Nippon Kayaku Co., Ltd.; "ESN475V" manufactured by Nippon Steel Chemical & Material Co., Ltd. "ESN4100V" (naphthalene-type epoxy resin); "ESN485" (naphthol-type epoxy resin) manufactured by Nippon Steel Chemical & Material Co., Ltd.; "ESN375" (dihydroxynaphthalene-type epoxy resin) manufactured by Nippon Steel Chemical & Material Co., Ltd.; "YX4000H", "YX4000", "YX4000HK", and "YL7890" (bixylenol-type epoxy resin) manufactured by Mitsubishi Chemical Corporation; "YL6121" (biphenyl-type epoxy resin) manufactured by Mitsubishi Chemical Corporation; "YX8800" (anthracene-type epoxy resin) manufactured by Mitsubishi Chemical Corporation. Examples include "YX7700" (phenol aralkyl type epoxy resin); "PG-100" and "CG-500" manufactured by Osaka Gas Chemicals Co., Ltd.; "YX7760" (bisphenol AF type epoxy resin) manufactured by Mitsubishi Chemical Corporation; "YL7800" (fluorene type epoxy resin) manufactured by Mitsubishi Chemical Corporation; "jER1010" (bisphenol A type epoxy resin) manufactured by Mitsubishi Chemical Corporation; "jER1031S" (tetraphenylethane type epoxy resin) manufactured by Mitsubishi Chemical Corporation; and "WHR991S" (phenolphthalimidine type epoxy resin) manufactured by Nippon Kayaku Co., Ltd.

[0077] The epoxy equivalent of any epoxy resin is preferably 50 g / eq. to 5,000 g / eq., more preferably 60 g / eq. to 3,000 g / eq., even more preferably 80 g / eq. to 2,000 g / eq., and particularly preferably 110 g / eq. to 1,000 g / eq.

[0078] The weight average molecular weight (Mw) of any epoxy resin is preferably 100 to 5,000, more preferably 250 to 3,000, and even more preferably 400 to 1,500. The weight average molecular weight can be measured by gel permeation chromatography (GPC) as a polystyrene-equivalent value.

[0079] The range of the amount of any epoxy resin in the resin composition layer is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, relative to 100% by mass of the nonvolatile components in the resin composition. Furthermore, the range of the amount of any epoxy resin in the resin composition relative to 100% by mass of the nonvolatile components in the resin composition is preferably the same as the above-mentioned range of the amount of any epoxy resin in the resin composition layer relative to 100% by mass of the nonvolatile components in the resin composition layer.

[0080] The range of the amount of any epoxy resin in the resin composition layer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, relative to 100% by mass of the resin components in the resin composition layer. Furthermore, the range of the amount of any epoxy resin in the resin composition relative to 100% by mass of the resin components in the resin composition is preferably the same as the above-mentioned range of the amount of any epoxy resin in the resin composition layer relative to 100% by mass of the resin components in the resin composition layer.

[0081] As the optional phenolic resin, a compound having one or more, preferably two or more, hydroxyl groups (phenolic hydroxyl groups) bonded to an aromatic ring such as a benzene ring or a naphthalene ring per molecule can be used. When combined with an epoxy resin, a phenolic resin can react with the epoxy resin to harden the resin composition layer, and is therefore sometimes called a "phenolic curing agent." From the viewpoint of heat resistance and water resistance, a phenolic resin having a novolac structure is preferred. From the viewpoint of adhesion, a nitrogen-containing phenolic resin is preferred, and a triazine skeleton-containing phenolic resin is more preferred. Among these, a triazine skeleton-containing phenolic novolac resin is preferred from the viewpoint of highly satisfying heat resistance, water resistance, and adhesion.

[0082] Specific examples of any phenolic resin include "MEH-7700", "MEH-7810", "MEH-7851", and "MEH-8000H" manufactured by Meiwa Chemical Industry Co., Ltd.; "NHN", "CBN", and "GPH" manufactured by Nippon Kayaku Co., Ltd.; and "SN-170", "SN-180", "SN-190", "SN-475", "SN-485", "SN-495", "SN-495V", and "SN" manufactured by Nippon Steel Chemical & Material Co., Ltd. -375" and "SN-395" manufactured by DIC Corporation; "TD-2090", "TD-2090-60M", "LA-7052", "LA-7054", "LA-1356", "LA-3018", "LA-3018-50P", "LA-1356", "TD2090", and "TD-2090-60M" manufactured by Gun-ei Chemical Co., Ltd.; and "GDP-6115L", "GDP-6115H", and "ELPC75" manufactured by Gun-ei Chemical Co., Ltd.

[0083] The range of the amount of any phenolic resin in the resin composition layer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, relative to 100% by mass of the nonvolatile components in the resin composition. Furthermore, the range of the amount of any phenolic resin in the resin composition relative to 100% by mass of the nonvolatile components in the resin composition is preferably the same as the above-mentioned range of the amount of any phenolic resin in the resin composition layer relative to 100% by mass of the nonvolatile components in the resin composition layer.

[0084] The range of the amount of the optional phenolic resin in the resin composition layer is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, relative to 100% by mass of the resin components in the resin composition layer. Furthermore, the range of the amount of the optional phenolic resin in the resin composition relative to 100% by mass of the resin components in the resin composition is preferably the same as the above-mentioned range of the amount of the optional phenolic resin in the resin composition layer relative to 100% by mass of the resin components in the resin composition layer.

[0085] As the optional carbodiimide resin, a compound having one or more, preferably two or more, carbodiimide structures in one molecule can be used. When combined with an epoxy resin, the carbodiimide resin can react with the epoxy resin to harden the resin composition layer, and therefore is sometimes called a "carbodiimide curing agent." Specific examples of the optional carbodiimide resin include aliphatic biscarbodiimides such as tetramethylene-bis(t-butylcarbodiimide) and cyclohexane-bis(methylene-t-butylcarbodiimide); aromatic biscarbodiimides such as phenylene-bis(xylylcarbodiimide); aliphatic polycarbodiimides such as polyhexamethylenecarbodiimide, polytrimethylhexamethylenecarbodiimide, polycyclohexylenecarbodiimide, poly(methylenebiscyclohexylenecarbodiimide), and poly(isophoronecarbodiimide); poly(phenylenecarbodiimide), poly Examples of polycarbodiimides include aromatic polycarbodiimides such as poly(naphthylenecarbodiimide), poly(tolylenecarbodiimide), poly(methyldiisopropylphenylenecarbodiimide), poly(triethylphenylenecarbodiimide), poly(diethylphenylenecarbodiimide), poly(triisopropylphenylenecarbodiimide), poly(diisopropylphenylenecarbodiimide), poly(xylylenecarbodiimide), poly(tetramethylxylylenecarbodiimide), poly(methylenediphenylenecarbodiimide), and poly[methylenebis(methylphenylene)carbodiimide].

[0086] Commercially available carbodiimide resins include, for example, "Carbodilite V-02B," "Carbodilite V-03," "Carbodilite V-04K," "Carbodilite V-05," "Carbodilite V-07," and "Carbodilite V-09" manufactured by Nisshinbo Chemical Inc.; and "Stavaxol P," "Stavaxol P400," and "Hykasil 510" manufactured by Lanxess AG.

[0087] The range of the amount of any carbodiimide resin in the resin composition layer is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.5% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, relative to 100% by mass of the nonvolatile components in the resin composition. Furthermore, the range of the amount of any carbodiimide resin in the resin composition relative to 100% by mass of the nonvolatile components in the resin composition is preferably the same as the above-mentioned range of the amount of any carbodiimide resin in the resin composition layer relative to 100% by mass of the nonvolatile components in the resin composition layer.

[0088] The range of the amount of any carbodiimide-based resin in the resin composition layer is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, relative to 100% by mass of the resin components in the resin composition layer, and is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. Furthermore, the range of the amount of any carbodiimide-based resin in the resin composition relative to 100% by mass of the resin components in the resin composition is preferably the same as the above-mentioned range of the amount of any carbodiimide-based resin in the resin composition layer relative to 100% by mass of the resin components in the resin composition layer.

[0089] The cyanate ester resin may be a compound having one or more, preferably two or more, cyanate groups in one molecule. When combined with an epoxy resin, the cyanate ester resin may react with the epoxy resin to harden the resin composition layer, and therefore may be referred to as a "cyanate ester curing agent." Examples of the optional cyanate ester resin include bifunctional cyanate ester resins such as bisphenol A dicyanate, polyphenol cyanate, oligo(3-methylene-1,5-phenylene cyanate), 4,4'-methylenebis(2,6-dimethylphenyl cyanate), 4,4'-ethylidene diphenyl dicyanate, hexafluorobisphenol A dicyanate, 2,2-bis(4-cyanate)phenylpropane, 1,1-bis(4-cyanatephenylmethane), bis(4-cyanate-3,5-dimethylphenyl)methane, 1,3-bis(4-cyanatephenyl-1-(methylethylidene))benzene, bis(4-cyanatephenyl)thioether, and bis(4-cyanatephenyl)ether; multifunctional cyanate ester resins derived from phenol novolac, cresol novolac, and the like; and prepolymers in which these cyanate ester resins are partially triazine converted. Specific examples of cyanate ester resins include "PT30" and "PT60" (phenol novolac type multifunctional cyanate ester resins) manufactured by Arxada, "BA230" and "BA230S75" (prepolymers in which part or all of bisphenol A dicyanate has been triazine converted to a trimer).

[0090] As the optional acid anhydride resin, a compound having one or more, preferably two or more, acid anhydride groups in one molecule can be used. When combined with an epoxy group, an acid anhydride resin can react with the epoxy resin to harden the resin composition layer, and therefore is sometimes called an "acid anhydride curing agent." Specific examples of the optional acid anhydride resin include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, hydrogenated methylnadic anhydride, trialkyltetrahydrophthalic anhydride, dodecenyl succinic anhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, trimellitic anhydride, pyromellitic anhydride, and benzophenone tetracarboxylic acid. dianhydride, biphenyltetracarboxylic dianhydride, naphthalenetetracarboxylic dianhydride, oxydiphthalic dianhydride, 3,3'-4,4'-diphenylsulfonetetracarboxylic dianhydride, 1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-C]furan-1,3-dione, ethylene glycol bis(anhydrotrimellitate), and polymeric acid anhydrides such as styrene-maleic acid resins, which are copolymers of styrene and maleic acid. Commercially available acid anhydride resins include, for example, "HNA-100," "MH-700," "MTA-15," "DDSA," and "OSA" manufactured by New Japan Chemical Co., Ltd.; "YH-306" and "YH-307" manufactured by Mitsubishi Chemical Corporation; "HN-2200" and "HN-5500" manufactured by Resonac Corporation; and "EF-30," "EF-40," "EF-60," and "EF-80" manufactured by Cray Valley Chemical Industries, Ltd.

[0091] The optional amine-based resin may be a compound having one or more, preferably two or more, amino groups in one molecule. When combined with an epoxy group, the amine-based resin may react with the epoxy resin to harden the resin composition layer, and is therefore sometimes referred to as an "amine-based curing agent." Examples of the optional amine-based resin include aliphatic amines, polyether amines, alicyclic amines, and aromatic amines, with aromatic amines being preferred. The amine-based resin is preferably a primary amine or secondary amine, with primary amines being more preferred. Specific examples of amine-based resins include 4,4'-methylenebis(2,6-dimethylaniline), 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, m-phenylenediamine, m-xylylenediamine, diethyltoluenediamine, 4,4'-diaminodiphenyl ether, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine, and 2,2-bis(3-amino-4-hydroxyphenyl)propanol. Examples of suitable bis(4-aminophenoxy)benzene include bis(4-aminophenyl)propane, 3,3-dimethyl-5,5-diethyl-4,4-diphenylmethanediamine, 2,2-bis(4-aminophenyl)propane, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis(4-(4-aminophenoxy)phenyl)sulfone, and bis(4-(3-aminophenoxy)phenyl)sulfone. Commercially available amine-based resins include, for example, "SEIKACURE-S" manufactured by Seika Corporation; "KAYABOND C-200S," "KAYABOND C-100," "KAYAHARD AA," "KAYAHARD AB," and "KAYAHARD AS" manufactured by Nippon Kayaku Co., Ltd.; "Epicure W" manufactured by Mitsubishi Chemical Corporation; and "DTDA" manufactured by Sumitomo Seika Chemicals Co., Ltd.

[0092] The optional benzoxazine resin may be a compound having one or more, preferably two or more, benzoxazine rings in one molecule. When combined with an epoxy resin, the benzoxazine resin reacts with the epoxy resin to harden the resin composition layer, and is therefore sometimes referred to as a "benzoxazine curing agent." Specific examples of the optional benzoxazine resin include "JBZ-OP100D" and "ODA-BOZ" manufactured by JFE Chemical Corporation; "HFB2006M" manufactured by Showa Polymer Co., Ltd.; and "Pd" and "Fa" manufactured by Shikoku Chemical Industry Co., Ltd.

[0093] Thiol-based resins, when combined with epoxy resins, can react with the epoxy resin to harden the resin composition layer, and are therefore sometimes referred to as "thiol-based curing agents." Examples of optional thiol-based resins include trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptobutyrate), and tris(3-mercaptopropyl)isocyanurate.

[0094] The functional group equivalent of any curing agent contained in the (D) optional curable resin is preferably 50 g / eq. to 3000 g / eq., more preferably 100 g / eq. to 1000 g / eq., even more preferably 100 g / eq. to 500 g / eq., and particularly preferably 100 g / eq. to 300 g / eq. The functional group equivalent represents the mass of the resin per equivalent of the functional group.

[0095] In one example, the weight average molecular weight (Mw) range of any curing agent may be the same as the weight average molecular weight (Mw) range of any epoxy resin.

[0096] The range of the amount of the optional curing agent in the resin composition layer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, and preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, relative to 100% by mass of the nonvolatile components in the resin composition. Furthermore, the range of the amount of the optional curing agent in the resin composition relative to 100% by mass of the nonvolatile components in the resin composition is preferably the same as the above-mentioned range of the amount of the optional curing agent in the resin composition layer relative to 100% by mass of the nonvolatile components in the resin composition layer.

[0097] The range of the amount of the optional curing agent in the resin composition layer is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 5% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, relative to 100% by mass of the resin components in the resin composition layer. Furthermore, the range of the amount of the optional curing agent in the resin composition relative to 100% by mass of the resin components in the resin composition is preferably the same as the above-mentioned range of the amount of the optional curing agent in the resin composition layer relative to 100% by mass of the resin components in the resin composition layer.

[0098] When the (D) optional curable resin contains a combination of an optional epoxy resin and an optional curing agent, the amount of optional curing agent is preferably set so that the ratio of the number of functional groups of the optional curing agent to the number of epoxy groups of the optional epoxy resin falls within a specific range. Specifically, when the number of epoxy groups of the optional epoxy resin is 1, the number of functional groups of the optional curing agent is preferably 0.01 or more, more preferably 0.1 or more, even more preferably 0.2 or more, and preferably 2.0 or less, more preferably 1.0 or less, even more preferably 0.5 or less. The "number of functional groups of optional curing agent" refers to the sum of all values ​​obtained by dividing the mass of the non-volatile components of optional curing agents present in the resin composition layer by their functional group equivalents. Furthermore, the "number of epoxy groups of optional epoxy resin" refers to the sum of all values ​​obtained by dividing the mass of the non-volatile components of optional epoxy resins present in the resin composition layer by their epoxy equivalents.

[0099] The range of the amount of the optional curable resin (D) in the resin composition layer is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 20% by mass or less, more preferably 16% by mass or less, even more preferably 13% by mass or less, relative to 100% by mass of the nonvolatile components in the resin composition layer. Furthermore, the range of the amount of the optional curable resin (D) in the resin composition relative to 100% by mass of the nonvolatile components in the resin composition is preferably the same as the above-mentioned range of the amount of the optional curable resin (D) in the resin composition layer relative to 100% by mass of the nonvolatile components in the resin composition layer.

[0100] The range of the amount of the optional curable resin (D) in the resin composition layer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, relative to 100% by mass of the resin components in the resin composition layer. Furthermore, the range of the amount of the optional curable resin (D) in the resin composition relative to 100% by mass of the resin components in the resin composition is preferably the same as the above-mentioned range of the amount of the optional curable resin (D) in the resin composition layer relative to 100% by mass of the resin components in the resin composition layer.

[0101] (E) Description of organic filler The resin composition layer and the resin composition contained in the resin composition layer may contain an organic filler (E) as an optional component. The organic filler (E) as the component (E) does not include components (A) to (D) described above. The organic filler (E) is contained in the resin composition layer in the form of particles, and is usually contained in the cured product layer while maintaining this particle state. The organic filler (E) can improve the thixotropy of the resin composition layer during lamination and suppress bleeding of the resin composition layer from the gap between the inner layer substrate and the support. This makes it possible to reduce the area of ​​the bleed-out portion. One type of organic filler (E) may be used alone, or two or more types may be used in combination.

[0102] Examples of the (E) organic filler include rubber particles, polyamide fine particles, silicone particles, core-shell type particles, etc. Among these, it is preferable to use either rubber particles or core-shell type particles, and it is more preferable to use core-shell type particles.

[0103] Examples of rubber components contained in the rubber particles include thermoplastic elastomers such as polybutadiene, polyisoprene, polychlorobutadiene, ethylene-vinyl acetate copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-isobutylene copolymer, acrylonitrile-butadiene copolymer, isoprene-isobutylene copolymer, isobutylene-butadiene copolymer, ethylene-propylene-diene terpolymer, and ethylene-propylene-butene terpolymer; and acrylic thermoplastic elastomers such as polypropyl(meth)acrylate, polybutyl(meth)acrylate, polycyclohexyl(meth)acrylate, and polyoctyl(meth)acrylate. The term "(meth)acrylic acid" includes acrylic acid, methacrylic acid, and combinations thereof, unless otherwise specified. Among these, olefin-based thermoplastic elastomers are preferred, and styrene-butadiene copolymers are more preferred. Silicone-based rubbers such as polyorganosiloxane rubbers may also be mixed with the rubber component. The rubber component contained in the rubber particles usually has a glass transition temperature of 0°C or lower, preferably -10°C or lower, more preferably -20°C or lower, and even more preferably -30°C or lower.

