JP7698472B2 - Metal foil laminated resin sheet and its manufacturing method - Google Patents

Description

The present invention relates to a novel metal foil laminated resin sheet. More specifically, it provides a metal foil laminated resin sheet that has high thermal conductivity and high peel strength.

Metal foil laminated resin sheets, such as copper-clad laminates, made by laminating metal foil such as copper foil with a resin composite material are used as substrate materials for electronic devices. In recent years in particular, the amount of heat generated has increased due to the progress in the high integration and miniaturization of devices, and there is often a demand for metal foil laminated resin sheets with high thermal conductivity that use a resin composite material containing a thermally conductive filler and a resin matrix as a measure to dissipate heat from the devices.

In such metal foil laminated resin sheets, it is important to have high adhesive strength between the metal foil and the resin composite material, and various studies have been conducted to obtain high peel strength. For example, Patent Document 1 discloses that the peel strength between the copper foil and the resin composite material is improved by forming a primer resin layer on the copper foil surface. Specifically, it discloses a copper-clad laminate manufactured by forming a primer resin layer (resin precursor layer) with a thickness of 1.5 μm on the copper foil surface, laminating FR-4 prepreg (a sheet of glass woven fabric made of glass fibers woven into a cloth-like material and impregnated with a curable epoxy resin) on the primer resin layer (resin precursor layer) and hot pressing the laminate. Note that the technology of Patent Document 1 does not intend to obtain a copper-clad laminate with high thermal conductivity.

JP 2005-53218 A

In order to obtain a resin composite material with high thermal conductivity, it is necessary to use a resin composite material filled with a thermally conductive filler. However, the inventors of the present invention have found that when the resin composite material is directly laminated to a metal foil, high peel strength cannot be obtained. Therefore, they tried to improve the peel strength by forming a resin layer on the metal foil surface as in Patent Document 1, but this caused a problem of a decrease in thermal conductivity, and it was not possible to achieve both high peel strength and high thermal conductivity. Therefore, the object of the present invention is to provide a metal foil laminated resin sheet that can exhibit high thermal conductivity and high peel strength when laminating a metal foil and a resin composite material.

As a result of intensive research conducted by the present inventors to solve the above problems, they discovered that a metal foil laminated resin sheet that achieves the above-mentioned objective can be obtained by laminating a metal foil layer and a resin composite material layer filled with a thermally conductive filler to form a resin layer having a specific thickness, and thus completed the present invention.

That is, the present invention is a metal foil laminated resin sheet that includes, in this order, a metal foil layer, a resin layer, and a resin composite material layer that includes a resin matrix and a thermally conductive filler, and the thickness of the resin layer is 0.01 μm or more and 1.0 μm or less.

It is preferable that the resin layer contains a thermosetting resin and that the resin matrix contains a thermosetting resin. It is also preferable that the surface roughness Rz of the metal foil layer that contacts the resin layer is 3.0 μm or less and the thickness is 5 to 500 μm.

The present invention further provides a method for producing a metal foil laminated resin sheet, which includes a resin layer forming step of forming a layer of a resin precursor on the surface of a metal foil so that the thickness of the resin layer after curing is 0.01 μm to 1.0 μm, and a lamination step of laminating a resin composite material precursor containing a resin matrix and a thermally conductive filler on the surface on which the layer of the resin precursor of the metal material has been formed.

The metal foil laminated resin sheet of the present invention makes it possible to provide copper-clad laminates and metal-based substrates that have high thermal conductivity and high peel strength. This makes it easy to manufacture electronic devices that have excellent heat dissipation properties and high reliability.

1 is an example of a schematic cross-sectional view of a metal foil laminated resin sheet of the present invention. 1 is a scanning electron microscope photograph of a cross section of a metal foil laminated resin sheet produced in Example 1.

The metal foil laminated resin sheet of the present invention has a laminated structure whose cross-sectional structure is shown in the schematic diagram of FIG. 1, and includes a metal foil layer 2, a resin layer 3, and a resin composite material layer 4, in that order. This cross-sectional structure can be confirmed by cutting the metal foil laminated resin sheet 1 and observing it with a scanning electron microscope or the like.

The metal foil layer in the present invention is not particularly limited in the type of metal, and may be, for example, copper foil, aluminum foil, stainless steel foil, etc., with copper foil being preferred. The copper foil is preferably electrolytic copper foil or rolled copper foil.

