Insulating resin composition and circuit board

Abstract

The present invention provides an insulating resin composition which has excellent thermal conductivity and excellent heat resistance and which can be highly filled with a thermally conductive filler, and a circuit board which uses said insulating resin composition. A circuit board according to the present embodiment comprises a first metal layer, an insulating layer, and a second metal layer in this order, wherein one of the first metal layer and the second metal layer is a metal substrate, and the other is a circuit. The insulating layer includes: a porous insulating layer containing a first polymerization catalyst and an epoxy resin homopolymer including a mesogenic backbone; and an adhesive containing a thermosetting resin and a second polymerization catalyst, wherein the adhesive infiltrates into the porous insulating layer, a part of the adhesive which has infiltrated discontinuously forms an adhesive layer between the first metal layer and the porous insulating layer, the mass ratio of the epoxy resin homopolymer including a mesogenic backbone and contained in the insulating layer to the sum of resin components contained in the porous insulating layer and the adhesive is 80 mass% or more, and the first polymerization catalyst and the second polymerization catalyst are basic polymerization catalysts.

Description

Insulating Resin Composition and Circuit Board

[0001] The present invention relates to an insulating resin composition and a circuit board.

[0002] Conventionally, as a substrate on which an integrated circuit or the like is mounted, a circuit board formed by laminating a circuit on a metal substrate via an insulating layer has been used (see, for example, Patent Documents 1 and 2). The insulating layer has a role of ensuring the breakdown voltage between the metal substrate and the circuit. Further, the insulating layer usually contains a thermal conductivity filler, and this filler plays a role of ensuring thermal conductivity and dissipating heat generated in the heat generating element on the circuit.

[0003] With the progress of miniaturization, large capacity, and high performance of electronic devices using semiconductors, the amount of heat generated from electronic devices mounted at high density is increasing more and more. Therefore, the above-described circuit board is required to have high heat dissipation characteristics (thermal conductivity). When the thermal conductivity filler is highly filled in the insulating layer to increase the thermal conductivity and reduce the thermal resistance, the flexibility of the insulating layer is lost as the filling rate increases, and it becomes easy to crack and difficult to handle. In particular, boron nitride-based fillers having high thermal conductivity have poor resin affinity, and peeling is likely to occur at the filler / resin interface. Such interface peeling can cause a decrease in heat resistance in the circuit board. That is, it can cause deterioration of thermal conductivity and insulation properties by high-temperature treatment at about 300° C. during mounting of semiconductor elements, for example. Further, when the filling rate of the boron nitride-based filler increases, unevenness is likely to occur during coating of the coating liquid for forming the insulating layer due to the poor affinity with the resin as described above, and there may also occur a problem that the performance as a circuit board becomes unstable.

[0004] Japanese Patent No. 6993540 International Publication No. 2015 / 141797

[0005] Patent Document 1 discloses a new adhesion technique between these layers in order to ensure high thermal conductivity while increasing the adhesion strength between the metal substrate and the insulating layer and between the insulating layer and the circuit. Here, a general epoxy resin is used as the resin component used for the insulating layer. In order to meet the high demand for high thermal conductivity in recent years, development of a resin composition capable of providing an insulating layer having high thermal conductivity and high heat resistance suitable for the new adhesion technique is required.

[0006] Patent Document 2 discloses a resin composition containing two epoxy compounds having a mesogenic structure and a phenol novolac resin, which is a polyaddition-type curing agent, with the aim of providing a resin composition that is flexible and easy to handle before curing, and has excellent adhesion and thermal conductivity at high temperatures after curing (claims 1, 4, paragraph 0062, [Examples], etc.). However, when the present inventors used the resin composition disclosed in Patent Document 2 instead of a conventional epoxy resin in the adhesion technology disclosed in Patent Document 1, they found that the desired improvement in thermal conductivity and heat resistance could not be obtained, and furthermore, the above-mentioned problem caused by high-filling with thermally conductive filler could not be resolved.

[0007] The present invention aims to provide an insulating resin composition that is excellent in thermal conductivity and heat resistance, and that can be highly filled with a thermally conductive filler, and a circuit board using the same.

[0008] According to one aspect of the present invention, a circuit board is provided comprising a first metal layer, an insulating layer, and a second metal layer in this order, wherein one of the first metal layer and the second metal layer is a metal substrate and the other is a circuit, the insulating layer comprises a porous insulating layer containing an epoxy resin homopolymer containing a mesogenic skeleton and a first polymerization catalyst, and an adhesive containing a thermosetting resin and a second polymerization catalyst, the adhesive penetrates the porous insulating layer, a portion of the penetrated adhesive forms a discontinuous adhesive layer between the first metal layer and the porous insulating layer, the mass ratio of the epoxy resin homopolymer containing a mesogenic skeleton contained in the insulating layer to the total resin components contained in the porous insulating layer and the adhesive is 80% by mass or more, and the first polymerization catalyst and the second polymerization catalyst are basic polymerization catalysts.

[0009] According to another aspect of the present invention, a circuit board is provided in which a further portion of the adhesive that has penetrated the porous insulating layer forms a discontinuous adhesive layer between the second metal layer and the porous insulating layer.

[0010] According to yet another aspect of the present invention, the epoxy resin homopolymer provides a circuit board relating to any of the above aspects that does not contain components derived from polyaddition curing agents.

[0011] According to yet another aspect of the present invention, a circuit board is provided which further contains a thermally conductive filler in the insulating layer, wherein the volume ratio of the thermally conductive filler to the insulating layer is 70% or more.

[0012] According to yet another aspect of the present invention, a circuit board relating to any of the above aspects is provided, wherein the first polymerization catalyst and the second polymerization catalyst are the same basic polymerization catalyst.

[0013] According to yet another aspect of the present invention, a circuit board is provided in which the basic polymerization catalyst is an imidazole compound having a cyanide group.

[0014] According to yet another aspect of the present invention, the epoxy resin homopolymer is an epoxy resin homopolymer comprising a crosslinked product of a first epoxy monomer containing a mesogenic skeleton that is solid at room temperature and a second epoxy monomer containing a mesogenic skeleton that is liquid at room temperature, and a circuit board according to any of the above aspects is provided, wherein the blending mass ratio of the first epoxy monomer to the second epoxy monomer, which is the first epoxy monomer / second epoxy monomer, is in the range of 0.25 to 3.

[0015] According to yet another aspect of the present invention, a circuit board is provided relating to any of the above aspects, wherein the epoxy resin homopolymer containing the mesogenic skeleton has a π-π stacking structure in its molecular structure.

[0016] According to yet another aspect of the present invention, a circuit board relating to either of the above aspects is provided, wherein the mesogenic skeleton is a naphthalene skeleton or a biphenyl skeleton.

[0017] According to yet another aspect of the present invention, a circuit board according to any of the above aspects is provided, wherein the adhesive contains an epoxy resin homopolymer containing the mesogenic skeleton as the thermosetting resin.

[0018] According to yet another aspect of the present invention, an insulating resin composition is provided which contains a first epoxy monomer containing a mesogenic skeleton, a second epoxy monomer containing a mesogenic skeleton, and a basic polymerization catalyst, and which does not contain a polyaddition curing agent.

[0019] According to yet another aspect of the present invention, an insulating resin composition is provided in which the first epoxy monomer is solid at room temperature, the second epoxy monomer is liquid at room temperature, and the blending mass ratio of the first epoxy monomer to the second epoxy monomer, which is the first epoxy monomer / second epoxy monomer ratio, is in the range of 0.33 to 2.0.

[0020] According to yet another aspect of the present invention, an insulating resin composition is provided relating to either of the above aspects, wherein the mesogenic skeleton is a naphthalene skeleton or a biphenyl skeleton.

[0021] According to yet another aspect of the present invention, an insulating resin composition according to any of the above aspects is provided, further containing a thermally conductive filler.

[0022] According to yet another aspect of the present invention, an insulating resin composition is provided relating to any of the above aspects, wherein the basic polymerization catalyst is an imidazole compound having a cyanide group.

[0023] In yet another aspect of the present invention, an insulating resin composition relating to any of the above aspects is provided for interlayer insulation of a circuit board.

[0024] According to yet another aspect of the present invention, a method for producing an insulating resin composition according to any of the above aspects is provided, comprising mixing a first epoxy monomer containing a mesogenic skeleton, a second epoxy monomer containing a mesogenic skeleton, and a basic polymerization catalyst, and without using a polyaddition curing agent.

[0025] According to the present invention, it is possible to provide an insulating resin composition that has excellent thermal conductivity and heat resistance, and can be highly filled with a thermally conductive filler, and a circuit board using the same.

[0026] Figure 1 is a schematic partial cross-sectional view showing an example of a circuit board according to the first embodiment of the present invention. Figure 2 is a schematic partial cross-sectional view showing a modified circuit board. Figure 3 is a schematic partial cross-sectional view showing another modified circuit board. Figure 4 is a process diagram illustrating one step included in the method for manufacturing a circuit board according to the first embodiment of the present invention. Figure 5 is a process diagram illustrating one step included in the method for manufacturing a circuit board according to the first embodiment of the present invention. Figure 6 is a process diagram illustrating one step included in the method for manufacturing a circuit board according to the first embodiment of the present invention. Figure 7 is a process diagram illustrating one step included in the method for manufacturing a circuit board according to the first embodiment of the present invention. Figure 8 is a process diagram illustrating one step included in the method for manufacturing a circuit board according to the first embodiment of the present invention. Figure 9 is a process diagram illustrating one step included in the method for manufacturing a circuit board according to the first embodiment of the present invention. Figure 10 is an explanatory diagram showing images obtained in an evaluation test of the example. Figure 11 is an explanatory diagram showing images obtained in an evaluation test of the comparative example. Figure 12 is a process diagram illustrating one step included in the method for manufacturing an insulating layer for physical property evaluation used in the example and comparative example. Figure 13 is a process diagram illustrating one step included in the method for manufacturing an insulating layer for physical property evaluation used in the example and comparative example. Figure 14 is a process diagram illustrating one step included in the method for manufacturing the insulating layer for physical property evaluation used in the examples and comparative examples. Figure 15 is a process diagram illustrating one step included in the method for manufacturing the insulating layer for physical property evaluation used in the examples and comparative examples.

[0027] The configuration of a circuit board according to the first embodiment of the present invention will be described below with reference to the drawings. In the drawings referred to below, elements having similar or identical functions are denoted by the same reference numerals, and redundant explanations are omitted. Also, the drawings are schematic, and some configurations may be omitted for the sake of explanation. Furthermore, the relationship between thickness and planar dimensions, the ratio of the thickness of each layer, etc., may differ from those in reality.

[0028] [Circuit Board] Figure 1 is a schematic partial cross-sectional view showing an example of a circuit board according to the first embodiment of the present invention. The circuit board 1A shown in Figure 1 comprises a metal substrate 10, an insulating layer 12, and a circuit 11. The insulating layer 12 includes a porous insulating layer 12a and an adhesive that has penetrated the porous insulating layer 12a, and a portion of the penetrating adhesive forms a discontinuous adhesive layer 12b between the metal substrate 10 and the porous insulating layer 12a. In Figure 1, adhesives that have penetrated the porous insulating layer 12a but do not form an adhesive layer 12b are omitted from the description.

[0029] <Metal Substrate> The metal substrate 10 is a metal layer that forms the base of the circuit board 1A, and is made of, for example, a single metal or an alloy. Examples of materials for the metal substrate 10 include aluminum, iron, copper, aluminum alloy, copper alloy, stainless steel, etc. The metal substrate 10 may further contain nonmetals such as carbon. For example, the metal substrate 10 may contain aluminum compounded with carbon. The metal substrate 10 may also have a single-layer structure or a multi-layer structure. The thickness of the metal substrate 10 is in the range of 0.1 to 5 mm in one example, and in another example, in the range of 0.5 to 3 mm. The metal substrate 10 is a substantially plate-shaped member here, but is not limited to this shape. The metal substrate 10 may be, for example, a heat sink with heat dissipation fins.

[0030] <Circuit> Circuit 11 is obtained by processing a metal layer, such as a metal conductor foil, into a circuit. Such a metal layer (hereinafter also referred to as the "circuit metal layer") is made of, for example, a single metal or an alloy. Examples of materials for the circuit metal layer include copper or aluminum. The thickness of the circuit metal layer is in the range of 0.1 to 2.5 mm in one example, and in the range of 0.5 to 2.0 mm in another example. Circuit processing of the circuit metal layer can be obtained, for example, by forming a mask pattern on a metal layer such as a metal conductor foil and removing the exposed parts of the metal layer by etching. Hereinafter, the metal substrate 10 and the circuit 11 (or circuit metal layer) will not be distinguished, and both will be referred to as the "metal layer".

[0031] <Insulating Layer> The insulating layer 12 is interposed between the metal substrate 10 and the circuit 11, and transmits the heat transferred from the heating element on the circuit 11 to the circuit 11 to the metal substrate 10. The thickness of the insulating layer 12 is in the range of 80 to 180 μm in one example, and in the range of 100 to 150 μm in other examples.

[0032] The insulating layer 12 contains a porous insulating layer 12a and an adhesive. The adhesive penetrates the porous insulating layer 12a, and a portion of the penetrating adhesive forms a discontinuous adhesive layer 12b between the metal substrate 10 and the porous insulating layer 12a. That is, in the circuit board 1A, the metal substrate 10 and the insulating layer 12 are bonded in part by the adhesive layer 12b, and in other parts the metal substrate layer 10 and the insulating layer 12 (porous insulating layer 12a) are in contact and bonded by the adhesive force of the resin component contained in the porous insulating layer 12a. The bonding structure between the insulating layer 12 and the metal layer formed by the adhesive that has penetrated the porous insulating layer 12a in this manner is sometimes called a "penetration bonding structure," and the bonding method is sometimes called a "penetration bonding method."

[0033] The porous insulating layer 12a is an insulating cured film formed using an insulating resin composition according to the second embodiment of the present invention, as described below, and has excellent thermal conductivity. In this way, the circuit board 1A has a penetration adhesive structure, and the interface between the metal substrate 10 and the insulating layer 12 is partially bonded by the adhesive layer 12b, while the other parts are in contact between the metal substrate 10 and the porous substrate layer 12a, thereby ensuring excellent thermal conductivity while increasing interlayer adhesion and suppressing delamination.

[0034] The porous insulating layer 12a contains an epoxy resin homopolymer containing a mesogenic skeleton (hereinafter also referred to as "mesogenic epoxy homopolymer") and a basic polymerization catalyst (first polymerization catalyst). Here, the mesogenic epoxy homopolymer refers to a polymer composed only of one or more epoxy monomer-derived components containing a mesogenic skeleton, and the polymer chain does not contain other monomer-derived components. Therefore, the mesogenic epoxy homopolymer does not contain polyaddition-type curing agent-derived components such as phenol novolac resin used in Patent Document 2, amine-based curing agents, acid anhydride-based curing agents, or mercaptan-based curing agents. This will be explained further.

[0035] Patent Document 2 describes that by forming a cured product using a mesogen-containing epoxy monomer and a phenol novolac resin, which is a polyaddition-type curing agent, it is easy to obtain a cured product with a highly regular structure and improve thermal conductivity. However, the present inventors have found that when using a mesogen-containing epoxy monomer, the thermal conductivity decreases when components derived from other compounds are incorporated into the polymer chain. Therefore, by not using a polyaddition-type curing agent (crosslinking initiator) as a curing agent (crosslinking initiator) for the mesogen-containing epoxy monomer, and instead using a polymerization catalyst to obtain a mesogen-containing epoxy homopolymer, the thermal conductivity is dramatically improved, and furthermore, the heat resistance is also improved.

