JP2004304134A - Wiring board and manufacturing method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board capable of reducing the influence of crosstalk noise even when high density mounting is conducted by using a one-to-one differential transmission system. <P>SOLUTION: This wiring board has at least a pair of wirings 4 forming a differential transmission line 3 among lines constituting a microstrip line by the differential transmission line 3 and a ground conductor 2. The differential transmission line 3 has a dielectric 6, which connects between the respective wirings 4 constituting the differential transmission line 3, with the relative permittivity higher than that of dielectrics arranged between air and the other pair of the differential transmission lines 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wiring board having a microstrip line structure having a plurality of differential transmission lines and a method for manufacturing the same.
[0002]
[Prior art]
2. Description of the Related Art In recent years, in electronic devices such as notebook personal computers, the operating frequency of a mounted microprocessor has entered the order of GHz, and rapid improvement has been achieved. However, the signal speed propagating through the printed circuit board is still, for example, about 133 MHz or 266 MHz in terms of the signal speed between the memory and the memory controller.
[0003]
This is due to the use of branch wiring as the form of the transmission line in order to transmit signals from the memory controller to a plurality of memories. That is, if there is a branch in the transmission line, the waveform of the pulse signal is disturbed due to reflection at the branch point, and there is a limit in increasing the transmission speed.
[0004]
Therefore, as a solution for increasing the signal transmission speed on a substrate, it has been studied to use a one-to-one transmission method to eliminate wiring branching and to use differential wiring. Normally, the differential transmission system has an advantage that it is more resistant to common mode noise due to the swing of the ground plane than the single-ended transmission system using the return current of a signal as the ground plane.
[0005]
However, when the one-to-one differential transmission system is used, while having the above-described advantages, the number of wirings is twice as large as the number of memories as compared with a wiring structure having branches. Therefore, a large wiring area is required to transmit a plurality of signals through the one-to-one differential transmission line.
[0006]
In high-speed data transmission, a wiring board having a microstrip line structure is often used. As shown in FIG. 5, this wiring board has a dielectric board b provided with a ground plane conductor a on the lower surface. The plurality of differential transmission lines c (only two are shown) are provided on the upper surface of the dielectric substrate b, and a dielectric layer d is provided thereon so as to cover the differential transmission lines c. b It is formed to a substantially uniform thickness over the entire surface.
[0007]
As shown in FIG. 6A, signals having mutually opposite voltage amplitudes are transmitted to each of the wires constituting each differential transmission line. Therefore, the electromagnetic field generated by signal transmission has a distribution that closes in these wirings, but also in wirings between other adjacent differential transmission lines, when these have voltage amplitudes in opposite directions, Large electromagnetic interference may occur, and may appear as crosstalk noise between the differential transmission lines as shown in FIG.
[0008]
Therefore, as shown in FIG. 5, in the conventional configuration, the crosstalk noise between the differential transmission lines is reduced by setting the wiring pitch between the differential transmission lines to about twice the width of the wiring. Was.
[0009]
[Problems to be solved by the invention]
Therefore, in the above-described wiring board, there is a limit in narrowing the pitch interval between the differential transmission lines, and large crosstalk noise may occur when mounted at high density.
[0010]
The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the influence of crosstalk noise even when high-density mounting is performed using a one-to-one differential transmission system. It is to provide a substrate.
[0011]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object, the present invention is configured as follows.
[0012]
(1) A wiring board having at least one set of wirings forming a differential transmission line among lines forming a microstrip line by a transmission line and another conductive layer, wherein the differential transmission line is It has a dielectric portion having a higher relative dielectric constant than a dielectric disposed between air and another pair of differential transmission lines, which connects between respective wirings constituting the dynamic transmission line. I do.
[0013]
(2) The wiring board according to (1), wherein the dielectric portion is provided between opposing surfaces of the respective wirings constituting the differential transmission line.
[0014]
(3) A method for manufacturing a wiring board having at least one set of wirings forming a differential transmission line among lines constituting a microstrip line by a transmission line and another conductive layer, wherein the differential transmission line is A first supply step of supplying a first dielectric having a higher relative dielectric constant than air to each of the transmission lines and the gaps between the transmission lines, and a gap on the transmission lines and between the transmission lines. And a second supplying step of supplying a second dielectric having a relative permittivity smaller than that of the first dielectric.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0016]
FIG. 1 is a cross-sectional view showing a configuration of a wiring board according to a first embodiment of the present invention, FIG. 2A is a schematic diagram showing a signal transmitted through a differential transmission line, and FIG. FIG. 5 is a schematic diagram illustrating crosstalk noise generated between the differential transmission lines when the signal illustrated in FIG.
