JPH0632420B2 - Manufacturing method of flexible wiring board with shield - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a shielded flexible wiring board in which an electromagnetic shield layer is formed using a conductive paste.

(Prior Art) The base insulating film and the insulating film are bonded to each other with a signal circuit and a ground circuit fixed in a predetermined arbitrary shape on the base insulating film, and the base insulating film and the insulating film are included on the ground circuit. To form a through hole with
A flexible wiring board with a shield in which an earth circuit and a shield layer are simultaneously formed by using a conductive paste has been proposed by the applicant of the present invention (see Japanese Utility Model Application No. 61-32587).

FIG. 2 is a top view of such a shielded flexible wiring board, and FIG. 3 is a cross-sectional view of the main part thereof.

Adhesive layer on the base insulation film (1) as shown in the drawing
A signal circuit (3) and a ground circuit (4) having a predetermined arbitrary shape are formed by etching a predetermined arbitrary pattern on a substrate to which a copper foil is adhered using (2). After the circuit is formed, the surface of the circuit is covered with an insulating film with an adhesive (5) and bonded to the base insulating film (1). At this time, the insulating film (5) and the base insulating film (1) are provided with a through hole (6 ') penetrating the earth circuit (4) to establish continuity with the earth circuit (4). The signal circuit (3) is insulated except for the terminal portion (10) and the through hole (6 '), and a conductive paste (7) is applied to the surfaces of the insulating film (5) and the base insulating film (1). At this time, the ground circuit
In (4), the conductive paste in the through hole (6 ')
The conductive paste (7) provided along the signal circuit (3) is electrically connected to the conductive paste (7) which is electrically connected to the through hole (6 '). And acts as a shield layer for the signal circuit (3). Then, a coverlay film (8) is applied to the outside of these with the adhesive (9) except for the terminal portion (10) to perform protective insulation.

(Problems to be Solved) In the above-mentioned conventional flexible wiring board with a shield, a sufficient connection can be obtained between the conductive pastes (7) on the front and back sides through the through holes (6 '), but a ground circuit.
Since the connection with (4) is made only at the circuit end face of the through hole (6), a sufficient contact area was not secured and the connection reliability was low.

In particular, when the ground circuit conductor had a thin thickness of 35 μm or less, the contact area was extremely small, which was not practical.

(Means for Solving the Problem) The present invention provides a method for manufacturing a flexible wiring board with a shield that solves the above-mentioned problems, and is characterized by a signal circuit fixed on a base insulating film in a predetermined arbitrary shape. And the base insulating film and the insulating film are adhered to each other with an earth circuit interposed therebetween, and then the insulating film side is embossed on the earth circuit to expose a part of the upper surface of the earth circuit and formed by the embossing. And forming a shield layer made of a conductive paste on the back surface of the base insulating film and on the insulating film including the concave portion, and at the same time connecting the ground circuit and the shield layer.

(Function) Conduction between shield layers formed on both upper and lower sides of the signal circuit by the conductive paste is relatively easy and reliable by providing a through hole in the ground circuit and embedding the conductive paste in the through hole. You can However, the conductive paste embedded in the through-hole and the ground circuit conductor generally do not have a sufficiently large fusion area due to the small thickness of the ground circuit conductor, and the electrical connection between the two becomes unstable. It was easy.

On the other hand, in the manufacturing method of the present invention, in connecting the shield layer and the ground circuit conductor with the conductive paste formed on the back surface of the base insulating film and the upper surface of the insulating film of the flexible wiring board, the insulating film is formed on the ground circuit. By embossing from the side, a part of the upper surface of the ground circuit conductor is exposed to sufficiently increase the area of fusion with the conductive paste so that the upper and lower shield layers are reliably connected.

(Example) FIG. 1 is a sectional view of a main part of a flexible wiring board with a shield obtained by the manufacturing method of the present invention. In the drawings, the same symbols as those in FIG. 3 represent the same parts.

The manufacturing method of the present invention will be specifically described below with reference to FIG.

Adhesive layer on the base insulation film (1) as shown in the drawing
A signal circuit (3) and a ground circuit (4) having a predetermined arbitrary shape are formed by etching a predetermined arbitrary pattern on a substrate to which a copper foil is adhered using (2). After the circuit is formed, the surface of the circuit is covered with an insulating film with an adhesive (5) and bonded to the base insulating film (1). After that, embossing (6) is applied from the side of the insulating film (5) on the earth circuit (4) to make the earth circuit (4).
Exposing a part of the upper surface of the conductor. Then, including the recess formed by the embossing (6), a shield layer (7) of conductive paste is formed on the back surface of the base insulating film (1) and the upper surface of the insulating film (5), and at the same time the ground circuit is formed. Connect (4) and shield layer (7).

(Prototype example) A 35 μm thick electrolytic copper foil is laminated on a 25 μm thick polyimide base film via an adhesive layer to form a copper-clad laminate, and a circuit circuit with a circuit width of 250 μm between circuits is formed on the laminate. Then, a ground circuit having a width of 1.2 mm was formed on both ends of the circuit to obtain an FPC.

On the above circuit, an insulating film in which 25 μm of polyimide film was coated with 30 μm of adhesive was adhered. After that, a 0.6 mm recess was formed on the ground circuit, and embossing was performed at 20 mm intervals in the length direction using a male mold that cuts the circuit only on the semicircle.

Thereafter, a copper paste was printed on the insulating film, and the copper paste was pressed into the recesses so that it could be connected to the ground circuit conductor. After drying the insulating film side, a copper paste was printed on the back surface of the base insulating film in the same manner as above to cover the signal circuit from above and below, and the copper paste was cured to form an electromagnetic shield layer having a thickness of 10 to 15 μm. A coverlay film having a coverlay adhesive was press-bonded to the outside of the electromagnetic shield layer to protect the shield layer, and a flexible wiring board with a shield was obtained.

In order to evaluate the performance of the obtained shielded flexible wiring board, a comparison test with one in which a 0.6 mm through hole was provided on the ground circuit as shown in Fig. 3 and copper paste was embedded to connect the upper and lower shield layers did.

The results are shown in Table 1, and it is confirmed that not only the initial conduction resistance of the shield layer is low, but also the change in conduction resistance is small after the bending test, the heat cycle test, and the constant temperature and humidity test. It was

(Effect of the invention) As described above, the shielded flexible wiring board obtained by the manufacturing method of the present invention can significantly reduce the conduction resistance of the ground circuit and the shield layer as compared with the conventional product, It is possible to realize a flexible wiring board with a shield, which has excellent practicality, heat cycle, and constant temperature and humidity, and is highly practical.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a flexible wiring board with a shield obtained by the manufacturing method of the present invention. FIG. 2 is a top view of a conventional shielded wiring board, and FIG. 3 is a cross-sectional view of the main part thereof. (1) ... Base insulating film, (2) ... Adhesive layer,
(3) ... Signal circuit, (4) ... Ground circuit, (5) ... Insulating film, (6) ... Embossing, (7) ... Shield layer, (8) ... Coverlay film, (9) ... Coverlay adhesion Agent.

Claims (1)

[Claims] 1. A base insulation film and an insulation film are adhered to each other with a signal circuit and a ground circuit fixed in a predetermined arbitrary shape on the base insulation film, and then embossed from the insulation film side on the ground circuit. Part of the upper surface of the ground circuit is exposed, and a shield layer of conductive paste is formed on the back surface of the base insulating film and on the insulating film including the recess formed by the embossing process, and at the same time the ground circuit and the shield layer are connected. A method of manufacturing a flexible wiring board with a shield, comprising: