JPH0575219A - Flexible circuit board and manufacture of flexible circuit board - Google Patents

Abstract

PURPOSE:To lighten a flexible circuit board without marring electromagnetic shield and electrostatic shield by forming metallic foil directly on the component mount surface and reverse surface of a flexible base material. CONSTITUTION:First, a base material is made by sticking aluminum foils 13 on both sides of a film base material 12, and the surface of the aluminum foil 13 is coated with a resist by dipping. Next, exposure and development are performed to from circuit patterns 11 only on the side to be mounted with parts, and further etching is performed. Lastly, the resist is removed. For the flexible circuit board being completed this way, electromagnetic shielding and electrostatic shielding are secured by the metallic foil 13 made directly on the circuit side and the reverse side of the film base material 12, so there is not necessity to use a thick aluminum plate or an aluminum foil laminate film, therefore it can be lightened without marring the function of electromagnetic shielding or electrostatic shielding.

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 and a method for manufacturing the flexible circuit board.

[0002]

2. Description of the Related Art Some conventional flexible circuit boards have an electromagnetic shield function and an electrostatic shield function.

FIG. 6 is a cross-sectional view for explaining an example of the structure of a conventional flexible circuit board having electromagnetic shield and electrostatic shield functions.

As shown in FIG. 1, a conventional flexible circuit board on which parts can be mounted is constructed such that the circuit board 61 is housed inside an aluminum plate 62 provided inside a plastic cabinet 63. There is. The aluminum plate 62 is provided for electromagnetically shielding and electrostatically shielding the circuit board 61.
A bent aluminum plate with a plate thickness of 1 to 2 mm is generally used.

FIG. 7 is a sectional view for explaining another example of the structure of a conventional flexible circuit board having electromagnetic shield and electrostatic shield functions.

As shown in the figure, the conventional flexible circuit board is constructed so that the circuit board 71 is housed inside a plastic case 73 with an aluminum foil laminate film 72 interposed therebetween. The aluminum foil laminated film 72 is provided for electromagnetically shielding and electrostatically shielding the circuit board 71. The aluminum foil laminate film 72 is formed by packing both sides of the aluminum foil with plastic films, and the total thickness of the aluminum foil laminate film 72 is about 150.
μm.

In the conventional method for manufacturing a flexible circuit board, the circuit board 71 is assembled by fitting a hole into the plastic case 73 through the aluminum foil laminate film 72. The circuit forming surface of the assembled circuit board 71, that is, the aluminum foil laminated film 72.
An aluminum foil is formed on the surface opposite to the surface provided with to form a circuit pattern.

[0008]

In such a conventional flexible circuit board, when the electromagnetic shield and the electrostatic shield are performed by the one configuration example shown in FIG. 6 and the other configuration example shown in FIG. Since it is necessary to use a thick aluminum plate 62 having a thickness of 1 to 2 mm and a thick aluminum foil laminate film 72 having a thickness of about 150 μm, there is a problem that the total weight increases.

Further, in such a conventional method for manufacturing a flexible circuit board, since the circuit board 71 is assembled by being hole-fitted into the plastic case 73 through the aluminum foil laminate film 72, the circuit board 71, the aluminum It is necessary to position the foil laminate film 72 and the plastic case 73, and an aluminum foil is formed on the circuit forming surface of the assembled circuit board 71 to form a circuit pattern, which is troublesome in design and manufacturing. There is a problem.

Therefore, an object of the flexible circuit board of the present invention is to provide a flexible circuit board which can be reduced in weight without impairing the electromagnetic shield and electrostatic shield functions.

An object of the method of manufacturing a flexible circuit board according to the present invention is to provide a method of manufacturing a flexible circuit board which can save design and manufacturing troubles.

[0012]

The flexible circuit board of the present invention comprises a film base material and a metal foil formed directly on the surface of the film base material opposite to the circuit forming surface.

The method of manufacturing a flexible circuit board according to the present invention comprises forming metal foils on both sides of a film base material simultaneously, and simultaneously forming resist layers on both sides of the film base material on which the metal foil is formed. A circuit pattern is formed by exposing, developing and etching the resist layer on the circuit formation surface side, and the resist layer is peeled off to form the circuit pattern.

[0014]

According to the flexible circuit board of the present invention, the electromagnetic shield and the electrostatic shield are provided by the metal foil directly formed on the surface of the film base material opposite to the surface on which the circuit is formed. Since it is not necessary to use a thick aluminum plate or an aluminum foil laminated film, the weight can be reduced. Therefore, the weight can be reduced without impairing the electromagnetic shield and electrostatic shield functions.

According to the method for manufacturing a flexible circuit board of the present invention, it is not necessary to position the film base material and the metal foil, and the metal foil is simultaneously formed on both surfaces of the film base material to form the circuit of the film base material. A circuit pattern is formed on the surface. Therefore, it is possible to save the labor for designing and manufacturing.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

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

As shown in the figure, the flexible circuit board of this embodiment is formed of a film base material 12 made of, for example, polyester and a thin aluminum foil 13.

