Laminate and method for producing same

Abstract

[Problem] To provide a laminate which has excellent heat dissipation properties in the thickness direction, heat diffusivity in the in-plane direction, and insulating properties in the thickness direction, and which is not susceptible to cracking. [Solution] A laminate comprising a metal layer A, an insulating layer provided on at least one surface of the metal layer A, and a metal layer B provided on the surface of the insulating layer opposite to the metal layer A. The insulating layer is characterized by comprising a support layer and a heat transfer layer containing at least an inorganic filler and a binder resin. The support layers and the heat transfer layers are alternately laminated in a direction substantially orthogonal to the thickness direction of the insulating layer, and the total number of the support layers and the heat transfer layers is three or more.

Description

Technical Field

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

[0002] In recent years, miniaturization of electronic components has been required, and high-density mounting and high performance have been demanded. Moreover, due to miniaturization and high power of semiconductor elements and the like, how to dissipate heat generated by semiconductor elements and the like in a narrow space has become a problem.

[0003] As one of the solutions to the above problems, the following method is adopted: a ceramic plate having a high thermal conductivity is used for the insulating layer of the substrate on which the components are mounted, and the heat generated in the components is efficiently dissipated to the case or the heat sink. However, a ceramic plate that is processed thin to reduce the thermal resistance in the thickness direction has a problem of being easily cracked.

[0004] In order to improve the cracking property of the substrate material, a countermeasure is taken to use a resin material having an increased thermal conductivity as the insulating layer instead of using a ceramic plate (see Patent Documents 1 and 2). Patent Document 1 studies high thermal conductivity by filling alumina powder in a resin. However, in Patent Document 1, since alumina powder is used, high filling of more than 80 vol% can be achieved, but since the thermal conductivity of alumina powder itself is low, there is a problem of low thermal conductivity of the substrate.

[0005] In Patent Document 2, high thermal conductivity is achieved with a low filler filling amount by using boron nitride powder and controlling its orientation. The primary particles of boron nitride powder are usually flaky. When it is dispersed as a filler in the insulating layer, the boron nitride powder is arranged in the plane direction during coating or press curing, and high thermal conductivity cannot be expected. However, by dispersing aggregates of boron nitride powder in the insulating layer and controlling the orientation in the vertical direction, high thermal conductivity is achieved, and a heat channel can be effectively formed. As a result, the filling amount can be reduced, and as a result, an increase in the withstand voltage value is also achieved. However, in Patent Document 2, the aggregate powder used has high particle strength so that the aggregate powder is not damaged during the substrate manufacturing process, and in addition, the condition is that there are few voids in the aggregate powder. Therefore, the particle strength is high and no deformation occurs, and it is difficult to fill the resin into the internal voids, and electrical characteristics such as electrical insulation are reduced, and the boron nitride powders cannot be sufficiently in contact with each other, and there is a problem that the effect of increasing the thermal conductivity is reduced.

[0006] In Patent Documents 3 and 4, a sheet obtained by dispersing carbon nanotubes in a thermoplastic fluororesin is roll-formed, and the obtained sheets are laminated and then hot-pressed to obtain a resin block, and then the resin block is sliced to obtain a resin sheet in which carbon nanotubes as fillers are oriented in the thickness direction. By orienting the carbon nanotubes in the thickness direction, a resin sheet excellent in thermal conductivity in the thickness direction can be obtained. However, the resin sheets disclosed in Patent Documents 3 and 4 contain conductive materials such as carbon nanotubes as fillers, so the obtained resin sheets are conductive, and there is a problem that they cannot be applied to circuit boards that require insulation.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Laid-Open No. 6-44824;

[0010] Patent Document 2: Japanese Patent Laid-Open No. 2010-157563;

[0011] Patent Document 3: Japanese Patent No. 7092299;

[0012] Patent Document 4: Japanese Patent Laid-Open No. 2021-4284. Summary of the Invention

[0013] Problems to be Solved by the Invention

[0014] An object of the present invention is to provide a laminate and a method for manufacturing the same, which are excellent in heat dissipation in the thickness direction, thermal diffusion in the in-plane direction, and insulation in the thickness direction, and are not easily cracked. Another object of the present invention is to provide a circuit board using the laminate.

[0015] Means for Solving the Problems

[0016] The inventors of the present application have found a solution to the above problems through the following scheme.

[0017] <Solution 1>

[0018] A laminate, characterized in that: it is a laminate comprising a metal layer A, an insulating layer provided on at least one surface of the metal layer A, and a metal layer B provided on the surface of the insulating layer opposite to the metal layer A, wherein the insulating layer comprises a support layer and a heat transfer layer containing at least an inorganic filler and an adhesive resin, and the support layer and the heat transfer layer are alternately laminated a total of 3 or more layers in a direction substantially orthogonal to the thickness direction of the insulating layer.

[0019] <Solution 2>

[0020] The laminate according to Embodiment 1, wherein the inorganic filler is plate-shaped and the inorganic filler material is substantially orthogonal to the in-plane direction of the laminate.

[0021] <Embodiment 3>

[0022] The laminate according to Embodiment 1 or 2, characterized in that the inorganic filler is hexagonal boron nitride particles.

[0023] <Embodiment 4>

[0024] The laminate according to any one of Embodiments 1 to 3, characterized in that the adhesive resin is an aromatic polyamide resin.

[0025] <Embodiment 5>

[0026] The laminate according to any one of Embodiments 1 to 4, characterized in that the tensile shear adhesive strength between the insulating layer and the metal layer is 0.1 MPa or more.

[0027] <Embodiment 6>

[0028] The laminate according to any one of Embodiments 1 to 5, characterized in that the elastic modulus of the support layer is 10 MPa or more.

[0029] <Embodiment 7>

[0030] A circuit board comprising the laminate according to any one of Embodiments 1 to 6.

[0031] <Embodiment 8>

[0032] A method for manufacturing a laminate, which is a method for manufacturing the laminate according to any one of Embodiments 1 to 6, comprising the following steps: a heat transfer layer manufacturing step of forming a film using a slurry containing a plate-shaped inorganic filler, an adhesive 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 pasting metal layers on both sides of the insulating layer.

[0033] Advantages of the Invention

[0034] According to the present invention, a laminate can be provided, which has excellent heat dissipation in the thickness direction, heat diffusion in the in-plane direction, and insulation in the thickness direction, and is not easily cracked. In addition, according to the present invention, a method for manufacturing such a laminate can be provided. The laminate of the present invention is particularly suitable for use as a circuit board that requires insulation and heat dissipation in the thickness direction. Description of the Drawings

[0035] Figure 1 Figure 1 A schematic cross-sectional view showing a laminate according to an embodiment of the present disclosure.

[0036] ​​​Figure 2 Figure 2 Scanning electron microscope photographs of a cross section perpendicular to the plane of the laminate according to the example are shown.

[0037] Figure 3 Figure 3 Scanning electron microscope photographs of a cross section perpendicular to the plane of the laminate according to Comparative Example 2 are shown.

[0038] Figure 4 Figure 4 Scanning electron microscope photographs of a cross section perpendicular to the plane of the laminate according to Comparative Example 3 are shown. Detailed Description of the Invention

[0039] Hereinafter, embodiments of the present invention will be described.

[0040] <<Laminate>>

[0041] The laminate of the present disclosure includes: a metal layer A, an insulating layer provided on at least one surface of the metal layer A, and a metal layer B provided on the surface of the insulating layer opposite to the metal layer A. In addition, the insulating layer has at least a structure in which a support layer and a heat transfer layer are alternately laminated a total of three or more layers. In addition, the heat transfer layer contains at least a plate-like inorganic filler. In addition, the inorganic filler is oriented in a direction substantially orthogonal to the insulating layer.

