KR20190108214A - flexible metal clad laminate - Google Patents

Abstract

The present invention relates to a soft metal foil clad laminate and, more specifically, to a soft metal foil clad laminate for a cross section, which has excellent adhesion to prepreg.

Description

Flexible metal clad laminate

The present invention relates to a flexible metal laminate. More specifically, the present invention relates to a flexible metal laminate for cross section having excellent adhesion to prepreg.

Flexible Metal Clad Laminate (FPCB) is used as a basic raw material for FPCB products that make up the circuit of electronic devices such as smartphones.

Recently, in accordance with the development of electronic devices and the demand for complex functions, high-speed transmission, low weight, thinness, and miniaturization of flexible printed circuit boards are progressing day by day. In order to meet these demands, fine patterning is progressing in terms of processing flexible printed circuit boards.

Substrates of electronic devices such as printed circuit boards are prepared by heating and pressing prepregs, such as epoxy resin-impregnated glass substrates, onto flexible metal foil laminates in which copper foils and polyimide layers are laminated to produce copper foil laminates, and etching them to form a network. And a device such as a semiconductor device is mounted thereon.

In order to improve the adhesion between the polyimide layer and the prepreg, such a substrate has generally been subjected to surface treatment such as atmospheric pressure plasma or reduced pressure plasma. However, there is a problem in that the yield is reduced and the productivity is lowered when treating such a surface treatment process, especially a reduced pressure plasma.

In addition, there is a study to improve the adhesive strength with prepreg by including an epoxy additive in the production of polyimide layer, but it is difficult to apply because it may decompose during heat treatment at a high temperature of polyimide curing temperature and contaminate the actual commercial line. have.

An object of the present invention is to provide a ductile metal laminate having excellent adhesion to a prepreg without containing an epoxy additive and without surface treatment of a polyimide layer.

More specifically, an object of the present invention is to provide a soft metal laminate having an adhesive strength with prepreg of 0.8 kgf / cm or more at room temperature.

In addition, the present invention is to provide a flexible metal laminate for the cross-section while being a flexible metal laminate.

One aspect of the present invention is a flexible metal foil laminate in which a polyimide laminate including at least one or more layers of polyimide layers is laminated on one surface of a metal foil,

The outermost layer of the polyimide laminate is a flexible metal foil laminate in which the mass of the unit structure represented by the following Chemical Formula 1 is 30 to 40% by weight of the total monomer mass used in the outermost layer.

[Formula 1]

The flexible metal laminate of the present invention can provide a flexible metal laminate having an adhesive force of 0.8 kgf / cm or more at room temperature without a separate surface treatment on the polyimide layer facing the prepreg.

In addition, productivity may be improved since additives such as epoxy are not included.

DETAILED DESCRIPTION Hereinafter, the present invention will be described in more detail with reference to the accompanying examples or embodiments. However, the following specific examples or examples are only one reference for describing the present invention in detail, but the present invention is not limited thereto and may be implemented in various forms.

Also, unless defined otherwise, all technical and scientific terms have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used in the description in the present invention are only for effectively describing specific embodiments and are not intended to limit the present invention.

Also, the singular forms used in the specification and the appended claims may be intended to include the plural forms as well, unless the context clearly indicates otherwise.

One aspect of the present invention is a flexible metal foil laminate in which a polyimide laminate including at least one or more layers of polyimide layers is laminated on one surface of a metal foil,

The outermost layer of the polyimide laminate is a flexible metal foil laminate in which the mass of the unit structure represented by the following Chemical Formula 1 is 30 to 40% by weight of the total monomer mass used in the outermost layer.

[Formula 1]

In one embodiment of the present invention, the outermost layer is 4,4'-bisphenol A dianhydride represented by the following formula (2) and 2,2-bis [4- (4-aminophenoxy) phenyl represented by the following formula (3) ] Can be polyimide derived from any one or a mixture thereof selected from propane.

[Formula 2]

[Formula 3]

In one aspect of the invention, the outermost layer comprises 10 to 60 mol% of 4,4'-bisphenol A dianhydride in the acid anhydride monomer, and 2,2-bis [4- (4-aminophenoxy in the diamine monomer C) phenyl] propane may be included in an amount of 75 to 100 mol%.

In one embodiment of the present invention, the outermost layer may be that the adhesive force with the prepreg at room temperature of 0.8 kgf / cm or more.

