JPH11177192A - Flexible printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible printed circuit board having a shielding layer and good flexibility. SOLUTION: A flexible printed circuit board comprises an insulating substrate 1 and electrolytic copper foils 5 laminated on both surfaces of the substrate 1, and has a predetermined conduction circuit, an earth circuit 6 formed on one surface, a through hole land 7 formed on the other surface, an insulating resin cover layer 8 made of polyimide film with adhesive and formed on the earth circuit 6, conductive cover layers 11 made of conductive paste containing thermoplastic resin and formed on the insulating resin cover layer 8 and the through hole land 7, and insulating resin layers 12 formed on both conductive cover layers 11.

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 shield layer and excellent in flexibility, particularly suitable for electromagnetic wave shielding.

[0002]

2. Description of the Related Art Conventionally, as a printed wiring board having a shield layer for electromagnetic wave shielding, a flexible printed wiring board having a shield layer made of a copper paste containing a thermosetting resin on an earth circuit as shown in FIG. Or a so-called multilayer board (circuit + shield 2 layers) in which copper foils are laminated and connected by through holes. As an example of the related art, a flexible printed wiring board compatible with electromagnetic waves will be described with reference to FIG. (A) to (E) of FIG.
Shows a schematic cross-sectional view of a flexible printed wiring board,
FIG. 4A is a material for a flexible printed wiring board in which an insulating base material 1 and an electrolytic copper foil 5 are integrally formed, and FIG.
A predetermined earth circuit 6 is formed by ordinary etching,
The state where the ground circuit 6 and the throughhole land 7 are conducted is shown. FIG. 4 (C) shows that an insulating resin coating layer 8 is provided by laminating a polyimide resin film with an adhesive on the surface of the ground circuit 6 and applying heat and pressure to the insulating resin coating layer 8.
FIG. 4 shows a state in which the earth circuit 6 is exposed.
(D) shows a state in which a copper paste containing a thermosetting resin is applied to both surfaces of the insulating resin coating layer 8 and a conductive coating layer 13, that is, a shield layer is provided. FIG. 4E shows a state where the conductive coating layers 13 on both surfaces are covered with the insulating resin layer 12.

[0003] The conductive coating layer 13 is made of a copper paste shown in FIG.
Is to increase the sheet resistance and reduce the sheet resistance by applying a thick copper paste. However, since the thermosetting resin is used as the binder, the conductive coating layer 13 after curing is hard, and particularly, the solder reflow. Thereafter, there is a problem that the curing proceeds further and becomes brittle and lacks flexibility. on the other hand,
The above-mentioned multilayer board does not have the flexibility required for the opening / closing part, cannot be applied to uses such as a notebook computer, and has been expensive.

[0004]

The present invention, as a result of various studies to solve such problems, provides a low-cost flexible wiring board having a shield layer and excellent flexibility. .

[0005]

SUMMARY OF THE INVENTION The present invention is a flexible printed circuit board having a predetermined conductive circuit, a ground circuit on one side, and a through-hole land on the other side, wherein copper foil is laminated on both sides of an insulating base material. An insulating resin coating layer made of a polyimide film with an adhesive on the ground circuit surface, a conductive coating layer made of a conductive paste containing a thermoplastic resin on the insulating resin coating layer and the throughhole land surface, and on both surfaces of the conductive coating layer. A flexible printed wiring board having an insulating resin layer.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below.
The material for a flexible printed wiring board in which copper foil is laminated on both surfaces of the insulating base material used in the present invention is a material obtained by laminating copper foil on both surfaces of a polyester resin film, a polyimide resin film, and the like, and integrally molding by heating and pressing. The material may be the same as a conventionally used material for a flexible printed wiring board. The polyimide film with an adhesive used as the insulating resin coating layer may be, for example, an acrylic photosensitive dry film resist used in this field, and is not particularly limited. The materials so far may be the same as those used for a conventional flexible printed wiring board.

[0007] The conductive paste containing a thermoplastic resin to be a conductive coating layer is composed of a thermoplastic resin and a conductive metal. Examples of the thermoplastic resin include ester resins, and polyester resins are preferred. Examples of the conductive metal include silver and copper, and silver is preferable from the viewpoint of flexibility. The conductive paste is heated and dried after coating the insulating resin coating layer by screen printing or the like to eliminate the tackiness of the paste.
The content of the conductive metal is preferably from 60 to 80% by weight, and more preferably from 65 to 75% by weight. The material used for the outermost insulating resin layer is not particularly limited as long as it is flexible and has an insulating function, but a polyimide film which has been conventionally used as a coverlay of a flexible printed wiring board may be used.

The present invention relates to a flexible printed wiring board having a predetermined conductive circuit, a ground circuit on one side, and a through-hole land on the opposite side, in which a copper foil is laminated on both sides of an insulating base material. Forming an insulating resin coating layer made of a polyimide film, providing an opening in the insulating resin coating layer, exposing a ground circuit, connecting the opposite surface to a through hole land through a through hole of the ground circuit, and further forming the insulating resin. A conductive coating layer of a conductive paste containing a thermoplastic resin is formed on the surface having the coating layer and the through-hole land and in the gap, and an insulating resin layer is formed on both surfaces thereof.

