Multilayer body and method for producing same

Abstract

[Problem] To provide a multilayer body which has excellent heat dissipation performance in the thickness direction, excellent thermal diffusibility in the in-plane direction, and excellent electrical insulation performance in the thickness direction, and which is not susceptible to cracking. [Solution] Disclosed is a multilayer body which comprises a metal layer A, an insulating layer that is provided on at least one surface of the metal layer A, and a metal layer B that is provided on a surface of the insulating layer, the surface being on the reverse side from the metal layer A. This multilayer body is characterized in that: the insulating layer comprises a supporting layer and a heat transfer layer that contains at least an inorganic filler and a binder resin; and the supporting layer and the heat transfer layer are alternately stacked in a direction that is generally perpendicular to the thickness direction of the insulating layer so that the total number of layers is 3 or more.

Description

Laminate and manufacturing method thereof

[0001] The present invention relates to a laminate having excellent heat dissipation properties, particularly heat dissipation properties in the thickness direction, and a method for producing the same.

[0002] In recent years, there has been a demand for miniaturization of electronic components, higher density packaging, and higher performance. Furthermore, as semiconductor elements and the like become smaller and more powerful, the issue of how to dissipate heat generated by semiconductor elements and the like in a small space has become an issue.

[0003] One solution to the above problem is to use a ceramic plate with high thermal conductivity as the insulating layer of the board on which the components are mounted, and to efficiently dissipate the heat generated by the elements to the housing or cooling fins.However, there is a problem in that the ceramic plate, which is processed to be thin in order to reduce thermal resistance in the thickness direction, easily cracks.

[0004] In order to improve the cracking tendency of substrate materials, measures have been taken to use a resin material with increased thermal conductivity instead of a ceramic plate as an insulating layer (see Patent Documents 1 and 2). Patent Document 1 considers increasing thermal conductivity by filling alumina powder into the resin. However, since Patent Document 1 uses alumina powder, although a high filling rate of over 80 vol% is possible, the alumina powder itself has low thermal conductivity, which is a problem in that the thermal conductivity of the substrate is low.

[0005] In Patent Document 2, high thermal conductivity is achieved with a low filler loading by controlling the orientation of boron nitride powder. Primary particles of boron nitride powder are typically flaky. When dispersed as a filler in an insulating layer, the boron nitride powder aligns in the plane during coating or press curing, resulting in poor thermal conductivity. However, by dispersing boron nitride powder aggregates in the insulating layer, the orientation is controlled in the vertical direction, achieving high thermal conductivity and efficiently forming a thermal path. This allows for a reduced loading, resulting in improved voltage resistance. However, Patent Document 2 requires that the agglomerated powder used have high particle strength to prevent breakage during the substrate fabrication process and minimal voids within the agglomerated powder. However, due to the high particle strength, deformation does not occur, making it difficult to fill the internal voids with resin, resulting in poor electrical properties such as electrical insulation, and insufficient contact between boron nitride powder particles, resulting in reduced thermal conductivity.

[0006] In Patent Documents 3 and 4, sheets of thermoplastic fluororesin having carbon nanotubes dispersed therein are rolled and molded, and the resulting sheets are laminated and then hot-pressed to obtain resin blocks. The resin blocks are then sliced ​​to obtain resin sheets in which the carbon nanotubes serving as a filler are oriented in the thickness direction. The orientation of the carbon nanotubes in the thickness direction allows for the production of resin sheets with excellent thermal conductivity in the thickness direction. However, because the resin sheets disclosed in Patent Documents 3 and 4 contain a conductive material such as carbon nanotubes as a filler, the resulting resin sheets are conductive, which presents a problem in that they cannot be used for circuit boards that require insulation.

[0007] Japanese Patent Application Laid-Open No. 6-44824 Japanese Patent Application Laid-Open No. 2010-157563 Japanese Patent Application Laid-Open No. 7092299 Japanese Patent Application Laid-Open No. 2021-4284

[0008] An object of the present invention is to provide a laminate that has excellent heat dissipation properties in the thickness direction, thermal diffusion properties in the in-plane direction, and insulation properties in the thickness direction, and is also resistant to cracking, and a method for producing the same. Another object of the present invention is to provide a circuit board using the laminate.

[0009] The present inventors have found that the above-mentioned problems can be solved by the following aspects: <Aspect 1> A laminate including a metal layer A, an insulating layer provided on at least one side of the metal layer A, and a metal layer B provided on the side of the insulating layer opposite to the metal layer A, wherein the insulating layer includes a support layer and a heat transfer layer containing at least an inorganic filler and a binder resin, and the support layer and the heat transfer layer are alternately stacked in a total of three or more layers in a direction substantially perpendicular to the thickness direction of the insulating layer. <Aspect 2> The laminate according to Aspect 1, wherein the inorganic filler is plate-shaped and extends substantially perpendicular to the in-plane direction of the laminate. <Aspect 3> The laminate according to Aspect 1 or 2, wherein the inorganic filler is hexagonal boron nitride particles. <Aspect 4> The laminate according to any one of Aspects 1 to 3, wherein the binder resin is an aramid resin. <Aspect 5> The laminate according to any one of Aspects 1 to 4, wherein the tensile shear adhesive strength between the insulating layer and the metal layer is 0.1 MPa or more. <Aspect 6> A laminate according to any one of Aspects 1 to 5, wherein the support layer has a modulus of elasticity of 10 MPa or more. <Aspect 7> A circuit board comprising the laminate according to any one of Aspects 1 to 6. <Aspect 8> A method for producing the laminate according to any one of Aspects 1 to 6, the method comprising: a heat transfer layer producing step of forming a film using a slurry containing a plate-like inorganic filler, a binder resin, and a solvent; an insulating layer producing step of alternately laminating heat transfer layers and support layers and then cutting the laminate; and a metal layer forming step of bonding metal layers to both sides of the insulating layer.

[0010] According to the present invention, it is possible to provide a laminate that has excellent heat dissipation properties in the thickness direction, thermal diffusivity in the in-plane direction, and insulation properties in the thickness direction, and is not easily cracked. Furthermore, according to the present invention, it is possible to provide a method for producing such a laminate. The laminate of the present invention can be suitably used as a circuit board that requires insulation properties and heat dissipation properties in the thickness direction, in particular.

[0011] Fig. 1 shows a schematic diagram of a cross section of a laminate according to an embodiment of the present disclosure. Fig. 2 shows a scanning electron micrograph of a cross section perpendicular to the surface direction of a laminate according to an example. Fig. 3 shows a scanning electron micrograph of a cross section perpendicular to the surface direction of a laminate according to Comparative Example 2. Fig. 4 shows a scanning electron micrograph of a cross section perpendicular to the surface direction of a laminate according to Comparative Example 3.

[0012] Hereinafter, embodiments of the present invention will be described. <<Laminate>> The laminate of the present disclosure comprises a metal layer A, an insulating layer provided on at least one side of the metal layer A, and a metal layer B provided on the insulating layer on the side opposite to the metal layer A. The insulating layer has at least a structure in which a total of three or more support layers and heat transfer layers are alternately stacked. The heat transfer layer contains at least a plate-like inorganic filler. The inorganic filler is oriented in a direction approximately perpendicular to the insulating layer.

[0013] FIG. 1 shows a schematic diagram of a cross section perpendicular to the plane direction of one embodiment of a laminate according to the present disclosure. As can be seen in FIG. 1, a laminate 11 has a configuration in which a metal layer A is provided on one side of a planar insulating layer 12 and a metal layer B is provided on the other side. An adhesive layer 13 may be provided between the insulating layer and the metal layer A, and between the insulating layer and the metal layer B. <Thickness> The thickness of the laminate may vary depending on the thermal resistance value and breakdown voltage required for the laminate, but is, for example, 0.05 to 20 mm, preferably 0.1 to 10 mm. <Thermal resistance value in the thickness direction> Preferably, the laminate according to the present disclosure has a thermal resistance of 0.60 (K cm) in the thickness direction. ２ ) / W or less.

