JP7621112B2 - Metal-clad laminate and its manufacturing method - Google Patents

Description

The present invention relates to a metal-clad laminate having an insulating resin layer with excellent thermal conductivity and suitable for use in heat dissipation substrates and circuit boards, and a method for manufacturing the same.

In recent years, there has been an increasing demand for smaller and lighter electronic devices, such as mobile phones and smartphones. As a result, flexible circuit boards, which are advantageous in making devices smaller and lighter, have come to be widely used in the electronic technology field. In addition, the miniaturization of electronic devices has led to an increase in the degree of circuit integration, and coupled with faster information processing speeds, means for dissipating heat generated within the devices have attracted attention. In order to provide flexible circuit boards that are easy to process and have excellent heat dissipation properties, studies have been conducted to improve the thermal conductivity in the thickness direction by blending a thermally conductive filler with the polyimide that constitutes the insulating resin layer (for example, Patent Documents 1 and 2).

However, when a large amount of thermally conductive filler is blended into the insulating resin layer to improve heat dissipation efficiency, some of the thermally conductive filler protrudes from the surface of the insulating resin layer, causing poor appearance and surface smoothness, and poor adhesion to the metal layer. It is also known that blending a large amount of thermally conductive filler reduces the mechanical strength of the insulating resin layer, such as the tear propagation resistance. In particular, when the insulating resin layer is thin, blending the thermally conductive filler can embrittle the insulating resin layer, causing serious problems such as tearing and poor adhesion.

The metal-clad laminate of Patent Document 1 has an insulating resin layer that is 60 μm or more thick, while the metal-clad laminate of Patent Document 2 has an insulating resin layer that is about 25 μm thick, so the above problems are relatively unlikely to occur even if a large amount of thermally conductive filler is added. However, in the future, with further progress in miniaturizing wiring and increasing requirements for heat dissipation efficiency, it is thought that it will become necessary to thin the insulating resin layer containing thermally conductive filler to, for example, 20 μm or less thick.

Patent Document 3 proposes that by blending α-alumina single crystal particles with an average particle size in the range of 0.3 μm to 1.5 μm into an insulating film with a thickness of 20 μm and a polyimide matrix resin, and by further laminating an adhesive film on top of this insulating film, it is possible to improve the properties with the metal layer laminated on top. However, since the adhesive film in Patent Document 3 is composed of a resin type different from the matrix resin of the insulating film, there is a risk that the heat conduction path will be blocked at the interface between the insulating film and the adhesive film, which may lead to a decrease in heat dissipation efficiency, and there is also a problem that peeling is likely to occur at the interface.

JP 2011-177929 A JP 2012-213899 A JP 2019-140094 A

As described above, there has been a demand for a metal-clad laminate in which the insulating resin layer is thinner than conventional ones, yet the insulating resin layer has sufficient mechanical strength for practical use, has good adhesion to the metal layer, and has excellent thermal conductivity.

Therefore, the present invention aims to provide a metal-clad laminate having an insulating resin layer that is thin, has excellent thermal conductivity, and has sufficient strength and adhesiveness for practical use.

As a result of extensive research into solving the above problems, the inventors discovered that the above problems could be solved by using a thermoplastic polyimide with a specific structure that has excellent thermal conductivity as the matrix resin of the insulating resin layer in which a thermally conductive filler is blended in a metal-clad laminate, and by devising a method for forming the insulating resin layer, and thus completed the present invention.

That is, the metal-clad laminate of the present invention is a metal-clad laminate having a metal layer and an insulating resin layer containing a thermally conductive filler laminated on the metal layer. In the metal-clad laminate of the present invention, the thermally conductive filler has a volume average particle diameter of 2 μm or more and 5 μm or less, and the insulating resin layer has a thickness in the range of 5 μm or more and less than 20 μm. In addition, the metal-clad laminate of the present invention has a thermoplastic polyimide matrix resin containing a structural unit represented by the following general formula (1).

In the formula, Ar represents a tetravalent acid anhydride residue derived from an aromatic tetracarboxylic dianhydride, and _R1 represents a divalent diamine residue derived from a diamine compound.

The metal-clad laminate of the present invention contains 40 or more molar parts of acid anhydride residues derived from a tetracarboxylic dianhydride having a ketone group (-CO-) in the molecule relative to a total of 100 molar parts of the acid anhydride residues, and contains a total of 50 or more molar parts of diamine residues derived from one or more diamine compounds selected from the group consisting of 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzanilide, and 4,4'-diamino-2'-methoxybenzanilide relative to a total of 100 molar parts of the diamine residues.

The metal-clad laminate of the present invention may have a thermally conductive filler content in the insulating resin layer within the range of 30 to 70 vol%.

The metal-clad laminate of the present invention may have a thermal conductivity in the thickness direction of the insulating resin layer of 0.7 W/m·K or more.

The metal-clad laminate of the present invention may have a tear propagation resistance of 10 mN or more when the insulating resin layer is a resin film.

The metal-clad laminate of the present invention may have a thermal expansion coefficient of 30 ppm/K or less when the insulating resin layer is a resin film.

The metal-clad laminate of the present invention may have a peel strength between the insulating resin layer and the metal layer of 0.8 kN/m or more.

The method for producing a metal-clad laminate of the present invention is a method for producing the above-mentioned metal-clad laminate. The method for producing a metal-clad laminate of the present invention includes the steps of applying a solution of a polyamic acid containing a thermally conductive filler onto a metal foil and drying the solution to form a first layer coating film;
applying a polyamic acid solution not containing a thermally conductive filler onto the first coating film and drying the solution to form a second coating film;
a step of heating the coating films of the first and second layers to imidize the polyamic acid and integrate the layers to form an insulating resin layer;
Contains:
In the method for producing a metal-clad laminate of the present invention, the first layer coating film is formed so that its thickness after curing is within a range of 60% to 95% of the thickness of the insulating resin layer,
The second coating film is formed so that its thickness after curing falls within the range of 5% to 40% of the thickness of the insulating resin layer.

