JP2001139807A - Method of manufacturing heat-resistant bonding sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a heat-resistant bonding sheet which excels in heat resistance to soldering, adhesion, dimensional stability, and low dielectric characteristics while possessing sufficient mechanical strength. SOLUTION: The method of manufacturing a heat-resistant bonding sheet which comprises a step of producing a partially imidated gel film of an amic acid of the precursor of (a) a polyaimide, a step of coating an organic solvent solution of an amic acid of the precursor of (b) a thermoplastic polyimide on the surface of the gel film, a step of subsequently converting the gel film and the coated thermoplastic film to the polyimide (a) and the thermoplastic polyimide (b), respectively, and a step of drying the resulting films in the process of producing a laminate constituted by laminating the thermoplastic polyimde (b) layer on one side or both sides of the polyimide (a) film can realize particularly high adhesion of the interface between the base film and the thermoplastic polyimide. The heat-resistant bonding sheet also excels in heat resistance, heat resistance to soldering and dimension stability. This heat-resistant bonding sheet can be used particularly for flexible copper-clad laminates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a bonding sheet having a thermoplastic polyimide layer on one or both sides of a polyimide film, and more particularly, to a method for producing a heat-resistant bonding sheet having excellent heat resistance, adhesiveness and dimensional characteristics. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In recent years, higher performance and higher functionality of electronic devices have been developed.
The miniaturization is rapidly progressing, and there is an increasing demand for miniaturization and weight reduction of electronic components used in electronic devices. Along with this, the heat resistance, mechanical strength,
Various physical properties such as electrical characteristics are further required, and a higher density, higher function, and higher performance are also required for a semiconductor element packaging method and a wiring board for mounting the same. With regard to flexible printed wiring boards (hereinafter referred to as FPC), fine wire processing, multilayer formation, etc. are performed, and component mounting FPs in which components are mounted directly on the FPC.
C, a double-sided FPC in which a circuit is formed on both sides, a multilayer FPC in which a plurality of FPCs are stacked, and the layers are connected by wiring have appeared.

In general, an FPC has a configuration in which a circuit pattern is formed on a flexible and thin base film, and a cover film is bonded to the surface of the circuit pattern. In addition, there is a need to improve the performance of insulating films and insulating adhesives used as adhesive materials. Specifically, it has high heat resistance and mechanical strength, and is excellent in workability, adhesiveness, low hygroscopicity, electrical characteristics, and dimensional stability.

At present, a film made of a polyimide resin having excellent properties is widely used as an insulating organic film of FPC. An epoxy resin or an acrylic resin that is excellent in low-temperature workability and workability is used as the insulating adhesive. However, these adhesives are not particularly satisfactory in heat resistance. For example, if the adhesive is exposed to a temperature of 150 ° C. or more for a long time, the adhesive is deteriorated and various properties are affected. Furthermore, when using these adhesives, the adhesive is applied to a base film, dried, and then bonded to a conductor layer (generally copper foil is used). Have to be heat-treated.

[0005] In particular, with the expanding use of FPCs, there is an urgent need to solve the problem of heat resistance. In order to solve this problem, a two-layer FPC having no adhesive layer and an FPC using a polyimide resin having excellent melt fluidity have been proposed. Regarding the two-layer FPC having no adhesive layer, a method in which a conductor layer is formed directly on an insulating film and a method in which an insulating layer is formed directly on a conductor layer are common. In the method of forming a conductor layer directly on an insulating layer, a method is used in which a thin layer of a conductor is formed by vapor deposition or sputtering, and then a thick layer of the conductor is formed by plating. There are problems that holes are easily generated and it is difficult to obtain a sufficient adhesive force between the insulating layer and the conductor layer.

On the other hand, in a method of forming an insulating layer directly on a conductor layer, a method of casting and drying a solution of a polyimide copolymer or a polyamic acid copolymer on the conductor layer and drying the same is used. In addition, the conductor layer is likely to be corroded by various solvents. Further, when a double-sided plate is manufactured, there is a problem that a complicated process is required such that two single-sided plates are manufactured and then these single-sided plates are adhered to each other.

Further, FPC using a polyimide resin having excellent melt fluidity is disclosed in Japanese Patent Application Laid-Open No. 2-138789.
JP-A-5-179224 and JP-A-5-11276
Although a bonding sheet having a thermoplastic polyimide layer on at least one surface of a base film made of a heat-resistant resin proposed in No. 8 is used, it is difficult to realize excellent adhesiveness, dimensional stability, solder heat resistance, and the like. Was.

