JPS58173890A - Multilayer circuit board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to means for reducing variations in characteristic impedance in a multilayer wiring board.

A multilayer wiring board consists of a power layer, a ground layer, and a signal wiring layer (hereinafter abbreviated as the signal layer). However, when the purpose is high-speed signal transmission such as for computers, the signal layer is a power layer or a connection layer. They often have a stripline structure sandwiched between strata. A sectional view of an example thereof is shown in FIG.

Here, 1 is a signal layer, 2 is a power supply/ground layer in which conductors are formed in a planar shape and serves as both a power supply layer and a ground layer, 3 is a through hole that penetrates each layer, and 4 is a signal wiring provided in signal layer 1. be. In this case, the power/ground layer 2 is provided for every 102 signal layers in order to reduce the number of layers. FIG. 2 is a plan view showing this type of configuration. In this figure, the signal wiring 4X in the X direction among the signal wirings is provided on the signal layer on the paper as shown by the solid line, and the signal wiring in the Y direction is The wiring 4Y is provided in the signal layer below it, as shown by the broken line. In this way, the power supply
The two signal layers sandwiched between the ground layers form a pair of orthogonal wiring lines 75! ; has been done.

Here, regarding a certain signal wiring, if the number of signal wirings of a set of upper and lower signal layers that intersect is normalized by the lattice pitch is called wiring crossing density, then in conventional wiring, the wiring crossing density is not constant. Also.

In conventional wiring, due to the spacing and density of the wiring, there is a large variation in ground capacitance per unit length of the signal wiring, which inevitably causes a disparity in characteristic impedance.The present invention eliminates the above drawback. However, it is an object of the present invention to provide a high-density wiring means for reducing variations in characteristic impedance of each signal wiring in a multilayer wiring board. That is, in the present invention, by providing additional wiring connected to the power supply/ground layer on all wiring grids that are not used in the signal layer, the wiring intersection density is kept constant and the ground capacitance of each signal wiring is reduced. This is to make the characteristics of each signal wiring constant by making them almost the same. Hereinafter, the present invention will be explained in more detail with reference to Example VC.

Figure 3 is a plan view showing a pair of signal layers, an upper signal layer and a lower signal layer, installed between the power supply and ground layers of a multilayer wiring board. Hall 3
A and a through hole 3B for power supply and grounding indicated by an X mark are provided, and wirings 4X and 4Y are provided to connect these. Here, in the conventional configuration, the wiring 4X of the upper signal layer (that is, only the wiring in the X direction is performed) is shown by a thick solid line.

There is only the wiring 4Y shown by the thick broken line in the lower signal layer (wiring in the Y direction only).

In the present invention, a thin solid wire 5X in the X direction connected to the power supply/ground layer is also connected to the upper signal layer.
Thin broken line Y-direction wiring 5Y connected to the ground layer is provided in the lower signal layer.

By doing this, the signal wiring is arranged for each grid.
That is, each through-hole will necessarily intersect with the wiring of the opposing signal layer once.

In this way, the interconnect density can be made uniform, and variations in characteristic impedance due to sparse interconnections can be suppressed.

Next, other embodiments of the present invention are shown in FIGS. 4(a) to 4(C). Here, (a) is for microstrip line structure, (b) is for two channels, and (C) is for power supply/
This is a case where the signal layer sandwiched between the ground layers is not only two layers but multilayered (three layers in the illustrated case).

In either case, by providing wiring 5 connected to the power supply/ground layer on all wiring grids where signal wiring 4 is not provided, characteristic impedance can be made constant and crosstalk noise can be reduced.

Note that by providing additional wiring connected to the power supply/ground layer in this way and crossing the signal wiring of the opposing signal layer, the signal wiring O-to-ground capacity may be increased in some cases, but multilayer wiring In the case of high frequency wiring on the board, the additional wiring according to the present invention is only a few orders of magnitude, and compared to the effect of increasing the ground capacitance, a greater effect can be obtained by keeping the characteristic innovation constant. .

As explained above, by performing additional wiring according to the invention, it is possible to make the characteristic impedance constant in a multilayer wiring board with high wiring density.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a conventional state in which wiring is performed on a multilayer wiring board; Fig. 2 is a plan view showing a conventional state in which wiring is performed in one set of signal layers of a multilayer wiring board; 4(a) to 4(c) are cross-sectional views showing each embodiment of the present invention. l...Signal wiring layer, 2...Power/ground layer, 3...
Through hole, 3A... Signal through hole, 3B.
...Through hole s4 for power supply and grounding...Signal wiring.

Claims (1)

[Claims] A power supply/ground layer with a planar conductor formed on the first insulating plate, and a second insulating plate sandwiched between the upper power supply/ground layer and a signal layer on the top of the second insulating plate in the row or column direction. In a multilayer wiring board consisting of a signal wiring layer on which a conductor is formed, the wiring connected to the power supply/ground layer is placed on all wiring grids that are not used for No. 1.3 wiring of the signal wiring layer. A multilayer wiring board characterized in that: