CN204721707U - Flexible printed circuit board - Google Patents

Abstract

An object of the present invention is to provide a flexible printed circuit board that is easy to adjust impedance and exhibits a high shielding effect. The flexible printed circuit board according to one embodiment of the present invention includes a conductive pattern, a first shielding layer provided on one side of the conductive pattern, a second shielding layer provided on the other side of the conductive pattern, and a flexible printed circuit board with a dielectric layer disposed between the first shielding layer and the second shielding layer so as to surround the conductive pattern, wherein the conductive pattern has one or more signal wiring and is disposed on the In the pair of shielded wirings on both sides of the signal wiring, the average interval between the signal wiring and the shielded wiring is equal to or greater than the average width of the signal wiring.

Description

Flexible Printed Circuit Board

technical field

The utility model relates to a flexible printed circuit board.

Background technique

Flexible printed circuit boards are used as printed circuit boards that transmit high-frequency signals, digital signals, and the like. As such a flexible printed circuit board, a flexible printed circuit board having a shielding function such as a stripline structure or a microstrip structure can be used for noise prevention, crosstalk prevention, and the like. The stripline structure and the microstrip structure are structures in which signal wiring is provided on one surface of a dielectric layer, and a shield layer (ground layer) is laminated on the other surface of the dielectric layer.

However, when the dielectric layer is thinned in order to reduce the thickness of the flexible printed wiring board with a shielding function, the parasitic capacitance between the signal wiring and the shielding layer affects the impedance of the flexible printed wiring board. Therefore, in order to obtain impedance conformity with other circuits, it is necessary to adjust the parasitic capacitance between the signal wiring and the shield layer to a constant value. However, when the width of the signal wiring is narrowed in order to keep the parasitic capacitance constant, there is a problem that the transmission loss in the signal wiring increases.

Therefore, it has been proposed to adjust the opposing area of the signal wiring and the shield layer by providing openings in the shield layer, thereby adjusting the parasitic capacitance (refer to Japanese Patent Application Laid-Open No. 2000-77802).

Prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2000-77802

Utility model content

Problems to be solved by utility models

However, in the flexible printed wiring board as described above, there is no shield on the side of the signal wiring to exert a shielding effect. Therefore, in the flexible printed circuit board described above, when an opening is provided in the shield layer to reduce the parasitic capacitance between the signal wiring and the shield layer to a desired value, the shielding effect may become insufficient. In addition, when the thickness of the dielectric layer is increased to reduce the parasitic capacitance between the signal wiring and the shielding layer, the flexibility of the flexible printed circuit board may become insufficient, or the shielding layer viewed from the signal wiring may The angle of the gap (the elevation angle of the outer edge of the shielding layer) becomes large, and the overall shielding effect may become insufficient.

This invention was made|formed in view of the said situation, and the object is to provide the flexible printed wiring board which performs impedance adjustment easily, and exhibits a high shielding effect.

Technical solutions for solving problems

In order to solve the above problems, the flexible printed circuit board according to one embodiment of the present invention includes a conductive pattern, a first shielding layer provided on one side of the conductive pattern, and a first shielding layer provided on the other side of the conductive pattern. A flexible printed circuit board with a second shielding layer on the top, a dielectric layer disposed between the first shielding layer and the second shielding layer to surround the above-mentioned conductive pattern, wherein the above-mentioned conductive pattern has one or more signal A wiring and a pair of shielding wiring provided on both sides of the signal wiring, wherein an average interval between the signal wiring and the shielding wiring is equal to or greater than an average width of the signal wiring.

The effect of utility model

The flexible printed circuit board according to one embodiment of the present invention facilitates adjustment of impedance and exhibits a high shielding effect.

Description of drawings

[ Fig. 1] Fig. 1 is a schematic cross-sectional view showing a flexible printed circuit board according to one embodiment of the present invention.

[ Fig. 2] Fig. 2 is a schematic plan view of the flexible printed circuit board of Fig. 1 .

Symbol Description

1 conductive pattern

2 1st shielding layer

3 2nd shielding layer

4 dielectric layer

5 1st resin film

6 Second resin film

7 adhesive layer

8 1st laminate

9 2nd laminate

10 Signal Wiring

11 Shielded wiring

12 through holes

13 opening

D1 Average spacing between signal wiring and shielding wiring

D2 The shortest distance between the outer edge of the first shielding layer and the outer edge of the signal wiring

W1 Average Width of Signal Wiring

W2 Average width of shielded wiring

Detailed ways

[description of embodiment of the present invention]

The flexible printed circuit board according to one embodiment of the present invention includes a conductive pattern, a first shielding layer provided on one side of the conductive pattern, a second shielding layer provided on the other side of the conductive pattern, and A flexible printed circuit board in which a dielectric layer is provided between the first shielding layer and the second shielding layer so as to surround the conductive pattern, the conductive pattern has one or more signal wiring and a signal wiring provided on the signal wiring. For the pair of shielded wires on both sides, the average interval between the signal wires and the shielded wires is equal to or greater than the average width of the signal wires.