The thickness of the metal foil layer is not particularly limited, but in conventional metal foil laminated resin sheets that do not have a resin layer, when the metal foil layer is thin, deformation of the metal foil layer tends to generate large stress at the interface between the metal foil layer and the resin composite material layer, which tends to reduce adhesion, and adhesion in particular has been a major issue. Therefore, when the metal foil layer is thin, the adhesiveness improving effect of the present invention is significant, so the metal foil layer is preferably 500 μm or less, and more preferably 150 μm or less. There is no particular lower limit to the thickness of the metal foil layer, but from the standpoint of manufacturing costs, durability, etc., a metal foil of 5 μm or more is generally used.

The surface structure of the metal foil is not particularly limited, but the surface roughness Rz of the surface in contact with the resin layer is preferably 3.0 μm or less, more preferably 2.0 μm or less. The small surface roughness of the metal foil surface makes it easy to form a thin and uniform resin layer, and makes it easy to achieve both high thermal conductivity and high peel strength. In addition, in a conventional metal foil laminated resin sheet that does not have a resin layer, if the metal foil surface is smooth, it is difficult to obtain an anchor effect, so the adhesion between the metal foil layer and the resin composite material layer tends to be low. When the surface roughness of the metal foil layer is small, the adhesiveness improving effect of the present invention is remarkable and can be said to be preferable. The surface roughness Rz in the present invention is measured by the method of JIS B0610:1994.

The resin layer in the present invention is a layer formed on the surface of the metal foil, and has a thickness of 0.01 μm to 1.0 μm. The presence of such a resin layer improves adhesion and makes it possible to obtain high peel strength. The reason why the resin layer provides high peel strength is not clear, but the inventors believe it to be as follows. That is, when a resin composite layer is directly laminated on a metal foil layer, the thermally conductive filler in the resin composite layer and the metal foil do not usually interact, so the adhesion between the metal foil layer and the resin composite layer is mainly due to the interaction between the resin matrix of the resin composite and the metal foil layer. Therefore, if the resin composite layer is highly filled with thermally conductive filler in order to obtain a high thermal conductivity, the amount of resin components that contribute to adhesion at the interface between the metal foil and the resin composite decreases, resulting in a decrease in adhesion. On the other hand, when a resin layer is formed between the metal foil layer and the resin polymerization material layer, high adhesion is obtained between the metal foil layer and the resin layer due to the interaction between the metal foil layer and the resin layer, and high adhesion is also obtained between the resin layer and the resin composite material layer due to the interaction between the resin of the resin layer and the resin matrix of the resin composite material layer. As a result, peeling is less likely to occur than when the resin composite material layer is laminated directly on the metal foil layer, and it is presumed that high peel strength is obtained.

Here, the resin layer has lower thermal conductivity than the metal foil layer and the resin composite layer, which can cause a decrease in the thermal conductivity of the metal foil laminated resin sheet. However, by controlling the thickness of the resin layer to 1.0 μm or less, the thermal resistance in the resin layer can be significantly reduced, making it possible to obtain high thermal conductivity. Since a thinner resin layer is more likely to obtain a higher thermal conductivity, the thickness of the resin layer is preferably 0.9 μm or less, and more preferably 0.6 μm or less. However, if the resin layer is too thin, it is difficult to form a uniform film during production, and the effect of improving adhesion tends to decrease, so the thickness of the resin layer is 0.01 μm or more, and preferably 0.1 μm or more.

The resin forming the resin layer is not particularly limited, and known resins can be used. For example, thermosetting resins such as epoxy resins, cyanate resins, phenolic resins, and silicone resins, acrylic resins, liquid crystal polymers, and polyimide resins can be used. Among these, thermosetting resins are preferable from the viewpoint of formability for forming a thin film on copper foil, and epoxy resins are particularly preferable. Examples of epoxy resins include bisphenol A type epoxy resins, bisphenol S type epoxy resins, bisphenol F type epoxy resins, hydrogenated bisphenol A type epoxy resins, polypropylene glycol type epoxy resins, polytetramethylene glycol type epoxy resins, naphthalene type epoxy resins, phenylmethane type epoxy resins, tetrakisphenolmethane type epoxy resins, biphenyl type epoxy resins, epoxy resins having a triazine nucleus in the skeleton, and bisphenol A alkylene oxide adduct type epoxy resins. One of these epoxy resins may be used alone, or two or more may be mixed together. In addition, amine-based resins, acid anhydride-based resins, phenolic resins, imidazoles, and the like may be used as curing agents. These curing agents may be used alone or in combination of two or more. In this specification, these curing agents are also included in the resin.