[0036] The reason is not entirely clear, but it is presumed that the incorporation of components derived from other compounds into the polymer chain hinders the orientation of the resin's mesogenic skeleton. Here, "polymerization catalyst" refers to a crosslinking initiator that may be added to the ends of the polymer chain but cannot be incorporated into the polymer chain itself, while "polyaddition curing agent" refers to a crosslinking initiator that is incorporated into the polymer chain, as described above.

[0037] The adhesive contains a thermosetting resin and a basic polymerization catalyst (second polymerization catalyst). Thus, in the circuit board 1A according to this embodiment, both the first polymerization catalyst contained in the porous insulating layer 12a and the second polymerization catalyst contained in the adhesive are basic compounds and belong to the same system. This is technically closely related to the fact that the adhesive penetrates the porous insulating layer 12a, as will be explained below.

[0038] For example, boron trifluoride monoethylamine is a polymerization catalyst commonly used in the curing reaction of thermosetting resins such as epoxy resins. Although boron trifluoride monoethylamine is an acidic compound, it does not mix well with basic imidazole compounds. For this reason, the inventors have confirmed that when a basic polymerization catalyst is used as the polymerization catalyst for the porous insulating layer 12a that is permeated by the adhesive, and an acidic polymerization catalyst is used as the polymerization catalyst for the permeating adhesive, the basic catalyst does not function as a polymerization catalyst. Specifically, this results in curing failure, for example, an extreme drop in the glass transition temperature (for example, from 200°C to 150°C). Alternatively, the acidic polymerization catalyst acts as a corrosive component, and in environments where voltage is applied for a long period of time under high temperature and humid conditions, the circuit board cannot maintain the insulation properties required.

[0039] As a result of further diligent research by the inventors, it was found that it is more preferable for the first polymerization catalyst and the second polymerization catalyst to be the same compound, and even more preferable for them to be the same compound and an imidazole compound having a cyanide group.

[0040] Mesogen-containing epoxy homopolymers enhance thermal conductivity and maintain a low coefficient of linear expansion even at high temperatures by exhibiting liquid crystalline properties through π-π stacking of the mesogen skeleton. When the coefficient of linear expansion is kept low, interfacial delamination with thermally conductive fillers is less likely to occur at high temperatures, suppressing a decrease in thermal conductivity and dielectric strength. Examples of mesogen skeletons include naphthalene skeletons, biphenyl skeletons, phenylbenzoate skeletons, azobenzene skeletons, stilbene skeletons, cyclohexylbenzene skeletons, and their derivatives.

[0041] The adhesive may or may not contain a mesogen-containing epoxy homopolymer as a thermosetting resin, as described later.

[0042] In the insulating layer 12, the ratio of the mesogen-containing epoxy resin homopolymer to the total of the resin components contained in the porous insulating layer 12a and the adhesive (in other words, the total of the resin components contained in the insulating layer 12) is 80% by mass or more. When the adhesive contains a mesogen-containing epoxy homopolymer, this ratio means the ratio of the total of the mesogen-containing epoxy resin homopolymers contained in the porous insulating layer 12a and the adhesive to the total of the resin components contained in the insulating layer 12. If the ratio of the mesogen-containing epoxy homopolymer in the insulating layer 12 is less than 80% by mass, the desired thermal conductivity and heat resistance cannot be obtained. The ratio of the mesogen-containing epoxy homopolymer in the insulating layer 12 is preferably 85% by mass or more. The upper limit value of the ratio of the mesogen-containing epoxy homopolymer in the insulating layer 12 can be appropriately set in relation to the amount of the adhesive used, etc., and may be, for example, 97.6% by mass or less.

[0043] The insulating layer 12 preferably contains a thermal conductivity filler in a preferred form. By the insulating layer 12 containing a thermal conductivity filler, the thermal conductivity of the circuit board 1A is improved. When the insulating layer 12 contains a thermal conductivity filler, the ratio of the thermal conductivity filler in the insulating layer 12 is, according to one example, 70% by volume or more, and according to another example, 80% by volume or more. Generally, when the ratio of the thermal conductivity filler in the insulating layer is 70% by volume or more, the adhesive strength with the adjacent metal layer decreases, so it has been difficult to highly fill the thermal conductivity filler to 70% by volume or more. However, since the circuit board 1A according to the present embodiment has the penetration adhesion structure described above, it is possible to highly fill the thermal conductivity filler. Further, the insulating layer 12 (porous insulating layer 12a) has excellent affinity with thermal conductivity fillers such as boron nitride, as described later, and such characteristics also contribute to enabling high filling of the thermal conductivity filler. Each component contained in the porous insulating layer 12a will be described in detail again in the insulating resin composition described below.

[0044] (Insulating Resin Composition) The insulating resin composition according to the second embodiment of the present invention is suitably used for an interlayer insulating layer of a circuit board. A porous insulating layer 12a is formed using the insulating resin composition according to this embodiment.

[0045] The insulating resin composition according to this embodiment has a high affinity for a heat conductive filler, and thus high filling is possible. The insulating resin composition according to this embodiment not only has a high affinity for a heat conductive filler, but also hardly causes coating unevenness in a dry coating film even when highly filled. Further, the insulating resin composition according to this embodiment is excellent in flexibility and easy to handle in a dry coating film, and a cured product obtained by heat-treating this is excellent in heat conductivity, heat resistance, and adhesiveness.

[0046] The insulating resin composition according to this embodiment contains at least a mesogen-containing first epoxy monomer and a mesogen-containing second epoxy monomer as a mesogen skeleton-containing epoxy monomer (hereinafter also referred to as a "mesogen-containing epoxy monomer"), and further contains a basic polymerization catalyst. By heat-treating the insulating resin composition, the basic polymerization catalyst functions as a crosslinking initiator, and the mesogen-containing epoxy monomer crosslinks and cures. In this case, the basic polymerization catalyst is not incorporated into the polymer chain formed by the crosslinking of the mesogen-containing epoxy monomer.

[0047] On the other hand, the insulating resin composition according to this embodiment contains a basic polymerization catalyst as described above, and does not require the use of a polyaddition-type curing agent such as a phenolic curing agent such as a phenol novolak resin, an amine-based curing agent, an acid anhydride-based curing agent, or a mercaptan-based curing agent. Therefore, the cured product of the insulating resin composition (for example, the porous insulating layer 12a of the circuit board 1A) contains a mesogen-containing epoxy homopolymer that does not contain components other than the components derived from the mesogen-containing epoxy monomer in the polymer chain. As a result, surprisingly, the heat conductivity and heat resistance in the cured product have been dramatically improved.

[0048] The epoxy monomer insulating resin composition containing a mesogen skeleton contains at least a mesogen-containing first epoxy monomer and a mesogen-containing second epoxy monomer as mesogen-containing epoxy monomers. From the viewpoint of flexibility and ease of handling in the dried coating film, it is preferable that the mesogen-containing first epoxy monomer is solid at room temperature (25°C) and the mesogen-containing second epoxy monomer is liquid at room temperature (25°C). Here, the mesogen-containing epoxy monomer that is liquid at room temperature (25°C) also includes compounds that are solid at 25°C but liquefy upon heating (e.g., 50°C) and can then remain liquid for a while, for example, HP-4032D (both manufactured by DIC Corporation) used in the [Examples] below. In this case, the mesogen-containing epoxy monomer may liquefy upon heating when mixed with an imidazole compound.

[0049] Examples of mesogenic skeletons include biphenyl skeletons, naphthalene skeletons, phenylbenzoate skeletons, azobenzene skeletons, stilbene skeletons, cyclohexylbenzene skeletons, and their derivatives. The mesogenic skeleton is, for example, a biphenyl skeleton or a naphthalene skeleton, or a derivative thereof.

[0050] A mesogen-containing first epoxy monomer that is solid at room temperature can be represented, for example, by the following general formula (I).

[0051] In the formula, M １ and M ２ Each of these independently represents a mesogenic skeleton, such as a biphenyl skeleton, naphthalene skeleton, phenylbenzoate skeleton, azobenzene skeleton, stilbene skeleton, cyclohexylbenzene skeleton, or a derivative thereof.

[0052] L represents a single bond or a divalent linking group. L is, for example, an alkylene group having 1 to 7 carbon atoms, preferably an alkylene group having 1 to 5 carbon atoms, more preferably an alkylene group having 1 to 3 carbon atoms, and even more preferably a methylene group.

[0053] A mesogen-containing second epoxy monomer that is liquid at room temperature can be represented, for example, by the following general formula (II).

[0054] In the formula, M represents a mesogenic skeleton, such as a biphenyl skeleton, naphthalene skeleton, phenylbenzoate skeleton, azobenzene skeleton, stilbene skeleton, cyclohexylbenzene skeleton, or a derivative thereof.

[0055] Commercially available epoxy monomers containing a mesogenic skeleton can also be used. As a first mesogenic epoxy monomer represented by general formula (I), for example, "EPICLON HP-4700" (manufactured by DIC Corporation) can be used. As a second mesogenic epoxy monomer represented by general formula (II), for example, "EPICLON HP-4032D" (manufactured by DIC Corporation) can be used.

[0056] The blending mass ratio (mesogen-containing first epoxy monomer / mesogen-containing second epoxy monomer) of a mesogen-containing first epoxy monomer that is solid at room temperature and a mesogen-containing second epoxy monomer that is liquid at room temperature is in the range of 0.25 to 3 in one example and in the range of 0.33 to 2 in another example.

[0057] The total content of mesogen-containing epoxy monomers in the insulating resin composition may be in the range of 0.1 to 2.5% by mass, or in the range of 0.5 to 2.0% by mass, relative to the total solid content in the insulating resin composition, from the viewpoint of thermal conductivity, heat resistance, etc., as in one example. Furthermore, when the insulating resin composition is used to form the porous insulating layer 12a of the circuit board 1A, as described above, the amount of mesogen-containing epoxy monomer used is appropriately determined so that the mass ratio of the mesogen-containing epoxy homopolymer to the total resin components contained in the porous insulating layer 12a and the adhesive is 80% by mass or more.

[0058] The basic polymerization catalyst insulating resin composition does not contain a polyaddition curing agent as a crosslinking initiator, but contains a basic polymerization catalyst (first polymerization catalyst). As described above, in order to fully exert its function as a crosslinking initiator and to suppress curing defects and a decrease in moisture resistance, a basic polymerization catalyst is also used as a crosslinking initiator (second polymerization catalyst) in the adhesive. In a preferred embodiment, the same basic polymerization catalyst is selected and used as both the first and second polymerization catalysts.

[0059] Examples of basic polymerization catalysts include imidazoles, amines, diazabicyclo compounds, phosphines, and phosphoniums. Among imidazoles, imidazole compounds having a cyanide group are preferred, and in particular, by using the same imidazole compound having a cyanide group as the first basic polymerization catalyst contained in the insulating resin composition and the second basic polymerization catalyst contained in the adhesive, moisture resistance is dramatically improved. Examples of imidazole compounds having a cyanide group include 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-isopropylimidazole, 1-cyanoethyl-2-phenylimidazole, and 1-cyanoethyl-2-arylimidazole compounds having a cyanoethoxymethyl group at the 4th and / or 5th position, such as 1-cyanoethyl-2-phenyl-5-cyanoethoxymethylimidazole, as well as modified products of these various imidazole compounds.

[0060] The content of the basic polymerization catalyst in the insulating resin composition may be in the range of 1 to 4% by mass, or in the range of 2 to 3% by mass, relative to the total solid content of the insulating resin composition, from the viewpoint of thermal conductivity, heat resistance, etc. If the content of the basic polymerization catalyst is low, the heat pressing time when heat pressing the laminate in the circuit board manufacturing method described later may be prolonged. On the other hand, if the content of the basic polymerization catalyst is high, the moisture resistance and durability required to maintain the insulation properties of the circuit board may decrease.

[0061] The thermally conductive filler insulating resin composition further contains a thermally conductive filler in a preferred form. The thermal conductivity of the porous insulating layer 12a is improved by containing the thermally conductive filler. Examples of thermally conductive fillers include silica, alumina, aluminum nitride, boron nitride, silicon carbide, and silicon nitride. The shape, particle size, and particle size distribution of the thermally conductive filler can be determined and blended as appropriate. The thermally conductive filler may be used alone or in combination of two or more types.

[0062] As described above, the insulating resin composition according to this embodiment has a high affinity for thermally conductive fillers, thus enabling high-density filling of thermally conductive fillers. Furthermore, when the insulating resin composition is used as a material for forming the porous insulating layer 12a of the circuit board 1A having the penetration adhesive structure described above, even higher filling is possible. The content of thermally conductive fillers in the insulating resin composition is appropriately set, as described above, so that the volume ratio of thermally conductive fillers in the insulating layer 12 falls within the above range.

[0063] The organic solvent insulating resin composition may contain an organic solvent as needed. Examples of organic solvents include cyclohexanone, methyl ethyl ketone (MEK), acetone, and toluene. The organic solvent may be used alone or in combination of two or more.

[0064] Other components: The insulating resin composition may contain other components as needed in addition to the above components. Examples of other components include dispersants, ion scavenging agents, silane coupling agents, etc.

[0065] As a method for producing an insulating resin composition, conventional methods for producing resin compositions can be used. For example, a homogeneous insulating resin composition can be obtained by dissolving or dispersing each mesogen-containing epoxy monomer, a basic polymerization catalyst, and a thermally conductive filler used as needed in a suitable organic solvent, and then mixing them to form a slurry. As a mixing method, a conventional stirrer, disperser, three-roll mill, ball mill, or other disperser can be appropriately combined.

[0066] (Adhesive) The adhesive contains a thermosetting resin and a basic polymerization catalyst as a second polymerization catalyst. The adhesive is used to form the aforementioned penetrating adhesive structure on the circuit board 1A, and a portion of the adhesive that penetrates the porous insulating layer 12a forms a discontinuously extended adhesive layer 12b. For this reason, the adhesive is preferably a viscous liquid at room temperature. In one example, the viscosity of the adhesive at room temperature (25°C) is in the range of 1000 to 7000 cp, and in another example, it is in the range of 3000 to 4000 cp.

[0067] • Thermosetting resins: Any thermosetting resin can be used that is solid at room temperature (25°C) but becomes liquid when heated to, for example, 50°C and exhibits adhesive properties upon curing. From the viewpoint of workability, thermosetting resins that are liquid at room temperature (25°C) and exhibit adhesive properties upon curing are preferred.

[0068] As such a thermosetting resin, epoxy resins that are liquid at 50°C (hereinafter referred to as "liquid epoxy resins") can be suitably used. Examples of liquid epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, and naphthalene type epoxy resins. Examples of commercially available products include bisphenol A type epoxy resins such as EPICLON® 840, 840-S, 850, 850-S, and EXA-850CRP (all manufactured by DIC Corporation), bisphenol F type epoxy resins such as EPICLON 830, 830-S, and EXA-830CRP (all manufactured by DIC Corporation), and naphthalene type epoxy resins such as EPICLON HP-4032 and HP-4032D (both manufactured by DIC Corporation).

[0069] Among these commercially available products, for example, EXA-850CRP (manufactured by DIC Corporation), a bisphenol A type epoxy resin, is liquid at room temperature (25°C) and offers excellent workability. HP-4032D (manufactured by DIC Corporation), a naphthalene type epoxy resin, is solid at room temperature and becomes liquid at 50°C, requiring heating before use. However, it has higher heat resistance than bisphenol A type epoxy resin, resulting in superior adhesion at high temperatures. Liquid epoxy resins should be selected and used depending on the situation.

