JPH1022635A - Multilayer board for high frequency circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer board for a high frequency circuit which can reduce the leakage of needless radiation. SOLUTION: A plurality of through holes 12, 12,... for prevention of leakage piercing the whole layers of a four-layer board 11 are provided successively in the direction of isolating both, between an input connector and a generation source of needless radiation. Moreover, the shield effect to that needless radiation can be improved by putting the interval between the through holes 12, 12,... for leak prevention to half or under the wavelength of needless radiation. Furthermore, the shield effect can be improved while maintaining the strength of a board by providing the through holes 12',12',... for leak prevention zigzag to the through holes 12, 12,... for leak prevention.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer board for a high-frequency circuit on which components used in a microwave band are mounted.

[0002]

2. Description of the Related Art At present, it is well known that a microwave circuit is formed by using a multilayer substrate to reduce the external dimensions of the microwave circuit. That is, for example, when a microwave circuit is formed using a four-layer substrate, a microstrip circuit is formed on the first layer, a ground plane is formed on the second layer, and other circuits are formed on the third and fourth layers. By configuring one microwave circuit in each layer, the external dimensions can be reduced.

Further, in order to reduce unnecessary radiation (spurious, leak of local signal, etc.) in a multilayer substrate, for example, as disclosed in Japanese Patent Application Laid-Open No. 63-90892, the inner layer pattern of the multilayer substrate is signaled. A multi-layer circuit board for high frequency has been proposed which is used for lines and has a shielding effect by using the surface layer as a ground plane. In addition, 5-2
As disclosed in No. 1473, a plurality of through holes are provided around a concave groove on a substrate on which an electronic component is mounted,
A printed circuit board for component mounting that suppresses unnecessary radiation from the concave groove has also been proposed.

[0004]

By the way, in a microwave circuit, the return loss at the circuit input end is improved,
In order to prevent leakage of unnecessary radiation from inside the circuit, an isolator is usually connected in series to the input portion. However, when a strip line type isolator is attached with the inner layer of the multilayer substrate as a ground plane and the surface layer as a microstrip line, the reverse isolation of the isolator may be reduced.

That is, as described above, the microstrip circuit is provided on the first layer of the four-layer substrate, the ground plane is provided on the second layer, and the third layer is provided on the third layer.
When another circuit is formed in the layer and the fourth layer, for example, if unnecessary radiation occurs in the circuit formed in the third layer, the unnecessary radiation does not pass through the isolator, and the second layer to the third layer It may leak into the signal input terminal through the insulating layer between the layers and between the third and fourth layers. In such a case, apparent reverse isolation in the isolator is reduced, and the effect of providing the isolator is reduced by half.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a multilayer substrate for a high-frequency circuit capable of further reducing unnecessary radiation leakage.

[0007]

According to a first aspect of the present invention, there is provided at least one circuit comprising a plurality of layers and having a circuit formed thereon.
One inner layer, at least one layer in which a ground pattern is formed over the entire surface, and an input terminal to which an external signal is input;
A plurality of through holes penetrating all layers of the multilayer substrate for high-frequency circuits are provided at predetermined intervals between the input end and the circuit forming portion between the inner layer circuit forming portion and the circuit forming portion. Multilayer substrate for high frequency circuits.

[0008] The invention described in claim 2 is the first invention.
In the multilayer board for a high-frequency circuit described in (1), the predetermined interval is not more than の of the wavelength of unnecessary radiation generated in the circuit formed in the inner layer.

[0009] The invention described in claim 3 is the first invention.
Alternatively, in the multilayer substrate for a high-frequency circuit described in 2, the through holes are provided in a staggered manner.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 and FIG. 2 are diagrams showing patterns of respective layers around an input portion of an RF signal in the four-layer substrate 1 of the present embodiment.
Is a top view showing a pattern of the first layer 1a of the four-layer substrate 1 in the present embodiment, and FIG. 1B is a perspective view showing a pattern of the second layer 1b. FIG. 2A shows the third layer 1.
FIG. 2B is a perspective view showing a pattern of a fourth layer 1d viewed from the upper surface. FIG. 3 is a cross-sectional view showing a cross section taken along the line AA in FIGS. 1 and 2. In FIGS. 1 to 3, a hatched portion indicates that a metal layer such as a copper foil is formed.

[0011] In these figures, the four-layer substrate 1 has an RF
A first layer 1a on which patterns 2 and 3 are formed, a second layer 1b which is a ground pattern over the entire surface of the substrate, and a third layer 1c on which power supply lines and other circuit patterns (not shown) are formed. , The fourth layer 1d. In addition, an insulating layer 4 is formed between the first layer 1a to the fourth layer 1d described above. Reference numeral 5 denotes an input connector to which an external RF signal is input, and a center conductor 5a thereof is electrically connected to the RF pattern 2. Reference numeral 6 denotes a surface mount type isolator, and RF input from the input connector 5
The signal is passed from the RF pattern 2 to the RF pattern 3 and the signal that is going to pass from the RF pattern 3 to the RF pattern 2 is attenuated.

Numerals 7 to 10 denote pads provided on the first layer 1a. Each pad is provided with a plurality of through holes 11, 11,... For securing ground, penetrating to the second layer 1b. At 1a, a ground plane is secured. Also,
The surface mount isolator 6 is mounted on these pads 7 to 10 by soldering or the like. Reference numerals 12, 12,... Denote through holes for preventing leakage provided through the first layer 1a to the fourth layer 1d, respectively. The RF leakage 13 generated in the third layer 1c is caused by the second layer 1b-the second layer 1b. The leakage through the insulating layer 4 between the third layer 1c and between the third layer 1c and the fourth layer 1d to the input connector 5 is prevented. Here, the RF leak 13 is a leak of a local signal from a mixer or the like used in the above-described other circuits.