The resin layer may contain other components in addition to the resin, as long as they do not significantly impair the effects of the present invention. Examples of other components include fillers, dispersants, coupling agents, and leveling agents.

The resin composite layer is formed from a resin composite material containing at least a resin matrix and a thermally conductive filler. The resin matrix contains a resin and, if necessary, a small amount of additives. The resin of the resin matrix is not particularly limited and can be a known resin, for example, thermosetting resins such as epoxy resins, cyanate resins, phenolic resins, and silicone resins, acrylic resins, liquid crystal polymers, and polyimide resins. Among these, from the viewpoint of moldability for forming a sheet by highly filling the thermally conductive filler, a thermosetting resin is preferable, and an epoxy resin is particularly preferable. Examples of epoxy resins include those mentioned above. In addition, it is preferable that the resin matrix contains the same type of resin as that contained in the resin layer from the viewpoint of improving the adhesion between the resin layer and the resin composite layer.

The additive components contained in the resin matrix are not particularly limited as long as they do not significantly impair the effects of the present invention. For example, dispersants, coupling agents, leveling agents, affinity agents, etc. can be used.

The thermally conductive filler is not particularly limited, and examples of the thermally conductive filler include silica, alumina, zinc oxide, magnesium oxide, titanium oxide, silicon nitride, aluminum nitride, boron nitride, aluminum hydroxide, magnesium hydroxide, silicon carbide, calcium carbonate, barium sulfate, talc, diamond, etc., which have high insulation properties, and graphite, carbon fiber, metal particles such as silver and aluminum, etc., which have high conductivity, can be used. In particular, when high insulation properties are required for the metal foil laminated resin sheet, alumina, silicon nitride, aluminum nitride, boron nitride, zinc oxide, magnesium oxide, and diamond, which have high insulation properties and thermal conductivity, are preferred. Multiple types of thermally conductive fillers may be used in combination.

The particle size of the thermally conductive filler is not particularly limited, but from the viewpoint of thermal conductivity and filling properties, the average particle size is preferably 0.01 to 250 μm, and more preferably 0.1 to 150 μm. The average particle size is preferably 0.7 times or less, and more preferably 0.5 times or less, the thickness of the resin composite material layer. The average particle size is the D50 value measured by a laser diffraction scattering method.

Furthermore, the shape of the thermally conductive filler is not particularly limited, and it is possible to use spherical, round, crushed, plate-like, fibrous, aggregated, etc., and particles of different shapes may be mixed.

The amount of the thermally conductive filler to be blended is not particularly limited, but in order to impart high thermal conductivity to the resin composite material layer, it is preferably 100 to 1,000 parts by volume, and more preferably 200 to 900 parts by volume, per 100 parts by volume of the resin matrix.
In the present invention, the resin composite material layer may contain a base material such as glass cloth in addition to the resin matrix and the thermally conductive filler.

The resin composite layer preferably has high thermal conductivity, and the thermal conductivity is preferably 5.0 W/m·K or more, more preferably 6.0 W/m·K or more, and even more preferably 10.0 W/m·K or more. The thermal conductivity of the resin composite layer can be measured by temperature wave thermal analysis.

The resin composite layer preferably has a high dielectric strength, preferably 20 kV/mm or more, more preferably 40 kV/mm or more, and even more preferably 55 kV/mm or more. The high dielectric strength of the resin composite layer is advantageous when using the metal foil laminated resin sheet of the present invention as a substrate material for electronic devices, such as a metal-clad laminate or a metal veil substrate.

The thickness of the resin composite layer is not particularly limited and may be appropriately determined depending on the application of the metal foil laminated resin sheet. For example, it is generally 10 μm to 2000 μm for metal-clad laminate applications, and 30 μm to 300 μm for the resin composite layer of a metal-base substrate.

As described above, the cross-sectional structure of the metal foil laminated resin sheet can be confirmed by cutting the metal foil laminated resin sheet and observing it with a scanning electron microscope or the like. Specifically, the metal foil laminated resin sheet can be cut perpendicular to the metal foil surface and the obtained cross section can be observed with a scanning electron microscope. Examples of the cutting method include ion milling and mechanical cutting. The cut cross section may be polished as necessary, or may be embedded in a transparent resin or the like to produce an observation sample. The ion milling method, which obtains a smooth cut surface suitable for observation, is particularly preferred as a method for preparing an observation sample. In scanning electron microscope observation, the metal foil layer and the resin layer can be distinguished because they have different contrasts, and the resin composite material layer can be distinguished from the resin layer because it contains a thermally conductive filler. Even when the resin layer contains a filler, the resin composite material layer and the resin layer can be distinguished by the difference in particle size and compounding ratio of the filler. In addition, in the observation with a scanning electron microscope, the observation conditions such as magnification are appropriately adjusted according to the thickness of the resin layer.

