JPH06314862A - Flexible circuit board - Google Patents

Abstract

PURPOSE:To provide a flexible circuit board excellent in flexibility and crosstalk preventive property and low in cost. CONSTITUTION:Two insulating films, a first insulating film 1 and a second insulating film 7, face each other, and a conductor circuit pattern 3 is formed on the first insulating film 1. And, an earth conductor circuit pattern 5 is made, in the condition of being positioned in gap between conductor circuit patterns 3, on the second insulating film 7 opposed to the first insulating film 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible circuit board used for high speed / high frequency electronic equipment and the like.

[0002]

2. Description of the Related Art Conventionally, flexible printed circuit boards have been widely used when connecting printed circuit boards having electronic components mounted thereon. In such a flexible printed circuit board, since the conductor circuit patterns provided are generally formed in parallel, the electromagnetic field coupling between the conductor circuit patterns is strong, crosstalk occurs, and the electronic device malfunctions. easy. In order to solve such a problem, for example, by providing a ground conductor circuit pattern on the conductor circuit pattern via an insulating layer, or by providing a ground conductor circuit pattern on the same plane as the conductor circuit pattern It has been proposed to prevent the reduction of electromagnetic field coupling.

[0003]

In the above-mentioned flexible printed circuit board, the method of providing the ground conductor circuit pattern on the above-mentioned conductor circuit pattern via the insulating layer is the greatest feature of the flexible printed circuit board. Occurs. Further, in the flexible printed circuit board in which the ground conductor circuit pattern is formed on the same surface as the conductor circuit pattern in the above, when the conductor circuit pattern and the ground conductor circuit pattern are formed by the subtractive method which is an etching process at a low manufacturing cost, In order to ensure the insulation between the conductor circuit pattern and the ground conductor circuit pattern, it is necessary to ensure a sufficient distance between the two circuit patterns. For this reason, the width of the entire flexible printed circuit board becomes large, the area occupied in the electronic device increases, and there arises a problem that high density mounting of electronic components and miniaturization of the electronic device itself are hindered. In addition, when the additive method in which both the conductor circuit pattern and the ground conductor circuit pattern are deposited and formed by plating or the like is used, the insulating property can be secured even if the interval between the both circuit patterns is narrow, but the manufacturing cost is very high. The problem arises.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a flexible circuit board which is excellent in flexibility and crosstalk preventing property and which is low in cost.

[0005]

In order to achieve the above-mentioned object, the flexible circuit board of the present invention has a first insulating film and a second insulating film facing each other, and the first insulating film. A conductor circuit pattern is formed on a surface of the first insulating film, and a ground conductor circuit pattern is formed on a surface of the second insulating film facing the film surface of the first insulating film.
It is formed so as to be positioned in the gap of the conductor circuit pattern.

[0006]

That is, the flexible circuit board according to the present invention is composed of the first insulating film and the second insulating film.
Two insulating films face each other, and a conductor circuit pattern is formed on the first insulating film. Then, a ground conductor circuit pattern is formed on the second insulating film surface facing the first insulating film surface in a state of being positioned in the gap of the conductor circuit pattern. Therefore, the coupling capacitance between the conductor circuit patterns is reduced without impairing the flexibility, and crosstalk is prevented.

Next, the present invention will be described in detail based on embodiments.

[0008]

1 is a sectional view showing an embodiment of a flexible circuit board according to the present invention. Reference numeral 1 denotes an insulating film, and a second insulating film 7 is provided so as to face the insulating film 1. Then, a conductor circuit pattern 3 having a trapezoidal cross section (having a narrow top) is formed on the surface of the first insulating film 1 with an adhesive layer 2 interposed therebetween. A ground conductor circuit pattern 5 is formed on the surface of the second insulating film 7 facing the surface of the first insulating film 1 with an adhesive layer 6 interposed therebetween. The ground conductor circuit pattern 6 is formed in a state of being positioned in the gap between the conductor circuit patterns 3. In this way, the conductor circuit pattern 3 and the ground conductor circuit pattern 5 are meshed with each other with a gap (space) provided therebetween. In the figure, 4 is an adhesive layer that fills the space between the conductor circuit pattern 3 and the ground conductor circuit pattern 5.

The insulating films 1 and 7 are not particularly limited, and conventionally known films having flexibility such as polyimide resin type, polyester resin type and fluororesin type can be used. The materials of the two insulating films 1 and 7 may be the same as or different from each other.

The metal material forming the conductor circuit pattern 3 and the ground conductor circuit pattern 5 is not particularly limited, and may be a conventionally known metal such as copper, aluminum, nickel, or a composite system of these metals. Further, the constituent materials of the two circuit patterns 3 and 5 may be the same as or different from each other. Furthermore, it is preferable that the thicknesses of both circuit patterns 3 and 5 are set within the range of 18 to 75 μm.

