JP2012213899A - Heat conductive polyimide-metal substrate - Google Patents

Abstract

[PROBLEMS] To provide not only excellent heat conduction characteristics, adhesion strength between a practical metal layer and an insulating layer, excellent heat resistance, but also small warpage of a metal laminate, and excellent workability and handling properties. An excellent thermally conductive polyimide-metal substrate is provided.
A thermally conductive polyimide-metal substrate includes a metal layer and an insulating layer laminated on the metal layer. The insulating layer has a high-density filler polyimide resin layer containing a thermally conductive filler in the range of 40 to 70 vol% in the polyimide resin. This polyimide resin is a thermoplastic polyimide resin synthesized using 50 mol% or more of 4,4′-diaminodiphenyl ether and having a glass transition point of 250 ° C. or more. 80 vol% or more of the thermally conductive filler in the high-density filler polyimide resin layer is a spherical filler having an average particle size of 5 μm or less.
[Selection figure] None

Description

  The present invention relates to a thermally conductive polyimide-metal substrate that has an insulating layer having excellent thermal conductivity and is preferably used for a heat dissipation substrate or a circuit board.

  In recent years, there has been an increasing demand for downsizing and weight reduction of electronic devices typified by mobile phones, and accordingly, flexible circuit boards that are advantageous for downsizing and weight reduction of devices are widely used in the electronic technology field. It has become to. Among them, a flexible circuit board using a polyimide resin as an insulating layer has been widely used since its heat resistance and chemical resistance are good (Patent Document 1).

  By the way, with the recent miniaturization of electronic devices, the degree of circuit integration has increased, and in conjunction with the speeding up of information processing, heat dissipation means for heat generated in the device has attracted attention. In addition, with the growing awareness of environmental issues such as global warming, there is a strong demand for products with low environmental impact and energy saving. A typical example is the rapid spread of LED lighting in place of incandescent lamps, but in order to fully demonstrate the performance of LED lighting, it is important to efficiently release the heat generated during use. .

  Then, in order to provide the flexible circuit board which is rich in workability and was excellent in heat dissipation, about the polyimide film which comprises an insulating layer, examination which improves the thermal conductivity of the thickness direction is made | formed (patent document 1). Moreover, the polyimide film composite material which disperse | distributed the heat conductive filler to the polyimide induced | guided | derived from siloxane diamine is also proposed regarding the heat conductive polyimide film containing a heat conductive filler (patent document 2).

  However, the thermal conductivity in the thickness direction of the above-described conventional polyimide film is insufficient in performance as a heat dissipation substrate for use in, for example, LED lighting, and needs to be improved. Therefore, a polyimide film composite material in which aluminum nitride is dispersed in polyimide for the purpose of improving thermal conductivity has also been proposed (Patent Document 3). However, the technology disclosed here considers the adhesiveness to the metal layer, or uses a polyimide resin having a low glass transition temperature for the polyimide resin constituting the insulating layer. Was insufficient.

  In addition, when the thermal conductive filler is dispersed in the polyimide resin at a high content for the purpose of improving the thermal conductivity in the thickness direction, there arises a problem that the substrate is warped. In order to suppress warpage, it is necessary to optimize the thermal expansion coefficient of the polyimide resin layer which is an insulating layer with respect to the thermal expansion coefficient of the metal foil. As a technique, it is effective to use a plate-like thermally conductive filler in addition to the spherical filler, but when the plate-like thermally conductive filler is contained in the polyimide resin, the filler is oriented in the plane direction. Since it is easy, anisotropy occurs in the thermal conductivity, and the thermal conductivity in the thickness direction tends to be lower than that of the spherical filler. Moreover, in the polyimide resin containing only the spherical filler, the thermal expansion due to the solvent volatilization in the manufacturing process tends to be large, the control of the thermal expansion coefficient is difficult, and it is difficult to suppress the warpage of the laminate.

  In addition, in order to improve the thermal conductivity of the polyimide resin, a thermal conductivity in which a polyimide resin layer having a specific structural unit containing a thermally conductive filler and a polyimide resin layer having a glass transition temperature lower than that of the polyimide resin layer are laminated. A conductive polyimide film has been proposed (Patent Document 4). Furthermore, as a thermally conductive filler, there is also a proposal of a highly thermally conductive polyimide film in which a plate-like filler having an average major axis of 0.1 to 15 μm and a spherical filler having an average particle diameter of 0.05 to 10 μm are combined in a predetermined ratio. (Patent Document 5).

  The flexible substrate laminate proposed in Patent Document 4 has thermal conductivity, but in order to maintain adhesive strength with the metal layer, a thermally conductive filler is blended with the metal layer. No polyimide resin layer is interposed as an adhesive layer. For this reason, there is a concern that the thermal conductivity is lowered depending on the thickness of the adhesive layer, and there remains room for improvement in that respect. In addition, the resin layer containing the thermally conductive filler also has an adhesive force with the metal layer which is essentially not sufficient, and an adhesive layer may be provided to ensure this. It was necessary.