[0104] As the rubber particles, commercially available products may be used, such as "EXL2655" manufactured by Dow Chemical Japan, and "AC3401N" and "AC3816N" manufactured by Aica Kogyo Co., Ltd.

[0105] Core-shell particles are particulate organic fillers comprising a core particle and one or more shell layers covering the core particle. The core particle preferably contains the rubber component described above. The shell preferably contains an appropriate polymer. The core-shell particles are preferably core-shell graft copolymer particles consisting of a core particle containing a rubber component and a shell obtained by graft copolymerization of a monomer component copolymerizable with the rubber component contained in the core particle. The term "core-shell" as used here does not necessarily refer only to particles in which the core particle and the shell are clearly distinguishable, but also includes particles in which the boundary between the core particle and the shell is unclear. The core particle may or may not be completely covered by the shell.

[0106] The amount of core particles contained in the core-shell particles is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, based on 100% by mass of the core-shell particles. The upper limit is not particularly limited, but may be, for example, 95% by mass or less, 90% by mass or less, from the viewpoint of sufficiently covering the core particles with the shell portion.

[0107] Examples of monomer components for the polymer forming the shell portion include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, and glycidyl (meth)acrylate; (meth)acrylic acid; N-substituted maleimides such as N-methylmaleimide and N-phenylmaleimide; maleimide; α,β-unsaturated carboxylic acids such as maleic acid and itaconic acid; aromatic vinyl compounds such as styrene, 4-vinyltoluene, and α-methylstyrene; and (meth)acrylonitrile. Among these, (meth)acrylic acid esters are preferred, and methyl (meth)acrylate is more preferred. One type of monomer component may be used alone, or two or more types may be used in combination.

[0108] Commercially available core-shell particles may be used. For example, commercially available core-shell graft copolymer particles include "CHT" manufactured by Samsung SDI Corporation; "B602" manufactured by Techno UMG Corporation; "Paraloid EXL-2602," "Paraloid EXL-2603," "Paraloid EXL-2655," "Paraloid EXL-2311," "Paraloid EXL-2313," "Paraloid EXL-2315," "Paraloid KM-330," and "Paraloid KM-3311" manufactured by Dow Chemical Japan. Examples include Pararoid KM-336P and Pararoid KCZ-201; Mitsubishi Rayon's Metablen C-223A, Metablen E-901, Metablen S-2001, Metablen W-450A, and Metablen SRK-200; and Kaneka's Kane Ace M-511, Kane Ace M-600, Kane Ace M-400, Kane Ace M-580, and Kane Ace MR-01.

[0109] The average particle size (average primary particle size) of the (E) organic filler is not particularly limited, but is preferably 20 nm or more, more preferably 50 nm or more, even more preferably 80 nm or more, and even more preferably 100 nm or more, and is preferably 5,000 nm or less, more preferably 2,000 nm or less, even more preferably 1,000 nm or less, and even more preferably 500 nm or less. The average particle size (average primary particle size) of the (E) organic filler can be measured using a zeta potential particle size distribution measuring device.

[0110] The range of the amount of the (E) organic filler in the resin composition layer is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.5% by mass or more, and preferably 2% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1% by mass or less, relative to 100% by mass of the nonvolatile components in the resin composition. Furthermore, the range of the amount of the (E) organic filler in the resin composition relative to 100% by mass of the nonvolatile components in the resin composition is preferably the same as the above-mentioned range of the amount of the (E) organic filler in the resin composition layer relative to 100% by mass of the nonvolatile components in the resin composition layer.

[0111] The range of the amount of the (E) organic filler in the resin composition layer is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 5% by mass or less, relative to 100% by mass of the resin components in the resin composition layer. Furthermore, the range of the amount of the (E) organic filler in the resin composition relative to 100% by mass of the resin components in the resin composition is preferably the same as the above-mentioned range of the amount of the (E) organic filler in the resin composition layer relative to 100% by mass of the resin components in the resin composition layer.

[0112] ((F) Explanation of hardening accelerator) The resin composition layer and the resin composition contained in the resin composition layer may contain a curing accelerator (F) as an optional component. The curing accelerator (F) as component (F) does not include components (A) to (E) described above. The curing accelerator (F) acts as a catalyst for the reaction of the curable resin, thereby accelerating the curing of the resin composition layer.

[0113] As the (F) curing accelerator, an appropriate one can be used depending on the type of curable resin. For example, when the (A) liquid resin and / or the (D) optional curable resin contains an epoxy resin, examples of the (F) curing accelerator that can accelerate the curing of the epoxy resin include phosphorus-based curing accelerators, urea-based curing accelerators, guanidine-based curing accelerators, imidazole-based curing accelerators, metal-based curing accelerators, and amine-based curing accelerators. One type of (F) curing accelerator may be used alone, or two or more types may be used in combination.

[0114] Examples of the phosphorus-based curing accelerator include aliphatic phosphonium salts such as tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tetrabutylphosphonium acetate, tetrabutylphosphonium decanoate, tetrabutylphosphonium laurate, bis(tetrabutylphosphonium)pyromellitate, tetrabutylphosphonium hydrogenhexahydrophthalate, tetrabutylphosphonium 2,6-bis[(2-hydroxy-5-methylphenyl)methyl]-4-methylphenolate, and di-tert-butyldimethylphosphonium tetraphenylborate; methyltriphenylphosphonium bromide, ethyltriphenylphosphonium bromide, propyltriphenylphosphonium bromide, butyltriphenylphosphonium bromide, benzyltriphenylphosphonium chloride, tetraphenylphosphonium bromide, p-tolyltriphenylphosphonium tetra-p-tolylborate, and tetraphenylphosphonium tetra-p-tolylborate. aromatic phosphonium salts such as tetraphenylborate, tetraphenylphosphonium tetra-p-tolylborate, triphenylethylphosphonium tetraphenylborate, tris(3-methylphenyl)ethylphosphonium tetraphenylborate, tris(2-methoxyphenyl)ethylphosphonium tetraphenylborate, (4-methylphenyl)triphenylphosphonium thiocyanate, tetraphenylphosphonium thiocyanate, and butyltriphenylphosphonium thiocyanate; aromatic phosphine-borane complexes such as triphenylphosphine-triphenylborane; aromatic phosphine-quinone adducts such as triphenylphosphine-p-benzoquinone adduct; aliphatic phosphines such as tributylphosphine, tri-tert-butylphosphine, trioctylphosphine, di-tert-butyl(2-butenyl)phosphine, di-tert-butyl(3-methyl-2-butenyl)phosphine, and tricyclohexylphosphine;Dibutylphenylphosphine, di-tert-butylphenylphosphine, methyldiphenylphosphine, ethyldiphenylphosphine, butyldiphenylphosphine, diphenylcyclohexylphosphine, triphenylphosphine, tri-o-tolylphosphine, tri-m-tolylphosphine, tri-p-tolylphosphine, tris(4-ethylphenyl)phosphine, tris(4-propylphenyl)phosphine, tris(4-isopropylphenyl)phosphine, tris(4-butylphenyl)phosphine, tris(4-tert-butylphenyl)phosphine, tris(2,4-dimethylphenyl)phosphine, tris(2,5-dimethylphenyl)phosphine, tris(2,6-dimethylphenyl)phosphine aromatic phosphines such as benzene, tris(3,5-dimethylphenyl)phosphine, tris(2,4,6-trimethylphenyl)phosphine, tris(2,6-dimethyl-4-ethoxyphenyl)phosphine, tris(2-methoxyphenyl)phosphine, tris(4-methoxyphenyl)phosphine, tris(4-ethoxyphenyl)phosphine, tris(4-tert-butoxyphenyl)phosphine, diphenyl-2-pyridylphosphine, 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane, 1,4-bis(diphenylphosphino)butane, 1,2-bis(diphenylphosphino)acetylene, and 2,2'-bis(diphenylphosphino)diphenyl ether;

[0115] Examples of the urea-based curing accelerator include 1,1-dimethylurea; aliphatic dimethylureas such as 1,1,3-trimethylurea, 3-ethyl-1,1-dimethylurea, 3-cyclohexyl-1,1-dimethylurea, and 3-cyclooctyl-1,1-dimethylurea; 3-phenyl-1,1-dimethylurea, 3-(4-chlorophenyl)-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, 3-(2-methylphenyl)-1,1-dimethylurea, 3-(4-methylphenyl)-1,1-dimethylurea, and 3-(3,4-dimethylphenyl)-1,1-dimethylurea. aromatic dimethylureas such as toluene bis(dimethylurea), 3-(4-isopropylphenyl)-1,1-dimethylurea, 3-(4-methoxyphenyl)-1,1-dimethylurea, 3-(4-nitrophenyl)-1,1-dimethylurea, 3-[4-(4-methoxyphenoxy)phenyl]-1,1-dimethylurea, 3-[4-(4-chlorophenoxy)phenyl]-1,1-dimethylurea, 3-[3-(trifluoromethyl)phenyl]-1,1-dimethylurea, N,N-(1,4-phenylene)bis(N',N'-dimethylurea), and N,N-(4-methyl-1,3-phenylene)bis(N',N'-dimethylurea) [toluene bisdimethylurea].

