JP2014060367A - Electronic apparatus and flexible wiring member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic apparatus having a flexible wiring member capable of improving high-speed transmission characteristics while improving flexibility.SOLUTION: A flexible wiring member comprises: an insulating layer; a first conductor line; a second conductor line; and a shield layer. The first conductor line is provided on a first surface of the insulating layer. The second conductor line is provided on the first surface of the insulating layer, and passes a current having an opposite phase to a current flowing through the first conductor line or is electrically connected to the ground. The shield layer is provided on a second surface of the insulating layer and has larger electrical resistivity than the first conductor line. When the width of the first conductor line is w, the distance between the first conductor line and the second conductor line is s, the thickness of the first conductor line is t, and the distance between the first conductor line and the shield layer is h, the following formula is satisfied: th/ws≥0.225.

Description

  Embodiments described herein relate generally to a flexible wiring member and an electronic apparatus having the flexible wiring member.

  There has been proposed a printed circuit board having an insulating layer, a conductor line provided on the insulating layer, and a ground layer provided on the opposite side of the conductor line with the insulating layer interposed therebetween. The conductor line and the ground layer are formed of the same material (for example, copper).

JP 2006-165438 A

  In recent years, flexible wiring members used in high-speed digital devices are required to have improved flexibility and high-speed transmission characteristics in addition to improved EMC (Electro-Magnetic Compatibility).

  Here, in order to improve the flexibility, it is conceivable to form the shield layer with a material softer than copper instead of the copper ground layer. However, materials that are softer than copper generally have a higher electrical resistivity than copper. For this reason, when the shield layer is formed of a material softer than copper, a signal flowing through the conductor line is greatly attenuated, and it is difficult to improve high-speed transmission characteristics.

  The objective of this invention is providing the flexible wiring member and electronic device which can aim at the improvement of a high-speed transmission characteristic, aiming at the improvement of a flexibility.

  According to one embodiment, an electronic device includes a housing and a flexible wiring member accommodated in the housing. The flexible wiring member includes an insulating layer, a first conductor line, a second conductor line, and a shield layer. The insulating layer includes a first surface and a second surface located on the opposite side of the first surface. The first conductor line is provided on the first surface of the insulating layer, and a signal flows. The second conductor line is provided on the first surface of the insulating layer, and a signal having a phase opposite to that of the first conductor line flows or is electrically connected to the ground. The shield layer is provided on the second surface of the insulating layer, includes a conductive material different from that of the first conductor line, and has a higher electrical resistivity than the first conductor line. The width of the first conductor line is w, the distance between the first conductor line and the second conductor line is s, the thickness of the first conductor line is t, and the first conductor line and the shield layer are When the distance between them is h, th / ws ≧ 0.225.

The perspective view of the electronic device which concerns on one embodiment. Sectional drawing of the flexible wiring member shown in FIG. The figure which shows typically the connection relation inside the flexible wiring member shown in FIG. The figure which shows the attenuation factor of the transmission line of the flexible wiring member shown in FIG.

  In the present specification, examples of a plurality of expressions are given to some elements. Note that these examples of expressions are merely examples, and do not deny that the above elements are expressed in other expressions. In addition, elements to which a plurality of expressions are not attached may be expressed in different expressions.

Hereinafter, embodiments will be described with reference to the drawings.
1 to 4 show an electronic apparatus 1 according to one embodiment. As shown in FIG. 1, an electronic apparatus 1 according to the present embodiment is a tablet portable computer (tablet terminal, slate PC). Note that electronic devices to which the present embodiment is applicable are not limited to the above examples. The present embodiment can be widely applied to various electronic devices such as a notebook portable computer, a television receiver, a mobile phone (including a smartphone), and a game machine.

  As shown in FIG. 1, the electronic device 1 has a flat housing 2, for example. The housing 2 accommodates a display device 3 (first module, first device, first unit) and a circuit board 4 (second module, second device, second unit). The electronic device 1 further includes a flexible wiring member 5 provided between the display device 3 and the circuit board 4.

