JPH0521900Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Industrial Application Field) The present invention relates to a shielded flexible wiring board in which an electromagnetic shielding layer is formed using a conductive paste. (Prior art) The base insulating film and the insulating film are bonded 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 bonded on the ground circuit. A flexible wiring board with a shield in which a through hole is formed and a ground circuit and a shield layer are simultaneously connected using a conductive paste was previously proposed by the applicant of the present application (Utility Application No. 32587/1986).
(see issue). FIG. 3 is a top view of such a shielded flexible wiring board, and FIG. 4 is a sectional view of the main parts thereof. As shown in the drawing, a signal circuit 3 and a ground circuit 4 of a predetermined arbitrary shape are formed on a substrate in which a copper foil is bonded to a base insulating film 1 using an adhesive layer 2 by etching a predetermined arbitrary pattern. After the circuit is formed, the circuit surface is covered with an adhesive-coated insulating film 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 ground circuit 4 to establish continuity with the ground circuit 4.
A through hole 6 is provided through the. 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 4 is electrically connected to the conductive paste 7 at the through hole 6, and the conductive paste 7 applied along the signal circuit 3 is electrically connected to the through hole 6.
It is electrically connected to the signal circuit 3 and acts as a shield layer for the signal circuit 3. Then, a coverlay film 8 is applied to the outside of these parts, except for the terminal part 10, with an adhesive 9 interposed therebetween for protection and insulation. (Problem to be Solved) In the conventional shielded flexible wiring board described above, a sufficient connection can be obtained between the conductive paste 7 on the front and back sides through the through hole 6, but the connection with the ground circuit 4 is made through the through hole. Since contact occurs only at the circuit end face of hole 6, sufficient contact area is not secured,
The connection reliability was low. In particular, when the thickness of the ground circuit conductor is as thin as 35 μm or less, the contact area is extremely small, making it impractical. (Means for Solving the Problems) The present invention provides a shielded flexible wiring board that solves the above-mentioned problems.The feature is that in the above-mentioned shielded flexible wiring board, the earth circuit and the shield layer are connected. The reason is that the insulating film in the through-hole portion is removed to a diameter larger than that of the through-hole. (Function) Continuity between the shield layers formed on both the upper and lower sides of the signal circuit using conductive paste can be established relatively easily and reliably by providing a through hole in the ground circuit and embedding the conductive paste therein. However, since the thickness of the ground circuit conductor is generally small, the contact area between the conductive paste embedded in the through hole and the ground circuit conductor cannot be made large enough, and the electrical connection between the two is unstable. It was easy to get next to her. In contrast, in the present invention, an insulating film with an adhesive is punched out with a diameter larger than the through-hole diameter at the position of the through-hole to be provided in the ground circuit on only the insulating film or on both the insulating film and the base insulating film. was used. By laminating the insulating film processed in this way, the conductive paste and the earth circuit conductor can be bonded together.
In addition to the contact area formed by the through hole, there is also a contact area with the conductive paste on the upper surface or both upper and lower surfaces of the ground circuit conductor, and highly reliable conduction can be obtained. At this time, the removed diameter of the through-hole portion of the insulating film is preferably about 3 to 10 times the diameter of the through-hole. (Example) FIG. 1 and FIG. 2 are both sectional views of essential parts of a specific example of the shielded flexible wiring board of the present invention. In the drawings, the same symbols as in FIG. 4 represent the same parts. In the specific example shown in FIG. 1, the insulating film 5 is removed at a diameter D ₂ that is larger than the diameter D ₁ of the through hole 6 formed in the ground circuit 4 section. Thereby, a contact area is formed between the ground circuit conductor and the conductive paste 7 on the upper surface of the ground circuit conductor in addition to the contact area formed by the through hole. In the specific example of FIG. 2, in addition to the specific example of FIG. 1, the base insulating film 1 is also removed with a diameter larger than the diameter of the through hole 6, as described above. . (Prototype example) An FPC board was created by using a 25 μm thick polyimide film as a base insulating film, applying epoxy adhesive as a base film adhesive to a thickness of 25 μm, and laminating a 35 μm thick electrolytic copper foil on top. A circuit pattern was formed on the copper foil of the substrate by screen printing, etched with cupric chloride, and then plated to form a signal circuit and a ground circuit. Thereafter, an insulating film made of a 25 μm thick polyimide film coated with epoxy adhesive to a thickness of 30 μm was punched out so that a diameter approximately 5 times larger than the conductor hole diameter was exposed at the terminal portion and through hole portion (product of the present invention). Two types were prepared, one was punched out as before, and the other was punched out so that only the surface of the through hole was exposed (comparative example), and it was glued onto the circuit, and after adhesion, the back side of the base insulating film and the top surface of the insulating film were made.
A shield layer was formed by printing copper paste ink in a mesh shape with a porosity of 50%. At this time, in the product of the present invention, the ground circuit is electrically connected to the exposed copper foil portion of the through hole and the circuit end surface of the through hole, and the through hole is filled with copper paste to ensure conduction between the front and back sides. The copper paste of the shield layer is made of phenolic resin binder.
By baking at 160°C for 1 hour, it was brought into close contact with the polyimide film. After that, apply a coverlay film (polyimide layer) so that only the terminals are exposed.
25μm epoxy adhesive (30μm) was punched out and press-bonded onto the shield layer to integrate the signal circuit, ground circuit, upper and lower shield circuits, and insulation layer.
We prototyped two types of shielded flexible wiring boards. Table 1 shows the results of measuring the conduction resistance between the ground circuit and the shield layer under the following conditions for the two types of flexible wiring boards, the prototype product of the present invention and the comparative example manufactured as described above. As is clear from this, it was confirmed that the conduction resistance of the product of the present invention was significantly reduced compared to the comparative example. Conditions: A: After immersion in a solder bath at 260℃ for 30 seconds, B: After 100 heat cycles of -50℃ to +125℃ for 30 minutes each, C: After aging at 100℃ for 1000 hours, D: R = 2.0500 MIT bending with gr load, after 300 times,

[Table] (Effects of the invention) As explained above, according to the shielded flexible wiring board of the invention, the conduction resistance between the ground circuit and the shield layer can be significantly reduced compared to conventional products, and the connection Reliability is greatly improved.

[Brief explanation of the drawing]

1 and 2 are both sectional views of essential parts of a specific example of the shielded flexible wiring board of the present invention. FIG. 3 is a top view of a conventional shielded flexible wiring board, and FIG. 4 is a cross-sectional view of its main parts. 1...Base insulating film, 2...Adhesive layer,
3... Signal circuit, 4... Earth circuit, 5... Insulating film, 6... Through hole, 7... Conductive paste, 8... Coverlay film, 9... Coverlay adhesive.

Claims (1)

[Claims for Utility Model Registration] (1) Bonding the base insulating film and the insulating film with a signal circuit and a grounding circuit fixed in a predetermined arbitrary shape on the base insulating film in between;
A shielded flexible wiring board in which a through hole is formed on the ground circuit including a base insulating film and an insulating film, and the ground circuit and the shield layer are simultaneously connected using a conductive paste, in which the ground circuit and the shield layer are connected. 1. A flexible wiring board with a shield, characterized in that an insulating film in a through-hole portion is removed to have a diameter larger than the diameter of the through-hole. (2) The shielded flexible wiring board according to claim (1), wherein the removed diameter of the through-hole portion of the insulating film is 3 to 10 times the diameter of the through-hole.