[0008]

As described above, the FPC having excellent heat resistance has problems in any form, but in consideration of productivity and characteristics, a base film made of a heat-resistant resin is required. It is considered that a method of bonding a copper foil and a bonding sheet obtained by laminating a thermoplastic polyimide on the substrate is advantageous. Therefore, the above-mentioned problems relating to this case, that is, adhesiveness, dimensional characteristics, solder heat resistance, further low water absorption, low heat absorption, to provide a heat-resistant bonding sheet used for FPC excellent in low dielectric properties. As a result, the present invention has been achieved.

[0009]

SUMMARY OF THE INVENTION The gist of the method for producing a heat-resistant bonding sheet according to the present invention is that a thermoplastic polyimide (b) layer is laminated on one or both sides of a polyimide (a) film. The step of producing a laminate comprises: a step of producing a gel film obtained by partially imidizing a polyamic acid as a precursor of a polyimide (a); and a step of forming a precursor of a thermoplastic polyimide (b) on the surface of the gel film. A step of applying a solution of a polyamic acid in an organic solvent as described above, a step of subsequently converting into a polyimide (a) and a thermoplastic polyimide (b), and a step of drying the film.

In this bonding sheet, the polyamic acid which is a precursor of the thermoplastic polyimide (b) is represented by the following general formula (1):

[0011]

Embedded image (In the formula, k is an integer of 1 or more, m and n are each an integer of 0 or more where m + n is 1 or more. A and B are tetravalent organic groups, and X and Y are divalent organic groups. )) (Claim 2). Further, claim 3 is that said A and B are of the following group (I):

[0012]

Embedded image Wherein X and Y are the following groups (II):

[0013]

Embedded image Wherein the polyimide (a) film is either a non-thermoplastic polyimide film or a thermoplastic polyimide film having a glass transition temperature of 350 ° C. or higher. It is characterized by the following.

The term “gel film” in the present invention
Is a film in a partially cured or partially dried state in the process of imidizing polyamic acid to form polyimide, and in a state in which polyamic acid and imidized polyimide are mixed, Refers to a film having supportability.

[0015]

Embodiments of the present invention will be described below.

First, the polyimide (a) of the present invention
The film will be described. The polyimide (a) film used in the present invention can be produced by a known method. That is, it can be obtained by casting an organic solvent solution containing a polyamic acid, which is a precursor substance of the polyimide (a), onto a support, and chemically or thermally imidizing the solution.

The polyamic acid, which is a precursor of the polyimide (a) used in the present invention, is usually composed of at least one aromatic dianhydride and at least one diamine in substantially equimolar amounts in an organic solvent. It is prepared by dissolving in it and stirring under controlled temperature conditions until the polymerization is complete.

Suitable acid anhydrides for synthesizing the polyamic acid corresponding to the polyimide (a) used in the present invention include pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride. Thing, 3,3 ', 4,4'-
Biphenyltetracarboxylic dianhydride, 1,2,5,6
-Naphthalenetetracarboxylic dianhydride, 2,2 ',
3,3′-biphenyltetracarboxylic dianhydride, 3,
3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl)
Propane dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) propane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) Ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride,
Bis (3,4-dicarboxyphenyl) ethane dianhydride, oxydiphthalic dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, p-phenylenebis (trimellitic acid monoester anhydride) , Ethylene bis (trimellitic acid monoester anhydride), bisphenol A bis (trimellitic acid monoester anhydride) and the like.

Among these, the most suitable acid dianhydrides for the polyimide (a) according to the present invention are pyromellitic dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and p-phenylenebis (trimellitic acid monoester acid anhydride), which can be used alone or in a mixture at any ratio.

Suitable diamines for synthesizing the polyamic acid corresponding to the polyimide (a) used in the present invention are 4,4'-diaminodiphenylpropane, 4,4 '
-Diaminodiphenylmethane, 3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine, 3,3'-
Dichlorobenzidine, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone,
4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 1,5-diaminonaphthalene, 4,4'-diaminodiphenyldiethylsilane,
4,4'-diaminodiphenylsilane, 4,4'-diaminodiphenylethylphosphine oxide, 4,4'-
Diaminodiphenyl N-methylamine, 4,4'-diaminodiphenyl N-phenylamine, 1,4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene, 1,2-diaminobenzene, and the like Including things.