[0014] In particular, when copper plates of 1 mm thickness are used on both sides of the laminate, the thermal resistance value in the thickness direction of the laminate is 0.60 (K cm ２ ) / W or less, 0.57 (K cm ２ ) / W or less, 0.54 (K cm ２ ) / W or less, 0.51 (K cm ２ ) / W or less 0.48 (K・cm ２ ) / W or less, 0.45 (K cm ２ ) / W or less, 0.42 (K cm ２ ) / W or less, 0.39 (K cm ２ ) / W or less, 0.36 (K cm２ ) / W or less, 0.33 (K cm ２ ) / W or less, 0.30 (K cm ２ ) / W or less or 0.26 (K cm ２ ) / W or less, and / or 0.06 (K cm ２ ) / W or more, 0.09 (K cm ２ ) / W or more, 0.12 (K・cm ２ ) / W or more, or 0.15 (K cm ２ When the laminate of the present invention is applied to a circuit board, from the viewpoint of imparting good heat dissipation properties to the laminate, the surface roughness may be 0.39 (K cm ２ ) / W or less, and 0.36 (K cm ２ ) / W or less is more preferable, and 0.33 (K cm ２ ) / W or less is more preferable, and 0.30 (K cm ２ ) / W or less is particularly preferred.

[0015] The thermal resistance value of the laminate can be determined by a steady-state method. <Breakdown voltage> Preferably, the dielectric breakdown voltage in the thickness direction of the laminate is 3 kV / mm or more, 4 kV / mm or more, 5 kV / mm or more, 6 kV / mm or more, 7 kV / mm or more, or 8 kV / mm or more. When it is 5 kV / mm or more, dielectric breakdown is unlikely to occur, and defects in electronic devices are avoided, which is preferable.

[0016] The dielectric breakdown voltage of the laminate is measured in accordance with the test standard ASTM D149-20 using a dielectric strength tester.

[0017] The elements constituting the laminate of the present disclosure are described in more detail below. <Insulating Layer> The insulating layer of the present disclosure uses a heat transfer layer with high in-plane thermal conductivity and a support layer that bonds the heat transfer layers together to maintain the structure. In the insulating layer of the present disclosure, the stacking direction of the heat transfer layer is approximately perpendicular to the thickness direction of the insulating layer, which results in a relatively high thermal conductivity in the thickness direction of the insulating layer and a relatively low thermal resistance value in the thickness direction of the laminate.

[0018] Here, in the present invention, "the stacking direction is approximately perpendicular to the thickness direction of the insulating layer" means that the angle between the stacking direction and the thickness direction is 45° to 135°, and preferably this angle is 55° to 125°, 65° to 115°, 75° to 105°, 85° to 95°, 87° to 93°, or 89° to 91°.

[0019] In the insulating layer according to the present disclosure, the heat transfer layer is preferably present continuously between one main surface and the other main surface of the insulating layer and is present in a manner that it is exposed at both the one main surface and the other main surface, so that heat can be dissipated from the member and metal layer in contact with one surface of the insulating layer to the member and metal layer in contact with the other surface of the insulating layer.

[0020] In the insulating layer according to the present disclosure, when a support layer is present, the support layer is preferably present continuously or discontinuously between one main surface and the other main surface of the insulating layer and is preferably present in a form that is exposed at one main surface and the other main surface. The presence of the support layer in this form provides particularly strong adhesion between the adhesive layer and the support layer, resulting in strong adhesive strength between the insulating layer and the adhesive layer and a preferable tensile shear adhesive strength between the insulating layer and the metal layer.

[0021] In the insulating layer according to the present disclosure, the heat transfer layer constituting the insulating layer occupies at least 50% by volume of the insulating layer, and in this case, the proportion of the heat transfer layer having a relatively high thermal conductivity in the thickness direction is increased, thereby making it possible to provide a laminate having a relatively low thermal resistance value in the thickness direction.

[0022] Preferably, the ratio of the heat transfer layer to the insulating layer may be 55% by volume or more, 60% by volume or more, 65% by volume or more, or 70% by volume or more, and / or may be 100% by volume or less, less than 100% by volume, less than 99% by volume, less than 98% by volume, less than 95% by volume, or less than 90% by volume.

[0023] The thickness of the heat transfer layer can be set arbitrarily, but may be 0.1 μm or more, 1 μm or more, 10 μm or more, or 20 μm or more, and / or may be 1000 μm or less, 100 μm or less, 80 μm or less, 70 μm or less, or 60 μm or less.

[0024] The greater the thickness of the heat transfer layer relative to the thickness of the support layer, the lower the thermal resistance value in the thickness direction of the resulting laminate. Therefore, it is preferable that the thickness of the heat transfer layer is relatively thick. For example, it is preferable that the thickness of the heat transfer layer in the stacking direction is at least twice the thickness of the support layer in the stacking direction. In this case, a laminate with an even lower thermal resistance value in the thickness direction can be provided.

[0025] The thinner the thickness of the heat transfer layer relative to the thickness of the support layer, the greater the tensile shear adhesive strength between the insulating layer and the metal layer of the laminate. Therefore, in order to increase the tensile shear adhesive strength between the insulating layer and the metal layer, it is better for the thickness of the support layer to be thicker relative to the thickness of the heat transfer layer. For example, it is preferable that the thickness of the heat transfer layer in the stacking direction is 100 times or less the thickness of the support layer in the stacking direction.

[0026] In order to increase the tensile shear adhesive strength between the insulating layer and the metal layer, the thickness of the heat transfer layer in the stacking direction may be preferably 0.8 times or more, 1 time or more, 1.2 times or more, 1.5 times or more, 2 times or more, 3 times or more, or 4 times or more, and / or 100 times or less, 80 times or less, 50 times or less, 40 times or less, 30 times or less, 20 times or less, 10 times or less, 8 times or less, 7 times or less, 6 times or less, or 5 times or less, of the thickness of the support layer in the stacking direction, and preferably , 1.5 times or more, 2 times or more, 3 times or more, or 4 times or more the thickness of the support layer in the stacking direction, and / or 50 times or less, 40 times or less, 30 times or less, 20 times or less, 10 times or less, 8 times or less, 7 times or less, 6 times or less, or 5 times or less, and more preferably the thickness of the heat transfer layer in the stacking direction is 2 times or more, or 3 times or more the thickness of the support layer in the stacking direction, and / or 30 times or less, 20 times or less, 10 times or less, 8 times or less, 7 times or less, 6 times or less, or 5 times or less.

[0027] Within the above range, the thermal conductivity of the insulating layer is sufficient to obtain low thermal resistance in the thickness direction of the laminate, and at the same time, the proportion of the surface of the main surface of the insulating layer where the support layer is exposed, which contributes greatly to the adhesive strength between the insulating layer and the adhesive layer, can be adjusted to an extent that ensures strong adhesion between the insulating layer and the adhesive layer, thereby achieving a low thermal resistance value in the thickness direction of the laminate without reducing the tensile shear adhesive strength between the insulating layer and the metal layer, which is preferable.

[0028] The total number of heat transfer layers and support layers included in the insulating layer can be set as desired, for example, 3 or more, preferably 11 or more, and more preferably 21 or more. There is no particular upper limit to the total number of heat transfer layers included in the insulating layer, but it may be, for example, 100,000 or less, 50,000 or less, 10,000 or less, or 5,000 or less. <Average value of thermal conductivity in in-plane direction> Preferably, the insulating layer according to the present disclosure has an average thermal conductivity of 15 W / (m·K) or more in the in-plane direction.

[0029] In particular, the average thermal conductivity of the insulating layer in the in-plane direction may be 17.5 W / (m·K) or more, or 20 W / (m·K) or more, and / or 60 W / (m·K) or less, 50 W / (m·K) or less, or 40 W / (m·K) or less.

[0030] The average thermal conductivity of the insulating layer in the in-plane direction can be calculated by adding the thermal conductivity in any direction X along the in-plane of the insulating layer and the thermal conductivity in direction Y along the in-plane of the insulating layer and perpendicular to direction X, and dividing the sum by 2.

[0031] The in-plane thermal conductivity of the insulating layer can be calculated by multiplying the in-plane thermal diffusivity, specific gravity, and specific heat together, i.e., (in-plane thermal conductivity) = (in-plane thermal diffusivity) × (specific heat) × (specific gravity).

[0032] The thermal diffusivity in the in-plane direction can be measured by cyclic heating radiation thermometry. The specific heat can be determined by a differential scanning calorimeter. The specific gravity can be determined from the external dimensions and weight of the insulating layer. <Average Thermal Conductivity in the Thickness Direction> Preferably, the insulating layer according to the present disclosure has a thermal conductivity of 20 W / (m·K) or more in the thickness direction.

[0033] In particular, the average thermal conductivity of the insulating layer in the thickness direction may be 22.5 W / (m·K) or more, or 25 W / (m·K) or more, and / or 70 W / (m·K) or less, 60 W / (m·K) or less, or 50 W / (m·K) or less.

[0034] The thermal conductivity of the insulating layer in the thickness direction can be calculated by multiplying the thermal diffusivity, specific gravity, and specific heat in the thickness direction together, i.e., (thermal conductivity in the thickness direction) = (thermal diffusivity in the in-plane direction) × (specific heat) × (specific gravity).

[0035] The thermal diffusivity in the thickness direction can be measured by temperature wave analysis. The specific heat can be determined by a differential scanning calorimeter. The specific gravity can be determined from the external dimensions and weight of the insulating layer. <Real Part of the Complex Dielectric Constant (Dielectric Constant) of the Insulating Layer> The real part of the complex dielectric constant (dielectric constant) of the insulating layer according to the present disclosure is preferably 15 or less, 12 or less, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, or 5 or less, and is preferably 1 or more, 2 or more, 3 or more, or 4 or more. More preferably, it is 2 or more and 10 or less, and even more preferably, it is 2 or more and 5 or less. Having the real part of the complex dielectric constant (dielectric constant) of the insulating layer within this range has the advantage of reducing the stray capacitance of the laminate. The frequency at which such a real part of the complex dielectric constant (dielectric constant) is obtained can be selected arbitrarily depending on the required frequency, but can be, for example, 1 kHz and / or 1 MHz. <Dielectric Loss Tangent of Insulating Layer> The dielectric loss tangent of the insulating layer according to the present disclosure is preferably in the range of 1 or less, 0.5 or less, 0.3 or less, 0.2 or less, 0.1 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, or 0.02 or less, and is 0.005, 0.006 or more, 0.007 or more, 0.008 or more, 0.009 or more, or 0.01 or more. More preferably, it is 0.006 or more and 0.5 or less, and even more preferably, it is 0.008 or more and 0.3 or less. Having the dielectric loss tangent of the insulating layer in this range has the advantage of reducing the transmission loss of the circuit, for example, when the laminate is used as a circuit board. The frequency at which such a dielectric loss tangent is obtained can be selected arbitrarily depending on the required frequency, and can be, for example, 1 kHz and / or 1 MHz.

[0036] The dielectric loss tangent of the insulating layer according to the present disclosure can be determined by dividing the imaginary part of the complex dielectric constant of the insulating layer by the real part of the complex dielectric constant (dielectric constant) of the insulating layer. <Heat Transfer Layer> The heat transfer layer according to the present disclosure contains at least a plate-like inorganic filler oriented in the in-plane direction of the heat transfer layer, and a binder resin. <Parts by Mass> Preferably, the inorganic filler contained in the heat transfer layer according to the present disclosure may be 70 parts by mass or more, 80 parts by mass or more, or 90 parts by mass or more, and / or 99 parts by mass or less, 97 parts by mass or less, 95 parts by mass or less, or 93 parts by mass or less, per 100 parts by mass of the heat transfer layer.

[0037] Preferably, the binder resin contained in the heat transfer layer according to the present disclosure may be 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, or 7 parts by mass or more, and / or 30 parts by mass or less, 20 parts by mass or less, or 10 parts by mass or less, per 100 parts by mass of the heat transfer layer. <Inorganic Filler> The inorganic filler is any particle that is insulating and has higher thermal conductivity than the binder resin. The inorganic filler is not particularly limited, and examples include particles such as silica, talc, mica, boron nitride, aluminum nitride, aluminum oxide, magnesium oxide, zinc oxide, silicon nitride, and silicon carbide, surface-oxidized metal silicon particles, and carbon fiber and graphite surface-coated with an insulating material such as resin. From the viewpoint of thermal conductivity and insulation in the planar direction, it is preferable that the inorganic filler be boron nitride particles, particularly hexagonal boron nitride particles.

[0038] The average particle size of the inorganic filler is preferably 1 to 200 μm, more preferably 5 to 200 μm, even more preferably 5 to 100 μm, and particularly preferably 10 to 100 μm.

[0039] The average particle size is the median diameter (the particle size at which, when a powder is divided into two at a certain particle size, the particles larger than that particle size and the particles smaller than that particle size are equal in amount, commonly referred to as D50) measured by laser diffraction using a laser diffraction / scattering particle size distribution analyzer. (Plate-shaped) The heat transfer layer according to the present disclosure preferably contains a plate-shaped inorganic filler. In the context of the present disclosure, particles being "plate-shaped" means that the particle shape is flat, scaly, or flake-like.

[0040] The aspect ratio of the plate-like inorganic filler is preferably 10 to 1000. An aspect ratio of 10 or more is preferable because it ensures the orientation important for improving thermal diffusivity and allows for high thermal diffusivity to be obtained. Furthermore, insulating thermally conductive particles with an aspect ratio of 1000 or less are preferable from the viewpoint of ease of processing because an increase in viscosity of the composition due to an increase in specific surface area is suppressed.

[0041] The aspect ratio is the major axis of a particle divided by the thickness of the particle, i.e., major axis / thickness. When a particle is spherical, the aspect ratio is 1, and as the particle becomes more flat, the aspect ratio increases.

[0042] The aspect ratio can be obtained by measuring the major axis and thickness of a particle at a magnification of 1500 times using a scanning electron microscope and calculating the ratio of major axis to thickness.

[0043] When the heat transfer layer contains a plate-shaped inorganic filler, the plate-shaped inorganic filler preferably accounts for 50% by volume or more of the total inorganic filler. When it is 50% by volume or more, good thermal conductivity in the in-plane direction of the heat transfer layer can be ensured. The proportion of the plate-shaped inorganic filler to the total inorganic filler is more preferably 60% by volume or more, even more preferably 70% by volume or more, even more preferably 80% by volume or more, particularly preferably 90% by volume or more, and most preferably the inorganic filler is composed of a plate-shaped inorganic filler. (Hexagonal boron nitride particles) Examples of the plate-shaped inorganic filler include hexagonal boron nitride particles.

[0044] The average particle size of the hexagonal boron nitride particles is, for example, 1 μm or more, preferably 1 to 200 μm, more preferably 5 to 200 μm, even more preferably 5 to 100 μm, and particularly preferably 10 to 100 μm. A particle size of 1 μm or more is preferred because the specific surface area of ​​the hexagonal boron nitride particles is small and compatibility with resins is ensured, while a particle size of 200 μm or less is preferred because uniformity of the thickness of the heat transfer layer can be ensured during heat transfer layer molding. The hexagonal boron nitride particles may be boron nitride particles having a single average particle size, or a mixture of multiple types of hexagonal boron nitride particles having different average particle sizes may be used. The aspect ratio of the hexagonal boron nitride particles is preferably 10 to 1000.

[0045] When hexagonal boron nitride particles are used as the inorganic filler, inorganic fillers other than boron nitride particles may be used in combination. Even in this case, it is preferable that the hexagonal boron nitride particles account for 50% by volume or more of the total inorganic filler. 50% by volume or more is preferable because good in-plane thermal conductivity in the heat transfer layer is ensured. The hexagonal boron nitride particles account for 60% by volume or more of the total inorganic filler, more preferably 70% by volume or more, even more preferably 80% by volume, and particularly preferably 90% by volume or more, or 95% by volume or more.

[0046] When hexagonal boron nitride particles and an inorganic filler having isotropic thermal conductivity are used together as the inorganic filler, the balance between the thermal conductivity in the thickness direction of the heat transfer layer and the thermal conductivity in the in-plane direction can be adjusted as needed, which is a preferred embodiment. (Orientation) From the viewpoint of obtaining particularly high heat dissipation in the thickness direction of the laminate, it is preferable that the plate-like inorganic filler is approximately perpendicular to the in-plane direction of the laminate. For this reason, it is also desirable that the plate-like inorganic filler is oriented in the in-plane direction of the heat transfer layer.