  In addition, in order to improve the adhesiveness of the heat conductive polyimide resin layer which mix | blended the heat conductive filler, it is also considered that a thermoplastic resin is mainly used for the resin layer which forms a heat conductive polyimide resin layer. However, when a thermoplastic resin is mainly used, there is a possibility that the dimensional stability required for circuit board use cannot be obtained due to the characteristic that the coefficient of thermal expansion is large. In addition, since the thermoplastic resin generally has low heat resistance, it is not possible to ensure sufficient heat resistance simply by applying the thermoplastic resin, and as a main resin layer of the heat dissipation board used in a high temperature environment. The application was considered unsuitable in the light of technical common sense, and so far has not been fully studied.

  Therefore, a metal-clad laminate that suppresses warpage in the metal-clad laminate, has a practical adhesive strength between the metal layer and the insulating layer without having an adhesive layer, and has excellent thermal conductivity of the insulating layer. It was desired to provide a laminate.

JP 2006-274040 A JP 2006-169533 A JP 2008-007590 A International Publication WO 2009/110387 International Publication WO 2010/027070

  The present invention has excellent heat conduction characteristics, has a practical adhesion strength between a metal layer and an insulating layer, has not only excellent heat resistance, but also can reduce the warp of the metal laminate, and further processing It aims at providing the heat conductive polyimide metal substrate excellent also in the property and handling property.

  As a result of repeated studies to solve the above problems, the present inventors used a polyimide resin having a specific structure for the resin of the insulating layer containing a high proportion of the heat conductive filler in the metal-clad laminate, It has been found that the above problems can be solved by containing a certain amount or more of a spherical filler having a specific average particle diameter as the thermally conductive filler, and the present invention has been completed.

  That is, the thermally conductive polyimide-metal substrate of the present invention is a thermally conductive polyimide-metal substrate provided with a metal layer and an insulating layer laminated on the metal layer. Here, the said insulating layer has a filler high density containing polyimide resin layer which contains a heat conductive filler in the range of 40-70 vol% in a polyimide resin, and the said polyimide resin is 4,4 as a diamine component. It is a thermoplastic polyimide resin synthesized using 50 mol% or more of '-diaminodiphenyl ether with respect to the total diamine component, and has a glass transition point of 250 ° C. or higher, and the thermal conductivity in the high-density filler-containing polyimide resin layer 80 vol% or more of the filler is a spherical filler having an average particle diameter of 5 μm or less.

  In the thermally conductive polyimide-metal substrate of the present invention, the spherical filler is preferably at least one selected from the group consisting of aluminum oxide and aluminum nitride.

  In the thermally conductive polyimide-metal substrate of the present invention, the thickness of the insulating layer is preferably in the range of 5 to 40 μm, and the thickness of the metal layer is preferably in the range of 5 to 50 μm.

  In the thermally conductive polyimide-metal substrate of the present invention, at least one surface of the insulating layer is in direct contact with the metal layer, and the insulating layer in direct contact with the metal layer is a high-density filler polyimide resin layer. preferable.

  In the thermally conductive polyimide-metal substrate of the present invention, the thermal conductivity in the thickness direction of the insulating layer is 1.5 W / mK or more, and the adhesiveness to the metal layer is 0.5 kN / m or more. It is preferable that

  Further, a flexible substrate of the present invention is provided with the heat conductive polyimide-metal substrate according to any one of the above, wherein the metal layer is a copper foil, and the surface of the adhesive surface with the insulating layer is rough. The degree (Ra) is in the range of 0.05 to 0.5 μm.

  The thermally conductive polyimide-metal substrate of the present invention has a practical adhesive strength between the metal layer and the insulating layer, and is excellent in heat resistance and thermal conductivity. In addition, since the warpage of the substrate is small, it has excellent handling characteristics during mass production and processing. Therefore, it can be widely used industrially as a substrate material for electronic devices and lighting devices that require high heat dissipation.

  The thermally conductive polyimide-metal substrate of the present invention includes a metal layer and an insulating layer. Hereinafter, the term “metal-clad laminate” in this specification refers to the thermally conductive polyimide-metal substrate of the present invention unless otherwise specified.

[Insulation layer]
The insulating layer of the metal-clad laminate of the present invention includes a polyimide resin layer as a matrix resin, and a high-density filler polyimide resin layer containing a thermally conductive filler in the range of 40 to 70 vol% in the resin. .

<Polyimide resin>
The polyimide resin that forms the matrix of the insulating layer is synthesized using 50 mol% or more of 4,4′-diaminodiphenyl ether (4,4′-DAPE) as a diamine component as a polyimide raw material with respect to the total diamine component. And a glass transition point (Tg) of 250 ° C. or higher. Generally, a polyimide resin is represented by the following general formula (1).

（式中、基Ａｒ₁は、少なくとも２価の芳香族ジアミン残基を示し、基Ａｒ_２は、４価の酸二無水物残基を示す。）

(In the formula, the group Ar ₁ represents at least a divalent aromatic diamine residue, and the group Ar ₂ represents a tetravalent acid dianhydride residue.)

In the general formula (1), since the group Ar ₁ represents a diamine residue, in the present invention, 50 mol of a structural unit in which the group Ar ₁ is a residue of 4,4′-diaminodiphenyl ether is contained in the polyimide resin. % Or more, and it is preferable to contain 80 mol% or more. More preferably, the polyimide resin contains 100 mol% of a structural unit in which the group Ar ₁ is a residue of 4,4′-diaminodiphenyl ether. When the content of the structural unit represented by the general formula (1) is less than 50 mol% in the polyimide resin, the polyimide resin layer is formed (from the drying of the polyamic acid layer as a precursor to the initial stage of curing). The amount of dimensional change of the resin layer increases, and the amount of warpage of the target substrate increases.

