JPS58190093A - Method of producing flexible circuit board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a flexible wiring board made of a polyimide metal clad plate having excellent heat resistance, electrical properties, and mechanical properties.

A flexible wiring board is a board for manufacturing a flexible printed circuit, and in recent years, it has been increasingly used mainly for the purpose of simplifying and increasing the density of electronic circuits.

As such flexible wiring boards, a composite material generally called a polyimide copper clad board, which is manufactured by bonding an aromatic polyimide film to a copper foil using an adhesive, has been used. However, since this conventional polyimide copper clad board is provided with an adhesive layer having a thickness of 10 to 30 gm, it takes the form of a laminate consisting of at least three layers. Therefore, the heat resistance of the polyimide copper clad board,
Properties such as electrical properties, chemical resistance, and mechanical properties tend to be determined by the properties of the resin that makes up the adhesive layer, rather than by the properties of aromatic polyimide, which is superior in these properties. There was a problem in that the advantages of using an aromatic polyimide film as a layer were not fully utilized.

Therefore, methods of manufacturing flexible wiring boards such as polyimide steel clad boards without using an adhesive layer have been studied. A typical example of such a method is the polymerization of aromatic compounds obtained by the polymerization of a tetracarboxylic acid such as pyromellitic acid with an aromatic primary amine, as shown in U.S. Pat. No. 3,179,634. Applying a solution of polyamic acid (also called aromatic polyamic acid, which is a precursor of aromatic polyimide) directly to copper foil, and heating it at a temperature of, for example, around 120°C and then around 300°C. The removal of the solvent and the integration reaction of polyamic acid are caused in copper foil-1- to convert it into male aromatic polyimide,
It is known how to make a polyimide copper clad board. but,
In this method, considerable volumetric shrinkage occurs when the solvent is evaporated from the polyamic acid coating layer and when the polyamic acid is converted into polyimide. Therefore, the resulting polyimide steel clad plate had a tendency to be severely curled (curved). The occurrence of such curling is a serious drawback for flexible wiring boards, so the method of manufacturing flexible wiring boards by directly applying aromatic polyamine chloride to copper foil and imidizing it is not practical. It was difficult to adopt it in the manufacturing process.

On the other hand, a method for manufacturing a flexible wiring board has also been proposed which aims to improve the drawbacks of the above manufacturing method. Specifically, JP-A No. 49-129862 discloses a polyimide which is partially ring-closed by reacting polyamic acid produced from pyromellitic dianhydride with diphenyl ether-4,4'-diincyanate, etc. After preparing amic acid in advance and applying it directly onto a conductive foil such as copper foil, the coating layer is coated with a liquid of, for example, 140 to 50 l.
A method is described in which a polyimide layer is formed by removing the solvent and ring-closing the unclosed portion of the polyimidoamic acid by heating at a temperature near '0 and then at a temperature near 300°C4-J. According to this method, the curling properties of the resulting copper-clad board are improved compared to the above-mentioned method in which unclosed polyamic acid is applied directly onto the copper foil and all condensation ring-closing reactions are performed on the copper foil. However, even with copper clad boards obtained by such a polyimide method, the degree of curl is still not sufficiently reduced, and the addition of a process to produce polyimide amic acid makes it difficult to manufacture industrially. It cannot be said that it is advantageous.

Therefore, a first object of the present invention is to provide a method for manufacturing a flexible wiring board made of an aromatic polyimide metal clad plate with improved curling properties.

The second object of the present invention is to improve the curling properties of flexible wiring boards, and to provide flexible wiring boards made of aromatic polyimide metal-clad boards that have various properties, especially excellent folding strength and alkali resistance. An object of the present invention is to provide a method for manufacturing an IX substrate. That is, since flexible wiring boards are often subjected to various deformations or mechanical impacts during their use, for example, in circuit boards, they are particularly required to have resistance to such deformations and impacts. Further, in the rejection process, the flexible wiring board is often subjected to alkali treatment such as photoresist removal treatment or plating treatment, and therefore, it is desirable that the flexible wiring board has sufficient alkali resistance. The present invention provides a method for manufacturing a flexible wiring board that achieves improvements in not only curling properties but also those characteristics.