The method for producing a metal-clad laminate of the present invention is a method for producing the above-mentioned metal-clad laminate. The method for producing a metal-clad laminate of the present invention includes the steps of applying a solution of a polyamic acid that does not contain a thermally conductive filler onto a metal foil and drying the solution to form a first layer coating film;
applying a polyamic acid solution containing a thermally conductive filler onto the first coating film and drying the applied film to form a second coating film;
applying a polyamic acid solution not containing a thermally conductive filler onto the second coating film and drying the applied film to form a third coating film;
a step of heating the coating films of the first, second and third layers to imidize the polyamic acid and integrate the layers to form an insulating resin layer;
Contains:
In the method for producing a metal-clad laminate of the present invention, the first layer coating film is formed so that its thickness after curing is within a range of 2% to 20% of the thickness of the insulating resin layer,
the second coating film is formed so that its thickness after curing is within a range of 60% to 96% of the thickness of the insulating resin layer;
The third coating film is formed so that its thickness after curing falls within the range of 2% to 20% of the thickness of the insulating resin layer.

The metal-clad laminate of the present invention has a metal layer and an insulating resin layer that have sufficient mechanical strength for practical use, good adhesion to the metal layer, and excellent thermal conductivity. In addition, the use of thermoplastic polyimide as the matrix resin ensures adhesion to the metal layer, while the incorporation of a thermally conductive filler makes it possible to bring the thermal expansion coefficient close to that of the metal layer, resulting in little warping and excellent handling characteristics during mass production and processing. Therefore, the metal-clad laminate of the present invention can be widely used industrially as a substrate material for flexible circuit boards, electronic devices, lighting equipment, and the like, which require high heat dissipation properties.

1 is a diagram showing a manufacturing process of a metal-clad laminate according to one embodiment of the present invention. 5 is a diagram showing a manufacturing process of a metal-clad laminate according to another embodiment of the present invention.

[Metal-clad laminate]
A metal-clad laminate according to an embodiment of the present invention includes a metal layer and an insulating resin layer containing a thermally conductive filler. The metal layer is laminated on one or both sides of the insulating resin layer.

[Insulating resin layer]
The insulating resin layer of the metal-clad laminate of the present invention uses a thermoplastic polyimide as a matrix resin and contains a thermally conductive filler in this resin.

<Polyimide>
The thermoplastic polyimide forming the matrix resin of the insulating resin layer is a polyimide containing a constitutional unit represented by the following general formula (1). Here, the thermoplastic polyimide generally means a polyimide that can be softened by heating and solidified by cooling repeatedly, has a clearly confirmed glass transition temperature (Tg), and has a storage modulus of less than 1.0×10 ⁸ Pa at 350° C. The non-thermoplastic polyimide means a polyimide that has a storage modulus of 1.0×10 ⁸ Pa or more at 350° C.

In the formula, Ar represents a tetravalent acid anhydride residue derived from an aromatic tetracarboxylic dianhydride, and _R1 represents a divalent diamine residue derived from a diamine compound.

In the above general formula (1), the group R ₁ represents a diamine residue, and in the present invention, the group R ₁ essentially contains at least one of the diamine residues (DAPE residue) derived from 4,4'-diaminodiphenyl ether (DAPE), the diamine residues (DABA residue) derived from 4,4'-diaminobenzanilide (DABA), and the diamine residues (MABA residue) derived from 4,4'-diamino-2'-methoxybenzanilide (MABA). DAPE, DABA, and MABA have appropriate flexibility based on their molecular structures, and therefore, in a polyamic acid/polyimide using these as the main diamine component (preferably the entire diamine component), it is possible to achieve a nearly balanced balance between thermal expansion and thermal contraction, and it is presumed that the warping of the metal-clad laminate can be suppressed and the adhesion is improved. The content of at least one of DAPE residue, DABA residue and MABA residue is at least 50 parts by mol in total, preferably at least 80 parts by mol, more preferably 100 parts by mol, relative to 100 parts by mol in total of the diamine residues. If the content of at least one of DAPE residue, DABA residue and MABA residue is less than 50 parts by mol in total, the amount of dimensional change of the insulating resin layer increases during the formation of the insulating resin layer (from the drying of the coating film of the precursor polyamic acid to the initial stage of curing), and the amount of warping of the intended metal-clad laminate increases.

In addition, in the above general formula (1), the group Ar represents an acid anhydride residue, and therefore in the present invention, the group Ar essentially contains an acid anhydride residue (hereinafter sometimes referred to as a "ketone group-containing residue") derived from a tetracarboxylic dianhydride having a ketone group (-CO-) in the molecule. By having an abundance of structural units based on the ketone group-containing residue in the polyimide, the adhesion between the insulating resin layer and the metal layer is improved by the interaction between the ketone group in the polyimide and the functional group present on the surface of the adjacently laminated metal layer.

Here, examples of tetracarboxylic dianhydrides having a ketone group (-CO-) in the molecule include 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 2,3',3,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 4,4'-(paraphenylene dicarbonyl)diphthalic anhydride, 4,4'-(metaphenylene dicarbonyl)diphthalic anhydride, etc. Among these, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 2,3',3,4'-benzophenonetetracarboxylic dianhydride and 2,2',3,3'-benzophenonetetracarboxylic dianhydride are preferred, with BTDA being particularly preferred.

The functional group having the property of interacting with a ketone group is not particularly limited as long as it is a functional group that can cause, for example, a physical interaction due to intermolecular forces or a chemical interaction due to a covalent bond with the ketone group, and a representative example of such a functional group is an amino group (-NH ₂ ). For example, a metal foil such as a copper foil is surface-treated with a silane coupling agent or the like, and functional groups such as an amino group (-NH ₂ ) are present on the surface.

