JP2007235006A - Reinforcing plate for flexible printed circuit board and flexible printed circuit board using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reinforcing plate for a flexible printed circuit board superior in adhesive property. <P>SOLUTION: The reinforcing plate for flexible printed circuit board has at least one polyimide resin layer, and has a thickness of 70-360 μm, wherein both contact angles of water of both surfaces are 50° or less at 25°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a reinforcing plate for a flexible printed circuit board.

  In recent years, electronic devices have been reduced in size, thickness, and density, and the role of a flexible printed circuit board has become important for mounting in a narrow space. Further, due to advances in mounting technology, the demand for high-density mounting has rapidly increased, and component-mounted flexible printed circuit boards that mount components directly on flexible printed circuit boards have been widely used. Since such a component mounting flexible circuit board does not have rigidity, a reinforcing plate is attached to an electronic component mounting or connector connecting portion. As such a reinforcing plate for a flexible circuit board, polyimide films are widely used because of excellent mechanical characteristics, electrical characteristics, chemical resistance, heat resistance, environmental resistance, and the like.

The purpose of the reinforcing plate is to give rigidity to the flexible printed circuit board. So far, it has been disclosed to use a polyimide film having a thickness of 120 μm or more as a reinforcing plate for a flexible circuit board (for example, see Patent Document 1). Since the reinforcing plate is usually bonded to the flexible printed circuit via an adhesive sheet, the adhesiveness to the adhesive sheet is important. However, conventionally known reinforcing plates for flexible circuit boards have sufficient adhesiveness. I did not.
Japanese Patent Laid-Open No. 2004-149591

  An object of the present invention is to solve the above-mentioned problems and to provide a flexible printed circuit reinforcing plate excellent in adhesiveness.

  An object of the present invention is a reinforcing plate for a flexible printed circuit board having at least one polyimide resin layer, the thickness is 70 μm or more and 360 μm or less, and the contact angles of water on both sides are both 25 ° C. Is achieved by a reinforcing plate for a flexible printed circuit board, which is characterized by being 50 degrees or less.

  ADVANTAGE OF THE INVENTION According to this invention, the reinforcement board for flexible printed circuits based on the polyimide film excellent in adhesiveness can be provided.

  The flexible printed circuit board reinforcing plate (hereinafter referred to as a reinforcing plate) of the present invention has at least one polyimide resin layer. By having a polyimide resin layer, it is excellent in mechanical properties, electrical properties, chemical resistance, heat resistance, and environmental resistance.

  The thickness of the reinforcing plate of the present invention is 70 μm or more and 360 μm or less. If it is less than 70 μm, the rigidity is insufficient and it is insufficient for use as a reinforcing plate. On the other hand, if it exceeds 360 μm, there is a problem in punching workability and workability, which is not practical. Preferably they are 175 micrometers or more and 300 micrometers or less.

  The reinforcing plate of the present invention is characterized in that the contact angles of water on both sides are 50 degrees or less at 25 ° C. Preferably it is 40 degrees or less. When the contact angle exceeds 50 degrees, the wettability is insufficient and the adhesiveness with the adhesive sheet is lowered. Examples of the method for setting the contact angle to 50 degrees or less include an easy adhesion treatment described later.

  In general, when the thickness of the polyimide film exceeds 175 μm, the film forming efficiency is extremely lowered and the cost is increased. In the present invention, when two or more layers of polyimide films having a general thickness of 50 μm to 175 μm are laminated via an adhesive layer, a flexible printed circuit board reinforcing plate having a thickness exceeding 175 μm can be stably obtained at a low cost. Is preferable.

  The adhesive layer is required to have adhesiveness, heat resistance, solder heat resistance, and chemical resistance in consideration of a flexible printed circuit manufacturing process such as a heating plate pressing process, a plating process, and a solder reflow process. In the present invention, the adhesive layer preferably contains an epoxy resin, a carboxyl group-containing acrylonitrile butadiene rubber and a curing agent.

  The epoxy resin is not particularly limited as long as it contains two or more epoxy groups in the molecule, and examples thereof include bisphenol A type epoxy resin, bisphenol F type epoxy resin, biphenol type epoxy resin, and novolak type epoxy resin. In order to impart flame retardancy, it is effective to use a halogenated epoxy resin, particularly a brominated epoxy resin. At this time, although the flame resistance can be imparted only with the brominated epoxy resin, the heat resistance of the adhesive is greatly reduced. Therefore, it is more effective to use a mixed system with a non-brominated epoxy resin. Two or more kinds may be used in consideration of bromine content and epoxy equivalent.

