JP7815919B2 - Laminated structure and method for manufacturing the same - Google Patents

Description

The present invention relates to a laminated structure useful as a substrate for power devices.

In recent years, electrical and electronic devices have rapidly become more powerful and smaller. This has led to an increase in the amount of heat generated by electrical elements. Therefore, metal-based circuit boards that mount power devices are required to have excellent heat dissipation capabilities in addition to insulation properties.

An example of a substrate used in a power device is one that has an insulating layer such as ceramic on a thermal conductor such as a metal substrate, and an electrode circuit made of metal foil such as copper on top of that (see, for example, Patent Document 1 and Patent Document 2).

On the other hand, a method for forming a green sheet involves forming a conductive pattern on the green sheet using copper paste (Patent Documents 4 and 5).

Japanese Patent Application Laid-Open No. 2017-64661 JP 2016-106395 A WO 98/24122 Japanese Unexamined Patent Publication No. 61-208889 Japanese Patent Application Publication No. 06-104552

The electrode circuits of power device substrates manufactured using the methods disclosed in the above patent documents are generally patterned by etching. As a result, thin metal foils of 200 μm or less are used as conductors, and wiring resistance has been a problem when used in circuits such as power semiconductors through which large currents flow. Furthermore, when copper foil is used as the conductor, copper ions remain on the insulating layer during etching. When copper ions remain, they migrate to the insulating layer, causing a problem of reduced insulating properties of the insulating layer.

On the other hand, to provide patterned electrodes without etching, a method is conceivable in which a pre-patterned electrode is placed on an insulating layer and then pressed to bond it to the insulating layer. However, when pressing the pre-patterned electrode portion, the pressing pressure is not applied to the areas of the insulating layer where the electrode is not laminated, which can result in depressions in part of the insulating layer. Furthermore, in the case of a resin insulating layer containing a heat-dissipating filler, voids can remain in the areas where the pressing pressure is not applied, which can cause problems with heat dissipation.
Furthermore, there is a method for manufacturing an electrode circuit in which electrodes are disposed on an insulating layer and then molded with molding resin (see Patent Document 3). In this case, there are problems such as the need for a mold for each module, which is costly, and when the circuit is large, the mold also becomes large, which is costly, and cracks are likely to occur due to the difference in linear expansion between the circuit and the substrate.

Furthermore, the method of forming a conductive pattern on a green sheet using copper paste can result in distortion or voids during firing, and the conductive layer obtained from the copper paste contains voids, resulting in insufficient electrical and thermal conductivity.
The present invention provides a laminated structure comprising an insulating layer in which the insulating properties of the insulating layer are not reduced and voids within the insulating layer are reduced, and a conductive layer that combines electrical conductivity and thermal conductivity by using a copper plate having a certain thickness or more.

As a result of intensive research into solving the above-mentioned problems, the inventors have found that a laminated structure that can solve the above-mentioned problems can be obtained by placing an electrode made of a copper plate that has already been patterned and has a thickness of 100 μm or more on an insulating layer, and then pressing it using a specific method.
The present invention includes the following aspects.

[1] A thermal conductor having a thermal conductivity of 10 W/m K or more;
an insulating layer laminated on at least one surface of the thermal conductor;
a conductive layer disposed on a surface of the insulating layer opposite to a surface on which the thermal conductor is laminated,
a laminated surface of the insulating layer and the conductive layer has a laminated portion where the insulating layer and the conductive layer are laminated and a blank portion where no conductive layer is present,
the laminated portion and the blank portion are present on the same plane on the laminated surface of the insulating layer and the conductive layer,
The conductive layer is a copper plate having a thickness of 100 μm or more,
and the copper concentration in the blank area on the surface of the insulating layer is 10,000 ppm or less.
[2] A thermal conductor having a thermal conductivity of 10 W/m K or more;
an insulating layer laminated on at least one surface of the thermal conductor;
a patterned conductive layer disposed on a surface of the insulating layer opposite to a surface on which the thermal conductor is laminated,
a laminated surface of the insulating layer and the conductive layer has a laminated portion where the insulating layer and the conductive layer are laminated and a blank portion where no conductive layer is present,
the laminated portion and the blank portion are present on the same plane on the laminated surface of the insulating layer and the conductive layer,
The conductive layer is a copper plate having a thickness of 100 μm or more,
and the angle formed by the side of the conductive layer and the insulating layer at the boundary between the blank portion and the laminated portion is 90°±10°.
[3] The laminated structure according to [1] or [2], wherein the insulating layer is a resin sheet containing a matrix resin containing agglomerated particles of boron nitride.
[4] A method for producing the laminate structure according to any one of [1] to [3],
the insulating layer is a resin sheet obtained using a resin composition containing an inorganic filler, a thermosetting resin, and a thermosetting catalyst;
the inorganic filler comprises an agglomerated inorganic filler;
the thermosetting resin comprises an epoxy resin;
The melting point of the thermosetting catalyst is 120°C or higher,
A method for producing a laminated structure, comprising the following steps (a) and (b):
(a) A step of forming a sheet using the resin composition; (b) A step of heating the sheet obtained in step (a) at 95°C or less to make the reaction rate of the sheet 50% or more. The reaction rate of the sheet can be calculated as follows.
(Response rate)
It is calculated from the calorific value of the exothermic peak obtained by differential scanning calorimetry (DSC) when the temperature is raised from 40° C. to 250° C. at a rate of 10° C./min, using the following formula:
Reaction rate (%) = (1 - (amount of heat generated after step (b) / amount of heat generated after step (a))) x 100
[5] The method for producing a laminate structure according to [4], wherein the thermosetting catalyst is contained in an amount of 5 mass % or less relative to the resin component of the resin composition.
The resin component here refers to the components obtained by excluding the inorganic filler and the solvent, if any, from the resin composition.
[6] The method for producing a laminate structure according to [4] or [5], wherein the thermosetting catalyst contains a compound having a structure derived from imidazole and/or dicyandiamide.
[7] The method for producing a laminate structure according to any one of [4] to [6], wherein in the step (b), the heating time of the sheet is 5 hours or less.
[8] The method for producing a laminate structure according to any one of [4] to [7], wherein in the step (b), a pressing pressure is applied in the range of 0.1 MPa to 1000 MPa simultaneously with heating.

The present invention provides a laminated structure that includes an insulating layer that reduces voids within the insulating layer without reducing the insulating properties of the insulating layer, and a conductive layer that combines electrical and thermal conductivity by using a copper plate with a certain thickness or greater.

1 is a cross-sectional view of a laminated structure according to an embodiment of the present invention; FIG. 2 is an enlarged schematic diagram of the dashed dotted line portion of FIG. 1 . FIG. 1 is a schematic diagram showing a laminated surface of a conventional laminate. FIG. 1 is a schematic diagram showing a laminated surface of a conventional laminate.

The present invention will be described in detail below. However, the following description of the constituent elements is one example (representative example) of an embodiment of the present invention, and the present invention is not limited to these contents, and various modifications can be made within the scope of the gist of the invention.

A laminated structure according to an embodiment of the present invention comprises a thermal conductor, an insulating layer laminated on at least one surface of the thermal conductor, and a conductive layer laminated on the surface of the insulating layer opposite to the surface on which the thermal conductor is laminated, wherein the conductive layer is a copper plate having a thickness of 100 μm or more.
The reasons why the laminated structure of the present invention exhibits excellent insulation and heat dissipation properties include the following. Since the copper concentration in the gaps on the surface of the insulating layer is 10,000 ppm or less, insulation between patterns is maintained. Furthermore, by using a copper plate with a thickness of 100 μm or more as the conductive layer, both electrical conductivity and thermal conductivity can be achieved. Furthermore, on the laminated surface between the insulating layer and the conductive layer, the laminated portion and the gaps are present on the same plane, which prevents electric field concentration, and by maintaining a constant thickness of the insulating layer, good insulation can be obtained.
Furthermore, by using a specific composition for the insulating layer and reacting it using a specific process, it is possible to obtain not only thermal conductivity and an insulating layer, but also a shelf life in the sheet state before curing and prevention of warping during curing.

One embodiment of the laminated structure according to this embodiment will be described with reference to Fig. 1. Fig. 1 schematically shows the laminated structure, which has a thermal conductor 1, an insulating layer 2, and a conductive layer 3.
<<<Thermal Conductor 1>>>
The thermal conductor 1 is a substance with high thermal conductivity, and the thermal conductivity is usually 10 W/m K or more, preferably 20 W/m K or more, and more preferably 30 W/m K or more. A material with a high thermal conductivity is more suitable as a heat dissipation substrate for a power device.

