JPH0442960Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a shielded flexible wiring board.

[Conventional technology and problems] Conventionally, as a shielded printed wiring board, the third
As shown in Figures A and B, when forming a circuit by etching copper foil adhered to a flexible base insulating film, a solid copper foil is left on one side, and after insulating the circuit, the solid copper foil is removed. The idea was to fold it over the circuit and cover the top and bottom to shield it.

In the figure, 1 is a base insulating film, 12 is a signal circuit, 13 is a solid copper foil, and 14 is an insulating coverlay.

By the way, because of the connection with the shield layer, even if you insert a ground circuit between the signal circuits, it is difficult to connect with the shield layer, and since the ground circuit and the shield layer are connected only at the circuit ends, the shielding effect Furthermore, as shown in Figure 2, the capacitance is unstable because the three layers are not integrated, and wrinkles occur in the solid copper foil due to bending. The capacitance was large, and the connection between the signal circuit and the ground circuit was inconsistent, resulting in large crosstalk. It also has poor flexibility.

[Purpose and structure of the invention] The purpose of the invention is to eliminate the above-mentioned drawbacks, and to obtain a flexible wiring board (hereinafter referred to as FPC) that has constant capacitance and has an electromagnetic shielding effect from the outside. The ground circuit adjacent to
It is connected to a mesh-shaped shield layer running parallel to the top and bottom of the signal circuit, and is etched so that the copper foil remaining ratio of the upper and lower portions of the mesh-shaped shield layer with respect to both the circuits is approximately equal to the circuit area. It is characterized by having holes.

The present invention will be explained below with reference to an embodiment shown in FIG. 1 and an external view of the embodiment shown in FIG.

FIG. 1 shows a cross section. In the figure, 1 indicates the base insulating film, 2 indicates the base adhesive,
3 is a signal circuit, 4 is a ground circuit, 5 is a mesh-like shield layer, 6 is a coverlay film, 7 is a coverlay adhesive, 8 is the shield layer 5 and the ground circuit 4
A cover lay film 6 is bonded to the signal circuit 3 and ground circuit 4 formed by etching on one side of the copper foil bonded to the base insulating film 1, and the cover lay film 6 is bonded to the other side of the copper foil. The signal circuit 3 and the ground circuit 4 are surrounded and covered with a mesh-shaped copper foil formed by etching as a shield layer to form a three-layer integrated flexible wiring board. The shield layer 5 is electrically connected to the base insulating film 1 and the cover lay film 6 through a plurality of ground holes.
The holes are formed in the shield layer so that the copper foil remaining ratios of the upper and lower parts of both circuits are approximately equal to or slightly larger than the areas of both circuits.

The base insulating film 1 is selected from, for example, polyimide film, polyparabanic acid film, polyester film, etc., and an adhesive is selected from, for example, epoxy type, urethane type, phenol type, butyral type, triazine type, etc.
A circuit is formed by etching a predetermined arbitrary pattern on a substrate to which a 70μ electrolytic and rolled copper foil is adhered.

As circuits, a signal circuit 3 and a ground circuit 4 are provided as shown in the figure, and the ground circuit 4 is always provided adjacent to the signal circuit 3. The adjacent portion is
This means that the ground circuit 4 is located next to or within the third signal circuit 3.

The ground circuit 4 is provided with a ground hole for connection to the upper and lower mesh-shaped shield layers 5, and is electrically connected with a conductive material.

As the conductive material, use soldering, solder cream, resin such as silver paste, copper paste, carbon paste, etc., fill the ground hole, and then
It is electrically connected to a shield layer 5, which will be described later.

The shield layer 5 is formed into a mesh shape by etching during circuit formation. It is preferable that the residual ratio of the mesh-shaped shriveled copper foil be approximately equal to or slightly larger than the circuit area. This is because if the area determined by the copper foil residual rate is smaller than the circuit area, the shielding effect will be lowered, and if it is too large, crosstalk will increase.

The signal circuit 3 is insulated by a coverlay adhesive 7 and a coverlay film 6, and then covered with a mesh-shaped shield layer 5.

[Prototype example] Epoxy adhesive on 25μ thick polyimide film
After applying a 25μ film and drying it, two holes were made at each ground position of the earth circuit, and a 35μ electrolytic copper foil was laminated to obtain an FPC board.

The pattern was aligned with the ground hole, one ground circuit was formed for every two 0.3 mm signal circuits, and the distance between each circuit was 0.25 mm. Furthermore, holes of 1.0 mm diameter were opened at a pitch of 1.4 mm by etching to form a mesh so that the copper foil remaining rate of the shield layer was 55%, which was approximately equal to the circuit area. The copper foil survival rate of the shield layer referred to here is the survival rate of the copper foil that covers the top or bottom of the signal circuit and the ground circuit, and the circuit area and the copper foil that goes inside the copper foil. Refers to the entire signal circuit and ground circuit formed by etching in a portion.

In other words, the degree of aperture in the copper foil and the area of the circuit spacing are approximately equal.

Thereafter, 30 μm of epoxy adhesive was applied to a coverlay film made of polyimide film with a thickness of 25 μm, punched out so that the ground hole and terminal portion were exposed, and the film was adhered onto the signal circuit and ground circuit described above.

After adhesion, the ground holes on the base insulating film and coverlay film were filled with conductive silver paste, so that the ground circuit could be electrically connected to the shield layer.

After that, the shield layer is folded so that the copper foil side faces the signal circuit side, and the ground circuit and the shield layer are in contact with the conductive adhesive made of conductive silver paste. The three layers consisting of the upper and lower shield layers are integrated,
Press molding was performed so that the three layers were parallel to each other.

Regarding the obtained shielded FPC, the capacitance between the signal circuit and the ground circuit and the electromagnetic shielding effect were measured. As a result, the capacitance was as low as 130PF/m, and the shielding effect was found to be attenuated by more than 30dB compared to an unshielded FPC.

Furthermore, even when this shielded FPC was placed in a soldering bath at 260°C or bent 180°, the shielding effect did not change, confirming that it is a stable shielded FPC.

[Effects of the invention] Crosstalk is eliminated because the copper foil remaining ratios of the upper and lower portions of the shield tank for both circuits are approximately equal to or slightly larger than the circuit area.

Since the signal circuit and the shield layer are parallel, the capacitance is kept constant.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the invention in cross section. FIG. 2 shows the external appearance of the embodiment. Figure 3A shows a developed view of a conventional flexible wiring board, and Figure 3B shows a wiring board formed by folding the wiring board of A to form a shielded FPC. 1...Base insulation film, 3...Signal circuit,
4...Earth circuit, 5...Mesh-shaped shield layer, 6...Coverlay film.

Claims (1)

[Scope of utility model registration request] A cover lay film is bonded to the signal circuit and ground circuit formed on one side of the copper foil bonded to the base insulating film, and the mesh-shaped copper foil formed on the other side of the copper foil is used as a shield layer to signal the signal. It is a flexible wiring board that integrates three layers by surrounding and covering a circuit and a ground circuit, and the ground circuit and the shield layer made of mesh copper foil are connected through a plurality of ground holes drilled in the base insulating film and the cover lay film. electrically connected, and the copper foil is etched into a mesh shape so that the residual ratio of the copper foil on the upper and lower parts of the mesh shield layer with respect to both circuits is approximately equal to or slightly larger than the area of the signal circuit and the ground circuit. A flexible wiring board with a shield characterized by having holes.