A third object of the present invention is a method for manufacturing a flexible wiring board made of an aromatic polyimide-based metal clad plate with improved curling properties while utilizing a method of directly applying aromatic polyamic acid to metal foil. Our goal is to provide the following.

The fourth object of the present invention is to create an aromatic polyimide-based material that utilizes a method of applying aromatic polyamic acid to metal foil as it is, while improving both curling properties after production and curling properties after etching treatment. An object of the present invention is to provide a method for manufacturing a flexible wiring board made of a metal clad plate. In other words, curling of flexible wiring boards is likely to occur not only in the post-manufactured state, but also after the metal foil has been removed during the wiring board manufacturing process, and in either case, it is possible to minimize curling. Desirably, it is also an object of the present invention to provide a method for manufacturing a flexible wiring board having such characteristics.

These purposes are based on biphenyltetracarboxylic components,
An organic solvent solution of aromatic polyamine citric acid obtained by polymerization with a symmetrical aromatic primary amine having no substituents is applied directly to metal foil, and at least 50% by weight of the aromatic polyaminic acid is applied at a temperature below 100°C. This can be achieved by the present invention, which comprises a method for manufacturing a flexible wiring board, characterized in that after removing the solvent, the remaining solvent is removed by heating and imidization is performed.

Next, the present invention will be explained in detail.

The biphenyltetracarboxylic acid component used in the present invention is biphenyltetracarboxylic acid or a derivative such as dianhydride of biphenyltetracarboxylic acid;
°, 4.4' integral (S integral), and 2,3.3',
For example, as an example of biphenyltetracarboxylic dianhydride, 3.3', 4.4°-biphenyltetracarboxylic dianhydride (S monolithic) can be used. ), and 2,3.3″,4
°-Biphenyltetracarboxylic dianhydride (a monolith) can be mentioned. These compounds can be used alone or in combination of two or more. However, in order to manufacture flexible wiring boards with particularly excellent various properties, the above three
．． It is preferable to use 3',4,4'-biphenyltetracarboxylic dianhydride (S monolithic).

In addition, the biphenyltetracarboxylic acid component may include other tetracarboxylic acids or derivatives thereof, such as benzophenonetetracarboxylic acid, pyromellitic acid, 2,2-bis(3,4-dicarboxyphenyl)propane, bis(3-dicarboxyphenyl)propane,
, 4-dicarboxyphenyl) ether or derivatives of these compounds, provided that the amount is within 10 mol %.

The amine component used in the present invention is a symmetrical aromatic primary amine having no substituents, and preferable examples thereof include compounds that can be represented by the following general formula. I can do it.

In the above general formula, X is divalent O, CH2, C(C
H3) Represents any group such as 2, s, co, so□, or SO, and each NH2 group is in a symmetrical position with respect to the X group.

Examples of aromatic primary amines represented by the above general formula include 4,4'-diaminodiphenyl ether, 4,4
'-Diaminodiphenylthioether, 4.4''-diaminobenzophenone, 4°4'-diaminodiphenylmethane, 4.4°-diaminodiphenyl sulfone, 2.2
'-Bis(4-7minophenyl)propane and the like can be mentioned. An aromatic polyimide film produced using an aromatic primary amine represented by the above general formula tends to have less curl, especially after etching (metal foil removal), and is therefore preferable for the purpose of the present invention.

Furthermore, the symmetrical aromatic primary amine having no substituents as the amine component used in the present invention is symmetrical phenylenediamine such as P-phenylenediamine, or 2,6-diaminopyridine, 3, Compounds not included in the above general formula, such as pyridine derivatives such as 5-diaminopyridine, may also be used.

In the present invention, these aromatic primary amines can be used alone or in combination.

The aromatic primary amine used in the present invention needs to have no substituents and be symmetrical as described in Section 2. Aromatic primary amines having substituents are not preferred as aromatic primary amines of the present invention even if they are symmetrical, and asymmetrical aromatic primary amines are not preferred as aromatic primary amines having substituents. Even if it is not, it is not preferable as the aromatic primary amine of the present invention. Polyimide metal clad plates obtained using such aromatic primary amines do not have sufficient bending strength, which is an essential property particularly for flexible wiring boards, and are not suitable for practical use.