The aluminum foil 13 is made of low-purity aluminum having a purity of about 99% used for aluminum foil, etc., and is directly formed on the surface of the film substrate 12. The thickness of the aluminum foil 13 is, for example, about 15 μm.
It is a degree.

A circuit pattern 11 made of high-purity aluminum having a purity of 99.9% or more is formed on the surface of the film substrate 12 opposite to the surface on which the aluminum foil 13 is formed.

The film substrate 12 is an example of the film substrate of the flexible circuit board of the present invention. The aluminum foil 13 is an example of the metal foil of the flexible circuit board of the present invention.

In the flexible circuit board having such a structure, an aluminum plate (aluminum plate 62 shown in FIG. 6) or an aluminum foil laminated film (aluminum foil laminated film 72 shown in FIG. 7) is used instead of the conventional flexible circuit board. Aluminum foil 13 is used for the circuit pattern formed on the film substrate 12.
The electromagnetic and electrostatic shields of 11 are the circuit patterns 11
The aluminum foil 13 is attached to the surface opposite to the surface on which is formed.

The flexible circuit board of this embodiment is constructed so as to be housed in a plastic cabinet, a plastic case or the like (not shown), like the conventional flexible circuit board.

According to the flexible circuit board of this embodiment, since the aluminum foil 13 formed directly on the surface of the film base material 12 opposite to the surface on which the circuit is formed provides electromagnetic and electrostatic shielding, Since it is not necessary to use a thick aluminum plate or an aluminum foil laminated film unlike the above, it is possible to reduce the weight. or,
Since the process of purifying low-purity aluminum from an aluminum raw material is generally simple, aluminum foil 13 formed by rolling refined low-purity aluminum is inexpensive,
It is possible to realize cost reduction. That is, using the low-purity aluminum foil 13 for the electromagnetic shield and the electrostatic shield can contribute to high cost performance.

On the other hand, since the circuit pattern 11 is made of high-purity aluminum, a fine pattern can be formed, corrosion resistance is excellent, and good electrical characteristics can be obtained.

Next, an embodiment of the method for manufacturing a flexible circuit board according to the present invention will be described.

To explain the outline, first, a base material is formed by laminating aluminum foils on both sides of a film base material, and the surface of the aluminum foils formed on both sides is dip-coated with a resist. Next, exposure and development are performed to form a circuit pattern only on the surface on which the component is mounted, and etching is further performed. Finally, the resist is peeled off to complete the flexible circuit board having the electromagnetic shield and electrostatic shield functions.

In one embodiment of the method for manufacturing a flexible circuit board according to the present invention, FIG. 2 is an explanatory view showing a laminating process, FIG. 3 is an explanatory view showing a resist film forming process, and FIG. 4 is an etching process. And FIG. 5 showing the process of FIG.
FIG. 4 is an explanatory view showing a step of peeling a photoresist.

As shown in FIG. 2, the film substrate 12 of FIG.
In the process of laminating the aluminum foil on both sides of the film, first, the film base material 21 made of, for example, polyester, which is the base, is unrolled from the roll 21R, and the adhesive is applied to both surfaces of the film base material 21 by the adhesive applicator 22. To do.

Next, the aluminum foils 23 and 24 are rolled 23
It is supplied from R 2 and R 2 respectively, and both sides of the film substrate 21 are simultaneously laminated. At this time, one of the aluminum foils 23 and 24 is a high-purity aluminum foil having a purity of 99.9% or more, and the other is a low-purity and inexpensive general-purpose aluminum foil having a purity of about 99%.

After the laminating process, the film 26 is passed through an oven 25 to cure the adhesive and the film 26 is rolled.
Take up on R. Here, the aluminum foils having different purities are simultaneously attached to both surfaces of the film base material 21, but the laminating process on both surfaces of the film base material 21 can be completed in one step.

Next, aluminum foils having different purities on both sides
The film 26, that is, the original film, in which 23 and 24 are laminated, is shown in FIG.
Liquid roll 27R from roll 26R
The film 29 having the resist film formed on both surfaces thereof is wound up on a roll 29R by being dipped in a film, coated with photoresist on both surfaces at the same time, and then dried by a drying oven 28.

Next, as shown in FIG. 4, the film 29 having the resist film formed on both surfaces thereof has a latent image of a circuit pattern formed by a photo technique by the exposure device 30 on the surface laminated with high-purity aluminum foil. Then, the resist film is formed in a circuit pattern through the developing tank 31.
At this time, since the surface side where the low-purity aluminum foil for the electromagnetic shield and the electrostatic shield is laminated is not exposed, the resist film remains on the entire surface. After this exposure and development, the exposed portion of the aluminum foil is passed through the etching tank 32 to be etched, and a circuit pattern is formed in the shape depicted by the exposure device 30. At this time, since the resist film remains on the entire surface side where the low-purity aluminum foil for shielding is laminated, it is not etched. After this etching process, the film 35 is passed through a cleaning tank 33 and then dried by an air dryer 34, and a film 35 having a circuit pattern formed on one surface is wound around a roll 35R.

