JP5235211B2 - Laminate for flexible substrate and thermally conductive polyimide film - Google Patents

Description

  The present invention relates to a laminate for a flexible substrate and a thermally conductive polyimide film that have an insulating layer excellent in heat conduction characteristics and are suitably used for a flexible circuit board.

  In recent years, there has been an increasing demand for downsizing and weight reduction of electronic devices typified by mobile phones. Accordingly, flexible circuit boards that are advantageous for downsizing and weight reduction of devices are widely used in the field of electronic technology. 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. With the recent miniaturization of electronic equipment, 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 equipment has attracted attention.

  Then, in order to provide the flexible circuit board excellent in heat dissipation, about the polyimide film which comprises an insulating layer, examination which makes the heat conductivity of thickness direction 0.1 W / m or more is made | formed (patent document 1). . Patent Document 2 describes a polyimide film composite material in which a thermally conductive filler is dispersed in a polyimide derived from siloxane diamine with respect to a thermally conductive polyimide film containing a thermally conductive filler.

  However, when these polyimide films are laminated on a conductor layer such as copper foil to obtain a laminate for a flexible substrate, it is usually necessary to use an epoxy-based adhesive or a thermoplastic resin as an adhesive. The interposition of the adhesive layer not only becomes a factor that hinders heat radiation generated in the conductor layer, but also causes deterioration in various characteristics such as heat resistance and flexibility required for a flexible substrate. Therefore, it has been desired to provide a laminate for a flexible substrate having a practical adhesive strength between the conductor layer and the insulating layer and suppressing a decrease in the thermal conductivity of the insulating layer, and a heat conductive polyimide film used in these. .

JP 2006-274040 A JP 2006-169533 A

  The present invention has an insulating layer with excellent heat conduction characteristics, has a practical adhesive strength between the conductor layer and the insulating layer, and also has good heat resistance, flex resistance, and dimensional stability required as a flexible wiring board An object of the present invention is to provide a laminate for a flexible substrate and a thermally conductive polyimide film.

  As a result of repeated studies to solve the above problems, the present inventors have at least a polyimide resin layer or a polyimide resin layer constituting a thermally conductive polyimide film of a laminate for a flexible substrate having a plurality of polyimide resin layers. It has been found that the above problem can be solved by forming one layer of a specific high thermal conductivity polyimide resin layer and further providing another resin layer, and the present invention has been completed.

（式中、Ａｒ₁はピロメリット酸二無水物の残基であり、Ｒは炭素数１〜６の低級アルキル基、低級アルコキシ基、フェニル基、フェノキシ基又はハロゲンである。）
That is, the present invention provides a flexible laminate having a metal layer on one or both sides of a polyimide resin layer (A1), and the polyimide resin layer (A1) has two or more different resin layers, A polyimide resin layer (i) in which a thermally conductive filler is contained in a range of 30 to 75 wt% in a polyimide resin in which at least one layer of the resin layer contains 50 to 95 mol% of a structural unit represented by the following general formula (1) And at least one layer is a polyimide resin layer (ii) having a glass transition temperature lower than that of the polyimide resin layer (i) by 20 ° C. or more and a glass transition temperature of 200 ° C. or more , and at least of the polyimide resin layer (ii) more is interposed between the metal layer and the polyimide resin layer (i), the layer in contact with the metal layer is a polyimide resin layer (ii), the thickness of the polyimide resin layer (i) is a polyimide trees A laminate for a flexible substrate, wherein at least 50% of the total thickness of the layer (A1).

(In the formula, Ar ₁ is a residue of pyromellitic dianhydride , and R is a lower alkyl group having 1 to 6 carbon atoms, a lower alkoxy group, a phenyl group, a phenoxy group, or a halogen.)

  In another aspect, the present invention provides a film composed of a flexible polyimide resin layer (A2), wherein the polyimide resin layer (A2) has two or more different resin layers, At least one layer is a polyimide resin layer (i) in which a thermally conductive filler is contained in a range of 30 to 75 wt% in a polyimide resin containing 10 to 95 mol% of the structural unit represented by the general formula (1), At least one layer is a polyimide resin layer (ii) having a glass transition temperature lower than that of the polyimide resin layer (i), and the thickness of the polyimide resin layer (i) is 50% or more of the total thickness of the polyimide resin layer (A2). The present invention relates to a thermally conductive polyimide film.

A preferred embodiment of the present invention will be described below.
1) Said laminated body for flexible substrates whose thickness of polyimide resin layer (i) is 70 to 95% of the thickness of a polyimide resin layer (whole), or said heat conductive polyimide film.
2) The linear expansion coefficient of the polyimide resin layer (A1) is 30 ppm / K or less, the thermal conductivity is 0.3 W / mK or more in the thickness direction λz of the polyimide resin layer, and 0.7 W / mK or more in the planar direction λxy, Said laminated body for flexible substrates whose peel strength of a polyimide resin layer and a metal layer is 0.8 kN / m or more.
3) The thermal conductivity of the polyimide resin layer (A2) is 30 ppm / K or less, the thermal conductivity is 0.3 W / mK or more in the thickness direction λz, and 0.7 W / mK or more in the planar direction λxy. Polyimide film.
4) Said laminated body for flexible substrates, or said heat conductive polyimide film whose tear propagation resistance of a polyimide resin layer (A1) or (A2) is 1.5-8 kN / m.
5) Said laminated body for flexible substrates or said heat conductive polyimide film whose glass transition temperature of a polyimide resin layer (i) is 310 degreeC or more.
6) The above flexible substrate, wherein the thermally conductive filler is at least one filler selected from silica, alumina, aluminum nitride, boron nitride, silicon nitride and magnesia, and has an average particle diameter in the range of 0.01 to 25 μm. Laminated body or the above-mentioned heat conductive polyimide film.

