JPH0648953Y2 - Flexible wiring board with shield - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a flexible wiring board with a shield.

[Conventional technology and problems]

Conventionally, when a circuit is formed by etching a copper foil adhered to a flexible base insulating film as a shielded printed wiring board as shown in FIG. 3, a solid copper foil is left and the circuit is insulated, A configuration has been considered in which the copper foil is folded over the circuit, covered up and down, and shielded. In the figure, 11 is an insulating film, 12 is a signal circuit, 13 is a solid copper foil, and 14 is an insulating coverlay film.

However, because many signal circuits are connected to the ground circuit only at the copper foil end, electrical energy coupling occurs between the circuits and the solid copper foil, crosstalk increases, and it is difficult to obtain a good signal. It was Further, since the three layers between the solid copper foil and the signal circuit are not integrated, the electrostatic capacitance of each signal circuit was not stable, and noise was generated in the transmission and reception of the voice signal and the image signal.

Further, the solid copper foil floats or wrinkles due to bending when the wiring board is attached, and the electromagnetic shielding effect from the outside also fluctuates, so that a flexible wiring board excellent in the shielding effect cannot be obtained.

[Purpose and structure of device]

The present invention eliminates the above-mentioned drawbacks, in particular, makes the capacitance constant,
To reduce crosstalk and obtain a flexible wiring board (hereinafter referred to as EPC) that has a shielding effect against external electromagnetic waves of 10 MHz or less.

The present invention has a signal circuit width of 0.3 m or less, a distance to the circuit shield layer is 1/2 or more of the circuit width, and is provided at a constant distance. The opening area of the shield layer is 30 to 60% and the opening portion is The FPC is characterized in that the intervals between the two are formed with a density not more than three times the circuit width.
Is.

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

FIG. 1 shows a cross section of the present invention. In the figure, 1 is a base insulating film, 2 is a base adhesive, 3 is a signal circuit, 44 'is a ground circuit, 55' is a shield layer, 6 is a coverlay film, 7 is a coverlay adhesive, and 8 is a base insulation. An adhesive layer for keeping the distance between the film 1 and the coverlay film 6 constant, and 9 denotes an opening of the shield layer.

What is specially mentioned in the present invention is that the distance between the signal circuit width and the shield layer and the opening state of the shield layer have an optimum range in electrical design.

As the base insulating film, for example, a polyimide film, a polyparabanic acid film, a polyetherimide film, a polyester film, or the like is selected, and an adhesive is added to this, for example, an epoxy-based, urethane-based, phenol-based,
Select from butyral type, triazine type, etc., 18-70μ
The FPC board with the copper foil adhered by electrolysis and rolling is used.

The substrate is formed with an arbitrary electric wiring pattern by a screen printing method or a photosensitizing method, and is etched with iron chloride or copper chloride to form a copper rotation.

As a circuit, a signal circuit 3, a ground circuit 4 and a shield layer 5 are provided as shown in the figure, but the circuit width x is 0.
3mm or less is desirable. For audio and video signal circuits, it is necessary to keep the current capacity and the shield characteristic to 0.3 mm or less, and if it is more than that, the electrostatic capacitance will rapidly increase and the electromagnetic shielding effect will be reduced, which is not preferable.

Ground circuits are always provided at both ends of the signal circuit, and they are electrically connected to the shield layer. The shield layers are provided above and below the signal circuit, and it is necessary to provide the distance y at a constant distance of 1/2 or more of the circuit width. For example, if the circuit width is 0.3 mm, the total thickness of at least the insulating film, the coverlay film, each adhesive, and the interlayer adhesive is 0.15 mm.
The above is necessary.

The distance between the signal circuit and the shield layer is short (1/2 of the circuit width
This is because the electrostatic capacitance becomes large, crosstalk becomes large, and the electromagnetic shielding effect varies.

The shield layer is provided in parallel with the signal circuit, and it is desirable that the shield layer is not a solid copper foil and has an opening area of 30 to 60%. If the open area of the copper foil is less than 30%, electrical energy coupling will occur between circuits and crosstalk will increase. On the other hand, if the opening area is 60% or more, noise signals from the outside will affect the signal circuit and a sufficient shielding effect cannot be obtained.

As a method of opening the shield layer, the shield layer is formed into a desired shape by etching when the signal circuit is formed. It is preferable that the holes have round holes, square holes, irregular holes, etc. formed uniformly over the entire surface of the shield layer, and the formation density thereof is 3 times the circuit width or less. For example, if the circuit width is 0.3mm, it is 0.1φmm to 0.9.
Form φmm round holes with a pitch of 0.9 mm or less. This is because if the mesh is opened at a pitch that is three times or more the circuit width, the variation in capacitance and the variation in the shield effect will increase depending on the signal circuit.