The connection between the conductive coating layer and the exposed portion of the earth circuit and the through-hole connection portion can be improved by treating the copper foil as the connection portion by electroless plating, electrolytic plating made of tin, solder, gold or the like. . The distance between the end of the component mounting land and the outer edge of the conductive coating layer is preferably 0.5 to 2 mm in consideration of printing deviation. Connection point diameter is 0.5 ~
It is preferable that the diameter be 3.0 Φmm. If the diameter is out of this range, there is a possibility that the through hole land may be peeled off at the time of bending.
Further, the number of connection between the conductive paste and the through hole land is 1 to
The number is 3 / cm ² , and it is preferable not to provide a connection point at the bent portion in order to prevent the peeling of the through-hole land at the time of bending. The area in the present invention refers to the entire one side of the conductive coating layer. If it is out of this range, the embedding property of the paste into the through-hole will be poor. Further, both surfaces of the conductive coating layer are covered with an insulating resin layer.

Hereinafter, the present invention will be described with reference to the drawings and embodiments, but the present invention is not limited to these embodiments. FIG.
FIG. 3 is a plan view showing a state before an insulating resin layer of the flexible printed wiring board of the present invention is bonded. A predetermined conductive circuit is formed in the component mounting section 2.

2 (A) to 2 (F), the configuration of the earth circuit section of the present invention will be described. 2A to 2F are enlarged schematic cross-sectional views of the ground circuit portion. FIG. 2F is a cross-sectional view after an insulating resin layer is bonded to both surfaces of the conductive coating layer of FIG. FIG. 2A shows an insulating substrate 1 and an electrolytic copper foil 5.
Is a material for flexible printed wiring boards that is integrally molded. FIG. 2B shows a state in which a predetermined conductive circuit is formed by ordinary etching, and the ground circuit 6 and the throughhole land 7 are made conductive. The steps in FIGS. 2A and 2B are the same as those of the conventional flexible wiring board, and are not particularly limited. FIG. 2 (C) shows that an insulating resin coating layer 8 is provided by laminating a polyimide resin film with an adhesive on the grounding circuit 6 and applying heat and pressure to expose a predetermined portion of the insulating resin coating layer 8 by a usual method. 3 shows a state in which an opening 9 is provided by developing and the earth circuit 6 is exposed.

FIG. 2 (D) shows that the grounding circuit 6 at the opening and the throughhole land 7 at the throughhole connection are formed by metal plating 1.
0 indicates a surface-treated state, and the contact resistance can be improved by performing metal plating 10. FIG. 2 (E) shows both sides,
A state in which the conductive coating layer 11 is formed by screen-printing a silver paste containing a thermoplastic resin in the openings, through-holes, and the like, and then drying by heating, that is, a state in which a shield layer is provided. By connecting the opening and the conductive paste, the connection between the signal section and the ground section becomes possible. By using a silver paste containing a thermoplastic resin, the flexibility required for a flexible printed wiring board can be maintained. The conductive shield layer fulfills the function of shielding electromagnetic waves. FIG. 2 (F)
Shows a state in which the conductive coating layers 11 on both surfaces are covered with the insulating resin layer 12. FIG. 3 is an enlarged plan view showing a boundary between the component mounting land 14 and the conductive coating layer 11 of the present invention. The distance between the end of the component mounting land 14 and the outer edge of the conductive coating layer 11 is preferably 0.5 to 2 mm.

[0013]

The flexible printed wiring board of the present invention has a shield layer and is excellent in bending resistance, and is particularly suitable as a material for shielding electromagnetic waves.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a flexible printed wiring board of the present invention before being covered with an insulating resin layer.

FIG. 2 is a schematic cross-sectional view showing a configuration of an earth circuit unit according to the present invention.

FIG. 3 is an enlarged schematic plan view of part A of the flexible printed wiring board of the present invention.

FIG. 4 is a schematic cross-sectional view of a ground circuit section of a conventional flexible printed wiring board.

Claims (6)

[Claims] 1. A flexible printed wiring board having copper foil laminated on both sides of an insulating base material, a predetermined conductive circuit, an earth circuit on one side, and a through-hole land on the other side,
An insulating resin coating layer made of a polyimide film with an adhesive on the ground circuit surface, a conductive coating layer made of a conductive paste containing a thermoplastic resin on the insulating resin coating layer and the through-hole land surface, and insulation on both surfaces of the conductive coating layer A flexible printed wiring board having a resin layer. 2. The flexible printed wiring board according to claim 1, wherein the conductive paste is a silver paste. 3. The insulating resin coating layer has an opening, and only the metal-plated ground circuit is exposed from the opening, and the ground circuit is connected to the conductive coating layer. Flexible printed wiring board. 4. The flexible printed wiring board according to claim 1, wherein a through-hole round surface of the through-hole connecting portion is metal-plated. 5. The flexible printed wiring board according to claim 1, wherein a distance between the component mounting land and the conductive coating layer is 0.5 to 2 mm. 6. The flexible printed wiring board according to claim 1, wherein the number of connection of the conductive paste and the throughhole land is 1 to 3 pieces / cm ² , and the diameter of the connection point is 0.5 to 3.
A flexible printed wiring board having a diameter of 0 mmΦ.