JPH11330651A - Flexible wiring board and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To deal with heat treatment requirements severer than conventional ones by enhancing the dimensional stability of flexible wiring board furthermore the heat treatment required for connecting it with other element. SOLUTION: The flexible wiring board comprises a flexible base film 1 and a conductive pattern layer 4 provided thereon. The base film 1 has a synthetic resin film 2 and a glass cloth mesh 3 included therein. The conductive pattern layer 4 is formed of a copper foil circuit pattern, and a metal plating covering the surface of the circuit pattern. The base film 1 preferably comprises a pair of synthetic resin layers and an impregnated glass cloth mesh sandwiched between wherein the impregnated glass cloth mesh comprises a glass cloth mesh and a synthetic resin impregnating the glass cloth mesh.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a flexible wiring board and a method for manufacturing the same.

[0002]

2. Description of the Related Art A flexible wiring board is used to connect an electrode terminal portion of a liquid crystal display element to an electrode terminal portion of a printed circuit board. It is used to connect an electrode terminal portion of a substrate and further package an electronic element such as a liquid crystal driving IC. Conventionally, as shown schematically in FIG. 4, a flexible wiring board is provided with an adhesive layer 11 on a flexible base film 10, a copper foil is laminated thereon, and the copper foil is etched to form a copper foil. A conductive pattern 4 was formed by plating a surface of the circuit pattern.

[0003]

Since the flexible wiring board manufactured by the conventional method includes the adhesive layer 11, when the flexible wiring board is joined to another electronic element, the heat resistance of the adhesive is reduced. Due to insufficient properties or thermal shrinkage, the dimensions of the flexible wiring board are likely to change, and there has been a problem that reliability is reduced. In addition, as the mounting density of electronic components has increased, mounting forms for packaging ICs as a TCP (tape carrier package) have been adopted, and heat generation from components has become a problem. Flexible wiring boards are required to have higher heat resistance than ever before. This request includes:
The three-layer flexible wiring board including the adhesive layer 11 cannot be used. Furthermore, in the conventional flexible wiring board, since the thickness of the adhesive layer 11 is about 20 μm, it is difficult to make the flexible wiring board thin. As a result, the improvement of the flexibility of the flexible wiring board and the space saving required for achieving high-density mounting of electronic components have been hindered.

SUMMARY OF THE INVENTION An object of the present invention is to further improve the dimensional stability of a flexible wiring board with respect to the heat treatment required for connecting the flexible wiring board to another element, and to cope with heat treatment conditions that are more severe than in the past. It is to be.

[0005]

The present inventor (see FIG. 1) has replaced a conventional three-layer flexible wiring board having a basically three-layer structure including an adhesive layer 11 with a conductive pattern layer 4,
A two-layer flexible wiring board having a two-layer basic structure composed of a base film 1 made of a synthetic resin 2 including a glass cloth mesh 3 has been conceived, and according to this two-layer flexible wiring board, dimensional stability during heat treatment has been achieved. Has been found to be significantly improved and the strength can be increased, and the present invention has been achieved.

To manufacture the flexible wiring board of the present invention, a base film made of a synthetic resin film containing a glass cloth mesh is formed on one side of a copper foil, and then the circuit pattern is formed by etching the copper foil. Then, the surface of the circuit pattern is plated with metal to form a conductive pattern layer.

Particularly preferably, a synthetic resin is mixed and dissolved in an organic solvent to produce a synthetic resin paint (a1) for forming a film having a solid content of 15 to 20% and a viscosity of 50 to 150 poise. This paint for forming a film is coated on the upper surface of the copper foil and dried by heating to form a first coating layer 6 as shown in FIG.

Next, the synthetic resin is mixed and dissolved in an organic solvent to obtain a synthetic resin paint (a2) for impregnation having a solid content of 2% -8% and a viscosity of 5-20 poise. The impregnating paint (a2) is impregnated into the glass cloth 3 and heated.
Dry to produce an impregnated glass cloth mesh. Particularly preferably, this impregnated glass cloth mesh 3 is again
It is impregnated with a synthetic resin, stuck on the coating layer 6, heated and dried to form an impregnated glass cloth mesh 7, whereby the strength is further improved. 13 is a synthetic resin. At this time, the impregnating paint is less solid than the film-forming paint, by lowering the viscosity,
The dimensional stability of the flexible wiring board is further improved.

Further, a synthetic resin paint for forming a film (a1)
Is coated on the upper surface of the impregnated glass cloth mesh 7, heated and dried to form a second coating layer 8, thereby producing the laminate 5 shown in FIG. The laminate 5 is heated and dried to obtain the base film 1.