The thickness of the resin layer is measured using the image obtained by the above-mentioned scanning electron microscope observation. Specifically, in the scanning electron microscope image, the distance from the interface between the metal foil layer and the resin layer to the interface between the resin layer and the resin composite material layer is measured and used as the thickness of the resin layer.

As described above, the metal foil laminated resin sheet of the present invention can achieve both high peel strength and high thermal conductivity. The peel strength of the metal foil laminated resin sheet of the present invention is preferably 4.50 N/cm or more, more preferably 5.50 N/cm or more, and even more preferably 6.00 N/cm or more. The thermal conductivity of the metal foil laminated resin sheet of the present invention is preferably 6.0 W/m·K or more, and more preferably 10.0 W/m·K or more. In this application, the thermal conductivity of the metal foil laminated resin sheet is the value measured by the thermal conductivity of the laminate of the resin layer and the resin composition layer obtained by peeling the metal foil from the metal foil laminated resin sheet.

Furthermore, the dielectric strength of the metal foil laminated resin sheet of the present invention is preferably 20 kV/mm or more, more preferably 40 kV/mm or more, and even more preferably 55 kV/mm or more. Due to its high dielectric strength, it can be particularly suitably used as a substrate material for electronic devices such as metal-clad laminates and metal-base substrates. Since the resin layer does not have a particular adverse effect on the dielectric strength, the present invention can easily obtain a metal foil laminated resin sheet that has high peel strength, high thermal conductivity, and also high dielectric strength. In this application, the dielectric strength of the metal foil laminated resin sheet is a value measured by the dielectric strength of the laminate of the resin layer and the resin composition layer obtained by peeling the metal foil from the metal foil laminated resin sheet.

The use of the metal foil laminated resin sheet of the present invention is not particularly limited, but it can be used, for example, as a metal clad laminate, particularly a copper clad laminate using copper foil as the metal foil. The metal clad laminate may be a single-sided metal clad laminate in which metal foil is laminated only on one side of the resin composite material layer, or a double-sided metal clad laminate in which metal foil is laminated on both sides of the resin composite material layer. When used as a double-sided metal clad laminate, it may be in a form in which only one side of the resin composite material layer has a resin layer, i.e., a form in which the layers are laminated in the order of a metal foil layer, a resin layer, a resin composite material layer, and a metal foil layer, or in a form in which the layers are laminated in the order of a metal foil layer, a resin layer, a resin composite material layer, a resin layer, and a metal foil layer. In the case of a metal clad laminate, particularly when the metal foil is copper foil, it can be particularly suitably used as a copper clad laminate for printed circuit boards and the like.

The metal foil laminated resin sheet of the present invention can also be used as a metal-based substrate, particularly suitable for use as a power module substrate or an LED substrate, by arranging a metal plate (copper plate, aluminum plate, stainless steel plate, etc.) having a thickness of about 0.5 mm to 3.0 mm on the side of the resin composite material layer opposite the metal foil.

The method for producing the metal foil laminated resin sheet of the present invention is not particularly limited, and it can be produced by laminating a resin composite material layer containing a resin and a thermally conductive filler on the surface of the metal foil via a resin layer adjusted to a thickness of 0.01 μm to 1.0 μm.

A suitable method for producing the metal foil laminated resin sheet of the present invention includes a resin layer forming step of forming a layer of a resin precursor on the surface of the metal foil so that the thickness of the resin layer after curing is 0.01 μm to 1.0 μm, a lamination step of laminating a resin composite material precursor containing a resin matrix and a thermally conductive filler on the surface on which the layer of the resin precursor of the metal material has been formed, and a curing step of curing the resin precursor and the resin composite material precursor.

In the resin layer forming process, the resin precursor layer is a layer that will be formed by a subsequent operation. For example, when the resin of the resin layer is a thermosetting resin, the resin precursor layer may be a composition containing a curable resin that is cured by a curing reaction with a curing agent. Specifically, when the resin of the resin layer is an epoxy resin, a composition containing an epoxy group-containing curable resin (curable epoxy resin) and a curing agent may be exemplified. The resin precursor composition may also be a semi-cured thermosetting resin. A specific example of the resin layer forming process is a method in which a varnish containing a resin precursor (for example, a composition containing an epoxy group-containing curable resin, a curing agent, and a solvent) is applied to the surface of a metal foil, and then the solvent is removed by drying or the like.