Heat conductors with such high thermal conductivity include various metals, specifically silver, copper, gold, aluminum, nickel, iron, alloys of these, and ceramics.

The shape and size of the thermal conductor are not particularly limited and are appropriately selected depending on the application of the laminated structure.
The thickness of the thermal conductor is not particularly limited. When used as a heat dissipation substrate for a power device, the thickness is usually 0.01 mm or more, preferably 0.1 mm or more, more preferably 1 mm or more, and usually 200 mm or less, preferably 100 mm or less, depending on the heat generation amount of the device. The size is not particularly limited, and it can be applied to substrates of 500 mm or more, which are usually difficult to mold with molding resin. In addition to the thickness, the size of the thermal conductor can also be large, and it can be applied to those with a side of 100 mm or more.
Furthermore, fins may be formed on the side of the thermal conductor where no insulating layer is laminated in order to improve heat dissipation.

<<<Insulating Layer 2>>>
The insulating layer 2 is an insulating layer because the conductive layer 3 can be used as an electrode. The insulating layer 2 is required to have a volume resistivity of usually 1× ¹⁰ Ωcm or more, preferably 1× ¹⁰ Ωcm or more, and more preferably 1× ¹⁰ Ωcm or more at room temperature.
On the other hand, when the laminated structure is used as a heat dissipation substrate, it is preferable that the insulating layer 2 has high thermal conductivity. In this case, the thermal conductivity is 0.5 W/m·K or more, preferably 1.0 W/m·K or more, more preferably 2.0 W/m·K or more, still more preferably 5.0 W/m·K or more, still more preferably 7.0 W/m·K or more, and still more preferably 10.0 W/m·K or more.

In this embodiment, the insulating layer 2 having such insulating properties and preferably thermal conductivity is preferably a resin sheet containing thermally conductive particles in the resin, and more preferably a resin sheet containing boron nitride particles in the resin.
The matrix resin forming the resin sheet may be either a curable resin or a thermoplastic resin, without any limitation. As the curable resin, a thermosetting resin, a photocurable resin, an electron beam curable resin, or the like may be used, with a thermosetting resin being preferred.
The resin sheet is formed using a resin composition containing a matrix resin, etc. The resin composition may contain a curable resin, a thermoplastic resin, thermally conductive particles, a curing agent, a thermosetting catalyst, etc.

<<Thermosetting resin>>
As the thermosetting resin, for example, those exemplified in WO 2013/081061 can be used, and it is particularly preferable to use an epoxy resin.

The epoxy resin is not particularly limited, but examples thereof include phenoxy resins having at least one skeleton selected from the group consisting of a naphthalene skeleton, a fluorene skeleton, a biphenyl skeleton, an anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton, a dicyclopentadiene skeleton, and a bisphenol skeleton; epoxy resins obtained by hydrogenating these; epoxy resins having an alicyclic epoxy; epoxy resins containing an aliphatic glycidyl group such as trimethylolpropane polyglycidyl or pentaerythritol polyglycidyl; and epoxy resins containing a glycidyl ester.
Among these, it is preferable to use a phenoxy resin having at least one skeleton selected from the group consisting of a bisphenol A skeleton, a bisphenol F skeleton, and a biphenyl skeleton. These epoxy resins may be used alone or in combination of two or more. Furthermore, two or more epoxy resins having different molecular weights may also be used.

The epoxy resin used in the present invention preferably contains a polyfunctional epoxy resin.
A polyfunctional epoxy resin is an epoxy resin having three or more oxirane rings (epoxy groups) per molecule.

From the viewpoint of increasing the storage modulus of the resin sheet of the present invention, particularly the storage modulus at high temperatures, which is important in applications such as power semiconductors that generate a large amount of heat, epoxy resins having two or more oxirane rings (epoxy groups) per molecule are preferred, epoxy resins having three or more oxirane rings (epoxy groups) per molecule are more preferred, and epoxy resins having four or more glycidyl groups per molecule are even more preferred. Having multiple oxirane rings (epoxy groups), particularly glycidyl groups, per molecule improves the crosslink density of the cured product, resulting in a stronger resin sheet. As a result, when internal stress is generated in the resin sheet during a moisture absorption reflow test, the resin sheet maintains its shape without deformation or destruction, thereby preventing the formation of voids or other voids in the resin sheet.
Furthermore, from the viewpoint of increasing the storage modulus of the resin sheet, the molecular weight of the polyfunctional epoxy resin is preferably 1,000 or less, and more preferably 800 or less. The lower limit is not particularly limited, but is at least 100. Furthermore, from the viewpoint of achieving lower moisture absorption and higher crosslinking, a polyfunctional epoxy resin that does not contain a nitrogen atom-containing amine or amide structure is more preferred.

The addition of a multifunctional epoxy resin makes it possible to introduce a high density of highly polar oxirane rings (epoxy groups), thereby enhancing the effects of physical interactions such as van der Waals forces and hydrogen bonding, and improving adhesion between the conductive layer and insulating layer (resin sheet) in the laminate structure. The addition of a multifunctional epoxy resin also increases the storage modulus of the resin sheet, which, after the cured resin composition penetrates into the irregularities of the metal adherend, exerts a strong anchoring effect, improving adhesion between the conductive layer and resin sheet.

However, while the introduction of multifunctional epoxy resins tends to increase the moisture absorption of resin compositions, improving the reactivity of the oxirane rings (epoxy groups) reduces the amount of hydroxyl groups during the reaction, thereby suppressing the increase in moisture absorption. Furthermore, by combining the specific epoxy resins and multifunctional epoxy resins mentioned above to produce a resin composition, it is possible to achieve both high elasticity and low moisture absorption in resin sheets.

Specifically, the polyfunctional epoxy resin is preferably an epoxy resin having three or more epoxy groups, and examples thereof include EX321L, DLC301, and DLC402 manufactured by Nagase ChemteX Corporation, and BATG and PETG manufactured by Showa Denko KK.
These polyfunctional epoxy resins may be used alone or in combination of two or more.

(Content)
The resin composition forming the resin sheet of the present invention preferably contains a thermosetting resin in an amount of 5 to 90% by mass, particularly 10 to 60% by mass, based on 100% by mass of the resin composition of the present invention excluding the solvent if a solvent is contained. When the content of the thermosetting resin component is equal to or greater than the lower limit, moldability is improved, and when it is equal to or less than the upper limit, the content of other components can be secured, resulting in improved thermal conductivity.

Furthermore, when the resin composition of the present invention contains an inorganic filler, a thermosetting catalyst, and a solvent, the main component excluding the solvent is preferably an epoxy resin. Here, the main component refers to the component that is present in the largest amount.
The proportion of epoxy resin in the resin composition excluding the inorganic filler and the thermosetting catalyst is not particularly limited, but is preferably 20% by mass or more, and more preferably 45% by mass or more. The upper limit may be 100% by mass, and all of the epoxy resin may be epoxy resin. Having the proportion of epoxy resin within the above range tends to provide low moisture absorption, high elastic modulus, high toughness, and easy reaction control, as well as high reflow resistance, high reliability in cycle tests, and high thermal conductivity.

The resin composition forming the resin sheet of the present invention preferably contains 5% by mass or more, and more preferably 10% by mass or more, of the aforementioned preferred polyfunctional epoxy resin based on the total epoxy resin. It also preferably contains 50% by mass or less, and more preferably 40% by mass or less. When the content of the polyfunctional epoxy resin is above the above-mentioned lower limit, the aforementioned effects of containing the polyfunctional epoxy resin can be effectively achieved. On the other hand, when the content of the polyfunctional epoxy resin is below the above-mentioned upper limit, the moisture absorption of the cured product is suppressed and the strength performance of the cured product is excellent, achieving both of these performance characteristics.

From the viewpoints of film-forming ability, low moisture absorption, and flexibility, the epoxy resin used in the present invention preferably contains a high-molecular-weight epoxy resin. Specifically, the high-molecular-weight epoxy resin is preferably an epoxy resin having a mass-average molecular weight of 10,000 or more, more preferably an epoxy resin having a mass-average molecular weight of 20,000 or more, particularly preferably an epoxy resin having a mass-average molecular weight of 30,000 or more, and even more preferably an epoxy resin having a mass-average molecular weight of 80,000 or less.
High molecular weight epoxy resins are preferred to be more hydrophobic, and specifically, the epoxy equivalent of the epoxy component should be as large as possible. Specifically, it is preferred that the epoxy equivalent be 5,000 g/equivalent or more, more preferably 7,000 g/equivalent or more, and preferably 20,000 g/equivalent or less.

Here, the mass average molecular weight of the epoxy resin is a value calculated in terms of polystyrene as measured by gel permeation chromatography. Furthermore, the epoxy equivalent is defined as "the mass of the epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.