  The carboxyl group-containing acrylonitrile butadiene rubber (hereinafter referred to as NBR-C) preferably used in the present invention is, for example, a terminal of a copolymer rubber obtained by copolymerizing acrylonitrile and butadiene in a molar ratio of about 10/90 to 50/50. Examples thereof include those obtained by carboxylating groups, or terpolymer rubbers of carboxyl group-containing polymerizable monomers such as acrylonitrile, butadiene, acrylic acid, and maleic acid. The amount of acrylonitrile is preferably 10 mol% or more from the viewpoint of chemical resistance of the cured product, and preferably 50 mol% or less from the viewpoint of solubility in a solvent. Further, the carboxyl group content is preferably 0.01 to 0.15 ephr. Here, ephr is an abbreviation for equivalent parts per hundred rubber, and means the equivalent of carboxyl groups per 100 parts by weight of NBR-C. If carboxyl group content is 0.01 ephr or more, the cured | curing material excellent in heat resistance will be obtained by reaction with an epoxy resin. On the other hand, if it is 0.15 ephr or less, an adhesive solution excellent in applicability when the adhesive layer is applied can be obtained. Furthermore, the range of 0.03-0.1 ephr is more preferable.

  20-200 weight part is preferable with respect to 100 weight part of epoxy resins, and, as for content of the said NBR-C, 30-100 weight part is more preferable. If it is 20 parts by weight or more, the adhesion is good, and if it is 200 parts by weight or less, the solder heat resistance is good.

  Curing agents preferably used in the present invention include amine compounds such as diaminodiphenylmethane, diaminodiphenyl sulfide, diaminobenzophenone, diaminodiphenylsulfone, and diethyltriamine, 2-alkyl-4-methylimidazole, and 2-phenyl-4-alkyl. Examples include imidazole derivatives such as imidazole, organic acids such as phthalic anhydride and trimellitic anhydride, boron trifluoride amine complexes such as boron trifluoride triethylamine complex, and dicyandiamide. Also good. Moreover, you may use phenol resins, such as a resol type and a novolak type phenol resin, as a hardening | curing agent. Examples of the phenolic resin include alkyl-substituted phenols such as phenol, cresol and pt-butylphenol, cyclic alkyl-modified phenols such as terpene and dicyclopentadiene, and functional groups containing heteroatoms such as nitro group, halogen group, amino group and cyano group. Examples thereof include those having a group and those having a skeleton such as naphthalene and anthracene.

  In the present invention, if necessary for the adhesive layer, metal hydroxide such as aluminum hydroxide, magnesium hydroxide, calcium aluminate hydrate, silica, alumina, zinc oxide, antimony trioxide, antimony pentoxide, Metal oxides such as magnesium oxide and titanium oxide, inorganic salts such as calcium carbonate, and inorganic particles such as carbon black may be contained singly or in combination. In addition to the above components, it is not limited at all to contain organic and inorganic components such as an antioxidant and an ion scavenger within a range not impairing the properties of the adhesive.

  Next, the example of the manufacturing method of the reinforcement board of this invention is demonstrated. The reinforcing plate of the present invention is characterized in that the contact angles of water on both sides are 50 degrees or less at 25 ° C. Preferably it is 40 degrees or less. Examples of the method of setting the contact angle to 50 degrees or less include a method of subjecting a polyimide resin layer to easy adhesion treatment such as corona discharge treatment, low temperature plasma treatment, sand mat surface treatment, and anchor coat treatment. A plurality of these processes may be combined.

  The corona discharge treatment may be performed after the surface of the reinforcing plate is not treated, or after treatment with an organic solvent such as acetone, isopropyl alcohol, ethyl alcohol or the like.

When performing the low temperature plasma discharge treatment, the pressure of the atmosphere is not particularly limited, but a range of 0.1 to 1500 Pa is preferable. If it is this pressure range, a functional group can be introduced moderately. More preferably, it is 0.1-100 Pa. The gas composition is not particularly limited, but preferably contains oxygen. Or it is also preferable to contain 20 mol% or more of noble gases. Examples of the rare gas include He, Ne, Ar, and Xe, and Ar is preferable. Rare gas _{CO 2, N 2, H 2} , H 2 O , etc. may be mixed to use, _CO 2 from the viewpoint of introducing an OH group or COOH group, _{O 2} is preferred. The plasma irradiation time is preferably about 1 second to 10 minutes. More preferably, it is 1 second to 1 minute. The applied voltage is preferably 1 to 8 kV.

  Next, an example of a method for manufacturing a reinforcing plate having two or more polyimide resin layers through an adhesive layer will be described.