[0047] Here, in the present invention, "the inorganic filler is substantially perpendicular to the in-plane direction of the laminate" means that the angle between the angle of the main plate surface of the plate-like inorganic filler and the main surface of the laminate is 45° to 135°, and preferably this angle is 55° to 125°, 65° to 115°, 75° to 105°, 85° to 95°, 87° to 93°, or 89° to 91°.

[0048] Whether the plate-shaped inorganic filler contained in the heat transfer layer is substantially perpendicular to the in-plane direction of the laminate can be determined by measuring and comparing the angle of the particle's major axis with the angle of the laminate surface at a magnification of 100 to 3000 times using a scanning electron microscope on a cross section perpendicular to the in-plane direction of the laminate. <Binder Resin> The binder resin is not particularly limited. Examples of binder resins include thermoplastic resins such as aramid resin (aromatic polyamide), as described below, and thermosetting resins such as silicone resin, polyimide resin, phenolic resin, and epoxy resin. These can be used alone or as a mixture of multiple resins. Aromatic polyamide is particularly preferred as the binder resin. Aromatic polyamide has superior strength compared to aliphatic polyamide, so using aromatic polyamide as the binder resin can provide a heat transfer layer with particularly excellent inorganic filler retention and layer shape stability. (Thermal Properties) From the perspective of the thermal properties of the heat transfer layer, it is preferable that the binder resin have excellent heat resistance and / or flame retardancy. In particular, it is preferable that the melting point or thermal decomposition temperature of the binder resin is 150° C. or higher.

[0049] The melting point of the binder resin is measured by a differential scanning calorimeter. The melting point of the binder resin is more preferably 200° C. or higher, even more preferably 250° C. or higher, and particularly preferably 300° C. or higher. The lower limit of the melting point of the binder resin is not particularly limited, but is, for example, 600° C. or lower, 500° C. or lower, or 400° C. or lower.

[0050] The thermal decomposition temperature of the binder is measured by a differential scanning calorimeter. The thermal decomposition temperature of the binder resin is more preferably 200°C or higher, even more preferably 300°C or higher, particularly preferably 400°C or higher, and most preferably 500°C or higher. The lower limit of the thermal decomposition temperature of the binder resin is not particularly limited, but is, for example, 1000°C or lower, 900°C or lower, or 800°C or lower.

[0051] When used as a laminate inside an electronic device for automotive applications, the resin material must also have a high heat resistance temperature. In the case of power semiconductors using silicon carbide, heat resistance of around 200°C is required. Therefore, resins with heat resistance of 200°C or higher are suitable for automotive applications, particularly for circuit board applications around power semiconductors. Examples of such resins include aramid resins. (Thermoplastic Resin) Furthermore, when the binder resin contains a thermoplastic resin, it is particularly preferred because it is believed that the voids in the heat transfer layer can be further reduced. While not intending to be limited by theory, when a thermoplastic resin is used as the binder resin, for example, by heat treatment during the press process in the production of the heat transfer layer, the thermoplastic resin softens, further facilitating the release of air bubbles trapped between the inorganic filler, and as a result, it is believed that the void reduction effect can be further enhanced.

[0052] Examples of thermoplastic resins that can be used as binder resins include aramid resin, polyvinylidene fluoride (PVDF), thermoplastic polyimide resin, polytetrafluoroethylene (PTFE) resin, liquid crystal polymer (LCP) resin, polyarylate (PAR) resin, polyetherimide (PEI) resin, polyethersulfone (PES) resin, polyamideimide (PAI) resin, polyphenylene sulfide (PPS) resin, polyetheretherketone (PEEK) resin, and polybenzoxazole (PBO). (Aramid Resin) In particular, it is preferable that the binder resin contains aramid resin (aromatic polyamide) or consists of aramid resin. When the binder resin contains aramid resin, it is preferable that the content of aramid resin is 90% by volume or more relative to the binder resin. When aramid resin is used as the binder resin, a heat transfer layer with even better mechanical strength is obtained, even when a high proportion of inorganic filler is filled. Also, from the viewpoint of thermal properties, it is preferable that the binder resin contains or consists of an aramid resin, since aramid resin has a relatively high thermal decomposition temperature, and a heat transfer layer using an aramid resin as the binder resin exhibits excellent flame retardancy.

[0053] Aramid resins are linear polymeric compounds in which 60% or more of the amide bonds are directly bonded to aromatic rings. Examples of aramid resins that can be used include polymetaphenylene isophthalamide and its copolymers, and polyparaphenylene terephthalamide and its copolymers, such as copolyparaphenylene-3,4'-diphenylether terephthalamide (also known as copolyparaphenylene-3,4'-oxydiphenylene terephthalamide). Aramid resins may be used alone or in combination. (Additives) The heat transfer layer of the present invention may contain a flame retardant, a discoloration inhibitor, a surfactant, a coupling agent, a colorant, a viscosity modifier, and / or a reinforcing material. Furthermore, a fibrous reinforcing material may be included to increase the strength of the sheet. Using aramid resin short fibers as the fibrous reinforcing material is preferred because the addition of the reinforcing material does not reduce the heat resistance of the heat transfer layer. The fibrous reinforcing material is preferably added in a range of 0.5 to 25 parts by volume, more preferably 1 to 20 parts by volume, per 100 parts by volume of the heat transfer layer. <<Support Layer>> The material for the support layer according to the present disclosure can be an insulating substance that can bond adjacent heat transfer layers together. For example, a thermoplastic resin, a thermoplastic elastomer, or a cross-linkable resin can be used.

[0054] Examples of thermoplastic resins that can be used include vinyl acetate resin, polyvinyl acetal, ethylene vinyl acetate resin, vinyl chloride resin, acrylic resin, polyamide, cellulose, and α-olefin.

[0055] Examples of thermoplastic elastomers that can be used include chloroprene rubber, nitrile rubber, styrene butadiene rubber, polysulfide, butyl rubber, silicone rubber, acrylic rubber, urethane rubber, silylated urethane resin, and telechelic polyacrylate.

[0056] Examples of crosslinkable resins include epoxy resins, phenolic resins, and urethane resins. Epoxy resins are particularly preferred in terms of heat resistance and adhesiveness of the heat-conductive layer.

[0057] From the viewpoint of obtaining high heat resistance of the insulating layer and good adhesion to the adhesive layer, when the support layer is a thermoplastic resin, the support layer is preferably vinyl acetate, polyvinyl acetal, ethylene vinyl acetate resin, vinyl chloride resin, acrylic resin, polyamide, or cellulose, and more preferably acrylic resin, polyamide, or cellulose. When the support layer is a thermoplastic elastomer, the support layer is preferably chloroprene rubber, nitrile rubber, styrene butadiene rubber, polysulfide, butyl rubber, acrylic rubber, urethane rubber, silylated urethane resin, or telechelic polyacrylate, and more preferably chloroprene rubber, nitrile rubber, styrene butadiene rubber, butyl rubber, acrylic rubber, or telechelic polyacrylate. When the support layer is a crosslinkable resin, the support layer is preferably epoxy resin, phenol resin, or urethane resin, more preferably epoxy resin or phenol resin, and even more preferably epoxy resin.

[0058] For the support layer, acrylic resin and epoxy resin are particularly preferred.

[0059] When the support layer is as described above, the insulating layer can have high heat resistance due to the high glass transition temperature and / or high deflection temperature under load of the material constituting the support layer. Also, when the support layer is as described above, the surface free energy of the material constituting the support layer is high, so that the surface free energy of the exposed portion of the support layer on the surface of the insulating layer can be increased, thereby achieving good adhesion to the adhesive layer.

[0060] The support layer may contain additives such as curing accelerators, discoloration inhibitors, surfactants, coupling agents, colorants, viscosity modifiers, and fillers, as long as the insulating properties and adhesive properties are not impaired.

