JP2002069420A - Adhesive film for fpc reinforcing sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive film for FPC reinforcing sheet having good adhesive properties, long-term heat resistance and heat resistance for soldering. SOLUTION: The good adhesive properties and long-term heat resistance can be achieved by a film comprising a soluble thermoplastic polyimide resin made of an ester acid dianhydride of a specific structure and a diamine, a thermoset resin and its curing agent. The adhesive film for FPC reinforcing sheet having the good heat resistance for soldering can be obtained by using a solvent of cyclic ether.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soluble thermoplastic polyimide-based adhesive film used for bonding a reinforcing plate for flexible printed circuit boards and FPC.

[0002]

2. Description of the Related Art In recent years, electronic devices have become more sophisticated and more sophisticated.
With miniaturization progressing, there has been a demand for miniaturization and weight reduction of electronic components used accordingly. For this reason, a semiconductor element packaging method and a wiring material or a wiring component for mounting the same are required to have higher density, higher function and higher performance. In particular, semiconductor packages, COL and LOC packages, MCM (M
Demand for high-density packaging materials such as multi-chip modules and flexible printed wiring board materials such as multilayer flexible printed boards has been increasing.

[0003] A flexible printed circuit board (hereinafter referred to as FPC) is characterized in that it is thin and can be folded and mounted, but has a lower rigidity than a general resin board.
2. Description of the Related Art Reinforcement is performed by bonding a resin substrate, a resin film, and the like using an adhesive film. In this field, phenolic, epoxy and acrylic adhesives are used. In recent years, there has been a demand for use in applications exposed to high temperatures, such as engine control units and plasma display applications, and in such applications, besides the role of a reinforcing plate, the role of a heat sink is also required. And metal reinforcing plates such as Al plates.

As a result, polyimide-based adhesives have been gradually used as heat-resistant adhesives not found in conventional adhesive films. Since polyimide has excellent heat resistance among various organic polymers, it is widely used in the fields of space and aviation, and is also used as an adhesive material. However, a polyimide-based adhesive having high heat resistance requires a high temperature of about 300 ° C. and a high pressure for bonding, and the adhesive strength is not so high. Further, polyimide adhesives have a problem that they have a high water absorption rate and are inferior in properties such as solder heat resistance.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present inventors
It is an object of the present invention to solve the above problems and to provide an adhesive film for bonding an FPC reinforcing plate having excellent solder heat resistance and excellent adhesiveness and long-term heat resistance, particularly when a metal plate is used as a reinforcing plate. Adhesive film for FPC reinforcement board, which has good adhesiveness, and also has good adhesiveness with both metal plate and coverlay film when laminated with a metal plate and a coverlay film made of polyimide film etc. via an adhesive film As a result, the present inventors have completed the present invention.

[0006]

The present invention can achieve the above object by the following means. 1) An adhesive film for bonding a reinforcing plate of a flexible printed board, wherein the adhesive strength of the film when the Al plate and the non-thermoplastic polyimide film are laminated via the adhesive film is 5 N / cm or more. And the adhesive strength after holding at 150 ° C. for 1000 hours is 5N
/ Cm or more adhesive film for flexible printed circuit board reinforcing plate. 2) The adhesive film for a flexible printed board reinforcing plate according to 1), wherein the reinforcing board of the flexible printed board is a metal plate. 3) The flexible printed circuit board reinforcing plate according to 1) or 2), wherein the adhesive film for a flexible printed circuit board reinforcing plate is used for bonding a coverlay of the flexible printed circuit board to a reinforcing plate of the flexible printed circuit board. For adhesive film. 4) The adhesive film for a flexible printed circuit board reinforcing plate according to 3), wherein the coverlay film is a polyimide film. 5) The adhesive film for a flexible printed circuit board reinforcing plate according to 3), wherein the coverlay film is a non-thermoplastic polyimide film. 6) the adhesive film is composed of at least 50% by weight or more of a soluble thermoplastic polyimide component;
In addition, the thermoplastic polyimide is a polyimide obtained from an acid dianhydride as a raw material, and 50 mol% or more of the total acid dianhydride has a general formula (1)