As described above, the distance between the signal circuit width and the shield layer, the opening area of the shield layer, and the opening density are not simply obtained from the conventional practice, but are obtained from many experimental results.

Hereinafter, description will be made based on a prototype example.

Trial Production Example A 25 μm thick polyimide film was coated with 25 μm of an epoxy adhesive and dried, and then a 35 μm electrolytic copper foil was laminated to obtain an FPC board.

After that, as the signal circuit width, 0.10mm, 0.15mm, 0.20mm,
Four 0.25 mm and 0.30 mm circuits were formed with 0.2 mm circuit intervals each.

As the shield layer, round holes of 0.3 mm, 0.5 mm, and 0.7 mm were formed with pitches of 0.4 mm, 0.6 mm, and 0.8 mm, respectively, and the open area of the shield layer was 44%, 55%, and 60%. Furthermore, a 25μ polyimide film is placed on the entire surface of the signal circuit and shield layer.
The Carvalley film was insulated using a 25μ epoxy adhesive. After that, the shield layer is integrated with the signal circuit using a 50μ acrylic adhesive to keep the distance to the circuit.
It was set to 150μ.

1MH for each signal circuit of the obtained shielded FPC
The capacitance of z and the electromagnetic shield effect were measured.

Compared to FPC without a shield layer, the electromagnetic shield effect is
The attenuation factor was calculated when a 5 MHz electromagnetic wave was applied to the sample of the present invention.

The results are shown in Table 1.

Comparative example Applying 15μ of epoxy adhesive to 25μ thick polyimide film, drying, and then laminating 35μ electrolytic copper foil to FPC
A substrate was obtained.

After that, 0.40mm and 0.50mm circuits for the signal circuit width, 4 for each
This was formed with 0.3 mm circuit intervals. 0.5φ as a shield layer
mm holes and 1.2φ mm round holes were formed at 1.0 mm and 1.2 mm pitch, respectively, and the open area of the shield layer was set to 20% and 78%. Further, a 25 μm polyimide film was used on the entire surface of the signal circuit and the shield layer using a 15 μm epoxy adhesive to insulate the coverlay film. After that, it is integrated with the signal circuit using a 30μ acrylic adhesive and the distance to the circuit is 110
was set to μ.

The same test as the prototype example was conducted on the obtained shielded FPC, and the results are shown in Table 2.

As can be seen from the results shown in Tables 1 and 2, the shielded FPC of the present invention has a low electrostatic capacitance of 130 PF / m or less, and has a sufficient shielding effect of 15 to 30 dB.

On the other hand, if the circuit width is wide as in the comparative example and the open area ratio of the shield layer is too low or too high, the electrostatic capacitance will increase to 150 PF / m or more, and the electromagnetic shielding effect will be as low as 5 dB or less. It turned out that it hardly appeared.

In addition, even if the shielded FPC of the present invention was attached to a solder bath at 260 ° C, the shielding effect did not change even when bent and bent at 180 °, and it was confirmed that the shielded FPC was stable.

[Effects] According to the present invention, the signal circuit width is 0.3 mm or less, and the distance between the circuit and the shield layer is set at a constant distance of 1/2 or more of the circuit width, and the open area of the shield layer is 30 to 60%. In addition, by forming the openings with a density of 3 times the circuit width or less, the capacitance becomes low, the crosstalk becomes small, and a sufficient electromagnetic shielding effect can be obtained.

This is obtained only by the structure of the present invention, and proves the superiority of the present invention.

[Brief description of drawings]

 FIG. 1 shows an embodiment of the present invention in cross section. FIG. 2 shows the appearance of the embodiment. FIG. 3 shows a cross section of a conventional flexible wiring board. 1 ... Base insulating film 2 ... Base adhesive 3 ... Signal circuit 4 ... Ground circuit 5 ... Shield layer 6 ... Coverlay film 7 ... Coverlay adhesive 8 ... Adhesive layer 9 ... Open Hole

Claims (1)

[Scope of utility model registration request] 1. A flexible wiring board with a shield,
The signal circuit width is 0.3 mm or less, the shield layer is provided at a constant distance from the signal circuit to the shield layer by 1/2 or more of the circuit width, and a large number of openings are provided in the shield layer. A flexible wiring board with a shield, characterized in that the intervals between the centers of the respective parts are formed to be not more than three times the circuit width, and the open area of the shield layer is 30 to 60% of the entire shield.