  In the general formula (1), specific examples of aromatic diamines other than 4,4'-diaminodiphenyl ether include the following aromatic diamine residues. Namely, 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylediamine, 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, 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 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,7-diaminodibenzofuran, 1,5-diaminofluorene, dibenzo-p-dioxin-2,7-diamine, 4,4'-diaminobenzyl, etc. It is done.

Ar ₂ is a tetravalent acid dianhydride residue, preferably an aromatic acid dianhydride residue. Specific examples of aromatic dianhydrides that give such acid dianhydride residues include pyromellitic dianhydride (PMDA), 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 2,2 ', 3,3'-benzophenone tetracarboxylic dianhydride, 2,3,3', 4'-benzophenone tetracarboxylic dianhydride, 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, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-2,3,6,7-tetracarboxylic dianhydride 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloro Phthalene-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 '-Biphenyltetracarboxylic 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, (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 Anhydride, phenanthrene-1,2,6,7-tetracarboxylic dianhydride, phenanthrene-1,2,9,10-tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic Acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetra Carboxylic dianhydride, 4,4'-oxy And diphthalic dianhydride.

  In the present invention, 4,4′-diaminodiphenyl ether is an essential component as a diamine component, and aromatic dianhydrides that can be used in combination with this component include 3,3 ′, 4,4′-benzophenone. Tetracarboxylic dianhydride is preferred. By using 4,4'-diaminodiphenyl ether and 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride in combination as raw materials for polyimide resin, the effect of suppressing warpage of the metal-clad laminate is maximized. To the limit.

  When synthesize | combining the polyimide resin which comprises a polyimide resin layer, only 1 type may be used for a diamine and an acid anhydride, respectively, and 2 or more types can also be used together.

  As above-mentioned, the glass transition point (Tg) of the polyimide resin which comprises a filler high-density containing polyimide resin layer is 250 degreeC or more, and is a thermoplastic polyimide which shows a thermoplastic characteristic. The glass transition point (Tg) of this thermoplastic polyimide is preferably in the range of 250 to 320 ° C. When the glass transition point (Tg) is less than 250 ° C., the heat resistance as a heat dissipation substrate is poor, and when it exceeds 320 ° C., there is a possibility that sufficient adhesion with the metal layer cannot be secured.

<Thermal conductive filler>
The content rate of the heat conductive filler in a polyimide resin layer needs to exist in the range of 40-70 vol%, and the inside of the range of 50-70 vol% is preferable. If the content ratio of the heat conductive filler is less than 40 vol%, the heat dissipation characteristic when the electronic component such as a circuit board is used is insufficient, and if it exceeds 70 vol%, the heat conductive filler is contained in the polyimide resin (polyamic acid). When contained, the varnish becomes highly viscous and it becomes difficult to produce a metal-clad laminate.

  Furthermore, 80 vol% or more of the thermally conductive filler used in the present invention needs to be a spherical filler having an average particle diameter of 5 μm or less. Here, the spherical shape means a shape having a spherical shape or a shape close to a spherical shape, and a ratio of an average major axis to an average minor axis close to 1 or 1 (preferably 0.8 or more). As the spherical filler, for example, it is preferable to include one or both of aluminum oxide and aluminum nitride. In particular, since high thermal conductivity is ensured and warpage can be effectively suppressed, all of the thermally conductive filler is nitrided. More preferably, aluminum is used.

  By using a spherical filler for most of the thermally conductive filler, high-density filling and uniform dispersion into the polyimide resin layer are possible, and the thermal conductivity can be improved. In the present invention, the reason why it is essential that 80 vol% or more of the thermally conductive filler is a spherical filler having an average particle diameter of 5 μm or less is as follows. That is, in the present invention, in order to fill the heat conductive filler with a high density of 40 vol% or more of the insulating layer, when the average particle size exceeds 5 μm or the content of non-spherical filler exceeds 20 vol% in total. , It becomes easy to cause poor appearance, and voids are likely to be generated at the interface between the filler and the resin, and the withstand voltage is likely to be lowered.

  In the present invention, other heat conductive fillers can be used in combination with the spherical filler having an average particle diameter of 5 μm or less within a range not impairing the effects of the invention. Examples of the heat conductive filler other than the above include aluminum, copper, nickel, silica, diamond, magnesia, beryllia, boron nitride, silicon nitride, silicon carbide and the like. Among these, a thermally conductive filler selected from silica, boron nitride, and silicon nitride is preferable. Since the polyimide resin layer acts as an insulating layer, the filler blended in the polyimide resin layer is suitable from that viewpoint.

  The particle size of the thermally conductive filler (spherical filler and non-spherical filler) is such that the average particle size is 5 μm or less from the viewpoint of improving thermal conductivity by uniformly dispersing the filler in the thickness direction of the polyimide resin layer. Is preferable, and it is more preferable that it exists in the range of 0.5-3 micrometers. If the average particle size of the thermally conductive filler is larger than 5 μm, the filler may protrude from the surface of the polyimide resin layer, causing a problem in appearance. Especially when the thickness of the insulating layer is 40 μm or less, it is important not to make the average particle diameter of the heat conductive filler too large. By making the average particle diameter 5 μm or less, problems in appearance can be avoided. it can.