Such high molecular weight epoxy resins may be used alone or in combination with two or more types, and may also be used in combination with other epoxy resins that do not have high molecular weights.

<<Curing agent>>
A curing agent that cures with these thermosetting resins can also be used. The curing agent contained in the sheet is not particularly limited, but preferred curing agents are phenolic resins, acid anhydrides having an aromatic or alicyclic skeleton, hydrates of such acid anhydrides, or modified products of such acid anhydrides. By using these preferred curing agents, a cured resin sheet having an excellent balance of heat resistance, moisture resistance, and electrical properties can be obtained. Only one type of curing agent may be used, or two or more types may be used in combination.

The phenolic resin is not particularly limited. Specific examples of the phenolic resin include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, polyparavinylphenol, bisphenol A novolac, xylylene-modified novolac, decalin-modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, and poly(di-p-hydroxyphenyl)methane. Among these, novolac-type phenolic resins with a rigid main skeleton and phenolic resins with a triazine skeleton are preferred for improving the mechanical properties and heat resistance of the resin sheet, as they can further enhance the flexibility and flame retardancy of the insulating sheet. Also, phenolic resins with allyl groups are preferred for improving the flexibility of the uncured sheet and the toughness of the resin sheet.

<<Thermosetting catalyst>>
The resin composition forming the resin sheet of the present invention may contain a thermosetting catalyst. In particular, it preferably contains a thermosetting catalyst having a melting point of 120° C. or higher. By using this thermosetting catalyst, the reaction rate of the thermosetting resin during storage can be reduced, thereby improving shelf life.

The thermosetting catalyst is not particularly limited as long as a thermosetting catalyst having a melting point of 120°C or higher is used. The melting point is preferably 150°C or higher, more preferably 200°C or higher. The upper limit is not particularly limited, but is 300°C or lower. By keeping the temperature within these ranges, the effect of slowing down the reaction rate of the thermosetting resin during storage tends to be obtained.
The thermosetting catalyst contained in the resin composition of the present invention may be one type or multiple types. When multiple types are used, it is sufficient that at least one of them has a melting point of 120°C or higher. When multiple types of thermosetting catalysts are used, their melting points are not particularly limited, but it is preferable that all of them are 120°C or higher.
When a thermosetting catalyst having a melting point of less than 120° C. is used in combination, the amount of the thermosetting catalyst is preferably 10% by mass or less of the total amount of the thermosetting catalyst.

Examples of thermosetting catalysts having a melting point of 120°C or higher include compounds having a structure derived from imidazole, dicyandiamide, linear or cyclic tertiary amines, organophosphorus compounds, quaternary phosphonium salts, diazabicycloalkenes such as organic acid salts, etc. Organometallic compounds, quaternary ammonium salts, metal halides, etc. can also be used. Examples of the organometallic compounds include zinc octoate, tin octoate, and aluminum acetylacetone complexes.
Among these, compounds having a structure derived from imidazole and/or dicyandiamide are preferred from the viewpoints of storage stability and heat resistance of the cured product.
The proportion of the compound having a structure derived from imidazole and dicyandiamide in the thermosetting catalyst is not particularly limited, but is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and still more preferably 90% by mass or more. There is no particular upper limit, and it may be 100% by mass.
When a compound having a structure derived from imidazole and dicyandiamide are used in combination, the ratio between them is not particularly limited.

Examples of compounds having a structure derived from imidazole and dicyandiamide, which have a melting point of 120°C or higher, include 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2-phenyl-4,5-dihydroxymethylimidazole, 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 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'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and dicyandiamide.

The content of the thermosetting catalyst in the resin composition is preferably 5% by mass or less, more preferably 4.5% by mass or less, and even more preferably 4% by mass or less, based on 100% by mass of the resin component. Although there is no particular lower limit, the content is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more.
Here, the resin component refers to the components obtained by excluding the inorganic filler and the solvent, if any, from the resin composition of the present invention.
By ensuring that the content of the curing catalyst is within the above range, the reaction rate of the thermosetting resin during storage can be reduced, and the shelf life tends to be improved.

The average particle size of the thermosetting catalyst is not particularly limited, but the average particle size of at least one thermosetting catalyst is preferably 15 μm or less, more preferably 10 μm or less. It is also preferably 50 nm or more, more preferably 100 nm or more, even more preferably 500 nm or more, and even more preferably 1000 nm or more. When the average particle size is below the upper limit, the solubility of the thermosetting catalyst in the resin component tends to be improved, and the reaction rate tends to be improved. Furthermore, the elastic modulus of the resin sheet can be increased, and the glass transition temperature tends to be increased. Furthermore, the dispersibility of the thermosetting catalyst tends to be improved, and storage stability tends to be improved. On the other hand, when the average particle size is above the lower limit, secondary aggregation of the thermosetting catalyst itself is suppressed, the dispersibility of the thermosetting catalyst is improved, and the storage stability of the resin composition tends to be improved. Furthermore, the handleability during production of the resin composition also tends to be good.
The average particle size of the plurality of thermosetting catalysts is not particularly limited, but may be within the above range.

<<Thermal conductive particles>>
The thermally conductive particles contained in the resin sheet can be any particles having thermal conductivity, but to maintain the insulation of the sheet, a highly insulating filler is used, and particularly, alumina, zinc oxide, boron nitride, aluminum nitride, silicon nitride, etc. are preferably used.
Since power semiconductor applications require insulation, the thermally conductive particles are preferably made of an inorganic compound with excellent insulation properties, such as a volume resistivity of 1×10 ¹³ Ω·cm or more, particularly 1×10 ¹⁴ Ω·cm or more. Among these, oxides and nitrides are preferred because they provide sufficient electrical insulation for the resin sheet. More specific examples of such thermally conductive particles include alumina (Al ₂ O ₃ , volume resistivity 1×10 ¹⁴ Ω·cm), aluminum nitride (AlN, volume resistivity 1×10 ¹⁴ Ω·cm), boron nitride (BN, volume resistivity 1×10 14 Ω·cm), silicon nitride (Si ₃ N ₄ , volume resistivity 1×10 ¹⁴ Ω·cm), and silica (SiO ₂ , volume resistivity 1×10 ¹⁴ Ω·cm). Of these, alumina, aluminum nitride, boron nitride, and silica are preferred, with alumina and boron nitride being ^particularly preferred.

The inorganic filler may be surface-treated with a surface treatment agent. A known surface treatment agent can be used as the surface treatment agent. The inorganic filler may be used alone or in any combination and ratio of two or more types.
From the viewpoint of high thermal conductivity and ease of handling, the inorganic filler is preferably boron nitride particles, more preferably boron nitride agglomerated particles, and more preferably boron nitride agglomerated particles having a house-of-card structure. The house-of-card structure is described, for example, in Ceramics 43 No. 2 (published by the Ceramic Society of Japan in 2008), and is a structure in which plate-like particles are layered in a complex manner without being oriented. More specifically, the boron nitride agglomerated particles having a house-of-card structure are aggregates of boron nitride primary particles, and have a structure in which the flat surfaces and end surfaces of the primary particles are in contact with each other.
The agglomerated morphology of the agglomerated boron nitride particles can be confirmed by a scanning electron microscope (SEM).

The boron nitride agglomerated particles have a peak intensity ratio I(100)/I(004) of the 100 axis to the 004 axis in XRD measurement of usually 3.0 or more, preferably 3.1 or more, more preferably 3.2 or more, and particularly preferably 3.3 or more. There is usually no upper limit, but it is 10 or less.
The breaking strength of the boron nitride agglomerated particles is usually 2.5 MPa or more, preferably 3.0 MPa or more, more preferably 3.5 MPa or more, and even more preferably 4.0 MPa or more, and is usually 20 MPa or less, preferably 15 MPa or less, and even more preferably 10 MPa or less.
The specific surface area of the boron nitride agglomerated particles is usually 1 m ² /g or more, preferably 3 m ² /g or more and 50 m ² /g or less, and more preferably 5 m ² /g or more and 40 m ² /g or less.

The boron nitride agglomerated particles have a volume-based maximum particle diameter D _max (sometimes simply referred to as "maximum particle diameter" in this specification) of usually 2 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and particularly preferably 10 μm or more. Also, it is usually 300 μm or less, preferably 200 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, and even more preferably 60 μm or less.

Furthermore, there are no particular restrictions on the volume-based average particle diameter _D50 of the boron nitride secondary particles (hereinafter sometimes simply referred to as "average particle diameter"), but for the same reasons as for the value of the volume-based maximum particle diameter, it is usually 1 μm or more, preferably 2 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. It is also usually 250 μm or less, preferably 150 μm or less, more preferably 90 μm or less, and even more preferably 70 μm or less. By setting the average particle diameter _D50 within the above range, it is possible to obtain a resin sheet that has sufficient thermal conductivity in the thickness direction of the resin sheet and good voltage resistance characteristics.

The average particle diameter can be determined, for example, by dispersing the boron nitride agglomerated particles in an appropriate solvent; specifically, by measuring the particle size distribution of a sample prepared by dispersing the boron nitride agglomerated particles in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer using a laser diffraction/scattering particle size distribution analyzer LA-920 manufactured by Horiba, Ltd., and then determining the average particle diameter of the boron nitride agglomerated particles from the obtained particle size distribution.
The boron nitride agglomerated particles have a house-of-card structure, and as long as they preferably satisfy the above-mentioned physical properties, there are no limitations on the method for producing them. For example, they can be produced by the methods described in JP-A-2015-193752, JP-A-2015-195287, JP-A-2015-195292, etc.

<Content of agglomerated inorganic filler>
The content of the aggregated inorganic filler in the insulating layer (resin sheet) of the present invention is preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 50% by mass or more, based on 100% by mass of the resin sheet, and is preferably 99% by mass or less, more preferably 90% by mass or less, and particularly preferably 80% by mass or less.
Furthermore, the combination of the upper and lower limits is not particularly limited, but is preferably 30% by mass or more and 99% by mass or less, more preferably 40% by mass or more and 90% by mass or less, and particularly preferably 50% by mass or more and 80% by mass or less.
The content of the aggregated inorganic filler in the resin composition forming the resin sheet of the present invention is preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 50% by mass or more, based on 100% by mass of the resin composition, and is preferably 99% by mass or less, more preferably 90% by mass or less, and particularly preferably 80% by mass or less.
Furthermore, the combination of the upper and lower limits is not particularly limited, but is preferably 30% by mass or more and 99% by mass or less, more preferably 40% by mass or more and 90% by mass or less, and particularly preferably 50% by mass or more and 80% by mass or less.
When the content of the aggregated inorganic filler is equal to or greater than the lower limit, the effect of improving thermal conductivity and the effect of controlling the linear expansion coefficient due to the inclusion of the aggregated inorganic filler tend to be sufficiently obtained. On the other hand, when the content is equal to or less than the upper limit, the formability of the resin sheet and the interfacial adhesion in the laminate structure tend to be improved.

When other non-agglomerated inorganic fillers are used in addition to the agglomerated inorganic filler, the content ratio of the agglomerated inorganic filler to the other non-agglomerated inorganic filler in the resin composition is not particularly limited, but is preferably 90:10 to 10:90 by mass, and more preferably 80:20 to 20:80.

<Breaking strength of agglomerated inorganic filler>
The breaking strength of the agglomerated inorganic filler is not particularly limited, but is preferably 300 MPa or less, more preferably 100 MPa or less, even more preferably 50 MPa or less, even more preferably 20 MPa or less, particularly preferably 15 MPa or less, and most preferably 10 MPa or less. When the breaking strength is below the upper limit, the agglomerated structure of the agglomerated inorganic filler is deformed during press treatment, making it easier for the agglomerated inorganic filler particles to come into surface contact with each other. On the other hand, the lower limit of the breaking strength is not particularly limited, but from the viewpoint of ease of handling, the breaking strength is preferably 2.5 MPa or more, more preferably 3 MPa or more, even more preferably 3.5 MPa or more, and particularly preferably 4 MPa or more.

<Elastic modulus of aggregated inorganic filler>
The elastic modulus of the aggregated inorganic filler is not particularly limited, but is preferably 10 MPa or more, more preferably 20 MPa or more, even more preferably 30 MPa or more, more preferably 50 MPa or more, and even more preferably 55 MPa or more. If the elastic modulus is equal to or greater than the above lower limit, the aggregated inorganic filler tends to undergo plastic deformation in the direction of the pressing pressure, and collapse of the aggregated structure can be suppressed. On the other hand, the upper limit of the elastic modulus is not particularly limited, but from the viewpoint of easily obtaining sufficient deformation, it is preferably 5 GPa or less, more preferably 2 GPa or less, even more preferably 1.5 GPa or less, even more preferably 1 GPa or less, still more preferably 500 MPa or less, particularly preferably 300 MPa or less, and most preferably 150 MPa or less.
When the agglomerated inorganic filler has an elastic modulus within the above range, it tends to maintain its spherical shape during press processing. On the other hand, when the breaking strength is within the above range, the contact portions of the agglomerated inorganic filler tend to deform, facilitating surface contact. While maintaining high thermal conductivity within the agglomerated inorganic filler, the contact thermal resistance at the agglomerated inorganic filler interface and the interface between the conductive layer and the insulating layer (resin sheet) can be reduced, thereby improving overall thermal conductivity.

When the agglomerated inorganic filler is contained in a resin sheet, the breaking strength and elastic modulus of the agglomerated inorganic filler can be measured after baking the resin of the resin sheet and removing the agglomerated inorganic filler to prevent deterioration of the agglomerated inorganic filler.

<Spherical filler>
A spherical filler may be used as the inorganic filler. The spherical filler of the present invention is not particularly limited, but preferably has a thermal conductivity of 10 W/m K or more, preferably 15 W/m K or more, more preferably 20 W/m K or more, for example, 20 to 30 W/m K, and a new Mohs hardness of 3.1 or more, for example, 5 to 10. By using such a spherical filler in combination with the above-mentioned agglomerated inorganic filler, the heat dissipation properties of the resulting resin sheet relative to metal can be further improved.

Here, "spherical" refers to anything that is generally recognized as spherical; for example, an average circularity of 0.4 or more may be considered spherical, or 0.6 or more. The upper limit of average circularity is usually 1. Circularity can be measured by image processing the projected image, and can be measured, for example, with Sysmex's FPIA series.

The spherical filler is preferably at least one selected from the group consisting of alumina, synthetic magnesite, crystalline silica, aluminum nitride, silicon nitride, silicon carbide, zinc oxide, and magnesium oxide. Use of these preferred spherical fillers can further enhance the heat dissipation properties of the resulting resin sheet.

The average particle size of the spherical filler is preferably in the range of 0.5 μm or more and 40 μm or less. This range makes it easier to maintain the dielectric breakdown characteristics of the resin sheet.

<Other fillers>
In the present invention, an organic filler may be used in combination with the inorganic filler. In the present invention, the organic filler is a component that does not contain an epoxy group, does not fall under the definition of a thermosetting catalyst, and is solid at room temperature, composed of organic components. Examples of organic fillers include natural products such as wood flour, optionally modified cellulose, starch, various organic pigments, thermoplastic resins, and thermosetting resins, which may be used in combination. Specific examples include acrylic resin particles, nylon resin particles, polyester resin particles, polystyrene resin particles, and silicone resin particles.
The inclusion of an organic filler may impart appropriate elongation to the resin composition, alleviate the stress that occurs, and suppress the occurrence of cracks in a temperature cycle test.

The upper limit of the average particle size of the organic filler is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. By keeping the particle size below these upper limits, resin sheets of various thicknesses can be produced without risking a decrease in thermal conductivity. The particle size of the organic filler is also the average particle size determined from the volume-averaged particle size distribution measurement results measured using a laser diffraction particle size distribution analyzer.

<<Other ingredients>>
The resin composition forming the resin sheet of the present invention may contain other components in addition to those described above, as long as the effects of the present invention are not impaired. Examples of other components include a surface treatment agent such as a silane coupling agent that improves the interfacial adhesive strength between the resin composition and an inorganic filler that is optionally used when producing a resin sheet using the resin composition, an insulating carbon component such as a reducing agent, a viscosity modifier, a dispersant, a thixotropy-imparting agent, a flame retardant, a colorant, an organic solvent, and a thermoplastic resin.
Among these, the inclusion of a dispersant makes it possible to form a uniform resin sheet, which may improve the thermal conductivity and dielectric breakdown characteristics of the resulting resin sheet. Furthermore, the inclusion of a thermoplastic resin may impart appropriate elongation to the resin composition, alleviate the stress generated, and suppress the occurrence of cracks in a temperature cycle test.

The resin composition according to the present invention may contain an organic solvent, for example, to improve the coatability when the resin composition is subjected to a coating step to form a sheet-like resin sheet.
Examples of organic solvents that may be contained in the resin composition according to the present invention include methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, propylene glycol monomethyl ether, etc. These organic solvents may be used alone or in combination of two or more.

When the resin composition according to the present invention contains an organic solvent, the content thereof is appropriately determined depending on the handleability of the resin composition when producing a resin sheet, the shape before curing, drying conditions, etc. When the resin composition is in the form of a slurry to be subjected to a coating step, the organic solvent is preferably used so that the solids concentration (total of components other than the solvent) in the resin composition or the resin composition of the present invention after addition of the inorganic filler described above is 10 to 90 mass %, particularly 40 to 80 mass %.
Furthermore, when the resin composition is in the form of a sheet that has been subjected to processes such as coating and drying, the organic solvent is preferably used so that the solid content (total of components other than the solvent) concentration in the resin composition of the present invention or in the resin composition of the present invention after the addition of an inorganic filler described below is 95 mass % or more, and more preferably 98 mass % or more.

<<<Conductive Layer 3>>>
The conductive layer 3 is a layer having high conductivity, and can serve as an electrode when the laminated structure of this embodiment is used as a heat dissipation substrate for a power device. The conductivity of the conductive layer 3 is usually 1×10 ⁵ Sm ⁻¹ or more, preferably 1×10 ⁶ Sm ⁻¹ or more, and more preferably 1×10 ⁷ Sm ⁻¹ or more.

The conductive layer is made of a copper plate, which provides good electrical and thermal conductivity.
The thickness of the conductive layer 3 is 100 μm or more, preferably 150 μm or more, more preferably 200 μm or more, more preferably 250 μm or more, and more preferably 300 μm or more. There is no particular upper limit, but the upper limit is 100,000 μm or less. By keeping the thickness within this range, good electrical and thermal conductivity can be obtained.
Furthermore, by not performing etching, it is easy to keep the amount of metal constituting the conductive layer remaining on the insulating layer in the blank areas, which will be described later, to a low level.
The thickness is measured using a film thickness meter at three or more points near the center of the copper plate, and the average value is used.

<<<Laminated structure>>>
One form of the laminated structure in this embodiment is characterized by a laminated structure of an insulating layer 2 and a conductive layer 3, and the laminated surface of the insulating layer 2 and the conductive layer 3 has a laminated portion where the insulating layer 2 and the conductive layer 3 are laminated and a blank portion where no conductive layer is present, and the laminated portion and the blank portion are present on the same plane P. Here, an enlarged view of the area enclosed by the dashed dotted line in FIG. 1 is shown in FIG. 2.
As shown in Fig. 2, the laminated portion, which is the laminated surface of the conductive layer 3 and the insulating layer 2, is on the same plane P as the blank portion, which is the surface of the insulating layer 2 facing the conductive layer 3 and where the conductive layer 3 is not present. Here, "on the same plane" means that the laminated surface of the insulating layer 2 and the conductive layer 3 is not recessed toward the insulating layer 2. When the conductive layer 3 and the insulating layer 2 are laminated and joined by pressure bonding, particularly when the insulating layer 2 contains a resin, a recess is generated in the insulating layer 2 due to the pressure from the conductive layer 3, as shown in Fig. 3. On the other hand, this embodiment is characterized in that the laminated surface of the insulating layer 2 and the conductive layer 3 is not recessed toward the insulating layer 2.
Note that "being on the same plane" does not mean excluding any depressions at all, but rather means that the insulating layer 2 may have a depression of 10% or less in the thickness direction, a depression of 5% or less, a depression of 3% or less, a depression of 2% or less, a depression of 1% or less, a depression of 0.5% or less, or a depression of 0.1% or less.
Furthermore, a molding resin may be laminated on a part of the insulating layer in the blank portion, but there must also be a blank portion where no molding resin is laminated.

Furthermore, in the surface of the insulating layer 2 facing the conductive layer 3, in blank areas where the conductive layer 3 is not present, the concentration of metals constituting the conductive layer 3 is 10,000 ppm or less. When the conductive layer 3 is formed by patterning through etching, the metals constituting the conductive layer 3 remain on the insulating layer 2. Such residual metals may affect the insulating properties of the insulating layer 2.
The residual metal concentration is preferably 10,000 ppm or less, more preferably 5,000 ppm or less, more preferably 3,000 ppm or less, more preferably 1,000 ppm or less, more preferably 500 ppm or less, more preferably 200 ppm or less, more preferably 100 ppm or less, more preferably 50 ppm or less, more preferably 30 ppm or less, more preferably 20 ppm or less, more preferably 10 ppm or less, more preferably 5 ppm or less, and more preferably 1 ppm or less.

Furthermore, at the boundary between the laminated portion and the blank portion, the angle formed by the intersection between the side of the conductive layer 3 and the insulating layer 2 is preferably 90°±10°, more preferably 90°±5°, more preferably 90°±3°, more preferably 90°±2°, and even more preferably 90°±1°. When the conductive layer 3 is formed by patterning through etching, the side of the conductive layer 3 may be tapered, depending on the thickness of the conductive layer, and the angle formed by the intersection between the side of the conductive layer 3 and the insulating layer 2 is likely to deviate from 90°±10°.

It is also preferable that the side surfaces of the conductive layer 3 are flat. When the conductive layer 3 is formed by patterning it through etching, warping or etching residue may occur on the side surfaces of the conductive layer 3. In such cases, the side surfaces of the conductive layer 3 may not be flat, as shown in Figure 4.

Alternatively, a pre-patterned conductive layer 3 can be molded with resin and then placed on the insulating layer 2, and the conductive and insulating layers can be bonded together. In this case, if the molded conductive layer is smaller in area than the insulating layer 2, a depression may form in part of the insulating layer, but the present invention can produce a laminate without any depressions.

<<<Manufacturing method>>>
Next, as representative examples of the method for manufacturing a laminated structure according to this embodiment, methods for manufacturing a resin sheet and methods A to C for manufacturing a laminated structure will be shown, but the laminated structures are not limited to those manufactured by these methods as long as they have the configuration described above.

<<Resin sheet manufacturing>>
The method for producing the insulating layer (resin sheet) of the present invention is not particularly limited. However, the insulating layer is obtained using a resin composition containing an inorganic filler, a thermosetting resin, and a thermosetting catalyst,
the inorganic filler comprises an aggregated inorganic filler, and the thermosetting resin comprises an epoxy resin;
It is preferable that the melting point of the thermosetting catalyst is 120° C. or higher and that the process comprises the following steps (a) and (b):
(a) a step of forming a sheet using the resin composition; (b) a step of heating the sheet obtained in step (a) at 95°C or less to make the reaction rate of the sheet 50% or more. The reaction rate of the sheet can be calculated as follows.
(Response rate)
It is calculated from the calorific value of the exothermic peak obtained by differential scanning calorimetry (DSC) when the temperature is raised from 40° C. to 250° C. at a rate of 10° C./min, using the following formula:
Reaction rate (%) = (1 - (amount of heat generated after step (b) / amount of heat generated after step (a))) x 100

In addition, other steps may be included in addition to steps (a) and (b).

<(a) Process>
Step (a) is a step of forming a sheet using the resin composition. The method for forming the sheet is not particularly limited and can be appropriately selected depending on the viscosity of the resin composition, the film thickness and size of the sheet to be formed, etc.
An example of a method for producing a resin sheet using, for example, a slurry-like resin composition will be described below.
First, a slurry resin composition is applied to the surface of a substrate to form a sheet (coating film; sheet-like resin composition). Specifically, a coating film is formed on the substrate using the slurry resin composition by a dip method, spin coating method, spray coating method, blade method, or any other method. A coating device such as a spin coater, slit coater, die coater, or blade coater can be used to apply the slurry resin composition. By using a coating device, it is possible to form a uniform coating film of any desired thickness on the substrate.
As the substrate, copper foil and PET film, which will be described later, are generally used, but there is no particular limitation.
Furthermore, when the resin composition of the present invention is in the form of a sheet that has been subjected to processes such as coating and drying, it may contain a solvent.

In step (a), the sheet formed using the resin composition may be dried at a temperature typically between 10 and 150°C, preferably between 25 and 120°C, and more preferably between 30 and 110°C, to remove solvents, low-molecular-weight components, and the like. If the drying temperature is below the upper limit, curing of the thermosetting resin in the sheet (coating) is suppressed, and the resin in the sheet (coating) tends to flow during the subsequent pressurization step, making it easier to remove voids. Furthermore, if the drying temperature is above the lower limit, solvents and the like can be removed effectively, tending to improve productivity.

