TWI384924B - Sided flexible circuit board - Google Patents

Description

Two-sided flexible circuit substrate

The present invention relates to a double-sided flexible circuit substrate, particularly in the mounted state, which is repeatedly slidably flexed.

The flexible circuit board is thin and bendable, and contributes to miniaturization and thinning of an electronic device, and is mounted on a mobile phone, a digital camera, a hard disk drive, and the like. In addition, in recent years, in order to be able to cope with the ease of assembly in a narrow portion, it is required to have higher flexibility than conventionally.

In particular, when a flexible circuit board is used to connect the movable portion and the fixed portion of the optical pickup, the flexible circuit substrate is repeatedly flexed by the so-called sliding buckling in which the buckling point relatively moves, and thus High buckling is required, and higher flexibility is also required in order to correspond to the low height of the optical actuator body or to increase the speed at which the optical pickup is searched, or to reduce the power consumption of the motor.

In the Japanese Patent Application No. 2005-160295 (JP-A-2006-339295), the balance between the elastic modulus and the thickness of the cover material and the substrate is defined, and the one-side folding is provided. The material which becomes the inner side at the time of bending has a thickness of 13 μm or less from the surface of the conductor wiring layer, and the average value of the longitudinal elastic modulus in the temperature range of use is a main layer having 6.4 GPa or more.

Further, in Japanese Patent No. 2753740, it is proposed to use a portion which is a flexural flexible portion of a flexible circuit board by bonding another conductor layer via a bonding agent on a single-sided non-conductive via layer, and removes the adhesive side. A method of manufacturing a flexible circuit board of a conductor layer (a mounting portion requiring heat resistance is a conductor layer on the side of a single-sided non-conductive layer layer).

Further, Japanese Patent No. 2753740 does not describe flexibility.

The cable portion for the optical pickup is only one side and is bent to the one side to be used for the flexible circuit board, or is used around the liquid crystal of a mobile phone or the like, and is only used on one side, and the bending is used. The flexible circuit board is a flexible circuit board that is not only one-sided wiring, but also a flexible circuit board that requires wiring on both sides.

Similarly, in the double-sided flexible circuit board, flexibility and buckling characteristics are required, and the base material used for producing the flexible circuit board is a case where the base material is a double-sided insulating layer having an insulating resin thickness of 13 μm or less. In the process of forming a circuit, the problem of breakage of the insulating resin layer occurs due to the pulling force between the rollers, the action of the chemical solution by the development of the image etching, the bending angle at the time of winding, and the like, and the yield of the finished product is lowered. In particular, the periphery of the portion of the bump which is accompanied by the double-sided wiring on the front and back sides is easily broken due to stress concentration.

As measures for breaking the insulating resin layer, measures for improving the production technique of the device used for forming the circuit, and structural measures for improving or thickening the insulating resin are listed.

First, as a technical countermeasure for production, there is a tension control, but it takes time to balance the spray pressure and the insulating resin characteristics when forming a circuit, and it is necessary to make a re-adjustment when it is made into a thin film. It is difficult to implement in reality.

Hereinafter, there are problems with the construction measures. First, there is an improvement in the insulating resin, and although it has the characteristics of a flexible circuit board, it is not easy to increase the end crack resistance (or the shredding propagation resistance). Moreover, in order to increase the end-cracking resistance (or to shred the propagation resistance, and to improve the yield of the breakage when forming the circuit, it is most easy to thicken the insulating resin, but if the resin is added, the market cannot be ensured. Softness.

On the other hand, Japanese Patent No. 2753740 discloses a two-sided volume guide sheet formed by adhering a conductor layer to a single-sided non-adhesive volume layer via an adhesive. Using this method, the end crack resistance (or breaking propagation resistance) generated by the thick film of the resin can be increased.

However, since the symmetrical structure with the lid member exhibits buckling property, the buckling portion that requires flexibility is a structure that uses a conductor on the adhesive side. In this configuration, even if a thin single-sided non-adjacent volumetric laminate is used, the flexibility is not sufficient.