In the present invention, the method for producing aromatic polyamic acid is not particularly limited, and methods similar to known methods can be used.

Examples include the following methods.

A substantially stoichiometric amount of a tetracarboxylic acid component and an aromatic primary amine are mixed in an organic polar solvent such as N-methyl-2-pyrrolidone, N,N'-dimethylformamide, or N,N''-dimethylacetamide. A solution of aromatic polyamic acid is obtained by reacting at a temperature of 0 to 80 ° C. The aromatic polyamic acid solution thus obtained can be used as it is, or the concentration can be adjusted by further adding an organic solvent. to make a coating solution.

The coating liquid made of an organic solvent solution of aromatic polyamic acid is preferably a solution containing 5 to 60% by weight of aromatic polyamic acid, and the aromatic polyamic acid contained has a logarithmic viscosity of 0. .1 or more (30'O1
Concentration 0, 5 g/100 mJ1・N-methyl-2
- measured value for pyrrolidone), particularly preferably from 0.5 to 4. Copper foil is generally used as the metal foil to which the polyamic acid coating liquid is applied, but metal foils made of other conductive metals such as aluminum foil and nickel foil can also be used. When manufacturing a flexible wiring board, the metal foil has a thickness of 10 to 1
00 is used. Further, the surface of the metal foil is preferably subjected to a roughening treatment.

The coating operation of the aromatic polyamic acid coating liquid onto the metal foil is preferably carried out by casting, and specifically,
The following methods are used:

Generally, a uniform thickness is achieved by discharging an aromatic polyamic acid coating liquid onto the surface of a metal foil through a film forming slit.
A coating layer of 50 to 10,007 t) is formed. As the coating means, it is also possible to use other known coating means such as a roll coater, knife coater, doctor blade, and flow coater.

The polyamic acid coating layer prepared as in L.
The solvent is then removed by heating. This operation of heating and removing the solvent must be carried out at a temperature of 100° C. or lower (preferably 90° C. or lower) until at least 50% by weight of the solvent is removed. Note that the heating operation can be performed under any conditions such as normal pressure, reduced pressure, or increased pressure.

゛In this way, the first half of the solvent removal operation from the aromatic polyamic acid solution coating layer is carried out at 100°C or lower (preferably 90°C or lower).
(0° C. or lower), the condensation reaction of the polyamic acid does not substantially proceed in this step, and therefore, the volumetric shrinkage of the coating layer due to the condensation reaction of the polyamic acid does not occur in this step. In addition, by removing half of the solvent at such a low temperature, the polyamic acid can be applied to the surface of the polyamic acid coating layer before the volume of the coating layer shrinks due to volatilization of the solvent. A film is formed. Once such a coating film is formed on the polyamic acid coating layer, the volume of the coating layer shrinks even during the process of removing the remaining solvent by heating at normal temperatures and the imidization reaction by condensation. is relatively minor.

The heating temperature of the aromatic polyamic acid coating layer is gradually increased after the above operation is completed, and the final heating temperature is 250 to 400°C to remove the solvent and remove the aromatic polyamic acid. Complete imidization. Also,
After a film is formed on the coating layer, the organic solvent contained in the coating layer is replaced with a poor solvent with a low boiling point (lower alkanol, lower ketone, etc.) to shorten the time required to remove the solvent. You can also do it. The thickness of the aromatic polyimide layer formed in this way is generally 10 to 150 mm.
be killed.

A flexible wiring board made of an aromatic polyimide metal clad plate manufactured by the present invention represented by the method described above does not contain an adhesive layer, and therefore has particularly high heat resistance among the characteristics necessary for a flexible wiring board. On the other hand, aromatic polyimide metal clad sheets manufactured by directly coating aromatic polyamic acid or its partially closed ring product on metal foil and causing solvent volatilization and imidization reaction to occur at relatively high temperatures. It has less tendency to curl compared to
Furthermore, since it has high mechanical strength and alkali resistance, it is highly practical as a flexible wiring board. Furthermore, the flexible wiring board obtained by the present invention has less curling even after the metal foil is removed by etching treatment, so it is highly practical in this respect as well.

Next, examples of the present invention and comparative examples will be shown.