  Below, the laminated body for flexible substrates of this invention and a heat conductive polyimide film are demonstrated in detail.

  The laminate for a flexible substrate of the present invention has a metal layer on one or both sides of a polyimide resin layer, and the polyimide resin layer is composed of a plurality of layers. Moreover, although the heat conductive polyimide film of this invention does not have a metal layer for wiring formation, the polyimide resin layer is similarly comprised by multiple layers. And much description of the polyimide resin layer (A1) which comprises the laminated body for flexible substrates, and the polyimide resin layer (A2) which comprises a heat conductive polyimide film is common. Hereinafter, common portions will be described together. The description of the polyimide resin layer common to the polyimide resin layers (A1) and (A2) is understood as the description of both polyimide resin layers. In this case, the polyimide resin layer (A) is understood to represent both the polyimide resin layers (A1) and (A2).

  Among the plurality of polyimide resin layers, at least one layer is the polyimide resin layer (i), and at least one layer is the polyimide resin layer (ii). When it is necessary to distinguish between each polyimide resin layer and the entire polyimide resin layer composed of the polyimide resin layer, the latter is referred to as the polyimide resin layer (A) or the entire polyimide resin layer. It is called a resin layer.

  Examples of the metal layer serving as the conductor layer in the laminate for a flexible substrate 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. The preferable thickness range of the conductor layer is 5 to 50 μm, and more preferably 8 to 35 μm.

  The polyimide resin layer (A) has two or more different resin layers, and at least one of the resin layers is heated to a polyimide resin containing 10 to 95 mol% of the structural unit represented by the general formula (1). From the polyimide resin layer (ii) in which the conductive filler is contained in the range of 30 to 75 wt%, and at least one of the resin layers has a glass transition temperature lower than that of the polyimide resin layer (i). Become.

  The content ratio of the heat conductive filler in the polyimide resin layer (i) needs to be in the range of 30 to 75 wt%, and preferably in the range of 40 to 70 wt%. If the content of the heat conductive filler is less than 30 wt%, the heat dissipation characteristics when the electronic component such as a flexible circuit board is not sufficient, and if it exceeds 75 wt%, the flexibility of the laminate of the present invention is characteristic. The decrease is remarkable, and the strength of the polyimide resin layer is also decreased. The thermally conductive filler is preferably a highly thermally conductive filler, and specifically includes aluminum, copper, nickel, silica, diamond, alumina, magnesia, beryllia, boron nitride, aluminum nitride, silicon nitride, and silicon carbide. . Among these, at least one filler selected from silica, alumina, aluminum nitride, boron nitride, silicon nitride, and magnesia is preferable. Since the polyimide resin layer acts as an insulating layer, the filler blended in the polyimide resin layer (i) is suitable from that viewpoint. The filler shape is not particularly limited, and may be a plate shape, a needle shape, or a rod shape. It is also preferable to use a spherical filler and a plate-like filler in combination when the content of the heat conductive filler is increased and the balance with characteristics such as heat conductivity is taken into consideration.

  From the viewpoint of uniformly dispersing the filler in the thickness direction of the polyimide resin layer, the particle size of the thermally conductive filler is preferably in the range of 0.01 to 25 μm and preferably in the range of 1 to 8 μm. Is more preferable. If the average particle diameter of the heat conductive filler is less than 0.01 μm, the heat conduction inside each filler is reduced, and as a result, the heat conductivity of the polyimide resin layer is not improved and the particles are aggregated. It tends to occur and it may be difficult to disperse uniformly. On the other hand, if it exceeds 25 μm, the possible filling rate of the polyimide resin layer is lowered, and the polyimide resin layer tends to become brittle due to the filler interface.

Incidentally, as the heat conduction filler, if the filler shape using a plate-like or scale-shaped plate-like filler, in the present invention, the particle size is expressed by an average long diameter D _L. When using the plate-like filler, the preferred range of the average long diameter D _L is in the range of 0.1-15, particularly preferably from 0.5 to 10 [mu] m. As the plate filler, boron nitride is preferably used. If the average major axis D _L is less than 0.1 μm, the thermal conductivity is lowered and the plate-like effect is reduced. On the other hand, if it exceeds 15 μm, it is difficult to orient at the time of film formation. Here, the average major axis D _L means the average value of the longitudinal diameters of the plate-like fillers. The average diameter means the median diameter, and the mode diameter is preferably one peak within the above range, and this is the same for the spherical filler. The particle size of the heat conductive filler is also related to the thickness of the polyimide resin layer (i). The average particle diameter or average major axis of the thermally conductive filler is 70% or less, preferably 50% or less of the thickness of the polyimide resin layer (i).

