JP2016034049A - Flexible printed wiring board and electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible printed wiring board that can exhibit a high shielding effect while maintaining matching property of an impedance and a transmission loss.SOLUTION: A flexible printed wiring board with a shielding function is provided, which includes a flexible dielectric layer, a signal line pattern layer deposited on one surface side of the dielectric layer, and a ground layer deposited on the other surface side of the dielectric layer. The signal line pattern layer includes a signal line and a shield wiring line continuously arranged to surround the signal line. It is preferable that: the ground layer is solid; an average interval between the signal line and the ground layer in a thickness direction is 25 μm or more and 200 μm or less; an average width of the signal line is 25 μm or more and 500 μm or less; the dielectric layer has an apparent specific permittivity of 2.0 or more and 4.0 or less; an average thickness of the signal line and the shield wiring line is 5 μm or more and 40 μm or less; and an average interval between the signal line and the shield wiring line in a width direction is 50 μm or more and 1000 μm or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a flexible printed wiring board and an electronic component.

  Flexible printed wiring boards are used for transmitting high-frequency signals, digital signals, and the like. As such a flexible printed wiring board, a flexible printed wiring board with a shielding function having a stripline structure, a microstrip structure, or the like is used for noise prevention, crosstalk prevention, and the like. In the stripline structure and the microstrip structure, a signal line is disposed on one surface side of a dielectric layer, and a ground layer is laminated on the other surface side of the dielectric layer.

  By the way, when thinning the dielectric layer in order to reduce the thickness of the flexible printed wiring board with a shield function, it is necessary to keep the parasitic capacitance constant for impedance matching, but to keep the parasitic capacitance constant. If the width of the signal line is narrowed, transmission loss in the signal line increases. For this reason, it has been proposed to keep the parasitic capacitance constant by providing an opening in the ground layer so as to reduce the area where the ground layer and the signal line face each other (see JP-A-2000-77802). .

JP 2000-77802 A

  However, when the opening is provided in the ground layer as described above, there is a disadvantage that the shielding effect may be insufficient due to the presence of the opening. Further, when the ground layer is solid to obtain a sufficient shielding effect, it is necessary to give the dielectric layer a certain thickness in order to suppress an increase in transmission loss of the signal line as described above. If the dielectric layer has a certain thickness, the shielding effect on the side surface of the dielectric layer may be insufficient.

  The present invention has been made in view of the above disadvantages, and provides a flexible printed wiring board capable of providing a high shielding effect while maintaining impedance matching and transmission loss, and an electronic component using the same. The task is to do.

The flexible printed wiring board according to the present invention made to solve the above problems is
A flexible printed wiring board with a shielding function, comprising a dielectric layer having flexibility, a signal line pattern layer laminated on one surface side of the dielectric layer, and a ground layer laminated on the other surface side of the dielectric layer Because
The signal line pattern layer has a signal line and a shield wiring continuously arranged so as to surround the signal line.

  Moreover, the electronic component which concerns on this invention is provided with the said flexible printed wiring board which consists of the said structure.

  The flexible printed wiring board can exhibit a high shielding effect while maintaining impedance matching and transmission loss by continuously arranging the shield wiring so as to surround the signal line in the signal line pattern layer.

FIG. 1 is a schematic end view showing a flexible printed wiring board according to an embodiment of the present invention. FIG. 2 is a schematic end view of the first laminate used in the printed wiring board of FIG. FIG. 3 is a schematic end view of a second laminate used in the printed wiring board of FIG. FIG. 4 is a schematic plan view of a first laminate used in the flexible printed wiring board of FIG. FIG. 5 is a schematic bottom view of the first laminate used in the flexible printed wiring board of FIG. 6 is a schematic plan view of a second laminate used in the flexible printed wiring board of FIG.

[Description of Embodiment of the Present Invention]
The flexible printed wiring board according to the present invention is
A flexible printed wiring board with a shielding function, comprising a dielectric layer having flexibility, a signal line pattern layer laminated on one surface side of the dielectric layer, and a ground layer laminated on the other surface side of the dielectric layer Because
The signal line pattern layer is a flexible printed wiring board having a signal line and shield wiring continuously arranged so as to surround the signal line.