This flexible printed circuit board has shielding layers on both sides of the above-mentioned conductive pattern, and at the same time, the conductive pattern has shielded wiring on both sides in the width direction of the signal wiring. Therefore, in a cross section perpendicular to the extending direction of the signal wiring, There are electromagnetic shields around the signal wiring, which has a high shielding function. In addition, the average interval between the signal wiring and the shielding wiring in the flexible printed circuit board is equal to or greater than the average width of the above-mentioned signal wiring, thereby, the parasitic capacitance between the signal wiring and the shielding wiring is relatively small, therefore, by adjusting The parasitic capacitance between the signal wiring and the shield layer makes it easier to adjust the impedance.

The first shield layer and the second shield layer may overlap with a pair of shield wires when viewed from the above-mentioned side in a cross-section with a cut surface in a direction perpendicular to the longitudinal direction of the signal wires. In this way, when the cross-section of the cut surface is viewed from the side in the direction perpendicular to the longitudinal direction of the signal wiring, since the first shielding layer and the second shielding layer overlap with the pair of shielding wiring, it is difficult for electromagnetic waves to pass through the shielding layers. And between each shielded wiring, therefore, the shielding effect is further improved.

When the cross-section of the cutting surface is viewed from the above-mentioned side in the direction perpendicular to the longitudinal direction of the signal wiring, the shortest distance between the outer edges of the first shielding layer and the second shielding layer and the outer edge of the signal wiring is preferably the above-mentioned 2 times or more the average width of the signal wiring. In this way, when the cross-section of the cutting surface is viewed from the above-mentioned side in the direction perpendicular to the longitudinal direction of the signal wiring, the shortest distance between the outer edges of the first shielding layer and the second shielding layer and the outer edge of the signal wiring is the above-mentioned At least twice the average width of the signal wiring, the elevation angle of the outer edge of the first shielding layer and the outer edge of the second shielding layer when viewed from the signal wiring becomes smaller, and the shielding effect is further improved.

The first shielding layer may have one or a plurality of openings in a region overlapping with the signal wiring when viewed in plan. In this way, since the first shielding layer has one or more openings in the region overlapping the signal wiring in plan view, it is possible to reduce the parasitic capacitance between the first shielding layer and the signal wiring, and to adjust impedance.

As an overlapping area ratio of the signal wiring and the first shielding layer in planar view, it is preferably 10% or more and 90% or less. Since the overlapping area ratio of the signal wiring and the first shielding layer in a planar view is within the above range, variations in impedance due to manufacturing errors in the overlapping area of the signal wiring and the first shielding layer are suppressed, thereby Impedance can be adjusted more accurately.

The dielectric layer may have a first resin film laminated between the conductive pattern and the first shielding layer, a second resin film laminated on one side of the second shielding layer, and a layer containing the first resin film and the conductive layer filled with the first resin film. An adhesive layer between the patterned laminate and the second resin film. In this way, since the dielectric layer has the adhesive layer filled between the laminate including the first resin film and the conductive pattern and the second resin film, the formation of the dielectric layer surrounding the conductive pattern becomes easier. easy.

[the details of the embodiment of the present invention]

Hereinafter, embodiments of the flexible printed circuit board according to the present invention will be described in detail with reference to the drawings.

[Flexible printed circuit board]

The flexible printed circuit board of FIG. 1 is formed in the shape of a belt in planar view, and is used as a flexible cable for high-speed transmission used for transmitting high-frequency signals in the vertical direction. FIG. 1 shows a cross section cut in a direction perpendicular to the longitudinal direction of the flexible printed circuit board.

This flexible printed circuit board comprises: a conductive pattern 1, a first shielding layer 2 provided on one side (upper side in FIG. The second shielding layer 3 on the top, and the dielectric layer 4 provided between the first shielding layer 2 and the second shielding layer 3 so as to surround the conductive pattern 1 . It should be noted that the first shielding layer 2 and the second shielding layer 3 are connected to the ground potential when the flexible printed circuit board is used.

The dielectric layer 4 includes: a first resin film 5 laminated between the conductive pattern 1 and the first shielding layer 2; a second resin film 6 laminated on the other surface of the second shielding layer 3; Adhesive layer 7 between resin film 5 and second resin film 6 .

In addition, this flexible printed circuit board can be formed by bonding the first laminated body 8 formed as a double-sided substrate having the conductive pattern 1, the first resin film 5, and the first shielding layer 2 with an adhesive that forms the adhesive layer 7. And the second laminated body 9 formed as a single-sided substrate having the second shield layer 3 and the second resin film 6 is manufactured.

＜Conductive pattern＞ 

The conductive pattern 1 has: a signal wiring 10 provided along the longitudinal direction of the flexible printed circuit board and serving as a circuit for transmitting a high-frequency signal; 11. Each shielding wire 11 is electrically connected to the first shielding layer 2 and the second shielding layer 3 through a plurality of through holes 12 . Therefore, each shielded wiring 11 is connected to the ground potential via the first shielding layer 2 or the second shielding layer 3 when the flexible printed circuit board is used. In addition, "substantially parallel" means that the angle formed by both is 10 degrees or less.