[0042] Figure 1 A schematic diagram of a cross section perpendicular to the plane of a laminate according to an embodiment of the present disclosure is shown. As Figure 1 seen, the laminate 11 has a form in which a metal layer A is provided on one surface of a planar insulating layer 12 and a metal layer B is provided on the other surface. An adhesive layer 13 may be included between the insulating layer and the metal layer A and between the insulating layer and the metal layer B.

[0043] <<Thickness>>

[0044] The thickness of the laminate may vary depending on the required thermal resistance value or insulation breakdown voltage of the laminate, and is, for example, 0.05 to 20 mm, preferably 0.1 to 10 mm.

[0045] <<Thermal Resistance Value in the Thickness Direction>>

[0046] Preferably, the laminate according to the present disclosure has a thermal resistance value of 0.60 (K·cm 2 ) / W or less in the thickness direction.

[0047] In particular, when copper plates with a thickness of 1 mm are used on both sides, the thermal resistance value in the thickness direction of the laminate can be 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·cm 2 ) / 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 may be 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 ) / W or more. When applying the laminate of the present invention to a circuit board, from the viewpoint of imparting good heat dissipation to the laminate, preferably 0.39 (K·cm 2 ) / W or less, more preferably 0.36 (K·cm 2 ) / W or less, further preferably 0.33 (K·cm 2 ) / W or less, particularly preferably 0.30 (K·cm 2 ) / W or less.

[0048] The thermal resistance value of the laminate can be obtained by a conventional method.

[0049] <Insulation breakdown voltage>

[0050] Preferably, the insulation 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. In the case of 5 kV / mm or more, insulation breakdown is less likely to occur, and defects in electronic devices can be avoided, so it is preferred.

[0051] The insulation breakdown voltage of the laminate is measured according to the test standard ASTM D149-20. An insulation resistance test device can be used in the measurement.

[0052] Hereinafter, each element constituting the laminate of the present disclosure will be described in more detail.

[0053] 《Insulating layer》

[0054] In the insulating layer according to the present disclosure, a heat transfer layer having a high in-plane thermal conductivity and a support layer for maintaining the structure are used between the adhesive heat transfer layers. In the insulating layer according to the present disclosure, the stacking direction of such a heat transfer layer is substantially orthogonal to the thickness direction of the insulating layer, whereby the thermal conductivity in the thickness direction of the insulating layer is high, and the thermal resistance value in the thickness direction of the laminate is low.

[0055] Here, in the present invention, "the stacking direction is substantially orthogonal to the thickness direction of the insulating layer" means that the angle between the stacking direction and the thickness direction is 45° to 135°, preferably, the angle is 55° to 125°, 65° to 115°, 75° to 105°, 85° to 95°, 87° to 93° or 89° to 91°.

[0056] In the insulating layer according to the present disclosure, the heat transfer layer preferably exists in such a manner that it continuously exists between one main surface and the other main surface of the insulating layer and is exposed on one main surface and the other main surface. By existing in this manner, heat can be dissipated from the member and the metal layer in contact with one surface of the insulating layer to the member and the metal layer in contact with the other insulating layer.

[0057] In the case where a support layer exists in the insulating layer according to the present disclosure, the support layer preferably exists in such a manner that it continuously or discontinuously exists between one main surface and the other main surface of the insulating layer and is exposed on one main surface and the other main surface. Since the support layer exists in this manner, in particular, the adhesive layer and the support layer are firmly bonded, a strong bonding strength is obtained between the insulating layer and the adhesive layer, and a preferable tensile shear bonding strength between the insulating layer and the metal layer can be obtained.

[0058] In the insulating layer according to the present disclosure, the heat transfer layer constituting the insulating layer accounts for at least 50% by volume of the insulating layer. In this case, since the proportion of the heat transfer layer having a high thermal conductivity in the thickness direction is increased, a laminate having an even lower thermal resistance value in the thickness direction can be provided.

[0059] Preferably, the proportion of the heat transfer layer relative to the insulating layer can be 55% by volume or more, 60% by volume or more, 65% by volume or more, or 70% by volume or more, and / or can 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.

[0060] The thickness of the heat transfer layer can be arbitrarily set, and the thickness of the heat transfer layer can be 0.1 μm or more, 1 μm or more, 10 μm or more, or 20 μm or more, and / or can be 1000 μm or less, 100 μm or less, 80 μm or less, 70 μm or less, or 60 μm or less.

[0061] The greater the thickness of the heat transfer layer relative to the thickness of the support layer, the lower the thermal resistance value of the resulting laminate in the thickness direction. Therefore, it is preferable that the thickness of the heat transfer layer is relatively thick. For example, the thickness of the heat transfer layer in the stacking direction is preferably 2 times or more 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.

[0062] The smaller the thickness of the heat transfer layer relative to the thickness of the support layer, the greater the tensile shear adhesion strength between the insulating layer and the metal layer of the laminate. Therefore, in order to increase the tensile shear adhesion strength between the insulating layer and the metal layer, it is preferable that the thickness of the support layer is relatively thick relative to the thickness of the heat transfer layer. For example, the thickness of the heat transfer layer in the stacking direction is preferably 100 times or less the thickness of the support layer in the stacking direction.

[0063] In order to increase the tensile shear adhesion strength between the insulating layer and the metal layer, preferably, the thickness of the heat transfer layer in the stacking direction can be 0.8 times or more, 1 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 the thickness of the support layer in the stacking direction, and / or can be 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. Preferably, the thickness of the heat transfer layer in the stacking direction is 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 is 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. 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 is 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.

[0064] If it is within the above range, the thermal conductivity of the insulating layer sufficient to obtain a low thermal resistance in the thickness direction of the laminate can be obtained, and at the same time, the proportion of the main surface of the insulating layer that contributes greatly to the adhesive force between the insulating layer and the adhesive layer and on which the support layer is exposed can reach the level where a strong adhesive bond between the insulating layer and the adhesive layer can be ensured. Therefore, a low thermal resistance value in the thickness direction of the laminate can be obtained without reducing the tensile shear adhesion strength between the insulating layer and the metal layer, so it is preferable.

[0065] The total number of heat transfer layers and support layers contained in the insulating layer can be set arbitrarily. For example, it is 3 layers or more, preferably 11 layers or more, and more preferably 21 layers or more. There is no particular upper limit to the total number of heat transfer layers contained in the insulating layer. For example, it can be 100000 layers or less, 50000 layers or less, 10000 layers or less, or 5000 layers or less.

[0066] <Average in-plane thermal conductivity>

[0067] Preferably, the insulating layer involved in the present disclosure has a thermal conductivity of 15 W / (m·K) or more in the in-plane direction.

[0068] In particular, the average value of the thermal conductivity in the in-plane direction of the insulating layer may be 17.5 W / (m·K) or more or 20 W / (m·K) or more, and / or may be 60 W / (m·K) or less, 50 W / (m·K) or less, or 40 W / (m·K) or less.

[0069] The average value of the thermal conductivity in the in-plane direction of the insulating layer can be calculated by adding the thermal conductivity along any direction X in the in-plane of the insulating layer and the thermal conductivity along the direction Y perpendicular to the direction X in the in-plane of the insulating layer and then dividing by 2.

[0070] The thermal conductivity in the in-plane direction of the insulating layer is calculated by multiplying the thermal diffusivity, specific gravity, and specific heat in the in-plane direction. That is, it can be calculated by (thermal conductivity in the in-plane direction) = (thermal diffusivity in the in-plane direction) × (specific heat) × (specific gravity).

[0071] The thermal diffusivity in the in-plane direction can be measured by the periodic heating radiation thermometry method. The specific heat can be obtained by a differential scanning calorimeter. In addition, the specific gravity can be obtained from the external dimensions and weight of the insulating layer.

[0072] <Average value of the thermal conductivity in the thickness direction>

[0073] Preferably, the insulating layer involved in the present disclosure has a thermal conductivity of 20 W / (m·K) or more in the thickness direction.

[0074] In particular, the average value of the thermal conductivity in the thickness direction of the insulating layer may be 22.5 W / (m·K) or more or 25 W / (m·K) or more, and / or may be 70 W / (m·K) or less, 60 W / (m·K) or less, or 50 W / (m·K) or less.

[0075] The thermal conductivity in the thickness direction of the insulating layer can be calculated by multiplying the thermal diffusivity, specific gravity, and specific heat in the thickness direction. That is, it can be calculated by (thermal conductivity in the thickness direction) = (thermal diffusivity in the in-plane direction) × (specific heat) × (specific gravity).

[0076] The thermal diffusivity in the thickness direction can be measured by the temperature wave analysis method. The specific heat can be obtained by a differential scanning calorimeter. In addition, the specific gravity can be obtained from the external dimensions and weight of the insulating layer.

[0077] <Real part of the complex dielectric constant of the insulating layer (relative dielectric constant)>

[0078] The preferred range of the real part of the complex dielectric constant (relative dielectric constant) of the insulating layer related to the present disclosure is 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 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 still more preferably, it is 2 or more and 5 or less. By having the real part of the complex dielectric constant (relative dielectric constant) of the insulating layer within this range, there is an advantage of being able to reduce the floating capacitance of the laminate. The frequency at which such a real part of the complex dielectric constant (relative dielectric constant) is obtained can be any frequency selected according to the required frequency. For example, it can be set to 1 kHz and / or 1 MHz.

[0079] <Dielectric loss tangent of the insulating layer>

[0080] The preferred range of the dielectric loss tangent of the insulating layer related to the present disclosure is 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 still more preferably, it is 0.008 or more and 0.3 or less. By having the dielectric loss tangent of the insulating layer within this range, for example, when using the laminate as a circuit board, there is an advantage of being able to reduce the transmission loss of the circuit. The frequency at which such a dielectric loss tangent is obtained can be any frequency selected according to the required frequency. For example, it can be set to 1 kHz and / or 1 MHz.

[0081] It should be noted that the dielectric loss tangent of the insulating layer related to the present disclosure can be obtained by dividing the imaginary part of the complex dielectric constant of the insulating layer by the real part of the complex dielectric constant (relative dielectric constant) of the insulating layer.

[0082] <Heat transfer layer>

[0083] The heat transfer layer related to the present disclosure contains at least a plate-like inorganic filler oriented in the in-plane direction of the heat transfer layer and an adhesive resin.

[0084] <Parts by mass>

[0085] Preferably, the inorganic filler contained in the heat transfer layer related to the present disclosure can be 70 parts by mass or more, 80 parts by mass or more, or 90 parts by mass or more, and / or can be 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 with respect to 100 parts by mass of the heat transfer layer.

[0086] Preferably, the binder resin contained in the heat transfer layer according to the present disclosure may be 1 part by mass or more, 3 part by mass or more, 5 part by mass or more, or 7 part by mass or more, and / or may be 30 part by mass or less, 20 part by mass or less, or 10 part by mass or less, based on 100 parts by mass of the heat transfer layer.

[0087] <Inorganic filler>

[0088] The inorganic filler is any particle having insulating properties and a higher thermal conductivity than the binder resin. There is no particular limitation on the inorganic filler, and examples thereof include particles such as silica, talc, mica, boron nitride, aluminum nitride, alumina, magnesia, zinc oxide, silicon nitride, and silicon carbide, metal silicon particles with a surface oxidation, carbon fibers and graphite surface-coated with an insulating material such as a resin. From the viewpoints of in-plane thermal conductivity and insulation properties, boron nitride particles, particularly hexagonal boron nitride particles, are preferred as the inorganic filler.

[0089] The average particle diameter of the inorganic filler is preferably 1 to 200 μm, more preferably 5 to 200 μm, further preferably 5 to 100 μm, and particularly preferably 10 to 100 μm.

[0090] The average particle diameter is the median diameter measured by the laser diffraction method using a laser diffraction / scattering particle size distribution measuring device (when a certain powder is divided into two parts by a certain particle diameter, the particle diameter at which the particles larger than this diameter and the particles smaller than this diameter are equal in amount, which is usually also referred to as D50).

[0091] (Plate-like)

[0092] The heat transfer layer according to the present disclosure preferably contains a plate-like inorganic filler. In the context of the present disclosure, a particle being "plate-like" means that the particle shape is flat, scaly, or flaky.

[0093] The aspect ratio of the plate-like inorganic filler is preferably 10 to 1000. When the aspect ratio is 10 or more, the orientation important for improving thermal diffusivity can be ensured, and high thermal diffusivity can be obtained, so it is preferred. In addition, insulating and thermally conductive particles having an aspect ratio of 1000 or less are preferred from the viewpoint of processability because an increase in the viscosity of the composition due to an increase in the specific surface area is suppressed.

[0094] The aspect ratio is a value obtained by dividing the major axis of the particle by the thickness of the particle, that is, major axis / thickness. When the particle is spherical, the aspect ratio is 1, and as the flatness increases, the aspect ratio increases.

[0095] The aspect ratio can be obtained by measuring the major axis and thickness of the particle at a magnification of 1500 times using a scanning electron microscope and calculating major axis / thickness.

[0096] When the heat transfer layer contains plate-like inorganic fillers, the plate-like inorganic fillers preferably account for 50% by volume or more of the total inorganic fillers. 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-like inorganic fillers relative to the total inorganic fillers is more preferably 60% by volume or more, further preferably 70% by volume or more, still further preferably 80% by volume or more, particularly preferably 90% by volume or more. Most preferably, the inorganic fillers are composed of plate-like inorganic fillers.

[0097] (Hexagonal boron nitride particles)

[0098] Examples of the plate-like inorganic fillers include hexagonal boron nitride particles.

[0099] The average particle size of the hexagonal boron nitride particles is, for example, 1 μm or more, preferably 1 - 200 μm, further preferably 5 - 200 μm, still further preferably 5 - 100 μm, particularly preferably 10 - 100 μm. When it is 1 μm or more, the specific surface area of the hexagonal boron nitride particles is small, ensuring compatibility with the resin, so it is preferred. When it is 200 μm or less, thickness uniformity of the heat transfer layer can be ensured during the molding of the heat transfer layer, so it is preferred. The hexagonal boron nitride particles can use boron nitride particles with a single average particle size, or can be used by mixing a variety of hexagonal boron nitride particles with different average particle sizes. The aspect ratio of the hexagonal boron nitride particles is preferably 10 - 1000.

[0100] When using hexagonal boron nitride particles as the inorganic fillers, inorganic fillers other than boron nitride particles can be used in combination. In this case, the hexagonal boron nitride particles also preferably account for 50% by volume or more of the total inorganic fillers. If it is 50% by volume or more, good in-plane thermal conductivity of the heat transfer layer can be ensured, so it is preferred. Relative to the total inorganic fillers, the hexagonal boron nitride particles are more preferably 60% by volume or more, further preferably 70% by volume or more, still further preferably 80% by volume, particularly preferably 90% by volume or more or 95% by volume or more.

[0101] When using hexagonal boron nitride particles and inorganic fillers with isotropic thermal conductivity as the inorganic fillers, the balance between the thermal conductivity in the thickness direction and the in-plane direction of the heat transfer layer can be adjusted as needed, so it is a preferred solution.

[0102] (Orientation)

[0103] From the viewpoint of obtaining particularly high heat dissipation in the thickness direction of the laminate, it is preferred that the plate-like inorganic fillers are substantially orthogonal to the in-plane direction of the laminate. Therefore, it is also preferred that the plate-like inorganic fillers are oriented along the in-plane direction of the heat transfer layer.

[0104] Here, in the present invention, "the inorganic filler is substantially orthogonal to the in-plane direction of the laminate" means that the angle between the main plate surface of the plate-shaped inorganic filler and the main surface of the laminate is 45° to 135°, preferably, the angle is 55° to 125°, 65° to 115°, 75° to 105°, 85° to 95°, 87° to 93°, or 89° to 91°.