  In the flexible printed wiring board, the ground layer laminated on the other surface side of the dielectric layer has a shielding function, and the shield wiring layer of the signal line pattern layer also has a shielding function. In this way, the flexible printed wiring board can also provide a shielding function by the shield layer disposed on the same layer (signal line pattern layer) as the signal line, so that the shielding effect also in the peripheral direction of the flexible printed wiring board. Play. In particular, the shield wiring is not discontinuous, but is continuously provided so as to surround the signal line. Therefore, the shield wiring is excellent in conduction in the shield wiring, and thus the shielding effect in the peripheral direction is high. For this reason, the flexible printed wiring board can exhibit a high shielding effect while maintaining impedance matching and transmission loss.

  The ground layer may be formed in a solid shape. Thereby, the flexible printed wiring board has a high shielding effect on the other surface side (the ground layer lamination side with respect to the dielectric layer). Note that the “solid shape” means a state in which there is substantially no opening in a region overlapping at least the signal line in plan view. Note that “substantially having no opening” includes not only the case where the opening does not exist completely, but also the case where a minute hole such as bubble removal exists.

  When the ground layer is formed in a solid shape as described above, the average distance (H) in the thickness direction between the signal line and the ground layer is 25 μm or more and 200 μm or less, and the average width (W1) of the signal line ) Is 25 μm or more and 500 μm or less, the apparent relative dielectric constant of the dielectric layer is 2.0 or more and 4.0 or less, the average thickness (T1) of the signal line and the shield wiring is 5 μm or more and 40 μm or less, The average distance (W2) in the width direction between the signal line and the shield wiring is preferably 50 μm or more and 1000 μm or less.

  Thus, the flexible printed wiring board is such that the average distance (H) in the thickness direction between the signal line and the ground layer, the average width (W1) of the signal line, and the apparent relative dielectric constant of the dielectric layer are within the above ranges. It has a suitable characteristic impedance. Furthermore, since the average thickness (T1) of the signal line and the shield wiring and the average interval (W2) in the width direction between the signal line and the shield wiring are within the above range, the presence of the shield wiring causes the parasitic of the flexible printed wiring board. The influence on the capacitance is small, and the characteristic impedance of the flexible printed wiring board can be easily and reliably adjusted. The average distance (H) in the thickness direction between the signal line and the ground layer means the average value of the shortest distances from the ground layer at any 10 points in the plane direction of the signal line. The average width (W1) of the signal line means the average value of the length of the signal line in the plane direction and the direction orthogonal to the transmission direction of the signal line, and the plane area of the signal line is the length in the transmission direction. It can be a divided value. The apparent relative dielectric constant of the dielectric layer is a value calculated by the dielectric constant of the members constituting the dielectric layer. When the dielectric layer is composed of a plurality of layers, the apparent dielectric constant depends on the relative dielectric constant and thickness of each layer. When the dielectric constant is calculated and the dielectric layer is a single layer, the relative dielectric constant of the layer becomes the apparent relative dielectric constant. The average thickness (T1) of the signal line and the shield wiring means an average value of thicknesses at arbitrary 10 points of each of the signal line and the shield wiring. The average distance (W2) in the width direction between the signal line and the shield wiring means an average value of the shortest distances between the signal lines and the shield wiring at arbitrary 10 positions in the transmission direction of the signal line.

  The flexible printed wiring board includes a first laminate having the signal line pattern layer and a first insulating film in which the signal line pattern layer is laminated, and a second insulation in which the ground layer and the ground layer are laminated. A second laminate having a film, and an adhesive layer for adhering the first laminate and the second laminate may be provided. Thereby, the said flexible printed wiring board can be manufactured easily and reliably by adhere | attaching a 1st laminated body and a 2nd laminated body with an adhesive bond layer.

  The main component of the first insulating film or the second insulating film is preferably a liquid crystal polymer. Thus, an insulating film whose main component is a liquid crystal polymer has a low dielectric constant, a low dielectric loss tangent, and excellent electrical characteristics.

  Further, in the flexible printed wiring board, the signal line pattern layer is laminated on the surface of the first insulating film facing the second laminated body, and the first laminated body is the first laminated body. It is good to further have the 2nd shield wiring laminated on the field opposite to the field which laminates the above-mentioned signal line pattern layer in an insulating film, and the field which overlaps with the above-mentioned shield wiring in plane view. As a result, the flexible printed wiring board has the second shield wiring disposed on the one surface side (the laminated side of the signal line pattern layer with respect to the dielectric layer) from the signal line. High shielding effect.