The conductive pattern 1 is formed by patterning a layered conductor. As the conductor forming the conductive pattern 1 , as long as it has conductivity, metals such as copper, nickel, aluminum, silver, and gold are preferably used, and copper, which is inexpensive and has excellent conductivity, is preferably used.

The patterning method of the conductive pattern 1 is not particularly limited. As an example, the metal layer laminated on the first resin film 5 is selectively removed by etching to form a conductive pattern having a desired planar shape. 1 method.

The method of laminating the metal layer on the first resin film 5 is not particularly limited, and for example, a bonding method in which a metal foil is bonded with an adhesive, or a resin that is a material of the first resin film 5 is coated on the metal foil may be used. The casting method of the composition, the sputtering/plating method of forming a metal layer by plating on a thin conductive layer (seed layer) with a thickness of several nm formed on the first resin film 5 by sputtering or vapor deposition, A lamination method in which a metal foil is attached by hot pressing, a printing method in which a conductive ink is applied on the first resin film 5, or the like.

The average thickness of the conductive pattern 1 is not particularly limited, but the lower limit of the average thickness of the conductive pattern 1 is preferably 1 μm, more preferably 5 μm. On the other hand, the upper limit of the average thickness of the conductive pattern 1 is preferably 100 μm, more preferably 50 μm, and still more preferably 25 μm. When the average thickness of the conductive pattern 1 is less than the said lower limit, the transmission loss (Joule loss) in the signal wiring 10 may become too large. On the contrary, when the average thickness of the conductive pattern 1 exceeds the above-mentioned upper limit, the flexibility of the flexible printed circuit board may become insufficient, or the parasitic capacitance between the signal wiring 10 and the shield wiring 11 may become large, and it may be difficult to Get the integrity of the impedance.

The above-mentioned signal wiring 10 is provided along the longitudinal direction at the center of the width direction of the first resin film 5 . The signal wiring 10 is configured to be connectable to an external circuit near the end of the flexible printed circuit board. As the connection structure of the signal wiring 10 to the external circuit, for example, a configuration that can connect to an external circuit through a part exposed without covering on the second laminated body 9, or a connection to the parting surface (land) by a via ( It is formed separately from other parts of the second shielding layer 3) so that it can be connected to an external circuit via this parting surface.

The average width W1 of the signal wiring 10 is not particularly limited, but the lower limit of the average width W1 is preferably 25 μm, more preferably 60 μm, and even more preferably 70 μm. On the other hand, the upper limit of the average width W1 is preferably 500 μm, more preferably 240 μm, and still more preferably 230 μm. When the said average width W1 is less than the said lower limit, the transmission loss (copper loss) in the signal wiring 10 may become too large. Conversely, when the average width W1 exceeds the upper limit, the parasitic capacitance between the signal wiring 10 and the first shielding layer 2 and the second shielding layer 3 becomes too large, and impedance conformity may not be obtained. In addition, the variation in the width of the signal wiring 10 is preferably within ±20% of the above average width W1.

The above-mentioned shielding wiring 11 realizes a shielding function of electromagnetically shielding both sides in the width direction of the signal wiring 10 .

The lower limit of the average width W2 of the shield wiring 11 is preferably 100 μm, more preferably 200 μm. On the other hand, the upper limit of the average width W2 of the shield wiring 11 is preferably 500 μm, more preferably 400 μm. When the average width W2 of the shielded wiring 11 is smaller than the above-mentioned lower limit, the conductivity of the shielded wiring 11 itself may not be sufficiently obtained, and the shielding effect by the shielded wiring 11 may not be sufficiently obtained. On the contrary, when the average width W2 of the shield wiring 11 exceeds the said upper limit, this flexible printed wiring board 1 may become unnecessarily large in the width direction.

Preferably, the thicknesses of the signal wiring 10 and the shielding wiring 11 are substantially constant. In addition, "substantially constant" means that the error is within 40% with respect to the above-mentioned average thickness.

The lower limit of the average interval D1 in the width direction between the signal wiring 10 and the shield wiring 11 is preferably 1 time, more preferably 1.5 times, and even more preferably 2 times the average width of the signal wiring 10 . On the other hand, the upper limit of the average interval D1 is preferably 5 times, more preferably 4 times, and even more preferably 3 times the average width of the signal wiring 10 . When the above average interval D1 is smaller than the above lower limit, the parasitic capacitance between the signal wiring 10 and the shield wiring 11 becomes large, and it may be difficult to obtain impedance conformity. Conversely, when the above-mentioned average interval D1 exceeds the above-mentioned upper limit, the flexible printed wiring board 1 may become unnecessarily large in the width direction.

The lower limit of the specific value of the average interval D1 in the width direction between the signal wiring 10 and the shield wiring 11 is preferably 50 μm, more preferably 100 μm, and still more preferably 200 μm. On the other hand, the upper limit of the specific value of the average interval D1 is preferably 1000 μm, more preferably 500 μm, and still more preferably 400 μm. When the above average interval D1 is smaller than the above lower limit, the parasitic capacitance between the signal wiring 10 and the shield wiring 11 becomes large, and it may be difficult to obtain impedance conformity. Conversely, when the above-mentioned average interval D1 exceeds the above-mentioned upper limit, the flexible printed wiring board 1 may become unnecessarily large in the width direction.

＜Through hole＞

As shown in FIG. 2 , a plurality of through holes 12 connecting the shielded wiring 11 and the first shielding layer 2 and the second shielding layer 3 are formed at regular intervals in the longitudinal direction (depth direction in FIG. 1 ). In this manner, by electrically connecting the shielded wiring 11 to the first shielding layer 2 and the second shielding layer 3 , the shielding effect by the shielded wiring 11 can be further enhanced.

The configuration of the through hole 12 can be a known configuration. As a specific example, through holes are formed in the first shield layer 2, the second shield layer 3, the shield wiring 11, and the dielectric layer 4, and metals such as copper, aluminum, silver, and gold are laminated on the inner peripheral surfaces of the through holes. In this way, the through-holes 12 for connecting the shielded wiring 11 to the first shielding layer 2 and the second shielding layer 3 can be formed.

The interval between the through holes 12 is not particularly limited, but is preferably within 1 cm. In addition, the inner diameter of the above-mentioned through hole 12 is not particularly limited, but is preferably, for example, not less than 50 μm and not more than 500 μm.

＜1st shielding layer＞

The first shielding layer 2 is laminated on one surface of the first resin film 5 . In addition, as shown in FIG. 2 , the first shield layer 2 has a plurality of openings 13 in a region overlapping with the signal wiring 10 in a planar view.

The first shield layer 2 serves as a shield to electromagnetically shield the signal wiring 10 side by covering the signal wiring 10 side of the conductive pattern 1 .

The material and formation method of the first shielding layer 2 may be the same as those of the conductive pattern 1 .

In addition, the first shielding layer 2 overlaps the pair of shielding wirings 11 when viewed from one side in a cross section whose cutting plane is in a direction perpendicular to the longitudinal direction of the signal wirings 10 . That is, the first shielding layer 2 overlaps at least a part of the two shielding wires 11 when viewed in plan at any position in the longitudinal direction. In this way, the first shielding layer 2 and the pair of shielded wirings 11 overlap each other in a planar view, so that electromagnetic waves are less likely to pass between the first shielding layer 2 and each shielded wiring 11 , thereby further improving the shielding effect.

Furthermore, when the cross-section of the cutting surface is viewed from one side in the direction perpendicular to the longitudinal direction of the signal wiring 10, that is, as the shortest distance between the outer edge of the first shielding layer 2 and the outer edge of the signal wiring 10 when viewed in a plan view, The lower limit of the distance D2 is preferably twice, more preferably 2.5 times, the average width W1 of the signal wiring 10 . On the other hand, as the upper limit of the shortest distance D2 between the outer edge of the first shielding layer 2 and the outer edge of the signal wiring 10 when viewed in plan, it is preferably five times the average width W1 of the signal wiring 10, more preferably 5 times the average width W1 of the signal wiring 10. 4 times. When the shortest distance D2 between the outer edge of the first shielding layer 2 and the outer edge of the signal wiring 10 in plan view is smaller than the above lower limit, the elevation angle of the side edge of the first shielding layer 2 viewed from the signal wiring 10 becomes large. , The shielding effect on the side of the signal wiring 10 may become insufficient. Conversely, when the shortest distance D2 between the outer edge of the first shielding layer 2 and the outer edge of the signal wiring 10 in planar view exceeds the upper limit, the width of the flexible printed circuit board may become unnecessarily large.

(opening)

The opening 13 of the first shield layer 2 is formed to reduce the parasitic capacitance between the first shield layer 2 and the signal wiring 10 and to adjust the impedance of the flexible printed circuit board. Generally, the opening 13 is formed so as to overlap the entire width of the signal wiring 10 in a part of the conductive pattern 1 in the longitudinal direction of the signal wiring 10 .

The planar shape of the opening 13 is not particularly limited, but it is preferably formed in a square shape so that calculation of parasitic capacitance becomes easy. In addition, the openings 13 are preferably formed with the same shape at equal intervals along the longitudinal direction of the signal wiring 10 so that the calculation of the parasitic capacitance becomes easy.

The lower limit of the overlapping area ratio of the signal wiring 10 and the first shielding layer 2 when viewed in plan and based on the area of the signal wiring 10 adjusted by the opening 13 is preferably 10%, more preferably 20%. , more preferably 30%. On the other hand, the upper limit of the overlapping area ratio of the signal wiring 10 and the first shielding layer 2 in planar view is preferably 90%, more preferably 80%, and still more preferably 70%. When the overlapping area ratio of the signal wiring 10 and the first shielding layer 2 in plan view is less than the above-mentioned lower limit, the manufacturing error of the parasitic capacitance between the first shielding layer 2 and the signal wiring 10 becomes large, and the flexible printed circuit board There is a possibility that the variation in impedance becomes large, or the shielding effect by the first shielding layer 2 becomes insufficient. Conversely, when the overlapping area ratio of the signal wiring 10 and the first shielding layer 2 in a planar view exceeds the above upper limit, the openings 13 cannot be uniformly distributed, and the calculation of impedance may not be easy.

