JP2003109989A - Polyimide film for flexible printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide film for flexible printed board that is superior in dimensional stability during the heating and wetting steps as well as in flexibility and handling property. SOLUTION: This polyimide film for flexible printed board is 5 to 20 μm in film thickness, and its Yong's modulus is 4 to 7 GPa and its coefficient of thermal expansion is 14 to 22 ppm/ deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyimide film for a flexible printed circuit board, which has a small coefficient of thermal expansion and a coefficient of humidity expansion, is excellent in dimensional stability, and is flexible and easy to handle.

[0002]

2. Description of the Related Art Conventionally, polyimide films for flexible printed circuit boards have been required to have flexibility such as flexibility and bending resistance, and polyamic acid composed of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride is imidized. Film thickness obtained by liquefying
m polyimide film has been mainly used. Although this polyimide film is highly flexible, it has a high coefficient of thermal expansion and high coefficient of humidity expansion, so there is a large dimensional change in the process until the flexible printed circuit board is made. It has become unsuitable for flexible printed circuit boards that require dimensional stability.

In order to improve the dimensional stability, the above-mentioned 2
A polyimide film obtained by imidizing a polyamic acid obtained by adding para-phenylenediamine to two components has been prepared. However, although this polyimide film is excellent in dimensional stability during heating, it has a drawback that it has a high water absorption coefficient and a high coefficient of humidity expansion, resulting in a large dimensional change during a wet process such as chemical cleaning. Further, the flexibility is impaired as compared with a polyimide film composed of 4,4′-diaminodiphenyl ether and pyromellitic dianhydride alone.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made as a result of studying the solution of the above-mentioned problems in the prior art, and is excellent in dimensional stability during the heating step and the wet step, and is flexible. The purpose of the present invention is to provide a polyimide film for a flexible printed circuit board, which is excellent in handleability and has good handleability.

[0005]

In order to achieve the above object, the polyimide film for a flexible printed board of the present invention has a film thickness of 5 to 20 μm, a Young's modulus of 4 to 7 GPa and a thermal expansion coefficient of 14 to 22 ppm. / ° C. Furthermore, the polyimide film for flexible printed circuit boards of the present invention has the following (1) to
It is preferable to have the condition (3) together. (1) Water absorption rate is 2.2% or less, humidity expansion coefficient is 20 pp
m /% RH or less. (2) The polyimide film has para-phenylenediamine as an aromatic diamine component, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether,
Consists of a polyimide containing at least two of 4,4'-diaminodiphenylmethane. (3) The polyimide film is composed of a polyimide containing at least one of pyromellitic acids, biphenyltetracarboxylic acids, and benzophenonetetracarboxylic acids as an aromatic tetracarboxylic acid compound component.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The polyimide film of the present invention will be described in detail below.

In manufacturing the flexible printed circuit board, the film thickness is 5 to 20 μm and the Young's modulus is 4 to 4 in order to maintain the handling property in the process and to give the flexibility of the manufactured flexible printed circuit board.
It is preferably within the range of 7 GPa. If the film thickness is thinner than this range, handling in the process
If the thickness is increased, the flexibility of the substrate is impaired, which is not preferable. Also, Young's modulus of 4 GPa or less impairs handleability and 7 GPa or more deteriorates flexibility, which is not preferable.

In order to reduce the dimensional change rate and the curl due to the bonding with copper, the coefficient of thermal expansion is 14 to 22.
It is preferably ppm / ° C. If it deviates from this range, the difference from the coefficient of thermal expansion of copper becomes large, and when it is bonded to copper, a strain occurs and a dimensional change becomes large, which is not preferable.

Further, in order to suppress the strain in the wet process, it is preferable to suppress the water absorption rate to 2.2% or less, and to reduce the dimensional change in the wet process, the humidity expansion coefficient is set to 20 ppm /% RH or less. It is preferable to suppress it.

Next, a polyamic acid solution which is a precursor for obtaining the polyimide film of the present invention will be described.

The polyamic acid solution used in the present invention is
Paraphenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether,
An aromatic diamine component containing at least two kinds of 4,4′-diaminodiphenylmethane and pyromellitic acid,
It is preferably obtained by polymerizing, in a solvent, an aromatic tetracarboxylic acid compound component containing at least one of biphenyltetracarboxylic acids and benzophenonetetracarboxylic acids.

The polymerization method may be carried out by any known method, for example, (1) first, the total amount of the aromatic diamine component is placed in a solvent, and then the aromatic tetracarboxylic acid component is added in an amount equivalent to the total amount of the aromatic diamine component. To add and polymerize.