  The electronic component according to the present invention includes the flexible printed wiring board having the above configuration. In the electronic component, the flexible printed wiring board exhibits a high shielding effect while maintaining impedance matching and transmission loss.

[Details of the embodiment of the present invention]
Hereinafter, embodiments of a flexible printed wiring board according to the present invention will be described in detail with reference to the drawings.

<Flexible printed wiring board>
A flexible printed wiring board 1 in FIG. 1 is laminated on a flexible dielectric layer 2, a signal line pattern layer 3 laminated on one surface of the dielectric layer 2, and the other surface side of the dielectric layer 2. The ground layer 4 is provided. Note that “one surface side” means the upper side in FIG. 1 and “the other surface side” means the lower side in FIG. 1. In the following description, the “side” is assumed to be “back” and the “other side” is assumed to be “front”.

  The flexible printed wiring board 1 is composed of a strip-shaped sheet body. 4 to 6 schematically show a rectangular shape in plan view, but in the flexible printed wiring board 1, the shape is appropriately changed depending on the place where it is used. .

  The specific configuration of the flexible printed wiring board 1 will be described. The flexible printed wiring board 1 includes a first laminate 7 and a second laminate formed by laminating a first insulating film 6 and the signal line pattern layer 3. A second laminated body 9 configured by laminating the insulating film 8 and the ground layer 4 and an adhesive layer 10 for bonding the first laminated body 7 and the second laminated body 9 are provided. The signal line pattern layer 3 is laminated on the back surface of the first insulating film 6, and the ground layer 4 is laminated on the back surface of the second insulating film 8. For this reason, in the flexible printed wiring board 1, the dielectric layer 2 is composed of a part of the second insulating film 8 and the adhesive layer 10 (part on the back side of the signal line pattern layer 3). The flexible printed wiring board 1 further includes a pair of coverlays 11 stacked on the front surface side of the first stacked body 7 and the back surface side of the second stacked body 9.

(First laminate)
The signal line pattern layer 3 of the first laminate 7 has a linear signal line 12 and shield wirings 13 continuously arranged so as to surround the signal line 12 as shown in FIG. . The first laminate 7 is laminated on the surface of the first insulating film 6 (the surface opposite to the surface on which the signal line pattern layer 3 is laminated) and in the area overlapping the shield wiring 13 in plan view. Two shielded wires 14 are further provided.

  The signal line 12 is arranged in the center along the strip-like longitudinal direction of the first insulating film 6. The average width (W1) of the signal line 12 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 further preferably 230 μm. If the average width (W1) is less than the lower limit, the transmission loss in the signal line 12 may be too large. On the other hand, if the average width (W1) exceeds the upper limit, the parasitic capacitance becomes too large and impedance matching may not be obtained.

  In the present embodiment, the shield wiring 13 of the signal line pattern layer 3 is formed in a substantially U shape in plan view surrounding the signal line 12. Specifically, as shown in FIG. 5, the shield wiring 13 has a pair of longitudinal portions 13a disposed along the longitudinal direction with a gap from the signal line 12 on both sides of the signal line 12. One end (the right end in FIG. 5) of the longitudinal direction portion 13a is disposed on the outer side (the right end in FIG. 5) outside one end (the right end in FIG. 5), and the other end (the left end in FIG. 5) is The signal line 12 is disposed on the outer side (right side of the figure) from one end (right side of the figure). The shield wiring 13 has a connecting portion 13b connected to one end of the pair of longitudinal portions 13a. Thereby, one end of a pair of longitudinal direction site | part 13a is continuing via the said connection site | part 13b. Note that the other ends of the pair of longitudinal portions 13a are not continuous.

  As described above, the signal line pattern layer 3 is an area where the shield wiring 13 does not surround the signal line 12 (hereinafter referred to as a non-enclosed area) in a portion facing the connecting part 13b (the other end side of the longitudinal part 13a). It is said that). Here, the angle γ of the non-enclosed region as viewed from the input / output unit 15 (the input / output unit 15 on the left side in FIG. 5) adjacent to the non-enclosed region among the input / output units 15 in the signal line 12 described later (this input / output unit). The angle between the first imaginary straight line connecting 15 and the other end of one longitudinal portion 13a and the second imaginary straight line connecting this input / output part 15 and the other end of the other longitudinal portion 13a is 45. It is preferable that the angle is within the range of 40 °, more preferably within the range of 40 °. Thereby, the shielding effect by the shield wiring 13 is fully exhibited. Note that the lower limit of the angle γ of the non-enclosed region is 0 °. The input / output unit 15 is formed by a through hole or a via hole.