  (A) A paint obtained by dissolving the adhesive composition in a solvent is applied on a polyimide film and dried. It is preferable to apply so that the thickness of the adhesive layer is 10 to 100 μm. Drying conditions are generally 100 to 200 ° C. and 1 to 5 minutes. Solvents are not particularly limited, but aromatics such as toluene, xylene and chlorobenzene, ketones such as methylethylketone and methylisobutylketone, and aprotic polar solvents such as dimethylformamide, dimethylacetamide and N-methylpyrrolidone alone or a mixture are preferred. It is.

  (B) Another polyimide film is laminated on the adhesive-coated polyimide film prepared in (a) to obtain a polyimide film laminate. In order to obtain a desired thickness, the thickness of the polyimide film and the film thickness of the adhesive may be adjusted. When the thickness is further increased, the polyimide film may be laminated a plurality of times through the adhesive layer.

  (C) By heat-treating the obtained polyimide film laminate, the adhesive is heat-cured and then subjected to the aforementioned easy adhesion treatment to obtain the reinforcing plate of the present invention. The heat treatment can be performed in the form of a roll or a sheet. In the case of heat treatment in a roll shape, in order to suppress swelling and foaming due to expansion when moisture in the polyimide film is vaporized, step treatment is performed at 60 ° C to 100 ° C for 1 to 2 hours and at 150 ° C to 160 ° C for 1 to 4 hours. It is preferable to implement.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The evaluation method will be described before the description of the examples.

(1) Sample preparation method for evaluation A reinforcing plate is placed on the glossy surface of 35 μm thick electrolytic copper foil (Nikko Materials Co., Ltd., JTC foil) via an adhesive sheet (DuPont Co., Ltd., Piralux R). Then, a sample for evaluation was produced by laminating under press conditions of 180 ° C., 30 kg / cm ² and 30 minutes.

(2) Contact angle of water For the measurement of the contact angle, a contact angle meter CA-D type manufactured by Kyowa Interface Science Co., Ltd. was used. As a method for measuring the contact angle, about 2.0 μl of distilled water was deposited on the surface of the reinforcing plate to produce a droplet, and the droplet was displayed on a screen with a CCD camera. The scale on the extension line of the line connecting the part and the apex was read and doubled as the contact angle.

(3) Adhesive force Using the sample for evaluation produced by the method of (1) above, a 2 mm wide polyimide film was peeled off at a rate of 50 mm / min in the 90 ° direction in accordance with JIS-C6481, The adhesive force was measured.

(4) Rigidity The numerical value calculated by the following formula (1) from the elastic modulus of the polyimide film used for the reinforcing plate and the thickness of the polyimide film layer excluding the adhesive layer was defined as rigidity.
Rigidity (N) = Elastic modulus (N / m ² ) × Thickness (m) × Thickness (m) (1)
(5) Solder heat resistance It carried out by the method based on JIS-C6481. The sample for evaluation produced by the above method (1) was conditioned for 24 hours in an atmosphere of 40 ° C. and 90% RH, then immediately floated on the solder bath for 30 seconds, and the maximum temperature without swelling and peeling was measured. .

Example 1
As the polyimide resin layer, a polyimide film with a thickness of 75 μm (Upilex S manufactured by Ube Industries, Ltd.) was used, and the surface and the back surface were subjected to low-temperature plasma discharge treatment under conditions of pressure 50 Pa, gas CO ₂ , voltage 3 kV for 5 seconds, A reinforcing plate having a thickness of 75 μm was obtained.

Example 2
A reinforcing plate having a thickness of 125 μm was obtained in the same manner as in Example 1 except that the thickness of the polyimide film was 125 μm.

Example 3
Aluminum hydroxide (manufactured by Showa Denko KK, H-421) was used as a toluene solution, and then sand milled to prepare an aluminum hydroxide dispersion. NBR-C (manufactured by JSR Corporation, PNR-1H), brominated epoxy resin (manufactured by Japan Epoxy Resin Corporation, Epicoat 5050 epoxy equivalent 395), non-brominated epoxy resin (Japan Epoxy Resin ( Co., Ltd., Epicoat 828 epoxy equivalent 189), 3,3′-diaminodiphenylsulfone (3,3′-DDS) and an equivalent weight of methyl ethyl ketone were added so as to have the composition ratio shown in Table 1, respectively. The mixture was stirred and mixed to prepare an adhesive solution.

This adhesive was applied to a 75 μm-thick polyimide film (Ube Industries, Upilex S) with a bar coater to a dry thickness of about 25 μm, dried at 150 ° C. for 5 minutes, and further 75 μm thick The polyimide film was laminated and heat-treated at 150 ° C. for 1 hour to obtain a reinforcing plate having a thickness of 175 μm. Thereafter, the surface and the back surface of the reinforcing plate were subjected to plasma discharge treatment under the conditions of pressure 30 Pa, gas CO ₂ and voltage 4 kV for 5 seconds.

Example 4
A reinforcing plate having a thickness of 225 μm was obtained in the same manner as in Example 3 except that the thickness of the polyimide film was changed to 75 μm and 125 μm.

Example 5
The adhesive obtained in the same manner as in Example 3 was applied to a 75 μm thick polyimide film with a bar coater to a dry thickness of about 25 μm, dried at 150 ° C. for 5 minutes, and further laminated with a 75 μm thick polyimide film. Thus, a polyimide film laminate having a thickness of 175 μm was obtained. An adhesive was further applied to this laminate with a bar coater to a dry thickness of 25 μm, dried at 150 ° C. for 5 minutes, and a 75 μm thick polyimide film was laminated to obtain a 275 μm thick reinforcing plate. Otherwise, heat treatment was performed in the same manner as in Example 3, and the front and back surfaces of the reinforcing plate were subjected to low-temperature plasma discharge treatment.

Example 6
In a 300 ml separable flask equipped with a DC stirrer, 19.43 g (97 mmol) of 4,4′-diaminodiphenyl ether and 149.5 g of N, N′-dimethylacetamide were placed and stirred at room temperature under a nitrogen atmosphere. After stirring for 30 minutes, 0.159 g (0.97 mmol) of 5-norbornene-2,3-dicarboxylic dianhydride was added and stirred. Further, 30 minutes to 1 hour later, 20.53 g (94 mmol) of pyromellitic dianhydride was added in several portions. After stirring for 1 hour, 10.58 g of a pyromellitic dianhydride N, N′-dimethylacetamide solution (6 wt%) was added dropwise over 30 minutes and the mixture was further stirred for 1 hour to prepare a polyamic acid solution.

  On the other hand, in a 300 ml separable flask equipped with a DC stirrer, 9.91 g (50 mmol) of 4,4′-diaminodiphenylmethane and 103.86 g of N, N′-dimethylacetamide were placed and stirred at room temperature under a nitrogen atmosphere. After stirring for 30 minutes, 10.63 g (33 mmol) of benzophenonetetracarboxylic dianhydride was added in several portions. After stirring for 1 hour, 5.41 g (33 mmol) of 5-norbornene-2,3-dicarboxylic anhydride was added and stirred for another 30 minutes to prepare a PMR solution.

  5.08 g of PMR solution was added to 100 g of polyamic acid solution, and a part of the polyamic acid mixture solution obtained by stirring and defoaming was taken on a polyester film, and a uniform film was formed using a spin coater. This was heated in an oven at 100 ° C. for 1 hour to obtain a self-holding polyamic acid film. The obtained polyamic acid film was heat-treated at 200 ° C. for 30 minutes, 300 ° C. for 20 minutes, and 400 ° C. for 5 minutes to obtain a polyimide film having a thickness of 175 μm.

  The polyimide film having a thickness of 175 μm thus obtained was coated with an adhesive so as to have a dry thickness of about 10 μm by the same method as in Example 3 and further laminated with the polyimide film having a thickness of 175 μm. . Thereafter, the adhesive was cured and subjected to low-temperature plasma discharge treatment in the same manner as in Example 3 to obtain a reinforcing plate having a thickness of 360 μm.

Comparative Example 1
Upilex 75S manufactured by Ube Industries, Ltd. was used as a reinforcing plate.

Comparative Example 2
As a reinforcing plate, Kapton 300V manufactured by Toray DuPont Co., Ltd. was used.

Comparative Example 3
Upilex 125S manufactured by Ube Industries, Ltd. was used as a reinforcing plate.

Comparative Example 4
A 175 μm thick polyimide film obtained in Example 6 was used as a reinforcing plate in a single layer.

  Table 2 shows the evaluation results of Examples 1 to 6 and Comparative Examples 1 to 4. From Table 2, it can be seen that the reinforcing plate obtained by the present invention is superior in adhesiveness to the comparative example.

Claims (4)

A reinforcing plate for a flexible printed circuit board having at least one polyimide resin layer, having a thickness of 70 μm or more and 360 μm or less, and a contact angle of water on both sides of 50 ° C. or less at 25 ° C. A reinforcing plate for a flexible printed circuit board. The reinforcing plate for a flexible printed circuit board according to claim 1, wherein the surface is treated by at least one method selected from corona discharge treatment, low temperature plasma treatment, sand mat surface treatment, and anchor coat treatment. The reinforcing plate for a flexible printed circuit board according to claim 1, comprising two or more polyimide resin layers through an adhesive layer. The flexible printed circuit board using the reinforcement board for flexible printed circuit boards in any one of Claims 1-3.