KR101259474B1 - Double sided flexible printed circuit board for use hinge region - Google Patents

Abstract

Provided is a double-sided flexible circuit board suitable for the transmission of high frequency signals and having a folded portion which enables thinning, suppression of conductor breakage and breakage, and high density of the circuit board.
The conductor circuit 2 and the cover member 1 are provided on both sides of the insulating layer 3, and the insulating layer is made of a liquid crystal polymer film having a thickness of 10 to 100 µm, and the cover member has a different thermal deformation temperature from the insulating layer. It is a double-sided flexible circuit board for bending uses which consists only of a liquid crystal polymer film, and has the circumferential rotation part used in 0.5 to 3% of copper foil deformation value Y computed by following formula (1).
Y (%) = (tCu + 1 / 2tLI) / (r + tCL. + TCu + 1 / 2tLI) × 100 (1)
However, tLI is an insulation layer thickness (micrometer), tCL. Is a cover material thickness (micrometer), tCu is copper foil thickness (micrometer), and r represents the bending radius of a circumferential rotation part.

Description

Double-sided flexible circuit board for repeated bending applications {DOUBLE SIDED FLEXIBLE PRINTED CIRCUIT BOARD FOR USE HINGE REGION}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-sided flexible circuit board suitable for applications in which repeated bending of a hinge part or the like of a cellular phone is frequently performed.

Mobile phones play an important role as key components of electronic devices, but as the miniaturization and high integration of electronic components are required, higher performance is required. In response to these demands, the high frequency of signals has been recently attracting attention not only for high density, light weight, and flexibility, but also for processing a large amount of information in circuit boards having wiring circuits.

In order to transmit a high frequency signal, it is necessary to use a material having a low dielectric constant and a low dielectric loss tangent. Here, the liquid crystal polymer film is known as a material excellent in high heat resistance, hygroscopic dimensional stability, high frequency electrical characteristics and the like. For example, in a conventional circuit board, a prepreg layer using glass fiber and a resin as an adhesive is used as an insulator in order to aim at dimensional stability, and in the case of a circuit board having fine wiring, the chargeability between the fine wirings is also used. In order to secure, the cover material is used using the film which apply | coated the adhesive agent. However, the material is not suitable for transmitting high frequency signals. Here, by using the insulating layer and the cover material as the same material or by using only the liquid crystal polymer film as the cover material, a flexible circuit board which does not impair the characteristics of the liquid crystal polymer film without considering the insulating layer and the cover material properties is prepared. Can be configured.

Flexible circuit boards are known as materials which have excellent flexibility and can be bent and used. In particular, a single-sided flexible circuit board has a conductor layer formed on one side of an insulating layer, and is used for repeated bending. In addition, in double-sided flexible circuit boards, circuits made of conductors are formed on both sides of the insulating layer, and are used for bending only once when mounted.

Single sided flexible circuit boards are used in electronic circuit boards requiring repeated bending applications. However, in the single-sided flexible circuit board, there is a problem that the mounting density of the circuit board is half of the double-sided flexible circuit board, or the cost is relatively high. For example, in Patent Document 1, a single flexible circuit board including a double-sided flexible circuit board and a single-sided flexible circuit board is formed by bending a single-sided flexible circuit board portion and forming a portion overlapped with another single-sided flexible circuit board as a bend. Improvement is shown. Patent Document 2 discloses that the arrangement structure in which a support member having a cylindrical surface is disposed inside the bending portion of the flexible circuit board prevents the bending and folding of the bending portion and suppresses the disconnection or breakage of the conductor. In addition, the application to the folding cell phone is also shown.

Japanese Patent Application Laid-Open No. 11-195850 Japanese Patent Application Laid-Open No. 15-258388

However, when the single-sided flexible circuit boards are combined and applied to the bends, the thickness of the layer itself of the flexible circuit boards to be increased increases the thickness and flexibility of the single-sided flexible circuit boards. In addition, when the flexible circuit board is provided with a reinforcing structure, the presence of the reinforcing structure hinders the densification of the circuit board in the electronic circuit or the electronic component.

SUMMARY OF THE INVENTION An object of the present invention is to provide a double-sided flexible circuit board which is suitable for the transmission of high frequency signals and which enables thinning, suppression of conductor breakage and breakage, and high density of the circuit board.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve the above subjects, the present inventors used only the liquid crystal polymer film for the cover material of the double-sided flexible circuit board for repeating bend applications, such as a mobile telephone, and was flexible similar to a single-sided flexible circuit board. It discovered that this was obtained and completed this invention.