The content of the ketone group-containing residue is 40 molar parts or more, preferably 50 molar parts or more, more preferably 80 molar parts or more, and even more preferably 100 molar parts, relative to a total of 100 molar parts of the acid anhydride residues. If the content of the ketone group-containing residue is less than 40 molar parts, the effect of improving adhesion due to interaction with the functional group of the adjacent laminated metal layer becomes insufficient.

Among the polyimides represented by the above general formula (1), the polyimide having a structural unit in which the group R ₁ is one or more of DAPE residue, DABA residue, or MABA residue, and the group Ar is BTDA residue, is the most preferred. That is, by using one or more of DAPE, DABA, or MABA as the diamine compound that is the raw material of the polyimide in combination with BTDA as the aromatic tetracarboxylic dianhydride, in addition to controlling the thermal expansion coefficient and improving adhesion, the skeleton that connects the aromatic rings is likely to form a planar structure and is likely to be polarized, so that it is likely to be oriented by intermolecular interaction and to form an ordered structure, and therefore the effect of improving the thermal conduction efficiency is maximized.

In the general formula (1), examples of diamine compounds which give diamine residues in which the group R ₁ is other than a DAPE residue, a DABA residue, and a MABA residue include 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 2,4-toluenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane, and 3,3'-diaminodiphenylpropane. , 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 3,3-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, benzidine, 3,3 '-Diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 4,4'-diamino-p-terphenyl, 3,3'-diamino-p-terphenyl, bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2 ,4-bis(β-amino-t-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,7-diaminodibenzofuran, 1,5-diaminofluorene, dibenzo-p-dioxin-2,7-diamine, 4,4'-diaminobenzyl, and the like.

Specific examples of aromatic tetracarboxylic dianhydrides that give acid anhydride residues in which the group Ar in the general formula (1) is other than a ketone group-containing residue include, for example, pyromellitic dianhydride (PMDA), naphthalene-2,3,6,7-tetracarboxylic dianhydride (NTCDA), naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene-1,2,4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, naphthalene-1,2,6,7-tetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,2',3,3'-biphenyltetracarbo dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3'',4,4''-p-terphenyltetracarboxylic dianhydride, 2,2'',3,3''-p-terphenyltetracarboxylic dianhydride, 2,3,3'',4''-p-terphenyltetracarboxylic dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3.4-dicarboxyphenyl) Methane dianhydride, bis(2,3-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, perylene-2,3,8,9-tetracarboxylic dianhydride, perylene-3,4,9,10-tetracarboxylic dianhydride, perylene-4,5,10,11-tetracarboxylic dianhydride, perylene-5,6,11,12-tetracarboxylic dianhydride, phenanthrene-1,2,7,8-tetracarboxylic dianhydride, phenanthrene-1, Examples include 2,6,7-tetracarboxylic dianhydride, phenanthrene-1,2,9,10-tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, and 4,4'-oxydiphthalic dianhydride.

When synthesizing the polyimide that constitutes the insulating resin layer, only one type of diamine or acid anhydride may be used, or two or more types may be used in combination.

The thermoplastic polyimide constituting the insulating resin layer preferably has a glass transition point (Tg) of 250°C or higher, and more preferably in the range of 250 to 320°C. If the glass transition point (Tg) is less than 250°C, the heat resistance will be poor, and if it exceeds 320°C, there is a risk that sufficient adhesion with the metal layer will not be ensured.

<Thermal conductive filler>
The content of the thermally conductive filler in the insulating resin layer is preferably within the range of 30 to 70 vol%, more preferably within the range of 50 to 70 vol%. If the content of the thermally conductive filler is less than 30 vol%, the heat dissipation characteristics when made into an electronic component such as a circuit board are insufficient, and if it exceeds 70 vol%, when the thermally conductive filler is contained in polyimide (polyamic acid), the varnish becomes highly viscous, making it difficult to produce a metal-clad laminate.

It is important that the particle size of the thermally conductive filler is in the range of 2 μm to 5 μm in terms of uniformly dispersing the filler in the thickness direction of the insulating resin layer to improve thermal conductivity. Here, the "volume average particle size" is the value at which the cumulative value in the frequency distribution curve obtained by volume-based particle size distribution measurement by the laser diffraction scattering method is 50%. If the volume average particle size of the thermally conductive filler is less than 2 μm, it is difficult to form a thermal conduction path in the thickness direction, and the improvement of thermal conduction efficiency is insufficient. If it is more than 5 μm, the filler protrudes from the surface of the insulating resin layer, causing problems with the appearance and surface smoothness, and problems with adhesion to any layer (such as a metal layer) further laminated on the insulating resin layer.

It is preferable that 80 vol% or more of the entire thermally conductive filler is spherical filler with a volume average particle diameter in the range of 2 μm to 5 μm. Here, "spherical" means that the shape is spherical or close to spherical, and the ratio of the average major axis to the average minor axis is 1 or close to 1 (preferably 0.8 or more). For example, the spherical filler preferably contains either aluminum oxide or aluminum nitride, or both. By using spherical fillers for the majority of the thermally conductive filler, high-density filling and uniform dispersion in the insulating resin layer are possible, and the thermal conductivity can be improved. If the content of non-spherical fillers exceeds 20 vol% in total, the appearance is likely to be poor, and voids are likely to occur at the interface between the filler and the resin, which may reduce the voltage resistance.

In the present invention, other thermally conductive fillers can be used in combination with the thermally conductive filler having a volume average particle size of 2 μm or more and 5 μm or less, as long as the effect of the invention is not impaired. Examples of thermally conductive fillers other than those mentioned above include aluminum, copper, nickel, silica, diamond, magnesia, beryllia, boron nitride, silicon nitride, silicon carbide, etc. Among these, thermally conductive fillers selected from silica, boron nitride, and silicon nitride are preferred.