<Insulation layer structure>
The insulating layer is not limited to a single layer, and may be a plurality of layers as long as it has the above-described high-density filler polyimide resin layer. For example, an insulating layer that does not contain a filler can be provided between the metal layer and the high-density filler polyimide resin layer. However, depending on the thickness of the insulating layer that does not contain a filler, the thermal conductivity of the metal-clad laminate decreases, so that the insulating layer in contact with the metal layer must contain a filler in order to maintain heat dissipation efficiency. Is preferred. In this case, in order to ensure adhesion with the metal layer, it is preferable to lower the filler content than the high-density filler-containing polyimide resin layer.

In addition, when the typical example of the laminated structure of the heat conductive polyimide-metal substrate by this invention is shown, the laminated structure of following A) -D) can be illustrated.
A) Metal layer 1 / Filler high-density polyimide resin layer B) Metal layer 1 / Filler high-density polyimide resin layer / Metal layer 2
C) Metal layer 1 / High density filler-containing polyimide resin layer / Polyimide resin layer / Metal layer 2
D) Metal layer 1 / Lower content polyimide resin layer / High density filler polyimide resin layer / Polyimide resin / Metal layer 2

  Among the laminated structures A) to D), A) to C) in which the filler high-density-containing polyimide resin layer and the metal layer are in direct contact are preferable from the viewpoint of obtaining excellent thermal conductivity in the thickness direction. A) and B) in which the insulating layer is formed only of a high-density filler-containing polyimide resin layer (single layer) is more preferable.

  For example, the thickness of the insulating layer is preferably in the range of 5 to 40 μm, and more preferably in the range of 10 to 40 μm. If the thickness of the insulating layer is less than 5 μm, the insulating layer is brittle and easily broken. On the other hand, if it exceeds 40 μm, the thermal resistance becomes high, so that the performance as a highly thermally conductive polyimide-metal substrate is hardly exhibited.

  The insulating layer preferably has a thermal conductivity in the thickness direction of 1.5 W / m · K or more, and more preferably 1.5 to 3.0 W / mK or more. The thermal conductivity in the thickness direction of the entire insulating layer is 1.5 W / mK or more, so the heat dissipation characteristics of the metal-clad laminate are excellent, and it can be applied to circuit boards used in high-temperature environments. become. Thus, the outstanding heat conductivity is realizable by making the addition amount of the heat conductive filler into the polyimide resin layer which comprises an insulating layer 40 vol% or more. When the amount of the thermally conductive filler added to the polyimide resin layer is less than 40 vol%, the overall thermal conductivity in the thickness direction of the insulating layer is less than 1.5 W / mK, and the heat dissipation characteristics are degraded. In the metal-clad laminate of the present invention, in particular, the ratio of the thickness of the high-density filler-containing polyimide resin layer in the total thickness of the insulating layer is 100%, and a high thermal conductivity is obtained by not interposing an adhesive layer. Can do. In the present specification, unless otherwise specified, the thermal conductivity means the thermal conductivity in the thickness direction of the layer (λzTC).

  The metal-clad laminate of the present invention not only has a thermal conductivity of 1.5 W / m · K or more in the thickness direction of the insulating layer, but also has an adhesion (peel strength) to the metal layer of 0.5 kN / m or more. It is preferable that it is in the range of 0.6 to 1.8 kN / m. In the present invention, 50 mol% of 4,4′-diaminodiphenyl ether is used as the diamine component constituting the polyimide resin in order to set the peel strength to 0.5 kN / m or more and to maintain other properties such as warpage reduction and heat resistance. Use above. If the amount of 4,4'-diaminodiphenyl ether is less than 50 mol% with respect to the total diamine component, the peel strength with the metal layer is less than 0.5 kN / m, and the adhesion with the metal layer may be insufficient.

  In the polyimide resin layer of the insulating layer, as long as the above physical properties are not impaired, for example, processing aids, antioxidants, light stabilizers, flame retardants, antistatic agents, surfactants, dispersants, antisettling agents are used. In addition, an optional component such as an organic or inorganic filler other than a thermal stabilizer, an ultraviolet absorber, and thermal conductivity can be included.

[Metal layer]
Examples of the metal layer in the metal-clad laminate of the present invention include conductive metal foils such as copper, aluminum, iron, silver, palladium, nickel, chromium, molybdenum, tungsten, zinc, and alloys thereof. Among these, a copper foil or an alloy copper foil containing 90% or more of copper is preferably used. Although the preferable thickness range of a metal layer can be set according to the use of a metal-clad laminated body, when using as board | substrate materials, such as an electronic device and a lighting device, it is preferable to set it as the range of 5-50 micrometers, for example. If the thickness of the metal layer is less than 5 μm, problems such as wrinkles may occur during conveyance in the manufacturing process. Conversely, if the thickness exceeds 50 μm, workability may be reduced.