[0070] The adhesive may contain the above-mentioned mesogen-containing epoxy homopolymer as a thermosetting resin.

[0071] ・Basic polymerization catalyst Specific examples of the basic polymerization catalyst (second polymerization catalyst) are the same as the specific examples described with respect to the first polymerization catalyst in the insulating resin composition. As mentioned above, it is preferable that the first polymerization catalyst and the second polymerization catalyst are the same compound, and it is more preferable that they are the same compound and are an imidazole compound having a cyanide group.

[0072] The content of the basic polymerization catalyst in the adhesive may be in the range of 2 to 10 parts by mass per 100 parts by mass of thermosetting resin, or in the range of 3 to 5 parts by mass per 100 parts by mass of thermosetting resin, from the viewpoint of thermal conductivity, heat resistance, etc.

[0073] [Modification 1] Next, a modification of the circuit board according to the first embodiment of the present invention will be described with reference to Figure 2. Figure 2 is a schematic partial cross-sectional view showing a circuit board according to a modification of the circuit board 1A shown in Figure 1.

[0074] The circuit board 1B shown in Figure 2 comprises a metal substrate 10, an insulating layer 12, and a circuit 11, and the insulating layer 12 includes a porous insulating layer 12a and adhesive that has permeated the porous insulating layer 12a, similar to the circuit board 1A shown in Figure 1. However, in circuit board 1A, a portion of the permeated adhesive forms a discontinuous adhesive layer 12b between the metal substrate 10 and the porous insulating layer 12a, whereas in circuit board 1B, a portion of the permeated adhesive forms a discontinuous adhesive layer 12b between the circuit 11 and the porous insulating layer 12a. Note that, as in Figure 1, in Figure 2 as well, adhesive that has permeated the porous insulating layer 12a but has not formed an adhesive layer 12b is omitted from the description.

[0075] Circuit board 1A and circuit board 1B are identical in that they both have the aforementioned penetrating adhesive structure formed by a discontinuously extending adhesive layer 12b, which is formed by a portion of the adhesive that has penetrated the porous insulating layer 12a. Therefore, the basic effects achieved by both circuit boards are the same.

[0076] [Modification Example 2] Another modification example of the circuit board according to the first embodiment of the present invention will be described with reference to FIG. 3. FIG. 3 is a partial cross-sectional view schematically showing a circuit board according to another modification example of the circuit board 1A shown in FIG. 1.

[0077] The circuit board 1C shown in FIG. 3 includes a metal substrate 10, an insulating layer 12, and a circuit 11. The insulating layer 12 includes a porous insulating layer 12a and an adhesive infiltrated into the porous insulating layer 12a, which is the same as the circuit board 1A shown in FIG. 1. However, in the circuit board 1A, a part of the infiltrated adhesive discontinuously forms an adhesive layer 12b between the metal substrate 10 and the porous insulating layer 12a, while there is no adhesive layer 12b between the circuit 11 and the porous insulating layer 12a. In contrast, in the circuit board 1C, a part of the adhesive infiltrated into the porous insulating layer 12a discontinuously forms an adhesive layer 12b between the metal substrate 10 and the porous insulating layer 12a, and furthermore, a further part of the adhesive infiltrated into the porous insulating layer 12a discontinuously forms an adhesive layer 12b between the circuit 11 and the porous insulating layer 12a, which is different. Also in FIG. 3, similar to FIG. 1, the description of the adhesive that does not form the adhesive layer 12b among the adhesives infiltrated into the porous insulating layer 12a is omitted.

[0078] The circuit board 1A and the circuit board 1C do not differ in that the penetration adhesion structure described above is formed by the discontinuously extending adhesive layer 12b formed by a part of the adhesive infiltrated into the porous insulating layer 12a. Therefore, the basic effects achieved by both circuit boards are the same.

[0079] [Manufacturing Method of Circuit Board] Hereinafter, an example of the manufacturing method of the circuit board according to the first embodiment of the present invention will be described with reference to FIGS. 4 to 9. FIGS. 4 to 9 are process diagrams for explaining one process included in the manufacturing method of the circuit board 1C shown in FIG. 3, and the respective processes are performed in the order of the figure numbers.

[0080] In the manufacturing of the circuit board 1C, first, a dry resin sheet that will serve as a precursor for the porous insulating layer 12a is formed. This process will be explained with reference to Figure 4. Here, a support 20 is prepared first. As the support 20, olefin films such as polyethylene and polypropylene, fluororesin-based films, polyethylene terephthalate (PET) films, triacetylcellulose films, etc., can be used. Films to which release properties have been given with silicone resin or the like are preferably used. The thickness of the support 20 is in the range of 10 to 200 μm in one example, and in the range of 30 to 100 μm in another example.

[0081] An insulating resin composition according to the second embodiment is applied to one surface of the support 20 and dried to obtain an adhesive sheet having a dried resin sheet 112a. This dried resin sheet 112a is a porous dried resin sheet that serves as a precursor to the porous insulating layer 12a, and it is preferable that it is flexible enough not to crack when bent.

[0082] The coating and drying methods for the insulating resin composition can be appropriately selected from commonly used methods. Specifically, coating methods include the comma coater method, die coater method, and dip coating method. Drying methods include heating and drying under normal or reduced pressure, natural drying, and freeze-drying.

[0083] Next, a liquid adhesive is applied to the surface of the adhesive sheet facing the dry resin sheet 112a to obtain the adhesive coating film 112b shown in Figure 5. If the adhesive is solid at room temperature, it is heated to a liquid state before use. The method of applying the adhesive is appropriately selected from commonly used methods, similar to the method of applying the insulating resin composition.

[0084] As an adhesive coating 112b is formed on the dried resin sheet 112a in this manner, a portion of the adhesive contained in the adhesive coating 112b penetrates into the dried resin sheet 112a. However, Figure 5 is a schematic diagram to clearly explain the process of forming a penetrating adhesive structure, and in reality, the adhesive applied to the dried resin sheet 112a penetrates as soon as it reaches the surface of the dried resin sheet 112a, so an adhesive coating 112b is not actually formed. Furthermore, even if the dried resin sheet 112a is hard before the adhesive is applied, it becomes flexible and easier to handle after the adhesive is applied due to the penetration of the adhesive.

[0085] A metal substrate 10 is prepared. The laminate shown in Figure 5 obtained in the above process is placed on the metal substrate 10 so that the adhesive coating 112b faces the metal substrate 10, thereby obtaining the laminate shown in Figure 6. This is heated and pressurized (first heat press) to further advance the penetration of the adhesive and at the same time cure the adhesive and the dry resin sheet 112a. As described above, in reality the adhesive coating 112b is not formed, but the adhesive that has penetrated the dry resin sheet 112a due to the first heat press seeps out at the interface with the metal substrate 10 and hardens. As a result, as shown in Figure 7, a porous insulating layer 12a and a discontinuous adhesive layer 12b are formed, and the insulating layer 12 and the metal substrate 10 are joined. In the areas where the adhesive layer 12b is not present and the porous insulating layer 12a and the metal substrate 10 are in contact, they are bonded by the adhesive force of the resin component of the porous insulating layer 12a.

[0086] The temperature, pressure, and time in the first hot press are set appropriately according to the material used. For example, the hot press is performed at a temperature of 150 to 200°C and a pressure of 15 to 30 MPa for 1 to 5 minutes.

[0087] Subsequently, the support 20 is peeled off (see Figure 7). By applying a liquid adhesive to the surface of the insulating layer 12 after peeling off the support 20, the adhesive coating film 112b shown in Figure 8 is obtained. However, Figure 8 is a schematic diagram to clearly explain the process of forming a penetrating adhesive structure, and as described above, the adhesive applied to the insulating layer 12 penetrates as soon as it reaches the surface of the insulating layer 12, so in reality, the adhesive coating film 112b is not formed. The adhesive used here may be the same as the adhesive used earlier, or it may be different. The method of applying the adhesive is appropriately selected from commonly used methods, similar to the method of applying the insulating resin composition.