That is, the present invention is a double-sided flexible circuit board provided with a conductor circuit and a cover material formed of copper foil on both sides of the insulating layer, wherein the insulating layer is made of a liquid crystal polymer film having a thickness of 10 to 100㎛, and the cover material is heated with the insulating layer. It consists only of the liquid crystal polymer film from which a deformation temperature differs, Copper foil strain value Y computed by following formula (1) is used in 0.5 to 3% of range, This double-sided flexible circuit board has a bending part and a non-bending part, A bent portion is a double-sided flexible circuit board having a circumferential rotating portion, which is used by being circumferentially rotated.

Y (%) = (tCu + 1 / 2tLI) / (r + tCL. + TCu + 1 / 2tLI) × 100 (1)

Where tLI is the insulation layer film thickness (µm), tCL. Is the liquid crystal polymer film thickness of the cover member (µm), tCu is the copper foil thickness (µm), and r is the radius of curvature of the circumferential rotation part (µm, where the radius of curvature is r ) Represents 2.0 to 5.0 mm).

Here, the double-sided flexible circuit board provides a double-sided flexible circuit board having a better performance of satisfying any one or more of the following requirements.

1) the insulating layer is made of a liquid crystal polymer film, its heat distortion temperature is in the range of 270 to 330 ° C., and the heat distortion temperature of the liquid crystal polymer film as a cover material is lower than that; 2) the conductor circuit is formed of copper foil, The thickness is in the range of 5 to 30 µm, 3) The thickness of the cover material is in the range of 10 to 100 µm, and 4) The bent portion of the double-sided flexible circuit board having the bent portion and the non-bended portion is rotated around. 5) The radius of curvature r of the circumferential rotating part is in the range of 2.0 to 5.0 mm.

The double-sided flexible circuit board is advantageously used in the folded portion of a foldable cellular phone. In addition, the present invention is a folding mobile phone, characterized in that the double-sided flexible circuit board is used in the folded portion of the folding mobile phone. In addition, the present invention is the above-mentioned folding mobile phone in which the angle of the open state is in the range of 10 to 180 ° when the folding mobile phone is in the closed state at 0 °.

[Effects of the Invention]

By applying the double-sided flexible circuit board of the present invention to repetitive bending applications such as mobile phones, it contributes to the transmission of high frequency signals, lightening and thinning of conductor breaks and breaks, and high density of circuit boards.

1 is a cross-sectional view for explaining an example of a double-sided flexible circuit board.
2 is a cross-sectional view for explaining another example of a double-sided flexible circuit board.
3 is a cross-sectional view illustrating a comparative example of a double-sided flexible circuit board.
4 is a cross-sectional view illustrating a comparative example of a double-sided flexible circuit board.
5 is a cross-sectional view illustrating a comparative example of a double-sided flexible circuit board.
6 is a schematic view for explaining the use of the double-sided flexible circuit board.
7 is a schematic diagram for explaining an example of a folding cellular phone.

Hereinafter, the double-sided flexible circuit board of the present invention will be further described.

The double-sided flexible circuit board of the present invention is preferable for use in bending points such as hinge parts of mobile phones, and when used, for example, in hinge parts of mobile phones, its repeated bending life can be 300,000 times or more. .

The double-sided flexible circuit board of the present invention is obtained by a known method such as circuit processing, but a conductor circuit is provided on both sides of an insulating layer made of a liquid crystal polymer film or a polyimide film, and a cover material composed of only a liquid crystal polymer film is provided on the outside thereof. It is structured.

The liquid crystal polymer film used as an insulating layer or a cover material is an arbitrary liquid crystal polymer film which can form an optically anisotropic molten phase, and is also called a thermotropic liquid crystal polymer. The polymer which can form an optically anisotropic molten phase is a polymer which has a property which transmits polarized light when observing the sample of a molten state under the polarizing microscope direct nicotine with a heating apparatus as well known to those skilled in the art.