[Example 1] 20.59 g (0.07 mol) of 3.3', 4.4'-biphenyltetracarboxylic dianhydride was placed in a reaction vessel.
4'-diaminodiphenyl ether 14.02g (0,
07 mol) and 138 g of N-methyl-2-pyrrolidone were charged and polymerized by stirring at 30° C. for 24 hours to obtain a solution containing 20% by weight of polyamic acid with a logarithmic viscosity of 0.78.

This polyamic acid solution was cast onto an electrolytic copper foil with a thickness of 35p and heated in a hot air dryer at 80°C for 2 hours to remove about 80% by weight of the solvent, and the polyamic acid was coated on the surface. This was a coating layer in which a coating film was formed. The radius of curvature of the copper foil having this coating layer (the measurement method will be described later) was 3.7 cm. Next, this copper foil with polyamic acid layer was heated at 300°.
C. for 30 minutes to obtain a flexible copper clad board with an aromatic polyimide film having a thickness of about 25 g.

Various performances of this copper clad board for use in printed wiring boards were measured by the methods described below.

(1) Surface resistance Measured in accordance with JIS C-6481.

(2) Peel resistance In accordance with JIS C, -6481, 180° peeling of a sample with a width of 10 mm was performed using an autograph at a tensile speed of 50 m.
Measured at 7 minutes.

(3) Solvent resistance In accordance with JIS C-6481, the sample was immersed in trichlene, acetone, and methylene chloride at room temperature, respectively.
Changes in appearance such as peeling of the polyimide coating layer were observed.

(4) Folding strength Measurement was carried out in accordance with JIS P-8115, with a bending surface radius of curvature of 0.88 mm and a restraining weight of 0.5 kg.

(5) Alkali resistance In accordance with JIS C-6481, the sample was immersed in a 10% by weight sodium hydroxide aqueous solution for 30 minutes at room temperature, and then measured by the method (4) above.

(6) Soldering resistance In accordance with JIS C-6481, the sample was immersed in a solder bath at 300'C for 1 minute, and then the appearance of "blister" etc. was visually judged.

(7) Warpage (radius of curvature) The radius of curvature of the curl of the flexible copper-clad board at a relative humidity of 60% and 20°0 was expressed as "warp."

(8) Warpage after etching The "warpage" of the polyimide film after dissolving and removing (etching) the copper foil from the flexible copper clad board using an aqueous ferric chloride solution was measured using the method described in (7) above. ,
Displayed in the same manner.

The measurement results are shown below.

(1) Surface resistance: 6.7 x 101”Ω (2
) Shochu Hiki Hakiri strong;! : 1.5kg/Cm (3) Solvent resistance: No abnormality 4) Folding strength: 59 times (5) Alkali resistance = 53 times (6) Soldering resistance: No abnormality 7) Warpage (radius of curvature) : 3.2 cm (8) Warp after etching: 21.5 cm [Example 2] 20.59 g (0.07 mol) of 3.3', 4.4°-biphenyltetracarboxylic dianhydride, 4.
4°-diaminodiphenylmethane 13.88g (0,0
7 mol) and 138 g of N-methyl-2=pyrrolidone were charged and polymerized by stirring at 30''C for 24 hours to obtain a solution containing 20% by weight of polyamic acid with an logarithmic viscosity of 1.03.

This polyamic acid solution was cast onto a copper foil in the same manner as in Example 1, and the solvent was removed and imidized by the method described in Example 1 to obtain a flexible film having an aromatic polyimide film with a thickness of approximately 25 μm. I got a copper clad board.

Various performances of this copper clad board for use in printed wiring boards were determined by the method described in Example 1 (A111). 1l
The l11 constant results are shown below.

(1) Surface resistance: 5.2 x 10”Ω (2)
Peeling strength +1.4kg/cm (3) Solvent resistance:
No abnormality 4) Cutting strength: 51 times (5) Alkali resistance: 46 times (6) Half resistance [H resistance: No abnormality 7) Warpage (radius of curvature): 3.5cm (8) Warpage after etching : 19. Ocm [Example 3] 29.42 g (0.1 mol) of 3,3°, 4,4'-biphenyltetracarboxylic dianhydride, 4.4
°-Diaminodiphenyl ether lO,O1g (0,0
5 mol), p-phenylenediamine 5.41 g (0,0
5 mol), and 300 g of N-methyl-2-pyrrolidone.
was charged and stirred at 30° C. for 24 hours to undergo condensation polymerization to obtain droplets containing 15% by weight of polyamic acid with a logarithmic viscosity of 4.0.