＜Second shielding layer＞

The second shield layer 3 is laminated on the other surface of the second resin film 6 . It is preferable that the second shield layer 3 is formed in a compact shape substantially without an opening so as to cover the entire surface of the other side of the second resin film 6 . The second shielding layer 3 covers the other side of the signal wiring 10 of the conductive pattern 1 and plays a role of electromagnetically shielding the other side of the signal wiring 10 .

The configuration and formation method of the second shielding layer 3 may be the same as those of the above-mentioned first shielding layer 2 except for the above-mentioned planar shape.

＜Dielectric layer＞ 

The dielectric layer 4 surrounds the signal wiring 10 in a cross section perpendicular to the longitudinal direction, and isolates the signal wiring 10 from the shielding wiring 11 , the first shielding layer 2 and the second shielding layer 3 to ensure electrical insulation.

Since the dielectric layer 4 is formed as a laminate of the first resin film 5, the second resin film 6, and the adhesive layer 7, a three-dimensional structure surrounding the signal wiring 10 is relatively easy to form. More specifically, by bonding the above-mentioned first laminated body 8 and second laminated body 9 together with the adhesive agent forming the adhesive agent layer 7, it is possible to easily manufacture a laminate including the dielectric layer 4 surrounding the signal wiring 10. The flexible printed circuit board.

The lower limit of the relative permittivity of the dielectric layer 4 is preferably as small as possible. In order to satisfy other conditions such as insulation and mechanical strength, 1.5 is actually considered to be the limit. On the other hand, the upper limit of the dielectric layer 4 is preferably 4, more preferably 3. When the relative permittivity of the dielectric layer 4 exceeds the above-mentioned upper limit, the dielectric loss may increase when a high-frequency signal is transmitted using the flexible printed circuit board. In addition, "relative dielectric constant" is the value measured based on JIS-C2138 (2007).

The lower limit of the dielectric loss tangent of the dielectric layer 4 at a frequency of 1 GHz is preferably smaller, and actually, 0.0001 is considered to be the limit. On the other hand, the upper limit of the dielectric loss tangent of the dielectric layer 4 at a frequency of 1 GHz is preferably 0.05, more preferably 0.005. When the dielectric loss tangent of the dielectric layer 4 at a frequency of 1 GHz exceeds the above-mentioned upper limit, the transmission loss of high-frequency signals of the flexible printed wiring board may increase. In addition, "dielectric loss tangent" is the value measured at a frequency of 1 GHz based on JIS-C2138 (2007).

(1st resin film)

The first resin film 5 is an insulating sheet-like member mainly composed of resin, and is a first laminate that separates the conductive pattern 1 from the first shielding layer 2 and supports the conductive pattern 1 and the first shielding layer 2 at the same time. 8 substrates.

The lower limit of the relative permittivity of the first resin film 5 is preferably as small as possible. In order to satisfy other conditions such as insulation and mechanical strength, 1.5 is actually considered to be the limit. On the other hand, the upper limit of the relative permittivity of the first resin film 5 is preferably 4, and more preferably 3. When the relative permittivity of the first resin film 5 exceeds the above-mentioned upper limit, the dielectric loss may increase when a high-frequency signal is transmitted by the flexible printed circuit board.

The lower limit of the dielectric loss tangent of the first resin film 5 at a frequency of 1 GHz is preferably smaller, and actually, 0.0001 is considered to be the limit. On the other hand, the upper limit of the dielectric loss tangent of the first resin film 5 at a frequency of 1 GHz is preferably 0.05, more preferably 0.005. When the dielectric loss tangent of the first resin film 5 at a frequency of 1 GHz exceeds the above-mentioned upper limit, the transmission loss of high-frequency signals of the flexible printed wiring board may increase.

The thickness of the first resin film 5 is appropriately set in accordance with the use of the flexible printed circuit board, etc., and is not particularly limited. Generally speaking, the lower limit of the average thickness of the first resin film 5 is preferably 5 μm, and more preferably 5 μm. 10 μm, more preferably 25 μm. On the other hand, the upper limit of the average thickness of the first resin film 5 is preferably 500 μm, more preferably 150 μm. When the average thickness of the first resin film 5 is less than the aforementioned lower limit, the parasitic capacitance between the conductive pattern 1 and the first shielding layer 2 may become too large, or the strength of the first resin film 5 may become insufficient. Conversely, when the average thickness of the first resin film 5 exceeds the above upper limit, the flexibility of the flexible printed wiring board may become insufficient, or the flexible printed wiring board may become unnecessarily thick.