In one aspect of the present invention, the flexible metal laminate may be one having a flexibility of 250 or more times.

Hereinafter, each configuration of the present invention will be described in more detail.

In one aspect of the present invention, the flexible metal laminate may include at least one or more layers, more specifically, one to three layers of a polyimide layer, but is not limited thereto. In addition, by including the structure represented by the formula (1) in the outermost layer of the polyimide layer can provide a flexible metal foil laminate excellent in flexibility while improving the adhesion to the prepreg.

More specifically, the first embodiment of the flexible metal laminate of the present invention may include a metal foil and a first polyimide layer laminated on one surface thereof. In this case, the first polyimide layer may include a unit structure represented by Formula 1 below. In addition, the prepreg may be laminated on the first polyimide layer.

[Formula 1]

More specifically, the first polyimide layer includes a polyimide derived from an acid anhydride and diamine, and the outermost layer is represented by 4,4'-bisphenol A dianhydride represented by the following Chemical Formula 2 and the following Chemical Formula 3. It may comprise a polyimide derived from any one or a mixture thereof selected from 2,2-bis [4- (4-aminophenoxy) phenyl] propane. That is, the acid anhydride includes 4,4'-bisphenol A dianhydride of formula (2), or diamine includes 2,2-bis [4- (4-aminophenoxy) phenyl] propane of formula (3) , May include all of them.

[Formula 2]

[Formula 3]

The second aspect of the flexible metal foil laminate of the present invention may include a metal foil and a polyimide laminate in which a first polyimide layer and a second polyimide layer are sequentially stacked on one surface thereof. In this case, the second polyimide layer may include a unit structure represented by Chemical Formula 1. In addition, the first polyimide layer may be used without limitation as long as it is a polyimide layer that is typically used in the art. In addition, the prepreg may be laminated on the second polyimide layer.

The third aspect of the flexible metal foil laminate of the present invention may include a metal foil and a polyimide laminate in which a first polyimide layer, a second polyimide layer, and a third polyimide layer are sequentially stacked on one surface thereof. In this case, the third polyimide layer may include a unit structure represented by Chemical Formula 1. In addition, the first polyimide layer and the second polyimide layer may be used without limitation as long as they are typically polyimide layers used in the art. In addition, the prepreg may be laminated on the third polyimide layer.

The first to third embodiments are not limited to the specific embodiments of the flexible metal laminate of the present invention.

The flexible metal laminate according to an aspect of the present invention includes a bisphenol A structure represented by Formula 1 in the polyimide layer of the outermost layer, and thus does not include an additive such as an additional surface treatment or epoxy, and thus adhesive strength with the prepreg. It is possible to express an excellent effect while being excellent in flexibility. However, the surface treatment of the outermost layer of the flexible metal laminate according to one embodiment of the present invention is not excluded. The surface treatment may include surface treatment such as plasma.

More specifically, the outermost layer may be 0.8 kgf / cm or more, more specifically 0.8 to 1.5 kgf / cm adhesive strength with the prepreg at room temperature. The room temperature is not limited but specifically, for example, may be 10 to 40 ℃. Since the adhesive force is applicable to the printed circuit board in the above range is preferable. More specifically, when evaluating the adhesion, the prepreg can be measured using the DS-7402 of Doosan Electronics.

In order to include the bisphenol A structure represented by Formula 1, at least any one or more of the acid anhydride and diamine used in the outermost layer may be used without limitation as long as it is a monomer containing a bisphenol A structure.

More specifically, 2,2-bis [4- (4-aminophenoxy) phenyl containing 4,4'-bisphenol A dianhydride represented by the following Chemical Formula 2 as an acid anhydride, or represented by the following Chemical Formula 3 as a diamine: ] Propane, or both.

[Formula 2]

[Formula 3]

In one embodiment of the present invention, the outermost layer may include 30 to 40% by weight of the unit structure represented by the formula (1). It is preferable because it is excellent in adhesive strength with the prepreg in the above range and excellent in bendability. If it is less than 30% by weight prepreg adhesion is low, if it is more than 40% by weight may be reduced in flexibility.

More specifically, the outermost layer contains 10 to 60 mol% of 4,4'-bisphenol A dianhydride in the acid anhydride monomer, and 2,2-bis [4- (4-aminophenoxy) phenyl in the diamine monomer. ] May contain 75 to 100 mol% propane, it is preferable to include both at the same time because it is more excellent adhesion.

In one embodiment of the present invention, the outermost layer may be to use an acid anhydride commonly used in addition to 4,4'-bisphenol A dianhydride as the acid anhydride. In this case, the 4,4'-bisphenol A dianhydride may be used in 10 to 60 mol% of the acid anhydride monomer. More specifically, 20 to 50 mole% may be used, and the remaining mole% may be used by mixing a common acid anhydride used in the production of polyimide. By using the content of 4,4'-bisphenol A dianhydride in the above range, it is preferable because it is excellent in the effect of exerting the adhesive force with the prepreg and at the same time can express the physical properties excellent in flexibility.

The acid anhydride is, in addition to 4,4'-bisphenol A dianhydride, specifically, for example, biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), 4,4'- Hexafluoroisopropylidene diphthalic anhydride (6FDA), benzophenonetetracarboxylic dione hydride (BTDA), 4,4'-oxydiphthalic dione hydride (ODPA) and bisdicarboxyphenoxy di It may further include any one or two or more acid anhydrides selected from phenyl sulfide dianhydride (BDSDA) and the like, but is not limited thereto. More preferably, any one or two selected from biphenyltetracarboxylic dianhydride (BPDA), benzophenonetetracarboxylic dianhydride (BTDA) and 4,4'-oxydiphthalic dianhydride (ODPA) and the like. The acid anhydride may be further included. In the case of including pyromellitic dihydride (PMDA), the adhesion to the prepreg may be lowered, but it is preferable not to use it, but this is not excluded.

In one embodiment of the present invention, the diamine may be a combination of diamines commonly used in addition to 2,2-bis [4- (4-aminophenoxy) phenyl] propane. In this case, the 2,2-bis [4- (4-aminophenoxy) phenyl] propane may be 75 to 100 mol%, more specifically 80 to 100 mol% of the diamine monomer. The remaining mole% may be a mixture of conventional diamines used in preparing the polyimide. By using the content of the 2,2-bis [4- (4-aminophenoxy) phenyl] propane in the above range, it is excellent in the effect of exhibiting the adhesive force with the prepreg, it is possible to express excellent physical properties.

The diamine is specifically, for example, m-tolidine, 1,3-bis (4-aminophenoxy) benzene, p-phenyl in addition to 2,2-bis [4- (4-aminophenoxy) phenyl] propane It may further include any one or two or more diamines selected from rendiamine (p-PDA) and 4,4'-diaminodiphenyl ether (ODA) and the like, but is not limited thereto.

In one aspect of the invention, the outermost polyimide layer is specifically an acid anhydride, for example, 40 to 90 mol% of biphenyltetracarboxylic dianhydride (BPDA) and 4,4'-bisphenol A dianone. It may be to use 10 to 60 mol% hydride. In addition, 2,2-bis [4- (4-aminophenoxy) phenyl] propane alone or as diamine, 75 to 95 mol% of 2,2-bis [4- (4-aminophenoxy) phenyl] propane and p- It may be to use 5 to 25 mol% phenylenediamine (p-PDA).

In one embodiment of the present invention, the thickness of the outermost layer of the polyimide laminate is not limited, but may be 2 to 55 μm, more specifically 3 to 38 μm. In the above range, while reducing the overall thickness of the flexible metal laminate, it is preferable because it can exhibit excellent adhesion to the prepreg and excellent physical properties.

In one aspect of the present invention, when the polyimide layer includes a polyimide laminate in which two or more layers are laminated, the remaining polyimide layer except for the outermost layer may be used without limitation as long as it is a polyimide layer commonly used in the art. Can be. More specifically, for example, as an acid anhydride, biphenyltetracarboxylic dione hydride (BPDA), pyromellitic dione hydride (PMDA), 4,4'-hexafluoroisopropylidene diphthalic anhydride (6FDA), benzophenonetetracarboxylic dianhydride (BTDA), 4,4'- oxydiphthalic dianhydride (ODPA) and bisdicarboxyphenoxy diphenylsulfide dianhydride (BDSDA) It may be to use one or more acid anhydrides. In addition, any of diamine selected from m-tolidine, 1,3-bis (4-aminophenoxy) benzene, p-phenylenediamine (p-PDA) and 4,4'-diaminodiphenyl ether (ODA) It may be to use one or more diamines. The thickness of the remaining polyimide layer except for the outermost layer may be 2 to 55 μm, more specifically 3 to 38 μm. In the above range, while reducing the overall thickness of the flexible metal laminate, it is preferable because it can exhibit excellent adhesion to the prepreg and excellent physical properties.

In one aspect of the present invention, the metal foil is not limited as long as it is commonly used in the art, specifically, for example, may be copper foil or aluminum foil. In one embodiment of the present invention, the thickness of the metal foil is not limited but may be 2 to 105 μm, and more specifically 6 to 105 μm. The metal foil may be an electrolytic foil, a rolled foil, or the like, but may be variously applied depending on the intended use.

In one aspect of the present invention, the flexible metal foil laminate may be one having a flexibility of 250 or more times. The flexibility is measured by Resistance to folding using Japanese Industrial Standard (JIS) C 6471. The pattern is formed by line / space = 1mm / 1mm, the radius of curvature is measured by 0.38mm, and the number of times until an electrical short circuit occurs. The higher the number of bends, the more flexible the flexible circuit board is, so that the excellent characteristics can be expressed in the actual use environment such as folding or bending. In addition, it is preferable that the flexibility can be ensured without peeling even when the prepreg and the adhesion in the range of bendability 250 times or more.

In one aspect of the invention, the prepreg may be a glass fiber substrate impregnated with a transparent polyimide resin or an epoxy resin.

The glass fiber included in the prepreg can use any conventional material known in the art without limitation. Non-limiting examples thereof include E glass fiber, C glass fiber, A glass fiber, S glass fiber, D glass fiber, NE glass fiber, T glass fiber, quartz glass fiber and the like. One type of glass fiber can be selected and used.

The impregnation amount of the epoxy resin impregnated in the glass fiber is not particularly limited, and can be appropriately adjusted in consideration of the physical properties and thickness of the prepreg to be produced. In order to form a favorable epoxy resin layer in glass fiber, 40-60 weight part of epoxy resin compositions can be impregnated based on 100 weight part of prepregs. In one example, the use ratio of the epoxy resin and the glass fiber may be 40 to 60: 60 to 40 weight ratio.

In one aspect of the present invention, the method for producing the prepreg can be used without limitation conventional methods known in the art, for example, it can be prepared by impregnating the glass fiber with an epoxy resin of a transparent property and then drying.

The prepreg may be used in various fields, and particularly, may be usefully used as a material for high heat resistance and transparent substrates for semiconductors and displays that require heat resistance and durability.

The following describes a method of manufacturing the flexible metal laminate according to one aspect of the present invention.

The first aspect of the method for producing the flexible metal laminate according to one aspect of the present invention

(a) coating and drying a polyimide precursor composition on one surface of the metal foil to form a polyimide precursor layer having at least one layer laminated thereon; And

(b) imidating the stacked polyimide precursor layers;

It may be to include.

Method for producing a flexible metal laminate according to another aspect of the present invention

Iii) applying and drying the polyimide precursor composition on the substrate to form a polyimide precursor layer having at least one layer laminated thereon;

Ii) imidating the laminated polyimide precursor layer; and

Iii) laminating a metal foil on the imidized laminate and then heating and compressing it.

In one aspect of the present invention, when the polyimide precursor layer is a polyimide laminate in which two or more layers are laminated, each polyimide layer may be the same or different in composition.

In one embodiment of the present invention, the polyimide precursor composition to be applied to the outermost layer of the polyimide precursor composition is 4,4'-bisphenol A dianhydride represented by the formula (2) and 2,2-bis represented by the formula (3) It may include any one selected from [4- (4-aminophenoxy) phenyl] propane or a mixture thereof.

[Formula 2]

[Formula 3]

More specifically, it may be included in the content described above.

In addition, the precursor composition may be one containing an organic solvent. The organic solvent is not particularly limited in kind, and specific examples thereof include dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and dimethylformsulfoxide (DMSO). ), Acetone, diethyl acetate, m-cresol and the like. Preferably dimethylacetamide or N-methyl-2-pyrrolidone may be used. In addition, the content of the organic solvent may be appropriately selected in consideration of the molecular weight of the thermoplastic polyamic acid is a copolymer derived from the monomers, it may be 80 to 97% by weight of the total composition. More preferably, it is 85 to 95 weight%. That is, the content of solids is more preferably 3 to 20% by weight, preferably 5 to 15% by weight.