[0105] Whether the plate-shaped inorganic filler contained in the heat transfer layer is substantially orthogonal to the in-plane direction of the laminate can be determined by measuring the major axis angle of the particles and the angle of the laminate surface on a cross-section perpendicular to the in-plane direction of the laminate at a magnification of 100 to 3000 times using a scanning electron microscope and comparing them.

[0106] <Adhesive resin>

[0107] There is no particular limitation on the adhesive resin. Examples of the adhesive resin include thermoplastic resins such as aromatic polyamide resins (aromatic polyamides) described later, thermosetting resins such as silicone resins, polyimide resins, phenolic resins, and epoxy resins, and these can be used alone or as a mixture obtained by combining multiple types. The adhesive resin is particularly preferably an aromatic polyamide. Compared with aliphatic polyamides, aromatic polyamides have excellent strength. Therefore, when an aromatic polyamide is used as the adhesive resin, a heat transfer layer with particularly excellent retention of inorganic fillers and stability of layer shape can be provided.

[0108] (Thermal properties)

[0109] From the viewpoint of the thermal properties of the heat transfer layer, it is preferred that the adhesive resin has excellent properties in terms of heat resistance and / or flame retardancy. In particular, it is preferred that the melting point or thermal decomposition temperature of the adhesive resin is 150°C or higher.

[0110] The melting point of the adhesive resin is measured by a differential scanning calorimeter. The melting point of the adhesive resin is more preferably 200°C or higher, further preferably 250°C or higher, and particularly preferably 300°C or higher. There is no particular limitation on the lower limit of the melting point of the adhesive resin, for example, it is 600°C or lower, 500°C or lower, or 400°C or lower.

[0111] The thermal decomposition temperature of the adhesive is measured by a differential scanning calorimeter. The thermal decomposition temperature of the adhesive resin is more preferably 200°C or higher, further preferably 300°C or higher, particularly preferably 400°C or higher, and most preferably 500°C or higher. There is no particular limitation on the lower limit of the thermal decomposition temperature of the adhesive resin, for example, it is 1000°C or lower, 900°C or lower, or 800°C or lower.

[0112] When used as a laminate inside an in-vehicle electronic device, a resin material with a high heat-resistant temperature is also required. In the case of a power semiconductor using silicon carbide, heat resistance of around 200 °C is required. Therefore, a resin having heat resistance of 200 °C or higher is suitable for in-vehicle applications, particularly for use as a circuit board around a power semiconductor. Examples of such resins include aromatic polyamide resins.

[0113] (Thermoplastic resin)

[0114] In addition, when the adhesive resin contains a thermoplastic resin, it is considered that the voids in the heat transfer layer can be further reduced, and thus it is particularly preferred. Although there is no intention to limit by theory, when a thermoplastic resin is used as the adhesive resin, for example, by heating during the pressing process in manufacturing the heat transfer layer, the thermoplastic resin softens, further promoting the discharge of air bubbles trapped between the inorganic fillers. As a result, it is considered that the effect of reducing voids can be further improved.

[0115] Examples of the thermoplastic resin that can be used as the adhesive resin include aromatic polyamide 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 polybenz oxazole (PBO), etc.

[0116] (Aromatic polyamide resin)

[0117] In particular, it is preferred that the adhesive resin contains an aromatic polyamide resin (aromatic polyamide) or is composed of an aromatic polyamide resin. When the adhesive resin contains an aromatic polyamide resin, it is preferably contained in an amount of 90% by volume or more relative to the adhesive resin. When an aromatic polyamide resin is used as the adhesive resin, a heat transfer layer with more excellent mechanical strength can be obtained even when inorganic fillers are filled in a high proportion. In addition, from the viewpoint of thermal properties, it is also preferred that the adhesive resin contains an aromatic polyamide resin or is composed of an aromatic polyamide resin. The aromatic polyamide resin has a high thermal decomposition temperature, and a heat transfer layer using the aromatic polyamide resin as the adhesive resin shows excellent flame retardancy.

[0118] An aromatic polyamide resin is a linear high-molecular compound in which more than 60% of the amide bonds are directly bonded to an aromatic ring. As the aromatic polyamide resin, for example, poly(m-phenylene isophthalamide) and its copolymers, poly(p-phenylene terephthalamide) and its copolymers can be used. For example, copoly(p-phenylene-3,4'-diphenylether terephthalamide) (alias: copoly(p-phenylene methylene-3,4'-oxy diphenylene terephthalamide)) can be cited. The aromatic polyamide resin can be used alone or in combination of several kinds.

[0119] (Additive)

[0120] The heat transfer layer of the present invention may contain a flame retardant, an anti-discoloration agent, a surfactant, a coupling agent, a coloring agent, a viscosity modifier, and / or a reinforcing material. Further, in order to improve the strength of the sheet, a fibrous reinforcing material may be contained. If short fibers of an aromatic polyamide resin are used as the fibrous reinforcing material, the heat resistance of the heat transfer layer will not be reduced by adding the reinforcing material, and thus it is preferred. With respect to 100 parts by volume of the heat transfer layer, the fibrous reinforcing material is preferably added in the range of 0.5 to 25 parts by volume, more preferably in the range of 1 to 20 parts by volume.

[0121] 《Support layer》

[0122] As the material of the support layer related to the present disclosure, an insulating substance that can bond adjacent heat transfer layers to each other can be used. For example, a thermoplastic resin, a thermoplastic elastomer, and a crosslinkable resin can be used.

[0123] As the thermoplastic resin, for example, vinyl acetate resin, polyvinyl acetal, ethylene-vinyl acetate resin, vinyl chloride resin, acrylic resin, polyamide, cellulose, and α-olefin can be used.

[0124] Among the thermoplastic elastomers, for example, chloroprene rubber, nitrile rubber, styrene-butadiene rubber, polysulfide, butyl rubber, silicone rubber, acrylic rubber, polyurethane rubber, silylated polyurethane resin, and telechelic polyacrylate can be used.

[0125] As the crosslinkable resin, for example, epoxy resin, phenolic resin, and polyurethane resin can be cited. From the viewpoints of heat resistance and adhesiveness of the heat transfer layer, epoxy resin is particularly preferred.

[0126] From the viewpoints of obtaining high heat resistance of the insulating layer and good adhesiveness 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. Further, 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, polyurethane rubber, silylated polyurethane resin, or telechelic polyacrylate, and more preferably chloroprene rubber, nitrile rubber, styrene-butadiene rubber, butyl rubber, acrylic rubber, or telechelic polyacrylate. Additionally, when the support layer is a crosslinkable resin, the support layer is preferably epoxy resin, phenolic resin, and polyurethane resin, and more preferably epoxy resin and phenolic resin, and still more preferably epoxy resin.

[0127] As the support layer, acrylic resin and epoxy resin are particularly preferred.

[0128] In the case where the support layer is as described above, since the material constituting the support layer has a high glass transition temperature and / or high heat deflection temperature, high heat resistance of the insulating layer can be obtained. Further, in the case where the support layer is as described above, since the surface free energy of the material constituting the support layer is high, the surface free energy at the position where the support layer is exposed on the surface of the insulating layer can be increased, and thus good adhesiveness to the adhesive layer can be obtained.

[0129] In the support layer, additives such as a curing accelerator, an anti-discoloration agent, a surfactant, a coupling agent, a colorant, a viscosity modifier, and a filler can be added within a range that does not impair the insulation and adhesiveness.

[0130] The elastic modulus of the support layer preferably ranges from 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 is 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. By the elastic modulus of the support layer being within this range, toughness preferable for the treatment of the insulating layer can be imparted to the insulating layer, and there is an advantage of good workability during the manufacture of the laminate. Further, by the elastic modulus of the support layer being within this range, when pressurization is performed in the metal layer formation process, there is an advantage of being able to reduce the occurrence frequency of defects such as buckling of the insulating layer during pressurization. Further, by the elastic modulus of the support layer being within this range, when the temperature of the laminate changes, stress generated between the layers of the laminate can be alleviated, and there is an advantage of being able to suppress cracking of the insulating layer or the adhesive layer and peeling of the metal layer during use of the laminate.

