Multi-layer printed board

Details Multi-layer printed board Multi-layer printed board

2000-08-14

2002-03-19

Paladini, Albert W. (Department: 2841)

Electricity: conductors and insulators

Conduits, cables or conductors

Preformed panel circuit arrangement

C174S255000, C333S012000, C333S185000, C361S795000

Reexamination Certificate

active

06359237

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-layer printed board which can reduce electromagnetic inductive interference due to power source current, when a multiplicity of high-speed and high-frequency circuit elements are mounted thereon.
2. Description of the Related Art
It is well known that with multi-layer printed boards on which are mounted high-speed and high-frequency circuit elements such as ICs (Integrated Circuits), LSIs (Large Scale Integrated circuits), that there is a problem in that since electromagnetic noise occurs, electronic equipment mounted on the printed board or other electronic equipment is subjected to EMI (Electro Magnetic Interference), thereby causing malfunction.
Of this EMI, one of particularly great significance is electromagnetic noise resulting from an RF source, caused by a large ground or a ground face used as a reference potential, also referred to as “common mode noise”. However, the presumed source of the common mode noise is diversified, and respective source mechanisms are complicated. Hence there has heretofore been no effective method for remedy in the vicinity of the source of release. Therefore, only measures for preventing leakage or radiation of the common mode noise to a cable serving as a main propagation path or as a radiation antenna, have heretofore been taken.
On the other hand, recent research has revealed the fact that one of the largest causes of the common mode noise in high-speed digital circuits is power source current to high-speed and high-frequency circuit elements mounted on a printed board. As an invention developed based on this fact, there is for example, the technique registered by Japanese Patent (Granted) Publication No. 273447 and the technique applied for in Japanese Patent Application, First Publication No. Hei 9-253519.
These technique are for supplying a DC power source with respect to high-speed and high-frequency circuit elements mounted on a printed board by using power source wiring in which an inductance element exhibiting a high impedance at the time of high frequencies, is inserted in the middle of a line. Alternatively this is done by using a power supply line in which characteristic impedance is made high by surrounding the periphery of the line with a magnetic body, as well as connecting a capacitor between the power source of circuit elements and the ground. As a result, while enabling smooth high speed and high frequency operation of circuit elements mounted on the printed board, high frequency power source current generated by the operation is prevented from diffusing over the printed board.
Studies confirming that the electromagnetic radiation level is largely suppressed by applying these techniques to high-performance computers, and that resistant strength (immunity) against electric or electromagnetic disturbance from the outside is improved, are typically published in, for example, “Magnetic body built-in decoupling reinforced multi-layer printed board” (Institute of Electrical Engineers, Magnetics Research Society; 1997-12), “Novel decoupling circuit enabling notable electromagnetic noise suppression and high-density packing in a digital printed circuit board” (IEEE International Symposium on Electromagnetic Compatibility; 1998-8, Denver).
In the above described background art, a line structure wherein an impedance of a DC power supply line of the printed board is made high in a high frequency domain (hereinafter referred to as “decoupling inductor”) is adopted, and a capacitor (hereinafter referred to as “bypass capacitor”) is used for efficiently splitting the high frequency power source current generated with the high speed and high frequency operation of circuit elements.
Below is a description of an example from Japanese Patent No. 273447, as background art known to have a noticeable EMI suppression effect.
FIG. 5
is a sectional view of a printed board in the prior art,
FIG. 6
is a plan view showing a power source layer in the printed board in the prior art,
FIG. 7
is a diagram showing an equivalent circuit (decoupling circuit) of a power supply circuit to which the prior art is applied, and
FIG. 8
is a diagram for explaining a diffusion suppression effect of a high frequency power source current in a printed board to which the prior art is applied.
The printed board in the prior art comprises, as shown in the sectional view in
FIG. 5
, a power source layer
101
, ground layers
102
, signal layers
103
, magnetic insulation layers
104
and dielectric insulation layers
105
, and in order of from the top to the bottom, there are formed the signal layer
103
, the dielectric insulation layer
105
, the ground layer
102
, the magnetic insulation layer resistant strength, the power source layer
101
, the magnetic insulation layer
104
, the ground layer
102
, the dielectric insulation layer
105
, and the signal layer
103
.
Here, the magnetic insulation layers
104
comprise an insulating material in which a magnetic body is incorporated, and the dielectric insulation layers
105
comprise an insulating material having only a dielectric property.
Moreover, in the power source layer
101
in a printed board in the prior art, as shown in a plan view of
FIG. 6
, there are arranged a main wiring
106
and a branch wiring
107
branched from the main wiring
106
, and IC/LSIs
108
fitted to a parts face (for example, the surface of the signal layer
103
) of the printed board are connected to the point of the branch wiring
107
through a wire hole (not shown), and a decoupling capacitor
109
fitted to a parts face (for example, the surface of the signal layer
103
) of the printed board is connected to a connection portion between the branch wiring
107
and the IC/LSIs
108
, respectively.
In the printed board of the prior art, as shown in
FIG. 7
, an equivalent circuit of the power supply circuit for each IC/LSI connects a power source III to an IC/LSI
110
via a power source wiring
112
, and connects the IC/LSI
110
and a return circuit of the power source III to a ground layer
113
.
At this time, since the magnetic insulation layers
104
are disposed above and below the power source layer, impedance of the power source wiring formed in the power source layer becomes high, becoming equivalent to the case where the decoupling inductor (L)
114
is inserted, as shown in FIG.
7
. The inductance
114
and the capacitance (C)
115
of the decoupling capacitor form a low pass filter. Hence, with operation of the IC/LSI
110
, the high frequency power source current flowing in the power supply line is suppressed. Moreover, the construction may be such that the decoupling conductor is increased by using an impedance added circuit comprising a meandering portion or the like, for the power source wiring
112
.
In this prior art, as seen from the respective figures, with operation of the IC or LSI, the high frequency power source current flowing into the power source layer is blocked by the inductor inserted in the wiring structure, and split by the bypass capacitor disposed in the vicinity of the IC or LSI.
The effect of suppressing diffusion of the high frequency power source current in a printed board to which the prior art shown in
FIG. 5
to
FIG. 7
is applied is shown in FIG.
8
. In
FIG. 8
, the magnetic field distribution in the vicinity of a substrate is shown, with a stronger magnetic field being a darker color.
With the conventional example shown in FIG.
8
(
a
), since the power source layer is a substrate comprising a flat board over the whole face, the high frequency power source current diffuses over the whole face of the substrate, and electronic equipment being a noise source, is shown in part with a particularly dark color. In the case of Japanese Patent No. 273447 shown in FIG.
8
(
b
), since the power source layer is wired, diffusion of the high frequency power source current decreases, and it is shown that a common mode radiation from the electronic equipment is also suppressed.
This can be consider

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