<Structure of insulating resin layer>
The insulating resin layer is substantially a single layer. As described later, the formation of the insulating resin layer includes a process of laminating a coating film containing a thermally conductive filler and a coating film not containing a thermally conductive filler by repeatedly applying a polyamic acid solution, which is a precursor of polyimide, multiple times. By repeatedly using the same type of polyamic acid as the polyamic acid used at this time, the multiple layers of coating films are fused and integrated by imidization to form an insulating resin layer having a single layer of thermoplastic polyimide as the matrix resin. Here, "same type" means that the type of raw material monomer of the polyamic acid is the same. In this way, by forming the insulating resin layer with a single type of thermoplastic polyimide, the thermal conduction efficiency in the thickness direction can be improved. In other words, it is important that the entire matrix resin of the insulating resin layer is composed of a thermoplastic polyimide represented by general formula (1). In this case, in the formation of the multiple layers of coating films, polyamic acids of the same type of raw material monomers and different composition ratios thereof (i.e., the same type of resin) may be used, but in order to improve the heat dissipation efficiency, it is preferable to use the same type (same type) of raw material monomers and the same composition ratios thereof (i.e., the same resin) for all of the multiple layers of coating films.

The thickness of the insulating resin layer is in the range of 5 μm or more and less than 20 μm, preferably in the range of 8 μm or more and 19 μm or less, and more preferably in the range of 10 μm or more and 18 μm or less. If the thickness of the insulating resin layer is less than 5 μm, the insulating resin layer becomes brittle and easily broken, while if it is 20 μm or more, the thermal resistance becomes high and the heat dissipation efficiency decreases.

The insulating resin layer preferably has a thermal conductivity in the thickness direction of 0.7 W/m·K or more, and more preferably 1.0 W/m·K or more. When the thermal conductivity in the thickness direction of the insulating resin layer is 0.7 W/m·K or more, the heat dissipation characteristics of the metal-clad laminate are excellent, and the metal-clad laminate can be applied to circuit boards and the like used in high-temperature environments. Such excellent thermal conductivity can be achieved by using a polyimide having a structural unit represented by general formula (1) in the insulating resin layer and setting the thickness within the above range. In addition, in the metal-clad laminate of the present invention, the insulating resin layer is particularly formed from a thermoplastic polyimide, and therefore the adhesiveness with the metal layer can be ensured without the interposition of an adhesive layer, and therefore a high thermal conductivity can be obtained. In this specification, unless otherwise specified, thermal conductivity means the thermal conductivity (λz) in the thickness direction of the layer.

The insulating resin layer preferably has a tear propagation resistance (TPR) of 10 mN or more, more preferably 15 mN or more, when the metal layer is removed to leave a polyimide film. If the tear propagation resistance (TPR) is less than 15 mN, it may cause breakage and may impair processability and flexibility. In the present invention, by devising the manufacturing process of the metal-clad laminate as described below, the thickness of the insulating resin layer can be reduced and good tear propagation resistance can be maintained even if a high concentration of thermally conductive filler is blended therein.

The insulating resin layer preferably has a thermal expansion coefficient of 30 ppm/K or less when the metal layer is removed to leave a polyimide film, and more preferably in the range of 10 to 25 ppm/K. Having a thermal expansion coefficient within the above range can prevent warping in the metal-clad laminate.

In the metal-clad laminate of the present invention, the adhesiveness (peel strength) between the insulating resin layer and the metal layer is preferably 0.8 kN/m or more, and more preferably 1.0 kN/m or more. In the present invention, in order to achieve a peel strength of 0.8 kN/m or more and to maintain other properties such as reduced warping and heat resistance, 50 mol% or more of tetracarboxylic acid dianhydride having a ketone group (-CO-) in the molecule is used as the aromatic tetracarboxylic acid dianhydride, which is the raw material for polyimide. If the amount of tetracarboxylic acid dianhydride having a ketone group (-CO-) in the molecule is less than 50 mol% of the total acid anhydride components, the peel strength with the metal layer will be less than 0.8 kN/m, and there is a risk of insufficient adhesion with the metal layer.

The insulating resin layer may contain optional components, such as processing aids, antioxidants, light stabilizers, flame retardants, antistatic agents, surfactants, dispersants, anti-settling agents, heat stabilizers, UV absorbers, and organic or inorganic fillers other than thermally conductive fillers, as long as the physical properties described above are not impaired.

[Metal Layer]
The metal layer in the metal-clad laminate of the present invention is a conductor layer for a heat dissipation substrate or a circuit board, and examples of such metal foils include conductive metal foils such as copper, aluminum, iron, silver, palladium, nickel, chromium, molybdenum, tungsten, zinc, and alloys thereof. Among these, copper foil or an alloy copper foil containing 90% or more of copper is preferably used. The preferred thickness range of the metal layer can be set according to the application of the metal-clad laminate, but when used as a substrate material for electronic devices, lighting equipment, etc., it is preferable to set it within the range of, for example, 5 to 50 μm. If the thickness of the metal layer is less than 5 μm, problems such as wrinkles may occur during transportation in the manufacturing process, and conversely, if it exceeds 50 μm, the processability may decrease.

In addition, in order to improve adhesion to the insulating resin layer, the conductive metal foil used as the metal layer preferably has a surface roughness (Rz) of 0.05 to 3.5 μm on the surface that is bonded to the insulating resin layer. If the surface roughness (Rz) of the surface that is bonded to the insulating resin layer is less than 0.05 μm, the metal layer and the insulating resin layer may easily peel off depending on the application of the metal-clad laminate, making it unsuitable, for example, for use as a flexible circuit board material. On the other hand, if the surface roughness (Rz) of the surface that is bonded to the insulating resin layer exceeds 3.5 μm, the adhesion between the metal layer and the insulating resin layer will be good due to the anchor effect caused by the roughening, but there is a concern that the wiring shape will deteriorate when the metal layer is processed into wiring.