The lower limit of the melting point of the first resin film 5 is preferably 250°C, more preferably 280°C. On the other hand, the upper limit of the melting point of the first resin film 5 is preferably 400°C, more preferably 350°C. When the melting point of the first resin film 5 is lower than the above-mentioned lower limit, deformation may occur during reflow soldering for mounting electronic components and the like, resulting in insufficient dimensional accuracy. Conversely, when the melting point of the first resin film 5 exceeds the above-mentioned upper limit, the cost may increase unnecessarily, or other characteristics such as the above-mentioned relative permittivity and dielectric loss tangent may not be made preferable. In addition, "melting point" means the peak value of the temperature change at the time of melting measured by differential scanning calorimetry (Differential Scanning Calorimetry).

As the main component of the first resin film 5, resins such as polyimide and polyethylene terephthalate can be used, for example, but resins having a small relative permittivity and dielectric loss tangent are preferable. In this way, by using a resin having a small relative permittivity and a small dielectric loss tangent as the main component of the first resin film 5 , the dielectric loss at the time of transmitting a high-frequency signal through the conductive pattern 1 can be reduced. Examples of resins having a small relative permittivity and a small dielectric loss tangent include fluororesins and liquid crystal polymers. In particular, by using a liquid crystal polymer as the main component of the first resin film 5, the effect of improving dimensional stability can also be obtained.

The above-mentioned liquid crystal polymer as the main component of the first resin film 5 has a thermotropic type showing liquid crystallinity in a molten state and a lyotropic type showing liquid crystallinity in a solution state, but it is preferable to use a thermotropic liquid crystal polymer in the present invention. .

The aforementioned liquid crystal polymer is, for example, an aromatic polyester synthesized from monomers such as aromatic dicarboxylic acid and aromatic diol or aromatic hydroxycarboxylic acid. Representative examples thereof include polymerizing monomers of the following formulas (1), (2) and (3) synthesized from p-hydroxybenzoic acid (PHB), terephthalic acid, and 4,4'-bisphenol. polymers, polymers synthesized from PHB, terephthalic acid and ethylene glycol, polymers of the following formula (3) and (4), polymers synthesized from PHB and 2,6-hydroxynaphthoic acid Polymers obtained by polymerizing monomers of formulas (2), (3) and (5), etc.

[chemical formula 1]

The liquid crystal polymer is not particularly limited as long as it exhibits liquid crystallinity, and each of the above-mentioned polymers may be used as a main body (50 mol% or more in the liquid crystal polymer) and other polymers or monomers may be copolymerized. In addition, the liquid crystal polymer may be liquid crystal polyester amide, liquid crystal polyester ether, liquid crystal polyester carbonate, or liquid crystal polyester imide.

The liquid crystal polyester amide is a liquid crystal polyester having an amide bond, and examples thereof include polymers obtained by polymerizing monomers of the following formula (6) and the above formulas (2) and (4).

[chemical formula 2]

The liquid crystal polymer is preferably produced by melt-polymerizing raw material monomers corresponding to its constituting units, and solid-state polymerizing the obtained polymer (prepolymer). Thereby, a high molecular weight liquid crystal polymer having high heat resistance, strength, and rigidity can be produced with good operability. Melt polymerization can be carried out under the presence of catalyst, as the example of this catalyst, metal compounds such as magnesium acetate, stannous acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate, antimony trioxide, or 4-( As nitrogen-containing heterocyclic compounds such as dimethylamino)pyridine and 1-methylimidazole, nitrogen-containing heterocyclic compounds are preferably used.

As the above-mentioned fluororesin which becomes the main component of the first resin film 5, for example, polytetrafluoroethylene (PTFE), polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene - Hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE) , polyvinyl fluoride (PVF), and thermoplastic fluororesin (THV) and fluoroelastomer composed of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride. In addition, mixtures or copolymers containing these compounds can also be used.

Among them, as the fluororesin used as the main component of the first resin film 5, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) and poly Tetrafluoroethylene (PTFE). By using these fluororesins, the first resin film 5 has flexibility, light transmittance, heat resistance, and flame retardancy.

The fluororesin of the first resin film 5 is preferably cross-linked. Specifically, carbon atoms in the polymer main chain of the fluororesin are preferably covalently bonded to each other. Thus, by crosslinking the fluororesin, deformation at the reflow temperature used for mounting electronic components and the like can be suppressed, and thus the dimensional accuracy of the flexible printed circuit board can be improved.

As a crosslinking method of the fluororesin, for example, a method of generating fluorine radicals by irradiating ionizing radiation is mentioned. In addition, the lower limit of the irradiation dose of ionizing radiation to the fluororesin of the first resin film 5 is preferably 0.1 kGy, and more preferably 1 kGy. On the other hand, the upper limit of the irradiation amount is preferably 1000 KGy, more preferably 900 KGy. When the said irradiation amount is less than the said lower limit, there exists a possibility that the bonding force of the 1st resin film 5 and the conductive pattern 1 cannot fully be acquired. On the contrary, when the above-mentioned irradiation dose exceeds the above-mentioned upper limit, the strength reduction accompanying the decomposition reaction of the fluororesin (competing reaction with crosslinking) and foaming at the interface between the first resin film 5 and the conductive pattern 1 may occur.