  In addition, the conductive metal foil used as the metal layer has a surface roughness (Ra) of a surface bonded to the insulating layer in the range of 0.05 to 0.5 μm, for example, in order to improve adhesion to the insulating layer. Preferably there is. When the surface roughness (Ra) of the surface to be bonded to the insulating layer is less than 0.05 μm, the metal layer and the insulating layer may be easily peeled off depending on the use of the metal-clad laminate. It becomes unsuitable when using as. On the other hand, when the surface roughness (Ra) of the surface to be bonded to the insulating layer exceeds 0.5 μm, the adhesion between the metal layer and the insulating layer is improved due to the anchor effect due to the roughening, but the metal layer was processed by wiring. There is concern about the deterioration of the wiring shape.

[Action]
In order to improve the heat dissipation characteristics of the metal-clad laminate, the insulating layer may be filled with a heat conductive filler at a high density. However, as described above, when the spherical heat conductive filler is contained in the polyimide resin layer at a high density (for example, 40 vol% or more), the metal-clad laminate is likely to be warped. As a result of advancing the elucidation of the mechanism of warping when the polyimide resin layer is filled with a thermally conductive filler at a high density, the present inventors do not contain a filler or differ from a metal-clad laminate containing only a low density. We obtained knowledge that warping occurred in the behavior. That is, the warp of the metal-clad laminate is mainly caused by the heat history from the heat drying of the polyamic acid layer, which is a precursor of the polyimide resin formed on the metal layer, to the initial stage of thermosetting, It is considered that the behavior at that time is specific in the case of an insulating layer filled with a thermally conductive filler at a high density.

  Although all the mechanisms by which the warpage of the metal-clad laminate is suppressed by the present invention have not been clarified, a rational explanation can be made by considering the following. The insulating layer is formed by applying a polyamic acid solution to be an insulating layer on a base material and imidizing the solution by heating. However, due to the heat of drying and curing at that time, a certain degree of expansion / Shrinkage occurs. When considering this in a system containing a filler at a high density, a polyimide resin having a small linear thermal expansion coefficient has a relatively small amount of thermal expansion in the drying stage of the polyamic acid layer. It is considered that the amount of shrinkage due to volatilization of slag increases, which becomes a dominant factor and warpage tends to occur. On the other hand, when the filler is contained in the thermoplastic polyimide resin at a high density, the thermal expansion amount due to heat drying of the polyamic acid layer and the shrinkage amount due to volatilization of the solvent and imidized water are offset. Rather, it is thought that warpage is suppressed. This idea is consistent with the fact that all the warp of the metal-clad laminate is curled toward the resin side in the examples described later (that is, the warp caused by the shrinkage of the resin). Thus, the warpage of the thermoplastic resin is suppressed more than the low thermal expansion resin is a phenomenon that has not been seen in the conventional metal-clad laminate that is not filled with the thermally conductive filler. It is clearly contrary to the common sense of technology.

  The present inventors have found that polyimide resin using 4,4′-diaminodiphenyl ether as a diamine component has a small dimensional change due to expansion / contraction from the heat drying of the polyamic acid layer to the initial stage of thermosetting. It was found that the degree of warpage was the smallest even when compared with the thermoplastic polyimide resin. The reason for this is not yet clear, but 4,4′-diaminodiphenyl ether has a high molecular structure and has an appropriate flexibility, so that it is used as the main diamine component (preferably all of the diamine components). It is presumed that the polyamic acid / polyimide resin used as a balance between thermal expansion and thermal shrinkage is almost balanced. Furthermore, it has been confirmed that this effect is remarkably exhibited when 4,4′-diaminodiphenyl ether and 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride are combined as a raw material for polyimide resin. It was. The above is the first reason why it is essential to use 50 mol% or more of 4,4′-diaminodiphenyl ether as the diamine component in the present invention.

  In addition, in a metal-clad laminate used for applications that require excellent heat dissipation characteristics, it is an essential requirement that the insulating layer be required to have high heat resistance. In the present invention, by using 50 mol% or more of 4,4′-diaminodiphenyl ether as the diamine component, the glass transition point of the polyimide resin can be easily set to 250 ° C. or more, and high heat resistance can be imparted. This is the second reason for selecting 4,4'-diaminodiphenyl ether as the diamine component.

  Furthermore, a polyimide resin obtained by using 50 mol% or more of 4,4′-diaminodiphenyl ether as a diamine component exhibits thermoplasticity and is excellent in adhesiveness with a metal layer. In conventional metal-clad laminates, in order to ensure the adhesion of polyimide resin layers with a small coefficient of linear thermal expansion, the occurrence of warpage is suppressed by laminating a thin film of thermoplastic polyimide resin with high adhesion as a binder layer. However, the adhesion to the metal layer was ensured. However, when an excellent heat dissipation characteristic is to be obtained, the presence of a thermoplastic polyimide resin binder layer between the metal layer results in a decrease in the thermal conductivity (λz) in the thickness direction by several tens of percent. And became a major obstacle. In the present invention, the binder layer can be omitted by directly filling a thermoplastic polyimide resin obtained by using 4,4′-diaminodiphenyl ether as a diamine component in an amount of 50 mol% or more with a high-density thermal conductive filler. . Therefore, it was possible to realize high heat dissipation characteristics that could not be obtained when the binder layer was interposed while ensuring adhesion with the metal layer. This is the third reason why 4,4'-diaminodiphenyl ether is selected as the diamine component in the present invention.

