JPH01286493A - Multilayer wiring board - Google Patents

Abstract

PURPOSE:To balance signal wirings in a differential transmission system and to decrease effect of external noise by arranging a pair of signal wiring layers above and below in parallel with each other between power supply layers, the signal wiring layers constituting a pair of transmission lines. CONSTITUTION:Between a pair of power supply layers 1 and 2 consisting of conductor plates, there are interposed signal wiring layers 6 and 7 formed of a conductor and constituting transmission lines. A dielectric 4 is provided between the power supply layers 1 and 2. Such assemblies consisting of the power supply layers and signal wiring layers are stacked to provide a multilayered structure. The signal wiring layers 6 and 7 are juxtaposed above and below in parallel with each other so as to provide a pair of transmission lines. These signal wiring layers 6 and 7 are formed of conductors having the same configurations and they are arranged above and below in a symmetrical relation so that they have equal characteristic impedance. More particularly, they are provided suitably for transmission of differential signals of opposite phases, respectively. For example, the signal wiring layer 6 may be of P-type and the signal wiring layer 7 may be of N-type so that a pair of balanced transmission lines are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multilayer wiring board, and particularly to a multilayer wiring board suitable for configuring a differential transmission system.

[Prior Art] Multilayer wiring boards used in computers and the like are required to have higher density and to stably transmit high-frequency signals.

This type of transmission line is composed of a power supply layer and a signal wiring layer, which are provided with a dielectric material in between. Usually, these transmission lines are stacked to form a multilayer wiring board.

In such a multilayer wiring board, the higher the density and the higher the frequency, the more susceptible to the influence of external noise, so countermeasures are required.

In particular, in a synchronous digital signal processing device, if noise such as crosstalk is superimposed on the clock signal that serves as a reference for synchronization, the temporal accuracy of synchronization decreases, which may cause the device to malfunction.

Therefore, in the conventional device, JP-A-62-1:l:17
As described in Publication No. 43, a wiring layer dedicated to clock signals is provided, or a pair of clock signals having opposite phases to each other is transmitted through two adjacent transmission lines, and the receiving side receives these two opposite phase signals. Efforts have been made to use a differential transmission system, which has the effect of detecting the difference between signals and canceling the in-phase noise superimposed during transmission.

[Problem to be solved by the invention] In a differential transmission system using conventional multilayer wiring technology, two signal wirings that transmit a pair of antiphase signals are connected to the same wiring as shown in Figure 2. They are wired in layers, and the amount of coupling between these two trees of differential signal wires is different from other nearby signal wires. For this reason, the amount of external noise that is applied to the two differential signal lines is different, so that the difference in the amount of noise or the amount of noise that affects the transmission system remains in the differential circuit at the receiving end.

An object of the present invention is to balance signal wiring in a differential transmission system and to realize a multilayer wiring board that is less affected by external noise.

[Means for Solving the Problem] The present invention provides a multilayer wiring board having a power supply layer and a signal wiring layer, and as a means for solving the above problem, a pair of transmission lines are formed vertically in parallel between the power supply layers. A feature is that two signal wiring layers are provided.

The power layer is formed of a conductive plate and is generally used for power supply, so it is connected to a power source and is given some potential including a ground potential. However, this electricity
The layer may be left unconnected to a power source.

Further, the power supply layer and the two signal wiring layers described above can be stacked to form a multilayer board. In this case, signal wiring layers having different wiring directions can be wired using different aN layers. In other words, a signal wiring layer can be formed in the X direction between certain power supply layers, and a signal wiring tIQ layer can be formed in the Y direction between adjacent power supply layers. be.

However, it is also possible to provide a mixture of two signal wiring layers arranged in parallel to form a pair of transmission lines and a signal wiring layer that does not form a pair between the same power supply layers.

In a preferred embodiment of the present invention, a pair of balanced transmission lines used for transmitting differential signals having mutually opposite phases are constructed by arranging two signal wiring layers vertically in parallel between power supply layers. It is also preferable to apply the present invention to providing a pair of balanced transmission lines for transmitting differential high-speed signals, such as clock signals.

[Function] The present invention provides two signals having opposite phases to each other in a differential transmission system.
By wiring the main signal wiring vertically in parallel between the power supply layers with the width direction facing each other, a balanced circuit with a higher degree of coupling can be realized. Since the amount of noise on the transmission line is made almost equal, the noises cancel each other out in the differential circuit at the receiving end, resulting in a transmission system with very little influence from external noise. .

[Example] Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows the structure of a first embodiment of the multilayer wiring board of the present invention. .

The embodiment shown in the figure shows the most basic aspect of the present invention, and has power supply layers 1 and 2 made of conductor plates, and between them, a signal layer made of a conductor and forming a transmission line, respectively. Wiring layers 6 and 7 are arranged. In addition, the power layer 1.
A dielectric 4 is provided between the two. Although only one layer is shown here to simplify the explanation, it goes without saying that a power supply layer and two signal wiring layers can be laminated to form a multilayer structure.

The signal wiring layers 6 and 7 are arranged between the power supply layers 1 and 2.
They are arranged vertically and in parallel to form a pair of transmission lines. These signal wiring layers 6 and 7.