  The flexible wiring member 5 is, for example, a flexible printed wiring board (FPC) or a flexible flat cable (FFC). The flexible wiring member 5 is a flat connection member having flexibility (flexibility, flexibility). A first end of the flexible wiring member 5 is connected to the display device 3. The second end of the flexible wiring member 5 is connected to the circuit board 4. Thereby, the flexible wiring member 5 electrically connects the display device 3 and the circuit board 4.

  Next, the flexible wiring member 5 according to the present embodiment will be described with reference to FIGS. The flexible wiring member 5 is, for example, a shielded FPC. As shown in FIG. 2, the flexible wiring member 5 includes a first insulating layer 11 (base), a first conductor line 12, a second conductor line 13, a second insulating layer 14 (cover), and a shield layer 15.

  The first insulating layer 11 is provided over the entire length of the flexible wiring member 5 and forms the main body of the flexible wiring member 5. The first insulating layer 11 has a first surface 11a and a second surface 11b located on the opposite side of the first surface 11a. The first surface 11 a and the second surface 11 b extend in the extending direction of the flexible wiring member 5. That is, the first surface 11 a and the second surface 11 b spread in a direction intersecting with the thickness direction of the flexible wiring member 5. The material of the first insulating layer 11 is, for example, polyimide, but is not limited to this.

  As shown in FIG. 2, the first conductor line 12 and the second conductor line 13 are provided on the first surface 11 a of the first insulating layer 11. The first conductor line 12 and the second conductor line 13 extend linearly in the extending direction of the flexible wiring member 5 (the depth direction in the drawing). The first conductor line 12 and the second conductor line 13 extend in parallel to each other. The first conductor line 12 and the second conductor line 13 are made of, for example, copper. The first conductor line 12 and the second conductor line 13 have, for example, the same thickness.

  The first conductor line 12 and the second conductor line 13 according to the present embodiment are a pair of signal lines used in a differential mode (differential mode). That is, the first conductor line 12 and the second conductor line 13 constitute a transmission line through which a differential signal flows. That is, signals having opposite phases flow through the first conductor line 12 and the second conductor line 13.

  In one modification of the present embodiment, the second conductor line 13 may be electrically connected to the ground. That is, the first conductor line 12 and the second conductor line 13 may be signal lines used for single-ended transmission.

  As shown in FIG. 2, the second insulating layer 14 is laminated on the first surface 11 a of the first insulating layer 11. The second insulating layer 14 covers the first conductor line 12 and the second conductor line 13. Thereby, the 1st conductor track 12 and the 2nd conductor track 13 are protected from the outside.

  As shown in FIG. 2, a shield layer 15 (ground layer) is provided on the second surface 11 b of the first insulating layer 11. The shield layer 15 is provided, for example, at substantially the entire width of the flexible wiring member 5. The shield layer 15 faces the first conductor line 12 and the second conductor line 13 with the first insulating layer 11 interposed therebetween. That is, the shield layer 15 covers the first conductor line 12 and the second conductor line 13 with the first insulating layer 11 interposed therebetween.

  The shield layer 15 is electrically connected to the ground. The shield layer 15 functions as a shield that suppresses unnecessary radiation (noise) radiated from the first conductor line 12 and the second conductor line 13.

  The shield layer 15 includes a conductive material different from that of the first conductor line 12 and the second conductor line 13. The shield layer 15 is formed of a conductive material that is softer than the material of the first conductor line 12 and the second conductor line 13. The shield layer 15 is made of a conductive material softer than copper, for example. By forming the shield layer 15 with a material softer than copper, the flexible wiring member 5 has great flexibility (high flexibility).

  In the present embodiment, the shield layer 15 is formed by curing, for example, an adhesive containing an anisotropic conductor (conductive adhesive) or a conductive paste (eg, silver paste). The shield layer 15 may be formed by sputtering. The shield layer 15 may be sputtered on the adhesive or paste, for example. The shield layer 15 may be formed by laminating the above-described plurality of materials. The shield layer 15 may be formed of a material other than the above.

  On the other hand, the shield layer 15 made of the material as described above is inferior in electrical resistivity (conductivity) as compared with a copper ground layer. That is, the shield layer 15 has a larger electrical resistivity than the first conductor line 12 and the second conductor line 13. For this reason, the signal flowing through the first conductor line 12 and the second conductor line 13 is attenuated by the influence of the shield layer 15. In other words, the shield layer 15 serves as an attenuator for signals flowing through the first conductor line 12 and the second conductor line 13. Attenuating the signal adversely affects high-speed transmission characteristics.