[0131] The elastic modulus of the support layer can be obtained from the tensile stress-strain curve of the support layer.

[0132] 《Metal layer A and metal layer B》

[0133] There is no particular limitation on the materials of metal layer A and metal layer B related to the present disclosure. As the types of metals, for example, pure metals such as titanium, aluminum, beryllium, magnesium, iron, lead, gold, platinum, silver, copper, chromium, cadmium, zinc, arsenic, manganese, cobalt, nickel, molybdenum, tungsten, tin, bismuth, or alloys containing these can be cited. Non-metal elements such as carbon or oxygen can be included as impurities and additives. In particular, from the viewpoints of heat dissipation or price, pure metals of copper or aluminum and alloys containing copper or aluminum are preferable. Further, metal layer A and metal layer B can be of the same material, or metals of different materials can be used according to the application.

[0134] Metal layer A and metal layer B can be in a uniform planar shape, or can be in a pattern shape such as a circuit, a dot shape, or a linear shape.

[0135] There is no particular limitation on the thicknesses of metal layer A and metal layer B. When the thickness of the metal layer is thin, there are the following advantages: the thermal resistance in the thickness direction is small, pattern formation of the metal layer is easy, the weight of the laminate is light, and the production cost of the laminate is low. On the other hand, when the thickness of the metal layer is thick, there are the following advantages: the in-plane thermal diffusivity of the laminate is high, and even when a soft insulating layer is used, the rigidity of the laminate can be ensured. Further, the thicknesses of metal layer A and metal layer B can be the same, or layers of different thicknesses can be used according to the application.

[0136] 《Adhesive layer》

[0137] As the material of the adhesive layer that can be included in the present disclosure, an insulating substance that can bond the insulating layer and the metal layer can be used. For example, a thermoplastic resin, a thermoplastic elastomer, or a crosslinkable resin can be used.

[0138] Among thermoplastic resins, for example, vinyl acetate resin, polyvinyl acetal, ethylene-vinyl acetate resin, vinyl chloride resin, acrylic resin, polyamide, cellulose, and α-olefin can be used.

[0139] Among thermoplastic elastomers, for example, chloroprene rubber, nitrile rubber, styrene-butadiene rubber, polysulfide, butyl rubber, silicone rubber, acrylic rubber, polyurethane rubber, silylated polyurethane resin, and telechelic polyacrylate can be used.

[0140] As crosslinkable resins, for example, epoxy resins, phenolic resins, and polyurethane resins can be cited. From the viewpoints of heat resistance and adhesiveness to the insulating layer and the metal layer, epoxy resins are particularly preferred.

[0141] From the viewpoints of obtaining high heat resistance of the adhesive layer and good adhesiveness to the insulating layer or / and the 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. In addition, 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, polyurethane rubber, silylated polyurethane resin, or telechelic polyacrylate, and more preferably chloroprene rubber, nitrile rubber, styrene-butadiene rubber, butyl rubber, acrylic rubber, or telechelic polyacrylate. In addition, when the adhesive layer is a crosslinkable resin, the adhesive layer is preferably epoxy resin, phenolic resin, and polyurethane resin, and more preferably epoxy resin and phenolic resin, and further preferably epoxy resin.

[0142] As the adhesive layer, acrylic resin and epoxy resin are particularly preferred, and epoxy resin is most preferred.

[0143] In the case where the adhesive layer is as described above, since the material constituting the adhesive layer has a high glass transition temperature and / or a high heat deflection temperature, high heat resistance of the adhesive layer can be obtained. In addition, in the case where the adhesive layer is as described above, since the surface free energy of the adhesive layer can be increased, good adhesiveness to the insulating layer or / and the metal layer can be obtained.

[0144] In the adhesive layer, additives such as a curing accelerator, an anti-discoloration agent, a surfactant, a coupling agent, a coloring agent, a viscosity modifier, and a filler can be blended within a range that does not impair insulation and adhesiveness. In particular, adding thermally conductive ceramic particles can further reduce the thermal resistance value in the thickness direction of the circuit board, and thus is a preferred embodiment.

[0145] 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 be generated between the insulating layer and the adhesive layer and between the metal layer and the insulating layer, so as to reduce the frequency of defects (peeling defects) in which peeling occurs between the insulating layer and the adhesive layer and between the metal layer and the insulating layer. Such stresses include, for example, the shear stress applied in the shear direction between the insulating layer and the metal layer in the use state of the laminate, and the stress between the insulating layer and the adhesive layer and between the metal layer and the insulating layer caused by the difference in the linear expansion amounts of the insulating layer and the metal layer due to temperature changes, but are not limited to these.

[0146] 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, further preferably 3 MPa or more, and particularly preferably 4 MPa or more. By the tensile shear adhesive strength between the insulating layer and the metal layer being within this range, there is an advantage that the frequency of peeling defects between the insulating layer and the adhesive layer and between the metal layer and the insulating layer can be reduced.

[0147] The tensile shear adhesive strength between the insulating layer and the metal layer can be obtained by a tensile test of the laminate.

[0148] The laminate of the present invention is excellent in heat dissipation in the thickness direction, heat diffusion in the in-plane direction, and insulation in the thickness direction, and is not easily cracked. Therefore, it can be used as a circuit board by processing the metal layer to form a prescribed conductor circuit.

[0149] [Method for manufacturing a laminate]

[0150] The present disclosure includes a method for manufacturing the laminate according to the present disclosure, the method including the following steps:

[0151] A heat transfer layer manufacturing process of forming a film using a slurry containing a plate-shaped inorganic filler, a binder resin, and a solvent, an insulating layer manufacturing process of alternately laminating the heat transfer layer and a support layer and then cutting, and a metal layer forming process of pasting metal layers on both sides of the insulating layer.

[0152] 《Heat Transfer Layer Manufacturing Process》

[0153] The heat transfer layer manufacturing process includes: a mixing process of at least mixing a plate-shaped inorganic filler, a binder resin, and a solvent to obtain a slurry; a forming process of shaping the slurry after the mixing process into a sheet and drying it to form a heat transfer layer precursor; and a pressing process of compressing the heat transfer layer precursor.

[0154] <Mixing Process>

[0155] In the mixing process of the heat transfer layer manufacturing process of the manufacturing method according to the present disclosure, a plate-shaped inorganic filler, a binder resin, and a solvent are mixed to obtain a slurry.

[0156] Regarding the inorganic filler and the binder resin, reference can be made to the above-mentioned content about the heat transfer layer.

[0157] In the mixing process, additives such as a flame retardant, an anti-discoloration agent, a surfactant, a coupling agent, a coloring agent, a viscosity regulator, and / or a reinforcing material can be optionally added. In order to improve the strength of the sheet, a fibrous reinforcing material can be added.

[0158] In the mixing process, anhydrous calcium chloride or anhydrous lithium chloride can be added. By adding anhydrous calcium chloride or anhydrous lithium chloride in the mixing process, sometimes the solubility of the binder resin in the solvent can be improved. Especially when using an aromatic polyamide resin as the binder resin, it is preferable to add anhydrous calcium chloride or anhydrous lithium chloride in the mixing process. In this case, the solubility of the aromatic polyamide resin in the solvent can be further improved.

[0159] (Solvent)

[0160] As the solvent, a solvent that can dissolve the binder resin can be used. For example, when using an aromatic polyamide resin as the binder resin, 1-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, or dimethyl sulfoxide can be used.

