JP2009200108A - Wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board equipped with a capacitor for AC coupling available for high speed transmission of several tens of bps. <P>SOLUTION: A wiring board 1 is equipped with an insulating layer 6 of a prescribed thickness, a first signal layer 7 formed on one surface of the insulating layer 6, and a second signal layer 8 formed on the other surface of the insulating layer 6. The first signal layer 7 is equipped with a first signal line 4 and a first signal pad 2. The first signal pad 2 is electrically connected to the end of the first signal line 4 and has a prescribed area. The second signal layer 8 is equipped with a second signal line 5 and a second signal pad 3. The second signal pad 3 is electrically connected to the end of the second signal line 5 and has a prescribed area. The first signal pad 2 is disposed opposite to the second signal pad 3 with an insulating layer 6 between them to form a capacitor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wiring board used for AC coupling (AC coupling).

  As the performance of electronic equipment such as computers improves, the frequency of signal transmission inside the electronic equipment has been increasing year by year. For example, there are electronic devices that require transmission speeds ranging from 10 Gbps to several tens of Gbps. In such high-speed transmission, AC coupling (AC coupling) is generally performed in which a DC component is cut and only a high-frequency signal of a signal component is allowed to pass. AC coupling is realized by inserting a capacitor in series on the signal wiring.

  For example, Patent Document 1 discloses a printed circuit board having a built-in bypass capacitor for eliminating noise included in a high-frequency signal. In the printed circuit board having a built-in capacitor described in Patent Document 1, the ferroelectric layer is sandwiched between the first low dielectric layer and the second low dielectric layer, and the ferroelectric layer and the first low dielectric are Conductor pads are disposed on the boundary surface between the ferroelectric layer and the second low dielectric layer so as to face each other with the ferroelectric layer interposed therebetween, and a pair disposed so as to face each other. And a ferroelectric layer portion sandwiched between the pair of conductor pads to form a capacitor, and a boundary surface between the ferroelectric layer and the first low dielectric layer and / or the second low dielectric layer A signal line for transmitting a high-frequency signal is formed at a portion different from the conductor pad of the first low dielectric layer on the side opposite to the ferroelectric layer side with respect to the signal line. Or / and matched to a predetermined value by the ground layer provided on the outer surface of the second low dielectric layer. It becomes Te.

Japanese Patent No. 3625394

  The following analysis is given from the perspective of the present invention.

  The ideal frequency characteristic of the capacitor is such that the impedance decreases as the frequency increases as shown in FIG. However, in practice, the impedance increases as shown in FIG. 6 when the frequency exceeds a certain frequency due to the inductor component (ESL) due to the lead wire or electrode pattern of the capacitor itself. This frequency is about several hundred MHz to several GHz for a general capacitor. Therefore, in the AC coupling generally used in serial transmission, when such a capacitor is inserted in series in the signal line for AC coupling of a high-speed signal having a transmission frequency of several tens of Gbps, the signal increases due to an increase in impedance. The component is attenuated and signal transmission becomes difficult. There are also special capacitors with excellent frequency characteristics, but they are expensive.

  Further, when the capacitor is mounted on the substrate, it is necessary to provide the signal wiring on the surface layer. Therefore, the impedance mismatch of the via hole or the through hole affects the signal transmission, and also increases the number of parts.

  In the printed circuit board in which the capacitor is built in Patent Document 1, since the conductor pad and the signal line are formed in different portions, the capacitor cannot efficiently AC-couple the transmission signal.

  An object of the present invention is to provide a wiring board including a capacitor for AC coupling that can be used in high-speed transmission of several tens of bps class.

  According to the first aspect of the present invention, the wiring board of the present invention includes an insulating layer having a predetermined thickness, a first signal layer formed on one surface of the insulating layer, and a second surface of the insulating layer. And a formed second signal layer. The first signal layer includes a first signal line and a first signal pad that is electrically connected to an end of the first signal line and has a predetermined area. The second signal layer includes a second signal line and a second signal pad that is electrically connected to an end of the second signal line and has a predetermined area. The first signal pad and the second signal pad are opposed to each other through an insulating layer so as to form a capacitor.