  The polyimide resin which comprises a polyimide resin layer (i) contains 10-95 mol% of the structural unit represented by General formula (1), Preferably it contains 50-95 mol%.

In General Formula (1), Ar ₁ is a tetravalent organic group having one or more aromatic rings, and R is a lower alkyl group having 1 to 6 carbon atoms, a lower alkoxy group, a phenyl group, a phenoxy group, or a halogen. . Since Ar ₁ can be regarded as a residue of an aromatic tetracarboxylic acid that is a polyimide raw material, Ar ₁ is understood by showing a specific example of an aromatic tetracarboxylic acid. R can be regarded as a part of the residue of aromatic diamine which is a polyimide raw material.

  Specific examples of aromatic tetracarboxylic acids include pyromellitic dianhydride (PMDA), 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride, 2,2', 3,3'-benzophenone Tetracarboxylic dianhydride, 2,3,3 ', 4'-benzophenonetetracarboxylic 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-dichloronaphthalene-1,4,5,8-tetracarboxylic acid Anhydride, 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 Anhydride, 2,2-bis (3,4-dicarboxyphenyl) -propane dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) methane Anhydride, bis (3.4-dicarboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) Hong dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-di Carboxyphenyl) 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, 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, 4,4 ' -Oxydiphthalic dianhydride It is.

As the structural unit other than the structural unit represented by the general formula (1), the aromatic tetracarboxylic acid residue which is a polyimide raw material and the aromatic diamine residue will be described separately. Examples of the residue include the same aromatic tetracarboxylic acid residues as those described above for Ar ₁ .

  Examples of the aromatic diamine residue include the following aromatic diamine residues. For example, 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, 3,3'- Diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 2,2-bis [4- (4-amino Phenoxy) phenyl] propane 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 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-amino (Cyclohexyl) 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-diamino Lysine, 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.

  When synthesizing the polyimide resin constituting the polyimide resin layer (i), each of the diamine and acid anhydride may be used alone or in combination of two or more. At least one of these uses 2 or more types. Preference is given to using diamines which give structural units of the general formula (1) such as 2,2′-dimethyl-4,4′-diaminobiphenyl as diamines and in addition to those represented by the general formula (1). It is better to use other diamines that give structural units that are not.

  In the present invention, since the polyimide resin layer (i) contains a thermally conductive filler, it is necessary to maintain the mechanical strength while maintaining the excellent heat resistance and dimensional stability of the polyimide resin. From such a viewpoint, as the other diamine, an aromatic diamine having a structure having less rigidity than the diamine that gives the structural unit represented by the general formula (1) is suitable. Advantageously, the diamine component contains 2,2'-dimethyl-4,4'-diaminobiphenyl as the main component, which includes 1,3-bis (3-aminophenoxy) benzene and 1,3-bis (4-amino). At least one diamine selected from phenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 3,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl ether as another diamine, It is preferable to use pyromellitic dianhydride as the main component for the anhydride. The proportion of other diamine used is preferably in the range of 5 to 50 mol%.

  The polyimide resin layer (ii) needs to have a glass transition temperature (Tg) lower than that of the polyimide resin layer (i), but a thermoplastic polyimide resin layer having a Tg of 200 ° C. or higher is preferable. More preferably, it is a thermoplastic resin having a Tg in the range of 200 to 350 ° C., and is a layer having a Tg lower by 20 ° C. or more than the polyimide resin layer (i), that is, the polyimide resin constituting the polyimide resin layer (i). It is good. On the other hand, since the polyimide resin layer (i) becomes a base layer having a thickness of 50% or more of the polyimide layer, the Tg is also preferably high, preferably 310 ° C. or higher, and in the range of 350 to 450 ° C. Is more preferable. As the polyimide resin constituting the polyimide resin layer (ii), a known polyimide resin can be used as long as the above physical properties are satisfied, and it can be obtained from the acid dianhydride component and the diamine component described above.

  Acid dianhydride components used to produce the polyimide resin layer (ii) include pyromellitic dianhydride (PMDA), 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (BPDA) ), 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3', 4,4'-diphenylsulfone tetracarboxylic dianhydride (DSDA), 4,4'- Aromatic dianhydrides such as oxydiphthalic dianhydride (ODPA) are exemplified. Examples of the diamine component include 2,2-bis (4-aminophenoxyphenyl) propane (BAPP), bis [4- (4-aminophenoxy) phenyl] sulfone (BAPS), 3,4′-diaminodiphenyl ether (3 , 4'-DAPE), 4,4'-diaminodiphenyl ether (4,4'-DAPE), 1,4-bis (4-aminophenoxy) benzene (TPE-Q), 4,4'-bis (4- Aminophenoxy) biphenyl (BAPB), 1,3-bis (3-aminophenoxy) benzene (APB), 1,3-bis (4-aminophenoxy) benzene (TPE-R), 1,3-bis (4- Aromatic diamines such as aminophenoxy) -2,2-dimethylpropane (DANPG) are preferred.