The organic solvents in the synthetic resin paints (a1) and (a2) are dimethylacetamide and N-methyl-
It is preferably at least one organic solvent selected from the group consisting of 2-pyrrolidone.

Each synthetic resin in the synthetic resin paints (a1) and (a2) is preferably a polyimide resin which has been imidized.

When forming the first coating layer and the second coating layer, preferably, after coating each synthetic resin coating, each coating is heated to 100 ° C.
Preliminary drying at a temperature of -130 ° C, then 150-170 ° C
Main drying at a temperature of ° C. When producing the impregnated glass cloth mesh, preferably, the glass cloth mesh is impregnated with a synthetic resin paint,
Dry at ℃. In the stage of producing the impregnated glass cloth mesh, performing the one-stage drying further improves the strength of the base film. Then, particularly preferably, the laminate 5
, The laminate 5 is heat-treated at 150 ° C. to 180 ° C., and further heat-treated at 230 ° C. to 250 ° C. to form the base film 1.

Next, as shown in FIG. 1, a copper circuit pattern is formed by a photoetching method on a surface different from the surface on which the copper foil base film is formed, and metal plating is performed on the copper circuit pattern. Thus, the conductive pattern layer 4 is formed. As a result, a two-layer flexible wiring board including the base film 1 and the conductive pattern 4 is manufactured. As metal plating,
Tin, nickel, nickel-gold, solder (Sn / Pb =
6: 4) and solder (Sn / Pb = 9: 1) are preferable.

If necessary, an insulating layer formed in a predetermined pattern can be formed on the base film 1 including the conductive pattern layer 4.

For example, as shown in FIG. 3, if necessary, (c) 10 to 30% by weight of the synthetic resin, and (d)
An insulating resist ink or an epoxy resist ink composed of 70 to 90% by weight of an organic solvent is printed on the base film 1 by a screen printing method so as to cover a part of the surface of the conductive pattern layer 4, and heated. After drying, an insulating resist layer 9 is formed.

As the synthetic resin in (c), a polyimide resin which has been completely imidized is particularly preferable. As the organic solvent in (d), an organic solvent composed of at least one of dimethylacetamide and N-methyl-2-pyrrolidone is particularly preferable.

The glass cloth mesh is preferably a glass cloth mesh made of glass fibers whose surface has been treated so as to increase the affinity with the imide resin. Preferably, the glass cloth mesh is
The mesh has a fiber density of 40 to 70 fibers / 25 mm, and the weave of the fibers is preferably a plain weave or a twill weave, and is a mesh exhibiting the effect of maintaining the dimensional stability and strength of the base film.

[0018]

EXAMPLES [Manufacture of Flexible Wiring Boards] (Example 1) 15% by weight of a polyimide resin which has been imidized is mixed with 85% by weight of N-methyl-2-pyrrolidone, dissolved and solid content is 15%. Thus, a polyimide resin paint (a1) having a viscosity of 98 poise was obtained. This paint (a1) is coated on the entire surface of one side of an electrolytic copper foil having a thickness of 18 μm, preliminarily dried at 120 ° C. in a far-infrared furnace, and finally dried at 170 ° C. in a far-infrared furnace. A first coating layer 6 made of a polyimide resin was formed. Next, 3% by weight of the imidized polyimide resin was mixed with 97% by weight of N-methyl-2-pyrrolidone and dissolved to obtain a polyimide resin paint (a2). The paint (a2) was impregnated into a glass cloth mesh and dried to produce a polyimide resin impregnated cloth. This polyimide resin impregnated cloth is again impregnated with the polyimide resin coating material (a2), bonded on the coating layer 6, and heated at 120 ° C. in a far-infrared furnace.
And dried by heating to produce an impregnated glass cloth mesh 7 having a thickness of 42 μm.

Further, the polyimide resin paint (a1) prepared above is coated on the entire surface of the impregnated glass cloth mesh 7, preliminarily dried at 120 ° C. in a far-infrared furnace, and dried at 170 ° C. in a far-infrared furnace. It dried and the coating layer 8 was formed. Next, the laminate 5 is put together with a copper foil in an electric furnace for 1 hour.
Heat treatment was performed at 50 ° C. for 2 hours, and further heat treatment was performed at 230 ° C. for 2 hours in an electric furnace to produce a 52 μm-thick base film 1 composed of two synthetic resin layers and one layer of impregnated glass cloth mesh. Next, of the copper foil, the base film 1
A copper circuit pattern was formed on a surface different from the surface on which was formed by photoetching, and tin plating was performed on the copper circuit pattern to form a conductive pattern layer 4.

The thus-formed two-layer flexible wiring board comprising the base film layer 1 and the conductive pattern layer 4 was cut into a predetermined length and width.

Example 2 In Example 1, after forming the first coating layer 6, the polyimide resin paint (a
1) is coated on the entire surface of the coating layer 6, a glass cloth mesh is stuck thereon, and temporarily dried at 120 ° C. in a far-infrared furnace, and dried by heating at 170 ° C. in a far-infrared furnace. A cross mesh layer was formed.
Except for this, a two-layer flexible wiring board was manufactured in exactly the same manner as in Example 1.

Example 3 In Example 1, after the glass cloth mesh was impregnated with the polyimide resin paint (a2), the glass cloth was not dried, and the impregnation was performed only once. Except for this point, a two-layer flexible wiring board was manufactured in the same manner as in Example 1.

Comparative Example 1 The conventional three-layer flexible wiring board shown in FIG. 4 was used. However, the base film 10
Consists of a polyimide resin that has been imidized. The adhesive layer 11 is made of an epoxy-based thermosetting resin.

(Evaluation) The dimensional stability and bending strength of the two-layer flexible wiring board manufactured in the example and the three-layer flexible wiring board manufactured in the comparative example were measured, and the results shown in Table 1 were obtained. For dimensional stability, the total pitch of the circuit pattern was measured, and the ratio of elongation to the specified size was shown. For the bending strength, the base film from which the copper foil had been removed by the MIT method was a predetermined size. At a load of 0.5 kgf, a bending angle of 135 ° C., and a speed of 175 cpm, and the number of cuts at an angular bending radius was measured.

[0025]

[Table 1]

In Example 1, both dimensional stability and bending strength were remarkably improved. Example 2 was inferior to Example 1, but had favorable characteristics. In the third embodiment,
The dimensional stability was comparable to that of Example 1, but the strength was slightly reduced.

[0027]

According to the present invention, the flexible wiring board manufactured according to the present invention is able to cope with heat resistance and dimensional stability which cannot be handled by the conventional three-layer flexible wiring board.
Further, by eliminating the need to use an adhesive layer from the flexible wiring board, the flexibility is improved, and the flexible wiring board can be made thinner.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a two-layer flexible wiring board according to an embodiment of the present invention.

FIG. 2 is a perspective view schematically showing a laminate 5 including a first coating layer 6, an impregnated glass cloth mesh 7, and a third coating layer 8.

FIG. 3 is a perspective view schematically showing a two-layer flexible wiring board according to another embodiment of the present invention.

FIG. 4 is a perspective view schematically showing a conventional three-layer flexible wiring board.

[Explanation of symbols]

 Reference Signs List 1 base film 2 synthetic resin film 3 glass cloth mesh 4 conductive pattern layer 5 laminated body 6 first coating layer 7 impregnated glass cloth mesh 8 second coating layer 9 insulating layer 13 impregnated synthetic resin

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kenji Doi 9-22, Karabashi-cho, Otsu-shi, Shiga Japan Graphite Industry Co., Ltd.

Claims (5)

[Claims] 1. A flexible base film comprising a synthetic resin film and a glass cloth mesh contained in the synthetic resin film, and a conductive pattern layer provided on the base film, A flexible wiring board, comprising: a copper foil circuit pattern; and a conductive pattern layer formed by metal plating that covers a surface of the circuit pattern. 2. The base film includes a pair of synthetic resin layers and an impregnated glass cloth mesh sandwiched between the pair of synthetic resin layers, and the impregnated glass cloth mesh is formed of the glass cloth mesh. 2. The flexible wiring board according to claim 1, wherein said flexible wiring board comprises: a synthetic resin impregnated in said glass cloth mesh. 3. A base film made of a synthetic resin film containing a glass cloth mesh is formed on one side of a copper foil, and then the copper foil is etched to form a circuit pattern. A method for manufacturing a flexible wiring board, comprising forming a conductive pattern layer by metal plating. 4. A method for coating said one side of said copper foil with a synthetic resin paint, heating and drying to form a first coating layer, impregnating said glass cloth mesh with a synthetic resin paint, and heating and drying to impregnate said copper cloth. Prepare a glass cloth mesh, place this impregnated glass cloth mesh on the first coating layer, then coat a synthetic resin paint on the impregnated glass cloth mesh, heat and dry to form a second coating layer And obtaining a laminate by heating and drying the laminate to produce the base film. 5. The method for producing a flexible wiring board according to claim 4, wherein the step of impregnating the glass cloth mesh with a synthetic resin paint and heating and drying is repeated twice or more.