  According to the second aspect of the present invention, the wiring board of the present invention is formed such that a first insulating layer having a predetermined thickness and one surface side of the first insulating layer face each other. A second insulating layer; a first signal layer formed between the first insulating layer and the second insulating layer; a second signal layer formed on the other surface of the first insulating layer; and the other of the second insulating layer. And a power supply layer or a ground layer formed on the surface. The first signal layer includes a first signal line and a first signal pad that is electrically connected to an end of the first signal line and has a predetermined area. The second signal layer includes a second signal line and a second signal pad that is electrically connected to an end of the second signal line and has a predetermined area. The first signal pad and the second signal pad are opposed to each other through the first insulating layer so as to form a capacitor. The power supply layer or the ground layer does not have a conductor layer at least in a region facing the first signal pad.

  The present invention has at least one of the following effects.

  According to the present invention, even a high frequency signal of several tens of Gbps can be AC-coupled without being affected by the inductor component due to the capacitor.

  According to the present invention, the equalizer function can be provided by adjusting the capacitor capacity.

  According to the present invention, it is possible to contribute to at least one of a reduction in mounting area, a reduction in the number of components, and a reduction in cost.

  According to the present invention, since a through hole or a via hole is unnecessary, signal transmission is not affected by these effects.

  A wiring board according to a first embodiment of the present invention will be described. FIG. 1 shows a schematic perspective view of a wiring board according to the first embodiment of the present invention. FIG. 2 shows an electrical conceptual diagram of the wiring board according to the first embodiment of the present invention. The wiring substrate 1 includes an insulating layer 6 having a predetermined thickness, a first signal layer 7 formed on one surface of the insulating layer 6, and a second signal layer 8 formed on the other surface of the insulating layer 6. And have.

  The first signal layer 7 is wired with a first signal line 4 and a first signal pad 2 electrically connected to an end of the first signal line 4 and having a predetermined area. On the other hand, the second signal layer 8 is similarly wired with the second signal line 5 and the second signal pad 3 electrically connected to the end of the second signal line 5 and having a predetermined area. Yes. The first signal pad 2 and the second signal pad 3 are disposed to face each other with an insulating layer 6 therebetween so as to form a capacitor 9. Accordingly, the first signal pad 2, the second signal pad 3, and the insulating layer 6 are capacitors that AC-couple the transmission signal of the first signal line 4 and the transmission signal of the second signal line 5, as shown in FIG. 9 will be operated.

  FIG. 3 is an electric circuit diagram showing an example of use of the wiring board of the present invention. A first signal line 4 is connected to the transmission circuit 10 as a transmission line, and a second signal line 5 is connected to the reception circuit 11 as a transmission line. A signal transmitted between the transmission circuit 10 and the reception circuit 11 is AC-coupled by a capacitor 9 formed by the first signal pad 2, the second signal pad 3, and the insulating layer 6.

Capacitor capacitance C is expressed by the following equation 1, relative permittivity ε _r of insulating layer 6, area S of first signal pad 2 and second signal pad 3, distance between first signal pad 2 and second signal pad 3. (Thickness of the insulating layer 6) d is determined. In Expression 1, ε ₀ is a vacuum dielectric constant (8.85 × 10 ⁻¹² F / m).
[Formula 1]
C = ε ₀ × ε _r × (S / d)

For example, the pad area S of the first signal pad 2 and the second signal pad 3 is 4 mm ² (2 mm square), the thickness d of the insulating layer 6 is 35 μm, and the relative dielectric constant ε _r of the insulating layer 6 is 3 The capacitor capacitance C when .46 is set is about 3.5 pF, and the impedance is about 2Ω in 40 Gbps transmission. The low frequency component that increases the impedance exhibits the effect of equalization.