  Therefore, in this embodiment, in order to reduce the attenuation, the dimensions of each component are adjusted based on the following equation (1).

That is, as shown in FIG. 2, the width (line width, wiring width) of the first conductor line 12 is w, the distance (space interval) between the first conductor line 12 and the second conductor line 13 is s, When the thickness of the one conductor line 12 is t and the distance between the first conductor line 12 and the shield layer 15 (the thickness of the first insulating layer 11) is h, the following expression (1) is satisfied.
th / ws ≧ 0.225 (1)
As shown in FIG. 2, in this embodiment, the distance h between the first conductor line 12 and the shield layer 15 (the thickness h of the first insulating layer 11) is the first conductor line 12 and the second conductor line. 13 is smaller than the distance s. Furthermore, the distance h between the first conductor line 12 and the shield layer 15 (the thickness h of the first insulating layer 11) is smaller than the width w of the first conductor line 12. Further, the distance s between the first conductor line 12 and the second conductor line 13 is smaller than the width w of the first conductor line 12.

Next, the technical meaning of the formula (1) will be described.
As described above, the signal flowing through the first conductor line 12 is attenuated because the first conductor line 12 is coupled to the shield layer 15 having a relatively large electrical resistivity.

  Therefore, in order to suppress signal attenuation, it is conceivable to increase the distance h between the first conductor line 12 and the shield layer 15 (thickness h of the first insulating layer 11). However, if the thickness h of the first insulating layer 11 is increased, the flexibility of the flexible wiring member 5 is lowered. In order to improve the flexibility, the thickness h of the first insulating layer 11 must be reduced. That is, the improvement in flexibility and the improvement in high-speed transmission characteristics require mutually conflicting conditions.

Therefore, the present inventors have introduced a new concept of a coupling ratio R (= th / ws), and have sought a range in which improvement in flexibility and improvement in high-speed transmission characteristics can be realized simultaneously.
Specifically, as shown in FIG. 3, when the coupling is considered as the capacitance of the capacitor, the degree of coupling between the signal and the shield can be represented by w / h. On the other hand, the degree of coupling between signals can be expressed as t / s. Therefore, the coupling ratio R of the coupling degree between the signals with respect to the coupling degree between the signal and the shield can be expressed as the following formula (2).
R = (t / s) / (w / h) = th / ws (2)
If the coupling ratio R increases, it means that the coupling between the signal and the shield is relatively small and the coupling between the signals is relatively large. That is, even when the thickness h of the first insulating layer 11 is reduced, the width w of the first conductor line 12, the first conductor line 12, and the second conductor line 13 are set so that the coupling ratio R is sufficiently large. The present inventors have found that the high-speed transmission characteristics can be improved by adjusting the distance s between the first conductor line 12 and the thickness t of the first conductor line 12.

  Therefore, the present inventors conducted experiments under various conditions to determine the range of the coupling ratio R in which the signal attenuation is sufficiently small. Note that the criterion for determining that the attenuation is sufficiently small was “the bandwidth per 10 cm is 1 Gbps or more”, which is a standard for high-speed transmission characteristics in the FPC field.

A part of the result of the experiment is shown in Table 1.

  The “wiring width w” in Table 1 is the width w of the first conductor line 12, and the “wiring interval s” is the distance s between the first conductor line 12 and the second conductor line 13. The “insulating layer thickness h” corresponds to the distance h between the first conductor line 12 and the shield layer 15, and the “signal conductor thickness t” corresponds to the thickness t of the first conductor line 12.

  As shown in Table 1, in the range of the coupling ratio R ≧ 0.225, a band of 1 Gbps or more is secured regardless of the size of the wiring width w, the wiring interval s, and the insulating layer thickness h. That is, even when the thickness h of the first insulating layer 11 is reduced in order to improve the flexibility, by adjusting the dimensions of the other components so that the coupling ratio R falls within the above range, high-speed transmission is possible. The characteristics can be secured at the same time. On the other hand, it can be seen that a flexible wiring member whose coupling ratio R is not adjusted to the above conditions is difficult to secure a sufficient band stably and is not suitable for a high-speed circuit.