The adhesive material for forming the adhesive layers 2, 4 and 6 may be any adhesive as long as it has high adhesiveness to the insulating films 1 and 7 and both circuit patterns 3 and 5, and a polyimide resin. It is possible to use a conventionally known adhesive containing a resin, an epoxy resin, a polyester resin, or a fluororesin as a main component. Similarly to the above, each of the adhesive layers 2, 4 and 6 may be formed of the same adhesive or different adhesives.

The flexible circuit board of the present invention is manufactured, for example, as follows. That is, first, the first
An adhesive layer 2 is formed on the surface of the insulating film 1 using an adhesive. Then, a conductor thin film layer is formed on the adhesive layer 2 using a metal material. Then, this conductor thin film layer is formed into a predetermined conductor circuit pattern 3 by a known method,
An insulating film 1 having a conductor circuit pattern 3 formed with an adhesive layer 2 as shown in FIG. 2 is produced. On the other hand, the adhesive layer 6 is formed on the surface of the second insulating film 7 in the same manner as above. Then, a conductor thin film layer is formed on the adhesive layer 6. Then, this conductor thin film layer is formed on a predetermined ground conductor circuit pattern 5 by a known method, and the insulating film 7 on which the ground conductor circuit pattern 5 is formed via the adhesive layer 6 as shown in FIG. Create. Then, the first
An adhesive is applied to the surface of the insulating film 1 on which the conductor circuit pattern 3 is formed, and the first insulating film 1 and
The two patterns 3 and 5 face each other so that the second insulating film 7 having the ground conductor circuit pattern 5 formed thereon is meshed with the conductor circuit pattern 3 and the ground conductor circuit pattern 5 with a space provided therebetween. It is manufactured by aligning and stacking, then pinning and adhering.

As a method of forming both the circuit patterns 3 and 5, a conventionally known etching process, for example, an unnecessary part of the conductor thin film layer is etched by using a cupric chloride solution or a ferric chloride solution. Examples include a method of forming a predetermined circuit pattern. Thus, when etching is used as a method of forming both circuit patterns 3 and 5, the cross-sectional shape of both circuit patterns 3 and 5 is formed in a trapezoidal shape with a narrow top (see FIG. 1). Therefore, since the two circuit patterns 3 and 5 are each formed in a trapezoidal cross section, a sufficient gap is provided when the two circuit patterns 3 and 5 are engaged with each other with a gap (space) provided therebetween. With this, it becomes possible to set the overall thickness thinner.

FIG. 4 is a sectional view showing another embodiment of the present invention. The flexible circuit board 9 is formed on the surface of the insulating film 1 directly without interposing an adhesive layer or the like on the conductor circuit pattern 3
Are formed. The ground conductor circuit pattern 5 is also directly formed on the surface of the insulating film 7.

The flexible circuit board 9 is manufactured, for example, as follows. That is, the conductor thin film layers are directly formed on the surfaces of the insulating films 1 and 7 by the vacuum deposition method or the like. The subsequent steps are performed in the same manner as described above, and the flexible circuit board 9 is manufactured.

Next, specific examples will be described together with comparative examples.

[0017]

SPECIFIC EXAMPLE 1 A 15 μm-thick adhesive layer made of an epoxy resin adhesive was formed on a 25 μm-thick polyimide film surface, and a 35 μm-thick copper foil was adhered and laminated on this adhesive layer. Then, ten conductor circuit patterns having a width of 500 μm are formed at intervals of 150 μm on the copper foil by a conventionally known etching method, and the conductor circuit pattern 3 is formed via the epoxy resin adhesive layer 2 shown in FIG. A first polyimide film 1 was prepared. On the other hand, by the same material and method as above, 11 second ground conductor circuit patterns 5 having a width of 100 μm were formed at intervals of 550 μm via the epoxy resin adhesive layer 6 as shown in FIG. The polyimide film 7 of was produced. Then, an epoxy resin adhesive is applied to the surface of the polyimide film 1 on which the conductor circuit pattern 3 is formed, and the first polyimide film 1 and the ground conductor circuit pattern 5 are applied.
The second polyimide film 7 on which is formed is overlapped with the above-mentioned patterns 3 and 5 so as to face each other and the conductor circuit pattern 3 and the ground conductor circuit pattern 5 are meshed with each other with a space provided therebetween. The flexible circuit board 8 shown in FIG. 1 was produced by pin-matching and adhering. In the figure, 4 is an epoxy resin adhesive layer.
The total thickness of this flexible circuit board 8 is 140 μm,
The width was 8 mm.