They are formed of conductors having the same shape and are arranged vertically symmetrically between the power supply layers 1 and 2 so that their characteristic impedances are equal. That is, a pair of balanced transmission lines suitable for transmitting differential signals having opposite phases to each other are formed, for example, in which the signal wiring layer 6 is of P type and the signal wiring layer 7 is of N type.

In this way, by arranging the two signal wiring layers 6 and 7 that form a pair of vertically parallel transmission lines between the power supply layers 1 and 2, the signal wiring layers 6 and 7 or the power supply layer 1 .2
They are arranged symmetrically in the longitudinal direction (thickness direction) between them. Therefore, signal lines M6 and M7 are affected by noise from the lateral direction to the same extent, so by transmitting differential signals with opposite phases to a pair of transmission lines, common-mode noise can be avoided. can offset the effects of

Note that external noise from above and below is shielded by the power layer layer 2, so the influence of this can be ignored. However, strictly speaking, if there is a bias in the distribution of the noise source or in the thickness direction between the power supply layers 1 and 2, there may be a slight difference between the signal wiring layers 6 and 7 due to the influence of noise. Zu(Iru.

This can be dealt with by providing two pairs of transmission lines adjacent to each other, as shown in FIG. In this case, the polarities of the pair of transmission lines may be set so that two adjacent sets are arranged upside down. this is,
It is applicable not only to this embodiment but also to other embodiments.

FIG. 3 shows a second embodiment of the multilayer wiring board of the present invention.

In the embodiment shown in the figure, a power supply layer and two signal wiring layers are alternately laminated, and the signal wiring layers having different wiring directions are wired in different laminated layers.

In FIG. 3, power supply layers 1.2 and 3 are laminated with signal wiring layers 8.9 and 1O111 sandwiched therebetween to form a two-layer wiring board. Between power supply layers 1.2 and 2.3, 4.5 dielectrics are provided respectively. Note that here, for the sake of simplicity, only two layers are shown, or it goes without saying that multiple layers can be formed by further laminating them.

The signal above! The i-layers 8 and 9 and the signal wiring layers 10 and 11 are wired in different directions and in different layers. That is, the signal wiring layers 8 and 9 are arranged vertically in parallel in the Y direction between the power supply layers 1 and 2, forming a pair of transmission lines. On the other hand, the signal wiring layers 10 and 11 are arranged vertically in parallel in the X direction between the power supply layers 2 and 3, forming a pair of transmission lines. These signal wiring layers 8 and 9,
The signal wiring layers IO and 11 are connected by through holes 12 and 13 as necessary.

Also in this embodiment, the signal wiring layers 8 and 9 and the signal wiring layers 10 and 11 constituting the pair of transmission lines are similar to the signal wiring layers 6 and 7 in the first embodiment in each pair. , are configured so that their characteristic impedances are equal. Then, as in the case of the first embodiment, differential signals having opposite phases are transmitted to the pair of transmission lines, thereby acting to cancel out the influence of common mode noise.

However, an unbalanced state occurs in the part connected by the through-holes 12 and 13, but since the noise that the through-hole part receives from the outside is sufficiently small, this effect can be ignored, and it is different from the case of the first embodiment. Similarly, a nearly balanced transmission system can be realized.

In each of the above embodiments, only two signal wiring layers arranged in parallel to form a pair of transmission lines are provided between one power supply layer, but a pair is provided between the same power supply layer. Of course, signal wiring layers that are not formed may also be provided.

Further, signal wiring layers having different wiring directions can be provided between the same power supply layers.

[Effects of the Invention] According to the present invention, a transmission system with a high degree of balance can be realized, so a transmission system with very little influence of external noise can be realized. Especially for clock signals, stable signals with high time accuracy can be obtained. In addition, since it is resistant to noise even with general signals, it is effective in improving zero-tolerance.

[Brief explanation of the drawing]

FIG. 1 is a cutaway perspective view of main parts showing the structure of a first embodiment of the multilayer wiring board of the present invention, FIG. 2 is a cutaway perspective view of main parts showing the structure of a conventional multilayer wiring board, and FIG. FIG. 4 is a cutaway perspective view of main parts showing the configuration of a second embodiment of the wiring board, and FIG. 4 is a cutaway perspective view of main parts showing a modification of the embodiment in the multilayer wiring board of the present invention. l, 2.3...Power supply layer 4.5...Dielectric material 6.7.8.9.1O111...Signal wiring layer 12.1
3...Through hole applicant: Hitachi, Ltd. Figure 1 Figure 2 Figure 3 Figure 4

Claims (5)

[Claims] 1. A multilayer wiring board having a power supply layer and a signal wiring layer, characterized in that two signal wiring layers forming a pair of vertically parallel transmission lines are disposed between the power supply layers. 2. 2. The multilayer wiring board according to claim 1, wherein a power supply layer and two signal wiring layers are alternately laminated, and signal wiring layers having different wiring directions are wired using different laminated layers. 3. 3. The multilayer wiring board according to claim 1, wherein two signal wiring layers arranged in parallel to form a pair of transmission lines and a signal wiring layer that does not form a pair are mixedly provided between the power supply layers. 4. A pair of balanced transmission lines used for transmitting differential signals having opposite phases to each other are provided between power supply layers by arranging two signal wiring layers vertically and in parallel. Multilayer wiring board. 5. 5. The multilayer wiring board according to claim 4, wherein the pair of balanced transmission lines is a pair of balanced transmission lines that transmit differential high-speed signals.