Prior to the resin layer formation step, the surface roughness of the metal foil on which the resin precursor layer is to be formed may be adjusted by polishing or blasting. In addition, anti-rust treatment using metal, chemical conversion treatment using a coupling agent, etc. may also be performed.

In the lamination process, a resin composite material precursor containing a resin matrix and a thermally conductive filler is laminated on the surface of the metal foil on which the resin precursor layer is formed. The resin composite material precursor is cured, dried, or otherwise processed to form a resin composite material layer.

When the resin matrix contains a thermosetting resin, an example of the resin composite material precursor is a composition containing a curable resin that is cured by a curing reaction with a curing agent and a thermally conductive filler. Specifically, when the resin of the resin matrix is an epoxy resin, a composition containing an epoxy group-containing curable resin, a curing agent, and a thermally conductive filler can be exemplified. The metal foil laminated resin sheet of the present invention can be obtained by laminating such a composition on the metal foil and then curing the curable resin. The resin composite material precursor may be a slurry containing a solvent. By including a solvent, a resin composition precursor layer may be easily formed by coating. When the resin composition precursor is a slurry containing a solvent, the solvent is removed by heating and drying or drying under reduced pressure after lamination, and then the curable resin is cured, thereby obtaining the metal foil laminated resin sheet of the present invention.

The resin composite material precursor may also be a sheet of semi-cured resin composite material (so-called "B-stage sheet"). The metal foil laminated resin sheet of the present invention can be obtained by laminating the B-stage sheet and metal foil, and then polymerizing and curing the sheet. In this case, lamination and polymerization and curing may be performed by heat pressing. The resin composite material precursor being a B-stage sheet is a preferred form in the present invention, since it is easy to obtain high peel strength by increasing the adhesive strength between the resin layer and the resin composite material layer while being easy to work with. The B-stage sheet can be produced, for example, by applying a slurry containing a curable resin, a curing agent, a thermally conductive filler, and a solvent onto a film such as a PET film, heating and drying the slurry to remove the solvent to produce an A-stage sheet, and then semi-curing the A-stage sheet.

When the metal foil laminated resin sheet is a double-sided metal-clad laminate, it can be manufactured by sandwiching a B-stage sheet between two metal foils with a resin precursor layer formed on their surfaces, and curing the resin precursor layer and the B-stage sheet by heat pressing. When the metal foil laminated resin sheet is a metal-based substrate, it can be manufactured by sandwiching a B-stage sheet between a metal foil with a resin precursor layer formed on its surface and a metal plate, and curing the resin precursor layer and the B-stage sheet by heat pressing.

Furthermore, another embodiment of the method for manufacturing the metal foil laminated resin sheet of the present invention is a method in which a layer of resin precursor is formed on the surface of a B-stage sheet, which is then laminated with metal foil, and the B-stage sheet and the resin precursor layer are then cured.

In addition, when the resin composite material layer contains glass cloth, for example, the glass cloth can be immersed in a slurry containing a curable resin, a thermally conductive filler, and a solvent to adhere the slurry to the glass cloth, and then dried to remove the solvent, to obtain a so-called prepreg, which can be used to manufacture a metal foil laminated resin sheet. Specifically, a metal foil laminated resin sheet can be manufactured by laminating a prepreg and a metal foil having a resin precursor layer formed thereon, or by sandwiching the prepreg between two sheets of metal foil having a resin precursor layer formed thereon, and then performing a heat press.

In the following, examples are described in order to specifically explain the present invention, but the present invention is not limited to these examples. Furthermore, the respective values in the examples and comparative examples were measured by the following methods.
(1) Measurement of peel strength The peel strength (N/cm) was measured using a universal testing machine (Shimadzu Corporation: Autograph AG-Xplus) and a peel test jig (adhesive tape peel kit) according to the method of JIS C6481. A 10 mm wide cut was made in the copper foil on one side of the metal foil laminated resin sheet, one end was peeled off, held in a chuck, and lifted (peeled off) at a speed of 50 mm/min.

(2) Measurement of thermal conductivity The copper foils on both sides of the metal foil laminated resin sheet were peeled off, and the thermal conductivity of the laminate of the resin layer and the resin composite layer was measured. The thermal conductivity (W/m·K) was calculated by thermal diffusivity (m ² /sec) × density (kg/m ³ ) × specific heat (J/kg·K). The thermal diffusivity was measured using a temperature wave thermal analysis method (ai-Phase Mobile u, ISO22007-3, manufactured by Ai-Phase Corporation), the density was measured using the Archimedes method (XS204V, manufactured by Mettler Toledo Corporation), and the specific heat was measured using a differential scanning calorimeter (DSC) method (Thermo Plus Evo DSC8230, manufactured by Rigaku Corporation).

(3) Measurement of dielectric strength The copper foils on both sides of the metal foil laminated resin sheet were peeled off, and the dielectric strength of the laminate of the resin layer and the resin composite material layer was measured. The dielectric strength (kV/mm) was measured using a withstand voltage tester YPAD-0225 manufactured by Kyonan Electric Co., Ltd., in accordance with the general test method for thermosetting plastics of JIS K6911.

(4) Observation of the cross section of the metal foil laminated resin sheet and measurement of the thickness of the resin layer The cross section of the metal foil laminated resin sheet was observed by processing a cross section sample using an ion milling device ArBlade5000 manufactured by Hitachi High-Technologies Corporation, and observing it using a scanning electron microscope (SEM) SU3500 manufactured by Hitachi High-Technologies Corporation. The thickness of the resin layer was measured from the observed SEM image.

Example 1
A liquid curable epoxy resin (manufactured by Mitsubishi Chemical: jER828, bisphenol A type epoxy resin, epoxy equivalent 184-194 g/eq) and an epoxy resin curing agent (manufactured by Mitsubishi Chemical: jER cure WA, modified aromatic amine, amine value 623-639) were mixed in a mass ratio of 4:1, and the composition obtained by adding cyclohexanone (manufactured by Wako Pure Chemical Industries, special grade) as a solvent and diluting it was applied to the non-roughened surface of a copper foil (manufactured by Fukuda Metal Foil Powder Industry: non-roughened ultra-low roughness electrolytic copper foil T9DA-SV, thickness 35 μm, surface roughness Rz: 0.4 μm) using an automatic coating device (manufactured by Tester Sangyo Co., Ltd.: PI-1210). The copper foil after coating was air-dried for 15 minutes in a draft, and then left to stand at 190 ° C. for 3 hours in a vacuum dryer to remove cyclohexanone and polymerize and cure, and a copper foil laminated with a resin layer was obtained.

Filler A (aluminum nitride filler, average particle size D50: 1.0 μm) as a thermally conductive filler, Filler B (aluminum nitride filler, average particle size D50: 4.5 μm), Filler C (spherical aluminum nitride filler, average particle size D50: 37 μm), liquid curing epoxy resin (manufactured by Mitsubishi Chemical, jER828, bisphenol A type epoxy resin, epoxy equivalent 184 to 194 g / eq), epoxy resin curing agent (manufactured by Mitsubishi Chemical, jER cure WA, modified aromatic amine, amine value 623 to 639), affinity agent (Toho Chemical Industry: phosphate ester type dispersant RS-710), and cyclohexanone (manufactured by Wako Pure Chemical Industries, special grade) as a solvent were measured out in the mixing ratio shown in Table 1, and stirred and mixed using a planetary mixer (manufactured by Kurabo: Mazerustar KK-250S) to obtain a slurry. The ratio of the epoxy resin to the epoxy resin hardener was 4:1 by mass, and the amount of the affinity agent was 0.3 parts by mass per 100 parts by mass of the filler. The amount of the solvent used was 1.71 times the total amount of the liquid curable epoxy resin and the epoxy resin hardener. The amounts were calculated assuming the densities of the aluminum nitride and epoxy resin to be 3.26 g/ ^cm3 and 1.17 g/ ^cm3 , respectively.

The above slurry was applied to the release-treated side of a release-treated polyethylene terephthalate (PET) film (Nippa PET50X1-FSC6, thickness 50 μm) using the automatic coating device at a coating thickness setting of 150 μm and 50 mm/sec. After coating, the film was air-dried for 15 minutes in a draft, and then vacuum-dried for 50 minutes at 130°C using a vacuum dryer to obtain a PET film with an A-stage sheet as an A-stage sheet of the resin composition precursor layer. Next, two of the above PET films with A-stage sheets were stacked with the release PET film on the outside so that the A-stage sheets were in contact with each other, and heat-pressed and pressed for 3 minutes at 100°C under reduced pressure with a pressure of 4 MPa using a vacuum heating press device (Imoto Seisakusho Co., Ltd.: manual hydraulic vacuum heating press) to bond them, forming a B-stage sheet of the resin composition precursor layer.

The release PET film on one side of the B-stage sheet of the resin composition precursor layer obtained above was peeled off, and the resin composition precursor layer was placed on top of the copper foil on which the resin layer was formed, with the resin layer side in contact with the resin composition precursor layer. The copper foil was then heat-pressed for 3 minutes at a pressure of 4 MPa under reduced pressure using a vacuum heating press device to bond the copper foil. Similarly, the copper foil on which the resin layer was formed was also bonded to the other side. The temperature was then raised to 170°C, and the B-stage sheet was heat-pressed for 60 minutes at a pressure of 20 MPa under reduced pressure to harden the sheet. The resin was then completely hardened by heat-treating the sheet at 165°C for 2 hours and then at 190°C for 2 hours using a box oven, to produce a metal foil laminated resin sheet.

The resin layer thickness, peel strength, thermal conductivity, and dielectric strength of the obtained metal foil laminated resin sheet were measured. The results are shown in Table 1. The thickness of the resin layer observed with an SEM was 0.2 μm. The thickness of the resin composite material layer was 122 μm. The peel strength of the metal foil laminated resin sheet was 7.46 N/cm, and the thermal conductivity was 15.4 W/m·K, both of which were high values.

(Examples 2, 3, and 4)
A metal foil laminated resin sheet was produced in the same manner as in Example 1, except that the thickness of the resin layer formed on the copper foil was as shown in Table 1. The evaluation results are shown in Table 1.

(Comparative Examples 1 and 2)
A metal foil laminated resin sheet was produced in the same manner as in Example 1, except that the thickness of the resin layer formed on the copper foil was as shown in Table 1. The thickness of the resin layer was adjusted by the dilution ratio of the resin and the solvent and the coating thickness. The evaluation results are shown in Table 1. Although the peel strength was high, a significant decrease in thermal conductivity was observed compared to Examples 1 to 4 due to the thick resin layer.

(Comparative Example 3)
A metal foil laminated resin sheet was produced in the same manner as in Example 1, except that no resin layer was formed on the copper foil. The evaluation results are shown in Table 1. Since there was no resin layer, the thermal conductivity was high compared to Examples 1 to 4, but the peel strength was significantly low.

(Examples 5 and 6)
A metal foil laminated resin sheet was produced in the same manner as in Example 1, except that the blending ratio of the thermally conductive filler was as shown in Table 1. The evaluation results are shown in Table 1.

(Comparative Example 4)
A metal foil laminated resin sheet was produced in the same manner as in Example 6, except that the thickness of the resin layer was as shown in Table 1. The evaluation results are shown in Table 1. Since the resin layer was thick, the peel strength was high compared to Example 6, but a significant decrease in thermal conductivity was observed.

(Comparative Example 5)
A metal foil laminated resin sheet was produced in the same manner as in Example 6, except that a resin layer was not formed on the copper foil. The evaluation results are shown in Table 1. Since there was no resin layer, the thermal conductivity was high compared to Example 6, but the peel strength was significantly lower.

(Example 7)
As in Example 1, a copper foil having a resin layer formed thereon, a slurry containing a curable epoxy resin, an epoxy curing agent, a thermally conductive filler, and a solvent was obtained, and then the slurry was directly applied to the resin layer surface of the copper foil without using a release PET film, to produce a metal foil laminated resin sheet.

That is, using the automatic coating device, the slurry was coated on the resin layer surface of the copper foil on which the resin layer was formed, with a coating thickness setting of 150 μm and at 50 mm/sec. After coating, the resin layer was air-dried in a draft for 15 minutes, and then vacuum-dried at 130° C. for 50 minutes using a vacuum dryer to obtain an A-stage sheet in which a resin composition precursor layer was laminated on one side of the copper foil. Next, two of the A-stage sheets were stacked with the copper foil facing outward so that the resin composition precursor layers were in contact with each other, and the vacuum hot press device was used to heat-press the sheets at 100° C. under reduced pressure at a press pressure of 4 MPa for 3 minutes to bond them together, forming a B-stage sheet of resin composition precursor layers on both sides of the copper foil, which was then removed from the vacuum hot press device.

Then, the vacuum hot press device was heated to 170°C, and the B-stage sheet was inserted and cured by hot pressing for 60 minutes at a reduced pressure of 20 MPa. The resin was then completely cured by heat treatment in a box oven at 165°C for 2 hours and then at 190°C for 2 hours, producing a metal foil laminated resin sheet.