[0116] Examples of guanidine curing accelerators include dicyandiamide, 1-methylguanidine, 1-ethylguanidine, 1-cyclohexylguanidine, 1-phenylguanidine, 1-(o-tolyl)guanidine, dimethylguanidine, diphenylguanidine, trimethylguanidine, tetramethylguanidine, pentamethylguanidine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1-methylbiguanide, 1-ethylbiguanide, 1-n-butylbiguanide, 1-n-octadecylbiguanide, 1,1-dimethylbiguanide, 1,1-diethylbiguanide, 1-cyclohexylbiguanide, 1-allylbiguanide, 1-phenylbiguanide, and 1-(o-tolyl)biguanide.

[0117] Examples of the imidazole curing accelerator include 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-methylimidazole. Phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl -(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct Examples of imidazole compounds include 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, and 2-phenylimidazoline, as well as adducts of imidazole compounds with epoxy resins. Commercially available imidazole curing accelerators include "1B2PZ," "2E4MZ," "2MZA-PW," "2MZ-OK," "2MA-OK," "2MA-OK-PW," "2PHZ," "2PHZ-PW," "Cl1Z," "Cl1Z-CN," "Cl1Z-CNS," and "C11Z-A" manufactured by Shikoku Chemicals Corporation; and "P200-H50" manufactured by Mitsubishi Chemical Corporation.

[0118] Examples of metal-based curing accelerators include organometallic complexes or organometallic salts of metals such as cobalt, copper, zinc, iron, nickel, manganese, and tin. Specific examples of organometallic complexes include organic cobalt complexes such as cobalt(II) acetylacetonate and cobalt(III) acetylacetonate, organic copper complexes such as copper(II) acetylacetonate, organic zinc complexes such as zinc(II) acetylacetonate, organic iron complexes such as iron(III) acetylacetonate, organic nickel complexes such as nickel(II) acetylacetonate, and organic manganese complexes such as manganese(II) acetylacetonate. Examples of organometallic salts include zinc octoate, tin octoate, zinc naphthenate, cobalt naphthenate, tin stearate, and zinc stearate.

[0119] Examples of the amine curing accelerator include trialkylamines such as triethylamine and tributylamine, 4-dimethylaminopyridine, benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, 1,8-diazabicyclo(5,4,0)-undecene, etc. Commercially available amine curing accelerators may be used, such as "MY-25" manufactured by Ajinomoto Fine-Techno Co., Inc.

[0120] The range of the amount of the (F) curing accelerator in the resin composition layer is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, and preferably 2% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, relative to 100% by mass of the nonvolatile components in the resin composition. The range of the amount of the (F) curing accelerator in the resin composition relative to 100% by mass of the nonvolatile components in the resin composition is preferably the same as the above-mentioned range of the amount of the (F) curing accelerator in the resin composition layer relative to 100% by mass of the nonvolatile components in the resin composition layer.

[0121] The range of the amount of the (F) curing accelerator in the resin composition layer is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less, relative to 100% by mass of the resin components in the resin composition layer. Furthermore, the range of the amount of the (F) curing accelerator in the resin composition relative to 100% by mass of the resin components in the resin composition is preferably the same as the above-mentioned range of the amount of the (F) curing accelerator in the resin composition layer relative to 100% by mass of the resin components in the resin composition layer.

[0122] (G) Description of optional additives The resin composition layer and the resin composition contained in the resin composition layer may further contain (G) optional additives as an optional component. The optional additives (G) as component (G) do not include those corresponding to the above-mentioned components (A) to (F). (G) Optional additives include, for example, radical polymerization initiators such as peroxide radical polymerization initiators and azo radical polymerization initiators; organometallic compounds such as organocopper compounds, organozinc compounds, and organocobalt compounds; colorants such as phthalocyanine blue, phthalocyanine green, iodine green, diazo yellow, crystal violet, titanium oxide, and carbon black; polymerization inhibitors such as hydroquinone, catechol, pyrogallol, and phenothiazine; leveling agents such as silicone leveling agents and acrylic polymer leveling agents; thickeners such as bentone and montmorillonite; antifoaming agents such as silicone antifoaming agents, acrylic antifoaming agents, fluorine-based antifoaming agents, and vinyl resin antifoaming agents; ultraviolet absorbers such as benzotriazole ultraviolet absorbers; adhesion improvers such as urea silane; triazole adhesion promoters, tetrazo Examples of the additives include adhesion promoters such as phenol-based adhesion promoters and triazine-based adhesion promoters; antioxidants such as hindered phenol-based antioxidants; fluorescent brighteners such as stilbene derivatives; surfactants such as fluorine-based surfactants and silicone-based surfactants; flame retardants such as phosphorus-based flame retardants (e.g., phosphate ester compounds, phosphazene compounds, phosphinic acid compounds, and red phosphorus), nitrogen-based flame retardants (e.g., melamine sulfate), halogen-based flame retardants, and inorganic flame retardants (e.g., antimony trioxide); dispersants such as phosphate ester-based dispersants, polyoxyalkylene-based dispersants, acetylene-based dispersants, silicone-based dispersants, anionic dispersants, and cationic dispersants; and stabilizers such as borate-based stabilizers, titanate-based stabilizers, aluminate-based stabilizers, zirconate-based stabilizers, isocyanate-based stabilizers, carboxylic acid-based stabilizers, and carboxylic anhydride-based stabilizers. (G) Optional additives may be used alone or in combination of two or more.

[0123] (H) Solvent Description The resin composition layer and the resin composition contained in the resin composition layer may further contain a (H) solvent as an optional volatile component in addition to the non-volatile components (A) to (G) described above. An organic solvent is typically used as the (H) solvent. Examples of the organic solvent include ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ether-based solvents such as tetrahydropyran, tetrahydrofuran, 1,4-dioxane, diethyl ether, diisopropyl ether, dibutyl ether, diphenyl ether, and anisole; alcohol-based solvents such as methanol, ethanol, propanol, butanol, and ethylene glycol; 2-ethoxyethyl acetate, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, ethyl diglycol acetate, γ-butyrolactone, and methyl methoxypropionate. Examples of suitable solvents include ether ester solvents such as ethyl acetate; ester alcohol solvents such as methyl lactate, ethyl lactate, and methyl 2-hydroxyisobutyrate; ether alcohol solvents such as 2-methoxypropanol, 2-methoxyethanol, 2-ethoxyethanol, propylene glycol monomethyl ether, and diethylene glycol monobutyl ether (butyl carbitol); amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; sulfoxide solvents such as dimethyl sulfoxide; nitrile solvents such as acetonitrile and propionitrile; aliphatic hydrocarbon solvents such as hexane, cyclopentane, cyclohexane, and methylcyclohexane; and aromatic hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, and trimethylbenzene. The (H) solvent may be used singly or in combination of two or more.

[0124] Usually, all or most of the (H) solvent is removed by drying during the formation of the resin composition layer. Therefore, the resin composition layer and the resin composition may not contain the (H) solvent. Furthermore, when the resin composition layer and the resin composition contain the (H) solvent, it is preferable that the amount of the (H) solvent is small. It is preferable that the specific amount of the (H) solvent is set so as to satisfy the above-mentioned requirement (R).

[0125] <Description of Characteristics of Resin Composition Layer> The resin composition layer can usually have a low minimum melt viscosity. The range of the minimum melt viscosity of the resin composition layer is preferably 3000 poise or less, more preferably 2500 poise or less, and even more preferably 2000 poise or less. A resin composition layer having a low minimum melt viscosity can satisfactorily embed components and conductor layers that may be provided on the surface of an inner layer substrate, but is prone to exudation of the resin composition layer, resulting in the formation of bleed-out portions. However, even when such bleed-out portions are formed, the resin sheet according to this embodiment can suppress swelling of the bleed-out portions. The lower limit of the minimum melt viscosity is preferably 200 poise or more, more preferably 500 poise or more, from the viewpoint of smoothly forming a resin composition layer of the desired thickness. The minimum melt viscosity of the resin composition layer can be measured using a dynamic viscoelasticity measuring device. Specifically, the minimum melt viscosity can be determined by measuring the dynamic viscoelastic modulus of a sample at a temperature rise rate of 5°C / min within a temperature range from a starting temperature of 60°C to 200°C, with a temperature interval of 2.5°C, a frequency of 1 Hz, and a strain of 5°C. The specific method for measuring the minimum melt viscosity may be the method described in "Test for measuring minimum melt viscosity" in the Examples section below.

