JPH05226500A - Mounting circuit board - Google Patents

Abstract

PURPOSE:To decrease cross talk between signal lines on a mounting circuit board by a method wherein the end of a first power supply layer except its part adjacent to the end of an insulating layer and the end of a second power supply layer are made to overlap each other interposing the insulating layer between them. CONSTITUTION:A first polyimide layer 2a is formed on a silicon substrate 1, and a first wiring layer composed of a first signal line 3a and a first ground electrode 4a is formed. A second polyimide layer 2b is formed, and a second wiring layer composed of a second signal line 3b and a second ground electrode 4b is provided. A third polyimide layer 2c is formed thereon, and a third signal line 3c and a cover polyimide layer 2d are successively formed thereon. An electromagnetic field between the first signal line 3a and the second signal line 3b is screened by an overlap region 6 where the electrodes 4a and 4b overlap each other, so that cross talk can be sharply lessened between signal lines.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting circuit board, and more particularly to a mounting circuit board in which crosstalk between wirings is greatly reduced.

[0002]

2. Description of the Related Art With the increase in size and speed of electronic equipment,
Higher performance is also required for mounted circuit boards. A multi-chip module in which a plurality of LSI chips are mounted on a substrate is widely used.

C. T. Barlett et al. Is IEEE P
rosecedings of 37th electr
onic Components Conference
e, 1987, pp. 518-525 "Multi-C
hip Packing Design for V
The contents reported in the "LSI-Based System" will be described with reference to FIGS. 2 (a) and 2 (b).

In FIG. 2 (a), a first polyimide layer 2a to be an insulating film is formed on a silicon substrate 1, a ground electrode 4 is formed, and a second polyimide layer 2b is formed on the ground electrode 4. Then, the first signal wiring layer is formed. A first signal line 3a and a second signal line 3b are formed on the first signal wiring layer. A third polyimide layer 2 on top of it
The third signal line 3 which forms c and serves as the second signal wiring layer
c is formed, and finally the cover polyimide layer 2d is formed.

First signal line 3a and second signal line 3b
Forms a microstrip line with the ground electrode 4, and the characteristic impedance of each signal line is 50 ± 5Ω.

FIG. 2 shows a structure in which crosstalk between wirings, which has been a problem in the mounting circuit board of FIG. 2A, is reduced.
This will be described with reference to (b). A ground electrode is formed between adjacent signal lines to shield the electromagnetic field.

After forming a first polyimide layer 2a to be an insulating film on a silicon substrate 1, a first ground electrode 4 is formed.
a is formed. A second polyimide layer 2b is formed thereon, and then a first signal wiring layer is formed. The first signal line 3a and the second ground electrode 4 are provided in the first signal wiring layer.
b, the second signal line 3b is formed. Third on it
Is formed, a third signal line 3c to be a second signal wiring layer is formed, and finally a cover polyimide layer 2d is formed.

First signal line 3a and second signal line 3b
Forms a microstrip line with the first ground electrode 4a, and the characteristic impedance of each signal line is 50 ± 5Ω.

[0009]

In the mounted circuit board of FIG. 2A, there is a problem that an electromagnetic field wraps around between the first signal line 3a and the second signal line 3b to cause crosstalk. is there.

In the mounted circuit board of FIG. 2 (b), it is not sufficient though it is shielded by the second ground electrode 4b. The electromagnetic field wraps around between the first signal line 3a and the second signal line 3b, and crosstalk of about half of FIG. 2A occurs.

With the miniaturization of wiring, the wiring interval has become narrower. Due to the higher speed, the rise time of the pulse is shortened and the signal of high frequency component is increased.

Further, in order to compensate for the increase in wiring resistance due to the miniaturization of wiring, it is necessary to increase the film thickness of the wiring.

In any case, this leads to an increase in crosstalk between wirings, and a significant reduction in crosstalk between wirings is an important issue.

[0014]

According to another aspect of the present invention, there is provided a mounted circuit board, wherein a first wiring layer composed of a first power supply layer and a first signal layer, a second power supply layer and a second power supply layer are provided with an insulating layer therebetween. A second wiring layer formed of two signal layers is formed, and the end portion of the first power supply layer except the vicinity of the end portion of the insulating layer, the second power supply layer and the end portion form the insulating layer. They are separated and overlap each other.