This polyamic acid melt was cast onto a copper foil 1- in the same manner as in Example 1, and the solvent was removed and imidized by the method described in Example 1. I'll give you a copper clad plate.

Various performances of this copper clad board for use in printed wiring boards were measured by the method described in Example 1. The measurement results are shown below.

(1) Surface resistance: 4.3 x 1016Ω (2
) #Peel strength + 1.6 kg/cm (3) #Solvent resistance: No abnormalities 4) Folding strength: 53 times (5) Alkali resistance: 49 times (6) Half-il resistance: No abnormalities 7) Warp (radius of curvature): 2.8cm(8)-r-
, 7 Warpage after ching: 11.6 cm "Example 4" 4,4 in place of 4,4'-diaminodiphenyl ether
”-diaminodiphenylthioether 15.14g (
Polyamic acid (logarithmic viscosity + 1:5) was added at 20% by weight in the same manner as in Example 1, except that 0.07 mol) was used.
A solution containing

This polyamic acid solution was applied to the copper foil 1 in the same manner as in Example 1. The mixture was cast and applied, and the solvent was removed and imidized by the method described in Example 1 to obtain a flexible copper-clad board having an aromatic polyimide film about 25 mm thick.

Various performances of this copper clad board for use in printed wiring boards were measured by the method described in Example 1. The Wl11 determination results are shown below.

(1) Surface resistance・3.4 x 101'Ω (2)
Peeling strength +1.3kg/cm (3) Solvent resistance:
No abnormality 4) #Bending strength: 46 times (5) Alkali resistance: 39 times (6) Half 1η resistance: No abnormality 7) Warpage (radius of curvature): 3. Ocm(8) Warpage after etching: 14.1cm [Comparative Example 1] 8 cm of solvent from polyamic acid solution cast on copper foil
The process of removing 0% by weight was carried out at 120°C in a hot air drying mold.
Solvent removal and imidization were carried out by the method described in Example 1, except that the method was performed in Example 1, and the thickness was about 25 mm. A flexible copper clad board with a film of

The performance of this copper clad board for use in printed wiring boards was measured by the method described in Example 1, and it was found that, except for warpage (radius of curvature), it was almost the same as the flexible copper clad board obtained in the above example. I got the result, but the sled (
The radius of curvature) was found to be 1.7 cm, indicating severe curling.

[Comparative Example 2] 15.27 g of pyromellitic dianhydride (0,
07 mol), 4,4'-diaminodiphenyl ether 1
4.02 g (0.07 mol) and 117 g of N-methyl-2-pyrrolidine were charged and polymerized by IW stirring at 30°C for 24 hours to produce aromatic polyamine citric acid with a logarithmic viscosity of 0.96. A solution (concentration: 20% by weight) was obtained. This solution was cast onto the electrolytic copper foil 42 of JRISA 35, and the temperature was 120°.
C for 2 hours, followed by heating at 300°C for 30 minutes to obtain a flexible copper clad board with an aromatic polyide film about 25μ thick.

When the folding strength of this copper clad plate was determined to be 4 (II) by the method described in Example 1, a high result of 66 times was obtained.However, after this copper clad plate was treated with alkali, When the bending strength was determined by 'A111', it showed a significant decrease of 13 times.Furthermore, when the warp (radius of curvature) was measured by the method described in Example 1, a result of 1.80 cm was obtained. , it became a strongly curled state.

Patent applicant: Ube Industries Co., Ltd. Agent: Patent attorney: Yasuo Yanagawa 475-

Claims (1)

[Claims] An organic solvent solution of an aromatic polyamic acid obtained by polymerizing a biphenyltetracarboxylic acid component and a symmetrical aromatic primary amine having no substituents is directly applied to a metal foil, and at a temperature of at least 50
1. A method for producing a flexible wiring board, which comprises removing % by weight of the solvent, followed by heat removal of the remaining solvent σ and imidization.