The resin layer thickness, peel strength, thermal conductivity, and dielectric strength of the obtained metal foil laminated resin sheet were measured. The results are shown in Table 1. As with the results of Example 1, a metal foil laminated resin sheet with high peel strength and thermal conductivity was obtained.

(Comparative Example 6)
A metal foil laminated resin sheet was produced in the same manner as in Example 7, except that the copper foil was directly coated with the slurry without forming a resin layer on the copper foil. The evaluation results are shown in Table 1. Compared to Example 7, the thermal conductivity was high, but the peel strength was significantly low.

(Example 8)
Metal foil laminated resin sheets were produced in the same manner as in Example 7, except that Filler D (alumina filler, particle size D50: 0.7 μm), Filler E (alumina filler, particle size D50: 3.0 μm), and Filler F (spherical alumina filler, particle size D50: 38 μm) were used as the thermally conductive fillers. The volumetric parts of the thermally conductive fillers and resin were calculated assuming the densities of alumina and epoxy resin to be 3.98 g/ ^cm3 and 1.17 g/ ^cm3 , respectively. The evaluation results are shown in Table 2.

Compared to Example 7, the thermal conductivity was slightly reduced by changing the thermally conductive filler from aluminum nitride to alumina, but a metal foil laminated resin sheet with high thermal conductivity and high peel strength was obtained.

(Comparative Example 7)
A metal foil laminated resin sheet was produced in the same manner as in Example 8, except that the thickness of the resin layer was as shown in Table 2. The evaluation results are shown in Table 1. Since the resin layer was thick, the peel strength was high compared to Example 8, but a significant decrease in thermal conductivity was observed.

(Comparative Example 8)
A metal foil laminated resin sheet was produced in the same manner as in Example 8, except that no resin layer was formed on the copper foil. The evaluation results are shown in Table 1. Since there was no resin layer, the thermal conductivity was high compared to Example 8, but the peel strength was significantly lower.

(Example 9)
A metal foil laminated resin sheet was produced in the same manner as in Example 1, except that a commercially available electrolytic copper foil (manufactured by Fukuda Metal Foil Powder Co., Ltd.: T8G-UN, thickness 35 μm, surface roughness Rz: 7.4 μm) was used as the copper foil. The evaluation results are shown in Table 1. The peel strength was higher than in Comparative Example 3 in which no resin layer was formed. On the other hand, the peel strength was slightly lower than in Example 1. This is thought to be because the surface roughness of the copper foil was greater than in Example 1, making the resin layer partially non-uniform.

(Example 10)
A metal foil laminated resin sheet was produced in the same manner as in Example 1, except that a rolled copper foil with an ultra-low roughness (manufactured by Fukuda Metal Foil Powder Co., Ltd.: RCT-T4X, thickness 35 μm, surface roughness Rz: 0.3 μm) was used as the copper foil. The evaluation results are shown in Table 1.

1 Metal foil laminated resin sheet 2 Metal foil layer 3 Resin layer 4 Resin composite material layer

Claims (5)

A metal foil laminated resin sheet comprising, in this order, a metal foil layer, a resin layer, and a resin composite material layer containing a resin matrix and a thermally conductive filler, wherein the resin layer has a thickness of 0.01 μm or more and 1.0 μm or less, the surface roughness Rz of the surface of the metal foil layer that is in contact with the resin layer is 3.0 μm or less, and the metal foil layer has a thickness of 5 to 500 μm . The metal foil laminated resin sheet according to claim 1, wherein the resin layer contains a thermosetting resin and the resin matrix contains a thermosetting resin. A method for producing a metal foil laminated resin sheet, comprising a resin layer forming step of forming a layer of a resin precursor on the surface of a metal foil so that the thickness of the resin layer after curing is 0.01 μm to 1.0 μm, a lamination step of laminating a resin composite material precursor containing a resin matrix and a thermally conductive filler on the surface on which the layer of the resin precursor of the metal material has been formed, and a curing step of curing the resin precursor and the resin composite material precursor. The method for producing a metal foil laminated resin sheet according to claim 3, wherein the resin precursor is an epoxy group-containing curable resin, and the resin matrix contains an epoxy group-containing curable resin. The method for manufacturing a metal foil laminated resin sheet according to claim 3 or 4, wherein the surface roughness Rz of the surface of the metal foil layer that contacts the resin layer is 3.0 μm or less, and the thickness is 5 to 500 μm.