  Although it is preferable that a polyimide resin layer (ii) does not contain a filler, you may contain a heat conductive filler in a fixed ratio as needed. Since the polyimide resin layer (ii) is provided mainly to increase the adhesive force with the metal layer, the thickness is preferably thin, and is preferably 3 μm or less.

  When the polyimide resin layer (ii) contains a heat conductive filler, it is preferably smaller than the content of the heat conductive filler in the polyimide resin layer (i). Moreover, it is preferable that the content rate is the range of 1-50 wt%, and the range of 10-40 wt% is more preferable. When the content rate of a heat conductive filler exceeds 50 wt%, adhesiveness will be inferior and the intensity | strength of a polyimide resin layer will also fall. In addition, when containing a heat conductive filler, it is preferable that the size is small, The preferable average particle diameter is 3 micrometers or less, and the range of 0.01-1.0 micrometer is more preferable. If the average particle size of the thermally conductive filler exceeds 3 μm, the filler cannot be uniformly dispersed and the surface becomes rough, which may reduce the adhesion to the metal layer, but less than 0.01 μm. In this case, the particles tend to aggregate and it is difficult to uniformly disperse the particles.

  The thickness of the polyimide resin layer (i) with respect to the total thickness of the polyimide resin layer (A) needs to be 50% or more, and preferably in the range of 70 to 95%. When the thickness of the polyimide resin layer (i) is less than 50%, not only the heat dissipation is not sufficient, but also when used as a flexible substrate, the dimensional stability is not sufficient and the heat resistance is low. The total thickness of the polyimide resin layer (A) is preferably in the range of 10 to 50 μm, and more preferably in the range of 15 to 40 μm. If the thickness of the polyimide resin layer is less than 10 μm, it is brittle and easily broken, while if it exceeds 50 μm, the bending resistance tends to decrease.

  The polyimide resin layer (A) of the laminate for a flexible substrate or the heat conductive polyimide film of the present invention has a linear expansion coefficient of 30 ppm / K or less, preferably 1 to 25 ppm / K, and a thermal conductivity of the polyimide resin layer. In the thickness direction λz, 0.3 W / mK or more, preferably 0.5 to 0.8 W / mK or more, and in the plane direction λxy, 0.7 W / mK or more, preferably 1.0 to 2.0 W / mK. The above is preferable.

  In the laminate for a flexible substrate of the present invention, the peel strength between the polyimide resin layer (A1) and the metal layer is preferably 0.8 kN / m or more, more preferably 1.0 to 1.8 kN / m.

  In order to obtain such a laminate for a flexible substrate and a heat conductive polyimide film, the thickness range of the polyimide resin layer (i) and the polyimide resin layer (ii) and the type and content of the heat conductive filler are set within an appropriate range. It is also possible by selecting the polyimide raw material to be used. When the linear expansion coefficient of the polyimide resin layer (A) exceeds 30 ppm / K, various problems such as curling and the shrinkage of the polyimide resin layer (A) being too large to be processed well can occur. If the thermal conductivity is less than 0.5 W / mK, the heat dissipation characteristics are degraded.

  The laminate for flexible substrate of the present invention or the polyimide resin layer (A) of the heat conductive polyimide film of the present invention preferably has a tear propagation resistance of 1.5 to 8 kN / m. If the tear propagation resistance is less than 1.5 kN / m, the flexible circuit board may be torn during processing or breakage. If the tear propagation resistance of the polyimide resin layer (A) exceeds 8 kN / m, the thermal expansion coefficient of the polyimide resin layer (A) increases and the dimensional stability tends to deteriorate. In order to set the tear propagation resistance of the polyimide resin layer (A) to 1.5 to 8 kN / m, the thickness of the polyimide resin layer (i) is set to 50% or more of the total thickness and represented by the general formula (1). It is preferable to contain 50 mol% or more of structural units. Furthermore, it is preferable that the glass transition temperature of the polyimide resin layer (i) is 310 ° C. or higher, but in this case as well, the thickness of the polyimide resin layer (i) is 50% or more and is represented by the general formula (1). It becomes controllable by containing 50 mol% or more of structural units.

  In the laminate for a flexible substrate of the present invention, at least one layer of the polyimide resin layer (A1) is formed by a polyimide resin layer (i) containing a thermally conductive filler in a polyimide resin, and further a metal layer and a polyimide resin layer (i ) Is provided with a polyimide resin layer (ii) having a good metal layer and adhesive layer. The polyimide resin layer (i) and the polyimide resin layer (ii) may each be provided in the polyimide resin layer (A), or one or both may be provided in two or more layers. However, increasing the number of layers causes problems such as an increase in the number of processes, so the polyimide resin layer (i) is one layer, the polyimide resin layer (ii) is one or two layers, and the layer in contact with the metal layer is polyimide resin. Layer (ii) is preferred. When providing a metal layer on both surfaces, it is good to make two layers which touch a metal layer into a polyimide resin layer (ii).

  Although the heat conductive polyimide film of the present invention does not have a metal layer, the polyimide resin layer (A2) has a layer structure similar to that of the polyimide resin layer (A1), and is suitable for use by being laminated on the metal layer. Film.