The drying time is not particularly limited and can be adjusted appropriately depending on the state of the sheet (coating film), the drying environment, etc. When drying at a temperature below 80°C, the drying time is preferably 1 minute or more, more preferably 2 minutes or more, even more preferably 5 minutes or more, even more preferably 10 minutes or more, particularly preferably 20 minutes or more, and most preferably 30 minutes or more. On the other hand, the drying time is preferably 4 hours or less, more preferably 2 hours or less. When drying at 80°C or higher, the drying time is preferably 1 minute or more, preferably 30 minutes or less, more preferably 20 minutes or less, more preferably 15 minutes or less, and more preferably 10 minutes or less.
When the drying time is equal to or longer than the lower limit, the solvent and the like can be sufficiently removed, and the residual solvent tends to be prevented from forming voids in the resin sheet. When the drying time is equal to or shorter than the upper limit, productivity tends to be improved, and manufacturing costs tend to be reduced.

<<Laminated structure fabrication>>
<Manufacturing method A>
Manufacturing method A is a method in which the periphery of the conductive layer is molded using a thermoplastic resin, and pressure is applied uniformly to the surface of the insulating layer facing the conductive layer, thereby adhering the conductive layer to the insulating layer.
a step of covering the conductive layer with a thermoplastic resin heated to a softening point or higher so that the insulating layer side surface of the conductive layer made of a copper plate with a thickness of 100 μm or more and the insulating layer side surface of the thermoplastic resin form the same plane;
a step of laminating the conductive layer and the insulating layer side of the thermoplastic resin, which form the same plane, on the insulating layer, and applying pressure at a temperature equal to or lower than the softening point of the thermoplastic resin to bond the conductive layer and the insulating layer together;
A method for manufacturing a laminated structure includes the steps of curing the insulating layer, and removing the cured thermoplastic resin.
The step of laminating the conductive layer and the insulating layer and curing them under pressure is preferably carried out in the step (b) described below.

The thermoplastic resin is not particularly limited, and typically polyolefins such as polyethylene and polypropylene are used, but are not limited to these. The shape is also not particularly limited, and pellets are usually used. The softening point of the thermoplastic resin is usually 30°C or higher, preferably 50°C or higher, and usually 300°C or lower, preferably 200°C or lower.

After curing, the thermoplastic resin is removed from the laminate of the insulating layer and the conductive layer. By using a thermoplastic resin, the resin softens when heated to a temperature close to its softening point, allowing the thermoplastic resin to be removed from the laminate of the insulating layer and the conductive layer without using a release agent.

<Manufacturing method B>
Manufacturing method B is a method in which the periphery of the conductive layer is molded using a thermosetting resin, and pressure is applied uniformly to the surface of the insulating layer facing the conductive layer, thereby adhering the conductive layer to the insulating layer.
covering the conductive layer with a thermosetting resin so that a surface of the conductive layer facing the insulating layer and a surface of the thermosetting resin facing the insulating layer form the same plane;
curing the thermosetting resin covering the conductive layer;
the conductive layer and the insulating layer side of the thermosetting resin, which form the same plane, are stacked together, and the insulating layer is pressed to harden the insulating layer; and the thermosetting resin is removed.
In the method for producing a laminated structure, the conductive layer is a copper plate having a thickness of 100 μm or more.
The step of laminating the conductive layer and the insulating layer and curing them under pressure is preferably carried out in the step (b) described below.

There are no particular limitations on the thermosetting resin, and typically, silicone resins with rubber properties are used, but this is not limited to these.

After hardening, the thermosetting resin is removed from the laminate of the insulating layer and the conductive layer. By using a thermosetting resin such as silicone rubber, the thermosetting resin can be removed from the laminate of the insulating layer and the conductive layer without using a release agent.

<Manufacturing method C>
In manufacturing method C, an insulating layer and a conductive layer are laminated together, and then the conductive layer is bonded to the insulating layer by isostatic pressing.
laminating an insulating layer and a conductive layer;
isostatically pressing the laminate;
curing the insulating layer;
In the method for producing a laminated structure, the conductive layer is a copper plate having a thickness of 100 μm or more.
The step of laminating the conductive layer and the insulating layer and curing them under pressure is preferably carried out in the step (b) described below.

There are no particular limitations on the type of isostatic pressing that can be used, as long as it is possible to apply equal pressure from various directions. For example, one example is hydrostatic lamination, in which a laminate of insulating and conductive layers is enclosed in a waterproof film that can conform to the laminate, and then pressed with hydrostatic pressure.

After curing, the laminate is removed from the waterproof film it was encased in during isostatic pressing. The waterproof film used here can be any commercially available product. Materials such as nylon, polyethylene, EVA, and bag-shaped films made by laminating these materials can be used. Furthermore, since these can be easily peeled off from the laminate, it is preferable to cover the laminate with a Teflon (registered trademark) sheet, silicone rubber sheet, or fluororubber sheet and encase it in the waterproof film.

<(b) Process>
In step (b), the sheet obtained in step (a) is heated to 95° C. or less to bring the reaction rate of the sheet to 50% or more. This step reduces cure shrinkage and ultimately reduces the amount of warpage.
The reactivity of the sheet (resin sheet) is sufficient as long as it is 50% or more, preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. The reactivity may be 100%. The upper limit of the reactivity can be appropriately adjusted depending on the use form of the resin sheet.

The heating temperature of the sheet is not particularly limited as long as it is 95°C or less, but 94°C or less is more preferable, and 93°C or less is even more preferable. There is also no particular lower limit, but 10°C or more is preferred, 20°C or more is more preferable, 30°C or more is even more preferable, 40°C or more is even more preferable, and 50°C or more is particularly preferable. By keeping the heating temperature within this range, curing shrinkage due to cooling is reduced, warping can be suppressed, and curing tends to proceed.

The heating time can be adjusted as needed to ensure that the sheet has a reaction rate of 50% or more, but is preferably 10 hours or less, more preferably 5 hours or less. There is no particular lower limit, but 1 hour or more is preferred, more preferably 2 hours or more. Keeping the heating time within the above range tends to reduce the manufacturing time for the resin sheet and cut production costs. It also tends to sufficiently remove voids and gaps within the resin sheet, improving heat transfer performance and voltage resistance.

In step (b), heating and pressure may be applied simultaneously. By applying pressure in addition to heating, the inorganic fillers are bonded to each other to form heat paths, and voids and gaps in the sheet can be suppressed.
The pressing time may be the same as or different from the heating time.
The pressing pressure is preferably 0.1 MPa or more, more preferably 0.5 MPa or more, and even more preferably 1 MPa or more, and is preferably 1000 MPa or less, more preferably 700 MPa or less, and even more preferably 500 MPa or less.
When the pressing pressure is within this range, the secondary particles of the inorganic filler are not destroyed, and a sheet having high thermal conductivity can be obtained in the sheet-like resin sheet without voids, etc. Furthermore, when the pressing pressure is equal to or greater than the lower limit, contact between the inorganic fillers is good, making it easier to form heat conduction paths, and therefore a resin sheet having high thermal conductivity tends to be obtained.

(Pressure application process)
A pressurizing step may be performed after the step (a) and before the step (b). By applying pressure, the inorganic fillers are bonded to each other to form heat paths, and voids and gaps in the sheet can be suppressed.
The time for the pressurizing step is not particularly limited. The time for the pressurizing step is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more. The time for the pressurizing step is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less.
When the pressing time is equal to or less than the upper limit, the manufacturing time of the resin sheet can be reduced, and the production cost tends to be reduced. On the other hand, when the pressing time is equal to or more than the lower limit, the gaps and voids in the resin sheet (insulating layer) can be sufficiently removed, and the heat transfer performance and the withstand voltage characteristics tend to be improved.
The pressing pressure is preferably 0.1 MPa or more, more preferably 0.5 MPa or more, and even more preferably 1 MPa or more, and is preferably 1000 MPa or less, more preferably 700 MPa or less, and even more preferably 500 MPa or less.
By keeping the pressing pressure within this range, it is possible to sufficiently remove gaps and voids in the resin sheet (insulating layer), which tends to improve the heat transfer performance and voltage resistance characteristics.

(Post-curing process)
A post-curing step may be included after step (b). By performing post-curing, the resin sheet is completely cured, and peeling of the sheet from the substrate during high-temperature storage tends to be suppressed. The means for post-curing is not particularly limited, but examples include heating, pressure, and a combination thereof.
The time for the post-curing step is not particularly limited. The time for the post-curing step is preferably 5 minutes or more, more preferably 10 minutes or more, even more preferably 20 minutes or more, and particularly preferably 30 minutes or more. The time for the post-curing step is preferably 5 hours or less, more preferably 4 hours or less, and even more preferably 3.5 hours or less.
When the time for the post-curing step is equal to or less than the upper limit, the time required for producing the resin sheet can be reduced, and production costs tend to be reduced. On the other hand, when the time is equal to or more than the lower limit, peeling from the substrate during high-temperature storage tends to be suppressed.
The heating temperature in the post-curing step is not particularly limited. The heating temperature in the post-curing step is preferably 100°C or higher, more preferably 120°C or higher, even more preferably 140°C or higher, and particularly preferably 160°C or higher. When the heating temperature is equal to or higher than the lower limit, the uncured portion of the resin can be cured, and by completely curing the resin, peeling of the resin sheet from the substrate during high-temperature storage tends to be suppressed.
The pressure conditions in the post-curing step are not particularly limited. The pressure in the post-curing step is preferably 30 MPa or less, more preferably 25 MPa or less, even more preferably 20 MPa or less, and particularly preferably 15 MPa or less.
When the pressure condition is equal to or less than the upper limit, cracks and the like are less likely to occur in the resin sheet during the post-curing step.