(2) A method in which the entire amount of the aromatic tetracarboxylic acid component is first placed in a solvent, and then the aromatic diamine component is added in an amount equal to that of the aromatic tetracarboxylic acid component to carry out polymerization.

(3) One of the aromatic diamine compounds was placed in a solvent and then mixed at a ratio of 95 to 105 mol% of an aromatic tetracarboxylic acid compound to the reaction components for a time required for the reaction. After that, an aromatic diamine compound different from the one previously added is added, and then an aromatic tetracarboxylic acid compound is added so that the wholly aromatic diamine component and the wholly aromatic tetracarboxylic acid component are approximately equal in amount. How to polymerize.

(4) After the aromatic tetracarboxylic acid compound is put in a solvent, and then mixed at a ratio of 95 to 105 mol% of one aromatic diamine compound to the reaction components for a time necessary for the reaction. , An aromatic tetracarboxylic acid compound is added, and then an aromatic diamine compound different from the one previously added is added so that the wholly aromatic diamine component and the wholly aromatic tetracarboxylic acid component are approximately equal in amount and polymerized. how to.

(5) A polyamic acid solution (A) is prepared by reacting one aromatic diamine component and an aromatic tetracarboxylic acid in a solvent so that one of them is in excess, and the polyamic acid solution (A) is prepared in another solvent. Prepares a polyamic acid solution (B) by reacting another aromatic diamine component and an aromatic tetracarboxylic acid so that either one becomes excessive. A method of mixing the thus obtained polyamic acid solutions (A) and (B) to complete the polymerization. At this time, when the aromatic diamine component is excessive when adjusting the polyamic acid solution (A), the aromatic tetracarboxylic acid component is excessive in the polyamic acid solution (B), and the aromatic tetracarboxylic acid component is excessive in the polyamic acid solution (A). When the acid component is excessive, the polyamic acid solution (B) contains excess aromatic diamine component, and the polyamic acid solutions (A) and (B) are added.
Are mixed so that the wholly aromatic diamine component and the wholly aromatic tetracarboxylic acid component used in these reactions are adjusted to be approximately equal in amount.

The polymerization method is not limited to these, and other known methods may be used.

Next, a method for obtaining a polyimide film from the obtained polyamic acid solution will be described.

First, a polyamic acid solution is chemically cyclized by using a cyclization catalyst and a dehydrating agent or thermally cyclized by heat treatment to obtain a polyimide gel film.

Next, fix the end of this gel film,
1.05-1.5 in the vertical direction, 1.05-2.0 in the horizontal direction
It is preferable to stretch at a magnification of. When such biaxial stretching is performed, the mechanical properties of the obtained polyimide film are improved,
Furthermore, the isotropic property is improved, which is preferable.

Among the aromatic tetracarboxylic acid compounds used in the present invention, examples of pyromellitic acid are pyromellitic acid or its dianhydride, and examples of biphenyltetracarboxylic acid are 3,3 '. , 4,4′-biphenyltetracarboxylic acid or a dianhydride thereof is used as an example of benzophenonetetracarboxylic acid, 3,3 ′,
4,4'-benzophenone tetracarboxylic acid or its dianhydride can be mentioned.

As the solvent used in the above polymerization, dimethyl sulfoxide, N, N-dimethylacetamide,
Examples thereof include N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethylformamide, N-methyl-2-pyrrolidone and dimethyl sulfone, and these are preferably used alone or in combination.

The polyamic acid obtained by the above polymerization is adjusted so as to be 10 to 30% by weight in the solvent.

When the obtained polyamic acid is cyclized into a polyimide film, it may be carried out by either a chemical ring-closing method of dehydrating using a dehydrating agent and a catalyst or a thermal ring-closing method of thermally dehydrating. The chemical ring closure method is preferable because the film obtained can have chemical etching properties.

Examples of the dehydrating agent used in the chemical ring closure method include aliphatic acid anhydrides such as acetic anhydride and aromatic acid anhydrides such as phthalic anhydride. These may be used alone or in combination. Is preferred. Further, as the catalyst, heterocyclic tertiary amines such as pyridine, picoline and quinoline, aliphatic tertiary amines such as triethylamine,
Examples thereof include aromatic tertiary amines such as N, N-dimethylaniline, and these are preferably used alone or in combination.

When the chemical ring-closing method is carried out, a catalyst and a dehydrating agent are mixed in a polyamic acid solution to imidize it and then the solution is coated to obtain a polyimide film, and a polyamic acid solution is coated to form a thin film. There is a method of obtaining a polyimide film by immersing it in a mixture of a catalyst and a dehydrating agent and then imidizing it.

An organic filler or an inorganic filler may be mixed with the polyamic acid solution in order to roughen the surface of the obtained polyimide film to give the film slipperiness and improve the process stability.

In order to impart adhesiveness to the obtained polyimide film, the film surface may be subjected to physical treatment such as electrical treatment such as corona treatment or plasma treatment or blast treatment, and further, thermal treatment. The film may be heat relaxed by an annealing treatment to stabilize it.

The polyimide film thus obtained has suitable properties for a flexible printed board. That is, a polyimide film having a small coefficient of thermal expansion and a coefficient of humidity expansion, excellent dimensional stability, rich flexibility, and excellent handling property can be obtained.

[0030]

EXAMPLES The present invention will be specifically described below with reference to examples.

In the examples, PPD is paraphenylenediamine, 4,4'-ODA is 4,4'-diaminodiphenyl ether, 3,4'-ODA is 3,4'-diaminodiphenyl ether, and PMDA is pyromellitic acid diester. Anhydride, BPDA represents 3,3′-4,4′-diphenyltetracarboxylic dianhydride, and DMAc represents N, N-dimethylacetamide, respectively.

Example 1 DMAc 239.1 g was put in a 500 ml separable flask, and PPD2.
311 g (21.4 mmol), 4,4'-ODA2
4.254 g (121.1 mmol), PMDA21.
757 g (99.7 mmol), BPDA12.578
g (42.7 mmol) was added, and the mixture was reacted at room temperature and atmospheric pressure for 1 hour to obtain a polyamic acid solution.

After taking 7.5 g of this polyamic acid solution and cooling it at -5 ° C, the polyamic acid was imidized by mixing 0.8 g of acetic anhydride and 0.8 g of β-picoline.

The polyimide polymer thus obtained was coated on a glass plate and heated at 100 ° C. for 5 minutes to obtain a gel film. The gel film was peeled off from the glass plate and the ends of the gel film were pinned. Then, it was stretched 1.1 times in the longitudinal direction and 1.3 times in the lateral direction. Then 300
The film was heated and dried at 20 ° C. for 20 minutes and then at 400 ° C. for 5 minutes to obtain a polyimide film having a thickness of 12.5 μm.

[Example 2] DMAc 239.1 g was put in a 500 ml separable flask, and PPD3.
116 g (28.8 mmol), 4,4'-ODA2
3.076 g (115.2 mmol), PMDA21.
994 g (100.8 mmol), BPDA 12.71
5 g (43.2 mmol) was added and the reaction was carried out at room temperature and normal pressure for 1 hour to obtain a polyamic acid solution.

After that, the thickness 1 is obtained by the same procedure as in the first embodiment.
A 2.5 μm polyimide film was obtained.

[Example 3] DMAc 239.1 g was put in a 500 ml separable flask, and PPD3.
937 g (36.4 mmol), 4,4'-ODA2
1.872 g (109.2 mmol), PMDA22.
236 g (101.9 mmol), BPDA 12.85
5 g (43.7 mmol) was added and the reaction was carried out at room temperature and atmospheric pressure for 1 hour to obtain a polyamic acid solution.

Thereafter, the thickness of 1 is obtained by the same procedure as in the first embodiment.
A 2.5 μm polyimide film was obtained.

[Example 4] DMAc 239.1 g was put in a 500 ml separable flask, and 3,4'-
ODA 14.574 g (72.8 mmol), 4,4 '
-ODA 14.574 g (72.8 mmol), PMD
A31.751 g (145.6 mmol) was added, and the mixture was reacted at room temperature and normal pressure for 1 hour to obtain a polyamic acid solution.

After that, the thickness 1 is obtained by the same procedure as in the first embodiment.
A 2.5 μm polyimide film was obtained.

[Comparative Example 1] DMAc (239.1 g) was put in a 500 ml separable flask, and 4,4'- was added thereto.
ODA 29.149 g (145.6 mmol), PMD
A31.751 g (145.6 mmol) was added, and the mixture was reacted at room temperature and normal pressure for 1 hour to obtain a polyamic acid solution.

After taking 15 g of this polyamic acid solution and cooling it at -5 ° C, the polyamic acid was imidized by mixing 1.5 g of acetic anhydride and 1.6 g of β-picoline.