The ground conductor circuit pattern 5 of the flexible circuit board 8 thus obtained is connected to the ground circuit of the impedance analyzer, and the adjacent conductor circuit patterns 3 are connected.
Was measured at a frequency of 1 MHz using the impedance analyzer, and the coupling capacitance between the conductor circuit patterns 3 was 6 pF / m per unit length. Further, the flexibility of the flexible circuit board 8 was not significantly reduced as compared with that before the ground circuit pattern 5 was laminated.

[0019]

Comparative Example 1 A 15 μm thick adhesive layer made of an epoxy resin adhesive was formed on a 25 μm thick polyimide film surface, and a 35 μm thick copper foil was bonded and laminated on this adhesive layer. Then, this copper foil was subjected to a conventionally known etching method to form a conductor circuit pattern 1 having a width of 500 μm.
Zero pieces were formed at intervals of 150 μm. After that, a thickness 50 made of an epoxy resin adhesive is formed on the conductor circuit pattern.
An adhesive layer of μm is formed, and a thickness of 3
A 5 μm copper foil is laminated to form a ground conductor layer pattern 15 with a gap provided on the conductor circuit pattern 12 as shown in FIG. 5, and a second polyimide film 16 is further provided with an adhesive layer 14 interposed therebetween. Were laminated. In this way, a flexible circuit board was obtained. In the figure, 10 is a first polyimide film, and 11 is an adhesive layer. This flexible circuit board had a total thickness of 145 μm and a width of 7 mm.

The ground conductor layer 15 of the flexible circuit board thus obtained is connected to the ground circuit of the impedance analyzer, and the coupling capacitance of the adjacent conductor circuit patterns 12 is measured at a frequency of 1 MHz using the impedance analyzer. As a result, the coupling capacitance between the conductor circuit patterns 12 was 21 pF / m per unit length. This is a coupling capacitance value which is 3.5 times as large as that of the specific example 1. Further, the flexibility of this flexible circuit board was significantly reduced as compared with that before the ground conductor layer 15 was laminated.

[0021]

Comparative Example 2 A 15 μm-thick adhesive layer made of an epoxy resin adhesive was formed on a 25 μm-thick polyimide film surface, and a 35 μm-thick copper foil was adhered and laminated on this adhesive layer. Then, this copper foil was subjected to a conventionally known etching method to form a conductor circuit pattern 1 having a width of 500 μm.
When 0 pieces and 11 pieces of ground conductor circuit patterns having a width of 150 μm are alternately formed at intervals of 25 μm, the conductor circuit patterns and the ground conductor circuit patterns are electrically connected, and a flexible circuit board can be obtained. There wasn't.

[0022]

As described above, in the flexible circuit board of the present invention, the two insulating films of the first insulating film and the second insulating film face each other, and the first insulating film has a conductor. A circuit pattern is formed. Then, a ground conductor circuit pattern is formed on the second insulating film surface facing the first insulating film surface in a state of being positioned in the gap of the conductor circuit pattern. Therefore, the coupling capacitance between the conductor circuit patterns is reduced without impairing the flexibility, and crosstalk is prevented.
Furthermore, even if the conductor circuit pattern and the ground conductor circuit pattern are not short-circuited even if they are manufactured according to the manufacturing method by an inexpensive etching process, it is possible to set the width of the flexible circuit board to a small value. Higher density can be promoted.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a flexible circuit board of the present invention.

FIG. 2 is a cross-sectional view showing a first insulating film on which a conductor circuit pattern of the above embodiment is formed.

FIG. 3 is a cross-sectional view showing a second insulating film having the ground conductor circuit pattern of the above embodiment.

FIG. 4 is a sectional view showing another embodiment of the flexible circuit board of the present invention.

FIG. 5 is a cross-sectional view showing a conventional flexible circuit board on which a ground conductor layer is formed.

[Explanation of symbols]

 1 1st insulating film 2, 4, 6 adhesive layer 3 conductor circuit pattern 5 grounding conductor circuit pattern 7 2nd insulating film

Claims (2)

[Claims] 1. A first insulating film and a second insulating film are faced to each other, a conductor circuit pattern is formed on the first insulating film surface, and the film surface of the first insulating film is formed. A flexible circuit board, wherein a grounding conductor circuit pattern is formed on a surface of a second insulating film facing the second insulating film in a state of being positioned in a gap between the conductor circuit patterns. 2. The flexible circuit board according to claim 1, wherein both of the conductor circuit pattern and the ground conductor circuit pattern are formed in a trapezoidal shape having a narrow top.