[0088] Alternatively, instead of forming the adhesive coating 112b on the surface of the insulating layer 12, the adhesive coating 112b may be formed on the circuit 11 by applying adhesive to the bonding surface of the circuit 11 to the insulating layer 12.

[0089] A circuit 11 is prepared. By placing the circuit 11 on the adhesive coating 112b of the laminate shown in Figure 8 obtained in the above process, the laminate shown in Figure 9 is obtained. This is heated and pressurized (second heat press) to further advance the penetration of the adhesive and at the same time cure the adhesive. As described above, in reality, the adhesive coating 112b is not formed, but the adhesive that has penetrated the insulating layer 12 seeps out at the interface with the circuit 11 and hardens due to the second heat press. As a result, as shown in Figure 3, an adhesive layer 12b is discontinuously formed between the circuit 11 and the insulating layer 12, and the insulating layer 12 and the circuit 11 are joined, and a circuit board 1C is obtained. In the circuit board 1C, in the parts where the adhesive layer 12b is absent and the porous insulating layer 12a and the circuit 11 are in contact, they are bonded by the adhesive strength of the resin component of the porous insulating layer 12a.

[0090] The temperature, pressure, and time in the second hot press are set appropriately according to the material used. For example, the hot press is performed at a temperature of 150 to 200°C and a pressure of 5 to 20 MPa for 1 to 5 minutes.

[0091] After the second hot pressing, it is preferable to anneal the resulting laminate. The annealing treatment is carried out, for example, at a temperature range of 150 to 200°C for 30 to 60 minutes.

[0092] The tests conducted in connection with the present invention are described below. <Material Components> The materials used in the preparation of the insulating resin composition and adhesive are shown below. ME1, ME2, BPA3E, BPA2E, Im-CN, Im, PHNOV, BN1, and BN2 shown below are abbreviations for material components.

[0093] (Resin component) • Mesogen-containing primary epoxy monomer ME1: EPICLON HP-4700 (manufactured by DIC Corporation) (solid / 25℃)

[0094] • Mesogen-containing second epoxy monomer ME2:EPICLON HP-4032D (manufactured by DIC Corporation) (liquid / 25°C)

[0095] • Bisphenol A type trifunctional epoxy monomer BPA3E:TECHMORE® VG3101L (manufactured by Printec Co., Ltd.) (solid / 25℃)

[0096] Bisphenol A diglycidyl ether BPA2E: EPICLON EXA-850CRP (manufactured by DIC Corporation) (liquid / 25°C)

[0097] • Phenol novolac PHNOV:TP-VG100 (manufactured by Printec Co., Ltd.) (solid / 25°C)

[0098] (Polymerization catalyst) ・Basic polymerization catalyst (1-cyanoethyl-2-ethyl-4-methylimidazole) IM-CN:2E4MZ-CN (manufactured by Shikoku Chemicals Co., Ltd.) • Acid polymerization catalyst: boron trifluoride monoethylamine

[0099] (Hardening agent) ・Dicyandiamide DICY7 (manufactured by Mitsubishi Chemical Corporation)

[0100] (Thermally conductive filler) ・Boron nitride particles BN1: HP-40J2W (Agglomerated boron nitride particles, median diameter (D) ５０ ) 12 μm) (Manufactured by JFE Mineral Co., Ltd.) BN2: HP-40MH100 (Agglomerated boron nitride particles, median diameter (D) ５０(18 μm) (Manufactured by JFE Mineral Co., Ltd.)

[0101] (Solvent) Cyclohexanone

[0102] 1. Example 1 <Preparation of insulating resin composition and adhesive> - Insulating resin composition 1 10 parts by mass of mesogen-containing primary epoxy monomer ME1 (solid / 25°C), 5 parts by mass of mesogen-containing secondary epoxy monomer ME2 (liquid / 25°C), and 0.3 parts by mass of basic polymerization catalyst IM-CN (1-cyanoethyl-2-ethyl-4-methylimidazole) were dissolved in 100 parts by mass of cyclohexanone to obtain varnish 1. Boron nitride particles BN1 and BN2 were added to varnish 1 in parts 23 parts by mass and 90 parts by mass, respectively, and ball mill grinding was performed to obtain a slurry-like insulating resin composition 1.

[0103] - Adhesive 1 A liquid adhesive 1 was obtained by mixing 2.5 parts by mass of liquid bisphenol A diglycidyl ether (BPA2E) with 0.1 parts by mass of polymerization catalyst IM-CN.

[0104] <Circuit board fabrication> The insulating resin composition 1 was coated onto a polyethylene terephthalate (PET) film (support) 20 and dried at 120°C for 10 minutes to obtain an adhesive sheet with a dried resin sheet 112a (see Figure 4).

[0105] Next, adhesive 1 was applied to the surface of the adhesive sheet facing the dried resin sheet 112a, allowing the adhesive 1 to penetrate the dried resin sheet 112a (see Figure 5).

[0106] A copper plate with a thickness of 2 mm was prepared as the metal substrate 10. A laminate was obtained by placing the adhesive sheet on the metal substrate 10 so that the adhesive coating surface of the dry resin sheet 112a (the side facing the adhesive coating film 112b in Figure 5) faced the metal substrate 10 (see Figure 6). This laminate was hot-pressed using a hot press machine at a temperature of 170°C and a pressure of 25 MPa for 3 minutes to cure the dry resin sheet 112a and the adhesive, and to bond the insulating layer 12 and the metal substrate 10. After that, the PET film 20 was peeled off (see Figure 7).

[0107] Next, adhesive 1 was applied to the surface of the insulating layer 12 from which the PET film 20 had been peeled off, allowing the adhesive 1 to penetrate the insulating layer 12 (see Figure 8).

[0108] Next, a circuit board 11 made of 2 mm thick copper foil was placed on the surface of the adhesive 1 applied to the insulating layer 12, and after being held at a temperature of 170°C for 1.5 minutes using a hot press machine, a circuit board 1C consisting of a metal substrate (2 mm thick), an insulating layer (0.12 mm thick), and a circuit (2 mm thick) was fabricated by hot pressing at a pressure of 12 MPa for 1.5 minutes.

[0109] In the obtained circuit board 1C, as shown in Figure 3, an adhesive layer 12b was partially formed between the insulating layer 12 and the metal substrate 10, and between the insulating layer 12 and the circuit 11, and the above-described penetrating adhesive structure was confirmed by observing the cross-section of the substrate with an electron microscope.

[0110] Furthermore, in circuit board 1C, the mass ratio of the mesogenic epoxy homopolymer to the total resin components contained in the insulating layer 12 (in other words, the total resin components contained in the porous substrate layer 12a and the adhesive) (hereinafter also referred to as the "mesogenic epoxy ratio") was 86% by mass. Here, "total resin components contained in the insulating layer 12" means the total mass of components excluding the thermal conductive filler and polymerization catalyst. The same applies to Comparative Examples 1 to 4. In Example 2, it further means the total mass excluding the curing agent (DICY).

[0111] Furthermore, a sample for evaluating the physical properties of the insulating layer 12 provided on the circuit board 1C (hereinafter referred to as the "insulating layer for physical property evaluation") was prepared by the following method.

[0112] <Preparation of insulating layer for physical property evaluation> An adhesive sheet was prepared using the same method as in Example 1, comprising a PET film 20 and a dry resin sheet 112a made of an insulating resin composition 1 (see Figure 4). Then, adhesive 1 was applied to the surface of the adhesive sheet facing the dry resin sheet 112a and allowed to penetrate (see Figure 5). Instead of a metal substrate 10, a copper foil 30 with a thickness of 0.5 mm was prepared. A laminate was obtained by placing the adhesive sheet on the copper foil such that the adhesive 1 coated surface of the dry resin sheet 112a (the surface facing the adhesive coating 112b in Figure 5) faced the copper foil 30 (see Figure 12). This laminate was heat-pressed under the same conditions as in Example 1 to cure the dry resin sheet 112a and the adhesive, and the insulating layer 12 and the copper foil 30 were joined. After that, the PET film 20 was peeled off to obtain a joint containing the insulating layer 12 and the copper foil 30 (see Figure 13). Two of these joints were prepared.

[0113] Next, the two bonded bodies were stacked so that the insulating layers 12 faced each other, and a hot press was used to hold the temperature at 170°C for 1.5 minutes, followed by hot pressing at a pressure of 12 MPa for another 1.5 minutes (see Figure 14). After that, the copper foil 30 was dissolved using an etching solution (H-20L, manufactured by Sunhayato Co., Ltd.), the remaining insulating layer 12 was washed with water, and dried to obtain the insulating layer 1 for physical property evaluation of Example 1 (thickness 0.24 mm) shown in Figure 15.

[0114] 2. Example 2 <Preparation of insulating resin composition and adhesive> - Insulating resin composition 1 The same insulating resin composition 1 as in Example 1 was prepared. - Adhesive 2 A liquid adhesive 2 was obtained by mixing 2.5 parts by mass of mesogen-containing second epoxy monomer ME2 (liquid / 25°C), 0.05 parts by mass of polymerization catalyst IM-CN, and 0.03 parts by mass of dicyandiamide (DICY) as a curing agent.

[0115] <Circuit board fabrication> Circuit board 1C was fabricated in the same manner as in Example 1, except that adhesive 1 was changed to adhesive 2. In the obtained circuit board 1C, as shown in Figure 3, it was confirmed in the same manner as in Example 1 that an adhesive layer 12b was partially formed between the insulating layer 12 and the metal substrate 10 and between the insulating layer 12 and the circuit 11, and that the above-described penetrating adhesive structure was formed.

[0116] Furthermore, in the circuit board 1C, the mesogenic epoxy ratio in the insulating layer 12, that is, the mass ratio of the total mesogenic epoxy homopolymer to the total resin components contained in the insulating layer 12, was 100% by mass.

[0117] <Preparation of insulating layer for physical property evaluation> An insulating layer 2 for physical property evaluation was prepared using the same method as in Example 1, except that adhesive 1 was changed to adhesive 2.

[0118] 2. Comparative Example 1 <Preparation of insulating resin composition and adhesive> - Insulating resin composition R1 Nine parts by mass of bisphenol A type trifunctional epoxy monomer BA3E, six parts by mass of curing agent PHNOV, and 0.1 parts by mass of basic polymerization catalyst Im-CN were dissolved in 100 parts by mass of cyclohexanone to obtain varnish R1. Boron nitride particles BN1 and BN2 were added to varnish R1 in parts 23 parts by mass and 90 parts by mass, respectively, and ball mill grinding was performed to obtain a slurry-like insulating resin composition R1.

[0119] - Adhesive R1 A liquid adhesive R1 was obtained by mixing 4.2 parts by mass of liquid bisphenol A diglycidyl ether (BPA2E) with 0.2 parts by mass of polymerization catalyst IM-CN.

[0120] <Fabrication of Circuit Board> Circuit board R1 was fabricated in the same manner as in Example 1, except that insulating resin composition 1 was changed to insulating resin composition R1 and adhesive 1 was changed to adhesive R1. In the obtained circuit board R1, as shown in circuit board 1C in Figure 3, it was confirmed in the same manner as in Example 1 that adhesive layers 12b were partially formed between the insulating layer 12 and the metal substrate 10 and between the insulating layer 12 and the circuit 11, and that the above-described penetrating adhesive structure was formed.

[0121] <Preparation of insulating layer for physical property evaluation> An insulating layer R1 for physical property evaluation was prepared in the same manner as in Example 1, except that insulating resin composition 1 was changed to insulating resin composition R1 and adhesive 1 was changed to adhesive R1.

[0122] 3. Comparative Example 2 <Preparation of Insulating Resin Composition and Adhesive> ・Insulating resin composition R2 5 parts by mass of mesogen-containing primary epoxy monomer ME1 (solid / 25°C), 2.5 parts by mass of mesogen-containing secondary epoxy monomer ME2 (liquid / 25°C), 7 parts by mass of curing agent PHNOV, and 0.1 parts by mass of basic polymerization catalyst Im-CN were dissolved in 100 parts by mass of cyclohexanone to obtain varnish R2. Boron nitride particles BN1 and BN2 were added to varnish R2 in 23 parts by mass and 90 parts by mass, respectively, and ball mill grinding was performed to obtain a slurry-like insulating resin composition R2.

[0123] - Adhesive R2 A liquid adhesive R2 was obtained by mixing 4.2 parts by mass of bisphenol A diglycidyl ether (BPA2E) as a liquid epoxy resin with 0.2 parts by mass of polymerization catalyst IM-CN.

[0124] <Fabrication of Circuit Board> Circuit board R2 was fabricated in the same manner as in Example 1, except that insulating resin composition 1 was changed to insulating resin composition R2 and adhesive 1 was changed to adhesive R2. In the obtained circuit board R2, as shown in circuit board 1A in Figure 1, it was confirmed in the same manner as in Example 1 that an adhesive layer 12b was partially formed between the insulating layer 12 and the metal substrate 10, and that the above-described penetrating adhesive structure was formed. In addition, the mesogenic epoxy ratio in the insulating layer 12 of circuit board R2 was 41% by mass.

[0125] <Preparation of insulating layer for physical property evaluation> An insulating layer R2 for physical property evaluation was prepared in the same manner as in Example 1, except that insulating resin composition 1 was changed to insulating resin composition R2 and adhesive 1 was changed to adhesive R2.

[0126] 4. Comparative Example 3 <Preparation of Insulating Resin Composition and Adhesive> - Insulating Resin Composition R3 7.5 parts by mass of mesogen-containing primary epoxy monomer ME1 (solid / 25°C), 4 parts by mass of mesogen-containing secondary epoxy monomer ME2 (liquid / 25°C), 3.5 parts by mass of curing agent PHNOV, and 0.1 parts by mass of basic polymerization catalyst Im-CN were dissolved in 100 parts by mass of cyclohexanone to obtain varnish R3. Boron nitride particles BN1 and BN2 were added to varnish R3 in 23 parts by mass and 90 parts by mass, respectively, and ball mill grinding was performed to obtain a slurry-like insulating resin composition R3.

[0127] <Preparation of Adhesive R3> Liquid adhesive R3 was obtained by mixing 4.2 parts by mass of bisphenol A diglycidyl ether (BPA2E) as a liquid epoxy resin with 0.2 parts by mass of polymerization catalyst IM-CN.

[0128] <Fabrication of Circuit Board> Circuit board R3 was fabricated in the same manner as in Example 1, except that insulating resin composition 1 was changed to insulating resin composition R3 and adhesive 1 was changed to adhesive R3. In the obtained circuit board R3, as shown in circuit board 1A in Figure 1, it was confirmed in the same manner as in Example 1 that an adhesive layer 12b was partially formed between the insulating layer 12 and the metal substrate 10, and that the above-described penetrating adhesive structure was formed. In addition, the mesogenic epoxy ratio in the insulating layer 12 of circuit board R3 was 59% by mass.

[0129] <Preparation of insulating layer for physical property evaluation> An insulating layer R3 for physical property evaluation was prepared in the same manner as in Example 1, except that insulating resin composition 1 was changed to insulating resin composition R3 and adhesive 1 was changed to adhesive R3.

[0130] 5. Comparative Example 4 <Preparation of insulating resin composition and adhesive> - Insulating resin composition 1 The same amount of insulating resin composition 1 was prepared in the same manner as in Example 1.

[0131] - Adhesive R4 was prepared in the same amount as in Example 1, except that the polymerization catalyst was changed from the basic polymerization catalyst IM-CN (1-cyanoethyl-2-ethyl-4-methylimidazole) to the acidic polymerization catalyst (boron trifluoride monoethylamine).