[0161] (Mixing)

[0162] In the mixing of the insulating particles, the binder resin, and the solvent, for example, ordinary kneading devices such as a paint shaker or a bead mill, a planetary mixer, a stirring type disperser, a rotation-revolution stirring mixer, a three-roll mill, a kneader, a single-screw or twin-screw kneader can be used.

[0163] <Forming Process>

[0164] In the shaping process of the heat transfer layer manufacturing process according to the present disclosure, the slurry after the mixing process is shaped into a sheet and dried to form a heat transfer layer precursor.

[0165] (Shaping)

[0166] In order to shape the slurry after the mixing process into a sheet, a known method such as a method of coating the slurry on a release film using a coater can be used.

[0167] (Drying)

[0168] Drying can be carried out according to a known method. For example, the slurry coated on a substrate can be dried, and then, after the shaped slurry is peeled off from the substrate in water, it can be dried again. The drying temperature can be, for example, 50°C to 300°C, and the drying time can be, for example, 30 seconds to 3 hours.

[0169] In the shaping process, a water washing treatment can be carried out. By carrying out the water washing treatment, the residual solvent and salts in the heat transfer layer can be reduced. The water washing treatment can be carried out, for example, by immersing the slurry coated on a substrate and shaped for 10 minutes to 3 hours in ion-exchanged water or distilled water after drying. The heat transfer layer precursor can be subjected to the water washing treatment. When anhydrous calcium chloride or anhydrous lithium chloride is added in the mixing process, it is preferable to carry out the water washing treatment.

[0170] The shaped slurry or the heat transfer layer precursor has more voids than the heat transfer layer after compression treatment, so it is considered to have high water permeability. Therefore, it is considered that by carrying out the water washing treatment at a stage before the compression treatment, the residual solvent and salts can be removed more effectively.

[0171] It should be noted that the water contained in the heat transfer layer can be reduced by drying after water washing or by compression treatment.

[0172] <Compression process>

[0173] In the compression process of the heat transfer layer manufacturing process according to the present disclosure, the heat transfer layer precursor is compressed.

[0174] 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.

[0175] In addition, when the heat transfer layer precursor is compressed, a heat transfer layer having a surface structure with higher smoothness can be obtained.

[0176] The compression process can use a common pressing device such as vertical planar pressing or roll pressing, for example. Roll pressing is preferred because it discharges the air contained in the heat transfer layer precursor and is easy to achieve high density and high thermal conductivity. The environment of the pressing device can be under atmospheric pressure or in a vacuum.

[0177] Rolling

[0178] Rolling can be carried out according to known methods. For example, the heat transfer layer precursor can be pressure-treated by a calender roll machine. The pressure applied to the heat transfer layer precursor in the rolling process is preferably 400 - 8000 N / cm in terms of linear pressure. By setting the linear pressure to 400 N / cm or more, the discharge of air bubbles to the outside of the heat transfer layer becomes significant. By the linear pressure being 8000 N / cm or less, the inorganic filler is tightly filled without being damaged, and the voids in the heat transfer layer can be reduced. The diameter of the roll used in rolling is preferably 200 - 1500 mm, for example.

[0179] In the compression process, it is preferable to heat the heat transfer layer precursor. The heating temperature can be appropriately set according to the type of adhesive resin used, etc. When using an aromatic polyamide resin as the adhesive resin, the heating temperature is preferably 100 - 350 °C. By setting the heating temperature to 100 °C or more, the adhesive resin is easily softened, and the effect of filling the gaps between the inorganic fillers by compression treatment can be easily obtained. By setting the heating temperature to 350 °C or less, the reduction in the strength of the adhesive resin caused by the heating process is less likely to occur.

[0180] Insulating Layer Manufacturing Process

[0181] The insulating layer manufacturing process includes: a laminating process of alternately laminating a heat transfer layer and a support layer, and a cutting process of cutting the laminated heat transfer layer / support layer in the thickness direction of lamination.

[0182] <Laminating Process>

[0183] The laminating process can be carried out by alternately laminating a plurality of heat transfer layers and support layers in the thickness direction. For example, a laminate can be obtained by laminating heat transfer layers and support layers that have been cut into appropriate sizes.

[0184] In addition, the laminating process can be carried out by folding or winding the heat transfer layer and the support layer. For example, in a state where a support layer is provided on one side of the heat transfer layer, it can be wound around a core material or a plate to form the first layer, and then a new layer can be wound thereon to form the second layer. This operation is repeated until the desired number of layers is reached, thereby obtaining an alternating laminate of the heat transfer layer / support layer. In addition, an alternating laminate of the heat transfer layer / support layer can also be obtained by simultaneously folding or winding the heat transfer layer and the support layer drawn from another shaft. In addition, a liquid or powder support layer can be coated each time a heat transfer layer is laminated.

[0185] A laminate can be produced by producing a plurality of laminates obtained by the above method and laminating them.

[0186] In the laminating process, after laminating the heat transfer layer / support layer, heat treatment may be further performed. When the support layer is a thermoplastic resin, the adhesion between the layers in the resulting laminate is further improved by further performing heat treatment. When the support layer is a thermosetting resin, the bonding strength between the layers is increased. The temperature of the heat treatment can be appropriately set according to the adhesive resin contained in the heat transfer layer or the type of the support layer, etc.

[0187] As the support layer used in the laminating process, for example, the molecular gradient film double-sided tape "200Y" (manufactured by Kyodo Chemical Co., Ltd.) can be used. When using 200Y 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 laminating process. Patent Document 5 (Japanese Unexamined Patent Application Publication No. 2006-232896) discloses that the peel strength is increased 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, it can be maintained under such conditions to improve the adhesion.

[0188] In addition, as the support layer used in the laminating process, for example, the heat dissipation insulating adhesive sheet "EAL" (manufactured by Arisawa Manufacturing Co., Ltd.) can be used. When using EAL 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 laminating process. In the catalog of the heat dissipation insulating adhesive sheet "EA series" (https: / / www.arisawa.co.jp / jp / products / data / CATALOG_EA_JP.PDF), as the conditions of heat treatment, 180°C, 60 minutes, and 3 to 20 MPa are disclosed. When heat treatment is performed after laminating the heat transfer layer / support layer, for example, it can be maintained under such conditions to improve the adhesion.

[0189] <Cutting Process>

[0190] In the cutting process, the laminate is cut along the approximate lamination direction of the heat transfer layer / support layer to obtain an insulating layer.

[0191] The cutting process is performed in such a manner that the thickness direction of the insulating layer obtained by cutting is substantially orthogonal to the lamination direction of the heat transfer layer constituting the insulating layer.

[0192] The cutting process can be performed by a known method. For example, it can be performed by a multi-knife method, a laser processing method, a water jet method, a tool processing method, etc. In addition, the cutting process can be performed, for example, using a common tool or cutting tool or cutting processing machine such as a cutting knife, a razor, or a Thompson knife equipped with a sharp blade. By using a cutting tool equipped with a sharp blade, etc., the disorder of the particle orientation near the surface of the heat sink obtained after the cutting process can be suppressed, and an insulating layer with a thinner thickness can be easily obtained.

[0193] There is no particular limitation on the thickness of the insulating layer obtained by cutting, for example, it is 0.02 to 5 mm, preferably 0.1 to 1 mm. By setting the thickness of the insulating layer within this range, a laminate can be provided 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.

[0194] "Metal Layer Forming Process"

[0195] The metal layer forming process can be carried out by any method that can sequentially stack metal layer A, adhesive layer, insulating layer, adhesive layer, and metal layer B and fix them.

[0196] When the raw material of the adhesive layer is liquid, a coater can be used to coat metal layer A, metal layer B, or the insulating layer.

[0197] The metal layer stacking process can include a heating process to strengthen the adhesion between layers after sequentially stacking metal layer A, adhesive layer, insulating layer, adhesive layer, and metal layer B by heating.