  The average thickness (T1) of the signal line 12 and the shield wiring 13 is not particularly limited, but the lower limit of the average thickness (T1) is preferably 5 μm, and more preferably 12 μm. On the other hand, the upper limit of the average thickness (T1) is preferably 40 μm, more preferably 33 μm, and even more preferably 25 μm. If the average thickness (T1) of the signal line 12 is less than the lower limit, the transmission loss in the signal line 12 may be too large. Further, if the average thickness (T1) of the shield wiring 13 is less than the lower limit, the shield wiring 13 itself may not have sufficient conductivity, and the shield effect by the shield wiring 13 may not be sufficiently obtained. Conversely, when the average thickness (T1) of the signal line 12 and the shield wiring 13 exceeds the upper limit, the flexibility of the flexible printed wiring board 1 may be excessively lowered, and the shield wiring 13 affects the parasitic capacitance. And impedance matching may be difficult to obtain.

  The signal line 12 preferably has a substantially uniform thickness at an arbitrary position in the plane direction. Similarly, the shield wiring 13 preferably has a substantially uniform thickness at an arbitrary position in the plane direction. Note that “substantially uniform” means that the error is within 40% of the average thickness (T1).

  The average distance (W2) in the width direction between the signal line 12 and the shield wiring 13 (the longitudinal portion 13a) is not particularly limited, but the lower limit of the average distance (W2) is 50 μm. Preferably, 100 μm is more preferable, and 200 μm is further preferable. On the other hand, the upper limit of the average interval (W2) is preferably 1000 μm, more preferably 600 μm, and still more preferably 400 μm. If the average interval (W2) is less than the lower limit, the shield wiring 13 may affect the parasitic capacitance, making it difficult to achieve impedance matching. Conversely, if the average interval (W2) exceeds the upper limit, the flexible printed wiring board 1 may become too large in the width direction.

  The average width of the shield wiring 13 is not particularly limited, but the lower limit of the average width is preferably 100 μm, and more preferably 200 μm. On the other hand, the upper limit of the average width is preferably 500 μm, and more preferably 400 μm. If the average width is less than the above lower limit, the continuity of the shield wiring 13 itself cannot be sufficiently obtained, and the shielding effect by the shield wiring 13 may not be sufficiently obtained. Conversely, when the average width exceeds the upper limit, the flexible printed wiring board 1 may become too large in the width direction.

  The average thickness of the first insulating film 6 is not particularly limited, and the lower limit of the average thickness of the first insulating film 6 is preferably 40 μm, and more preferably 50 μm. On the other hand, the upper limit of the average thickness of the first insulating film 6 is preferably 100 μm, and more preferably 90 μm. If the average thickness of the first insulating film 6 is less than the lower limit, the strength of the first insulating film 6 may be inferior, and the lamination process of the signal lines 12 and the like may be difficult. Conversely, if the average thickness of the first insulating film 6 exceeds the upper limit, the flexibility of the flexible printed wiring board 1 may be excessively lowered.

  In the illustrated example, a pair of the second shield wires 14 are disposed on both sides of the signal line 12 in plan view (see FIG. 4). The average thickness and average width of the second shield wiring 14 are not particularly limited, but can be the average thickness and average width of the first shield wiring 13.

  As shown in FIGS. 4 and 5, the first laminated body 7 has an input / output unit 15 penetrating in the front and back direction at both ends of the signal line 12. In FIG. 4, the circuit lines from the input / output unit 15 or the mounting connection pads are not shown.

  The first laminate 7 also has through-holes 16 penetrating in the front and back directions in the region where the shield wiring 13 and the second shield wiring 14 are disposed. For this reason, desired conduction in the front and back direction can be obtained by plating the inner wall of the through hole 16 or filling the through hole 16 with a conductive material. The through hole 16 may be formed as a via hole.

  The location, number, size, and the like of the through holes 16 are not particularly limited and can be appropriately designed. In the present embodiment, the plurality of through holes 16 are disposed along the transmission direction of the signal line 12 in the region where the shield wiring 13 and the second shield wiring 14 are disposed. The interval L (see FIG. 4) between the through holes 16 adjacent to each other in the transmission direction of the signal line 12 is not particularly limited, but is preferably within 1 cm. Thereby, the shielding effect by the shield wiring 13 can be improved more. The inner diameter of the through hole 16 is not particularly limited, but is preferably 50 μm or more and 500 μm or less, for example. Similarly, the inner diameter of the input / output unit 15 is not particularly limited, but is preferably 50 μm or more and 500 μm or less, for example.

  The first insulating film 6 is composed of a sheet-like member having flexibility and electrical insulation. Specifically, a resin film can be employed as the first insulating film 6. As the main component of this resin film, for example, polyimide, polyethylene terephthalate or the like can be used, but it is preferable to use a liquid crystal polymer (LCP) having excellent electrical characteristics.

  The liquid crystal polymer includes a thermotropic type exhibiting liquid crystallinity in a molten state and a lyotropic type exhibiting liquid crystallinity in a solution state. In the present invention, it is preferable to use a thermotropic liquid crystal polymer.

  The liquid crystal polymer is, for example, an aromatic polyester obtained by synthesizing an aromatic dicarboxylic acid and a monomer such as an aromatic diol or an aromatic hydroxycarboxylic acid. A typical example is a polymer obtained by polymerizing monomers of the following formulas (1), (2) and (3) synthesized from parahydroxybenzoic acid (PHB), terephthalic acid and 4,4′-biphenol. , A polymer obtained by polymerizing monomers of the following formulas (3) and (4) synthesized from PHB, terephthalic acid and ethylene glycol, the following formula (2) synthesized from PHB and 2,6-hydroxynaphthoic acid, Examples thereof include a polymer obtained by polymerizing the monomers (3) and (5).

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

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

  The liquid crystal polymer is preferably produced by melt polymerization of raw material monomers corresponding to the constituent units constituting the liquid crystal polymer, and solid-phase polymerization of 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 may be carried out in the presence of a catalyst. Examples of this catalyst include metal compounds such as magnesium acetate, stannous acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate, and antimony trioxide, And nitrogen-containing heterocyclic compounds such as 4- (dimethylamino) pyridine and 1-methylimidazole, and nitrogen-containing heterocyclic compounds are preferably used.

  In addition, when the main component of the 1st insulating film 6 is made into a liquid crystal polymer, a filler, an additive, etc. may be included.

  The signal line 12, the shield wiring 13 and the second shield wiring 14 are formed by etching a metal layer laminated on the front surface and the back surface of the first insulating film 6, for example. The metal layer constituting each line can be formed of a conductive material, but by forming it with a copper foil, a pattern having a desired shape in plan view can be easily and reliably formed. The etching for forming this pattern can be dry etching or wet etching. From the viewpoint of productivity in terms of etching speed, wet etching is preferable. This etching is performed by masking the metal layer for a portion that becomes the signal line 12 and the like, and removing a desired portion (unmasked portion) of the metal layer using an etching solution. As the liquid, for example, sulfuric acid / hydrogen peroxide (mixed liquid of sulfuric acid and hydrogen peroxide solution), sodium sulfate sulfate or the like can be used.

  In addition, it does not specifically limit as a method of laminating | stacking the said metal layer on the 1st insulating film 6, For example, the resin composition which is the material of the 1st insulating film 6 on the metal foil, the adhesion method which bonds metal foil with an adhesive agent Casting method for applying an object, sputtering / plating method for forming a metal layer by electrolytic plating on a thin conductive layer (seed layer) having a thickness of several nm formed on the first insulating film 6 by sputtering or vapor deposition, metal A laminating method or the like in which the foil is attached by hot pressing can be used.

(Second laminate)
The 2nd laminated body 9 has the 2nd insulating film 8 and the ground layer 4 laminated | stacked on the back surface of this 2nd insulating film 8 as mentioned above (refer FIG. 3). The ground layer 4 may be a mesh pattern or the like, but is formed in a solid shape having substantially no opening in a region overlapping at least the signal line in plan view (see FIG. 6). The through hole 16 described in the first stacked body 9 also penetrates the second stacked body 9, and the ground layer 4 is electrically connected to the shield wiring 13 and the second shield wiring 14 through the through hole 16.

  Since the said 2nd insulating film 8 can be formed with the material similar to the said 1st insulating film 6, description of the material of the 2nd insulating film 8 is abbreviate | omitted.