The thickness of the resin sheet (insulating layer) that has undergone step (b) or step (b) plus the post-curing step is not particularly limited, but is preferably 50 μm or more, more preferably 80 μm or more, and even more preferably 100 μm or more. The thickness of the resin sheet is preferably 400 μm or less, more preferably 300 μm or less. When the thickness of the resin sheet is equal to or greater than the lower limit, voltage resistance characteristics are obtained and the breakdown voltage tends to improve. When the thickness of the resin sheet is equal to or less than the upper limit, the device can be made smaller and thinner, and the thermal resistance of the resulting resin sheet tends to be reduced.

The present invention will be described in more detail below with reference to examples, but it goes without saying that the scope of the present invention is not limited to the examples.
[raw materials]
The raw materials used in the examples and comparative examples are as follows.

<Thermosetting resin>
Resin component 1: Bifunctional epoxy resin disclosed in Resin component 1 of JP 2020-63438 A Resin component 2: Biphenyl-type solid epoxy resin manufactured by Mitsubishi Chemical Corporation Resin component 3: Multifunctional epoxy resin containing a structure having four or more glycidyl groups per molecule manufactured by Showa Denko K.K.

<Agglomerated inorganic filler>
Inorganic filler 1: boron nitride agglomerated particles having a house-of-cards structure, produced in accordance with the method for producing boron nitride agglomerated particles disclosed in the examples of WO 2015/119198
New Mohs hardness: 2
Volume average particle size: 45 μm

<Other fillers>
Inorganic filler 2: spherical alumina particles manufactured by Admatechs Co., Ltd.
Peak particle size: 15 μm, 0.6 μm

<Curing agent>
Curing agent 1: Phenolic resin curing agent ("MEH-8000H" manufactured by Meiwa Kasei Co., Ltd.)

<Thermosetting catalyst component>
Thermosetting catalyst 1: 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine. This catalyst contains both an imidazole-derived structure and a triazine-derived structure in a single molecule ("Curesol 2E4MZ-A" manufactured by Shikoku Chemical Industries, Ltd.).
Molecular weight: 247
Melting point: 215-225°C
Thermosetting catalyst 2: 2-phenyl-4,5-dihydroxymethylimidazole ("Curezol 2PHZ-PW" manufactured by Shikoku Chemical Industries, Ltd.)
Molecular weight: 204
Melting point: 230°C or higher (decomposes at 230°C)

<Measurement of copper concentration in the blank area on the surface of the insulating layer>
The copper concentration in the blank area on the surface of the insulating layer was measured using XPS.
The measurement conditions are as follows.
X-ray Photoelectron Spectroscopy (abbreviated as XPS, or ESCA)
・Device: KRATOS ULTRA2
・X-ray source: Monochromatic Al-Kα, output 15kV-225W (15mA)
Charge neutralization: Filament current, Filament bias, Charge balance = 0.43 V, 1 V, 4 V
Spectroscopic system: Pass energy wide spectrum 160 eV
Narrow spectrum 80 eV (Na1S, Zn2p, Cu2p, Fe2p, Ca2p, Cl2p, S2p, Al2s, Al2p, Br3s)
40eV (Si2p)
20eV (B1s, C1s, N1s, O1s)
・Measurement area (Collimation, lens):
Wide spectrum, narrow spectrum 700 μm x 300 μm (Slot, Hybrid)
・Removal angle (from surface): 90°
Energy correction: B1s = 190.9 eV @ BN

[Example 1]
<Preparation of Resin Composition (Synthesis Example 1)>
Using a planetary stirring device, resin component 1, resin component 2, resin component 3, curing agent 1, thermosetting catalyst 1, thermosetting catalyst 2, inorganic filler 1, and inorganic filler 2 were mixed to obtain a mixture in the mass ratios shown in Table 1 below. When preparing this mixture, a slurry-like resin composition was prepared using 18% by mass each of methyl ethyl ketone and cyclohexanone so that the mixture accounted for 64% by mass (solids concentration) of the coating slurry.

<(a) Process>
The resulting slurry-like resin composition was applied onto a PET film by a doctor blade method, and then dried by heating at 60° C. for 120 minutes.

The sheet that had undergone step (a) was pressed at 50°C and 147 MPa for 10 minutes to obtain a sheet with a thickness of 150 μm. The total content of methyl ethyl ketone and cyclohexanone in the sheet was 1% by mass or less (solids concentration of 99% by mass or more). This sheet is designated Sheet 1.

A peelable PET film (MRV50 manufactured by Mitsubishi Chemical Corporation) was placed on a stainless steel plate with the peeled surface facing up, and a 20 mm diameter, 0.5 mm thick, disk-shaped copper electrode was placed on top of it. 30 g of polyethylene pellets were placed on top of the electrode, and the peelable PET film was placed on top of that with the peeled surface facing down, and then a 150 mm × 150 mm × 3 mm thick stainless steel plate was placed on top.
The electrode was slowly pressed (up to 5 MPa) for 10 minutes at 175°C using a press, then sandwiched between two 150 mm x 150 mm x 15 mm thick SUS plates and slowly cooled. The PET films on both sides were peeled off to obtain a polyethylene sheet in which the lower surface of the electrode and the surrounding resin were flush with each other.

<(b) Process>
Sheet 1 was attached to a 40 mm x 80 mm x 2 mm copper plate with the coated side facing down. The PET film was peeled off, and a polyethylene sheet with the lower surface of the electrode and the surrounding resin flush with each other was placed on top of it with the electrode side facing down. The sheet was then pressed at 90°C and a pressure of 4.9 MPa for 4 hours. The sheet was then allowed to cool naturally while maintaining the pressure in the press.
The polyethylene was then peeled off while being heated at 80°C, yielding a laminate comprising an insulating layer (Sheet 1) and a patterned conductor (disk-shaped copper electrode) on a thermal conductor (copper plate). The laminated surface of the insulating layer and the electrode was flush with the electrode-side surface of the insulating layer. The copper concentration in the area surrounding the electrode on the insulating layer was measured by XRF, and was found to be below the detection limit (1,000 ppm or less).
The insulating layer of the resulting laminate had a reaction rate of 85% or more.
The angle formed by the side surface of the conductive layer and the insulating layer was within 90°±5°.
A withstand voltage test was carried out on the obtained laminate, and the BDV was found to be 8000 V. The withstand voltage measurement was carried out in an insulating medium (Fluorinert) under the conditions of increasing the voltage in 500 V steps, with each step lasting 1 minute.

[Example 2]
<(b) Process>
Sheet 1 prepared in Example 1 was attached to a 40 mm x 80 mm x 2 mm thick copper plate with the coated side facing down. The PET film was peeled off, and a 20 mm diameter, 0.5 mm thick disc-shaped copper electrode was placed on top of it. Silicone rubber sheets were placed on top and bottom of the electrode. This was placed in a vacuum packing plastic bag (Hiryu) and vacuum laminated using a vacuum laminator.

This was isostatically pressed at 90°C and 4.9 MPa for 4 hours using a hot water laminator. The vacuum-packing plastic bag was then opened to obtain a laminate comprising an insulating layer (the sheet prepared in Synthesis Example 1) and a patterned conductor (disk-shaped copper electrode) on a thermal conductor (copper plate). The lamination surface of the insulating layer and the electrode was flush with the electrode-side surface of the insulating layer. The copper concentration in the area surrounding the electrode on the insulating layer (blank area on the insulating layer surface) was measured by XRF, and was found to be below the detection limit (1,000 ppm or less).
The insulating layer of the resulting laminate had a reaction rate of 85% or more.
The angle formed by the side surface of the conductive layer and the insulating layer was within 90°±5°.
A withstand voltage test was carried out on the obtained laminate, and the BDV was found to be 8000 V. The withstand voltage measurement was carried out in an insulating medium (Fluorinert) under the conditions of increasing the voltage in 500 V steps, with each step lasting 1 minute.