The polyimide polymer thus obtained was coated on a glass plate and heated at 100 ° C. for 5 minutes to obtain a gel film. The gel film was peeled off from the glass plate, and the ends of the gel film were pinned. Then, it was stretched 1.1 times in the longitudinal direction and 1.3 times in the lateral direction. Then 300
The film was heated and dried at 20 ° C. for 20 minutes and then at 400 ° C. for 5 minutes to obtain a polyimide film having a thickness of 25 μm.

[Comparative Example 2] DMAc (239.1 g) was placed in a 500 ml separable flask, and 5.056 g (46.8 mmol) of paraphenylenediamine was added thereto.
4'-ODA 21.847 g (109.1 mmol),
33.997 g (155.9 mmol) of PMDA was added and the reaction was carried out at room temperature and normal pressure for 1 hour to obtain a polyamic acid solution.

Thereafter, the thickness of 2 is obtained by the same procedure as in Comparative Example 1.
A 5 μm polyimide film was obtained. <Evaluation Method of Each Property of Polyimide Film> (1) Film Thickness It was measured using a Lightmatic (Series 318) manufactured by Mitutoyo. (2) Young's modulus device: RTM-250 is used, tensile speed: 100 mm
It was measured under the condition of / min. (3) Thermal expansion coefficient device: TMA-50 is used, measurement temperature range: 50 to 2
The measurement was carried out under the conditions of 00 ° C. and temperature rising rate: 10 ° C./min. (4) Water absorption rate: 98%, allowed to stand in a desiccator under RH atmosphere for 2 days,
The evaluation was made by the weight% increase with respect to the dry weight. (5) A film was attached to the inside of the TM7000 furnace at a humidity expansion coefficient of 25 ° C., a dry gas was fed into the furnace to dry the film, and then the inside of the TM7000 furnace was changed to 9 by supplying air from the HC-1 type steam generator.
The humidity expansion coefficient was calculated from the dimensional change during humidification to 0% RH. (6) Number of times of bending resistance It was measured by a method according to JIS P8115. <Preparation of Flexible Printed Circuit Board> Copper foil and 130
Bonding at ℃ (roll type), 120 ℃ for 1 hour, 14
Heat treatment was performed at 0 ° C. for 1 hour and 160 ° C. for 1 hour to obtain a copper-clad laminate (CCL). After that, baking under the conditions shown in Table 1
A flexible printed board was obtained through the steps of development, etching, acid cleaning, and reflow.

[0046]

[Table 1] <Evaluation of Various Flexible Printed Circuit Boards> The dimension (L0) at the time of CCL and the dimension (L1) after making the flexible printed circuit board were measured, and the dimensional change rate was obtained by the following formula.

Dimensional change rate (%) = (L1-L0) /
L0 × 100 Table 2 shows the results of Examples among various results obtained by the above.
The results of comparative examples are summarized in Table 3.

[0048]

[Table 2]

[0049]

[Table 3]

[0050]

INDUSTRIAL APPLICABILITY The polyimide film of the present invention has a small coefficient of thermal expansion and a coefficient of humidity expansion, is excellent in dimensional stability, is flexible, and is excellent in handleability, and therefore can be suitably used for a flexible printed circuit board.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koji Inukai             31 Tora-cho, Tokai-shi, Aichi 6 Toray Du             Pon Co., Ltd. Tokai Plant F-term (reference) 4F071 AA60 AF43 AF53 AH13 BA02                       BB02 BC02                 5F044 KK03 MM06 MM48

Claims (4)

[Claims] 1. A polyimide film for a flexible printed circuit board, which has a film thickness of 5 to 20 μm, a Young's modulus of 4 to 7 GPa, and a thermal expansion coefficient of 14 to 22 ppm / ° C. 2. The polyimide film for a flexible printed circuit board according to claim 1, which has a water absorption of 2.2% or less and a humidity expansion coefficient of 20 ppm /% RH or less. 3. A polyimide film comprising a polyimide containing at least two or more of paraphenylenediamine, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether and 4,4′-diaminodiphenylmethane as an aromatic diamine component. The polyimide film for a flexible printed board according to claim 1 or 2, characterized in that. 4. The polyimide film according to claim 1, wherein the polyimide film comprises a polyimide containing at least one of pyromellitic acid, biphenyltetracarboxylic acid, and benzophenonetetracarboxylic acid as an aromatic tetracarboxylic acid compound component. 2. A polyimide film for flexible printed circuit board according to item 1.