The present invention has been made in view of the above circumstances, and an object of the invention is to provide a flexible circuit board in which an engineered resin breakage measure is applied without impairing flexibility.

In order to achieve the above object, the present invention provides a double-sided flexible circuit board, which belongs to the other side of a single-sided non-conductive layered sheet formed on one side of a conductor layer formed on a substrate, and has other conductors adhered via an adhesive layer. The layer has a bent portion between the end portions in the longitudinal direction, and the bent portion is the adhesive layer in which the other conductor layer is removed to expose the other surface of the bent portion, and has only one side In the conductor layer of the single-sided non-conductive layer layer, the longitudinal elastic modulus of the adhesive layer is lower than the longitudinal elastic modulus of the substrate.

The conductor layer using the one-sided adhesive copper laminate according to the present invention constitutes a bent portion of the double-sided flexible circuit substrate formed by adhering the conductor layer on the single-sided non-conductive via layer, and has a double-sided flexible circuit substrate Since the adhesive of the predetermined longitudinal elastic modulus is exposed to the other surface, it is possible to provide a flexible circuit board to which an engineering resin is broken without impairing flexibility.

In the present invention, it is used to form a two-sided conductive layer of a conductor layer on a substrate side of a single-sided non-advanced volume layer via a laminated conductor layer, but the flexibility and buckling of the flexible circuit substrate using the two-sided volumetric laminate are required. The portion is wired only to the non-adhesive surface, and the side of the layer is removed by etching or the like, and the wiring is applied to the single-sided non-conductive volume layer. Moreover, the adhesive layer which adheres to the board|substrate side of the base material side of the single-sided non-conducting volume-s The longitudinal elastic modulus of the adhesive layer is made softer than the insulating resin layer having no single-sided adhesive layer.

Further, the longitudinal elastic modulus of the adhesive layer is preferably half or less of the longitudinal elastic modulus of the substrate.

Here, the non-adjacent-volume-volume laminate refers to a case of a non-conducting volume-conducting layer formed by a casting method, a laminated plate method, and a metallization method, and is used as a flexible circuit substrate material using a copper foil, for example, a casting. The legal person is sold by Japan Nippon Steel Chemical Co., Ltd. under the trade name ESPANEX, and the laminate method is owned by Mitsui Chemicals Co., Ltd., which is sold by Niefufux, and Japan Ube Industries Co., Ltd. Sold by "You Bishe N".

The three-layer non-adhesive copper laminates of the three companies are provided with a thermoplastic polyimine as a bonding layer between the polyimide resin and the copper foil, but are referred to as a copper-free laminate or a two-layer laminate. Included in the single-sided, non-adjacent volumetric laminate of the present invention.

In addition, as a non-adhesive copper laminate which does not use thermoplastic polyimide, there is a casting method manufactured by Nippon Seisakusho Co., Ltd., which is manufactured by AZOTEK Co., Ltd., and is a metal formed by sputtering and electroplating. The spray coating method includes S'PERFLEX manufactured by Sumitomo Metal Mining Co., Ltd., and "Metta Loyallu" made by the company's Toray Film Processing Co., Ltd., which is called a non-adhesive copper laminate. Or 2 layers can be utilized in the present invention.

In the present invention, a two-sided volume guide layer of a laminated layer conductor layer for a resin cracking countermeasure is used on the substrate side of the single-sided non-advanced volume laminate, and the flexible circuit substrate using the two-sided volumetric laminate is used. The portion requiring flexibility and buckling is a structure in which only one side is wired and the other side is removed by etching or the like.

Further, when buckling property is required, the longitudinal elastic modulus and thickness of the insulating resin sandwiching the conductor layer may be considered. That is, a first flexible insulating resin layer composed of a cover material and a layer attached thereto is provided on one side of the covering conductor layer, and the other surface of the conductive layer is covered by the substrate and A second flexible insulating resin layer composed of the above adhesive. Moreover, the sum of the average value of the longitudinal elastic modulus (the thickness of the first flexible insulating resin layer at the time of use) of each layer constituting the first flexible insulating resin layer is taken as A, and the second flexibility is formed. When the sum of the layers of the insulating resin layer (the average value of the longitudinal elastic modulus of the temperature at the time of use × the thickness of the second flexible insulating resin layer) is B, when the first flexible insulating resin layer is located inside the conductor, it is A. /B=0.66~2.06, when the second flexible insulating resin layer is located inside the conductor, it is B/A=0.66~2.06.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(Example)

Fig. 1 is a side sectional view showing a flexible circuit board for sliding buckling according to the present invention. The flexible circuit board is attached to a sliding flexure of a practical device, and a conductor layer is adhered via the adhesive layer 4 on the side of the substrate 3 on the side opposite to the conductor layer 1 on the side of the conductor layer 1 having no single-conductor layer. In the two-sided lead-volume laminate, the two-sided copper-clad laminate is removed from the conductor layer 2 by etching or the like in the wiring pattern, and the cover film and the cover adhesive are not laminated at the portion.

The flexible circuit board is a user who relatively linearly moves one end to the other end and slides and flexes the flexible circuit board, that is, a buckling mode in which the buckling point is moved at the same degree of buckling. Further, in the flexible circuit board, it is necessary to first confirm whether or not the insulating resin layer is broken during the production, and it is necessary to evaluate whether or not it has appropriate flexibility and flexibility at the time of mounting. That is, three items of fracture, softness, and buckling must be tested.

2(a) and 2(b) are front and side views showing a sample of a fracture test method used for the insulating resin layer. As shown in the second (a) and (b), as the sample, the flexible substrate 3 having the same shape and the same shape and formed at positions corresponding to the patterns 1 and 2 was prepared.

In the example shown in Fig. 2, a sample of a copper foil was formed on both front and back sides of a rectangular flexible substrate 3 having a width of 20 mm to constitute a sample 10. The patterns 1 and 2 are vertically long rectangles having a width of 10 mm, and the upper end of the figure is formed into a triangular shape at a vertex of 90 degrees.

3(a) and (b) are diagrams showing a test method for resin breakage, and the sample 10 shown in Fig. 2 is a triangle apex of a pattern around a rod having a diameter of 10 mm as shown in Fig. 3(a). It is wound up vertically as it is upward. Further, as shown in Fig. 3(b), when the upper end of the flexible substrate 3 is pulled downward, the flexible substrate 3 is tested by applying stress at the apex of the triangle of the pattern 1, 2 of the sample 10. Whether it breaks.

Figure 4 is another test method showing the breakage of the resin. In this evaluation, in the sample 10 shown in Fig. 4(a), as shown in Fig. 4(b), the pressing force was applied to the end of the rod having a diameter of 10 mm to measure the magnitude of the force generated by the fracture.

Fig. 5 is a view showing the evaluation of the flexibility of the flexible circuit board. This is a measure of the springback force when the sample 10 is bent into a predetermined state by the electronic scale 20. The bend radius is taken as 3.75 mm.

Further, the buckling test is not illustrated, but the test is performed by a general buckling test method, that is, a method of measuring the number of times by repeating the predetermined buckling.

Hereinafter, each of these evaluation methods will be described.

Confirmation of effect

In order to confirm the present invention, the following description of the fracture of the insulating resin of the flexible circuit board was carried out, 2. Evaluation of flexibility, and evaluation of buckling property.

1. Evaluation of resin fracture of flexible circuit board (see Fig. 2, Fig. 3)

1) Evaluation method A pattern having a width of 10 mm and a front end angle of 90° was formed on the flexible circuit board at a corresponding position on both sides, and a portion having a distance of 5 mm from the left and right sides of the pattern was cut out to obtain a sample. Thereafter, the sample was wound on a rod having a diameter of 10 mm, and each pattern was peeled off at an angle of 90° on the front end side of the iminoimine (substrate) at the upper end of the figure, and in the opposite direction to the 180° direction (illustration Bottom) pull hard. From this, the pattern was used as the starting point to confirm whether the quinone imine was broken.

2. Evaluation of softness (refer to Figure 4)

1) The structural sample of the evaluation sample is a one-side surface of the double-sided volume-conducting layer, with a conductor width = 0.1 mm, a conductor spacing = 0.1 mm straight wiring, and the other side is in addition to the conductor layer (full etching) The substrate was bonded to a 13 μm-made lid material made of Duka Company's “Calcium 50H” (elasticity: 3.0 GPa) and an epoxy-based adhesive having an elastic modulus of 2.3 GPa, and was produced in the wiring direction (longitudinal direction). A flexible circuit board having a length of 50 mm and a length in the width direction of 10 mm. Further, the thickness of the conductor was 18 μm, and the thickness of the capping agent on the conductor was 6 μm.

2) Evaluation Method As shown in Fig. 5, the flexible circuit board was bent, and the springback force of the flexible circuit board was measured using an electronic balance. The bending radius of the flexible circuit board at this time was evaluated by setting it at 3.75 mm.

3. Flexibility evaluation

As a sliding buckling test, an IPC buckling test was performed.

1) Test condition Buckling radius = 1.35 mm Bucking rate = 1,000 rpm Stroke = 30 mm Test environment = 80 °C disconnection detection = resistance value 50% rise

2) The structural sample of the test sample is on one side of the two-sided volumetric laminate, with a conductor width = 0.1 mm, a conductor spacing = 0.1 mm straight wiring, and the other side without a conductor layer (full etching) The substrate is adhered to a 13 μm DuPont company's "card ordinary 50H" [elasticity 3.0 GPa (at 80 ° C: 2.7 GPa)] and an elastic modulus of 2.3 GPa (80 ° C: 2.0 GPa) epoxy-based adhesive. The number of wirings produced by the manufacturer of the cover material was 10 pieces. Further, the thickness of the conductor was 18 μm, and the thickness of the capping agent on the conductor was 6 μm.

4. Evaluation materials

The samples used for the effect confirmation were as follows in the following Example 3 and Comparative Example 3.

Elasticity Measurement The elastic modulus of the above table was measured in accordance with the following conditions.

Test method: Refer to the IPC-TM-650 2.4.19 method for testing. Sample size: 10mm × 150mm Distance between chucks: 100mm crosshead speed: 50mm/min Elasticity: Calculate the measurement environment in the field of elasticity where the deformation is less than 1.5%: room temperature

However, the measurement of the adhesive was carried out by measuring the sample coated with the adhesive on both sides of "Abidika 12.5 NPI" manufactured by Konica Corporation according to the test method.

E ₁ =EV/V ₁ -E ₂ V ₂ /V ₁ where E: the elastic modulus of the composite material (film coated with the adhesive) V: the thickness E _{1 of the} composite material (film coated with the adhesive): The elastic modulus of the subsequent agent E ₂ : the elastic modulus of the Abidika NPI V ₁ : the thickness of the adhesive V ₂ : the thickness of the Abidika NPI

5. Evaluation results

The resins of the above Examples 1 to 3 and Comparative Examples 3 were broken, and the evaluation results of the flexibility and the buckling test were as follows.

The total thickness of the substrate in the above table refers to the sum of the thicknesses of the insulating resin layer having no single-sided guide layer and the adhesive applied to the substrate side.

Reference: Example 1 was that an adhesive was applied at a thickness of 5 μm, but a sample coated with a thinner thickness of 2 μm did not cause breakage of the insulating resin. In the above table, when Comparative Example 1 was compared with Example 1, the flexibility (rebound force) and the buckling property were the same (Example 1 was increased by about 10% compared with Comparative Example 1), and only the resin fracture evaluation was The difference was observed, that is, the comparative example was broken, but Example 1 was not broken. Therefore, Example 1 is better than Comparative Example 1.

Comparing Example 2 with Example 3 and Comparative Example 3, the total thickness of the same substrate was the same, and no resin cracking occurred in the resin crack evaluation. However, in the three cases, the flexibility was the minimum rebound force of Example 2. , that is, soft.

On the one hand, it was confirmed from this evaluation that Comparative Example 3 was the hardest. In other words, in view of the difficulty in breaking the film, the thickening of the substrate is considered. However, when the flexibility is considered, it is known that the layer of the adhesive which is softened by applying the insulating resin such as the single-sided non-conductive layered sheet of the present invention is increased. The thickness of the insulating resin layer without the via layer is also effective.

Here, in Comparative Example 3, the modulus of elasticity of the insulating resin without the via-volume laminate was 4.8 GPa, and Example 2 was an adhesive for coating the elastic modulus of 1.2 GPa on the insulating resin layer of the non-conductive layer laminate having an elastic modulus of 4.8 GPa. On the other hand, in Example 3, an adhesive having an elastic modulus of 2.3 GPa was applied to the insulating resin layer of the 4.8 GPa non-conductive volume layer.

That is, both of Examples 2 and 3 were coated with an adhesive having an elastic modulus of at least half of the modulus of elasticity of the applied insulating resin without the via-lead laminate. Further, in comparison between Examples 2 and 3, the second embodiment was softer, and both of Examples 2 and 3 were 12 μm, and only the elastic modulus was different. That is, the applied adhesive is softer and has less adverse effect on softness.

Comparing Example 1 with Comparative Example 2, both of them were coated with a 5 μm adhesive having an elastic modulus of 1.2 GPa in a two-layer material having an elastic modulus of 4.8 GPa, but the flexibility and the conductor forming surface during the buckling test were carried out. Example 1 is the side without the via layer, and Comparative Example 2 is the adhesive side (the conductor on the back side is completely etched). The structure was different from that of the softness, and Example 1 was softer and more favorable than Comparative Example 2, and Example 1 was superior to Comparative Example 2 in terms of buckling property.

From the above results, there is an effect that the resin is easily broken and the thickness of the insulating resin layer is increased. Regarding the coating thickness of the adhesive, the physical properties (end crack resistance or fracture propagation resistance) and the hardness of the copper foil (the strength of the waist) can be easily changed depending on the thickness of the insulation of the adhesive layer. Therefore, it must be adjusted to an appropriate thickness. The evaluation of the fracture of the insulating resin was carried out by using the coating thickness adjustment as an index, and if it was confirmed that it was not broken, it can be said that the yield of the resin-based breakage in the work was suppressed.

As described above, it is understood that the resin broken portion is mainly a portion in which the conductor wiring forms a front and back, and is particularly broken by a change in the engineering flow (the striking force of the liquid during patterning, the bending angle at the time of winding, etc.) In this evaluation, in the case of the front-back consistent pattern, the ease of fracture at the time of occurrence of the bending is evaluated. Therefore, if the test is not broken, there is no sudden abnormality in the engineering flow. fracture.

Regarding the softness, when applying an adhesive which is softer than the insulating resin without the adhesive layer, the layer of the adhesive is disposed on the outermost layer of the flexible circuit substrate at the time of buckling, and the laminated layer is not provided. The insulating resin layer (for resin cracking measures) is formed into a thick film, and the adverse effect on flexibility can be reduced.

At this time, the elastic modulus of the adhesive was measured by the above test, and it was confirmed that the elastic modulus of the substrate was half thicker than that of the insulating resin having no adhesive layer. Further, when the adhesive agent is not on the outermost layer of the flexible circuit board (as in the case of Comparative Example 2), the rebound force is increased in some cases.

Confirmation of the limit of resin breakage (refer to Figure 4)

The following test was carried out for the purpose of confirming the limit of resin breakage. As shown in Fig. 4, a two-sided copper plate having a width of 15 mm was used to produce a pattern with a front and back of 10 mm in diameter (PI portion 1 mm wide), and the sample was set in a tensile tester (manufactured by Shimadzu Corporation, Shimadzu Automatic Chart AGS- 50P), pulling (applying tensile force) like a pressure of 0.1 MPa applied to the sample.