[0198] When the adhesive layer is a thermoplastic resin and a thermoplastic elastomer, the thermoplastic resin dissolves, and the thermoplastic resin adheres to the metal layer and the insulating layer, having the advantage of strengthening the adhesion between layers. Additionally, when the adhesive layer is a curable resin, crosslinking of the resin is promoted by heating, having the advantage of strengthening the adhesion between layers.

[0199] When a crosslinkable resin is used as the adhesive layer, after sequentially stacking metal layer A, adhesive layer, insulating layer, adhesive layer, and metal layer B, the resin constituting the adhesive layer can be crosslinked by any method of crosslinking the adhesive layer. By adopting any method of crosslinking the adhesive layer, there is an advantage of strengthening the adhesion between layers.

[0200] As any method of crosslinking the adhesive layer, light irradiation, radiation, etc. can be used, but it is not limited to these.

[0201] The metal layer forming process can include a process of applying pressure to a laminate including metal layer A, adhesive layer, insulating layer, adhesive layer, and metal layer B using a pressing device. The environment of the pressing device can be under atmospheric pressure or in a vacuum.

[0202] Examples

[0203] Hereinafter, the invention related to the present disclosure will be specifically described by way of examples.

[0204] "Examples 1 to 7, Comparative Examples 1 to 3"

[0205] The heat transfer layer, insulation layer, metal layer, and laminate related to Examples 1 to 7, and the laminates related to Comparative Examples 1 to 3 were fabricated. The properties of the obtained heat transfer layer, insulation layer, metal layer, and laminate were measured. The measurement was carried out by the following methods.

[0206] (1) Thermal conductivity in the in-plane direction and thickness direction

[0207] The thermal conductivity of the heat transfer layer and the insulation layer was obtained by multiplying the thermal diffusivity, specific gravity, and specific heat in the thickness direction and in-plane direction all together.

[0208] (Thermal conductivity) = (Thermal diffusivity) × (Specific heat) × (Specific gravity)

[0209] The thermal diffusivity in the thickness direction was obtained by the temperature wave analysis method. The measuring device used was ai-Phase mobile M3 type1 manufactured by ai-Phase Co., Ltd. The thermal diffusivity in the in-plane direction was obtained by the periodic heating and radiation thermometry method. The measuring device used was TA-33 manufactured by Bethel Co., Ltd. The specific heat was obtained using a differential scanning calorimeter (DSCQ10 manufactured by TA Instruments). The specific gravity was obtained from the external dimensions and weight of the insulating sheet.

[0210] (2) Dielectric breakdown voltage

[0211] The dielectric breakdown voltage of the insulation layer was measured according to the test specification ASTM D149-20. The measuring device used was an insulation withstand voltage test device manufactured by Tokyo Transformer Co., Ltd. To avoid surface discharge at the ends of the insulation layer, the measurement was carried out in insulating oil.

[0212] (3) Thermal resistance in the thickness direction

[0213] The thermal resistance in the thickness direction of the laminate was measured using a 40 mm × 40 mm test piece and a constant thermal conductivity measuring device SS-H40 manufactured by Bethel Co., Ltd. The thermal resistance was measured under the conditions of an upper heater temperature of 70 °C, a lower cooling water temperature of 23 °C, and a pressing pressure of 1200 N. A small amount of oil compound (G-746 manufactured by Shin-Etsu Chemical Co., Ltd.) was evenly coated on the interface between each metal layer of the laminate and the device side contact part (copper box). By setting the obtained thermal resistance value between the copper boxes to 16 times, the converted value of the thermal resistance per square centimeter was obtained.

[0214] (4) Orientation of the inorganic filler

[0215] The presence or absence of an inorganic filler in the internal insulating layer of the laminate and the orientation of the inorganic filler were confirmed by observing, at 250 times magnification, the cross-section of the laminate exposed using an ordinary cutting machine with a scanning electron microscope (TM4000 manufactured by Hitachi High-Tech Corporation).

[0216] (5) Dielectric constant and dissipation factor of the insulating layer

[0217] The real part (relative dielectric constant) of the complex dielectric constant and the dissipation factor 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 under test was regarded as an equivalent circuit composed of a parallel combination of a capacitor and a resistor. The measurement was carried out by applying a sine wave of 100 mV, and the frequencies were set to 1 kHz and 1 MHz. The real part (relative dielectric constant) of the complex dielectric constant and the dissipation factor were obtained by the following formulas.

[0218] (Real part of the complex dielectric constant (relative dielectric constant)) = [(Capacitance) × (Distance between parallel plates)] / [(Dielectric constant of vacuum) × (Area of parallel plates)]

[0219] (Dissipation factor) = [(Conductance) × (Real part of the complex dielectric constant (relative dielectric constant))] / [(Frequency) × (Capacitance)]

[0220] (6) Elastic modulus of the support layer

[0221] The elastic modulus of the support layer was measured using a tensile testing machine (TENSILON RTC-1210, manufactured by A&D Company, Limited). The elastic modulus of the support layer was obtained by clamping the support layer for elastic modulus measurement on a tensile testing machine with a gauge length of 50 mm, applying a tensile displacement at a rate of 1 mm / minute, obtaining the tensile stress-strain curve from the state where the strain was 0 to the breaking point, calculating the slope of the curve between the point where the strain was 0.0005 and the point where the strain was 0.0025 using the least squares method, and dividing the slope by the cross-sectional area. When the strain at the breaking point was 0.0025 or less, the slope of the curve between the point where the strain was 0.2 times the strain at the breaking point and the point where the strain was 0.8 times the strain at the breaking point was calculated using the least squares method, and the slope was divided by the cross-sectional area to obtain the elastic modulus.

[0222] (7) Tensile shear adhesion strength between the insulating layer and the metal layer

[0223] The tensile shear adhesion strength between the insulating layer and the metal layer was measured using a tensile testing machine (manufactured by A&D Company, Limited, TENSILON RTC-1210). Two copper plates of the laminate used for measuring the tensile shear adhesion strength were respectively clamped on the tensile testing machine. When a tensile displacement was applied under the condition of 1 mm / minute, a tensile stress-strain curve was obtained from the state where the strain was 0 until the fracture point was reached, and it was obtained by dividing the stress at the fracture point by the bonding area. It should be noted that the bonding area is the area of the main surface of the insulating layer of the laminate for measuring the tensile shear adhesion strength.

[0224] Example 1

[0225] Manufacture of the heat transfer layer

[0226] 9.3 parts by mass of the para-aramid resin "Technora" (manufactured by Teijin Limited) as an adhesive resin and 8.1 parts by mass of calcium chloride (manufactured by FUJIFILM Wako Pure Chemical Corporation) were dissolved in 363 parts by mass of 1-methyl-2-pyrrolidone. Under this state, 90.7 parts by mass of plate-like hexagonal boron nitride particles "HSPD" (manufactured by Dandong Chemical Engineering Institute Co., average particle diameter 45 μm, aspect ratio 35) were added, and the mixture was stirred for 120 minutes with a planetary stirrer while heating to 80 °C to obtain a uniform slurry.

[0227] Using a slot coater, the obtained slurry was coated on a PET film to form a sheet shape, and dried at an average temperature of 120 °C for 20 minutes. After that, the shaped slurry was peeled off from the PET film, immersed in water for 5 minutes, and dried at 150 °C for 2 minutes to obtain a heat transfer layer precursor with a thickness of 150 μm. Under the conditions of a temperature of 220 °C and a line pressure of 640 kgf / cm (6270 N / cm), the obtained heat transfer layer precursor was subjected to a compression treatment using a calender roller machine to obtain a heat transfer layer with a thickness of 42 μm. The in-plane thermal conductivity of this heat transfer layer was 42 W / (m·K).