[0061] The range of the elastic modulus of the support layer is preferably 10 MPa or more, 20 MPa or more, 30 MPa or more, 40 MPa or more, 50 MPa or more, 70 MPa or more, 100 MPa or more, 200 MPa or more, 300 MPa or more, 400 MPa or more, and 50 GPa or less, 40 GPa or less, 30 GPa or less, 20 GPa or less, 10 GPa or less, 7 GPa or less, 5 GPa or less, 4 GPa or less, 3 GPa or less, 2 GPa or less, 1 GPa or less. When the elastic modulus of the support layer is in this range, it is possible to impart stiffness to the insulating layer that is suitable for handling of the insulating layer, which has the advantage of improving handleability during laminate production. In addition, when pressure is applied in the metal layer formation process, when the elastic modulus of the support layer is in this range, it has the advantage of reducing the frequency of defects such as buckling of the insulating layer during pressure application. In addition, by having the elastic modulus of the support layer within this range, it is possible to alleviate the stress that occurs between the layers of the laminate when the temperature of the laminate changes, which has the advantage of being able to suppress cracking of the insulating layer and adhesive layer and peeling of the metal layer during use of the laminate.

[0062] The elastic modulus of the support layer can be determined from the tensile stress-strain curve of the support layer. <Metal Layer A and Metal Layer B> The materials of the metal layer A and metal layer B according to the present disclosure are not particularly limited. Examples of metals include pure metals such as titanium, aluminum, beryllium, magnesium, iron, lead, gold, platinum, silver, copper, chromium, cadmium, zinc, arsenic, manganese, cobalt, nickel, molybdenum, tungsten, tin, and bismuth, as well as alloys containing these metals. Non-metallic elements such as carbon and oxygen may be included as impurities and additives. In particular, pure metals such as copper or aluminum, and alloys containing copper or aluminum, are desirable from the standpoints of heat dissipation and cost. Furthermore, the metal layer A and metal layer B may be made of the same material, or different materials may be used depending on the application.

[0063] The metal layer A and the metal layer B may be in the form of a uniform surface, or may be in the form of a pattern such as a circuit, a dot shape, or a line shape.

[0064] The thicknesses of metal layer A and metal layer B are not particularly limited. A thin metal layer has the advantages of low thermal resistance in the thickness direction, easy patterning of the metal layer, a light weight laminate, and low production costs for the laminate. On the other hand, a thick metal layer has the advantages of high thermal diffusivity in the in-plane direction of the laminate and ensuring the rigidity of the laminate even when a flexible insulating layer is used. Furthermore, the thicknesses of metal layer A and metal layer B may be the same or different depending on the application. <Adhesive Layer> Materials for the adhesive layer that can be included in the present disclosure include insulating substances that can bond the insulating layer and the metal layer. For example, thermoplastic resins, thermoplastic elastomers, and cross-linkable resins can be used.

[0065] Examples of thermoplastic resins that can be used include vinyl acetate resin, polyvinyl acetal, ethylene vinyl acetate resin, vinyl chloride resin, acrylic resin, polyamide, cellulose, and α-olefin.

[0066] Examples of thermoplastic elastomers that can be used include chloroprene rubber, nitrile rubber, styrene butadiene rubber, polysulfide, butyl rubber, silicone rubber, acrylic rubber, urethane rubber, silylated urethane resin, and telechelic polyacrylate.

[0067] Examples of crosslinkable resins include epoxy resins, phenolic resins, and urethane resins. Epoxy resins are particularly preferred in terms of heat resistance and adhesion to the insulating layer and metal layer.

[0068] From the viewpoint of obtaining high heat resistance of the adhesive layer and good adhesion to the insulating layer and / or metal layer, when the adhesive layer is a thermoplastic resin, the adhesive layer is preferably vinyl acetate, polyvinyl acetal, ethylene vinyl acetate resin, vinyl chloride resin, acrylic resin, polyamide, or cellulose, and more preferably acrylic resin, polyamide, or cellulose. When the adhesive layer is a thermoplastic elastomer, the adhesive layer is preferably chloroprene rubber, nitrile rubber, styrene butadiene rubber, polysulfide, butyl rubber, acrylic rubber, urethane rubber, silylated urethane resin, or telechelic polyacrylate, and more preferably chloroprene rubber, nitrile rubber, styrene butadiene rubber, butyl rubber, acrylic rubber, or telechelic polyacrylate. When the adhesive layer is a crosslinkable resin, the adhesive layer is preferably epoxy resin, phenol resin, or urethane resin, more preferably epoxy resin or phenol resin, and even more preferably epoxy resin.

[0069] The adhesive layer is particularly preferably made of an acrylic resin or an epoxy resin, and most preferably made of an epoxy resin.

[0070] When the adhesive layer is as described above, the adhesive layer can have high heat resistance due to the high glass transition temperature and / or high deflection temperature under load of the material constituting the adhesive layer. Furthermore, when the adhesive layer is as described above, the surface free energy of the adhesive layer can be increased, thereby achieving good adhesion to the insulating layer and / or metal layer.

[0071] The adhesive layer may contain additives such as curing accelerators, discoloration inhibitors, surfactants, coupling agents, colorants, viscosity modifiers, and fillers, as long as the insulating properties and adhesiveness are not impaired. In particular, adding thermally conductive ceramic particles is a preferred embodiment because it can further reduce the thermal resistance value in the thickness direction of the circuit board.

[0072] The tensile shear adhesive strength between the insulating layer and the metal layer can be set to a value greater than the shear stress expected to occur between the insulating layer and the adhesive layer or between the metal layer and the insulating layer in order to reduce the frequency of peeling failures (peel failures) between the insulating layer and the adhesive layer or between the metal layer and the insulating layer. Examples of such stress include, but are not limited to, shear stress applied between the insulating layer and the metal layer when the laminate is in use, and stress between the insulating layer and the adhesive layer or between the metal layer and the insulating layer that occurs due to a difference in the linear expansion of the insulating layer and the metal layer caused by temperature changes.

[0073] The tensile shear adhesive strength between the insulating layer and the metal layer is preferably 0.1 MPa or more, 0.2 MPa or more, 0.3 MPa or more, 0.4 MPa or more, 0.5 MPa or more, 0.7 MPa or more, 1 MPa or more, 2 MPa or more, 3 MPa or more, 4 MPa or more, 5 MPa or more, and 1000 MPa or less, 700 MPa or less, 500 MPa or less, 400 MPa or less, 300 MPa or less, 200 MPa or less, 100 MPa or less, 70 MPa or less, 50 MPa or less, 40 MPa or less, 30 MPa or less, 20 MPa or less. More preferably, it is 2 MPa or more, even more preferably 3 MPa or more, and particularly preferably 4 MPa or more. Having the tensile shear adhesive strength between the insulating layer and the metal layer in this range has the advantage of reducing the frequency of peel failure between the insulating layer and the adhesive layer, and between the metal layer and the insulating layer.

[0074] The tensile shear adhesive strength between the insulating layer and the metal layer can be determined by a tensile test of the laminate.

[0075] The laminate of the present invention has excellent heat dissipation properties in the thickness direction, thermal diffusivity in the in-plane direction, and insulation properties in the thickness direction, and is also crack-resistant. Therefore, it can be used as a circuit board by processing the metal layer to form a predetermined conductor circuit. [Laminate Manufacturing Method] The present disclosure includes a method for manufacturing the laminate of the present disclosure, including the following: a heat transfer layer manufacturing step in which a film is formed using a slurry containing a plate-shaped inorganic filler, a binder resin, and a solvent; an insulating layer manufacturing step in which heat transfer layers and support layers are alternately laminated and then cut; and a metal layer forming step in which metal layers are bonded to both sides of the insulating layer. <Heat Transfer Layer Manufacturing Step> The heat transfer layer manufacturing step includes a mixing step in which at least a plate-shaped inorganic filler, a binder resin, and a solvent are mixed to obtain a slurry; a molding step in which the slurry obtained after the mixing step is formed into a sheet and dried to form a heat transfer layer precursor; and a pressing step in which the heat transfer layer precursor is compressed. <Mixing Step> In the mixing step of the heat transfer layer manufacturing method of the present disclosure, a plate-shaped inorganic filler, a binder resin, and a solvent are mixed to obtain a slurry.

[0076] For the inorganic filler and binder resin, reference can be made to the contents already described regarding the heat transfer layer.

[0077] Optionally, additives such as flame retardants, anti-tarnish agents, surfactants, coupling agents, colorants, viscosity modifiers, and / or reinforcing materials may be added during the mixing process. Fibrous reinforcing materials may also be added to increase the strength of the sheet.