Thereafter, the load was applied to the front and back pattern portion of the direct 10 mm by a rod having a diameter of 10 mm, and the value at which the fracture occurred was recorded. The phase difference of the initial value (the intensity multiplied by the tensile force) from the intensity at which the fracture occurred was divided by the area of the rod, and the pressure at which the fracture occurred was determined.

The results of the following table were obtained by this test.

In the first embodiment, the pressure at which the fracture occurred was 0.55 MPa, and it was found that the fracture difficulty of the comparative example 1 of 0.25 MPa was twice or more, and it was found that even the thickness was thicker than the comparative example 3 in which the fracture generation pressure was 0.52 MPa. good.

Japanese Patent No. 2753740 discloses that the conductor layer is on the adhesive side and has a symmetrical structure in the thickness direction, so that the buckling property is good, but the Japanese Patent Application No. 2005-160260 (Japanese Patent) In the case where the ratio of the elastic modulus and the thickness of the substrate and the lid member is within a predetermined range, it is preferable to use a wiring without an adhesive.

In the Japanese Patent No. 2753740, the shape is formed into a symmetrical structure in the thickness direction, so that the shape of the polyimide cover is formed by a conductor, and the application is made in Japanese Patent Application No. 2005-160260. In the document (Japanese Laid-Open Patent Publication No. 2006-339295), a symmetrical structure is formed by a force ratio of an elastic modulus and a thickness.

The predetermined range here means "the conductor wiring layer having the first and second faces, and the first flexible insulating resin layer on the first surface of the conductor wiring layer and the second surface on the second surface. The second flexible insulating resin layer includes a flexible circuit board having a bent portion in which the first flexible insulating resin layer is bent inside, and the first flexible insulating portion of the bent portion is insulated The average value of the longitudinal elastic modulus of the resin layer (the thickness of the first flexible insulating resin layer at the time of use) is A, and the temperature of the second flexible insulating resin layer of the above-mentioned bent portion is used. The average value of the longitudinal elastic modulus × the thickness of the second flexible insulating resin layer) is B/A = B = 0.66 to 2.06. Here, the average value of the longitudinal elastic modulus means (the elastic modulus of each layer × thickness) / total thickness) of the sum.

That is, the first embodiment is the first flexible insulating resin layer in the inner layer of the cap layer (the average value of the longitudinal elastic modulus of the temperature at the time of use × the thickness of the first flexible insulating resin layer), that is, A The value is "card ordinary 50H" manufactured by DuPont Co., Ltd. having a cover layer PI of 13 μm (elasticity at 80 ° C: 2.7 GPa), adhesive at 80 ° C, elastic modulus: 2.0 GPa epoxy-based adhesive, on the conductor The thickness was 6 μm, and the calculation "elasticity: 2.7 (GPa) × thickness: 13 (μm) / total thickness: 13 + 6 = 19 (μm)" and "elasticity: 2.0 (GPa) × thickness: 6 (μm) / total 47.1 (GPa. μm) of the product of 2.47 (GPa) and thickness 18 (μm) of the sum of thickness: 13 + 6 = 19 (μm)".

Moreover, the average value of the longitudinal elastic modulus of the second flexible insulating resin layer (the thickness of the first flexible insulating resin layer at the time of use), that is, the B value, is the Nippon Steel Chemical Co., Ltd. having a substrate of 13 μm. The elastic modulus of SC18-12-00FR80°C manufactured by the company was 3.9GPa), and the elastic modulus of the adhesive was 80°C: 0.5GPa epoxy adhesive was applied to 5μm, and the “elasticity: 3.9 (GPa) was calculated. × thickness: 13 (μm) / total thickness: 13 + 5 = 18 (μm)" and "elasticity: 0.5 (GPa) × thickness: 5 (μm) / total thickness: 13 + 5 = 18 (μm)", the sum of 2.96 ( 53.2 (GPa. μm) of the product of GPa) and thickness 18 (μm) becomes A/B = 0.88, and enters the above-specified range.

When the cover material is used as the outer side, it is also A/B=1.13, and this also enters the above-specified range. If it is within the predetermined range, the material in contact with the conductor is advantageous in that it has a function of suppressing the progress of the crack generated by the buckling fatigue of the copper foil.

In particular, as shown in the Japanese Patent Application Laid-Open No. Hei. No. 2006-339295, the elastic modulus is 6.4 GPa or more, and the buckling property is advantageous. When the substrate or the cover material is thin, when it is actually mounted in a casing such as an optical pickup, the actual flexural radius is larger than that of the thick flexible circuit substrate, which is advantageous.

As described above, in the present invention, it is possible to provide a substrate having a thick film and a flexibility as a countermeasure against breakage of a resin in a flexible film substrate which is required to have a film. Further, in the case where the buckling property is required, the desired product can be obtained by using the product of the elastic modulus of the cover material or the substrate and the thickness.

1. . . Conductor layer

2. . . a conductor layer adhered to the adhesive layer

3. . . Substrate layer

4. . . Subsequent layer

5. . . Cover with adhesive layer

6. . . Cover film

10. . . sample

20. . . Electronic scale

30. . . Baton

Fig. 1 is a side sectional view showing a flexible circuit board for sliding buckling according to the present invention.

2(a) and 2(b) are explanatory views showing evaluation samples of the fracture of the insulating resin.

3(a) and 3(b) are explanatory views showing a method of evaluating the fracture of the insulating resin.

4(a) and 4(b) are explanatory views showing the method of confirming and evaluating the limit of the breakage of the insulating resin.

Fig. 5 is an explanatory view showing a method of measuring the biasing force of the softness evaluation.

1. . . Conductor layer

2. . . a conductor layer adhered to the adhesive layer

3. . . Substrate layer

4. . . Subsequent layer

5. . . Cover with adhesive layer

6. . . Cover film

Claims (5)

A double-sided flexible circuit board, which belongs to the other surface of a single-sided non-advanced volume layer formed on one side of a conductor layer formed on a substrate, and is formed by bonding another conductor layer via an adhesive layer, and at the end in the longitudinal direction The bent portion is characterized in that the bent portion is the above-described adhesive layer from which the other conductor layer is removed and the other surface of the bent portion is exposed, and the conductor having the single-sided non-conductive lead laminate is provided on only one side In the layer, the longitudinal elastic modulus of the adhesive layer is lower than the longitudinal elastic modulus of the substrate. The double-sided flexible circuit board according to the first aspect of the invention, wherein the longitudinal elastic modulus of the adhesive is an elastic modulus of at least half of a longitudinal elastic modulus of the base material. The double-sided flexible circuit board according to the first aspect of the invention, comprising: a lid member and a layer attached thereto, wherein the conductor layer covering the bent portion is provided on one side of the conductor layer a first flexible insulating resin layer, and the second flexible insulating resin layer provided on the other surface of the conductor layer of the bent portion, comprising the substrate and the adhesive; The sum of the average value of the longitudinal elastic modulus (the thickness of the first flexible insulating resin layer at the time of use) of each layer of the flexible insulating resin layer is A, and the layers constituting the second flexible insulating resin layer are formed. When the sum of (the average value of the longitudinal elastic modulus of the temperature at the time of use and the thickness of the second flexible insulating resin layer) is B, when the first flexible insulating resin layer is located inside the conductor, it is A/B = 0.66~ 2.06, and when the second flexible insulating resin layer is located inside the conductor, it is B/A=0.66 to 2.06. The double-sided flexible circuit board according to claim 1, wherein the bent portion is slidably flexed when used after being assembled in an electronic device. The double-sided flexible circuit board according to claim 1, wherein the adhesive layer exposed in the bent portion faces the inner side surface side.