[Metal-clad laminate manufacturing method]
Next, an example of a method for producing a metal-clad laminate will be described. A metal-clad laminate can be formed by directly applying a polyamic acid, which is a precursor of polyimide, onto a metal substrate that will become a metal layer, and then drying and curing the polyamic acid. Here, a metal foil such as a copper foil can be used as the metal substrate.

The filler-containing polyamic acid solution can be applied to the metal substrate by a known method, such as a bar coating method, a gravure coating method, a roll coating method, a die coating method, or the like.

In order to more clearly explain the present invention, an example of the manufacture of a metal-clad laminate having a metal layer on one side of an insulating resin layer is shown with reference to the drawings.

1 shows an example of a manufacturing process for a metal-clad laminate 100 according to an embodiment of the present invention. First, a metal foil 10 such as a copper foil that constitutes a metal layer in the metal-clad laminate 100 is prepared. As shown in FIG. 1(a), a polyamic acid solution containing a thermally conductive filler 30 is applied onto this metal foil 10, and then dried at a temperature of 140° C. or less to remove a certain amount of the solvent, thereby forming a first layer coating film 21.
Next, as shown in FIG. 1B, a polyamic acid solution not containing the thermally conductive filler 30 is applied onto the coating film 21 and dried in the same manner as above to form a coating film 23 as a second layer.
Next, as shown in FIG. 1C, the coating films 21 and 23 are heat-treated at high temperature to imidize the polyamic acid, thereby forming a single insulating resin layer 20 in which the coating films 21 and 23 are fused together.

As shown in FIG. 1, by laminating a coating film 23 not containing a thermally conductive filler 30 on a coating film 21 containing a thermally conductive filler 30 and then performing thermal imidization, the thermally conductive filler 30 does not protrude from the surface of the insulating resin layer 20, so that it is possible to effectively prevent poor appearance and surface smoothness, and a decrease in mechanical strength such as tear propagation resistance, while also achieving excellent thermal conductivity. In addition, by forming the matrix resin of the insulating resin layer 20 from the same type (preferably the same) of thermoplastic polyimide, it is no longer necessary to provide a separate adhesive layer made of a different resin material, and excellent thermal conductivity can be maintained. It is preferable that the thickness of the coating film 23 not containing a thermally conductive filler 30 is as thin as possible as long as the above-mentioned action and effect are expressed. For example, the first coating film 21 is formed so that its thickness after curing is within the range of 60% to 95% of the total thickness of the insulating resin layer 20, and preferably within the range of 80 to 95%, and the second coating film 23 is formed so that its thickness after curing is within the range of 5% to 40% of the total thickness of the insulating resin layer 20, and preferably within the range of 5 to 20%.

2 shows an example of a manufacturing process for a metal-clad laminate 100 according to another embodiment of the present invention. First, a metal foil 10 such as a copper foil that constitutes the metal layer of the metal-clad laminate 100 is prepared. As shown in FIG. 2(a), a polyamic acid solution that does not contain a thermally conductive filler 30 is applied onto this metal foil 10, and then dried at a temperature of 140° C. or less to remove a certain amount of the solvent, thereby forming a first layer coating film 25.
Next, as shown in FIG. 2B, a polyamic acid solution containing a thermally conductive filler 30 is applied onto the coating film 25 and dried in the same manner as above to form a coating film 27 as a second layer.
Next, as shown in FIG. 2C, a polyamic acid solution not containing the thermally conductive filler 30 is applied onto the coating film 27 and dried in the same manner as above to form a third coating film 29 .
Next, as shown in FIG. 2D, the coating films 25, 27, and 29 are heat-treated at high temperature to imidize the polyamic acid, thereby forming a single insulating resin layer 20 in which the coating films 25, 27, and 29 are fused together.

As shown in FIG. 2, by laminating a coating film 29 not containing a thermally conductive filler 30 on a coating film 27 containing a thermally conductive filler 30 and then performing thermal imidization, the thermally conductive filler 30 does not protrude from the surface of the insulating resin layer 20, so that it is possible to effectively prevent poor appearance and surface smoothness, and a decrease in mechanical strength, while also achieving excellent thermal conductivity. In addition, by forming the matrix resin of the insulating resin layer 20 from the same (preferably the same) thermoplastic polyimide, it is not necessary to separately provide an adhesive layer made of a different resin material, and excellent thermal conductivity can be maintained. In addition, by forming a coating film 25 not containing a thermally conductive filler 30 and then forming a coating film 27 containing a thermally conductive filler 30 on it, it is possible to prevent a decrease in adhesion between the metal foil 10 and the insulating resin layer 20. It is preferable that the thickness of the coating films 25 and 29 not containing a thermally conductive filler 30 is as thin as possible as long as the above-mentioned action and effect are expressed. For example, the first coating film 25 is formed so that its thickness after curing is within the range of 2% to 20% of the total thickness of the insulating resin layer 20, preferably within the range of 5 to 15%; the second coating film 27 is formed so that its thickness after curing is within the range of 60% to 96% of the total thickness of the insulating resin layer 20, preferably within the range of 70 to 90%; and the third coating film 29 is formed so that its thickness after curing is within the range of 2% to 20% of the total thickness of the insulating resin layer 20, preferably within the range of 5 to 15%.

Here, the heat treatment for imidization is preferably carried out stepwise for about 15 to 60 minutes at a heating temperature in the range of 130 to 360°C. Such stepwise heat treatment can reduce the dimensional change of the insulating resin layer 20 during the heat curing stage and suppress warping. If the heat treatment temperature is lower than 130°C, the dehydration ring-closing reaction of polyimide does not proceed sufficiently, and conversely, if it exceeds 360°C, the insulating resin layer 20 and metal foil 10 may deteriorate due to oxidation, etc.