Among these, suitable diamines for the polyimide (a) according to the present invention are particularly preferably 4,4'-diaminodiphenyl ether and p-phenylenediamine. 1
A mixture mixed at a ratio of 0:90 can be preferably used.

Solvents for synthesizing polyamic acid include amide solvents, ie, N, N-dimethylformamide,
Examples thereof include N, N-dimethylacetamide and N-methyl-2-pyrrolidone, and N, N-dimethylformamide can be particularly preferably used.

The polyamic acid solution obtained by polymerizing an acid anhydride and a diamine in the above organic solvent is preferably obtained at a concentration of 15 to 25% by weight as a polyamic acid solid content. . This is for obtaining an appropriate molecular weight and solution viscosity when the concentration is in this range.

The polyimide (a) is obtained by imidizing a polyamic acid. For the imidization, either a thermal curing method or a chemical curing method is used. Of these, the chemical cure method is more preferred. The thermal curing method is a method in which an imidization reaction proceeds only by heating without the action of a dehydrating ring-closing agent or the like.

The chemical curing method is a method in which a chemical conversion agent and a catalyst are allowed to act on a polyamic acid organic solvent solution. Chemical conversion agents include, for example, aliphatic anhydrides, aromatic anhydrides, N, N'-dialkylcarbodiimides, lower aliphatic halides, halogenated lower fatty acid anhydrides, arylphosphonic dihalides, thionyl halides or Mixtures of two or more thereof are mentioned. Among them, aliphatic anhydrides such as acetic anhydride, propionic anhydride, and lacnic anhydride or a mixture of two or more thereof can be preferably used.

As the catalyst, an aliphatic tertiary amine, an aromatic tertiary amine, a heterocyclic tertiary amine or the like is used.
Among them, isoquinoline, β-picoline, pyridine and the like can be particularly preferably used.

A heat curing method may be used in combination with the chemical curing method. The reaction conditions for imidization are the type of polyamic acid,
It may vary depending on the thickness of the film, the selection of the thermal curing method and / or the chemical curing method, and the like.

Specifically, a method for producing a polyimide film from a polyamic acid organic solvent solution will be described below by taking a chemical curing method as an example. After mixing the chemical conversion agent and the catalyst with the obtained polyamic acid composition, the mixture is cast on a support and coated. Next, by gentle heating at, for example, about 100 ° C., the chemical conversion agent and the catalyst are activated to transfer to a partially cured or partially dried polyamic acid film (hereinafter, referred to as a gel film).

The gel film is at an intermediate stage of imidization of the polyamic acid to the polyimide, and has a self-supporting property. The gel film is in a partially cured or partially dried state, and contains a polyamic acid and imidized polyimide. This gel film is adjusted so that the volatile component content and the imidization ratio are within a certain range. The volatile component content is calculated from Equation 1.

(AB) × 100 / B (1) In the formula 1, A and B represent the following. A is the weight of the gel film. B is the weight of the gel film after heating at 450 ° C. for 20 minutes.
Is calculated from (C / D) × 100 / (E / F) Formula 2 In Formula 2, C, D, E, and F represent the following. C: Absorption peak height of gel film at 1370 cm ^-1 D: Absorption peak height of gel film at 1500 cm ^-1 E: Absorption peak height of polyimide film at 1370 cm ^-1 F: Absorption peak of polyimide film at 1500 cm ^-1 Height The volatile content is in the range of 5 to 300%, preferably 5 to 300%.
-100%, more preferably 5-50%. The imidation ratio is in the range of 50% or more, preferably 70% or more, more preferably 80% or more, and most preferably 85% or more.

In order to suppress shrinkage in the tenter process, the obtained gel film is held at the edge of the film with a tenter clip or pin for suppressing shrinkage, and is heated stepwise to dry and imidize the film. Into a polyimide (a) film. Specifically, heating is performed stepwise from about 200 ° C., and finally to a temperature of about 400 ° C.
It is preferable to heat for 5 to 400 seconds. Further, the thickness of the final bonding sheet is preferably 6 to 100 μm, particularly preferably 15 to 90 μm in terms of flexibility and handling. At this time, the thickness of the polyimide (a) film is 5 to 80 μm.
m, especially 12 to 75 μm, and the thickness of the thermoplastic polyimide (b) layer is preferably 1 to 20 μm, particularly preferably 3 to 15 μm.