It should be noted that the first resin film 5 may contain fillers, additives, and the like in addition to the above-mentioned main components such as liquid crystal polymers and fluororesins.

(2nd resin film)

The second resin film 6 is an insulating sheet-like member mainly composed of resin, and serves as a base material for supporting the second shielding layer 3 . In addition, the second resin film 6 is a layer defining a space filled with the adhesive layer 7 .

The configuration of the second resin film 6 may be the same as that of the first resin film 5 described above.

(adhesive layer)

The adhesive layer 7 is formed of an adhesive. The adhesive layer 7 is a layer in three directions (upper and left and right in the figure) that bonds the first laminated body 8 and the second laminated body 9 and surrounds the signal wiring 10 of the conductive pattern 1 .

The adhesive forming the adhesive layer 7 is preferably an adhesive having excellent flexibility or heat resistance, and examples of such adhesives include modified polyphenylene ether-based, styrene resin-based, Various resin adhesives such as epoxy resin, butyral resin, acrylic resin, etc.

As the main component of the adhesive layer 7 , that is, the main component of the adhesive forming the adhesive layer 7 , a thermosetting resin is preferable. The lower limit of the curing temperature of the thermosetting resin serving as the main component of the adhesive layer 7 is preferably 120°C, more preferably 150°C. On the other hand, the upper limit of the curing temperature of the thermosetting resin constituting the main component of the adhesive bond layer 7 is preferably 230°C, more preferably 200°C. When the curing temperature of the thermosetting resin constituting the main component of the adhesive layer 7 is lower than the aforementioned lower limit, handling of the adhesive that is a raw material of the adhesive layer 7 may become difficult. Conversely, when the curing temperature of the thermosetting resin which is the main component of the adhesive layer 7 exceeds the above upper limit, when the adhesive is cured to form the adhesive layer 7, the first resin film 5 and the second resin film 6 There is a possibility of deformation due to heat, thereby impairing the dimensional accuracy of the flexible printed circuit board. In addition, "curing temperature" means the peak value of the temperature change at the time of curing measured by differential scanning calorimetry (Differential Scanning Calorimetry).

As the thermosetting resin constituting the main component of the adhesive layer 7 , it is preferable to use a modified polyphenylene ether or a styrene-based resin because the relative permittivity and the dielectric loss tangent can be reduced.

The lower limit of the relative permittivity of the adhesive layer 7 is preferably as small as possible. In order to satisfy other conditions such as insulation and mechanical strength, 1.5 is actually considered to be the limit. On the other hand, the upper limit of the relative permittivity of the adhesive layer 7 is 3, preferably 2.8, and more preferably 2.6. In addition, when the relative permittivity of the adhesive layer 7 exceeds the above-mentioned upper limit, the dielectric loss may increase when a high-frequency signal is transmitted by the flexible printed circuit board.

In addition, it is preferable that the relative permittivity of the adhesive layer 7 is smaller than the relative permittivity of the first resin film 5 and the second resin film 6 . In this way, by making the relative permittivity of the adhesive layer 7 smaller than the relative permittivity of the first resin film 5 and the second resin film 6, the first resin film 5 and the second resin film can be separated without using an adhesive. Compared with the case of thermocompression bonding, it is possible to reduce the dielectric loss when transmitting a high-frequency signal through the signal wiring 10 of the conductive pattern 1.

The lower limit of the dielectric loss tangent of the adhesive layer 7 at a frequency of 1 GHz is preferably smaller, and actually 0.0001 is considered to be the limit. On the other hand, the upper limit of the dielectric loss tangent of the adhesive layer 7 at a frequency of 1 GHz is 0.05, preferably 0.01, and more preferably 0.005. When the dielectric loss tangent of the adhesive layer 7 at a frequency of 1 GHz exceeds the above-mentioned upper limit, the transmission loss of the high-frequency signal of the flexible printed wiring board may increase.

In addition, it is preferable that the dielectric loss tangent of the adhesive layer 7 is smaller than the dielectric loss tangent of the first resin film 5 and the second resin film 6 . In this way, by making the dielectric loss tangent of the adhesive layer 7 smaller than the dielectric loss tangent of the first resin film 5 and the second resin film 6, the first resin film 5 and the second resin film can be separated without using an adhesive. Compared with the case of thermocompression bonding, it is possible to reduce the dielectric loss when transmitting a high-frequency signal through the signal wiring 10 of the conductive pattern 1.

＜Advantages＞

The flexible printed circuit board has a first shielding layer 2 that electromagnetically shields one side of the signal wiring 10 of the conductive pattern 1 and a second shielding layer 3 that electromagnetically shields the other side of the conductive pattern 1. There is a pair of shield wires 11 that electromagnetically shield both sides of the signal wire 10 in the width direction, and therefore, electromagnetic shields exist around the signal wire 10 in a cross section perpendicular to the direction in which the signal wire 10 extends. , has a high shielding function.