The leak preventing through holes 12, 1
Are provided on a straight line substantially orthogonal to the direction in which the RF leak 13 propagates to the input connector 5. Here, the leak prevention through holes 12, 12,
By setting the distance between... To be equal to or less than half the wavelength of the RF leak 13, a shielding effect against the RF leak 13 can be obtained. However, in consideration of the dimensions and strength of the multilayer substrate, the gap should be provided as densely as possible. preferable. 14,15
Is a metal case to which the four-layer board 1 is attached.

In the above-described four-layer substrate 1, between the insulating layer 4 in which the circuit for generating the RF leak 13 is formed and the input connector 5, the leak preventing through holes 12, 1 are provided.
Are provided in the direction (the vertical direction in FIG. 1A) separating the input connector 5 from the insulating layer 4 on which the circuit is formed. It is installed continuously. That is, the RF leak 13
Are provided in a direction substantially orthogonal to the direction in which the signal propagates to the input connector 5. For this reason, the second layer 1b-
When the RF leak 13 leaking into the insulating layer 4 between the third layer 1c and between the third layer 1c and the fourth layer 1d propagates in the direction in which the input connector 5 is provided, these leak preventing through holes 12, 12 are provided. , ... will be greatly attenuated.

Further, through holes 12, 1 for preventing leakage are provided.
The interval between 2,... Is 1/1 / the wavelength of the RF leak to be blocked when the shielding effect on the RF leak is considered.
It is desirable to set it to 2 or less. In the present embodiment,
Pads 7 and 10 on which surface mount isolator 6 is mounted
, And the pads 8 and 9, the distance between the leak preventing through holes 12, 12,... Can be reduced, thereby improving the shielding effect against the RF leak 13.

Furthermore, through holes 12 for preventing leakage are provided.
By providing a plurality of through-hole rows like 12,... And arranging the through-holes in a staggered manner, the shielding effect can be improved. In this case, there is an advantage that the strength of the substrate can be maintained as compared with the case where the distance between the through holes 12, 12,... In FIG. 1A, the through holes 12 for preventing leakage
By providing further leak preventing through holes 12 ', 12',... On both sides of
The shielding effect against the leak 13 is further improved.

In FIG. 1A, the pads 7,
Due to the distance between the pad 10 and the pads 8, 9, only two through holes 12 'for preventing leakage are provided on both sides of the through holes 12, 12, ... for preventing leakage. If there is room in the space between the pads 8 and 9, the through holes may be continuous from the upper part to the lower part of the substrate in the drawing, as in the case of the through holes 12 for preventing leakage.

In the arrangement shown in FIG. 1A, when 11 leak-preventing through-holes having a diameter of 1 mm are provided at intervals of 2 mm, when the through-holes are not provided, the leakage current is -56 dBm. It has been confirmed that the leak of the local signal in the 6 GHz band has been improved to -68 dBm.

[0019]

As described above, according to the multilayer substrate for a high-frequency circuit according to the first aspect, a high-frequency circuit for a high-frequency circuit is provided between an input terminal to which a signal is input from the outside and a circuit forming portion of the inner layer. Since a plurality of through holes penetrating all layers of the multilayer substrate are provided in a direction separating the input end and the circuit forming portion, a shield that attenuates unnecessary radiation generated in a circuit provided in an inner layer and propagated to the input end is provided. The effect can be obtained.

Further, according to the multilayer substrate for a high-frequency circuit according to the second aspect, the interval between the through holes is set to be equal to or less than half the wavelength of the unnecessary radiation, so that the shielding effect can be improved.

Furthermore, according to the multilayer substrate for a high-frequency circuit according to the third aspect, the through holes are provided in a staggered manner.
In addition to improving the shielding effect against unnecessary radiation, the strength of the multilayer substrate can be maintained.

[Brief description of the drawings]

FIG. 1 is a top view and a perspective view showing a pattern of each layer of a multilayer substrate for a high-frequency circuit according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a pattern of each layer of the multilayer substrate for a high-frequency circuit.

FIG. 3 is a cross-sectional view showing a cross section taken along a line AA in FIGS. 1 and 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 4-layer board 2, 3 RF pattern 4 Insulation layer 5 Input connector 6 Surface mount type isolator 7-10 Pad 11 Grounding securing through hole 12, 12 'Leak prevention through hole 13 RF leak 14, 15 Metal case

Claims (3)

[Claims] 1. A high-frequency device comprising a plurality of layers, at least one inner layer on which a circuit is formed, at least one layer on which a ground pattern is formed over the entire surface, and an input terminal to which an external signal is input. In the circuit multilayer board, between the input terminal and the circuit forming portion of the inner layer, a through hole penetrating all layers of the high frequency circuit multilayer substrate is provided in a direction separating the input terminal and the circuit forming portion. A multilayer substrate for a high-frequency circuit, wherein a plurality of the substrates are provided at intervals. 2. The multilayer board for a high-frequency circuit according to claim 1, wherein the predetermined interval is set to be equal to or less than の of a wavelength of unnecessary radiation generated in a circuit formed in the inner layer. 3. The multilayer substrate for a high-frequency circuit according to claim 1, wherein the through holes are provided in a staggered manner.