[0007]

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Wherein X represents-(CH ₂ ) k-or a divalent group containing an aromatic ring, and k is an integer of 1 or more and 10 or less. The adhesive film for a flexible printed circuit board reinforcing plate according to any one of 1) to 5), wherein: 7) The thermoplastic polyimide comprises an ester dianhydride represented by the general formula (1) and the following general formula (2)

[0009]

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Wherein Y is the same or different and
(= O) -, - SO 2 -, - O -, - S -, - (CH 2)
_{m -, - NHCO -, -} C (CH 3) 2 -, - C (CF 3)
_A bond is shown to at least one selected from _2- , -C (= O) O- and a single bond. m and n are integers of 1 or more and 5 or less. The adhesive film for a flexible printed board reinforcing plate according to 6), which is a polyimide obtained using the diamine compound represented by the formula (1) as a raw material. 8) The thermoplastic polyimide is represented by the following formula (3)

[0011]

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A polyimide obtained by using an ester dianhydride represented by the following formula and a diamine compound represented by the general formula (2) as a raw material: Adhesive film. 9) The adhesive film for a flexible printed circuit board reinforcing plate according to 1) to 8), which is obtained from a soluble thermoplastic polyimide-based adhesive obtained by mixing a thermosetting resin and a curing agent with the soluble thermoplastic polyimide. 10) The adhesive film according to claim 9, wherein the thermosetting resin is an epoxy resin. 11) The solution of an adhesive in which the soluble thermoplastic polyimide-based adhesive contains an organic solvent, wherein the organic solvent contains 30% by weight or more of a cyclic ether-based solvent. Adhesive film for flexible printed circuit board reinforcement plate. 12) The soluble thermoplastic polyimide-based adhesive according to any one of 9) to 11) is cast or applied on a support,
An adhesive film for a flexible printed circuit board reinforcing plate, wherein the adhesive film after drying is obtained by peeling it off from a support. 13) Adhesiveness for a flexible printed board reinforcing plate obtained by casting or applying the soluble thermoplastic polyimide-based adhesive solution according to 9) to 11) on at least one surface of a polyimide film, and then drying the solution. the film. 14) 5 to 5 soluble thermoplastic polyimide adhesive layers
The adhesive film for a flexible printed circuit board reinforcing plate according to any one of 6) to 13), which has a thickness of 0 μm.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The adhesive film for an FPC reinforcing plate of the present invention has an adhesive strength of 5 N / cm when an Al plate and a non-thermoplastic polyimide film are laminated via the adhesive film of the present invention. And at 150 ° C.
The adhesive strength after holding for 1000 hours is 5 N / cm or more. 150 ° C, 1000 due to heat resistance of polyimide
An adhesive sheet excellent in long-term heat resistance expressed by the adhesive strength after time can be obtained. Further, since the soluble thermoplastic polyimide in the present invention exhibits low water absorption, an adhesive film having excellent solder heat resistance can be obtained. Further, since the polyimide component is soluble in the solvent, the adhesive can be used in the form of a solution, and a thermosetting resin for improving the adhesiveness can be blended. At this time, as a solvent that can be used for the polyimide-based adhesive solution, to reduce the residual solvent,
Low boiling point solvents are desirable, and cyclic ether solvents such as tetrahydrofuran (THF), 1,4-dioxane and dioxolane can be preferably used from the viewpoint of processability of the adhesive film. When a mixed organic solvent obtained by mixing a plurality of solvents is used, it is preferable to use the mixed organic solvent in combination with a polar organic solvent. It is more desirable to contain them. Examples of the organic polar solvent to be combined with the cyclic ether solvent include sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, formamide solvents such as N, N-dimethylformamide and N, N-diethylformamide, N, N-dimethylacetamide,
Acetamide solvents such as N, N-diethylacetamide are exemplified.

The thermoplastic polyimide of the present invention is a thermoplastic polyimide obtained from a dianhydride as a raw material, wherein at least 50 mol% of the total acid dianhydride is represented by the general formula (1):

[0015]

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(Wherein X represents-(CH ₂ ) k- or a divalent group containing an aromatic ring, and k is an integer of 1 or more and 10 or less). It is preferred that With such a structure, a polyimide soluble in the organic solvent can be obtained.

Preferred examples of the acid dianhydride represented by the general formula (1) include 2,2-bis (4-hydroxyphenyl) propanedibenzoate-3,3 ', 4,4'-tetracarboxylic acid Dianhydride, p-phenylene bis (trimellitic acid monoester anhydride), 4,4′-biphenylene bis (trimellitic acid monoester anhydride), 1,4
-Naphthalene bis (trimellitic acid monoester anhydride), 1,2-ethylene bis (trimellitic acid monoester anhydride), 1,3-trimethylene bis (trimellitic acid monoester anhydride), 1,4- Examples include tetramethylene bis (trimellitic acid monoester anhydride), 1,5-pentamethylene bis (trimellitic acid monoester anhydride), 1,6-hexamethylene bis (trimellitic acid monoester anhydride), and the like. However, from the viewpoint that the obtained polyimide has good solubility and good balance with heat resistance, the formula (3)

[0018]

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2,2-bis (4-hydroxyphenyl) propanedibenzoate-3,3 ', 4
4'-tetracarboxylic dianhydride is particularly preferred.

The diamine component to be reacted with the above-mentioned acid dianhydride is represented by the following general formula (2):

[0021]

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(Wherein Y is the same or different and
(= O) -, - SO 2 -, - O -, - S -, - (CH 2)
_{m -, - NHCO -, -} C (CH 3) 2 -, - C (CF 3)
_A bond is shown to at least one selected from _2- , -C (= O) O- and a single bond. m and n are integers of 1 or more and 5 or less. ), Particularly, bis (aminophenoxyphenyl) sulfone and 1,3-bis (3-aminophenoxy) benzene. In the general formula (2), a plurality of Ys may be the same or different between each repeating unit, and hydrogen of each benzene ring may be appropriately substituted with various substituents within a range conceivable by those skilled in the art. Can be replaced. For example, a hydrocarbon group such as a methyl group and an ethyl group and a halogen group such as Br and Cl can be exemplified, but the substituent is not limited thereto. Furthermore, among the diamine compounds represented by the general formula (2), a diamine compound having an amino group at the meta position has excellent processability due to good solubility of a thermoplastic polyimide in an organic solvent using the diamine compound. It is preferable to obtain an agent solution. The general formula (2)
May be used in combination of two or more.

The thermoplastic polyimide dissolved in the polyimide adhesive solution of the present invention can be obtained by dehydrating and ring-closing a polyamic acid polymer as a precursor thereof. This polyamic acid solution is obtained by using the above-mentioned acid dianhydride and the above-mentioned diamine compound in substantially equimolar amounts and polymerizing in an organic polar solvent.

The polyamic acid is first obtained from a polyamic acid polymer obtained by dissolving or diffusing a diamine compound and an acid dianhydride in an organic polar solvent in an inert atmosphere such as argon or nitrogen.

The order of addition of each component is not particularly limited. An acid dianhydride is first added to an organic polar solvent, and a diamine compound is added to form a solution of a polyamic acid polymer. A suitable amount may be added first to an organic polar solvent, then an acid dianhydride is added, and finally, the remaining diamine compound is added to form a solution of a polyamic acid polymer. There are various other polymerization methods known to those skilled in the art.

Examples of the organic polar solvent used in the reaction for producing the polyamic acid solution include sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide.
Formamide solvents such as N, N-dimethylformamide and N, N-diethylformamide; acetamido solvents such as N, N-dimethylacetamide and N, N-diethylacetamide; and pyrrolidone solvents such as N-methyl-2-pyrrolidone Phenol, o-, m- or p-cresol, xinol, halogenated phenols, phenols such as catechol, or hexamethylphosphoramide, γ-butyrolactone.
Further, if necessary, these organic polar solvents can be used in combination with an aromatic hydrocarbon such as xylene or toluene.

The polyamic acid polymer obtained above is dehydrated and ring-closed by a thermal or chemical method to obtain a thermoplastic polyimide. As a method of imidation, any of a thermal method of heating and dehydrating a polyamic acid solution and a chemical method of dehydrating with a dehydrating agent are used. Examples of the dehydrating agent by a chemical method include aliphatic acid anhydrides such as acetic anhydride, and aromatic acid anhydrides. Examples of the catalyst include aliphatic tertiary amines such as triethylamine, aromatic tertiary amines such as dimethylaniline, and heterocyclic tertiary amines such as pyridine and isoquinoline. The thermoplastic polyimide obtained as described above can be used as it is as a solution for preparing the polyimide adhesive solution of the present invention. Alternatively, the solvent used for the polymerization of the polyamic acid is dissolved well, but the polyimide solution is poured into a poor solvent in which the polyimide is difficult to dissolve, the polyimide resin is precipitated, the unreacted monomer is removed, purified, dried and solidified. Can be used in the adhesive solution of the present invention as appropriate. As poor solvents used, acetone, methanol, ethanol,
Isopropanol, benzene, methyl cellosolve, methyl ethyl ketone and the like.

As a thermal method, for example, there is a method in which a polyamic acid is polymerized, then put into a vacuum oven, heated under reduced pressure, imidized, and taken out as a solid polyimide resin.

The adhesive film of the present invention is preferably an adhesive film obtained from an adhesive obtained by further mixing an epoxy resin with the thermoplastic polyimide. It is preferably an epoxy resin that dissolves in the adhesive solution. Bisphenol A-type resin such as Epicoat 828 (manufactured by Yuka Shell Co.), ortho-cresol novolac resin such as 180S65 (manufactured by Yuka Shell), 157S70 (oiling shell) Novolac resin such as 1032
Trishydroxyphenylmethane novolak resin such as H60 (manufactured by Yuka Shell), naphthalene aralkyl novolak resin such as ESN375, tetraphenylolethane 1031S (manufactured by Yuka Shell), YGD414S (Toto Kasei), Trishydroxyphenylmethane EPPN50
2H (Nippon Kayaku), special bisphenol VG3101L
Glycidylamine type resins such as (Mitsui Chemicals), specialty naphthol NC7000 (Nippon Kayaku), TETRAD-X, TETRAD-C (manufactured by Mitsubishi Gas Chemical Co., Ltd.) and the like are mentioned as typical examples.

The mixing ratio of the epoxy resin is preferably 1 to 50 parts by weight, more preferably 5 to 30 parts by weight, based on 100 parts by weight of the solid content of the thermoplastic polyimide resin. If the amount is too small, the adhesive strength tends to be low. If the amount is too large, flexibility and heat resistance tend to be poor.

In the present invention, it is preferable that a curing agent for an epoxy resin is further added to the adhesive. As the curing agent dissolved in the solution, any one may be used as long as it is generally used as a curing agent for an epoxy resin. The curing agent is added to the adhesive solution to improve water absorption, heat resistance, adhesiveness, etc., and is a typical curing agent for epoxy such as acid dianhydride type, amine type, imidazole type, etc. , An accelerator, or various coupling agents.

The composition of the polyimide-based adhesive solution of the present invention has been described above. The concentration of the adhesive solution is represented by the solid content (thermoplastic polyimide + epoxy resin + curing agent) whose denominator is the solution weight. 5 to 50% by weight, preferably 1
It is from 0 to 40% by weight, particularly preferably from 15 to 30% by weight. The dissolution procedure and the like may be appropriately determined in consideration of workability and the like.

As a method for obtaining the adhesive film for an FPC reinforcing plate of the present invention, the above-mentioned polyimide adhesive solution is cast or applied on a polymer film or a metal support, and the adhesive coating film after drying is applied. Method of peeling off from the support,
Alternatively, a method in which a polyimide-based adhesive solution is cast or applied to at least one surface of a polyimide film and then dried to obtain an adhesive film for a polyimide film-based FPC reinforcing plate having a polyimide-based adhesive layer on the surface is used. The adhesive film for an FPC reinforcing plate obtained in the former case is a single-layer film of a polyimide-based adhesive, which may be laminated with a polyimide film to form an adhesive film for an FPC reinforcing plate having the same configuration as the latter. In any case, the thickness of the polyimide-based adhesive layer on the surface of the polyimide film-based adhesive film for an FPC reinforcing plate is 5 to 50 (the actual required thickness is 35 μm).
μm is appropriate. If the thickness is too small, the adhesiveness may be reduced. If the thickness is too large, it is difficult to remove and dry the organic solvent or foaming may occur.

The adhesive film for an FPC reinforcing plate according to the present invention obtained as described above has characteristics that can be suitably used for TAB tapes, composite lead frames, laminated materials and the like. Specifically, it shows a low water absorption, has excellent solder heat resistance, and is excellent in both heat resistance and adhesiveness, and can be bonded at a temperature of about 250 ° C. or less when used as an adhesive.

The adhesive film for an FPC reinforcing plate of the present invention is suitable for bonding when a metal reinforcing plate used for applications requiring high heat resistance is used as the reinforcing plate. In particular,
The adhesiveness between the cover lay film and the metal reinforcing plate in the FPC is excellent, and the adhesiveness is particularly excellent when a polyimide film is used as the cover lay.

The adhesive used for the FPC reinforcing plate of the present invention,
The FPC with a reinforcing plate is obtained by bonding a metal foil or a metal plate to the cover lay film side of the flexible printed circuit board by heating and pressing through the adhesive film for the FPC reinforcing plate. Examples of the metal foil or metal plate include copper foil, copper plate / aluminum foil, aluminum plate / 42 alloy, SUS foil, SUS
Plates and the like can be mentioned. The type of the FPC coverlay film is not particularly limited, and examples thereof include a polyimide film and a polyester film. Conventional polyimide adhesives have insufficient adhesion to metals such as copper foil and resin films such as polyimide, and mixing with epoxy resin has been difficult due to its poor solubility. Such an adhesive film for an FPC reinforcing plate has excellent workability in use, such as good adhesion to a metal foil such as a copper foil or a polyimide film, and adhesion at a low temperature. As an example of the bonding conditions in this case, a heating temperature of 150 ° C. to 25 ° C.
The conditions are 0 ° C., a pressure of 0.1 to 10 MPa, and a heating time of about 5 to 20 minutes.

[0037]

(Example 1) In a glass flask having a capacity of 1000 ml, 263 g of dimethylformamide (hereinafter referred to as DMF) and 3,3'-bis (aminophenoxyphenyl) sulfone (hereinafter referred to as BAPS-M) 0.1 were added.
12 mol, and stirring under a nitrogen atmosphere.
0.112 mol of 2-bis (4-hydroxyphenyl) propanedibenzoate-3,3 ′, 4,4′-tetracarboxylic dianhydride (hereinafter referred to as ESDA) was gradually added. Stir for 30 minutes in an ice bath, viscosity 1500p
When the oil reached oise, the stirring was stopped to obtain a polyamic acid solution. 113 g of DMF and β
After adding 26 g of picoline and 45 g of acetic anhydride and stirring for 30 minutes, the mixture was further stirred at 100 ° C. for 1 hour to imidize. The solution was then dripped little by little into methanol stirred at high speed. The filamentous polyimide precipitated in methanol was pulverized with a mixer, washed with Soxhlet with methanol, and dried at 110 ° C. for 2 hours to obtain a polyimide powder.