[Example 3]
<(b) Process>
Sheet 1 prepared in Example 1 was attached to a 40 mm x 80 mm x 2 mm thick copper plate with the coated side facing down. The PET film was peeled off, and a 20 mm diameter, 1.0 mm thick disc-shaped copper electrode was placed on top of it. Silicone rubber sheets were placed on top and bottom of the electrode. This was placed in a vacuum packing plastic bag (Hiryu) and vacuum laminated using a vacuum laminator.

This was isostatically pressed at 90°C and 4.9 MPa for 4 hours using a hot water laminator. The vacuum-packing plastic bag was then opened, and a laminate was obtained comprising an insulating layer (Sheet 1 prepared in Example 1) and a patterned conductor (disk-shaped copper electrode) on a thermal conductor (copper plate). The lamination surface of the insulating layer and the electrode was flush with the electrode-side surface of the insulating layer. The copper concentration in the area surrounding the electrode on the insulating layer (blank area on the insulating layer surface) was measured by XRF, and was found to be below the detection limit (1,000 ppm or less).
The insulating layer of the resulting laminate had a reaction rate of 85% or more.
The angle formed by the side surface of the conductive layer and the insulating layer was within 90°±5°.
The obtained laminate was subjected to a withstand voltage test up to 2500 V, and it did not break down at voltages up to 2500 V. The withstand voltage measurement was carried out in an insulating medium (Fluorinert) under conditions of 500 V step increase with each step lasting 1 minute.

[Comparative Example 1]
Sheet 1 prepared in Example 1 was attached to a 40 mm x 80 mm x 2 mm copper plate with the coated side facing down. The PET film was peeled off, and a 20 mm diameter, 0.5 mm thick disc-shaped copper electrode was placed on top. A 0.5 mm thick silicone rubber sheet and 20 sheets of fine paper were placed on top of the electrode, and the electrode was pressed at 90°C with a pressure of 4.9 MPa. The electrode was then allowed to cool naturally while maintaining pressure in the press. The electrode surface and the insulating layer were not flush with each other, and some electrode sinking was observed.
The reaction rate of the insulating layer of the resulting laminate was 85% or more, but the angle formed by the side of the conductive layer and the insulating layer could not be measured due to the sinking of the electrode.
The resulting laminate had a withstand voltage of less than 500 V. The withstand voltage measurement was carried out in an insulating medium (Fluorinert) under the conditions of increasing the voltage in 500 V steps, with each step lasting 1 minute.

[Comparative Example 2]
Sheet 1 prepared in Example 1 was attached to a 40 mm x 80 mm x 2 mm copper plate with the coated side facing down. The PET film was peeled off, and a 20 mm diameter, 0.5 mm thick, circular copper electrode was placed on top. A 0.5 mm thick silicone rubber sheet cut out to a 20 mm diameter was placed around the electrode and pressed at 90°C with a pressure of 4.9 MPa. The sheet was then allowed to cool naturally while maintaining pressure in the press. The electrode surface and the insulating layer were not flush with each other, and some electrode sinking was observed. The insulating layer of the resulting laminate had a reaction rate of 85% or higher, but the angle formed by the side of the conductive layer and the insulating layer could not be measured due to the electrode sinking.
A withstand voltage test was carried out on the obtained laminate, and the BDV was found to be 2500 V. The withstand voltage measurement was carried out in an insulating medium (Fluorinert) under the conditions of increasing the voltage in 500 V steps, with each step lasting 1 minute.

[Comparative Example 3]
The sheet 1 prepared in Example 1 was attached to a copper plate measuring 40 mm × 80 mm × 2 mm thick with the coated side facing down. The PET film was peeled off, and a copper plate measuring 40 mm diameter × 80 mm × 1 mm thick was placed on top of it.
The plate was pressed at 90° C. under a pressure of 4.9 MPa for 4 hours, and an attempt was made to etch it, but the upper copper plate was too thick and etching was difficult.

[Comparative Example 4]
Sheet 1 prepared in Example 1 was sandwiched between a 40 mm × 80 mm × 2 mm thick copper plate and a 40 mm × 80 mm × 0.3 mm thick copper plate, and cured at 10 MPa, 120 °C for 30 minutes, and then 175 °C for 30 minutes. After curing, the sheet was patterned using an etching solution containing ferric chloride as the main component, washed with a cleaning solution containing sodium hydroxide as the main component, and the copper concentration in the area surrounding the copper pattern (blank areas on the surface of the insulating layer) was measured by XRF, and was found to be 11,000 ppm to 17,000 ppm.

1 Thermal conductor 2 Insulating layer 3 Conductive layer P Plane

Claims (7)

a thermal conductor having a thermal conductivity of 10 W/m K or more;
an insulating layer laminated on at least one surface of the thermal conductor;
a conductive layer disposed on a surface of the insulating layer opposite to a surface on which the thermal conductor is laminated ;
a laminated surface of the insulating layer and the conductive layer has a laminated portion where the insulating layer and the conductive layer are laminated and a blank portion where no conductive layer is present,
the laminated portion and the blank portion are present on the same plane on the laminated surface of the insulating layer and the conductive layer,
The conductive layer is a copper plate having a thickness of 100 μm or more,
and the copper concentration in the blank portion on the surface of the insulating layer is 10,000 ppm or less ,
the insulating layer is a resin sheet obtained using a resin composition containing an inorganic filler, a thermosetting resin, and a thermosetting catalyst;
the inorganic filler comprises an aggregated inorganic filler;
the thermosetting resin includes an epoxy resin;
The melting point of the thermosetting catalyst is 120°C or higher,
A method for producing a laminated structure, comprising the following steps (a) and (b):
(a) forming a sheet using the resin composition
(b) a step of heating the sheet obtained in the step (a) at 95°C or less to make the reaction rate of the sheet 50% or more.
The reaction rate of the sheet is calculated as follows.
(Response rate)
It is calculated from the calorific value of the exothermic peak obtained by differential scanning calorimetry (DSC) when the temperature is raised from 40° C. to 250° C. at a rate of 10° C./min, using the following formula:
Reaction rate (%) = (1 - (amount of heat generated after step (b) / amount of heat generated after step (a))) x 100 a thermal conductor having a thermal conductivity of 10 W/m K or more;
an insulating layer laminated on at least one surface of the thermal conductor;
a patterned conductive layer disposed on a surface of the insulating layer opposite to a surface on which the thermal conductor is laminated ;
a laminated surface of the insulating layer and the conductive layer has a laminated portion where the insulating layer and the conductive layer are laminated and a blank portion where no conductive layer is present,
the laminated portion and the blank portion are present on the same plane on the laminated surface of the insulating layer and the conductive layer,
The conductive layer is a copper plate having a thickness of 100 μm or more,
and an angle formed by a side surface of the conductive layer and the insulating layer at a boundary portion between the blank portion and the laminated portion is 90°±10° ,
the insulating layer is a resin sheet obtained using a resin composition containing an inorganic filler, a thermosetting resin, and a thermosetting catalyst;
the inorganic filler comprises an aggregated inorganic filler;
the thermosetting resin includes an epoxy resin;
The melting point of the thermosetting catalyst is 120°C or higher,
A method for producing a laminated structure, comprising the following steps (a) and (b):
(a) forming a sheet using the resin composition
(b) a step of heating the sheet obtained in the step (a) at 95°C or less to make the reaction rate of the sheet 50% or more.
The reaction rate of the sheet is calculated as follows.
(Response rate)
It is calculated from the calorific value of the exothermic peak obtained by differential scanning calorimetry (DSC) when the temperature is raised from 40° C. to 250° C. at a rate of 10° C./min, using the following formula:
Reaction rate (%) = (1 - (amount of heat generated after step (b) / amount of heat generated after step (a))) x 100 3. The method for producing a laminated structure according to claim 1, wherein the insulating layer is a resin sheet containing a matrix resin containing agglomerated particles of boron nitride. The method for producing a laminate structure according to any one of claims 1 to 3 , wherein the resin composition contains the thermosetting catalyst in an amount of 5 mass % or less relative to the resin component of the resin composition.
The resin component here refers to the components obtained by excluding the inorganic filler and the solvent, if any, from the resin composition. The method for producing a laminate structure according to any one of claims 1 to 4 , wherein the thermosetting catalyst contains a compound having a structure derived from imidazole and/or dicyandiamide. The method for producing a laminate structure according to any one of claims 1 to 5 , wherein in the step (b), the heating time of the sheet is 5 hours or less. The method for producing a laminate structure according to any one of claims 1 to 6 , wherein in the step (b), a pressing pressure in the range of 0.1 MPa to 1000 MPa is applied simultaneously with heating.