[0017]
The wiring board shown in FIG. 1 has a rectangular plate-shaped dielectric substrate 1. On the lower surface of the dielectric substrate 1, a thin plate-like ground conductor 2 (another conductive layer) is provided in close contact, and on the upper surface, a plurality of differential transmission lines 3 (only two pairs are shown) are provided at predetermined intervals G. In the present embodiment, they are arranged side by side with a gap 21 made of about 1 × 10 ⁻⁴ [m].
[0018]
Each differential transmission line 3 is composed of a pair of wirings 4 arranged substantially in parallel, and these wirings 4 have the same signal inverted in phase as indicated by + and-in FIG. Is transmitted in a state where As shown in FIG. 1, each wiring 4 is formed of a metal plate having a width of W, which is about 1 × 10 ⁻⁴ [m] in this embodiment. In the embodiment, the space portion 5 is formed of about 1 × 10 ⁻⁴ [m].
[0019]
A first dielectric 6 (dielectric part) is in close contact with the upper surface of the wiring 4 constituting the differential transmission line 3 and the space 5 between these wirings 4 so as to connect the two wirings 4. Is provided. As a material for the first dielectric 6, a solder resist made of an epoxy resin having a relative dielectric constant of 4 to 5 is used. That is, since the air layer outside the first dielectric 6 has a relative dielectric constant of approximately 1, the inside of each first dielectric 6 has a larger relative dielectric constant than its surroundings.
[0020]
Next, a method of forming the first dielectric 6 on the differential transmission line 3 provided on the upper surface of the dielectric substrate 1 will be described.
[0021]
When the first dielectric 6 is formed on the differential transmission line 3, screen printing is used. That is, by screen printing, on the upper surface of the dielectric substrate 1, the sum of the width dimension W of two wirings 4 and the spacing dimension S of the space portion 5 between the wirings 4, that is, 2W + S solder resist supply section 22, and This can be realized by alternately forming the solder resist non-supply portions 23 having the spacing dimension G between the differential transmission lines 3.
[0022]
However, in actuality, the solder resist supply unit 22 and the solder resist non-supply unit 23 may have substantially the same size in consideration of the spread of the applied solder resist. When screen printing is used in this manner, even when the wiring pitch becomes finer due to high-density mounting, it is possible to cope with the finer screen printing. Alternatively, the first dielectric 6 may be provided only between the wirings 4 that selectively form a pair using a photosensitive polyimide resin or epoxy resin.
[0023]
According to the wiring board having the above configuration, the first dielectric 6 is provided on the upper surfaces of the pair of wirings 4 constituting the differential transmission line 3 and on the space 5 between the wirings 4 so as to connect the two wirings 4. Was. That is, by making the relative dielectric constant around each differential transmission line 3 larger than the outside of the first dielectric 6, the relative dielectric constant in the gap between the adjacent differential transmission lines 3 is relatively reduced. . As a result, the value of the mutual capacitance between the differential transmission lines 3 relatively decreases, and the coupling capacitance between the differential transmission lines 3 decreases.
[0024]
Therefore, the electromagnetic field generated around each wiring 4 due to signal transmission concentrates inside the first dielectric 6 having a relatively large relative dielectric constant, so that the electromagnetic field is generated outside the first dielectric 6. Will be reduced. As a result, as shown in FIG. 2B, crosstalk noise generated between the differential transmission lines 3 can be reduced as compared with the conventional noise level shown in FIG. 6B.
[0025]
Since the relative permittivity is increased by providing the first dielectric 6 within each pair of wires 4 constituting the differential transmission line 3, the value of the mutual capacitance is increased, and mutual noise is received. Although it is easier, the same signal is transmitted to each wiring 4 in a state where the phases are inverted, and the receiving side inverts the phase of the signal from one wiring 4 and adds them up. Since the noise component is used, the noise component is canceled and the influence of the crosstalk noise is almost eliminated.
[0026]
FIG. 3 is a cross-sectional view illustrating a configuration of a wiring board according to a modified example of the first embodiment. In this modification, a second dielectric 7 is formed over the entire upper surface of the dielectric substrate 1 so as to cover the first dielectric 6 on the differential transmission line 3. As a material of the second dielectric 7, a material having a relative dielectric constant smaller than that of the first dielectric 6 is used.
[0027]
Therefore, as described above, the relative permittivity around the differential transmission line 3 can be made larger than the outside, so that the electromagnetic field generated by signal transmission can be concentrated inside the first dielectric 6. it can. Thereby, the influence of the crosstalk noise can be suppressed as described above.
[0028]
Further, by providing the second dielectric 7 in this manner, the first dielectric 6 can be formed of the first dielectric 6 without using a dielectric having a large relative dielectric constant. By using a dielectric having a relative permittivity smaller than that of the dielectric 6, the same effect as described above can be obtained. That is, it is only necessary that the relative permittivity of the first dielectric 6 can be made relatively larger than the relative permittivity of the second dielectric 7.