It is preferable that a liquid crystal polymer film has a transition temperature to an optically anisotropic molten phase in the range of 200-400 degreeC, especially 250-350 degreeC from a heat resistance and workability. Moreover, a lubricant, antioxidant, filler, etc. may be mix | blended in the range which does not impair the characteristic of a film. Although the liquid crystal polymer film used by this invention can apply | coat and use a film form or a solution, it is advantageous to make it a film form, and to adhere to copper foil.

The liquid crystal polymer film is obtained by a known method such as extrusion molding. In the case of extrusion molding, any extrusion molding method can be applied, but known T-die method, laminate stretching method, inflation method and the like are industrially advantageous. In particular, in the inflation method and the laminate stretching method, stress is applied not only to the mechanical axis direction (hereinafter referred to as MD direction) of the film, but also to a direction (hereinafter referred to as TD direction) that is directly parallel thereto. The balanced film of the mechanical property of is obtained.

Although the film used for an insulating layer may be a liquid crystal polymer film, a polyimide film may be sufficient as it. The polyimide film can use what is known for FPC, and a polyimide film layer may consist of two or more layers of polyimide film layers.

As a cover material, the liquid crystal polymer film or polyimide film used for an insulating layer uses the liquid crystal polymer film from which a heat distortion temperature differs. It is preferable that heat distortion temperature differs in the range of 10-100 degreeC. When using a liquid crystal polymer film for an insulating layer, the heat distortion temperature exists in the range of 270-330 degreeC, and the liquid crystal polymer film of a cover material is lower than that, Preferably it is 10-100 degreeC low.

In the method of manufacturing the double-sided flexible circuit board of the present invention, the step of laminating the conductor layers on both sides of the insulating layer, the step of making the conductor layer a circuit, and the step of laminating the cover material on each of the conductor circuit layers on both sides are provided. have. Copper foil (including copper alloy foil) is suitable as a material which forms a conductor layer. Hereinafter, although the conductor layer may be represented by copper foil, it is not limited to copper foil.

For example, when an insulating layer is a liquid crystal polymer film, it rough-processes both surfaces of copper foil, laminates with a liquid crystal polymer film, and laminates under heating and pressurization. Next, the circuit processing of copper foil is performed by a well-known method. Next, after arrange | positioning the liquid crystal polymer film used as a cover material on both surfaces, it laminates under heating and pressurization. As a cover material, when arrange | positioning a liquid crystal polymer film on a conductor circuit, it is 1) the method of arrange | positioning only a liquid crystal polymer film, and heating and pressurizing, and 2) the liquid crystal polymer film surface of the laminated body of a liquid crystal polymer film and copper foil. Is heated on the conductor circuit, pressurized, and thereafter, there is a method of removing copper foil by etching. According to the present invention, any method may be used.

When the insulating layer is a polyimide film, the roughening treatment of the copper foil surface in contact with the polyimide film is not necessarily required, and the polyimide film can be formed by applying, drying or curing in the form of a polyimide solution or a precursor solution thereof. .

Copper foil roughening Although there exist dry roughening methods, such as a blast process and grinding | polishing, and a wet roughening method with a chemical liquid, it is especially preferable to use blackening process.

The preferable thickness range of an insulating layer is 200 micrometers or less, Especially preferably, it is 10-100 micrometers. If the film thickness does not meet 10 µm, the film is easily torn, so handling becomes difficult. If the thickness exceeds 100 µm, the film becomes rigid and difficult to roll into a roll.

When a double-sided flexible circuit board is manufactured by superimposing liquid crystal polymer films having different heat deformation temperatures, it is preferable that the heat deformation temperature differs by at least 10 ° C between the insulating layer and the cover material. If the difference between the heat distortion temperatures is less than 10 DEG C, when a double-sided flexible circuit board is formed by using an insulating layer made of a liquid crystal polymer film and a cover material, the liquid crystal polymer film is thermally deformed simultaneously by the pressure during lamination, and all the conductor circuits are This is because there is a risk that the movement of the conductor becomes easy and the positioning control of the conductor circuit becomes difficult. Here, when an insulating layer is a liquid crystal polymer film, the heat distortion temperature shall be 260 degreeC or more, Especially preferably, it is the range of 270-330 degreeC. If the heat deformation temperature is less than 270 ° C., there is a possibility that the heat deformation only of the liquid crystal polymer film used for the insulating layer and the liquid crystal polymer film as the cover material cannot be distinguished. On the other hand, if the heat deformation temperature is 330 ° C. or more, the melting point of the liquid crystal polymer film is exceeded, and it is difficult to maintain the shape of the circuit board. Also in the case where the insulating layer is polyimide, the thermal deformation temperature of the insulating layer and the cover member needs to be different, and it is preferable that the thermal deformation temperature of the cover member is lower than that of the insulating layer by 10 ° C or more.