[0078] In the mixing step, anhydrous calcium chloride or anhydrous lithium chloride may be added. Adding anhydrous calcium chloride or anhydrous lithium chloride in the mixing step may improve the solubility of the binder resin in the solvent. In particular, when an aramid resin is used as the binder resin, adding anhydrous calcium chloride or anhydrous lithium chloride in the mixing step is preferable, and in this case, the solubility of the aramid resin in the solvent can be further improved. (Solvent) As the solvent, a solvent capable of dissolving the binder resin can be used. For example, when an aramid resin is used as the binder resin, 1-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, or dimethyl sulfoxide can be used. (Mixing) To mix the insulating particles, binder resin, and solvent, a common kneading device such as a paint shaker, a bead mill, a planetary mixer, an agitation disperser, a planetary agitation mixer, a three-roll mill, a kneader, or a single- or twin-screw kneader can be used. <Forming Step> In the forming step of the heat transfer layer preparation step of the manufacturing method according to the present disclosure, the slurry after the mixing step is shaped into a sheet and dried to form a heat transfer layer precursor. (Shaping) To form the slurry after the mixing step into a sheet, a known method such as applying the slurry to a release film using a coater can be used. (Drying) Drying may be performed by a known method. For example, the slurry applied to the substrate may be dried, and then the shaped slurry may be peeled off from the substrate in water and further dried. The drying temperature may be, for example, 50°C to 300°C, and the drying time may be, for example, 30 seconds to 3 hours.

[0079] In the molding step, a water-washing treatment may be performed. By performing the water-washing treatment, the residual solvent in the heat transfer layer and, if present, salts can be reduced. The water-washing treatment may be performed, for example, by drying the slurry that has been applied to the substrate and shaped, and then immersing it in ion-exchanged water or distilled water for 10 minutes to 3 hours. The water-washing treatment may also be performed on the heat transfer layer precursor. When anhydrous calcium chloride or anhydrous lithium chloride is added in the mixing step, it is preferable to perform the water-washing treatment.

[0080] The shaped slurry or heat transfer layer precursor has more voids than the heat transfer layer that has been compressed, and is therefore more permeable to water. Therefore, by performing a water washing process before the compression process, it is thought that residual solvent and salt can be removed more efficiently.

[0081] The water content of the heat transfer layer can be reduced by drying the heat transfer layer after washing with water or by compressing the heat transfer layer precursor. <Compression Step> In the compression step of the heat transfer layer preparation step of the manufacturing method according to the present disclosure, the heat transfer layer precursor is compressed.

[0082] As described above, by compressing the heat transfer layer precursor, a heat transfer layer having excellent thermal conductivity in the in-plane direction can be obtained.

[0083] Furthermore, when the heat transfer layer precursor is compressed, a heat transfer layer having a surface structure with relatively high smoothness can be obtained.

[0084] The compression step can be performed using a common press, such as a vertical flat press or a roll press. Roll presses are preferred because they facilitate the removal of air from the heat transfer layer precursor, thereby increasing its density and thermal conductivity. The atmosphere of the press may be atmospheric pressure or a vacuum. (Roll Press) Roll presses may be performed using a known method, such as a calender roll machine to pressurize the heat transfer layer precursor. The pressure applied to the heat transfer layer precursor in the roll press step is preferably a linear pressure of 400 to 8000 N / cm. A linear pressure of 400 N / cm or higher significantly expels air bubbles from the heat transfer layer. A linear pressure of 8000 N / cm or less allows the inorganic filler to be packed densely enough to avoid destruction, thereby reducing voids within the heat transfer layer. The diameter of the rolls used in the roll press is preferably, for example, 200 to 1500 mm.

[0085] During the compression process, it is preferable to heat the heat transfer layer precursor. The heating temperature can be appropriately set depending on the type of binder resin used, etc. When aramid resin is used as the binder resin, the heating temperature is preferably 100 to 350°C. A heating temperature of 100°C or higher facilitates softening of the binder resin, making it easier to fill gaps between the inorganic fillers through the compression process. A heating temperature of 350°C or lower reduces the strength of the binder resin due to thermal history. <Insulating Layer Preparation Process> The insulating layer preparation process includes a lamination process in which heat transfer layers and support layers are alternately stacked, and a cutting process in which the stacked heat transfer layers / support layers are cut in the thickness direction of the laminate. <Lamination Process> The lamination process may be performed by stacking multiple heat transfer layers and support layers alternately in the thickness direction. For example, a laminate may be obtained by stacking heat transfer layers and support layers cut to an appropriate size.

[0086] The lamination process may be performed by folding or winding the heat transfer layer and the support layer. For example, a heat transfer layer with a support layer applied to one side thereof may be wound around a core or plate to form a first layer, and then a new layer may be wound on top of that to form a second layer, repeating this process until the desired number of layers is reached to obtain an alternating laminate of heat transfer layers and support layers. Alternatively, an alternating laminate of heat transfer layers and support layers may be obtained by simultaneously folding or winding a heat transfer layer and a support layer unwound from separate shafts. A liquid or powdered support layer may also be applied each time a heat transfer layer is laminated.

[0087] A plurality of laminates obtained by these methods may be prepared and then laminated to prepare a laminate.

[0088] In the lamination step, a heat treatment may be further performed after laminating the heat transfer layer / support layer. When the support layer is a thermoplastic resin, the heat treatment further improves the adhesion between the layers in the resulting laminate. When the support layer is a thermosetting resin, the adhesive strength between the layers is improved. The temperature of the heat treatment may be appropriately set depending on the binder resin contained in the heat transfer layer, the type of support layer, etc.

[0089] The support layer used in the lamination process can be, for example, molecular gradient film double-sided tape "200Y" (manufactured by Kyodo Giken Chemical Co., Ltd.). When 200Y is used as the support layer, in order to improve the adhesion between the support layer and the heat transfer layer, heat treatment can be performed after laminating the heat transfer layer / support layer in the lamination process. Patent Document 5 (JP 2006-232896 A) discloses that peel strength is improved at a heating temperature of 150°C or higher and 200°C or lower. When heat treatment is performed after laminating the heat transfer layer / support layer, for example, by maintaining the heat treatment under such conditions, adhesion can be improved.

[0090] The support layer used in the lamination process can be, for example, the heat dissipation insulating adhesive sheet "EAL" (manufactured by Arisawa Manufacturing Co., Ltd.). When EAL is used as the support layer, heat treatment can be performed after laminating the heat conduction layer and support layer in the lamination process to improve adhesion between the support layer and the heat transfer layer. The catalog for the heat dissipation insulating adhesive sheet "EA Series" (https: / / www.arisawa.co.jp / jp / products / data / CATALOG_EA_JP.PDF) discloses heat treatment conditions of 180°C, 60 minutes, and 3 to 20 MPa. When heat treatment is performed after laminating the heat conduction layer and support layer, for example, maintaining the heat treatment under such conditions can improve adhesion. <Cutting Process> In the cutting process, the laminate is cut approximately along the lamination direction of the heat conduction layer / support layer to obtain the insulating layer.

[0091] The cutting process is carried out so that the thickness direction of the insulating layer obtained by cutting and the stacking direction of the heat transfer layers that make up the insulating layer are substantially perpendicular to each other.

[0092] The cutting process may be carried out by a known method, such as a multi-blade method, a laser processing method, a water jet method, or a knife processing method. The cutting process may also be carried out using a common blade or cutting tool or cutting machine, such as a sharp-edged cutter knife, a razor, or a Thomson blade. By using a cutting tool or the like with a sharp blade, it is possible to suppress the disorder of particle orientation near the surface of the heat dissipation sheet obtained after the cutting process, and it is also possible to easily obtain a relatively thin insulating layer.

[0093] The thickness of the insulating layer obtained by the cutting process is not particularly limited, but is, for example, 0.02 to 5 mm, preferably 0.1 to 1 mm. By ensuring that the insulating layer has a thickness within this range, it is possible to provide a laminate that has low thermal resistance in the thickness direction, excellent heat dissipation in the thickness direction, and high insulation between metal layer A and metal layer B. <Metal Layer Forming Step> The metal layer forming step can be performed by any method that can laminate and fix the metal layer A, adhesive layer, insulating layer, adhesive layer, and metal layer B in this order.

[0094] When the raw material for the adhesive layer is liquid, the metal layer A, the metal layer B, or the insulating layer can be applied using a coater.

[0095] The metal layer lamination process may include a heating process in which metal layer A, adhesive layer, insulating layer, adhesive layer, and metal layer B are laminated in this order, and then heated to strengthen the adhesion between the layers.

[0096] When the adhesive layer is made of a thermoplastic resin or a thermoplastic elastomer, the thermoplastic resin melts and adheres to the metal layer and the insulating layer, which has the advantage of strengthening the adhesion between the layers. When the adhesive layer is made of a curable resin, heating promotes cross-linking of the resin, which has the advantage of strengthening the adhesion between the layers.

[0097] When a crosslinkable resin is used as the adhesive layer, the resin constituting the adhesive layer can be crosslinked by any method for crosslinking the adhesive layer after laminating the metal layer A, adhesive layer, insulating layer, adhesive layer, and metal layer B in this order. Using any method for crosslinking the adhesive layer has the advantage of strengthening the adhesion between the layers.

[0098] Any method for crosslinking the adhesive layer can be used, including but not limited to light irradiation and radiation irradiation.

[0099] The metal layer forming step may include a step of applying pressure using a press to a laminate including a metal layer A, an adhesive layer, an insulating layer, another adhesive layer, and a metal layer B. The atmosphere of the press may be atmospheric pressure or may be in a vacuum.

[0100] The invention according to the present disclosure will be specifically described below with reference to examples. Examples 1 to 7, Comparative Examples 1 to 3 Heat transfer layers, insulating layers, metal layers, and laminates according to Examples 1 to 7, and laminates according to Comparative Examples 1 to 3 were produced. The properties of the obtained heat transfer layers, insulating layers, metal layers, and laminates were measured. The measurements were carried out by the following methods. (1) Thermal Conductivity in In-Plane and Thickness Directions The thermal conductivity of the heat transfer layer and insulating layer was calculated by multiplying the thermal diffusivity, specific gravity, and specific heat in the thickness direction and in the in-plane direction, respectively.

[0101] (Thermal Conductivity) = (Thermal Diffusivity) × (Specific Heat) × (Specific Gravity) The thermal diffusivity in the thickness direction was determined by temperature wave analysis. The measurement device used was an ai-Phase Mobile M3 Type 1 manufactured by ai-Phase Corporation. The thermal diffusivity in the in-plane direction was determined by cyclic heating radiation thermometry. The measurement device used was a TA-33 manufactured by Bethel Corporation. The specific heat was determined using a differential scanning calorimeter (DSCQ10 manufactured by TA Instruments). The specific gravity was determined from the external dimensions and weight of the insulating sheet. (2) Breakdown Voltage The breakdown voltage of the insulating layer was measured in accordance with the test standard ASTM D149-20. The measurement device used was a dielectric strength test device manufactured by Tokyo Transformer Co., Ltd. The measurement was carried out in insulating oil to avoid creeping discharge at the end of the insulating layer. (3) Thermal Resistance in the Thickness Direction The thermal resistance in the thickness direction of the laminate was measured using a 40 mm x 40 mm test piece and a steady-state thermal conductivity measuring device SS-H40 manufactured by Bethel Corporation. Thermal resistance was measured at an upper heater temperature of 70°C, a lower cooling water temperature of 23°C, and a pressure of 1200 N. A small amount of oil compound (G-746 manufactured by Shin-Etsu Chemical Co., Ltd.) was uniformly applied to the interface between each metal layer of the laminate and the device-side contact portion (copper cartridge). The thermal resistance value between the obtained copper cartridges was multiplied by 16 to obtain a converted value of thermal resistance per square centimeter. (4) Orientation of Inorganic Filler The presence or absence of inorganic filler in the insulating layer within the laminate and its orientation were confirmed by exposing the cross section of the laminate using a conventional cutting machine and then observing it at 250x magnification using a scanning electron microscope (TM4000 manufactured by Hitachi High-Tech Corporation). (5) Dielectric Constant and Dielectric Loss Tangent of Insulating Layer The real part of the complex dielectric constant (dielectric constant) and dielectric loss tangent of the insulating layer were measured by the parallel plate method. Using a semiconductor parameter analyzer (Keythley 4200-SCS, manufactured by Keithley Instruments), the capacitance of the capacitor and the conductance of the resistor were measured when the object to be measured was considered as an equivalent circuit in which a capacitor and a resistor were connected in parallel. The measurement was performed by applying a 100 mV sine wave at frequencies of 1 kHz and 1 MHz. The real part of the complex dielectric constant (dielectric constant) and dielectric loss tangent were obtained using the following formulas.

[0102] (Real part of complex dielectric constant (relative dielectric constant)) = [(Capacitance) × (Distance between parallel plates)] / [(Dielectric constant of vacuum) × (Area of ​​parallel plates)] (Dielectric loss tangent) = [(Conductance) × (Real part of complex dielectric constant (relative dielectric constant))] / [(Frequency) × (Capacitance)] (6) Elastic Modulus of Support Layer The elastic modulus of the support layer was measured using a tensile tester (TENSILON RTC-1210, manufactured by A&D Co., Ltd.). The elastic modulus of the support layer was measured by holding the support layer for elastic modulus measurement in a tensile tester with a chuck distance of 50 mm and applying a tensile displacement at a rate of 1 mm / min. The tensile stress-strain curve was obtained from the strain of 0 to the breaking point, and the gradient of the curve between the strain of 0.0005 and the strain of 0.0025 was calculated using the least squares method and divided by the cross-sectional area. When the strain at the breaking point was 0.0025 or less, the gradient of the curve between the strain at the breaking point multiplied by 0.2 and the strain at the breaking point multiplied by 0.8 was calculated using the least squares method and divided by the cross-sectional area. (7) Tensile shear bond strength between insulating layer and metal layer The tensile shear bond strength between the insulating layer and the metal layer was measured using a tensile tester (TENSILON RTC-1210, manufactured by A&D Co., Ltd.). Each of the two copper plates of the laminate for measuring the tensile shear bond strength was held in the tensile tester, and a tensile displacement of 1 mm / min was applied. A tensile stress-strain curve was obtained from a state where the strain was 0 to the breaking point, and the stress at the breaking point was divided by the bonding area. The bonding area was the area of ​​the main surface of the insulating layer of the laminate for measuring the tensile shear bond strength. Example 1 Production of Heat Transfer Layer 9.3 parts by mass of para-aramid resin "Technora" (manufactured by Teijin Limited) as a binder resin and 8.1 parts by mass of calcium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were dissolved in 363 parts by mass of 1-methyl-2-pyrrolidone, and 90.7 parts by mass of plate-shaped hexagonal boron nitride particles "HSPD" (manufactured by Dandong Chemical Engineering Institute Co., average particle size 45 μm, aspect ratio 35) were added to the solution, and the mixture was stirred with a planetary mixer for 120 minutes while heating to 80° C. to obtain a uniform slurry.

[0103] The obtained slurry was applied to a PET film using a slit die coater, formed into a sheet, and dried at an average temperature of 120 ° C. for 20 minutes. The formed slurry was then peeled off from the PET film, immersed in water for 5 minutes, and dried at 150 ° C. for 2 minutes to obtain a 150 μm thick heat transfer layer precursor. The obtained heat transfer layer precursor was compressed using a calendar roll at a temperature of 220 ° C. and a linear pressure of 640 kgf / cm (6270 N / cm) to obtain a 42 μm thick heat transfer layer. The in-plane thermal conductivity of this heat transfer layer was 42 W / (m K). <Production of insulating layer> The obtained heat transfer layer and a die bonding film "HS-260" (crosslinkable resin (epoxy type), thickness 10 μm, manufactured by Resonac Inc. (formerly Showa Denko Materials Inc.)) as a support layer were alternately laminated to form 1000 layers, and pressed using a vacuum heat press under conditions of a temperature of 130°C, a pressure of 3 MPa, and a vacuum degree of 0.5 Pa for 2 hours to obtain an insulating layer precursor. The obtained insulating layer precursor was cut twice at 0.2 mm intervals with a razor blade substantially perpendicular to the main surface of the heat transfer layer to obtain an insulating layer with a thickness of 0.2 mm. The thermal conductivity of this insulating layer in the thickness direction was 34 W / mK, and the thermal conductivity in the in-plane direction was 23 W / (m·K). <Formation of Metal Layer (Laminate Fabrication)> One of the main surfaces of the obtained insulating layer was coated with room temperature curing two-component epoxy resin "2088E" (manufactured by ThreeBond Co., Ltd.) to a thickness of approximately 1 to 5 μm. A 10 μm thick copper foil was then attached to the entire surface. The laminate was then heated at 120°C in air for 90 minutes while being pressed with a barco-type clamp. Similarly, a 10 μm thick copper foil was formed on the other side of the insulating layer, resulting in a laminate for cross-section observation in which copper foil was formed on both sides of the insulating layer. Similarly, a laminate for thermal resistance measurement was prepared by attaching 1 mm thick copper plates to both sides of the insulating layer. The thickness of the support layer in the stacking direction between the support layer and the heat transfer layer of the resulting laminate was 10.6 μm. Furthermore, in the insulating layer, the thickness of the heat transfer layer in the stacking direction between the heat transfer layer and the support layer was 3.96 times the thickness of the support layer in the stacking direction.<Measurement of Elastic Modulus of Support Layer> The die bonding film "HS-260" (manufactured by Resonac Inc. (formerly Showa Denko Materials Inc.), thickness 10 μm) used to form the support layer was heated at a temperature of 130°C for 2 hours and then cut to a width of 10 mm and a length of 100 mm to obtain a film for measuring elastic modulus. The elastic modulus was 425 MPa. <Measurement of Tensile Shear Adhesion Strength> The tensile shear adhesive strength between the insulating layer and the metal layer in the laminate thus obtained was 7.3 MPa. Example 2 A laminate for measuring thermal resistance was produced in the same manner as in Example 1, except that a bonding sheet "A11F" (manufactured by Arisawa Manufacturing Co., Ltd.) was used as the support layer, and that pressing was performed for 1 hour under conditions of a temperature of 160°C, a pressure of 3 MPa, and a vacuum degree of 0.5 Pa to form the insulating layer precursor in the manufacturing process of the insulating layer.

[0104] The thickness of the support layer of the thus obtained laminate was 14.3 μm. Furthermore, in the insulating layer, the thickness of the heat transfer layer in the stacking direction of the heat transfer layer and the support layer was 2.94 times the thickness of the support layer in the stacking direction. Example 3: A laminate for thermal resistance measurement was prepared in the same manner as in Example 2, except that the thickness of the insulating layer was 0.4 mm. The ratio of the thickness of the support layer and the thickness of the heat transfer layer in the stacking direction to the thickness of the support layer in the stacking direction was the same as in Example 2. Example 4: A laminate for thermal resistance measurement was prepared in the same manner as in Example 2, except that a heat-dissipating bonding sheet "EAL" (manufactured by Arisawa Manufacturing Co., Ltd.) was used as the adhesive layer. The thickness of the support layer and the ratio of the thickness of the heat transfer layer in the stacking direction to the thickness of the support layer in the stacking direction were the same as in Example 2. Example 5 A laminate for measuring thermal resistance was prepared in the same manner as in Example 2, except that a 1 mm thick copper plate was formed on one side of the insulating layer as metal layer A, and a 0.01 mm thick copper foil was formed on one side of the insulating layer as metal layer B. The thickness of the support layer and the ratio of the thickness of the heat transfer layer in the stacking direction to the thickness of the support layer in the stacking direction were the same as in Example 2. Example 6 A laminate for measuring thermal resistance was prepared in the same manner as in Example 5, except that a heat-dissipating insulating adhesive sheet "EAL" was used as the adhesive layer, and the insulating layer precursor was formed during the insulating layer manufacturing process by pressing under conditions of 180°C, 4 MPa, and 60 minutes. The thickness of the support layer and the ratio of the thickness of the heat transfer layer in the stacking direction to the thickness of the support layer in the stacking direction were the same as in Example 2. Example 7 A laminate for measuring thermal resistance was produced in the same manner as in Example 1, except that a molecularly oriented film double-sided tape "200Y" was used as the support layer, and that the insulating layer precursor was formed in the insulating layer production process by pressing under the conditions disclosed in Patent Document 5.

[0105] The thickness of the support layer of the thus obtained laminate was 17.8 μm. In the insulating layer, the thickness of the heat transfer layer in the stacking direction of the heat transfer layer and the support layer was 2.36 times the thickness of the support layer in the stacking direction. Comparative Example 1: A typical low thermal resistance metal-based substrate was produced and evaluated. A 0.12 mm insulating heat dissipation resin (manufactured by Risho Kogyo Co., Ltd., epoxy resin + alumina particles + aluminum nitride particles) was applied as an insulating layer to a 1 mm thick copper plate, and a 70 μm thick copper foil was attached, followed by thermal curing of the insulating heat dissipation resin, to produce a laminate for thermal resistance measurement. Comparative Example 2: A 0.2 mm thick insulating heat dissipation sheet "TC-20EG" (spherical inorganic filler + silicone resin) manufactured by Shin-Etsu Chemical Co., Ltd. was used as the insulating layer, and a laminate for cross-sectional observation and thermal resistance measurement was produced using the same method as in the Examples. Comparative Example 3 A laminate for cross-sectional observation and thermal resistance measurement was produced in the same manner as in the examples, using a 0.2 mm thick insulating heat dissipation sheet "TC-20BG" (plate-shaped inorganic filler + silicone resin) manufactured by Shin-Etsu Chemical Co., Ltd. as an insulating layer.

[0106] The preparation conditions and measurement results for the example and comparative examples 1 to 3 are shown in Table 1.

[0107]

[0108] The laminate of the present invention can be suitably used as a laminate for mounting a semiconductor element that generates a large amount of heat or that requires high insulation properties.

[0109] REFERENCE SIGNS LIST 11 Laminate 12 Insulating layer 13 Adhesive layer 14 Metal layer 15 Metal layer A 16 Metal layer B 17 Heat transfer layer 18 Support layer 19 Plate-shaped inorganic filler 20 Binder resin

Claims

1. A laminate comprising a metal layer A, an insulating layer provided on at least one side of the metal layer A, and a metal layer B provided on a surface of the insulating layer opposite to the metal layer A, wherein the insulating layer includes a support layer and a heat transfer layer containing at least an inorganic filler and a binder resin, and the support layer and the heat transfer layer are alternately laminated in a total of three or more layers in a direction substantially orthogonal to the thickness direction of the insulating layer. A laminate characterized by this.

2. The laminate according to claim 1, wherein an adhesive layer is included between the insulating layer and the metal layer A and between the insulating layer and the metal layer B.

3. The laminate according to claim 2, wherein the adhesive layer is made of a material different from the binder resin.

4. The laminate according to claim 2, wherein the binder resin includes an aramid resin, and the adhesive layer is made of an acrylic resin, an epoxy resin, a phenolic resin, or a urethane resin.

5. The laminate according to claim 1 or 2, having a thermal resistance value of 0.60 (K·cm2) / W or less in the thickness direction.

6. The laminate according to claim 1 or 2, wherein the inorganic filler is plate-shaped and the inorganic filler is substantially orthogonal to the in-plane direction of the laminate.

7. The laminate according to claim 1 or 2, wherein the inorganic filler includes hexagonal boron nitride particles.

8. The laminate according to claim 1 or 2, wherein the binder resin includes an aramid resin.

9. The laminate according to claim 1 or 2, wherein the tensile shear adhesive strength between the insulating layer and the metal layer A is 0.1 MPa or more.

10. The laminate according to claim 1 or 2, wherein the elastic modulus of the support layer is 10 MPa or more.

11. A circuit board comprising the laminate according to claim 1.

12. A method for manufacturing a laminate according to claim 1 or 2, comprising a heat transfer layer manufacturing step of forming a film using a slurry containing a plate-shaped inorganic filler, a binder resin, and a solvent, an insulating layer manufacturing step of alternately laminating the heat transfer layer and the support layer and then cutting, and a metal layer forming step of bonding the metal layers A and B to respective surfaces of the insulating layer. A method for manufacturing a laminate.