  Next, a wiring board according to a second embodiment of the present invention will be described. FIG. 4 is a schematic perspective view of a wiring board according to the second embodiment of the present invention. The wiring board 21 has in its part a configuration corresponding to the wiring board 1 according to the first embodiment. Further, the wiring substrate 21 further includes a second insulating layer 26 formed so that one surface side and one surface of the first insulating layer 6 face each other with the first signal layer 7 interposed therebetween, and a second insulating layer. 26 has a solid pattern power supply layer or ground layer 28 formed on the other surface. Thus, the first signal layer 7 is disposed between the first insulating layer 6 and the second insulating layer 26 and faces the power supply layer or the ground layer 28 via the second insulating layer 26. Become.

  The power supply layer or the ground layer 28 has a clearance portion 23 from which at least a solid pattern (conductor layer) in a region facing the first signal pad 2 is deleted. Thereby, formation of a capacitor between the first signal pad 2 and the power supply layer or the ground layer 28, that is, AC coupling with the power supply layer or the ground layer 28 can be prevented.

  In the present embodiment, the power supply layer or ground layer 28 faces only one signal layer (first signal layer 7), but the power supply layer faces one signal layer (first signal layer 7). However, in the form in which the ground layer is opposed to the other signal layer (second signal layer 8), a clearance portion can be formed in both the power supply layer and the ground layer.

  The wiring board of the present invention has been described based on the above-described embodiment, but is not limited to the above-described embodiment, and is within the scope of the present invention and based on the basic technical idea of the present invention. It cannot be overemphasized that various deformation | transformation, a change, and improvement with respect to a form can be included. Further, various combinations, substitutions, or selections of various disclosed elements are possible within the scope of the claims of the present invention.

  Further problems, objects, and developments of the present invention will become apparent from the entire disclosure of the present invention including the claims.

1 is a schematic perspective view of a wiring board according to a first embodiment of the present invention. The electrical conceptual diagram of the wiring board which concerns on 1st Embodiment of this invention. The electric circuit diagram which shows the utilization example of the wiring board which concerns on 1st Embodiment of this invention. The schematic perspective view of the wiring board which concerns on 2nd Embodiment of this invention. Schematic of ideal frequency characteristics of a general capacitor. Schematic diagram of actual frequency characteristics of a general capacitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,21 Wiring board 2 1st signal pad 3 2nd signal pad 4 1st signal line 5 2nd signal line 6 (1st) Insulation layer 7 1st signal layer 8 2nd signal layer 9 Capacitor 10 Transmission circuit 11 Reception circuit 23 Clearance part 26 Second insulating layer 28 Power supply layer or ground layer

Claims (2)

An insulating layer having a predetermined thickness;
A first signal layer formed on one surface of the insulating layer;
A second signal layer formed on the other surface of the insulating layer, and a wiring board comprising:
The first signal layer includes a first signal line and a first signal pad electrically connected to an end of the first signal line and having a predetermined area;
The second signal layer includes a second signal line, and a second signal pad that is electrically connected to an end of the second signal line and has a predetermined area.
The wiring board according to claim 1, wherein the first signal pad and the second signal pad are opposed to each other through the insulating layer so as to form a capacitor. A first insulating layer having a predetermined thickness;
A second insulating layer formed so that one surface side and one surface of the first insulating layer face each other;
A first signal layer formed between the first insulating layer and the second insulating layer;
A second signal layer formed on the other surface of the first insulating layer;
A power supply layer or a ground layer formed on the other surface of the second insulating layer,
The first signal layer includes a first signal line and a first signal pad electrically connected to an end of the first signal line and having a predetermined area;
The second signal layer includes a second signal line, and a second signal pad that is electrically connected to an end of the second signal line and has a predetermined area.
The first signal pad and the second signal pad are opposed to each other through the first insulating layer so as to form a capacitor,
The wiring board according to claim 1, wherein the power supply layer or the ground layer does not have a conductor layer at least in a region facing the first signal pad.

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