In one aspect of the present invention, the coating method may be selected from knife coating, roll coating, die coating, curtain coating, casting coating, and the like. It may be carried out through, but is not limited thereto.

In one aspect of the invention, the drying may be dried by heat treatment for 1 minute to 2 hours, preferably 1 minute to 1 hour at 100 to 200 ℃, for example, 100 to 200 ℃ specific. In addition, the drying may be carried out in a separate drying oven, but is not necessarily limited thereto.

In one aspect of the present invention, the imidation can be cured through a known imidization method, for example, thermal imidization method, chemical imidization method, thermal imidization method and chemical imidization method in combination. However, it is not limited thereto. In addition, prior to thermal imidization, a dehydrating agent and an imidization catalyst may be added to perform chemical imidization. The dehydrating agent is not limited as long as it is conventionally used, and specifically, for example, one or a mixture of two or more selected from acetic anhydride, phthalic anhydride, maleic anhydride and the like may be used. Can be. The imidation catalyst is not limited as long as it is conventionally used, and specifically, for example, pyridine, isoquinoline, β-quinoline, and any one or two or more mixtures selected from the like may be used. May be, but is not necessarily limited thereto.

The thermal imidization method may be to perform a heat treatment step by step. Preferably the first heat treatment at 80 to 100 ℃, more specifically at 90 to 100 ℃ for 1 minute to 2 hours, the second heat treatment at 100 to 200 ℃, more specifically at 150 to 200 ℃ for 1 minute to 2 hours, 250 To 300 ° C, more specifically, may be to perform a stepped heat treatment of the third heat treatment for 1 minute to 2 hours at 280 to 300 ℃. At this time, the stepped heat treatment may be to increase the temperature in the range of preferably 1 to 20 ℃ / min during each step movement. When heat treatment is performed at once without heat treatment step by step as described above, the solvent that is not dried may be trapped in the film and may not be evaporated even at high temperature heat treatment. Therefore, the solvent may be dried and imidized by heat treatment in multiple stages. It may be to practice.

In one aspect of the present invention, the hot pressing may be performed by any one or more devices selected from, for example, a heat press, a vacuum press, a laminator, a vacuum laminator, a thermal roll laminator, a vacuum thermal roll laminator, and the like, but is not limited thereto. It doesn't happen.

In addition, the present invention can provide a flexible printed circuit board comprising a flexible metal laminate according to an aspect of the present invention described above.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the following Examples and Comparative Examples are only examples for explaining the present invention in more detail, the present invention is not limited by the following Examples and Comparative Examples.

Hereinafter, physical properties were measured as follows.

1) adhesion

In order to measure the peel strength between the polyimide resin and the metal foil, a specimen is manufactured according to JIS (Japanese Industrial Standard) C 6471. A specimen is prepared by vacuum pressing the polyimide layer to be measured at both sides with the prepreg in the center. After fabrication of the specimen, the polyimide layer was bitten by a universal testing machine and the peel strength of 180˚ was measured. The prepreg was a 60 μm thick prepreg of Doosan's DS-7402BS, and the press condition was molded under the condition that the maximum temperature was maintained at 170 ° C. for 80 minutes.

2) Flexibility

Resistance to folding was measured using JIS C 6471. The pattern was formed by line / space = 1mm / 1mm, the bending radius was measured by 0.38mm, and the number of times until an electrical short circuit occurred was measured.

[Production Examples 1 to 9]

In a nitrogen atmosphere, an aromatic diamine was added to N, N-dimethylacetamide (DMAc) at a component and content ratio shown in Table 1 below, followed by sufficient stirring, followed by stirring for 24 hours until dissolution of an aromatic dianhydride, and dissolving and The reaction was carried out to prepare a thermoplastic polyimide precursor composition. At this time, the content of each monomer was added to the mol% as shown in Table 1, the solid content was adjusted to 10% by weight, the temperature of the reactor was maintained at 30 ℃.

The abbreviations described in Table 1 below are as follows.

BPDA: Biphenyl-Tetracarboxylic Dionhydride

BTDA: 3,3 ', 4,4'-benzophenone tetracarboxylic anhydride

BPADA: 4,4'-bisphenol A Dionhydride

PDA: p-phenylene diamine

ODA: 4,4'-diaminodiphenyl ether

BAPP: 2,2-bis [4- (4-aminophenoxy) phenyl] propane

BPA: Bisphenol A structure represented by the following formula (1)

[Formula 1]

[Examples 1 to 4]

The polyimide precursor composition prepared in Preparation Example 1 was applied onto a rolled copper foil (BHY-82F-HA-V2 manufactured by JX) having a thickness of 12 μm, and then dried at 140 ° C. for 20 minutes to form a first polyimide layer.

