JPH0260233B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a flexible wiring board, and particularly to a high-quality flexible wiring board with excellent heat resistance.

[Prior Art] Flexible wiring boards are highly flexible and thin, so they are widely used in the field of electronic equipment. However, the manufacturing process of the conventional flexible wiring board manufacturing method is complicated, and the flexible wiring board manufactured by the conventional method has drawbacks that inevitably arise from its structure.

In other words, the conventional flexible wiring board
An example of the insulating base film 1 is shown in the figure.
A material on which a copper foil 3 is bonded using an adhesive 2 is used, and an insulating coverlay film 5 is further provided on the copper foil using an adhesive 4.

For this reason, even when polyimide film is used as an insulating film, rubber-modified epoxy resin or rubber-modified phenol resin is used as the adhesive layer, resulting in poor heat resistance, especially soldering heat resistance. Resin blistering or peeling may occur during dip coating.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned conventional drawbacks and provides flexible wiring that is of high quality, particularly has excellent heat resistance, is easy to connect externally, and has high reliability of electrical connection. The purpose is to provide a board.

[Means for Solving the Problem] In order to achieve such an object, the flexible wiring board of the present invention has a terminal portion formed of a metal conductor layer at least at one end, and the terminal portion is made of polyimide resin. The metal conductor layer is exposed without being covered by a polyimide resin, and both the front and back surfaces of the portion of the metal conductor layer other than the terminal portion are directly covered with a polyimide resin.

[Function] The flexible wiring board of the present invention has a structure in which the metal conductor layer is directly coated with polyimide resin without adhesive, so the advantages of polyimide resin are fully utilized, and it can exhibit excellent heat resistance and Since the terminal portion of the conductor layer is exposed without being covered with polyimide resin, both the front and back sides of the terminal portion can be used for connection.
Therefore, external connection is easy and the reliability of electrical connection is also improved.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an example of a wiring board having terminals as an embodiment of the flexible wiring board of the present invention.

Figure 1a is a plan view of the portion of the flexible wiring board that includes the terminal section, and Figure 1b is the line X in Figure 1a.
1c is a sectional view taken along line Y--X in FIG. 1a.

In Figures 1 a to c, 11 is a conductor such as copper;
11A is a terminal portion, 12 and 12' are insulating materials made of polyimide resin, and 13 is a photoresist layer.

As shown in the figure, in the flexible wiring board according to the present invention, both the front and back surfaces of the conductor 11, except for the terminal portion 11A, are directly covered with polyimide resin layers 12 and 12' having excellent heat resistance and flexibility.

A flexible wiring board with such a structure has a third
It can be easily made by the steps shown in FIG. 4 and FIG.

3a to 3e show cross sections along the line XX in FIG. 1a, and FIGS. 4 a to 4e show cross sections along the line YY.

Next, each process will be briefly explained.

(1) Photoresist pattern 2 on thin metal plate 21
2 (Fig. 3a, Fig. 4a).

(2) Resist pattern 2 is created by pattern plating.
A conductor pattern 23 is placed on the thin metal plate 21 along the
(Fig. 3b, Fig. 4b).

(3) By pattern coating, the first insulating layer 24 is formed only on necessary portions of the resist pattern 22 and the conductor pattern 23 (FIGS. 3c and 4c).

(4) Remove the thin metal plate 21 (Fig. 3 d, Fig. 4 d).

(5) By pattern coating, pattern 22
and a second insulating layer 24' is formed only on the necessary portions of the exposed surfaces of 23 (Fig. 3 e, 4
Figure e).

In this way, a flexible wiring board having terminals as shown in FIG. 1 is produced.

Next, specific examples of the flexible wiring board of the present invention will be shown.

Example 1 A negative resist "Microresist 747" manufactured by Eastman Kodak Co., Ltd. was applied to a film thickness of 5 μm on an 80 μm thick aluminum thin plate. The resist-coated aluminum plate was pre-baked, exposed to light through a high-pressure mercury lamp through the wiring board pattern, developed using a special developer and rinse solution, and post-baked to form a resist pattern on one side of the aluminum thin plate. .

Next, electrolytic copper plating was performed using a copper pyrophosphate plating bath using the aluminum thin plate on which the resist pattern was formed as a cathode. The obtained conductor pattern has a conductor width of 200 μm, a conductor spacing of 250 μm,
The conductor thickness was 40 μm.

Thereafter, using a stainless steel metal mask, a polyimide resin "varnish" manufactured by Ube Industries, Ltd. was pattern-coated by, for example, screen printing, except for the terminal portion, and dried and cured to obtain an insulating layer with a thickness of 20 μm. The thin aluminum plate was then etched away using 10% by weight hydrochloric acid. At this time, the photoresist left on the terminal part has weak mechanical strength and is not supported by the insulating layer, so
It is cut at the end of the insulating layer (section 12A in Figure 1a). Therefore, no photoresist remains in the terminal area. Again, using a stainless steel metal mask,
The "varnish" was pattern coated on the back side, except for the terminal areas, and dried and cured to form an insulating layer with a thickness of 20 μm, thereby obtaining a flexible wiring board with terminals. After that, flux treatment is applied to the terminal area,
Solder coating was performed by dipping it in a solder bath at 280°C for about 5 seconds, but no deterioration was observed in the resin layer.

Example 2 As in Example 1, after forming a resist pattern on a thin aluminum plate, copper plating was performed, and the conductor width was
A conductor pattern of 300 μm, conductor spacing of 350 μm, and conductor thickness of 35 μm was obtained.