Copper foil deformation value Y calculated from Formula (1) of the double-sided flexible circuit board of this invention is 0.5 to 3% of range. If the copper foil strain value does not satisfy 0.5%, the insulation layer thickness, the copper foil thickness in contact with it, and the thickness of the cover member become thin, which may cause disconnection of the conductor circuit. On the other hand, when the copper foil deformation value exceeds 3%, the practical application to the repeated bending use of the mobile phone characterized by thinning and flexibility by increasing the thickness of each layer forming the double-sided flexible circuit board and increasing the bending radius increases. It becomes difficult.

The preferable thickness range of a conductor layer is 100 micrometers or less. When a conductor layer is copper foil, it is preferable that the thickness is 5-30 micrometers. It is preferable to reduce the thickness of the copper foil from the point that a fine pattern can be formed. However, if the thickness becomes too thin, not only wrinkles occur in the copper foil during the manufacturing process, but also breakage of the wiring even when a circuit is formed as a wiring board. This may occur or the reliability of the circuit board may be lowered. On the other hand, when copper foil thickness increases, a taper will generate | occur | produce in the circuit side surface at the time of etching copper foil, and becomes unpreferable in fine pattern formation.

As copper foil used by this invention, what is manufactured by the rolling method or the electrolysis method can be used. Even if the copper foil is subjected to physical surface treatment such as roughening treatment or chemical surface treatment such as pickling, for the purpose of securing the adhesive strength with the liquid crystal polymer film as the insulating layer, the effect of the present invention is not impaired. good.

The preferable thickness range of the cover material which consists only of a liquid crystal polymer film is 300 micrometers or less, Especially preferably, it is 10-100 micrometers. If the thickness of the cover member does not satisfy 10 µm, the copper foil deformation value is remarkably large, and there is a fear that the protection of the conductor circuit serving as the cover member becomes difficult. On the other hand, when the thickness of the cover material exceeds 100 µm, the total thickness becomes too thick, making it difficult to apply practically to repeated bending applications characterized by thinning and flexibility.

EMBODIMENT OF THE INVENTION Hereinafter, the double-sided flexible circuit board of this invention and its usage example are demonstrated with drawing. 1 is a cross-sectional view for explaining an example of a layer structure of a double-sided flexible circuit board, having a conductor circuit layer 2 on both sides of an insulating layer 3 made of a liquid crystal polymer film, and on the liquid crystal polymer film 1 thereon. ) Cover material is installed. FIG. 2 is a cross-sectional view for explaining an example of another layer structure of a double-sided flexible circuit board, having a conductor circuit layer 2 on both sides of an insulating layer 4 made of a polyimide film, and a liquid crystal polymer film ( The cover material of 1) is provided.

3 is a cross-sectional view for explaining another example of the layer structure of a double-sided flexible circuit board, having a conductor circuit layer 2 on both sides of the insulating layer 3 made of a liquid crystal polymer film, and an epoxy-based adhesive layer ( The polyimide film 5 with 6) is used as a cover material. 4 is an example in which the insulating layer 3 in FIG. 3 is used as the insulating layer 4 made of a polyimide film. FIG. 5: is an example which made the composite material which consists of the liquid crystal polymer film 1 and the polyimide adhesive film 6 into the insulating layer 4 which consists of polyimide films as a cover material. 3 to 5 show double-sided flexible circuit boards outside the scope of the present invention.

FIG. 6 is a schematic view for explaining an example in which the double-sided flexible circuit board of the present invention is used for the hinge portion, and has a double-sided flexible circuit board 7 having curved portions 8 curved in an S shape as shown in (A). As shown in (B), the cross section is wound so as to have a circular shape near the bent portion, and is rotated circumferentially. In addition, by circumferential rotation, when seen from above, the surface of the non-bending part 9 on both sides of a circumferential rotation part becomes the same surface. When rotating circumferentially, you may use a cylindrical body for the part used as the circumferential rotational shaft 10.

Fig. 6B is an example of a usage form used in a mobile phone repeated bending application, but the double-sided flexible circuit board of the bending portion is rotated once in the circumferential rotation portion, and the bending radius at the circumferential rotation portion is in the range of 2.0 to 5.0 mm. to be. When used in a folding cell phone, the opening and closing angle is in the range of 10 ° to 180 °. 6 (B) shows that the bent portion 8 of the double-sided flexible circuit board having the bent portion and the non-bended portion is rotated by one rotation, and this portion is referred to as the α volume.

The radius of curvature of the bend radius at the circumferential rotation part (approximately equal to the radius of the circumferential rotation shaft 10) is in the range of 2.0 to 5.0 mm. If the bending radius does not satisfy 2.0 mm, it may be difficult to maintain the bending shape. On the other hand, when the bending radius exceeds 5.0 mm, practical application to the mobile phone repeated bending use characterized by light thinning and flexibility becomes difficult.

7 shows a schematic diagram of a folding cellular phone, in which a double-sided flexible circuit board 7 is circumferentially rotated at the hinge portion 11 to connect the main body (button portion) 12 and the lid portion (display portion) 13. have. The preferred angle range of the opening and closing angles made by the main body 12 and the cover portion 13 is in the range of 10 to 180 degrees. There exists a possibility that a practical trouble may arise that opening and closing angle cannot open and close unless it does not satisfy 10 degrees. On the other hand, when the opening-and-closing angle exceeds 180 degrees, it becomes a bending use rather than a mobile phone repeated bending use.

[Example]

Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited at all by these Examples.

Copper foil processing

The dry film was laminated | stacked on the double-sided copper clad laminated board which consists of a liquid crystal polymer film, and the circuit pattern was formed by UV exposure using the pattern film with a resist width of 100 micrometers, and a circuit width of 100 micrometers. Next, copper foil was etched using the copper chloride etching liquid. Using the optical microscope, the obtained double-sided conductor circuit board was checked for peeling of the circuit and the presence or absence of copper residues between the circuits.

* Thickness measurement

According to JISC5016, the insulating layer, the cover material, and copper foil thickness were measured using the film thickness measuring device (dial gauge 215-153 by Mitsutoyo Corporation).

Initial resistance measurement

In accordance with JISC5016, the resistance value of the double-sided conductor circuit board before the press of the cover material was measured using the resistance measuring device (CX-180N by a custom company).

* Calculation of Copper Strain

The copper foil thickness used for the double-sided flexible circuit board, the insulation layer thickness, the cover material thickness, and the bending radius were calculated by the formula (1) from the copper foil deformation value.

* Cell phone repeated bending test

The mobile telephone repeated bending test of the double-sided flexible circuit board was done using the internal hinge bending tester (PIS-FPJ310 by Pross company). The breaking condition of the double-sided flexible circuit board was a resistance value rise of 5% from the initial resistance value.

(Example 1)

Both sides which use the 25-micrometer-thick liquid crystalline polymer film 280 (Bexstar, Kuraray Co., Ltd., heat distortion temperature 280 degreeC) as an insulating layer, and have the rolling copper foil (BHY-22B-T by Nikko Materials) of 18 micrometers in thickness on both surfaces. The dry film was laminated | stacked on the copper clad laminated board, and the circuit pattern was formed by UV exposure using the pattern film with a resist width of 100 micrometers, and a circuit width of 100 micrometers. Next, copper foil was etched using the copper chloride etching solution, and the double-sided conductor circuit board W was produced. Next, in order to make the 25-micrometer-thick liquid-crystal polymer film 260 (Bexstar, Kuraray Co., Ltd., heat distortion temperature 260 degreeC) into the cover material of a double-sided conductor circuit board W, the said rolled copper foil with a thickness of 18 micrometers was made to the single side | surface. Single-sided copper clad laminated board S was prepared.

Here, the liquid crystal polymer film surfaces of the double-sided conductor circuit board (W) and the single-sided copper-clad laminate (S) were washed with pure water, and washed with pure water and then dried in a hot air oven at 90 ° C. In addition, in order to adhere | attach the copper foil and the liquid crystal polymer film as a cover material, blackening process was performed to the copper surface of a double-sided conductor circuit board. Thereafter, the double-sided conductor circuit board (W) is sandwiched, and a single-sided copper clad laminate (S) having a liquid crystal polymer film having a different flow temperature as a resin layer is laminated, and the press is pressed at a pressure of 260 ° C. and 9 MPa with a precision press. The circuit board was made into a circuit board. After press, the outermost layer copper foil of the obtained circuit board was etched and removed, and the insulating layer and the cover material were made into the double-sided flexible circuit board (FIG. 1) which consists of a liquid crystal polymer.

The double-sided flexible circuit board obtained as described above was cut into a shape shown in Fig. 6A to obtain a test piece. The bending part of this test piece was rotated circumferentially, and it was set to alpha volume, and the hinge bending test was done so that the circuit surface of line / space = 100/100 (micrometer) may be inward (refer FIG. 6 (B)). Moreover, the copper foil deformation value of each test piece after completion of the inner hinge bending test was calculated.

(Example 2)

A double-sided flexible circuit board was produced and evaluated in the same manner as in Example 1 (Reference Example), except that a 50 μm thick liquid crystal polymer film 260 was used as the cover material.

Example 3 (Reference Example)

Dry film is laminated on double-sided copper clad laminate (M) (Spanex M grade made by Shinnitetsu Chemical Co., Ltd.) having a rolled copper foil having a thickness of 18 µm on both sides of a polyimide having a thickness of 25 µm, and a resist width of 100 µm and a circuit width of 100. The circuit pattern was formed by UV exposure using the pattern film of micrometers. Next, copper foil was etched using the copper chloride etching solution to prepare a double-sided conductor circuit board. Next, in order to make the 25-micrometer-thick liquid crystalline polymer film 260 the cover material of the said double-sided conductor circuit board, the single-sided copper clad laminated board which has the rolled copper foil of thickness 18micrometer on one side was prepared. In the form of sandwiching the double-sided conductor circuit board, a single-sided copper clad laminate comprising a liquid crystal polymer film as a resin layer was laminated, and pressed at a pressure of 260 ° C. and 9 MPa by a precision press to form a circuit board. After press, the outermost layer copper foil of the obtained circuit board was etched and removed, and it was set as the double-sided flexible circuit board (FIG. 2) in which the polyimide film and the cover material were made only the liquid crystal polymer film in the insulating layer, and the heterogeneous resin layer was laminated | stacked.

(Comparative Example 1)

The insulating layer was made into a liquid crystal polymer film 280 having a thickness of 25 μm, and a dry film was laminated on a double-sided copper clad laminate having a rolled copper foil having a thickness of 18 μm on both sides thereof, using a pattern film having a resist width of 100 μm and a circuit width of 100 μm. The circuit pattern was formed by UV exposure. Next, copper foil was etched using the copper chloride etching solution to prepare a double-sided conductor circuit board. Next, using a polyimide film cover material in which an epoxy-based adhesive layer was formed on polyimide film K (Kapton: registered trademark), the double-sided conductor circuit board was sandwiched with a precision press at 160 to 170 ° C for 2 to 7 degrees. Pressing was performed at a pressure of MPa to obtain a double-sided flexible circuit board (FIG. 3).

(Comparative Example 2)

As a cover material, it evaluated similarly to Comparative Example 1 except having used the polyimide film cover material (3 types) of the thickness structure shown in Table 1 which provided the epoxy type adhesive layer in the polyimide film K.

(Comparative Example 3)

Dry film is laminated on double-sided copper clad laminate M having a rolled copper foil having a thickness of 18 μm on both sides of a polyimide having a thickness of 25 μm, and a pattern is formed by UV exposure using a pattern film having a resist width of 100 μm and a circuit width of 100 μm. did. Next, copper foil was etched using the copper chloride etching solution to prepare a double-sided conductor circuit board. Next, using a polyimide film cover material in which an epoxy-based adhesive layer was formed on the polyimide film K, the double-sided conductor circuit board was sandwiched with a precision press at a pressure of 160 to 170 ° C. and a pressure of 2 to 7 MPa. The double-sided flexible circuit board (Fig. 4) was used.

(Comparative Example 4)

As a cover material, it evaluated similarly to Comparative Example 1 except having used the polyimide film cover material (3 types) of the thickness structure shown in Table 1 which provided the epoxy type adhesive layer in the polyimide film K.