[0228] Manufacture of the insulating layer

[0229] The obtained heat transfer layer and the chip bonding film "HS-260" (manufactured by Resonac Corporation (formerly Showa Denko Materials Co., Ltd.), crosslinkable resin (epoxy-based), thickness 10 μm) as the support layer were alternately laminated to 1000 layers, and pressed for 2 hours under the conditions of a temperature of 130 °C, a pressing pressure of 3 MPa, and a vacuum degree of 0.5 Pa using a vacuum hot press, thereby obtaining a precursor of the insulating layer. The obtained precursor of the insulating layer was made substantially perpendicular to the main surface of the heat transfer layer, and cut twice with a razor blade at intervals of 0.2 mm, thereby obtaining an insulating layer with a thickness of 0.2 mm. The thermal conductivity in the thickness direction of this insulating layer was 34 W / m·K, and the thermal conductivity in the in-plane direction was 23 W / (m·K).

[0230] <Formation of metal layer (manufacture of laminate)>

[0231] On one side of the main surface of the obtained insulating layer, a room-temperature curing two-component epoxy resin "2088E" (manufactured by ThreeBond Co., Ltd.) was coated over the entire surface with a thickness of about 1 to 5 μm, a copper foil with a thickness of 10 μm was pasted, and while pressing with a Bahco-type vise, it was heated at 120 °C in the atmosphere for 90 minutes. In addition, similarly, a 10-μm copper foil was also formed on the other surface of the insulating layer, thereby obtaining a laminate for cross-sectional observation with copper foils formed on both surfaces of the insulating layer. A laminate for thermal resistance measurement with 1-mm-thick copper plates pasted on both surfaces of the insulating layer was also manufactured in the same manner. The thickness of the support layer in the lamination direction of the support layer and the heat transfer layer of the laminate obtained by such operations was 10.6 μm. In addition, in the insulating layer, the thickness of the heat transfer layer in the lamination direction of the heat transfer layer and the support layer was 3.96 times the thickness of the support layer in the lamination direction.

[0232] <Measurement of elastic modulus of support layer>

[0233] It should be noted that the chip bonding film "HS-260" (manufactured by Resonac Corporation (formerly Showa Denko Materials Co., Ltd.), thickness 10 μm) used for forming the support layer was heated at 130 °C for 2 hours and then cut into a width of 10 mm and a length of 100 mm, thereby obtaining a film for elastic modulus measurement. The elastic modulus was 425 MPa.

[0234] <Measurement of tensile shear bond strength>

[0235] The tensile shear bond strength between the insulating layer and the metal layer in the laminate obtained by such operations was 7.3 MPa.

[0236] <<Example 2>>

[0237] Except for the following items, the laminate for thermal resistance measurement was produced in the same manner as in Example 1:

[0238] The bonding sheet “A11F” (manufactured by Arisawa Manufacturing Co., Ltd.) was used as the support layer;

[0239] In the manufacturing process of the insulating layer, during the formation of the insulating layer precursor, it was pressed for 1 hour under the conditions of a temperature of 160 °C, a pressing pressure of 3 MPa, and a vacuum degree of 0.5 Pa.

[0240] The thickness of the support layer of the laminate obtained by such operation was 14.3 μm. In addition, in the insulating layer, the thickness of the heat transfer layer in the lamination direction of the heat transfer layer was 2.94 times the thickness of the support layer in the lamination direction.

[0241] 《Example 3》

[0242] Except for setting the thickness of the insulating layer to 0.4 mm, the laminate for thermal resistance measurement was produced in the same manner as in Example 2. The thickness of the support layer and the ratio of the thickness of the heat transfer layer in the lamination direction to the thickness of the support layer in the lamination direction were the same as those in Example 2.

[0243] 《Example 4》

[0244] Except for using the heat-dissipating bonding sheet “EAL” (manufactured by Arisawa Manufacturing Co., Ltd.) as the adhesive layer, the laminate for thermal resistance measurement was produced in the same manner as in Example 2. The thickness of the support layer and the ratio of the thickness of the heat transfer layer in the lamination direction to the thickness of the support layer in the lamination direction were the same as those in Example 2.

[0245] 《Example 5》

[0246] Except for forming a copper plate with a thickness of 1 mm as Metal Layer A on one side of the insulating layer and forming a copper foil with a thickness of 0.01 mm as Metal Layer B on one side of the insulating layer, the laminate for thermal resistance measurement was produced in the same manner as in Example 2. The thickness of the support layer and the ratio of the thickness of the heat transfer layer in the lamination direction to the thickness of the support layer in the lamination direction were the same as those in Example 2.

[0247] 《Example 6》

[0248] Except for using the heat-dissipating insulating adhesive sheet “EAL” as the adhesive layer and, in the manufacturing process of the insulating layer, pressing under the conditions of 180 °C, 4 MPa, and 60 minutes during the formation of the insulating layer precursor, the laminate for thermal resistance measurement was produced in the same manner as in Example 5. The thickness of the support layer and the ratio of the thickness of the heat transfer layer in the lamination direction to the thickness of the support layer in the lamination direction were the same as those in Example 2.

[0249] 《Example 7》

[0250] Except for the following items, the laminate for thermal resistance measurement was produced in the same manner as in Example 1:

[0251] The molecular orientation film double-sided tape "200Y" was used as the support layer;

[0252] In the manufacturing process of the insulating layer, during the formation of the insulating layer precursor, pressing was performed under the conditions disclosed in Patent Document 5.

[0253] The thickness of the support layer of the laminate obtained in this way 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.

[0254] <<Comparative Example 1>>

[0255] An ordinary low thermal resistance metal substrate was produced and evaluated. An insulating heat dissipation resin (manufactured by Risho Kogyo Co., Ltd., epoxy resin + alumina particles + aluminum nitride particles) with a thickness of 0.12 mm was coated on a copper plate with a thickness of 1 mm as the insulating layer, and a copper foil with a thickness of 70 μm was pasted, and the insulating heat dissipation resin was thermally cured to produce a laminate for thermal resistance measurement.

[0256] <<Comparative Example 2>>

[0257] The insulating heat dissipation sheet "TC-20EG" (spherical inorganic filler + silicone resin) manufactured by Shin-Etsu Chemical Co., Ltd. with a thickness of 0.2 mm was used as the insulating layer, and laminates for cross-section observation and thermal resistance measurement were produced in the same manner as in the Example.

[0258] <<Comparative Example 3>>

[0259] The insulating heat dissipation sheet "TC-20BG" (plate-shaped inorganic filler + silicone resin) manufactured by Shin-Etsu Chemical Co., Ltd. with a thickness of 0.2 mm was used as the insulating layer, and laminates for cross-section observation and thermal resistance measurement were produced in the same manner as in the Example.

[0260] The production conditions and measurement results of the Example and Comparative Examples 1 to 3 are shown in Table 1.

[0261]

[0262] Industrial Applicability

[0263] The laminate of the present invention can be suitably used as a laminate for mounting semiconductor elements with a large amount of heat generation or high insulation requirements.

[0264] Symbol Explanation

[0265] 11: Laminate;

[0266] 12: Insulating layer;

[0267] 13: Adhesive layer;

[0268] 14: Metal layer;

[0269] 15: Metal layer A;

[0270] 16: Metal layer B;

[0271] 17: Heat transfer layer;

[0272] 18: Support layer;

[0273] 19: Plate-shaped inorganic filler;

[0274] 20: Adhesive resin.

Claims

1. A laminate, characterized in that: It is a laminate including a metal layer A, an insulating layer provided on at least one surface 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 an adhesive resin, and the support layer and the heat transfer layer are alternately laminated a total of three or more layers in a direction substantially orthogonal to the thickness direction of the insulating layer.

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

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

4. The laminate according to claim 1 or 2, wherein the adhesive resin is an aromatic polyamide resin.

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

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

7. A circuit board, which is composed of the laminate according to claim 1.

8. A method for manufacturing a laminate, which is a method for manufacturing the laminate according to claim 1 or 2, including the following steps: a heat transfer layer manufacturing step of forming a film using a slurry containing a plate-shaped inorganic filler, an adhesive 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 pasting the metal layer A and B on each surface of the insulating layer.

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