  Furthermore, the polyimide resin layer (A) can be provided with other polyimide resin layers in addition to the polyimide resin layer (i) and the polyimide resin layer (ii). However, providing other polyimide resin layers has disadvantages such as an increased number of synthesis steps. It is preferable that the ratio of the thickness of the polyimide resin layer (i), the polyimide resin layer (ii), and other polyimide resin layers (the total in the case of multiple layers) to the polyimide resin layer (A) is in the following range. . The polyimide resin layer (i) is 50 to 95%, preferably 70 to 95%. The polyimide resin layer (ii) is 5 to 50%, preferably 5 to 30%. The other polyimide resin layer is 0 to 30%, preferably 0 to 10%.

The polyimide resin layer (A) having two or more resin layers is prepared by directly applying a polyamic acid (formal name; polyamic acid, the same shall apply hereinafter) solution , which is a precursor of the polyimide resin layer, onto an appropriate support a plurality of times. It can be formed by applying, drying and curing. Here, if metal foils, such as copper foil mentioned above, are used for a support body as a conductor layer of a wiring board, it can be set as the laminated body for flexible substrates. Moreover, if a laminated body is formed using a glass plate, metal foil, etc. as a support body and a polyimide resin layer is removed from a support body by means, such as peeling, it can be set as a heat conductive polyimide film.

  In this invention, since a polyimide resin layer is made into multiple layers, 2 or more types are used for a polyamic acid solution, and at least 1 type shall contain a heat conductive filler. The polyamic acid solution can be applied by a known method, for example, by appropriately selecting from a bar code method, a gravure coating method, a roll coating method, a die coating method and the like.

  In order to explain the present invention more clearly, an example of its production will be shown by taking as an example a laminate for a flexible substrate having metal layers on both sides of a polyimide resin layer. First, a metal foil such as a copper foil constituting the metal layer of the laminate for a flexible substrate is prepared, and a polyamic acid solution for forming a polyimide resin layer (ii) is applied on the metal foil and dried at a temperature of 140 ° C. or lower. After removing a certain amount of solvent, a polyamic acid solution for forming the polyimide resin layer (i) containing filler is applied and dried. Next, a polyamic acid solution for forming the polyimide resin layer (ii) is again applied thereon and dried to form a plurality of polyamic acid layers. Thereafter, the polyamic acid is imidized by heat treatment at a higher temperature to obtain a laminate having a metal layer on one side of the polyimide resin layer. Here, the heat treatment conditions for imidization are preferably 150 to 360 ° C. and stepwise for about 15 to 20 minutes. And the laminated body for double-sided flexible substrates which has metal foil on both surfaces by laminating | stacking metal foil, such as copper foil, on the polyimide resin layer side of the laminated body which has a metal layer on one side obtained in this way by thermocompression bonding is Can get.

Although it does not specifically limit about the hot press temperature at the time of the said thermocompression bonding, It is desirable that it is more than the glass transition temperature of the polyimide resin to be used. The hot press pressure is preferably in the range of 1 to 500 kg / cm ² , although it depends on the type of press equipment used. The metal foil used at this time can be the same as the metal foil described above. The laminate for a flexible substrate of the present invention may be a laminate for a single-sided flexible substrate having a conductor layer only on one side, or a laminate for a double-sided flexible substrate having a metal foil on both sides.

  In addition, the laminate for a single-sided flexible substrate is coated with a polyamic acid solution for forming a polyimide resin layer (ii) on a metal foil, dried at a temperature of 140 ° C. or less to remove a certain amount of solvent, and then filled with polyimide. The polyamic acid solution for forming the resin layer (i) can be obtained by a method such as imidization by heat treatment at a high temperature after being applied and dried.

  The polyamic acid solution containing the thermally conductive filler used in the present invention can be obtained by, for example, adding a certain amount of thermally conductive filler to a polyamic acid solution containing a solvent obtained by polymerization in advance and dispersing with a stirrer or the like. Examples thereof include a preparation method and a method in which a diamine and an acid anhydride are added and polymerized while dispersing a thermally conductive filler in a solvent.

  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, it can be obtained by dissolving the diamine in a solvent such as N, N-dimethylacetamide under a nitrogen stream, adding aromatic tetracarboxylic dianhydride, and reacting at room temperature for about 3 hours. The preferable degree of polymerization of the polyamic acid suitable for forming the polyimide resin layer is, when expressed in the viscosity range, the solution viscosity is in the range of 5 to 2,000 P, and more preferably in the range of 10 to 300 P. 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.

  EXAMPLES Hereinafter, although the content of this invention is demonstrated concretely based on an Example, this invention is not limited to the range of these Examples.

The abbreviations used in the examples represent the following compounds.
m-TB: 2,2′-dimethyl-4,4′-diaminobiphenyl 4,4′-DAPE: 4,4′-diaminodiphenyl ether TPE-R: 1,3-bis (4-aminophenoxy) benzene BAPP: 2,2-bis (4-aminophenoxyphenyl) propane PMDA: pyromellitic dianhydride BPDA: 3,3′4,4′-biphenyltetracarboxylic acid ODPA: 4,4′-oxydiphthalic acid dianhydride DMAc: N, N-dimethylacetamide

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

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

[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 ° peel test was conducted according to 2.4.19. In the table, those where the peel strength exceeded the measurement limit and an accurate value was not obtained were expressed as> 1.6.