[0029]
Further, by forming a layer of the second dielectric 7 over the entire upper surface of the dielectric substrate 1, the entire surface of the wiring 4 can be covered with the second dielectric 7, so that the corrosion of the wiring 4 is prevented. can do.
[0030]
Next, a second embodiment of the present invention will be described with reference to FIG. Here, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
[0031]
FIG. 4 is a sectional view showing a configuration of a wiring board according to a second embodiment of the present invention. In the present embodiment, the first dielectric 6 is provided on the upper surface of each wiring 4 constituting the differential transmission line 3 and the space portion 5 between these wirings 4 in the first embodiment. On the other hand, the first dielectric 6 is provided only in the space 5 between the wirings 4.
[0032]
By providing the first dielectric 6 so as to fill the gap between the wirings forming the differential transmission line 3, the distribution of the electromagnetic field can be concentrated in one set of the differential transmission lines. Therefore, crosstalk noise can be further suppressed.
[0033]
The provision of the first dielectric 6 between the wirings 4 causes the characteristic impedance of the differential transmission line 3 to fluctuate. However, by considering in advance the value of the relative dielectric constant of the dielectric, the length and width of the wiring, and the like, it is possible to prevent the influence on the shape of the transmitted signal waveform.
[0034]
According to the above-described embodiment, the following configuration is obtained.
[0035]
(Supplementary Note 1) In a wiring board having a plurality of differential transmission lines 3 provided on a dielectric substrate 1 and having a pair of wirings arranged in parallel at a predetermined interval, the differential transmission lines 3 Wherein a dielectric is provided between the first transmission line 4 and the second transmission line 4 that form the wiring board.
[0036]
(Supplementary Note 2) A first dielectric is formed on the upper surface of the dielectric substrate 1 and a second dielectric layer is formed so as to cover the entire surface of the dielectric substrate 1, and the relative permittivity of the second dielectric is as described above. 2. The wiring board according to claim 1, wherein the relative dielectric constant of the dielectric board 1 itself is equal to that of the wiring board.
[0037]
It should be noted that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention at the stage of implementation. Various inventions can be formed by appropriately combining a plurality of components disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment.
[0038]
【The invention's effect】
According to the present invention, by concentrating the electromagnetic field generated around each wiring in the wiring pair, the electromagnetic field outside the wiring pair can be weakly suppressed, so that the crosstalk noise between adjacent differential transmission lines is suppressed. can do.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a configuration of a wiring board according to a first embodiment of the present invention;
FIGS. 2A and 2B show transmission signals according to the embodiment, FIG. 2A is a schematic diagram showing signals propagating through a differential transmission line, and FIG. 2B is a diagram showing the signal shown in FIG. FIG. 4 is a schematic diagram illustrating crosstalk noise generated between differential transmission lines when transmitting signals simultaneously.
FIG. 3 is an exemplary sectional view showing the configuration of a wiring board according to a modification of the embodiment;
FIG. 4 is a cross-sectional view illustrating a configuration of a wiring board according to a second embodiment of the present invention.
FIG. 5 is a cross-sectional view illustrating a configuration of a conventional wiring board.
FIGS. 6A and 6B show transmission signals according to the related art, wherein FIG. 6A is a schematic diagram showing a signal propagating through a differential transmission line, and FIG. 6B is a diagram showing a case where the signal shown in FIG. FIG. 3 is a schematic diagram showing crosstalk noise generated between differential transmission lines when the transmission is performed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Dielectric substrate (substrate), 4 ... wiring, 3 ... differential transmission line, 6 ... 1st dielectric, 7 ... 2nd dielectric.

Claims (3)

A wiring board having at least one pair of wirings forming a differential transmission line among lines forming a microstrip line by a transmission line and another conductive layer,
The differential transmission line has a higher relative permittivity than a dielectric disposed between air and another pair of differential transmission lines, which connects the respective wirings constituting the differential transmission line. A wiring board having a dielectric part. 2. The wiring board according to claim 1, wherein the dielectric portion is provided between opposing surfaces of respective wirings constituting the differential transmission line. A method of manufacturing a wiring board having at least one pair of wirings forming a differential transmission line among lines forming a microstrip line by a transmission line and another conductive layer,
A first supply step of supplying a first dielectric having a higher relative dielectric constant than air to each of the transmission lines constituting the differential transmission line and to a gap between the transmission lines;
A second supplying step of supplying a second dielectric having a relative permittivity smaller than that of the first dielectric to the gap between the transmission lines and between the transmission lines;
A method for manufacturing a wiring board, comprising:

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