  FIG. 4 shows a graph of the attenuation rate under conditions A and D in Table 1. As shown in FIG. 4, it can be seen that there is a difference of about double in the characteristic difference between the transmission path of the condition A in which the predetermined adjustment is performed with respect to the coupling ratio R and the transmission path of the condition D in which the predetermined adjustment is not performed. .

  Note that if the distance s between the first conductor line 12 and the second conductor line 13 is too small, the high-speed transmission characteristics may be deteriorated due to the proximity effect. Therefore, it is more preferable that the coupling ratio R is adjusted in the range of s ≧ 25 μm. In order to further improve the flexibility and high-speed transmission characteristics at the same time, it is more preferable that the coupling ratio R is adjusted in the range of 25 μm ≦ s ≦ 40 μm.

  According to the flexible wiring member 5 having such a configuration, it is possible to improve high-speed transmission characteristics while improving flexibility. That is, the flexible wiring member 5 according to the present embodiment includes the insulating layer 11, the first conductor line 12, the second conductor line 13, and the shield layer 15. The first conductor line 12 is provided on the first surface 11 a of the first insulating layer 11. The second conductor line 13 is provided on the first surface 11 a of the insulating layer 11, and a signal having a phase opposite to that of the first conductor line 12 flows. The shield layer 15 is provided on the second surface 11 b of the insulating layer 11, includes a conductive material different from the first conductor line 12, and has a higher electrical resistivity than the first conductor line 12.

  In the present embodiment, the shield layer 15 is formed of a material softer than the material of the first conductor line 12. For this reason, the flexible wiring member 5 which concerns on this embodiment is excellent in a flexibility. In addition, since the shield layer 15 is provided, good EMC (Electro-Magnetic Compatibility) is ensured.

  On the other hand, the shield layer 15 of the flexible wiring member 5 according to this embodiment has a larger electrical resistivity than the first conductor line 12. For this reason, the signal flowing through the flexible wiring member 5 is likely to be attenuated due to the influence of the shield layer 15.

  However, the dimensions of each part of the flexible wiring member 5 according to the present embodiment are adjusted by a new concept parameter called the coupling ratio R. That is, the flexible wiring member 5 according to the present embodiment has the width w of the first conductor line 12, the first conductor line 12, and the second conductor line 13 so that the condition of the coupling ratio R ≧ 0.225 is satisfied. The distance s between them, the thickness t of the first conductor line 12, and the distance h between the first conductor line 12 and the shield layer 15 (thickness h of the first insulating layer 11) are adjusted.

  As long as the above condition of the coupling ratio R is satisfied, even if the dimensions of each part are set variously, there is no significant attenuation and a sufficiently large band can be secured. As a result, it is possible to improve high-speed transmission characteristics while improving flexibility. The flexible wiring member 5 according to the present embodiment is suitable for a digital product device having a high-speed circuit of USB 2.0 (480 Mbps) or higher, for example.

  Here, for comparison, consider a case where two lines of the first conductor line 12 and the second conductor line 13 are used in single-ended transmission. In this case, if an attempt is made to reduce the distance s between the first conductor line 12 and the second conductor line 13, the crosstalk between the two lines increases, causing noise. For this reason, it is difficult to reduce the distance s between the first conductor line 12 and the second conductor line 13.

  In addition, when two lines of the first conductor line 12 and the second conductor line 13 are used for single-ended transmission, the return current passes through the shield layer 15, so that the transmission characteristics are deteriorated. This is the same when the first conductor line 12 and the second conductor line 13 are used in the common mode.

  On the other hand, the first conductor line 12 and the second conductor line 13 according to the present embodiment are used in a differential mode. In this case, if the coupling between the two lines is strengthened, the return current flows so as not to pass through the shield layer 15 but to pass through the counterpart line (precisely cancel each other). For this reason, transmission characteristics can be improved. Similarly, even in the case of single-ended transmission in which one of the two lines is electrically connected to the ground, the return current does not pass through the shield layer 15 but passes through the counterpart line. For this reason, transmission characteristics can be improved.