[0126] A cured layer of the resin composition layer can be obtained by curing the resin composition layer. This cured layer contains the cured product of the resin composition contained in the resin composition layer, and preferably contains only the cured product. An insulating layer can be formed using this cured layer. During the curing process, heat is usually applied to the resin composition layer, and the volatile component (H) solvent contained in the resin composition layer can volatilize due to the heat during curing. Therefore, the cured layer can contain the non-volatile components of the resin composition layer or their reaction products.

[0127] Generally, in a method for manufacturing a circuit board using a resin sheet, a resin composition layer is cured to form an insulating layer, a conductor layer is formed on the insulating layer, and then an annealing treatment is performed to heat the insulating layer and the conductor layer. Typically, prior to this annealing treatment, the cured material layer of the resin composition layer that forms the insulating layer is in a semi-cured state in which the curing reaction has not yet been completed. It is presumed that stress is generated in this semi-cured cured material layer by the heat of the annealing treatment, which has previously caused swelling in the bleed-out portion. In this embodiment, even if the bleed-out portion of the insulating layer is formed by such a semi-cured cured material layer, swelling in the bleed-out portion can be suppressed.

[0128] The cured material layer obtained by curing the resin composition layer typically has a low dielectric loss tangent Df. Therefore, the resin composition layer can form an insulating layer with a low dielectric loss tangent Df. In one example, the dielectric loss tangent of the cured material layer is preferably less than 0.0030, more preferably 0.0029 or less, and even more preferably 0.0028 or less. There is no particular lower limit, and the dielectric loss tangent can be, for example, 0.0001 or more. The dielectric loss tangent can be measured by a cavity resonance perturbation method at a measurement frequency of 5.8 GHz and a measurement temperature of 23°C. When the sample is a resin composition layer before curing, the resin composition layer is cured under curing conditions of 190°C for 90 minutes to obtain a cured material layer, and the dielectric loss tangent of the cured material layer can be measured. The dielectric loss tangent can be measured as described in the "Dielectric Loss Tangent Measurement Test" section of the Examples below.

[0129] The cured material layer obtained by curing the resin composition layer typically has a small linear thermal expansion coefficient. Therefore, the resin composition layer can form an insulating layer with a small linear thermal expansion coefficient, thereby suppressing warping of the circuit board. The average linear thermal expansion coefficient (CTE) of the cured material layer is preferably 100 ppm / °C or less, more preferably 50 ppm / °C or less, even more preferably 30 ppm / °C or less, and particularly preferably 20 ppm / °C or less. The lower limit is not particularly limited, but may be, for example, 0.01 ppm / °C or more. The average linear thermal expansion coefficient can be measured in a temperature range of 25°C to 150°C by thermomechanical analysis at a heating rate of 5°C / min from 25°C to 250°C. When the sample is a resin composition layer before curing, the resin composition layer can be cured at 190°C for 90 minutes to obtain a cured material layer, and the average linear thermal expansion coefficient (CTE) of the cured material layer can be measured. As a specific method for measuring the average coefficient of linear thermal expansion, the method described in <Measurement test for average coefficient of thermal expansion CTE> in the examples described later can be adopted.

[0130] <Thickness of Resin Composition Layer> From the viewpoint of thinning, the thickness of the resin composition layer is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. The lower limit of the thickness of the resin composition layer can be, for example, 1 μm or more, 5 μm or more, or 10 μm or more.

[0131] <Description of support> The resin sheet according to one embodiment of the present invention includes a support, such as a plastic film, a metal foil, or a release paper, with a plastic film or a metal foil being preferred.

[0132] When a film of a plastic material is used as the support, examples of the plastic material include polyesters such as polyethylene terephthalate (hereinafter sometimes abbreviated as "PET") and polyethylene naphthalate (hereinafter sometimes abbreviated as "PEN"), polycarbonate (hereinafter sometimes abbreviated as "PC"), acrylics such as polymethyl methacrylate (PMMA), cyclic polyolefins, triacetyl cellulose (TAC), polyether sulfide (PES), polyether ketone, polyimide, etc. Among these, polyethylene terephthalate and polyethylene naphthalate are preferred, with inexpensive polyethylene terephthalate being particularly preferred.

[0133] When a metal foil is used as the support, examples of the metal foil include copper foil and aluminum foil, with copper foil being preferred. The copper foil may be a foil made of a single metal, copper, or an alloy of copper and another metal (e.g., tin, chromium, silver, magnesium, nickel, zirconium, silicon, titanium, etc.).

[0134] The surface of the support that is to be bonded to the resin composition layer may be subjected to a surface treatment such as matte treatment, corona treatment, or antistatic treatment.

[0135] The support may be a support with a release layer, which has a release layer on the surface that bonds with the resin composition layer. Examples of the release agent used in the release layer of the support with a release layer include one or more release agents selected from the group consisting of alkyd-based release agents, polyolefin-based release agents, urethane-based release agents, and silicone-based release agents. Commercially available products may be used as the support with a release layer, including PET films having a release layer primarily composed of a silicone-based release agent or an alkyd resin-based release agent, such as "PET501010," "SK-1," "AL-5," and "AL-7" manufactured by Lintec Corporation; "Lumirror T60" manufactured by Toray Industries, Inc.; "Purex" manufactured by Teijin Limited; and "Uni-Peel" manufactured by Unitika Limited.

[0136] The thickness of the support is not particularly limited, but is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and is preferably 75 μm or less, more preferably 60 μm or less, even more preferably 50 μm or less. When a support with a release layer is used, it is preferable that the thickness of the entire support with a release layer is within the above range.

[0137] <Description of optional members that may be provided on the resin sheet> The resin sheet may include any member other than the support and the resin composition layer, as necessary. For example, the resin sheet may include a protective film that protects the resin composition layer. The protective film is usually provided on the surface of the resin composition layer that is not bonded to the support (i.e., the surface opposite to the support). The thickness of the protective film is not particularly limited, but is, for example, 1 μm to 40 μm. When a protective film is provided, adhesion of dust and scratches to the surface of the resin composition layer can be suppressed. When the resin sheet includes a protective film, the resin sheet can usually be used by peeling off the protective film.

[0138] <Description of resin sheet manufacturing method> The resin sheet can be produced, for example, by a method including forming a resin composition layer on a support. Specifically, the resin sheet may be produced by a production method including, in this order, a step of preparing a resin varnish containing the resin composition, a step of applying the resin varnish to a support, and a step of drying the applied resin varnish to form a resin composition layer.

[0139] The resin varnish may be produced by mixing the components that can be contained in the resin composition and a solvent. The solvent (H) described above may be used as the solvent for the resin varnish. The components may be mixed partially or entirely at the same time, or may be mixed sequentially. The temperature may be appropriately set during the process of mixing the components, and thus heating and / or cooling may be performed temporarily or throughout. Furthermore, stirring or shaking may be performed during the process of mixing the components.

[0140] The resin varnish can be applied using a coating device such as a die coater. Drying can be performed by, for example, heating, hot air blowing, or other drying methods. The drying conditions are preferably set so as to obtain a mass loss rate that satisfies the above-mentioned requirement (R). For example, the drying temperature is preferably 70°C or higher, more preferably 80°C or higher, and even more preferably 90°C or higher, and is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. The drying time is preferably 60 seconds or higher, more preferably 90 seconds or higher, and even more preferably 120 seconds or higher, and is preferably 10 minutes or shorter, more preferably 8 minutes or shorter, and even more preferably 6 minutes or shorter.

[0141] The produced resin sheet can be wound into a roll and stored.

[0142] <Applications of resin sheets> The resin sheet according to this embodiment can be used to form an insulating layer, and is particularly preferably used to form an insulating layer for a circuit board. The resin sheet may also be used for other purposes, such as forming a solder resist, an underfill material, a die bonding material, a hole filling resin, a sealing resin, a component embedding resin, etc.

[0143] <Circuit board> A circuit board according to one embodiment of the present invention includes a cured material layer formed by curing the resin composition layer of the resin sheet described above. Typically, a circuit board includes an insulating layer, which includes a cured material layer formed by curing a resin composition layer. Therefore, the insulating layer includes a cured material of the resin composition. The insulating layer may include only the cured material. The thickness of the insulating layer is not particularly limited and may be, for example, within the same range as the thickness of the resin composition layer of the resin sheet. Since the insulating layer is formed by a cured material layer formed by curing a resin composition layer, it can typically have a low dielectric loss tangent within the same range as the dielectric loss tangent of the cured material layer. Furthermore, the insulating layer can typically have a low average linear thermal expansion coefficient within the same range as the average linear thermal expansion coefficient of the cured material layer.

[0144] Preferably, the circuit board includes an inner layer substrate and the insulating layer is provided on the inner layer substrate. The circuit board may also include a conductor layer. For example, the conductor layer may be provided on an insulating layer. An example of a preferred method for manufacturing a circuit board will be described below.