The polyamic acid solution containing the thermally conductive filler 30 can be prepared, for example, by adding a predetermined amount of the thermally conductive filler 30 to a polyamic acid solution containing a solvent obtained by polymerization in advance, and dispersing the filler using a stirrer or the like, or by adding a diamine and an acid anhydride while dispersing the thermally conductive filler 30 in a solvent, and polymerizing the filler. Here, the polyamic acid can be produced by a known method in which an aromatic diamine component and an aromatic tetracarboxylic dianhydride component are used in substantially equimolar amounts and polymerized in a solvent. That is, for example, the aromatic diamine component is dissolved in a solvent such as N,N-dimethylacetamide under a nitrogen stream, and then the aromatic tetracarboxylic dianhydride is added and reacted at room temperature for about 3 hours to obtain the polyamic acid.

The preferred degree of polymerization of polyamic acid suitable for the purpose of forming the insulating resin layer 20 is, when expressed in terms of its viscosity range, preferably a solution viscosity within the range of 500 cps to 100,000 cps. If the viscosity is within the above range, the thermally conductive filler 30 can be mixed in and still be kept in a uniformly dispersed state. If the viscosity is outside the above range, defects such as uneven thickness and streaks are likely to occur in the film during coating operations using a coater or the like. The solution viscosity can be measured using a cone-plate viscometer equipped with a thermostatic water bath. Examples of solvents that can be used include N,N-dimethylacetamide, n-methylpyrrolidinone, 2-butanone, diglyme, xylene, etc., and these can be used alone or in combination of two or more kinds.

In this manner, a metal-clad laminate 100 having a structure in which an insulating resin layer 20 is laminated on a metal foil 10 as a metal layer can be manufactured. Furthermore, by laminating a metal foil on the insulating resin layer 20 by a method such as thermocompression bonding, it is also possible to form a double-sided metal-clad laminate having a laminate structure of metal foil 10/insulating resin layer 20/metal layer (not shown). When the metal-clad laminate 100 of the present invention is a double-sided metal-clad laminate, the insulating resin layer 20 formed of thermoplastic polyimide not only has excellent adhesion to the metal foil 10, which is the substrate on which the coating film is cast, but also has excellent adhesion to the metal layer (not shown) on the laminate side.

As described above, the metal-clad laminate 100 of this embodiment employs a manufacturing method including a multiple coating step in which a polyamic acid solution containing a thermally conductive filler 30 is applied and then a polyamic acid solution not containing a thermally conductive filler 30 is applied. As a result, even if the thickness of the insulating resin layer 20 is within a range of 5 μm or more and less than 20 μm, it is possible to obtain a layer having excellent thermal conductivity while avoiding poor appearance and surface smoothness and reduced mechanical strength caused by the incorporation of the thermally conductive filler 30. In addition, since the entire insulating resin layer 20 is formed of thermoplastic polyimide, it has a practical adhesive strength between the metal layer (metal foil 10) and the insulating resin layer 20 without the need for an adhesive layer. In addition, the metal-clad laminate 100 of this embodiment has excellent handling characteristics during mass production and processing because it has little warping. Therefore, by using it as a circuit board material represented by a flexible printed circuit board (FPC), the reliability of electronic devices can be improved. Furthermore, the metal-clad laminate 100 of this embodiment can be widely used industrially as a heat dissipation substrate for electronic devices, lighting equipment, and other devices that require high heat dissipation properties.

[Circuit board]
The circuit board according to one embodiment of the present invention can be manufactured by processing the metal layer of the metal-clad laminate into a pattern by a conventional method to form a metal wiring layer. The patterning of the metal layer can be performed by any method using, for example, photolithography and etching.

[Polyimide film]
The polyimide film according to one embodiment of the present invention is a thermoplastic polyimide film consisting of an insulating resin layer containing a thermally conductive filler, excluding the metal layer of the metal-clad laminate. The polyimide film of this embodiment has the same structure as the insulating resin layer of the metal-clad laminate, and can be produced by removing the metal layer of the metal-clad laminate by etching using a conventional method. Alternatively, in the structure shown in Figures 1 and 2, a peelable substrate is used instead of the metal foil 10, and the polyimide film of this embodiment may be produced by carrying out a process of peeling the substrate after the formation of the insulating resin layer 20.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to the scope of these examples.

The abbreviations used in the examples represent the following compounds.
BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride DAPE: 4,4'-diaminodiphenyl ether DABA: 4,4'-diaminobenzanilide MABA: 4,4'-diamino-2'-methoxybenzanilide PMDA: pyromellitic dianhydride BAPP: 2,2-bis(4-aminophenoxyphenyl)propane m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl DMAc: N,N-dimethylacetamide

The characteristics evaluated in the examples were evaluated according to the following methods.

[Viscosity measurement]
The viscosity of the polyamic acid solution was measured at 25° C. using a cone-plate viscometer equipped with a thermostatic water bath (manufactured by Tokimec Co., Ltd.).

[Measurement of volume average particle diameter _D50 ]
[Measurement of volume average particle diameter _D50 ]
The particle size was measured by a laser diffraction particle size distribution measuring device (Malvern Instruments, trade name: Master Sizer 3000) using water as a dispersion medium by a laser diffraction/scattering measuring method.