[0132] <Circuit board fabrication> Circuit board R4 was fabricated in the same manner as in Example 1, except that adhesive 1 was changed to adhesive R4. In the obtained circuit board R4, as shown in circuit board 1A in Figure 1, it was confirmed in the same manner as in Example 1 that an adhesive layer 12b was partially formed between the insulating layer 12 and the metal substrate 10, and that the above-described penetrating adhesive structure was formed. In addition, the mesogenic epoxy ratio in the insulating layer 12 of circuit board R4 was 86% by mass.

[0133] <Preparation of insulating layer for physical property evaluation> The insulating layer R4 for physical property evaluation was prepared using the same method as in Example 1, except that adhesive 1 was changed to adhesive R4.

[0134] <Evaluation> Each circuit board and insulating layer for physical property measurement obtained above was evaluated using the following evaluation method. The results are shown in Table 1.

[0135] (Thermal Conductivity) The thermal conductivity in the thickness direction was measured for each insulating layer (thickness 0.24 mm) used for physical property measurement by the laser flash method. Two samples were prepared for each insulating layer used for physical property measurement, and the thermal conductivity was measured both before and after solder heat treatment. Solder heat treatment was performed by treating the sample before removing the copper foil 30 (see Figure 14) in a 300°C solder bath for 5 minutes. The thermal conductivity was measured on the sample after solder treatment, from which the copper foil 30 was removed using the method described above.

[0136] (Presence or absence of cracks after solder heat treatment) For each insulating layer used for physical property measurement that underwent solder heat treatment for thermal conductivity measurement, the presence or absence of cracks was observed. The observation was performed on SEM images of the cross-section of the insulating layer. Figure 10 is the SEM image of Example 1, and Figure 11 is the SEM image of Comparative Example 2. No cracks were observed in Figure 10 (Example 1). The same was true for Example 2. On the other hand, cracks were observed in Figure 11 (Comparative Example 2). The arrows in Figure 11 indicate a part of the crack. Cracks were similarly observed in Comparative Examples 1, 3, and 4.

[0137] (Coefficient of Linear Expansion) For the insulating layer (thickness 0.24 mm) of each insulating layer used for physical property measurement, the coefficient of linear expansion was measured using the tensile mode of the TMA (Thermo-mechanical analysis) method, in a temperature range of -50 to 300°C, a heating rate of 5°C / min, a tensile load of 100 mN, and a nitrogen atmosphere. The coefficient of linear expansion at 300°C is shown in Table 1.

[0138] (Coating unevenness) The dried resin sheet 112a (see Figure 4) formed on the support 20 was visually inspected for the presence or absence of coating unevenness.

[0139] <High Temperature and High Humidity Bias Test> For Example 1 and Comparative Example 4, the circuit board was cut to 30 mm x 30 mm, and a land size of φ20 mm was placed in the center of the board by etching. DC 1 kV was applied to the land while the board was placed in a constant temperature and humidity chamber at 85°C and 85%, and failure was determined when the leakage current reached 5 mA, and the time until failure was measured. Good bias test results mean that the circuit board has the moisture resistance and durability to maintain the necessary insulation as a circuit board even in an environment where electronic components are actually mounted and the operating environment is a high temperature, humid environment with voltage applied for a long period of time.

[0140]

[0141] It should be noted that the present invention is not limited to the embodiments described above, and can be modified in various ways during implementation without departing from its essence. Furthermore, each embodiment may be combined as appropriate, and in that case, the combined effects can be obtained. Moreover, the above embodiments include various inventions, and various inventions can be extracted by selecting combinations from the multiple constituent elements disclosed. For example, if the problem can be solved and effects obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiment, then the configuration with these deleted constituent elements can be extracted as an invention.

[0142] 1A...Circuit board, 1B...Circuit board, 1C...Circuit board, 10...Metal substrate, 11...Circuit, 12...Insulating layer, 12a...Porous insulating layer, 12b...Adhesive layer, 20...Support, 30...Copper foil, 112a...Dry resin sheet (precursor for porous insulating layer), 112b...Adhesive coating

Claims

1. A circuit board comprising a first metal layer, an insulating layer, and a second metal layer in this order, wherein one of the first metal layer and the second metal layer is a metal substrate and the other is a circuit, the insulating layer comprises a porous insulating layer containing an epoxy resin homopolymer containing a mesogenic skeleton and a first polymerization catalyst, and an adhesive containing a thermosetting resin and a second polymerization catalyst, the adhesive penetrates the porous insulating layer, and a portion of the penetrated adhesive forms a discontinuous adhesive layer between the first metal layer and the porous insulating layer, the mass ratio of the epoxy resin homopolymer containing a mesogenic skeleton contained in the insulating layer to the total resin components contained in the porous insulating layer and the adhesive is 80% by mass or more, and the first polymerization catalyst and the second polymerization catalyst are basic polymerization catalysts.

2. The circuit board according to claim 1, wherein a further portion of the adhesive that has penetrated the porous insulating layer forms a discontinuous adhesive layer between the second metal layer and the porous insulating layer.

3. The circuit board according to claim 1 or 2, wherein the epoxy resin homopolymer does not contain components derived from a polyaddition curing agent.

4. The circuit board according to any one of claims 1 to 3, wherein the insulating layer further contains a thermally conductive filler, and the volume ratio of the thermally conductive filler to the insulating layer is 70% or more.

5. The circuit board according to any one of claims 1 to 4, wherein the first polymerization catalyst and the second polymerization catalyst are the same basic polymerization catalyst.

6. The circuit board according to claim 5, wherein the basic polymerization catalyst is an imidazole compound having a cyanide group.

7. The epoxy resin homopolymer is an epoxy resin homopolymer comprising a crosslinked product of a first epoxy monomer containing a mesogenic skeleton that is solid at room temperature and a second epoxy monomer containing a mesogenic skeleton that is liquid at room temperature, and the circuit board according to any one of claims 1 to 6, wherein the blending mass ratio of the first epoxy monomer to the second epoxy monomer, which is the first epoxy monomer / second epoxy monomer, is in the range of 0.25 to 3.

8. The circuit board according to any one of claims 1 to 7, wherein the epoxy resin homopolymer containing the mesogenic skeleton has a π-π stacking structure in its molecular structure.

9. The circuit board according to any one of claims 1 to 8, wherein the mesogenic skeleton is a naphthalene skeleton or a biphenyl skeleton.

10. The circuit board according to any one of claims 1 to 9, wherein the adhesive contains an epoxy resin homopolymer containing the mesogenic skeleton as the thermosetting resin.

11. An insulating resin composition containing a first epoxy monomer containing a mesogenic skeleton, a second epoxy monomer containing a mesogenic skeleton, and a basic polymerization catalyst, but without a polyaddition curing agent.

12. The insulating resin composition according to claim 11, wherein the first epoxy monomer is solid at room temperature, the second epoxy monomer is liquid at room temperature, and the blending mass ratio of the first epoxy monomer to the second epoxy monomer, which is the first epoxy monomer / second epoxy monomer, is in the range of 0.25 to 3.

13. The insulating resin composition according to claim 11 or 12, wherein the mesogenic skeleton is a naphthalene skeleton or a biphenyl skeleton.

14. The insulating resin composition according to any one of claims 11 to 13, further comprising a thermally conductive filler.

15. The insulating resin composition according to any one of claims 11 to 14, wherein the basic polymerization catalyst is an imidazole compound having a cyanide group.

16. An insulating resin composition according to any one of claims 11 to 15, for use as interlayer insulation for circuit boards.

17. A method for producing the insulating resin composition according to claim 16, comprising mixing a first epoxy monomer containing a mesogenic skeleton, a second epoxy monomer containing a mesogenic skeleton, and a basic polymerization catalyst, and without using a polyaddition curing agent.

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