  The average thickness of the second insulating film 8 is not particularly limited, but the lower limit of the average thickness of the second insulating film 8 is preferably 15 μm, more preferably 40 μm, and even more preferably 50 μm. On the other hand, the upper limit of the average thickness of the first insulating film 6 is preferably 190 μm, more preferably 100 μm, and still more preferably 90 μm. If the average thickness of the second insulating film 8 is less than the lower limit, the parasitic capacitance becomes too large, and impedance matching may not be obtained. On the contrary, when the average thickness of the second insulating film 8 exceeds the upper limit, the flexibility of the flexible printed wiring board 1 may be excessively lowered.

  The relative dielectric constant of the second insulating film 8 is not particularly limited as long as impedance matching is obtained, but the upper limit of the relative dielectric constant is preferably 4.0, more preferably 3.0, 2.0 is more preferable. If the relative permittivity exceeds the upper limit, parasitic conductance tends to increase, and impedance matching becomes difficult to obtain. In addition, the minimum of the dielectric constant of the 2nd insulating film 8 is not specifically limited, What is necessary is just to be larger than one.

  The ground layer 4 can be composed of, for example, a metal layer laminated on the back surface of the second insulating film 8. The metal layer constituting the ground layer 4 can be the same as the metal layer constituting the signal line 12 or the like. Specifically, for example, the ground layer 4 is made of copper foil or gold-plated copper foil. Can be formed.

(Adhesive layer)
The adhesive layer 10 is a layer that bonds the first laminate 7 and the second laminate 9 as described above. Specifically, the adhesive layer 10 is formed on the back surface of the first laminate 7 ( Between the back surface of the signal line 12 and the shield wiring 13 and the back surface of the first insulating film 6) and the surface of the second laminate 9 (the surface of the second insulating film 8). Yes.

  The thickness of the adhesive layer 10 (the distance from the back surface of the first insulating film 6 to the surface of the second insulating film 8) is not particularly limited as long as it is larger than the thickness of the signal line 12 and the shield wiring 13, but the adhesive layer 10 The lower limit of the average thickness is preferably 15 μm, and more preferably 20 μm. On the other hand, the upper limit of the average thickness of the adhesive layer 10 is preferably 50 μm, more preferably 30 μm, and even more preferably 25 μm. If the average thickness of the adhesive layer 10 is less than the above lower limit, the formation of the adhesive layer 10 becomes difficult, and a good adhesion state between the first laminate 7 and the second laminate 9 may not be obtained. Conversely, if the average thickness of the adhesive layer 10 exceeds the above upper limit, the flexibility of the flexible printed wiring board 1 may be excessively lowered, and the apparent dielectric constant of the dielectric layer 2 described later may be increased. .

  The relative dielectric constant of the adhesive layer 10 is not particularly limited, but the upper limit of the relative dielectric constant is preferably 4.0, more preferably 3.0, and further preferably 2.0. If the relative dielectric constant exceeds the upper limit, the presence of the adhesive layer 10 may increase the apparent dielectric constant of the dielectric layer 2 described later.

  Although it does not specifically limit as an adhesive agent which comprises the adhesive bond layer 10, The thing excellent in the softness | flexibility and heat resistance is preferable, As such an adhesive agent, a nylon resin type, an epoxy resin type, a butyral, for example Various resin-based adhesives such as a resin-based resin and an acrylic resin-based resin can be used.

  The dielectric layer 2 is configured as described above by a part of the adhesive layer 10 (the part on the back side of the signal line 12) and the second insulating film 8. Here, the lower limit of the average thickness of the dielectric layer 2, that is, the average distance (H) in the thickness direction between the signal line 12 and the ground layer 4, is preferably 25 μm, more preferably 55 μm, and even more preferably 65 μm. The upper limit of the average interval (H) is preferably 200 μm, more preferably 115 μm, and further preferably 105 μm. If the average interval (H) is less than the lower limit, the parasitic capacitance becomes too large, and it is difficult to obtain impedance matching. On the contrary, when the average interval (H) exceeds the upper limit, the flexibility of the flexible printed wiring board 1 may be excessively lowered.

  The apparent dielectric constant of the dielectric layer 2 is determined by the relative dielectric constant and thickness of the second insulating film 8 and the relative dielectric constant and thickness of the adhesive layer 10. The upper limit of the apparent dielectric constant is 4.0. 3.0 is more preferable, and 2.1 is more preferable. If the apparent dielectric constant exceeds the upper limit, parasitic conductance tends to increase and impedance matching becomes difficult to obtain. The lower limit of the relative dielectric constant of the apparent dielectric constant is not particularly limited, and is preferably 2.0 or more. The “apparent dielectric constant” in the present embodiment means the apparent relative dielectric constant.

  In the flexible printed wiring board 1, the dielectric loss tangent (1 GHz) is preferably 0.05 or less, and more preferably 0.005 or less. Thereby, the flexible printed wiring board 1 has a small transmission loss in the signal line.

(Coverlay)
The cover lay 11 has an insulating layer 17 and an adhesive layer 18 as shown in FIG. Here, the insulating layer 17 is disposed on the outer surface side, and the adhesive layer 18 is disposed on the inner surface side. Specifically, one of the pair of cover lays 11 has an inner surface on the surface of the first laminate 7. The other side is adhered to the rear surface of the second laminate 9 via the inner surface (front surface) adhesive layer 18.

  The lower limit of the average thickness of the insulating layer 17 of the coverlay 11 is preferably 5 μm and more preferably 10 μm. When the average thickness of the insulating layer 17 of the cover lay 11 is less than the above lower limit, the insulating property may be insufficient. On the other hand, the upper limit of the average thickness of the insulating layer 17 of the coverlay 11 is preferably 25 μm and more preferably 12.5 μm. When the average thickness of the insulating layer 17 of the cover lay 11 exceeds the upper limit, the flexibility of the flexible printed wiring board 1 may be excessively lowered.

  Further, the average thickness of the adhesive layer 18 of the cover lay 11 is not particularly limited, but is preferably 20 μm or more and 30 μm or less. If the average thickness of the adhesive layer 18 of the cover lay 11 is less than the lower limit, the adhesiveness may be insufficient, and if it exceeds the upper limit, the flexibility of the flexible printed wiring board 1 may be excessively lowered. is there.

  The material of the insulating layer 17 is not particularly limited, and the same material as the resin film constituting the first insulating film 6 can be used. Further, the adhesive layer 18 of the cover lay 11 is made of an adhesive, and as the adhesive constituting the adhesive layer 18 of the cover lay 11, the same type of adhesive as that constituting the adhesive layer 10 may be used. Since it can do, description here is abbreviate | omitted.

<Advantages>
Since the flexible printed wiring board 1 has a shield function by the ground layer 4 disposed on the back side of the signal line 12 and the shield layer disposed around the planar direction of the signal line 12, the flexible printed wiring board 1 A high shielding effect is exhibited not only on the back surface of the wiring board 1 but also in the peripheral direction. In addition, since the second shield wiring 14 is disposed on the surface side of the signal line 12, the second shield wiring 14 also provides a surface shielding effect. Further, since the shield wiring 13 of the signal line pattern layer 3 is continuously provided so as to surround the signal line 12 instead of being discontinuous, the shield wiring 13 is excellent in conduction within the shield wiring 13, and thus the shielding effect in the peripheral direction is provided. Is expensive. Further, by forming the ground layer 4 in a solid shape, the flexible printed wiring board 1 exhibits a high shielding effect even on the back surface side. For this reason, the flexible printed wiring board 1 can exhibit a high shielding effect while maintaining impedance matching and transmission loss.

  Furthermore, by using a liquid crystal polymer as the main component of the first insulating film 6 and the second insulating film 8, the first insulating film 6 and the second insulating film 8 have a small dielectric constant, a small dielectric loss tangent, and electrical characteristics. Excellent. In particular, since the main component of the second insulating film 8 is a liquid crystal polymer, since the dielectric constant is small as described above, the parasitic capacitance can be kept small, and impedance matching can be easily and reliably achieved. Furthermore, as the main component of the 1st insulating film 6 and the 2nd insulating film 8 is a liquid crystal polymer as mentioned above, the 1st insulating film 6 and the 2nd insulating film 8 have a small water absorption rate, and also have a linear expansion coefficient. Small, low thermal shrinkage, high dimensional stability, and excellent gas barrier properties, flame retardancy, heat resistance, flame retardancy and the like.

  In the flexible printed wiring board 1, the signal line pattern layer 3 is laminated on the surface of the first insulating film 6 facing the second laminated body 9, and the first laminated body 7 has the second shield wiring 14 laminated on the surface of the first insulating film 6 opposite to the surface on which the signal line pattern layer 3 is laminated, and in a region overlapping the shield wiring 13 in plan view. Since the second shield wiring 14 is disposed on the one surface side (the laminated side of the signal line pattern layer 3 with respect to the dielectric layer 2) than the signal line 12, the shielding effect on the one surface side is high. .