  In the present embodiment, the distance h between the first conductor line 12 and the shield layer 15 is smaller than the distance s between the first conductor line 12 and the second conductor line 13. According to such a configuration, since the thickness h of the insulating layer 11 can be sufficiently reduced, the flexibility of the flexible wiring member 5 can be further improved while improving the high-speed transmission characteristics.

  In the present embodiment, the distance h between the first conductor line 12 and the shield layer 15 is smaller than the width w of the first conductor line 12. According to such a configuration, since the thickness h of the insulating layer 11 can be sufficiently reduced, the flexibility of the flexible wiring member 5 can be further improved while improving the high-speed transmission characteristics.

  In the present embodiment, the distance s between the first conductor line 12 and the second conductor line 13 is smaller than the width w of the first conductor line 12. According to such a configuration, since the coupling ratio R can be easily set relatively high, the flexibility of the flexible wiring member 5 and the high-speed transmission characteristics can be further improved.

  In the present embodiment, the shield layer 15 is formed of a conductive adhesive or a conductive paste. According to such a configuration, since the shield layer 15 is sufficiently soft, the flexibility of the flexible wiring member 5 can be further improved.

  Note that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

  For example, in the experimental results of Table 1, the thickness t of the first conductor line 12 is constant, but the embodiment is not limited to this. The thickness t of the first conductor line 12 may be arbitrarily changed in the same manner as the dimensions of other components. In addition, as long as the coupling ratio R satisfies the above conditions, the size relationship between the constituent elements is not limited to the above example.

  DESCRIPTION OF SYMBOLS 1 ... Electronic device, 2 ... Housing | casing, 5 ... Flexible wiring member, 11 ... Insulating layer, 11a ... 1st surface, 11b ... 2nd surface, 12 ... Conductor line, 13 ... Conductor line, 14 ... Insulating layer, 15 ... Shield layer.

Claims (10)

A housing,
A flexible wiring member housed in the housing,
The flexible wiring member is
An insulating layer including a first surface and a second surface located opposite to the first surface;
A first conductor line provided on the first surface of the insulating layer and through which a signal flows;
A second conductor line provided on the first surface of the insulating layer and having a signal that is opposite in phase to the first conductor line, or electrically connected to ground;
A shield layer provided on the second surface of the insulating layer, including a conductive material different from the first conductor line, and having a higher electrical resistivity than the first conductor line;
Have
The width of the first conductor line is w, the distance between the first conductor line and the second conductor line is s, the thickness of the first conductor line is t, and the first conductor line and the shield layer are When the distance between is h,
th / ws ≧ 0.225
Is an electronic device. In the description of claim 1,
The first conductor line and the second conductor line are electronic devices through which a differential signal flows. In the description of claim 1 or claim 2,
An electronic device in which a distance between the first conductor line and the shield layer is smaller than a distance between the first conductor line and the second conductor line. In any one of Claims 1 to 3,
The distance between the said 1st conductor track | line and the said shield layer is an electronic device smaller than the width | variety of the said 1st conductor track | line. In any one of Claims 1 to 4,
An electronic apparatus in which a distance between the first conductor line and the second conductor line is smaller than a width of the first conductor line. In any one of Claims 1 to 5,
The shield layer is an electronic device formed of a conductive adhesive or a conductive paste. An insulating layer including a first surface and a second surface located opposite to the first surface;
A first conductor line provided on the first surface of the insulating layer and through which a signal flows;
A second conductor line provided on the first surface of the insulating layer and having a signal that is opposite in phase to the first conductor line, or electrically connected to ground;
A shield layer provided on the second surface of the insulating layer, including a conductive material different from the first conductor line, and having a higher electrical resistivity than the first conductor line;
Have
The width of the first conductor line is w, the distance between the first conductor line and the second conductor line is s, the thickness of the first conductor line is t, and the first conductor line and the shield layer are When the distance between is h,
th / ws ≧ 0.225
A flexible wiring member. In the description of claim 7,
The first conductor line and the second conductor line are flexible wiring members through which differential signals flow. In the description of claim 7 or claim 8,
The flexible wiring member, wherein a distance between the first conductor line and the shield layer is smaller than a distance between the first conductor line and the second conductor line. In any one of Claims 7 thru | or 9,
The flexible wiring member, wherein a distance between the first conductor line and the shield layer is smaller than a width of the first conductor line.

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