[0145] A preferred example of a method for manufacturing a circuit board includes the steps of: a step (I) of laminating an inner layer substrate and a resin sheet so that the inner layer substrate and the resin composition layer are bonded to each other; a step (II) of curing the resin composition layer; Includes:

[0146] A preferred example of a method for manufacturing a circuit board includes a step (I) of laminating a resin sheet and an inner layer substrate. The resin sheet and the inner layer substrate are laminated so that the resin composition layer of the resin sheet and the inner layer substrate are bonded. This lamination forms a resin composition layer on the inner layer substrate.

[0147] An "inner layer substrate" is a member that serves as the base material of a circuit board, and examples thereof include glass epoxy substrates, metal substrates, polyester substrates, polyimide substrates, BT resin substrates, and thermosetting polyphenylene ether substrates. The inner layer substrate may have a conductor layer on one or both sides. The conductor layer of the inner layer substrate may be patterned. An inner layer substrate having a conductor layer (circuit) formed on one or both sides of the substrate is sometimes called an "inner layer circuit board." The term "inner layer substrate" also includes intermediate products on which insulating layers and / or conductor layers are to be further formed during the production of a circuit board. In addition, inner layer substrates with built-in components may also be used.

[0148] The inner layer substrate and the resin sheet can be laminated, for example, by thermocompression bonding the resin sheet to the inner layer substrate from the support side. Examples of the member for thermocompression bonding the resin sheet to the inner layer substrate (hereinafter also referred to as the "thermocompression bonding member") include a heated metal plate (such as a SUS plate) or a metal roll (such as a SUS roll). Note that rather than pressing the thermocompression bonding member directly onto the resin sheet, it is preferable to press it via an elastic material such as heat-resistant rubber so that the resin sheet can sufficiently conform to the surface irregularities of the inner layer substrate.

[0149] The inner layer substrate and the resin sheet may be laminated by a vacuum lamination method. In the vacuum lamination method, the thermocompression temperature is preferably in the range of 60°C to 160°C, more preferably 80°C to 140°C, the thermocompression pressure is preferably in the range of 0.098MPa to 1.77MPa, more preferably 0.29MPa to 1.47MPa, and the thermocompression time is preferably in the range of 20 seconds to 400 seconds, more preferably 30 seconds to 300 seconds. The lamination is preferably carried out under reduced pressure conditions of 26.7hPa or less.

[0150] Lamination can be performed using a commercially available vacuum laminator, such as a vacuum pressure laminator manufactured by Meiki Seisakusho Co., Ltd., a vacuum applicator manufactured by Nikko Materials Co., Ltd., or a batch-type vacuum pressure laminator.

[0151] FIG. 1 is a schematic cross-sectional view illustrating a method for manufacturing a circuit board according to one embodiment of the present invention. As shown in FIG. 1, when laminating an inner substrate 100 and a resin sheet 200, most of the resin composition layer 210 is provided in a gap 300 between the inner substrate 100 and the support 220, but a portion 230 of the resin composition layer 210 seeps out of the gap 300. Thus, step (I) involves the portion 230 of the resin composition layer 210 seeping out of the gap 300. This seeped portion 230 forms a bleed-out portion. In the following description, the bleed-out portion will be denoted by the same reference numeral "230" as the portion 230 of the resin composition layer 210 seeping out of the gap 300. By using the resin sheet described above, swelling of the bleed-out portion 230 can be suppressed.

[0152] The method for manufacturing a circuit board shown in this example may include smoothing the resin sheet after lamination under normal pressure (atmospheric pressure), for example, by pressing a thermocompression member from the support side. The pressing conditions for the smoothing may be the same as the conditions for thermocompression bonding of the lamination. The smoothing may be performed using a commercially available laminator. The lamination and smoothing may be performed consecutively using the commercially available vacuum laminator.

[0153] The method for producing a circuit board according to this example includes a step (II) of curing the resin composition layer after the step (I). By curing the resin composition layer in the step (II), an insulating layer can be formed.

[0154] Specific curing conditions for the resin composition layer may be those typically employed when forming an insulating layer for a circuit board. Typically, curing of a resin composition proceeds by thermal curing. Therefore, step (II) may include thermally curing the resin composition layer. The thermal curing conditions for the resin composition layer may vary depending on the type of resin composition. For example, the curing temperature is preferably 120°C to 240°C, more preferably 150°C to 220°C, and even more preferably 170°C to 210°C. The curing time is preferably 5 to 120 minutes, more preferably 10 to 100 minutes, and even more preferably 15 to 100 minutes.

[0155] Furthermore, when the resin composition layer is thermally cured, the method for producing a circuit board may include preheating the resin composition layer at a temperature lower than the curing temperature before the thermal curing. For example, prior to thermal curing of the resin composition layer, the resin composition layer may be preheated for typically 5 minutes or more, preferably 5 minutes to 150 minutes, more preferably 15 minutes to 120 minutes, and even more preferably 15 minutes to 100 minutes, at a temperature of typically 50°C to 150°C, preferably 60°C to 140°C, and more preferably 70°C to 130°C. Preheating is typically performed after step (I). Furthermore, when a smoothing treatment is performed after laminating the inner layer substrate and the resin sheet, preheating can be performed after the smoothing treatment.

[0156] The method for producing a circuit board shown in this example may include a step of peeling off the support of the resin sheet after laminating the inner layer substrate and the resin sheet. Peeling off the support may be performed between steps (I) and (II), or after step (II). Furthermore, when the method for producing a circuit board includes step (III) of forming holes in the insulating layer, step (IV) of roughening the insulating layer, and step (V) of forming a conductor layer, as described below, peeling off the support may be performed between steps (II) and (III), between steps (III) and (IV), or between steps (IV) and (V).

[0157] The method for producing a circuit board according to this example may include a step (III) of forming holes such as via holes or through holes in the insulating layer after step (II). The method for forming the holes may be selected depending on factors such as the composition of the resin composition used to form the insulating layer. For example, holes may be formed by processing methods such as drilling, laser processing, and plasma processing, with laser processing being preferred among them. For example, holes may be formed by irradiating the insulating layer with laser light after peeling off the support, or by irradiating the insulating layer with laser light through the support. The dimensions and shape of the holes may be determined appropriately depending on the design of the circuit board.

[0158] The method for manufacturing a circuit board according to this embodiment may include a step (IV) of roughening the insulating layer. The roughening treatment can roughen the surface of the insulating layer. Furthermore, the roughening treatment can remove smears (resin residues) from the insulating layer. Therefore, this roughening treatment is sometimes called a "desmear treatment." For example, when holes are formed in step (III), smears may form in the holes. Therefore, it is preferable to perform the roughening treatment of step (IV) after step (III) to remove the smears.

[0159] The procedure and conditions for the roughening treatment are not particularly limited, and known procedures and conditions that are commonly used when forming an insulating layer for a circuit board can be adopted. For example, the roughening treatment may be performed by subjecting the insulating layer to a swelling treatment using a swelling liquid, an oxidation treatment using an oxidizing agent, and a neutralization treatment using a neutralizing liquid in this order.

[0160] Examples of swelling liquids used in the roughening treatment include alkaline solutions and surfactant solutions, with alkaline solutions being preferred. Examples of the alkaline solution include sodium hydroxide solution and potassium hydroxide solution. Examples of commercially available swelling liquids include "Swelling Dip Securigance P" and "Swelling Dip Securigance SBU" manufactured by Atotech Japan. Swelling treatment using a swelling liquid can be performed by immersing the insulating layer in the swelling liquid at 30°C to 90°C for 1 to 20 minutes. From the viewpoint of suppressing swelling of the resin in the insulating layer to an appropriate level, it is preferable to immerse the insulating layer in the swelling liquid at 40°C to 80°C for 5 to 15 minutes.

[0161] Examples of oxidizing agents used in the roughening treatment include alkaline permanganate solutions prepared by dissolving potassium permanganate or sodium permanganate in an aqueous solution of sodium hydroxide. Oxidation treatment using an oxidizing agent such as alkaline permanganate solution is preferably carried out by immersing the insulating layer in an oxidizing agent solution heated to 60°C to 100°C for 10 to 30 minutes. The concentration of permanganate in the alkaline permanganate solution is preferably 5% by mass to 10% by mass. Commercially available oxidizing agents include alkaline permanganate solutions such as "Concentrate Compact CP" and "Dosing Solution Securigance P" manufactured by Atotech Japan.

[0162] The neutralizing solution used in the roughening treatment is preferably an acidic aqueous solution, and a commercially available product such as "Reduction Solution Securigant P" manufactured by Atotech Japan can be cited as an example. Neutralization treatment using a neutralizing solution can be carried out by immersing the surface that has been oxidized with an oxidizing agent in a neutralizing solution at 30°C to 80°C for 5 to 30 minutes. From the standpoint of workability, a preferred method is to immerse the object that has been oxidized with an oxidizing agent in a neutralizing solution at 40°C to 70°C for 5 to 20 minutes.

[0163] The method for producing a circuit board according to this embodiment may include a step (V) of forming a conductor layer on an insulating layer. When the method for producing a circuit board includes the steps (III) or (IV), the step (V) of forming a conductor layer is usually preferably carried out after the steps (III) and (IV).