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

  That is, in the flexible printed wiring board, a signal line pattern layer can be laminated on the surface of one insulating film constituting the dielectric layer, and a ground layer can be laminated on the back surface. However, it is preferable to form the first laminated body and the second laminated body by bonding with an adhesive layer as in the above-described embodiment, whereby the flexible printed wiring board is easily and reliably manufactured.

  Further, in the above embodiment, the case where the average thickness of the signal line and the average thickness of the shield wiring are the same has been described, but the case where the thickness of the signal line and the shield wiring is different is also within the intended scope of the present invention. is there.

  In the above embodiment, the shield wiring of the signal line pattern layer is formed in a substantially U shape in a plan view from a pair of longitudinal portions and a connecting portion connected to one end of the longitudinal portion. However, it is also possible to provide another connecting part connected to the other end of the longitudinal part, that is, to provide the shield wiring in an annular shape from a pair of longitudinal parts and a pair of connecting parts.

  Further, the second shield wiring is not an essential constituent element of the present invention, and even when the second shield wiring is provided, the second shield wiring is not limited to the configuration of the above embodiment. It is also possible to form a solid shape like the wiring. In addition, the second laminate includes a conductive bridge-like or mesh-like member disposed on the surface of the second shield wiring and the first insulating film so as to bridge the pair of second shield wirings as in the above embodiment. It is also possible to change the design so that it has.

  In the above embodiment, the signal line is described as being linear, but it is also possible to provide the signal line in a curved line. However, it is preferable that the signal line is linear between at least a pair of input / output units, and thereby the area of the signal line can be reduced.

  The present invention is also directed to an electronic component using the flexible printed wiring board. Specifically, in the present invention, for example, the flexible printed wiring board as in the above embodiment and a plurality of electronic devices electrically connected by the flexible printed wiring board are within the intended range.

  The present invention can be suitably used, for example, as a flexible printed wiring board that transmits a high-frequency signal.

DESCRIPTION OF SYMBOLS 1 Flexible printed wiring board 2 Dielectric layer 3 Signal line pattern layer 4 Ground layer 6 First insulating film 7 First laminated body 8 Second insulating film 9 Second laminated body 10 Adhesive layer 11 Coverlay 12 Signal line 13 Shield wiring 13a Longitudinal part 13b Joint part 14 Second shield wiring 15 Input / output part 16 Through hole

Claims (7)

A flexible printed wiring board with a shielding function, comprising a dielectric layer having flexibility, a signal line pattern layer laminated on one surface side of the dielectric layer, and a ground layer laminated on the other surface side of the dielectric layer Because
The flexible printed wiring board, wherein the signal line pattern layer includes a signal line and a shield wiring continuously disposed so as to surround the signal line.   The flexible printed wiring board according to claim 1, wherein the ground layer is formed in a solid shape. The average distance (H) in the thickness direction between the signal line and the ground layer is 25 μm or more and 200 μm or less,
The average width (W1) of the signal line is 25 μm or more and 500 μm or less,
The apparent dielectric constant of the dielectric layer is 2.0 or more and 4.0 or less,
The average thickness (T1) of the signal line and shield wiring is 5 μm or more and 40 μm or less,
The flexible printed wiring board according to claim 2, wherein an average interval (W2) in the width direction between the signal line and the shield wiring is 50 μm or more and 1000 μm or less. A first laminate having the signal line pattern layer and a first insulating film on which the signal line pattern layer is laminated;
3. A second laminated body having the ground layer and a second insulating film on which the ground layer is laminated, and an adhesive layer for bonding the first laminated body and the second laminated body. Or the flexible printed wiring board of Claim 3.   The flexible printed wiring board according to claim 4, wherein a main component of the first insulating film or the second insulating film is a liquid crystal polymer. The signal line pattern layer is laminated on the surface of the first insulating film facing the second laminate,
The first laminated body further includes a second shield wiring that is laminated on a surface of the first insulating film opposite to a surface on which the signal line pattern layer is laminated, and a region overlapping the shield wiring in a plan view. The flexible printed wiring board according to claim 4 or 5.   An electronic component comprising the flexible printed wiring board according to any one of claims 1 to 6.

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