[Thickness direction thermal conductivity (λzTC)]
The polyimide resin film was cut into a size of 30 mm x 30 mm, and the thermal diffusivity in the thickness direction by the periodic heating method (FTC-1 apparatus made by ULVAC-RIKO), the specific heat by DSC, and the density by the underwater substitution method were measured. Based on this, the thermal conductivity (W / m · K) was calculated.

[Surface direction thermal conductivity (λxyTC)]
A polyimide resin film is cut into a size of 30 mm × 30 mm, and the thermal diffusivity in the surface direction by the optical alternating current method (Laser PIT device manufactured by ULVAC-RIKO), the specific heat by DSC, and the density by the underwater substitution method are measured, respectively. And thermal conductivity (W / m · K) was calculated.

[Coefficient of thermal expansion (CTE)]
A tensile test is performed on a polyimide resin film of 3 mm × 15 mm in a temperature range 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. The linear expansion coefficient (ppm / K) was measured from the elongation amount of the polyimide film with respect to temperature.

[Glass transition temperature (Tg)]
When a polyimide resin film (10 mm × 22.6 mm) is heated at a rate of 5 ° C./min from 20 ° C. to 500 ° C. with a dynamic thermal instrument analyzer (official name; dynamic viscoelasticity measuring device (DMA)) The dynamic viscoelasticity was measured to determine the glass transition temperature (tan δ maximum value: ° C.).

[Tear Propagation Resistance (TPR)]
A 63.5 mm × 50 mm polyimide resin film was used as a test piece, a 12.7 mm length cut was made in the test piece, and measurement was performed using a light load tear tester manufactured by Toyo Seiki.

[Film MIT]
Using a MIT fatigue resistance tester DA type manufactured by Toyo Seiki Seisakusho Co., Ltd., a polyimide resin film cut into a strip shape having a width of 10 mm and a length of 140 mm was prepared as a test piece, load 500 g, bending angle 135 °, bending Under the measurement conditions of a speed of 175 rpm and a bending radius R = 0.38 mm, the number of bendings until the film broke was determined. Evaluation criteria were determined as follows according to the number of flexing.
Film ○: More than 5,000 times of bending
Δ: Number of flexion 1,000 times or more and less than 5,000 times
×: Number of bendings is less than 1,000 or measurement is impossible

[Laminate MIT]
A laminated body having a copper foil on one side is subjected to circuit processing so that a 12.5 μm-thick polyimide film faces a 25 μm epoxy adhesive layer on the surface on which the circuit is formed, and 18.3 kgf / cm ² A test piece was obtained by thermocompression bonding using a high-temperature vacuum press under conditions of pressure and 170 ° C. for 30 minutes. Using a MIT fatigue resistance tester DA type manufactured by Toyo Seiki Seisakusho Co., Ltd., a metal laminate MIT test piece cut into a strip shape having a width of 10 mm and a length of 150 mm was prepared as a test piece, and the load was 500 g and the bending angle was 135. The number of bendings until the circuit was disconnected was determined under the measurement conditions of °, bending speed 175 rpm, bending radius R = 0.38 mm. Evaluation criteria were determined as follows according to the number of flexing.
Laminate ○: Number of flexion 1,000 times or more
△: Number of bendings 100 times or more and less than 1,000 times
×: Number of bending times is less than 100 times or measurement is not possible

Synthesis Examples 1-10
In order to synthesize polyamic acids A to J, a 500 ml separable flask equipped with a stirrer was immersed in a water bath of an ultrasonic device, and a highly thermally conductive spherical alumina filler (with a maximum particle size of 15 μm, an average particle size of 0.6 μm filler 20 wt% mixed filler, specific surface area 0.65 m ² / g) and DMAc were added and stirred for about 2 hours while irradiating with ultrasonic waves. Next, the diamine shown in Table 1 was added and dissolved while stirring, and then the tetracarboxylic dianhydride shown in Table 1 was added while maintaining stirring. Then, the polymerization reaction was continued for 3.5 hours at room temperature to obtain a viscous solution of polyamic acids A to J as polyimide precursors. In addition, the numerical value of the diamine in Tables 1-2, tetracarboxylic dianhydride, and a filler represents the weight part of each component. Moreover, although the content rate of an alumina filler is shown collectively, in the synthesis example 10, the alumina filler is not used.

Synthesis Example 11
As the spherical alumina filler, a filler having a maximum particle size of 4.0 μm and an average particle size of 0.3 μm was used, and the diamine and tetracarboxylic dianhydride shown in Table 2 were used in the same manner as in Synthesis Examples 1 to 9. Thus, a viscous solution of polyamic acid K serving as a polyimide precursor was obtained.

Synthesis Example 12
In order to synthesize polyamic acid L, a 500 ml separable flask equipped with a stirrer was added and dissolved with stirring with the diamine shown in Table 2 under a nitrogen stream. Tetracarboxylic dianhydride was added. Thereafter, the polymerization reaction was continued for 3.5 hours at room temperature to obtain a viscous solution of polyamic acid serving as a polyimide precursor. The polyamic acid was mixed with a filler having an average major axis of 4.5 μm as a plate-like boron nitride filler, and mixed with a centrifugal stirrer until uniform to obtain a polyamic acid solution L containing 30 wt% filler.

Synthesis Example 13
A polyamic acid solution M was obtained in the same manner as in Synthesis Example 12 except that the blending ratio of the plate-like boron nitride filler to be blended with the polyamic acid was 50 wt%.

Synthesis Example 14
A polymerization reaction was performed using the monomer raw materials shown in Table 2 to obtain a viscous polyamic acid solution. This polyamic acid is mixed with a plate-like boron nitride filler having an average major axis of 4.5 μm and a spherical alumina filler having an average particle size of 3 μm, and mixed with a centrifugal stirrer until uniform, to obtain a polyamic acid solution N containing 50 wt% filler. It was. Here, the ratio between the plate-like boron nitride filler and the spherical alumina filler was 50 wt%.

Synthesis Example 15
A polymerization reaction was performed using the monomer raw materials shown in Table 2 to obtain a viscous polyamic acid solution. This polyamic acid is mixed with a plate-like boron nitride filler having an average major axis of 4.5 μm and a spherical alumina filler having an average particle size of 3 μm, and mixed with a centrifugal stirrer until uniform, and a polyamic acid solution O containing 50 wt% filler is added. Obtained. At this time, the ratio between the plate-like boron nitride filler and the spherical alumina filler was 50 wt%.

  Each of the solutions of polyamic acids A to O obtained in Synthesis Examples 1 to 15 is applied onto a copper foil using an applicator, and is applied so that the thickness after curing is about 25 μm. The laminate was dried for 30 minutes and heated in a stepwise manner in the temperature range of 130 to 360 ° C. over 30 minutes to form a laminate. About this laminated body, the copper foil was etched away using the ferric chloride aqueous solution, and it was set as the polyimide film. The results of measuring the glass transition temperature (Tg) and the linear expansion coefficient (CTE) of the polyimide film thus obtained are shown in Tables 1-2.

Example 1
On a copper foil having a thickness of 18 μm (rolled copper foil, Rz = 0.7 μm), the solution of the polyamic acid resin J obtained in Synthesis Example 10 was applied so that the thickness after curing was 2 μm, at 120 to 140 ° C. The solvent was removed by heating and drying. Next, the solution of polyamic acid resin B obtained in Synthesis Example 2 was applied thereon so that the thickness after curing was 23 μm, and dried by heating at 120 ° C. to remove the solvent. Then, it heated up in steps over 30 minutes in the temperature range of 130-360 degreeC, and produced the laminated body M1 for flexible substrates which consists of two polyimide layers on copper foil. The thickness of the polyimide layer on the copper foil is 2/23 μm in the order of J / B from the copper foil side. In order to evaluate the characteristics of the polyimide resin layer in the laminate for a flexible substrate, the copper foil was etched away in the same manner as described above to produce a polyimide resin film M1, and CTE, thermal conductivity, tear propagation resistance (TPR), and MIT were determined. Each was evaluated. Further, the flexibility of the laminate for a flexible substrate and the peel strength between the polyimide resin layer and the copper foil were evaluated. The polyimide resin film obtained from the laminate M1 is referred to as film M1, and the same shall apply hereinafter.

Example 2
A laminate M2 and a film M2 were obtained in the same manner as in Example 1 except that the polyamic acid resin G obtained in Synthesis Example 7 was used instead of the polyamic acid resin B.

Comparative Examples 1 and 2
In place of the polyamic acid resin B, the laminates M3 and M4 and the film M3 were obtained in the same manner as in Example 1, except that the polyamic acid resins D and E having a spherical alumina filler content of 20 wt% and 80 wt%, respectively, were used. , M4 was obtained. In addition, since the film M4 was brittle and easily cracked under pressure, the thermal conductivity in the thickness direction could not be measured.

Comparative Examples 3, 4, 5
In the same manner as in Example 1, laminates M5, M6, and M7 and films M5, M6, and M7 were obtained using the polyamic acid resins F, H, and I obtained from Synthesis Examples 6, 8, and 9, respectively. In addition, since the film M5 was brittle and easily cracked under pressure, the thermal conductivity in the thickness direction could not be measured.

Example 3
On the same copper foil as used in Example 1, a solution of polyamic acid resin J was applied to a thickness of 2 μm after curing, and dried by heating at 120 ° C. to remove the solvent. Next, the solution of polyamic acid resin A obtained in Synthesis Example 1 was applied thereon so that the thickness after curing was 21 μm, and dried by heating at 120 ° C. to remove the solvent. Further, a solution of polyamic acid resin J was applied thereon so that the thickness after curing was 2 μm, and dried by heating at 120 ° C. to remove the solvent. Then, it heated up in steps over 30 minutes in the temperature range of 130-360 degreeC, and produced the laminated body M8 for wiring boards which consists of a three-layer polyimide layer on copper foil. The thickness of the polyimide layer on the copper foil is 2/19/2 μm in the order of J / A / J from the copper foil side. In the same manner as in Example 1, a film M8 was obtained from the laminate M8 and evaluated in the same manner.