Thereafter, a solvent-soluble polyamideimide resin synthesized from diamino-diphenyl ether and trimellitic acid chloride was pattern-coated by screen printing using a stainless steel metal mask, except for the terminals, dried, and heat-treated to a thickness of 30 μm.
A thick insulation layer was obtained. Next, the thin aluminum plate was removed by etching with 10% hydrochloric acid.
Resist stripper “N-500” manufactured by Nagase Chemical Industries, Ltd.
The photoresist was removed using Again, using a stainless steel metal mask, the solvent-soluble polyamide-imide resin was pattern coated on the back surface, dried and heat treated to form an insulating layer with a thickness of 30 μm to obtain a flexible wiring board with terminals. Thereafter, the terminals were subjected to flux treatment, and solder coating was performed by dipping them in a solder bath at 300°C for about 20 seconds, but no deterioration was observed in the resin layer. Adhesive strength and dimensional accuracy were also excellent.

In addition, in these Examples, the conductor pattern was formed on the metal thin plate by electroplating.
It is also possible to form a conductor pattern by pattern etching after forming a uniform conductor layer.

It is also possible to form a conductive pattern by pattern-coating an insulating layer on one side of the metal foil at the required portions, drying and heat-treating, and then etching the pattern.

Any metal that can be electroplated may be used as the conductor metal, but copper is preferred from the viewpoint of conductivity and economy.

The thin metal plate can be removed not by etching as in this embodiment, but by peeling off. However, in order not to disturb the conductor pattern, etching is preferable, and if etching is used, it is preferable to use a material that has etching characteristics different from those of the conductor metal. When copper is used as the conductor metal as in this example, aluminum,
It is desirable to use tin, zinc, etc.

It is also preferable to peel off the photoresist used for pattern plating of the conductor layer at an appropriate time after plating, for example, after plating or after removing the thin metal plate.

The polyimide resin used in the present invention is pattern coated and is therefore solvent soluble. Unlike when turning film into metal foil,
Since it is coated with a liquid, there are no air bubbles left between the metal and the insulating layer, improving adhesion, and since no external force is applied, the dimensional accuracy of the product can be improved.

Examples of the polyimide resin include polyamic acid, polyimide resin, polyamide-imide resin, polyester-modified imide resin, silicone imide resin, etc., and solvent-soluble imide group-containing polymers, particularly solvent-soluble polyamide-imide resins, are preferable.
There are no pinholes or bubbles, and a product with excellent adhesiveness and dimensional accuracy can be obtained.

FIG. 5 shows another embodiment of the flexible wiring board of the present invention, and is a sectional view corresponding to FIG. 1c. This embodiment is an example in which the second insulating layer 12' is provided after the photoresist is peeled off as described above.

FIGS. 6 and 7 show other embodiments having different terminal portion structures. If there is no problem even if only one side of the terminal part is exposed and the other side is insulated, when pattern coating the insulating layers 12, 12', the first insulating layer 12 is The second insulating layer 12' is provided uniformly up to the tip of the terminal portion 11A, and the second insulating layer 12' is not provided on the terminal portion. or,
As shown in FIG. 7, it is also possible to provide the end portion of the first insulating layer 12 only on the terminal portion 11A. In this way, the insulating layer 12 can also be used as a reinforcing material for the terminal portion 11A.

The explanation so far has mainly been about a flexible wiring board with terminals, but the terminal portions do not necessarily have to be provided in advance. It is also possible to cut out necessary dimensions from a flexible wiring board with no exposed terminal portions, and remove the polyimide resin with a corrosive solution such as hydrazine to expose the terminal portions.

[Effects of the Invention] As described above, according to the present invention, polyimide resin is used as the insulating layer, and the metal conductor layer is bonded to the insulating layer without interposing an adhesive layer between the metal conductor layer and the insulating layer. Therefore, since it is directly coated, there is no deterioration due to heat caused by the adhesive, and the heat-resistant features of polyimide resin are utilized, making it possible to obtain a high-quality flexible wiring board with excellent heat resistance. Since the terminal part of the metal conductor layer is exposed without being covered with polyimide resin, both the front and back sides of the metal conductor layer in the terminal part can be used for external connection. This is easy, and the reliability of the electrical connection is also improved.

[Brief explanation of the drawing]

FIG. 1a is a plan view showing an embodiment of the flexible wiring board of the present invention, FIGS. 1b and c are sectional views taken along lines X-X and Y-Y of FIG. 1a, respectively, and FIG. FIGS. 3 a-e and 4 a-e are sectional views illustrating the manufacturing process of the flexible wiring board of the present invention, and FIG. 5 is a cross-sectional view showing the structure of the flexible wiring board of the present invention. FIG. 6 and FIG. 7 are cross-sectional views showing two other embodiments of the terminal portion of the flexible wiring board of the present invention. 1... Base film, 2, 4... Adhesive, 3
...Conductor, 5...Cover lay film, 11...
Conductor, 11A...Terminal portion, 12, 12'...Insulating layer made of polyimide resin, 13...Photoresist layer, 21...Metal thin plate, 22...Resist pattern, 23...Conductor pattern, 24, 24' …
...Insulating layer made of polyimide resin.

Claims (1)

[Claims] 1. Having a terminal portion formed of a metal conductor layer on at least one end portion, the terminal portion being exposed without being covered with polyimide resin, and both the front and back surfaces of the portion of the metal conductor layer other than the terminal portion. A flexible wiring board characterized by being directly coated with a polyimide resin.