In addition, by setting the average interval between the signal wiring 10 and the shielding wiring 11 of the flexible printed wiring board within the above-mentioned range, the parasitic capacitance between the signal wiring 10 and the shielding wiring 11 is relatively small. Therefore, in this flexible printed circuit board, the overall impedance can be adjusted relatively easily by adjusting the parasitic capacitance between the signal wiring 10 and the first shield layer 2 through the opening 13 .

[Other Embodiments]

Embodiments disclosed this time are illustrative in every respect, and should not be considered as limiting in particular. The scope of the present invention is not limited to the constitution of the above-mentioned embodiment, but is shown by the scope of the claims, and it is intended that all changes within the meaning and range equivalent to the scope of the claims are included.

In this flexible printed wiring board, the dielectric layer may not have the adhesive layer, or may not have the first resin film or the second resin film. Specifically, the dielectric layer can be formed by integrating the first resin film of the first laminate and the second resin film of the second laminate by thermocompression bonding. In addition, by pasting on the other side of the first laminated body what is coated with an adhesive on one side of the metal foil forming the second shielding layer, a dielectric layer can be formed by the first resin film and the adhesive layer. body layer.

In addition, in this flexible printed wiring board, the opening is not essential, and the opening may be formed in the second shield layer.

In addition, in this flexible printed circuit board, the conductive pattern may have a plurality of signal wirings.

In addition, in this flexible printed circuit board, the shielded wiring and the first shielding layer and the second shielding layer may be directly or indirectly connected by any configuration other than the via including the through hole in the above-mentioned embodiment or a combination of via and other configurations. connect.

In addition, in this flexible printed circuit board, it is only necessary for the dielectric layer to surround at least the signal wiring of the conductive pattern, and a gap may be formed between the first shielding layer and the second shielding layer at a portion other than the vicinity of the signal wiring. . Specifically, the dielectric layer may be formed so as to exist at least within a region of preferably within 10 μm, more preferably within 25 μm, and still more preferably within 50 μm from the signal wiring when viewed in plan.

The flexible printed circuit board is not limited to transmitting high-frequency signals, but can also handle low-frequency signals.

In addition, the flexible printed circuit board is not limited to a flexible printed circuit board used as a cable for transmitting signals, and may be a flexible printed circuit board on which electronic components are mounted to form a circuit board.

In addition, the flexible printed circuit board may have layers other than those described in the above embodiments, for example, a cover layer laminated on one side of the first shielding layer or on the other side of the second shielding layer, a layer provided between the conductive pattern and the other side of the second shielding layer. Another adhesive layer or the like between the first shielding layer and the first resin film or between the second shielding layer and the second resin film.

In addition, in this flexible printed circuit board, when a conductive layer such as a metal foil forming a conductive pattern is laminated on the first resin film using an adhesive, it is preferable to use as the adhesive an adhesive that is formed and filled in the first laminated body and the first laminated body. The same adhesive as the adhesive of the adhesive layer between the second resin films.

In addition, in this flexible printed wiring board, the thickness of the signal wiring of a conductive pattern and the thickness of one or more shield wiring may differ.

In addition, in this flexible printed circuit board, the opening for adjusting impedance may be one opening.

Industrial availability

This flexible printed circuit board can be suitably used as, for example, a flexible printed circuit board for high-speed transmission that transmits high-frequency signals.

Claims (6)

1. a flexible printed circuit board, possesses:

Conductive pattern,

Be arranged at the 1st screen on the side of this conductive pattern,

Be arranged at the 2nd screen on the opposite side of described conductive pattern and

With the dielectric layer arranged around the mode of described conductive pattern between described 1st screen and the 2nd screen,

It is characterized in that, described conductive pattern has one or more signal wirings and is arranged at a pair of both sides shielding distribution of this signal wiring,

The equispaced of described signal wiring and shielding distribution is more than the mean breadth of described signal wiring.

2. flexible printed circuit board according to claim 1, is characterized in that,

During from the cross section that described unilateral observation is cut surface with the direction vertical with the longitudinal direction of described signal wiring, described 1st screen and the 2nd screen are with to shield distribution a pair overlapping.

3. flexible printed circuit board according to claim 2, is characterized in that,

During from the cross section that described unilateral observation is cut surface with the direction vertical with the longitudinal direction of described signal wiring, the beeline of the outer rim of the 1st screen and the 2nd screen and the outer rim of signal wiring is more than 2 times of the mean breadth of described signal wiring.

4. flexible printed circuit board according to claim 1, is characterized in that,

Described 1st screen has one or more peristomes in region overlapping with described signal wiring during viewed in plan.

5. flexible printed circuit board according to claim 4, is characterized in that,

Be less than more than 10% 90% with the overlapping area rate of signal wiring described during viewed in plan and the 1st screen.

6. flexible printed circuit board according to claim 1, is characterized in that,

Described dielectric layer has:

Be laminated in the 1st resin molding between described conductive pattern and the 1st screen,

Be laminated in the 2nd resin molding on the side of described 2nd screen and

Be filled in the bond layer between duplexer and described 2nd resin molding comprising described 1st resin molding and conductive pattern.