Finally, as shown in FIG. 5, the film 35 having the circuit pattern formed on one surface is passed from the roll 35R through the resist stripping tank 36, the resist films formed on both sides are stripped, and air-dried. After being dried by the container 37, the film 38 is wound on the roll 38R to complete the whole process.

The film 38 wound around the roll 38R by these steps corresponds to the flexible circuit board of the above-described embodiment.

Therefore, as in the conventional method of manufacturing a flexible circuit board, the flexible circuit board is assembled by fitting the circuit board into the plastic case through the aluminum foil laminate film, so that the circuit board and the aluminum foil are assembled. It is necessary to position the laminate film and the plastic case, and since the aluminum foil is formed on the circuit forming surface of the assembled circuit board to form the circuit pattern, it takes time in designing and manufacturing. According to the manufacturing method, it is not necessary to position the film base material 21 and the aluminum foils 23 and 24, and the aluminum foils 23 and 24 are simultaneously formed on both surfaces of the film base material 21, so that the design and manufacturing You can save time.

Generally, the purity of the aluminum foil used for forming the circuit pattern has a great influence in the etching process shown in FIG. 4 for forming the circuit pattern. That is, when low-purity aluminum foil with a purity of 99.9% or less is etched, the influence of impurities contained in aluminum (acceleration of etching speed due to formation of local battery)
As a result, the etching surface becomes jagged and local over-etching (a portion where the etching speed is high) becomes large, so that a fine and precise circuit pattern cannot be formed. Moreover, pinholes often occur on the etching side surface due to the formation of local batteries, and cleaning residues of chemicals (etching solution, resist stripping solution) used in the process of forming the circuit pattern are likely to occur, resulting in corrosion of the circuit pattern. It tends to deteriorate reliability. In order to solve such a problem, by using a high-purity aluminum foil having a purity of 99.9% or more, it is possible to form a more precise circuit pattern with fewer pinholes on the etched side surface.

In the above-mentioned manufacturing process, the films 26, 29 and 35 being processed are manufactured so as to be wound up by rolls 26R, 29R and 35R, respectively. It may be a manufacturing process that proceeds from one process to the next process.

[0039]

As described above, the flexible circuit board of the present invention includes the film base material and the metal foil directly formed on the surface of the film base material opposite to the circuit forming surface. .. Therefore, it is necessary to use a thick aluminum plate or aluminum foil laminate film as in the past, because electromagnetic shielding and electrostatic shielding are performed by the metal foil directly formed on the surface of the film base opposite to the circuit forming surface. Since there is no, it is possible to reduce the weight.

In the method for producing a flexible circuit board of the present invention, the metal foil is simultaneously formed on both sides of the film base material, and the resist layer is simultaneously formed on both sides of the film base material on which the metal foil is formed. A circuit pattern is formed by exposing, developing and etching the resist layer on the circuit formation surface side, and the resist layer is peeled off to form the circuit pattern. Therefore, it is possible to save the labor for designing and manufacturing.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an embodiment of a flexible circuit board according to the present invention.

FIG. 2 is an explanatory view showing a laminating process in one example of the method for manufacturing a flexible circuit board according to the present invention.

FIG. 3 is an explanatory view showing a step of forming a resist film in one example of the method for manufacturing a flexible circuit board according to the present invention.

FIG. 4 is an explanatory view showing an etching step in one example of the method for manufacturing a flexible circuit board according to the present invention.

FIG. 5 is an explanatory view showing a step of removing the photoresist in the embodiment of the method for manufacturing a flexible circuit board according to the present invention.

FIG. 6 is a cross-sectional view for explaining an example of a configuration of a conventional flexible circuit board having an electromagnetic shield function and an electrostatic shield function.

FIG. 7 is a cross-sectional view for explaining another example of the configuration of a conventional flexible circuit board having an electromagnetic shield function and an electrostatic shield function.

[Explanation of symbols]

 11 Circuit pattern 12, 21 Film substrate 13, 23, 24 Aluminum foil 26, 29, 35, 38 Film 21R, 23R, 24R, 26R, 29R, 35R, 38R Roll 22 Adhesive coater 25 Oven 27 Photoresist 28 Drying oven 30 Exposure device 31 Development tank 32 Etching tank 33 Cleaning tank 34, 37 Air dryer 36 Resist stripping tank

Claims (2)

[Claims] 1. A flexible circuit board comprising a film base material and a metal foil formed directly on the surface of the film base material opposite to the circuit formation surface. 2. A metal foil is simultaneously formed on both sides of a film base material, and a resist layer is simultaneously formed on both sides of the film base material on which the metal foil is formed. A method of manufacturing a flexible circuit board, comprising forming a circuit pattern by exposing, developing and etching a resist layer, and peeling the resist layer.