[0015]

EXAMPLE FIG. 1A shows a first example of the present invention.
Will be described.

A first polyimide layer 2 on a silicon substrate 1
After forming a, the first wiring layer is formed. The first wiring layer is composed of the first signal line 3a and the first ground electrode 4a. Next, the second polyimide layer 2
b is formed, and the second wiring layer is formed. The second wiring layer is composed of the second signal line 3b and the second ground electrode 4b. A third polyimide layer 2c is formed on it, and a third signal line 3c is formed. Further, a cover polyimide layer 2d is formed on it.

The first signal line 3a is connected to the second ground electrode 4
b, the second signal line 3b is connected to the first ground electrode 4
A microstrip line is formed with a, and the characteristic impedance of each signal line is 50 ± 5Ω.

In this embodiment, the electromagnetic field between the first signal line 3a and the second signal line 3b is shielded by the first ground electrode 4a and the second ground electrode 4b, so that the crosstalk is greatly reduced. There is a great advantage that it can be reduced.

Table 1 shows the results of simulation and measurement using a pulse having a rise time of 1 ns and a sufficiently long wiring of 20 cm.

[0020]

[Table 1]

From this result, it was found that the present embodiment can reduce crosstalk by 5 digits as compared with the prior art. This is because in the area 6 where the first ground electrode 4a and the second ground electrode 4b overlap, a remarkable electromagnetic wave shielding effect is produced.

Next, a second embodiment of the present invention will be described with reference to FIG.

FIG. 1 shows the first embodiment of the present invention.
This will be described with reference to (b).

First polyimide layer 2 on silicon substrate 1
After forming a, the first wiring layer is formed. The first wiring layer is composed of the first signal line 3a and the first ground electrode 4a. Next, the second polyimide layer 2
b is formed. The via layer 5 is formed on the second polyimide layer 2b.
And then a second wiring layer is formed. The second wiring layer is the second signal line 3b and the second ground electrode 4
It consists of b. A third polyimide layer 2 on top of it
c is formed, and the third signal line 3c is formed. Further, a cover polyimide layer 2d is formed on it.

The first signal line 3a is connected to the second ground electrode 4
b, the second signal line 3b is connected to the first ground electrode 4
A microstrip line is formed with a, and the characteristic impedance of each signal line is 50 ± 5Ω.

In this embodiment, the electromagnetic field between the first signal line 3a and the second signal line 3b is the first ground electrode 4a,
It is completely shielded by the second ground electrode 4b and the via layer 5.

From the simulation and the actual measurement, it was found that in this embodiment, the crosstalk is further reduced as compared with the first embodiment, and it becomes almost zero. By eliminating crosstalk altogether, it has become possible to operate high-speed signals.

[0028]

The crosstalk problem can be solved without increasing the wiring layers and without changing the characteristic impedance and wiring resistance of the wiring.

[Brief description of drawings]

FIG. 1A is a sectional view showing a first embodiment of the present invention. (B) is a sectional view showing a second embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a conventional mounted circuit board.

[Explanation of symbols]

 1 Silicon Substrate 2a First Polyimide Layer 2b Second Polyimide Layer 2c Third Polyimide Layer 2d Cover Polyimide Layer 3a First Signal Line 3b Second Signal Line 3c Third Signal Line 4 Ground Electrode 4a First Ground electrode 4b Second ground electrode 5 Via layer 6 Region where ground electrodes overlap

Claims (4)

[Claims] 1. A first wiring layer composed of a first power supply layer and a first signal layer and a second wiring layer composed of a second power supply layer and a second signal layer with an insulating layer interposed therebetween. And the end portion of the first power supply layer and the end portion of the second power supply layer excluding the vicinity of the end portion of the insulating layer overlap with each other with the insulating layer interposed therebetween. 2. The mounted circuit board according to claim 1, wherein the first power supply layer and the second power supply layer are connected to each other through a via layer. 3. The mounted circuit board according to claim 1, wherein the potentials of the first power supply layer and the second power supply layer are ground. 4. The mounted circuit board according to claim 1, wherein a plurality of bare chips are mounted to form a multichip module.