In the present invention, the polyamic acid solution for forming the thermoplastic polyimide (b) layer is immersed in the gel film stage of the polyimide (a) film,
A method using a T-die, a method using a doctor blade,
Alternatively, lamination is performed by a coating method such as a method using a reverse coater, but a polyimide (a) film obtained by a normal method obtained without laminating them is a non-thermoplastic polyimide film or a thermoplastic polyimide having a glass transition temperature of 350 ° C. or more. One of the films is preferred in terms of heat resistance.

Next, a method for preparing a polyamic acid used as a precursor of the thermoplastic polyimide (b) layer will be described. Polyamic acid, which is a precursor of the thermoplastic polyimide (b) layer, can be obtained basically in the same manner as the above-mentioned precursor of the polyimide (a) film. Those represented by the general formula (2) are preferred.

[0034]

Embedded image In the formula, R ¹ represents a tetravalent organic group selected from the following group (I);

[0035]

Embedded image It is particularly preferable to select two or more tetravalent organic groups from the group (I) and synthesize a polyamic acid using the corresponding acid dianhydride.

As the diamine component used for synthesizing the polyamic acid which is a precursor of the thermoplastic polyimide (b) layer, those represented by the following general formula (3) are preferable.

[0037]

Embedded image In the formula, R ² represents a divalent organic group selected from the following group (II);

[0038]

Embedded image It is particularly preferable to select two or more divalent organic groups from the group (II) and synthesize a polyamic acid using the corresponding diamine.

The molecular weights of the polyamic acid copolymer and the polyimide copolymer in the thermoplastic polyimide (b) layer are not particularly limited, but in order to maintain the strength as a heat-resistant adhesive, a number average molecular weight is required. The molecular weight is preferably 50,000 or more, more preferably 80,000 or more, and particularly preferably 100,000 or more. The molecular weight of the polyamic acid copolymer (solution) as the adhesive can be measured by GPC (gel permeation chromatography).

Although the embodiment of the heat-resistant bonding sheet according to the present invention has been described above, the present invention is not limited to this, and the present invention is based on the knowledge of those skilled in the art without departing from the scope of the present invention. , Various improvements,
The present invention can be implemented in a form in which changes and modifications are made. Hereinafter, the present invention will be described more specifically with reference to examples.

[0041]

EXAMPLE 1 The whole system was cooled with ice water and placed in a 2000 ml three-neck separable flask purged with nitrogen.
Aminophenoxy) phenyl] propane (hereinafter BAP
It is called P. ) 123.1 g was charged using 716.2 g of dimethylformamide (hereinafter referred to as DMF) and
Stirred for minutes. Subsequently, 33.8 g of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride (hereinafter referred to as “BTDA”) was charged using 20 g of DMF. Subsequently, 3,3 ′, 4,4′-ethylene glycol dibenzoate tetracarboxylic dianhydride (hereinafter referred to as TM
EG. ) 76.0 g was added using 20 g of DMF and stirred for 30 minutes. After stirring for 30 minutes, a solution in which 4.1 g of TMEG was dissolved in 36.9 g of DMF was gradually added while paying attention to the viscosity of the solution in the flask.
After that, it was left for 1 hour with stirring, and the solid concentration was 23%.
A polyamic acid solution for a thermoplastic polyimide (b) layer was obtained.

On the other hand, pyromellitic dianhydride / p-phenylene bis (trimellitic acid monoester anhydride)
After defoaming a 17% by weight DMF solution of polyamic acid, which was synthesized at a molar ratio of 5/5/4/6 / p-phenylenediamine / 4,4'-diaminodiphenyl ether, the final thickness was 17 μm. Was applied by casting on an aluminum foil. The polyamic acid solution on the aluminum foil was heated at 110 ° C. for 4 minutes to obtain a gel film having self-supporting properties. This gel film was immersed in a polyamic acid solution as a precursor of the thermoplastic polyimide (b) prepared above, and excess polyamic acid was removed so that the final one-sided thickness of the thermoplastic polyimide (b) layer was 4 μm. rear,
Heating was performed at 150 ° C., 200 ° C., 250 ° C., 300 ° C., and 350 ° C. for 1 minute each to obtain a bonding sheet having a total thickness of 25 μm. An 18 μm-thick rolled copper foil is laminated on the thermoplastic polyimide (b) surface of the obtained bonding sheet,
A 25 μm-thick polyimide film was provided thereon as a release film, and was laminated with a double belt press (DBP) to obtain a copper-clad laminate. Laminating temperature is 28
The temperature was 0 ° C., the pressure was 70 kgf / cm ² , and the lamination time was about 5 minutes. Regarding the obtained copper-clad laminate, JIS C
6481, adhesive strength (kgf / cm), JIS6
471, the solder heat resistance was measured. Table 1 shows the results.
Shown in Solder heat resistance after normal condition adjustment (20 ° C, 60% R
H, after adjusting for 24 hours, soak at 300 ° C for 1 minute), after absorbing moisture (40 ° C, 90% RH, after adjusting for 96 hours, 280 ° C)
(Dipping for 10 seconds). Table 1 shows the results.

Example 2 Preparation of a polyamic acid solution as a precursor of a thermoplastic polyimide and preparation of a gel film of a polyimide (a) film were performed in the same manner as in Example 1, and the gel film was applied to the gel film using a comma coater. Polyamic acid was applied to a final thickness of 4 μm. Thereafter, drying, production of a copper-clad laminate, and measurement of physical properties were performed in the same manner as in Example 1. Table 1 shows the results.

Example 3 The entire system was cooled with ice water, and 82.2 g of BAPP was placed in a 2000 ml three-neck separable flask purged with nitrogen.
It was charged using 0.0 g of DMF and stirred for 15 minutes. Subsequently, 21.3 g of BTDA was charged using 40 g of DMF. Subsequently, 2,2'-bis (hydroxyphenyl)
71.5 g of propane dibenzoate tetracarboxylic dianhydride (hereinafter referred to as ESDA) was added using 20 g of DMF and stirred for 30 minutes. After stirring for 30 minutes, a solution in which 5.8 g of ESDA was dissolved in 52.2 g of DMF was gradually added while paying attention to the viscosity of the solution in the flask. A 23% polyamic acid solution for the thermoplastic polyimide (b) layer was obtained.

A gel film of the polyimide (a) film was prepared in the same manner as in Example 1, and a polyamic acid was applied to the gel film so as to have a final thickness of 4 μm using a comma coater. Thereafter, drying, production of a copper-clad laminate, and measurement of physical properties were performed in the same manner as in Example 1. Table 1 shows the results.

[0046]

[Table 1]

[0047]

As described above, the bonding sheet according to the present invention is excellent in heat resistance, the peel strength at the interface between the base film and the thermoplastic polyimide and between the thermoplastic polyimide and the copper foil, and the dimensional characteristics, and the bonding sheet according to the present invention. It is suitable for use in new high-density packaging materials such as flex board materials, COF and LOC packages, and MCM.

Claims (4)

[Claims] 1. A process for producing a laminate comprising a thermoplastic polyimide (b) layer laminated on one side or both sides of a polyimide (a) film comprises a step of partially removing a polyamic acid which is a precursor of the polyimide (a). Producing an imidized gel film, applying an organic solvent solution of polyamic acid, which is a precursor of the thermoplastic polyimide (b), to the surface of the gel film, and then applying the polyimide (a) and the thermoplastic A method for producing a heat-resistant bonding sheet, comprising a step of converting into a polyimide (b) and a step of drying the film. 2. A polyamic acid, which is a precursor of the thermoplastic polyimide (b) layer, has the general formula (1): ## STR1 ## (In the formula, k is an integer of 1 or more, m and n are each an integer of 0 or more where m + n is 1 or more. A and B are tetravalent organic groups, and X and Y are divalent organic groups. )),
A method for producing the heat-resistant bonding sheet according to claim 1. 3. A group (I) wherein A and B in the general formula (1) are as follows: Wherein X and Y are groups (II) shown below: The method for producing a heat-resistant bonding sheet according to claim 2, wherein the divalent organic group is selected from the group consisting of: 4. The polyimide (a) film is a non-thermoplastic polyimide film or a glass transition temperature of 350 ° C.
The method for producing a heat-resistant bonding sheet according to any one of claims 1 to 3, wherein the method is any one of the thermoplastic polyimide films described above.