JPH10335791A - Flexible printed wiring board and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a fine wiring circuit which dispenses with a coverlet, is excellent in electrical characteristics such as electrical insulation characteristics, and moreover, is light and has a flexibility, by a method wherein the circuit only of a flexible printed wiring board is selectively subjected to surface covering with a polyimide resin. SOLUTION: A polyimide resin is painted on the surface covering part of a circuit by an electrodeposition painting method, and an electrodeposition painted film 5 is obtained. At this time, there is the need to perform selectively an electrodeposition painting on the surface of the circuit, and there is the need to hold provided previously lead wires on the extension of the circuit for making a current flow through the circuit. After the electrodeposition painting, a post-drying curing treatment of the polyimide resin is performed to the formulation of the resin used for the electrodeposition painting, the removal of resist ink used for a masking and a cutting treatment of lead wires used for the connection of electrodes subjected to electrodeposition painting are conducted to obtain a purposed flexible printed wiring board with the circuit surface covered selectively by the electrodeposition painting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed wiring board having a surface coating formed only on a circuit by an electrodeposition coating method, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Flexible printed wiring boards have been attracting attention as printed wiring boards that respond to recent demands for miniaturization and weight reduction of electronic devices, and their applications are expanding. In particular, with the miniaturization of semiconductor packages and high-density mounting by increasing the number of pins, there is a strong demand for thinner circuits. In addition to flexibility, which is an essential characteristic of a flexible printed wiring board, flexibility is beginning to be required as a new characteristic. In general, the surface of a flexible printed wiring board is covered with a polyester resin film, a polyimide resin film or the like to protect the circuit. Conventionally, as shown in FIG. 2, a surface coating of a circuit is performed by using a film 7 (hereinafter referred to as a coverlay) such as a polyester resin film or a polyimide resin film coated with an adhesive.
Place it on a circuit board created by etching and heat
Pressurization is performed to form a single circuit. However, when a thin wire circuit having a circuit width of 80 μm or less and an interval between circuits of 80 μm or less is formed, it is difficult to completely fill the unevenness between the circuits with an adhesive.

[0003] A method of lowering the melt viscosity of the adhesive, a method of increasing the amount of the adhesive, a method of increasing the molding pressure and molding temperature, and a selection of a cushion material at the time of integral molding, etc. in order to enhance the integral molding property. Taking measures to improve the above, the embedding property between the circuits is improved, but it is not a sufficient solution, for example, the flow of the adhesive increases and the molding is deformed due to the high molding pressure. Another problem with thinning is migration. As the distance between the circuits becomes narrower, the occurrence of migration in which the insulation resistance between the circuits deteriorates due to anion adhering to the coverlay and the adhesive of the circuit board is inevitable. On the other hand, the flexibility is to improve the efficiency of the mounting operation by, for example, easily mounting and fixing the flexible printed wiring board in a bent state in a bent state. The flexibility is inversely proportional to the cross-sectional area of the flexible printed wiring board when compared with the same material configuration, and therefore, there is a limit in the conventional resin configuration. In a recent flexible printed wiring board used for a liquid crystal display panel, a fine line circuit having a circuit width and a circuit interval of about 40 μm has been required. The method is becoming more and more difficult.

[0004]

As a result of various studies to solve such a problem, the present invention does not require a coverlay, is excellent in electric characteristics such as electric insulation characteristics, and is light and flexible. A flexible printed wiring board for a fine wire circuit having

[0005]

According to the present invention, there is provided a flexible printed circuit board in which a circuit is electrically insulated and protected by a surface covering, wherein only the circuit is selectively covered with a polyimide resin. It is a wiring board and its manufacturing method.

The substrate from which the flexible printed wiring board used in the present invention is based is the same as the substrate used in the conventional overlay coating method, and is not particularly limited.
Examples of the polyimide resin used for the surface coating of the circuit include thermosetting resins such as amide acid type and bismaleimide type. A cured product of a polyimide resin that covers the surface of a circuit by an electrodeposition coating method has heat resistance and high electrical reliability, and is optimal as a material for covering the surface of a circuit.

Hereinafter, the present invention will be described with reference to the drawings. FIG.
1 is an embodiment of a method for manufacturing a flexible printed wiring board obtained by the present invention, and shows a cross-sectional view thereof. FIG.
(A) is a single-sided copper-clad board composed of an insulating base material 1 and a copper foil 2,
It is the same as the copper clad board substrate used in the conventional overlay coating method. FIG. 1B shows a state in which the copper foil 2 is removed into a predetermined shape by etching by a normal method, and a circuit 3 is formed. FIG. 1 (C) shows a state in which a resist ink 4 is applied in advance to a part connection portion or the like not covered with a polyimide resin and masked during electrodeposition coating. Since a capacitor or the like is connected to the component connection portion or the like, it is necessary to mask in advance so that the surface is not coated by the electrodeposition coating method. FIG. 1 (D) shows a state in which a polyimide resin is applied to the surface coating by an electrodeposition coating method to obtain an electrodeposition coating film 5.
At this time, it is necessary to selectively perform electrodeposition coating on the circuit surface, and it is necessary to provide a lead wire on a circuit extension in advance in order to flow a current. FIG. 1E shows the state of the circuit exposed portion 6 after the electrodeposition is selectively applied to the circuit surface and the resist ink is removed. After electrodeposition coating, according to the prescription of the polyimide resin used for electrodeposition coating, perform curing after drying, remove the resist ink used for masking, and cut the lead wire used for electrode connection for electrodeposition coating. By doing so, a flexible printed wiring board in which the target circuit surface is selectively coated by electrodeposition coating is obtained.

[0008]

The flexible printed wiring board of the present invention does not require a coverlay, is excellent in electrical characteristics such as electrical insulation characteristics, and is light and flexible, and can be used for fine wire circuits. Also, by selectively covering only the circuit part with the surface, it has excellent characteristics of insulation between circuits. It is possible to produce by roll / roll method, so that stable yield and mass productivity can be achieved. It is an excellent manufacturing method, and the processing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a single-sided copper-clad board for a flexible printed wiring board according to the present invention.

FIG. 2 is a schematic cross-sectional view of a single-sided copper-clad board of a conventional flexible printed wiring board.

Claims (2)

[Claims] 1. A flexible printed wiring board in which a circuit is electrically insulated and protected by a surface coating, wherein only the circuit is selectively covered with a polyimide resin. 2. A flexible printed wiring board in which a circuit is electrically insulated and protected by a surface coating, wherein only the circuit is selectively surface-coated with a polyimide resin by an electrodeposition coating method. Method.