(Comparative Example 5)

Dry film was laminated on double-sided copper clad laminate M having a rolled copper foil having a thickness of 18 µm on both sides of a polyimide having a thickness of 25 µm, and the circuit pattern was subjected to UV exposure using a pattern film having a resist width of 100 µm and a circuit width of 100 µm. Formed. Next, copper foil was etched using the copper chloride etching solution to prepare a double-sided conductor circuit board. Next, the single-sided copper clad laminate having a rolled copper foil having a thickness of 18 μm on one side of the liquid crystal polymer film 260 having a thickness of 25 μm was prepared. Next, the double-sided conductor circuit board was laminated via a polyimide adhesive film (bonding sheet SPB manufactured by Shin-Nitetsu Chemical Co., Ltd.) with a single-sided copper clad laminate using a liquid crystal polymer film as a resin layer. The pressure was applied to form a circuit board. After press, the outermost layer copper foil of the obtained circuit board was etched and removed, and it was set as a double-sided flexible circuit board (FIG. 5).

Table 1 shows the evaluation results. In addition, the value in () of the cover material thickness column in a comparative example shows the thickness (micrometer) of PF: polyimide film, LCPF: liquid crystal polymer film, Ad: epoxy clock, or a polyimide adhesive layer.

Cover material thickness
(Μm) Hinge bending test
Copper foil deformation value (%) Hinge bending life
(Retrieved) Example 1 25 0.8578 30 ~ Example 2 50 0.8518 30 ~ Example 3 25 0.8578 30 ~ Comparative Example 1 35
(PF: 12.5, Ad: 22.5) 0.8554 2 to 8 Comparative Example
2-1 36.8
(PF: 10.0, Ad: 26.8) 0.8550 3-15 Comparative Example
2-2 38
(PF: 12.5, Ad: 25.5) 0.8547 3 ~ 11 Comparative Example
2-3 53.6
(PF: 25.0, Ad: 28.6) 0.8510 4 ~ 11 Comparative Example 3 35
(PF: 12.5, Ad: 22.5) 0.8554 2 Comparative Example
4-1 36.8
(PF: 10.0, Ad: 26.8) 0.8550 3 Comparative Example
4-2 38
(PF: 12.5, Ad: 25.5) 0.8547 3 Comparative Example
4-3 53.6
(PF: 25.0, Ad: 28.6) 0.8510 4 Comparative Example
4-4 60
(PF: 25.0, Ad: 35.0) 0.8495 3 Comparative Example 5 40
(LCPF: 25.0, Ad: 15.0) 0.8542 5 ~ 7

1: liquid crystal polymer film cover material 2: conductor circuit layer
3: liquid crystal polymer film insulation layer 4: polyimide film insulation layer
5: Polyimide film cover material 6: Adhesive layer
7: Test piece 8: Bend
9: non-bending portion 10: circumferential rotation axis of the bending portion
11: Hinge 12: Body
13: Cover

Claims (7)

In a double-sided flexible circuit board which is formed of copper foil on both sides of the insulating layer and has a conductor circuit having a thickness of 5 to 30 µm and a cover member is directly provided, the insulating layer has a thickness of 10 to 100 µm and a heat deformation temperature of 270 to 330 ° C. It consists of a liquid crystal polymer film which is a phosphor, and a cover material is 10-100 micrometers in thickness, and consists only of the liquid crystal polymer film whose heat distortion temperature is lower than an insulating layer, and copper foil deformation value (Y) calculated by following formula (1) is 0.5 A double-sided flexible circuit board having a circumferential rotating portion, wherein the double-sided flexible circuit board has a bent portion and a non-bended portion, and the bent portion is used by being circumferentially rotated.
Y (%) = (tCu + 1 / 2tLI) / (r + tCL. + TCu + 1 / 2tLI) × 100 (1)
(TLI is the insulation layer film thickness (µm), tCL. Is the liquid crystal polymer film thickness of the cover member (µm), tCu is the copper foil thickness (µm), r is the radius of curvature of the circumferential rotation part (µm, where the radius of curvature (r ) Represents 2.0 to 5.0 mm.) delete delete delete The double-sided flexible circuit board according to claim 1, wherein the double-sided flexible circuit board is used in a folded portion of a folding cellular phone. A folding cellular phone, wherein the double-sided flexible circuit board according to claim 1 is used in a folding part of a folding cellular phone. The foldable cellular phone according to claim 6, wherein when the foldable cellular phone is in a closed state at 0 °, the angle of the open state is in a range of 10 to 180 °.

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