After applying the polyimide precursor composition prepared in Preparation Example 2 on the first polyimide layer, and dried for 20 minutes at 140 ℃ to form a second polyimide layer.

After applying the polyimide precursor composition shown in Table 2 on the second polyimide layer and dried for 20 minutes at 140 ℃ to form a third polyimide layer.

Subsequently, in a roll-to-roll infrared curing machine, the temperature was raised to 380 ° C. at a temperature increase rate of 2 ° C./min, and cured by laminating the first polyimide layer 3 μm / second polyimide layer 19 μm / third polyimide layer 3 μm. A flexible metal laminate having a total thickness of 25 μm was prepared. It was shown in Table 2 to measure the flexibility of the produced flexible metal laminate.

A 60 μm-thick epoxy prepreg (DS-7402 of Doosan Electronics) was laminated on the third polyimide layer of the imidized laminate, and then bonded using a high temperature laminator to form a flexible metal foil laminate on which the prepreg was laminated. A sieve was prepared and the adhesion between the prepreg and the third polyimide layer was measured and is shown in Table 2 below.

[Comparative Examples 1 to 3]

A soft metal laminate was prepared in the same manner as in Example 1, except that the composition for forming the third polyimide layer was changed as in Table 2 below.

The physical properties of the produced flexible metal laminates are measured and shown in Table 2 below.

First polyimide layer Second polyimide layer Third polyimide layer Adhesion
(kgf / cm) Flexibility
(Count) Example 1 Preparation Example 1 Preparation Example 2 Preparation Example 3 1.1 312 Example 2 Preparation Example 1 Preparation Example 2 Preparation Example 4 1.3 269 Example 3 Preparation Example 1 Preparation Example 2 Preparation Example 5 0.9 377 Example 4 Preparation Example 1 Preparation Example 2 Preparation Example 6 0.8 362 Comparative Example 1 Preparation Example 1 Preparation Example 2 Preparation Example 7 0.3 270 Comparative Example 2 Preparation Example 1 Preparation Example 2 Preparation Example 8 0.4 264 Comparative Example 3 Preparation Example 1 Preparation Example 2 Preparation Example 9 1.3 160

As shown in Table 2 above, the third polyimide layer, which is the outermost layer, contains BPADA and BAPP, and the adhesion to the prepreg is 0.8 kgf / in Examples 1 to 4, wherein the content is 30 to 40 wt%. It was confirmed that the flexural property satisfies all 250 or more while being more than cm.

In addition, it was found that it is necessary to use an appropriate amount because the flexibility is slightly reduced when the content of BPADA increases.

In addition, as shown in Comparative Examples 1 and 2 it was confirmed that the adhesive strength is very low when it contains less than 30% by weight BPA structure. In addition, when the BPA structure exceeds 40% by weight as in Comparative Example 3, it was confirmed that the adhesive strength is high but the flexibility is very low.

Claims (5)

In a flexible metal foil laminate in which a polyimide laminate including at least one or more polyimide layers is laminated on one surface of a metal foil,
The outermost layer of the polyimide laminate is a flexible metal foil laminate in which the mass of the unit structure represented by the following formula (1) is 30 to 40% by weight of the total monomer mass used in the outermost layer.
[Formula 1]

The method of claim 1,
The outermost layer is any one selected from 4,4'-bisphenol A dianhydride represented by the following formula (2) and 2,2-bis [4- (4-aminophenoxy) phenyl] propane represented by the following formula (3) Or a polyimide derived from a mixture thereof.
[Formula 2]

[Formula 3]

The method of claim 2,
The outermost layer comprises 10 to 60 mol% of 4,4'-bisphenol A dianhydride in the dianhydride monomer, and 2,2-bis [4- (4-aminophenoxy) phenyl] propane in the diamine monomer. A flexible metal laminate comprising 75 to 100 mol%. The method of claim 1,
The outermost layer is a flexible metal laminate having an adhesive strength of 0.8 kgf / cm or more with the prepreg at room temperature. The method of claim 1,
The flexible metal laminate is a flexible metal laminate having a flexibility of more than 250 times.