  The effect of 4,4′-diaminodiphenyl ether as described above is manifested when the thermally conductive filler is filled at a high density of 40 vol% or more. In addition, when a spherical filler having an average particle size of 5 μm or less is included as a thermally conductive filler at a high density, the particle size is sufficiently small, and the shape is spherical and easily dispersed uniformly. Due to the homogenization of the physical properties of the insulating layer, the polyamic acid / polyimide resin in which 4,4′-diaminodiphenyl ether is used as a diamine component in a ratio of 50 mol% or more (preferably 100 mol%) is used between drying and thermal curing. It is considered that the balance between thermal expansion and thermal contraction is optimized and warpage is suppressed.

[Production method]
Next, an example of a method for producing a thermally conductive polyimide-metal substrate (metal-clad laminate) will be described. In the metal-clad laminate, a filler-containing polyamic acid obtained by dispersing a thermally conductive filler in polyamic acid, which is a polyimide resin precursor, is directly applied onto a metal substrate, which is a metal layer of a metal substrate. It can be formed by drying and curing. In this case, another polyimide resin layer optionally containing a filler may be laminated on the high-density filler polyimide resin layer in the same manner. Here, as a metal base material, metal foils, such as above-mentioned copper foil used as the conductor layer of a thermal radiation board | substrate or a circuit board, can be used.

  Application of the filler-containing polyamic acid solution on the metal substrate can be performed by a known method, for example, appropriately selected from a barcode method, a gravure coating method, a roll coating method, a die coating method, and the like. it can.

  In order to explain the present invention more clearly, a production example of a metal-clad laminate having a metal layer on one side of an insulating layer is shown. Here, the case where a polyimide resin layer is comprised only with one filler high density containing polyimide resin layer is mentioned as an example, and is demonstrated. First, a metal foil such as a copper foil constituting the metal layer of the metal-clad laminate is prepared. A polyamic acid solution containing a thermally conductive filler for forming a high-density filler polyimide resin layer on the metal foil is applied and dried at a temperature of, for example, 140 ° C. or less to remove a certain amount of solvent. Thereafter, the polyamic acid is imidized by further heat treatment at a high temperature to obtain a metal-clad laminate having a metal layer on one side of the high-density filler-containing polyimide resin layer. Here, the heat treatment for imidization is preferably performed at a heating temperature within a range of 130 to 360 ° C., for example, in a time step of about 15 to 60 minutes. Such stepwise heat treatment makes it possible to reduce the dimensional change of the insulating layer in the thermosetting stage and suppress warping. If the temperature of the heat treatment is lower than 130 ° C., the dehydration ring-closing reaction of polyimide does not proceed sufficiently. On the contrary, if it exceeds 360 ° C., the polyimide resin layer and the metal layer may be deteriorated due to oxidation or the like.

  In addition, the preparation of the polyamic acid solution containing the above heat conductive filler is, for example, adding a predetermined amount of the heat conductive filler to the polyamic acid solution containing a solvent obtained by preliminarily polymerizing, and dispersing with a stirrer or the like. And a method in which a diamine and an acid anhydride are added and polymerization is performed while dispersing a thermally conductive filler in a solvent. 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, after the aromatic diamine component is dissolved in a solvent such as N, N-dimethylacetamide under a nitrogen stream, an aromatic tetracarboxylic dianhydride is added and reacted at room temperature for about 3 hours. An acid is obtained.

  The preferred degree of polymerization of the polyamic acid suitable for the purpose of forming a high-density filler-containing polyimide resin layer is preferably in the range of, for example, a solution viscosity of 5 to 2,000 P when expressed in its viscosity range, More preferably within the range of 300P. If it is the said viscosity range, even if it mix | blends a heat conductive filler, it can maintain a uniform dispersion state. The solution viscosity can be measured with a cone plate viscometer with a thermostatic water bath. Examples of the solvent include N, N-dimethylacetamide, n-methylpyrrolidinone, 2-butanone, diglyme, xylene, and the like, and these can be used alone or in combination of two or more.

  As described above, in the metal-clad laminate of the present embodiment, the type and content of the heat conductive filler are within an appropriate range, and the polyimide raw material to be used is selected. As a result, it has a practical adhesive strength between the metal layer and the polyimide resin layer containing a high density of filler without interposing an adhesive layer, and the insulating layer has sufficient heat resistance and excellent thermal conductivity. It will be. In addition, the metal-clad laminate of the present embodiment has excellent handling characteristics during mass production and processing because of its small warpage. Therefore, the metal-clad laminate of the present embodiment can be widely used industrially as a substrate material for electronic devices and lighting devices that are required to have high heat dissipation. For example, the metal-clad laminate is representative of a heat dissipation substrate and a flexible substrate. It is particularly suitable for use in applications such as circuit boards.

The abbreviations used in the examples represent the following compounds.
m-TB: 2,2′-dimethyl-4,4′-diaminobiphenyl TPE-R: 1,3-bis (4-aminophenoxy) benzene BAPP: 2,2-bis [4- (4-aminophenoxy) Phenyl] propane 4,4′-DAPE: 4,4′-diaminodiphenyl ether APB: 1,3-bis (3-aminophenoxy) benzene BTDA: 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride PMDA: pyromellitic dianhydride BPDA: 3,3′4,4′-biphenyltetracarboxylic dianhydride DMAc: N, N-dimethylacetamide

  Moreover, the following evaluation method was followed about each characteristic evaluated in the Example.

[CCL curl (maximum warpage)]
The laminate was cut into a size of 50 mm × 50 mm, left in a constant temperature and humidity environment (23 ° C., 50% RH) for 24 hours, and then measured for the amount of warping at four corners using a caliper. At this time, when the warp was on the resin surface side, it was +, and when the warp was on the metal surface side, it was −, and the portion with the largest warp amount was defined as the CCL maximum warp amount. In this case, the case where the absolute value of the maximum warp amount was 15 mm or less was judged as “good”, and the case where it was 5 mm or less was judged as “excellent”.

[Copper foil peel strength (peel strength)]
The copper foil layer of the laminate was pattern-etched into a long rectangle having a width of 1.0 mm and a length of 180 mm, and a test piece was cut out to a width of 20 mm and a length of 200 mm so that the pattern was in the center, and IPC-TM-650. A 180 ° peeling test was performed according to 2.4.19 (manufactured by Toyo Seiki).

[Thickness direction thermal conductivity (λzTC)]
A sample of a polyimide film having a thickness of 100 μm was separately prepared with the same resin composition and blending amount of the heat conductive filler as in each of the examples and comparative examples. This polyimide film was cut into a size of 20 mm × 20 mm, subjected to vapor deposition with platinum and blackening treatment, and then the thermal diffusivity in the thickness direction by a laser flash method (Xenon flash analyzer LFA 447 Nanoflash manufactured by NETZSCH), specific heat by DSC, The density by the gas displacement method was measured, and the thermal conductivity (W / m · K) was calculated based on these results.

[Coefficient of thermal expansion (CTE)]
A polyimide film having a size of 3 mm × 15 mm is heated from 30 ° C. to 260 ° C. at a constant heating rate (20 ° C./min) while applying a 5 g load with a thermomechanical analysis (TMA) apparatus (manufactured by Seiko Instruments Inc.). A tensile test was performed in the temperature range, and the coefficient of thermal expansion (ppm / K) was measured from the amount of elongation of the polyimide film with respect to temperature.

[Glass transition temperature (Tg)]
Dynamic viscoelasticity when a polyimide film (10 mm × 22.6 mm) is heated from 20 ° C. to 500 ° C. at a rate of 5 ° C./min with a dynamic thermoanalyzer (manufactured by TA Instruments). Was measured, and the glass transition temperature (tan δ maximum value: ° C.) was determined.

[appearance]
Visual judgment was performed on the surface of the insulating layer from which the metal layer of the laminate for a flexible substrate was removed. Samples having aggregates on the surface and having irregularities were evaluated as bad (x), and smooth samples were evaluated as good (◯).

Synthesis example 1
Under a nitrogen stream, 4,4′-DAPE (17.29 g, 0.0863 mol) was dissolved in 255 g of solvent DMAc with stirring in a 500 ml separable flask. BTDA (27.65 g, 0.0858 mol) was then added. Thereafter, the solution was stirred at room temperature for 3 hours to carry out a polymerization reaction to obtain a pale yellow viscous polyamic acid solution (P1).

Synthesis example 2
Under a nitrogen stream, BAPP (28.91 g, 0.070 mol) was dissolved in 255 g of solvent DMAc with stirring in a 500 ml separable flask. Then BPDA (1.067 g, 0.0036 mol) and PMDA (15.03 g, 0.069 mol) were added. Thereafter, the solution was stirred at room temperature for 3 hours to carry out a polymerization reaction, thereby obtaining a brownish brown viscous polyamic acid solution (P2).

Synthesis example 3
Under a nitrogen stream, m-TB (19.01 g, 0.090 mol) and TPE-R (2.91 g, 0.010 mol) were dissolved in 255 g of solvent DMAc with stirring in a 500 ml separable flask. Then BPDA (5.82 g, 0.020 mol) and PMDA (17.26 g, 0.079 mol) were added. Thereafter, the solution was stirred at room temperature for 3 hours to carry out a polymerization reaction to obtain a brownish brown viscous polyamic acid solution (P3).

Synthesis example 4
Under a nitrogen stream, APB (44.95 g, 0.154 mol) was dissolved in 210 g of solvent DMAc with stirring in a 500 ml separable flask. BPDA (45.05 g, 0.153 mol) was then added. Thereafter, the solution was stirred at room temperature for 3 hours to carry out a polymerization reaction to obtain a colorless viscous polyamic acid solution (P4).

Example 1
200 parts by weight of a polyamic acid solution (P1) having a solid content concentration of 15 wt%, and 73 parts by weight of aluminum nitride as a spherical filler [made by Tokuyama Corporation, trade name: AlN (H grade), spherical, average particle size 1.1 μm] Were mixed with a centrifugal stirrer until uniform, and then 40 parts by weight of DMAc was added and mixed again with a centrifugal stirrer until uniform, to obtain a polyamic acid solution containing a thermally conductive filler. This polyamic acid solution was applied so that the thickness after curing was 25 μm, and dried by heating at 130 ° C. to remove the solvent. Thereafter, heating is performed stepwise in a temperature range of 130 to 300 ° C. over 20 minutes, and the thermally conductive filler is dispersed in the polyimide resin on a 12 μm thick electrolytic copper foil (Ra = 0.11 μm). The insulating layer thus formed was formed to produce a metal-clad laminate. The content of aluminum nitride in this insulating layer is 50 vol%.