20 g of the polyimide powder obtained above, 5 g of Epicoat 1032H60 (manufactured by Yuka Shell Co., Ltd.),
4'-diaminodiphenylsulfone (curing agent) 1.5
g was added to 102 g of THF, and dissolved by stirring. A polyimide-based adhesive solution was obtained (solid content concentration: SC
= 20%). The polyimide-based adhesive solution was cast on a PET film to a thickness of 35 μm after drying.
It was dried by heating for 10 minutes to obtain an adhesive sheet. (Example 2) A polyimide powder was obtained in the same manner as in Example 1 except that 1,3-bis (3-aminophenoxy) benzene was used as the diamine. An adhesive sheet was obtained in the same manner as in Example 1 using the obtained polyimide powder. (Example 3) A polyamic acid solution was obtained in the same manner as in Example 1. 300 g of this polyamic acid solution is placed in a vat coated with Teflon (registered trademark) and placed in a vacuum oven for 1 hour.
50 ° C for 1 hour, 180 ° C for 1 hour, 200 ° C for 3 hours, 5
It was heated under reduced pressure at a pressure of mmHg. An adhesive sheet was obtained in the same manner as in Example 1 using the obtained polyimide resin. (Example 4) 1,4 instead of THF as an organic solvent
-An adhesive sheet was obtained in the same procedure as in Example 1 except that dioxane was used. (Example 5) An adhesive sheet was obtained in the same procedure as in Example 1, except that dioxolan was used instead of THF as the organic solvent. (Example 6) The polyimide powder obtained in Example 1 was used for 20 times.
g, naphthalene aralkyl novolak resin ESN-375
5 g of Nippon Steel Chemical Co., Ltd. and 1.5 g of 4,4′-diaminodiphenylsulfone (curing agent) in 102 g of THF
To obtain an adhesive sheet. (Example 7) The polyimide powder obtained in Example 1 was used for 20 times.
g, 5 g of biphenyl type epoxy resin NC3000P (manufactured by Nippon Kayaku Co., Ltd.) and 1.5 g of 4,4'-diaminodiphenylsulfone (curing agent) are added to 102 g of THF, and the mixture is dissolved by stirring, and the adhesive sheet is obtained. I got (Comparative Example 1) 10 g of Platabond M1276 (copolymer nylon, manufactured by Nippon Rilsan Co., Ltd.), Epicoat 828
20 g (manufactured by Yuka Shell) and 1 g of diaminodiphenylsulfone were dissolved in 83 g of DMF. The obtained varnish was cast on a PET film and dried at 150 ° C. for 10 minutes to obtain an adhesive sheet having a thickness of 35 μm. (Comparative Example 2) Example 1 except that the acid dianhydride component was changed to benzophenonetetracarboxylic dianhydride (BTDA).
In the same manner as above, a polyimide powder was obtained. This polyimide powder did not dissolve in THF, 1,4-dioxane, and 1,3-dioxolan.

Comparative Example 3 A polyimide powder was obtained in the same manner as in Example 1, except that pyromellitic dianhydride (PMDA) was used as the acid dianhydride component and diaminodiphenyl ether (ODA) was used as the diamine component. This polyimide powder is T
It did not dissolve in HF, 1,4-dioxane, 1,3-dioxolane.

(Evaluation of Characteristics of Adhesive Film for FPC Reinforcement Plate) The characteristics of the adhesive film for FPC reinforcement plate were evaluated in the following procedure. ● Preparation of evaluation sample 25 μm polyimide film (Apical 25AH, manufactured by Kanegafuchi Chemical Industry Co., Ltd.) via an adhesive film for FPC reinforcement
And a degreasing Al plate at a temperature of 200 ° C. and a pressure of 3 MPa for 2 hours.
It was heated and pressed for 0 minutes to obtain a polyimide film with a reinforcing plate. (Measurement of Peeling Strength) The peeling strength of the obtained polyimide film with a reinforcing plate when the polyimide film was peeled in a 90 ° direction was measured with an autograph S-110-C (manufactured by Shimadzu Corporation). did. However, the film width is 3
mm. (Evaluation of Solder Heat Resistance) Regarding the solder heat resistance, the appearance was evaluated by immersion in a 260 ° C. solder bath for 10 seconds.

Table 1 shows the results of evaluating the properties of the adhesive films for FPC reinforcing plates of the examples and comparative examples.

[0042]

[Table 1]

[0043]

The adhesive film for an FPC reinforcing plate of the present invention can be bonded at a temperature of about 200 ° C. Unlike conventional heat-resistant adhesives, it does not require high temperatures for bonding, exhibits high adhesive strength to polyimide films, and maintains high adhesive strength up to high temperatures. Furthermore, it has excellent long-term heat resistance without any decrease in adhesiveness after standing at 150 ° C. for 1000 hours. Further, it has solder heat resistance that does not cause blistering or the like when immersed in a solder bath. As described above, it is extremely useful industrially as an adhesive film for an FPC reinforcing plate that requires high reliability and heat resistance.

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Claims (14)

[Claims] An adhesive film for bonding a reinforcing plate of a flexible printed circuit board, wherein the adhesive strength of the film when an Al plate and a non-thermoplastic polyimide film are laminated via the adhesive film is 5 N /. An adhesive film for a flexible printed circuit board reinforcing plate, which has an adhesive strength of not less than 5 N / cm after holding at 150 ° C. for 1000 hours. 2. The adhesive film for a flexible printed circuit board reinforcing plate according to claim 1, wherein the reinforcing plate of the flexible printed circuit board is a metal plate. 3. The flexible print according to claim 1, wherein the adhesive film for a flexible printed board reinforcing plate is used for bonding a coverlay of the flexible printed board to a reinforcing plate of the flexible printed board. Adhesive film for substrate reinforcement plate. 4. The adhesive film according to claim 3, wherein the cover lay film is a polyimide film. 5. The adhesive film according to claim 3, wherein the coverlay film is a non-thermoplastic polyimide film. 6. The adhesive film comprises at least 50% by weight or more of a soluble thermoplastic polyimide component, and the thermoplastic polyimide is a polyimide obtained from an acid dianhydride as a raw material. More than 50 mol% of the anhydride has the general formula (1) (Wherein, X represents — (CH ₂ ) k — or a divalent group containing an aromatic ring, and k is an integer of 1 or more and 10 or less). The adhesive film for a flexible printed circuit board reinforcing plate according to any one of claims 1 to 5, characterized in that: 7. The thermoplastic polyimide comprises an ester dianhydride represented by the general formula (1) and the following general formula (2): (Wherein Y is the same or different, and -C (= O)-,-
SO ₂ —, —O—, —S—, — (CH ₂ ) _m —, —NHC
_{O -, - C (CH 3} ) 2 -, - C (CF 3) 2 -, - C (=
O) A bond is shown to at least one selected from O- or a single bond. m and n are integers of 1 or more and 5 or less. 7. The adhesive film for a flexible printed circuit board reinforcing plate according to claim 6, which is a polyimide obtained using the diamine compound represented by the formula (1) as a raw material. 8. The thermoplastic polyimide according to the following formula (3): The adhesiveness for a flexible printed circuit board reinforcing plate according to claim 7, wherein the polyimide is obtained by using an ester acid dianhydride represented by the following formula and a diamine compound represented by the general formula (2) as raw materials. the film. 9. The adhesive for a flexible printed circuit board reinforcing plate according to claim 1, which is obtained from a soluble thermoplastic polyimide-based adhesive obtained by mixing a thermosetting resin and a curing agent with the soluble thermoplastic polyimide. the film. 10. The adhesive film for a flexible printed circuit board reinforcing plate according to claim 9, wherein the thermosetting resin is an epoxy resin. 11. A solution of an adhesive in which the soluble thermoplastic polyimide adhesive contains an organic solvent, wherein the organic solvent contains at least 30% by weight of a cyclic ether solvent. 11. The adhesive film for a flexible printed circuit board reinforcing plate according to 10. 12. A method in which the soluble thermoplastic polyimide-based adhesive according to claim 9 is cast or coated on a support, and the dried adhesive film is peeled off from the support. An adhesive film for a flexible printed circuit board reinforcing plate. 13. A flexible printed circuit board reinforcing plate obtained by casting or applying the soluble thermoplastic polyimide-based adhesive solution according to claim 9 to at least one surface of a polyimide film, followed by drying. For adhesive film. 14. The adhesive film according to claim 6, wherein the soluble thermoplastic polyimide adhesive layer has a thickness of 5 to 50 μm.