[Copper foil peel strength]
The copper foil layer of the laminate was pattern-etched into a rectangular shape with a width of 1.0 mm and a length of 180 mm, and a test specimen with a width of 20 mm and a length of 200 mm was cut out so that the pattern was at the center, and a 180° peel test was performed based on IPC-TM-650 (The Institute for Interconnecting and Packaging Electronic Circuits Test Method 650) 2.4.19.
○: 0.8 kN/m or more ×: less than 0.8 kN/m

[Adhesive peel strength]
A fluororesin sheet was placed partially on the polyimide layer of the single-sided metal-clad laminate, and an adhesive sheet (polyimide-based, manufactured by Nippon Steel Chemical & Material Co., Ltd., trade name: NB25A-M, thickness: 25 μm) and copper foil 1 (electrolytic copper foil, manufactured by Fukuda Metal Foil & Powder Co., Ltd., trade name: CF-T4M-DS-HD-35, thickness: 35 μm, Rz = 1.4 μm) were laminated in order, and then the laminate was subjected to heat compression bonding at 160 ° C. for 1 hour at a pressure of 3.5 MPa per unit area to prepare a test piece. The copper foil side of the laminate having a width of 5 mm and a length of 100 mm as the test piece was fixed to an aluminum plate with double-sided tape, and the adhesive sheet with the copper foil was peeled off at a speed of 50 mm / min in a 180 ° direction starting from the place where the fluororesin sheet was placed, and the adhesive peel strength (peel strength) was obtained.
○: 0.8 kN/m or more ×: less than 0.8 kN/m

[Thermal conductivity in the thickness direction (λz)]
The polyimide resin film was cut into a size of 20 mm x 20 mm, and the thermal diffusivity in the thickness direction was measured by a laser flash method (NETZSCH, product name: Xenon Flash Analyzer LFA447 Nanoflash device), the specific heat was measured by DSC, and the density was measured by a water substitution method. Based on these results, the thermal conductivity (W/m K) was calculated.

[Measurement of coefficient of thermal expansion (CTE)]
A polyimide film (3 mm × 15 mm) was heated from 30° C. to 280° C. at a heating rate of 10° C./min while applying a load of 5.0 g in a thermomechanical analysis (TMA) device, and then cooled from 250° C. to 100° C., and the thermal expansion coefficient was measured from the elongation (linear expansion) of the polyimide film during cooling.

Tear Propagation Resistance (TPR)
A polyimide resin film of 63.5 mm×50 mm was used as a test piece, a 12.7 mm long cut was made in the test piece, and the tear propagation resistance was measured using a light load tear tester manufactured by Toyo Seiki Seisakusho Co., Ltd.
○: 10 mN or more ×: less than 10 mN

(Synthesis Example 1)
Under a nitrogen stream, DAPE (17.31 g, 0.0864 mol) was dissolved in 255 g of DMAc solvent in a 500 ml separable flask while stirring. Then, BTDA (27.69 g, 0.0858 mol) was added. The solution was then stirred at room temperature for 3 hours to carry out a polymerization reaction, and a pale yellow viscous polyamic acid solution A was obtained.

(Synthesis Examples 2 to 6)
In the same manner as in Synthesis Example 1, the diamines and tetracarboxylic dianhydrides shown in Table 1 were added and a polymerization reaction was carried out to obtain viscous solutions of polyamic acids B to F, which serve as polyimide precursors.

(Formulation Example 1)
39.6 parts by weight of polyamic acid solution A with a solid content concentration of 15 wt % and 40.4 parts by weight of aluminum oxide particles [manufactured by Sumitomo Chemical Co., Ltd., product name: AA-3, spherical, volume average particle diameter D ₅₀ 3.0 μm] as a thermally conductive filler were mixed uniformly using a centrifugal mixer to obtain a thermally conductive filler-containing polyamic acid solution G. The content of aluminum oxide particles in this insulating resin layer was 70 vol %.

(Composition Examples 2 to 8)
Similarly to Formulation Example 1, the polyamic acid solutions and aluminum oxide particles shown in Table 2 were mixed in a centrifugal mixer until homogeneous, to obtain polyamic acid solutions H to N containing thermally conductive fillers.
In addition, in Formulation Examples 3 and 4, aluminum oxide particles (manufactured by Sumitomo Chemical Co., Ltd., product name: AA-2, spherical, volume average particle size D ₅₀ 2.0 μm) were used as the thermally conductive filler.

Example 1
On the copper foil 1, the polyamic acid solution G obtained in Formulation Example 1 was applied so that the thickness after curing was 13 μm, and the solution was dried by heating at 90 to 140 ° C. to remove the solvent. Next, the polyamic acid solution B obtained in Synthesis Example 2 was applied thereon so that the thickness after curing was 1.5 μm, and the solution was dried by heating at 120 ° C. to remove the solvent. Thereafter, the temperature was raised stepwise over 30 minutes in the temperature range of 130 to 360 ° C. to prepare a flexible substrate laminate M1 consisting of two polyimide layers on the copper foil 1. The thickness of the polyimide layer on the copper foil 1 was 13 μm/1.5 μm in the order of G/B from the copper foil 1 side. In order to evaluate the properties of the polyimide layer in the flexible substrate laminate M1, the copper foil 1 was etched away to prepare a film M1, and the CTE, thickness direction thermal conductivity, and tear propagation resistance (TPR) were evaluated.

(Examples 2 to 4, 7, and 8, and Comparative Examples 2 and 4)
By changing the type and thickness of the polyamic acid solution used, laminates for flexible substrates M2 to M4, M7, M8, M10, and M12 and films M2 to M4, M7, M8, M10, and M12 were obtained in the same manner as in Example 1, and were similarly evaluated.

Example 5
On the copper foil 1, the polyamic acid solution B obtained in Synthesis Example 2 was applied so that the thickness after curing was 1.0 μm, and the solution was heated and dried at 120 ° C to remove the solvent. The polyamic acid solution I obtained in Formulation Example 3 was applied so that the thickness after curing was 14 μm, and the solution was heated and dried at 90 to 140 ° C to remove the solvent. Next, the polyamic acid solution B obtained in Synthesis Example 2 was applied thereon so that the thickness after curing was 1.0 μm, and the solution was heated and dried at 120 ° C to remove the solvent. After that, the temperature was raised stepwise over 30 minutes in the temperature range of 130 to 360 ° C to produce a flexible substrate laminate M5 consisting of three polyimide layers on the copper foil 1. The thicknesses of the polyimide layers on the copper foil 1 are 1.0 μm/14 μm/1.0 μm in the order of B/I/B from the copper foil 1 side. In order to evaluate the characteristics of the polyimide layer in the laminate M5 for flexible substrates, the copper foil 1 was removed by etching to prepare a film M5, and the CTE, thermal conductivity through thickness, and tear propagation resistance (TPR) were evaluated.

(Example 6, Comparative Example 3)
Flexible substrate laminates M6 and M11 and films M6 and M11 were obtained in the same manner as in Example 5, except that the type and thickness of the polyamic acid solution used were changed, and these were evaluated in the same manner.

(Comparative Example 1)
The polyamic acid solution G obtained in Formulation Example 1 was applied onto copper foil 1 so that the thickness after curing would be 18 μm, and the solution was dried by heating at 90 to 140° C. to remove the solvent. The solution was then heated stepwise over 30 minutes in a temperature range of 130 to 360° C. to produce a flexible substrate laminate M9 consisting of one polyimide layer on copper foil 1. In order to evaluate the properties of the polyimide layer in the flexible substrate laminate M9, the copper foil 1 was etched away to produce a film M9, and the CTE, thickness direction thermal conductivity, and tear propagation resistance (TPR) were evaluated.

The above results are summarized in Tables 3 and 4.

From the above results, the metal-clad laminates of Examples 1 to 8 obtained by a manufacturing method including a process of repeatedly applying the same type or composition of polyamic acid solution multiple times to laminate a coating film containing a thermally conductive filler and a coating film not containing a thermally conductive filler in this order were thin films less than 20 μm in thickness, and had excellent peel strength on both the copper foil side and the adhesive side, as well as good thermal conductivity through thickness and tear propagation resistance (TPR). In contrast, Comparative Example 1, which used only a coating film containing a thermally conductive filler, Comparative Example 2, in which the order of forming the coating film containing a thermally conductive filler and the coating film not containing a thermally conductive filler was reversed, and Comparative Examples 3 and 4, which used a resin type different from that of the present invention, did not satisfy all of the evaluation items.

The above describes in detail the embodiment of the present invention for illustrative purposes, but the present invention is not limited to the above embodiment and various modifications are possible.

10...metal foil, 20...insulating resin layer, 21, 23, 25, 27, 29...coating film, 30...thermally conductive filler, 100...metal-clad laminate

Claims (7)

A metal-clad laminate comprising a metal layer and an insulating resin layer containing a thermally conductive filler laminated on the metal layer,
The thermally conductive filler has a volume average particle size of 2 μm or more and 5 μm or less,
The insulating resin layer has a thickness in the range of 5 μm or more and less than 20 μm, and when made into a resin film, has a tear propagation resistance of 10 mN or more, and contains a constitutional unit represented by the following general formula (1):

[In the formula, Ar represents a tetravalent acid anhydride residue derived from an aromatic tetracarboxylic dianhydride, and _R1 represents a divalent diamine residue derived from a diamine compound]
The matrix resin is a thermoplastic polyimide.
A metal-clad laminate comprising: an acid anhydride residue derived from a tetracarboxylic dianhydride having a ketone group (-CO-) in the molecule in a total of 40 molar parts relative to a total of 100 molar parts of the acid anhydride residues; and a diamine residue derived from one or more diamine compounds selected from the group consisting of 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzanilide, and 4,4'-diamino-2'-methoxybenzanilide in a total of 50 molar parts relative to a total of 100 molar parts of the diamine residues. The metal-clad laminate according to claim 1, wherein the content of the thermally conductive filler in the insulating resin layer is within the range of 30 to 70 vol%. The metal-clad laminate according to claim 1 or 2, wherein the thermal conductivity in the thickness direction of the insulating resin layer is 0.7 W/m·K or more. 4. The metal-clad laminate according to claim 1, wherein the insulating resin layer has a thermal expansion coefficient of 30 ppm/K or less when made into a resin film. The metal-clad laminate according to any one of claims 1 to 4 , wherein a peel strength between the insulating resin layer and the metal layer is 0.8 kN/m or more. A method for producing the metal-clad laminate according to any one of claims 1 to 5 , comprising the steps of:
A step of applying a solution of a polyamic acid containing a thermally conductive filler onto a metal foil and drying the applied solution to form a first layer coating film;
applying a polyamic acid solution not containing a thermally conductive filler onto the first coating film and drying the solution to form a second coating film;
a step of heating the coating films of the first and second layers to imidize the polyamic acid and integrate the layers to form an insulating resin layer;
Including,
the first coating film is formed so that its thickness after curing is within a range of 60% to 95% of the thickness of the insulating resin layer;
A method for producing a metal-clad laminate, characterized in that the second layer coating film is formed so that its thickness after curing is within the range of 5% to 40% of the thickness of the insulating resin layer. A method for producing the metal-clad laminate according to any one of claims 1 to 5 , comprising the steps of:
A step of applying a solution of a polyamic acid containing no thermally conductive filler onto a metal foil and drying the applied solution to form a first layer of a coating film;
applying a polyamic acid solution containing a thermally conductive filler onto the first coating film and drying the applied film to form a second coating film;
applying a polyamic acid solution not containing a thermally conductive filler onto the second coating film and drying the applied film to form a third coating film;
a step of heating the coating films of the first, second and third layers to imidize the polyamic acid and integrate the layers to form an insulating resin layer;
Including,
the first coating film is formed so that its thickness after curing is within a range of 2% to 20% of the thickness of the insulating resin layer;
the second coating film is formed so that its thickness after curing is within a range of 60% to 96% of the thickness of the insulating resin layer;
A method for producing a metal-clad laminate, characterized in that the third layer coating film is formed so that its thickness after curing is within a range of 2% to 20% of the thickness of the insulating resin layer.

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