  In order to evaluate the characteristics of the insulating layer in the obtained metal-clad laminate, the copper foil was removed by etching to produce an insulating film (F1), and the glass transition temperature was evaluated. Moreover, the measurement of thermal conductivity was implemented with the sample of thickness 100nm prepared separately. The results are shown in Table 2. Further, Table 3 shows the results of the characteristic evaluation of the metal clad laminate.

Example 2
In the same manner as in Example 1 except that aluminum oxide (manufactured by Sumitomo Chemical Co., Ltd., trade name: AA-1.5, spherical, average particle size 1.5 μm) was used as the spherical filler, the metal-clad laminate and An insulating film (F2) was produced. In the same manner as in Example 1, the glass transition temperature, thermal conductivity, and characteristics of the metal-clad laminate were evaluated.

Example 3
A metal-clad laminate and an insulating film (F3) were used in the same manner as in Example 1 except that aluminum oxide (manufactured by Sumitomo Chemical Co., Ltd., trade name: AA-3, spherical, average particle size 3 μm) was used as the spherical filler. ) Was produced. In the same manner as in Example 1, the glass transition temperature, thermal conductivity, and characteristics of the metal-clad laminate were evaluated.

Comparative Example 1
A metal-clad laminate and an insulating film (F4) were produced in the same manner as in Example 1 except that P2 was used as the polyamide acid varnish. In the same manner as in Example 1, the glass transition temperature, thermal conductivity, and characteristics of the metal-clad laminate were evaluated.

Comparative Example 2
A metal-clad laminate and an insulating film (F5) were produced in the same manner as in Example 1 except that P3 was used as the polyamide acid varnish. In the same manner as in Example 1, the glass transition temperature, thermal conductivity, and characteristics of the metal-clad laminate were evaluated.

Comparative Example 3
A metal-clad laminate and an insulating film (F6) were produced in the same manner as in Example 1 except that P4 was used as the polyamide acid varnish and 50 parts by weight of additional DMAc was added. In the same manner as in Example 1, the glass transition temperature, thermal conductivity, and characteristics of the metal-clad laminate were evaluated.

Comparative Example 4
A metal-clad laminate and an insulating film (F7) were used in the same manner as in Example 1 except that aluminum oxide (manufactured by Electrochemical Co., Ltd., trade name: DAW-07, spherical, average particle size 7 μm) was used as the spherical filler. ) Was produced. In the same manner as in Example 1, the glass transition temperature, thermal conductivity, and characteristics of the metal-clad laminate were evaluated.

  The result of the said Example and a comparative example is as showing in Tables 1-3.

From the results shown in Tables 1 to 3, a thermoplastic polyimide resin synthesized using 4,4′-diaminodiphenyl ether was used as the diamine component, and 80 vol% or more of the thermally conductive filler had an average particle size of In the metal-clad laminates of Examples 1 to 3, which are spherical fillers having a diameter of 5 μm or less, the amount of warpage was suppressed to be small, and all of heat resistance, thermal conductivity, adhesiveness, and appearance were good. On the other hand, when a material other than 4,4′-diaminodiphenyl ether was used as the diamine component, Comparative Examples 1 and 2 had a large amount of warpage, and Comparative Example 3 had poor heat resistance. Moreover, in the comparative example 4 using the spherical filler whose average particle diameter exceeds 5 micrometers, the malfunction was recognized by the external appearance.

Claims (6)

A thermally conductive polyimide-metal substrate comprising a metal layer and an insulating layer laminated on the metal layer,
The insulating layer has a polyimide resin layer containing a high-density filler containing a thermally conductive filler in a range of 40 to 70 vol% in the polyimide resin,
The polyimide resin is a thermoplastic polyimide resin synthesized using 50 mol% or more of 4,4′-diaminodiphenyl ether as a diamine component with respect to the total diamine component, and having a glass transition point of 250 ° C. or higher.
80 vol% or more of the heat conductive filler in the high-density filler-containing polyimide resin layer is a spherical filler having an average particle diameter of 5 μm or less.   The thermally conductive polyimide-metal substrate according to claim 1, wherein the spherical filler is at least one selected from the group consisting of aluminum oxide and aluminum nitride.   3. The thermally conductive polyimide-metal substrate according to claim 1, wherein the insulating layer has a thickness of 5 to 40 μm, and the metal layer has a thickness of 5 to 50 μm.   The thermal conductivity according to any one of claims 1 to 3, wherein at least one surface of the insulating layer is in direct contact with the metal layer, and the insulating layer in direct contact with the metal layer is a high-density filler polyimide resin layer. Polyimide-metal substrate.   The thermal conductivity in the thickness direction of the insulating layer is 1.5 W / mK or more, and the adhesiveness with the metal layer is 0.5 kN / m or more. Thermally conductive polyimide-metal substrate. A flexible substrate comprising the thermally conductive polyimide-metal substrate according to any one of claims 1 to 5,
The flexible substrate, wherein the metal layer is a copper foil, and the surface roughness (Ra) of the adhesive surface with the insulating layer is in a range of 0.05 to 0.5 μm.