Examples 4 to 10, Comparative Example 6
Laminated bodies M9 to M16 and films M9 to M16 were obtained and evaluated in the same manner as in Example 3 except that the type of polyamic acid resin used was changed and the configuration of the polyimide resin layer was changed.

  Table 3 shows the evaluation results and layer structure of the laminate, and Table 4 shows the evaluation results of the polyimide resin film. In Table 3, the thickness indicates the thickness of each resin layer constituting the film layer.

Industrial applicability

  ADVANTAGE OF THE INVENTION According to this invention, it is excellent in heat dissipation and the laminated body for flexible substrates and heat conductive polyimide film which are used suitably for a flexible circuit board can be provided. These flexible substrate laminates and thermally conductive polyimide films exhibit good heat dissipation and excellent adhesion to metal layers, so small electronic devices such as mobile phones and notebook computers that require these characteristics. Can be suitably used.

Claims (12)

In a flexible laminate having a metal layer on one or both sides of a polyimide resin layer, the polyimide resin layer has two or more different resin layers, and at least one of the resin layers is represented by the following general formula (1). A polyimide resin layer (i) in which a thermally conductive filler is contained in a range of 30 to 75 wt% in a polyimide resin containing 50 to 95 mol% of the structural unit represented, at least one layer being from the polyimide resin layer (i). Is a thermoplastic polyimide resin (ii) having a glass transition temperature of 20 ° C. or higher and a glass transition temperature of 200 ° C. or higher. At least one of the polyimide resin layers (ii) is composed of a metal layer and a polyimide resin layer (i). The polyimide resin layer (ii) is a layer in contact with the metal layer, and the thickness of the polyimide resin layer (i) is 50 times the total thickness of the polyimide resin layer. Laminate for a flexible substrate, characterized in that at least.

Here, Ar ₁ is a residue of pyromellitic dianhydride , and R is a lower alkyl group having 1 to 6 carbon atoms, a lower alkoxy group, a phenyl group, a phenoxy group, or a halogen.   The laminate for a flexible substrate according to claim 1, wherein the thickness of the polyimide resin layer (i) is 70 to 95% of the total thickness of the polyimide resin layer. The linear expansion coefficient of the polyimide resin layer is 30 ppm / K or less, the thermal conductivity is 0.3 W / mK or more in the thickness direction λz of the polyimide resin layer, and 0.7 W / mK or more in the planar direction λxy. The laminate for a flexible substrate according to claim 1 or 2 , wherein a peel strength with the layer is 0.6 kN / m or more. The laminate for a flexible substrate according to any one of claims 1 to 3, wherein the tear propagation resistance of the polyimide resin layer is 1.5 to 8 kN / m. The laminate for a flexible substrate according to any one of claims 1 to 4, wherein the glass transition temperature of the polyimide resin layer (i) is 310 ° C or higher. The heat conductive filler is at least one filler selected from silica, alumina, aluminum nitride, boron nitride, silicon nitride, and magnesia, and has an average particle diameter in the range of 0.01 to 25 µm . The laminated body for flexible substrates in any one . In the flexible film which consists of a polyimide resin layer, this polyimide resin layer has two or more different resin layers, and at least one layer of the resin layer contains 50 to 50 structural units represented by the following general formula (1). A polyimide resin layer (i) containing 95 mol% of a polyimide resin containing a heat conductive filler in a range of 30 to 75 wt%, and at least one layer has a glass transition temperature of 20 ° C. or higher than that of the polyimide resin layer (i). It is a low-temperature thermoplastic polyimide resin layer (ii) having a glass transition temperature of 200 ° C. or higher, and the thickness of the polyimide resin layer (i) is 50% or more of the total thickness of the polyimide resin layer. Thermally conductive polyimide film.

Here, Ar ₁ is a residue of pyromellitic dianhydride , and R is a lower alkyl group having 1 to 6 carbon atoms, a lower alkoxy group, a phenyl group, a phenoxy group, or a halogen.   The thermally conductive polyimide film according to claim 7, wherein the thickness of the polyimide resin layer (i) is 70 to 95% of the total thickness of the polyimide resin layer. The thermal conductivity according to claim 7 or 8 , wherein the linear expansion coefficient of the polyimide resin layer is 30 ppm / K or less, the thermal conductivity is 0.3 W / mK or more in the thickness direction λz, and 0.7 W / mK or more in the planar direction λxy. Conductive polyimide film. The thermally conductive polyimide film according to any one of claims 7 to 9, wherein the tear propagation resistance of the polyimide resin layer is 1.5 to 8 kN / m. The thermally conductive polyimide film according to any one of claims 7 to 10, wherein the glass transition temperature of the polyimide resin layer (i) is 310 ° C or higher. Thermally conductive filler is silica, alumina, aluminum nitride, boron nitride, at least one filler selected from silicon nitride and magnesia, any claim 7 to 11 having an average particle diameter in the range of 0.01~25μm The heat conductive polyimide film of crab .