[0164] The conductive material used for the conductor layer is not particularly limited. In a preferred embodiment, the conductor layer contains one or more metals selected from the group consisting of gold, platinum, palladium, silver, copper, aluminum, cobalt, chromium, zinc, nickel, titanium, tungsten, iron, tin, and indium. The conductor layer may be a single metal layer or an alloy layer. Examples of alloy layers include layers formed from an alloy of two or more metals selected from the above group (e.g., nickel-chromium alloy, copper-nickel alloy, and copper-titanium alloy). Among these, from the viewpoints of versatility in forming the conductor layer, cost, ease of patterning, etc., single metal layers of chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or alloy layers of nickel-chromium alloy, copper-nickel alloy, or copper-titanium alloy are preferred. Single metal layers of chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or alloy layers of nickel-chromium alloy are more preferred, and single metal layers of copper are even more preferred.

[0165] The conductor layer may have a single layer structure or a multi-layer structure including two or more single metal or alloy layers made of different types of metals or alloys. When the conductor layer has a multi-layer structure, the layer in contact with the insulating layer is preferably a single metal layer of chromium, zinc, or titanium, or an alloy layer of a nickel-chromium alloy.

[0166] The thickness of the conductor layer depends on the design of the circuit board, but is preferably 3 μm to 35 μm, and more preferably 5 μm to 30 μm.

[0167] The conductor layer may be formed by plating. For example, a conductor layer having a desired wiring pattern can be formed by plating the surface of the insulating layer using a conventionally known technique such as a semi-additive method or a full-additive method. From the viewpoint of ease of production, the semi-additive method is preferred. An example of forming a conductor layer by a semi-additive method will be described below.

[0168] First, an electroless plated layer (plating seed layer) is formed on the surface of the insulating layer by electroless plating. Next, a mask pattern is formed on the formed electroless plated layer, exposing a portion of the electroless plated layer corresponding to the desired wiring pattern. After forming an electroless plated layer on the exposed electroless plated layer by electrolytic plating, the mask pattern is removed. Thereafter, unnecessary electroless plated layer is removed by etching, thereby forming a conductor layer having the desired wiring pattern.

[0169] When a conductor layer is formed on an insulating layer, the manufacturing method of a circuit board usually includes performing an annealing treatment after the formation of the conductor layer. The annealing treatment can improve the adhesion between the insulating layer and the conductor layer. Furthermore, while the heat of the annealing treatment has conventionally caused swelling in the bleed-out portion, this embodiment can suppress swelling in the bleed-out portion. The annealing treatment can be performed, for example, by heating at 150°C to 210°C for 20 to 180 minutes.

[0170] In the method for manufacturing a circuit board, each of the above steps may be performed only once or may be repeated two or more times. For example, steps (I) to (V) may be performed repeatedly to form a circuit board having a multilayer structure, such as a multilayer printed wiring board having a plurality of insulating layers and conductor layers.

[0171] The method for manufacturing a circuit board may further include any optional steps in addition to the steps described above. For example, the method for manufacturing a circuit board may include a step of providing a semiconductor chip so that the semiconductor chip is bonded to the conductor layer. Specifically, when manufacturing a circuit board for a semiconductor chip package including a semiconductor chip, the method for manufacturing a circuit board may include a step of providing the semiconductor chip. The semiconductor chip may be bonded under appropriate conditions that allow conductive connection between the terminal electrodes of the semiconductor chip and the conductor layer formed on the insulating layer. For example, conditions used in flip-chip mounting may be employed. The semiconductor chip may be bonded via an insulating adhesive or by reflow bonding. If necessary, the provided semiconductor chip may be filled with a mold underfill material. The method for manufacturing a circuit board may also include, for example, a step of forming a sealing layer, a step of forming a solder resist layer, and a step of dicing the manufactured circuit board into individual pieces.

[0172] Examples of circuit boards include printed wiring boards and semiconductor chip packages. Examples of semiconductor chip packages include FC-CSP, MIS-BGA package, ETS-BGA package, fan-out type WLP (Wafer Level Package), fan-in type WLP, fan-out type PLP (Panel Level Package), and fan-in type PLP. In these semiconductor chip packages, it is preferable to form a rewiring formation layer using an insulating layer obtained by curing the above-mentioned resin composition layer. However, the circuit board is not limited to those exemplified here.

[0173] <Description of semiconductor device> The circuit board can be used to manufacture a semiconductor device. The semiconductor device includes the circuit board described above. Examples of the semiconductor device include various semiconductor devices used in electrical appliances (e.g., computers, mobile phones, smartphones, tablet devices, wearable devices, digital cameras, medical equipment, and televisions) and vehicles (e.g., motorcycles, automobiles, trains, ships, and aircraft). [Example]

[0174] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. In the following description, "parts" and "%" representing amounts mean "parts by mass" and "% by mass", respectively, unless otherwise specified. Furthermore, the temperature and pressure conditions were room temperature (23°C) and atmospheric pressure (1 atm), unless otherwise specified.

[0175] <Examples 1 to 7, Comparative Examples 1 and 2, and Reference Example 1> <Production of resin varnish> The components were weighed and mixed in the amounts shown in Tables 1 and 2 below, and then 10 parts of methyl ethyl ketone and 10 parts of cyclohexanone were added and uniformly dispersed using a high-speed rotary mixer to obtain a resin varnish. The amount of each component shown in Tables 1 and 2 is expressed in parts by mass. Details of each component shown in Tables 1 and 2 are as follows:

[0176] (A) Liquid resin: A-TMPT: Trimethylolpropane triacrylate, radical reactive group equivalent weight 99 g / eq., viscosity at 25°C 105 mPa·s, manufactured by Shin-Nakamura Chemical Co., Ltd. DAD: Diallyl diphenate, radical reactive group equivalent weight 161 g / eq., viscosity at 20°C 59 mPa·s, manufactured by Nisshoku Techno Fine Chemical Co., Ltd. ZX1658GS: Cyclohexanedimethanol type epoxy resin, epoxy equivalent 133g / eq., viscosity 34mPa·s at 25℃, manufactured by Nippon Steel Chemical & Material Co., Ltd. and Mitsubishi Chemical Corporation CDMDG: Cyclohexanedimethanol epoxy resin, epoxy equivalent 135g / eq., viscosity at 25℃ 34mPa·s, manufactured by Showa Denko K.K. A-DOG: a compound represented by the above formula (a-1), having a radical reactive group equivalent of 163 g / eq. and a viscosity at 25°C of 300 mPa·s, manufactured by Shin-Nakamura Chemical Co., Ltd.

[0177] (B) Active ester resin: HPC-8150-62T: Active ester equivalent weight 230 g / eq., non-volatile content 62% by mass in toluene solution, manufactured by DIC Corporation

[0178] (C) Inorganic filler: SO-C2: Spherical silica surface-treated with an amine-based alkoxysilane compound ("KBM573" manufactured by Shin-Etsu Chemical Co., Ltd.), with an average particle size of 0.5 μm and a specific surface area of ​​5.8 m 2 / g, manufactured by Admatechs Co., Ltd.

[0179] (D-1) Optional epoxy resin: YX4000HK: Bixylenol-type epoxy resin, epoxy equivalent 194g / eq., manufactured by Mitsubishi Chemical Corporation NC-3000L: Biphenyl type epoxy resin, epoxy equivalent 270g / eq., manufactured by Nippon Kayaku Co., Ltd. HP-4032-SS: Naphthalene-type epoxy resin, epoxy equivalent 144g / eq., manufactured by DIC Corporation

[0180] (D-2) Optional hardener: V-03: Carbodiimide resin, functional group equivalent weight 216 g / eq., toluene solution with 50% non-volatile content, manufactured by Nisshinbo Chemical Inc. LA-3018-50P: Phenolic resin, phenolic hydroxyl equivalent 151g / eq., 1-methoxy-2-propanol solution containing 50% non-volatile matter, manufactured by DIC Corporation

[0181] (E) Organic fillers: EXL-2655: Core-shell particles containing rubber components in the core, manufactured by Dow

[0182] (F) Curing accelerator: 1B2PZ: Imidazole curing accelerator, manufactured by Shikoku Chemicals Corporation

[0183] <Production of Resin Sheet A> A polyethylene terephthalate film ("AL5" manufactured by Lintec Corporation, thickness 38 μm) with a release layer was prepared as a support. The resin varnish was uniformly applied onto the release layer of this support so that the thickness of the resin composition layer after drying would be 40 μm. The applied resin varnish was then dried at 100°C for the times shown in Tables 1 and 2 to obtain a resin sheet A with a support and a resin composition layer.

[0184] <Manufacturing test of evaluation boards equivalent to circuit boards> (1) Preparation of inner layer board: Both sides of a glass cloth-based epoxy resin double-sided copper-clad laminate (copper foil thickness 18 μm, substrate thickness 0.8 mm, Panasonic "R1515A", substrate dimensions 510 mm × 340 mm) with an inner layer circuit formed on it were etched 1 μm in the thickness direction using a microetching agent (MEC "CZ8101") to roughen the copper surface.

[0185] (2) Lamination of resin sheet A: Resin sheet A was cut to a size of 490 mm x 320 mm. The resin sheet A thus cut was laminated onto both sides of the inner layer substrate using a batch-type vacuum pressure laminator (Nikko Materials Co., Ltd., two-stage build-up laminator "CVP700") so that the resin composition layer was in contact with the inner layer substrate. This lamination was performed by reducing the pressure for 30 seconds to 13 hPa or less, and then heating at 120°C and a pressure of 10 kgf / cm. 2 Then, the adhesive was applied at 120°C and a pressure of 14 kgf / cm for 30 seconds. 2 The laminate was then heat-pressed for 60 seconds at 100° C. Due to the lamination and heat-pressing, a part of the resin composition layer oozed out from the gap between the inner layer substrate and the support, forming a bleed-out portion.

[0186] (3) Thermal curing of the resin composition layer: The inner layer substrate laminated with resin sheet A was then placed in an oven at 130°C and heated for 30 minutes, and then transferred to an oven at 170°C and heated for 30 minutes to thermally cure the resin composition layer and form an insulating layer. The support was then peeled off to obtain cured substrate A having the insulating layer, inner layer substrate, and insulating layer in this order.

[0187] (4) Roughening treatment: A desmear treatment as a roughening treatment was performed on the cured substrate A. The desmear treatment was the following wet desmear treatment.

[0188] Cured Substrate A was immersed in a swelling solution (Atotech Japan's "Swelling Dip Securigant P," an aqueous solution of diethylene glycol monobutyl ether and sodium hydroxide) at 60°C for 5 minutes. It was then immersed in an oxidizing solution (Atotech Japan's "Concentrate Compact CP," an aqueous solution of approximately 6% potassium permanganate and 4% sodium hydroxide) at 80°C for 20 minutes. It was then immersed in a neutralizing solution (Atotech Japan's "Reduction Solution Securigant P," an aqueous sulfuric acid solution) at 40°C for 5 minutes. It was then dried at 80°C for 15 minutes.

[0189] (5) Formation of the conductor layer: A conductor layer was formed on the roughened surface (roughened surface) of the insulating layer using a semi-additive process. Specifically, the roughened cured substrate A was immersed in an electroless plating solution containing PdCl2 at 40°C for 5 minutes. The cured substrate A was then immersed in an electroless copper plating solution at 25°C for 20 minutes to form an electroless plated layer. Next, the cured substrate A was heated at 150°C for 30 minutes for annealing, after which an etching resist was formed on the electroless plated layer and a pattern was formed by etching. Subsequently, copper sulfate electroplating was performed to form an electrolytic plated layer on the electroless plated layer, resulting in a conductor layer with a thickness of 25 μm, including the electroless plated layer and the electrolytic plated layer. The substrate was then annealed at 190°C for 60 minutes to obtain an evaluation substrate.

[0190] The bleed-out portion formed at the end of the insulating layer of the evaluation substrate was visually observed to check for the presence or absence of swelling in the bleed-out portion.

[0191] <Dielectric loss tangent measurement test> The resin sheet A obtained in each of the Examples, Comparative Examples, and Reference Examples was heated in an oven at 190°C for 90 minutes to cure the resin composition layer. The support was then peeled off to obtain a cured resin composition layer. The cured layer was cut into a length of 80 mm and a width of 2 mm to obtain a cured layer for evaluation.

[0192] For each cured material layer for evaluation, the dielectric loss tangent (Df value) was measured by the cavity resonance perturbation method using a measuring device (Agilent Technologies "HP8362B") at a measurement frequency of 5.8 GHz and a measurement temperature of 23°C. Measurement was performed on two cured material layers for evaluation, and the average was calculated.

[0193] <Measurement test of average coefficient of thermal expansion (CTE)> The resin sheet A obtained in each of the Examples, Comparative Examples, and Reference Examples was heated in an oven at 190°C for 90 minutes to cure the resin composition layer. The support was then peeled off to obtain a cured resin composition layer. This cured layer was cut into a length of 20 mm and a width of 6 mm to obtain a cured layer for evaluation.

[0194] Each cured material layer for evaluation was subjected to thermomechanical analysis using a TMA device (thermomechanical analyzer, manufactured by Rigaku Corporation) at a temperature increase rate of 5°C / min from 25°C to 250°C to measure the average coefficient of linear thermal expansion CTE [ppm / °C] in the range from 25°C to 150°C. The same cured material layer for evaluation was measured twice, and the second value was recorded.

[0195] <Minimum melt viscosity measurement test> A portion of the resin composition layer was peeled off from the resin sheet A obtained in each of the Examples, Comparative Examples, and Reference Examples to prepare 1 g of a sample resin composition. The melt viscosity of this sample resin composition was measured using a dynamic viscoelasticity measuring device (Rheosol-G3000, manufactured by UBM). Specifically, using parallel plates with a diameter of 18 mm, the temperature was raised from an initial temperature of 60°C to 200°C at a heating rate of 5°C / min. The dynamic viscoelasticity was measured under the following measurement conditions: measurement interval temperature 2.5°C, frequency 1 Hz, and strain 5°C, and the minimum melt viscosity (poise) was calculated. The measured minimum melt viscosity was evaluated according to the following criteria. "Excellent": 3000 poise or less. "Poor": Over 3000 poise.

[0196] <Mass loss rate evaluation test> The resin sheet A obtained in each of the Examples, Comparative Examples, and Reference Examples was laminated with a polyimide film (UBE's "UPILEX") to obtain an intermediate laminate having a layer structure of support / resin composition layer / polyimide film. This intermediate laminate was placed in a 130°C oven and heated for 30 minutes, then transferred to a 170°C oven and heated for 30 minutes to thermally cure the resin composition layer. The support and polyimide film were then peeled off to obtain a test layer. Since the resin composition layer was cured by heating at 130°C for 30 minutes and 170°C for 30 minutes, the test layer contained a semi-cured cured product layer of the resin composition layer. The mass loss rate of the obtained test layer was measured using a thermogravimetric differential thermal analyzer (TG-DTA: Hitachi High-Tech's "STA200") when the temperature was maintained at 200°C for 90 minutes.

[0197] <Result> The results of the above-mentioned Examples, Comparative Examples and Reference Examples are shown in Tables 1 and 2 below.

[0198] [Table 1]

[0199] [Table 2] [Explanation of symbols]

[0200] 100 Inner layer board 200 Resin Sheet 210 Resin composition layer 220 Support 230 Bleed-out portion (part of the resin composition layer) 300 Gap

Claims

1. A resin sheet comprising a support and a resin composition layer formed on the support; the resin composition layer contains (A) a liquid resin, (B) an active ester-based resin, and (C) an inorganic filler; A resin sheet in which, when an evaluation test is conducted in which a test layer obtained by heating a resin composition layer on a support at 130°C for 30 minutes and 170°C for 30 minutes is heated at 200°C for 90 minutes, the mass loss rate of the test layer due to heating at 200°C for 90 minutes is 5.5% or less.

2. The evaluation test laminating the resin sheet and the polyimide film so that the resin composition layer and the polyimide film are in contact with each other; The resin composition layer is heated at 130°C for 30 minutes and 170°C for 30 minutes, and the support and the polyimide film are peeled off to obtain a test layer; and Heating the test layer at 200°C for 90 minutes; The resin sheet according to claim 1 , comprising the above in this order.

3. The resin sheet according to claim 1 , wherein the amount of the liquid resin (A) is 1% by mass or more and 25% by mass or less relative to 100% by mass of the resin component in the resin composition layer.

4. The resin sheet according to claim 1, wherein the amount of the inorganic filler (C) is 65% by mass or more relative to 100% by mass of the nonvolatile components in the resin composition layer.

5. 2. The resin sheet according to claim 1, wherein the cured product layer obtained by heating the resin composition layer at 190°C for 90 minutes has an average linear thermal expansion coefficient in the temperature range of 25°C to 150°C of less than 20 ppm / °C.

6. The resin sheet according to claim 1, wherein the cured product layer obtained by heating the resin composition layer at 190°C for 90 minutes has a dielectric loss tangent of less than 0.0030.

7. The resin sheet according to claim 1 , wherein the resin composition layer has a minimum melt viscosity of 3,000 poise or less.

8. The resin sheet according to claim 1 , wherein the liquid resin (A) is a liquid curable resin.

9. A circuit board comprising a cured layer obtained by curing a resin composition layer of the resin sheet according to any one of claims 1 to 8.

10. a step of laminating an inner layer substrate and the resin sheet according to any one of claims 1 to 8 so that the inner layer substrate and the resin composition layer are in contact with each other; and curing the resin composition layer; A method for manufacturing a circuit board, wherein the step of laminating an inner layer substrate and a resin sheet includes allowing a portion of a resin composition layer to seep out from a gap between the inner layer substrate and the support.

11. A semiconductor device comprising the circuit board according to claim 9.

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