JPH10163713A - Connection structure of high frequency transmission line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set the transmission loss of a high frequency signal to be small and to transmit the signal in a vertical direction by permitting the various sizes of an electromagnetic connection part to satisfy a specified relation in accordance with the frequency of the transmitted high frequency signal and the dielectric rate of a dielectric. SOLUTION: Micro strip lines A and B formed in different layers through the dielectrics 1A and 1B are electromagnetically connected. The end parts of center conductors 2A and 2B in the micro strip lines A and B are formed in symmetrical positions through a slot hole 4 provided for a ground layer 3 by making them face each other. When the frequency of the high frequency signal transmitted through the line is set to be f(GHz), the dielectric constant of the dielectrics 1A and 1B to be ε, a distance to line end parts 5A and 5B from the center of the slot hole 4 of the first and second micro strip lines A and B to be ML (mm), the length of the longitudinal direction of the slot hole 4 to be SL (mm) and the width of the slot hole 4 to be SW(mm), the relations of the formulas are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coupling structure of a high-frequency transmission line for interconnecting a high-frequency semiconductor element, a passive component, and a connection terminal, and more particularly, to a high-frequency signal having a high frequency in a millimeter wave region of 30 GHz or more. , Which can transmit from a transmission line to another transmission line with a small loss.

[0002]

2. Description of the Related Art In recent years, society has become more computerized, and information has been transmitted wirelessly and personally, as represented by mobile phones. Under these circumstances, in order to enable even higher-speed and large-capacity information transmission, millimeter-wave (30 to 300 GHz)
The development of a semiconductor device operating in the z) region is in progress. Recently, with the advance of such high-frequency semiconductor device technology, various application systems using millimeter wave radio waves, such as inter-vehicle radar and wireless LAN, have been proposed.

For example, an inter-vehicle radar (1) using millimeter waves
995 IEICE Electronics Society Conference, SC-7-6), cordless camera system (1995 IEICE Electronics Society Conference, C-137), high-speed wireless LAN (1
995, IEICE Electronics Society Conference, C-139).

As described above, the application of millimeter waves has entered the system construction stage, and the main subject of development is shifting to how to reduce the shape and cost while satisfying the required performance. As one of means for reducing the size and cost of a high-frequency circuit, there is a method in which circuit elements are mounted on a single substrate and modularized. In order to reduce the size by this method, it is necessary to mount the circuit elements as close as possible. Therefore, the formation density of wiring connecting elements or between the elements and the outside of the substrate increases,
In order to arrange the wirings at a high density, a technique for making the wirings multi-layered is indispensable.

In order to transmit a transmission signal through a multi-layered wiring, it is necessary to transmit the transmission signal in a vertical direction and connect the transmission signal between wirings of different layers. A via-hole conductor is usually used for connection with a wiring formed in such another layer. However, when high-frequency signals such as millimeter-wave signals are transmitted using via-hole conductors, there is a problem that transmission loss is large. Therefore, a transmission line coupling structure that can transmit high-frequency signals vertically with small transmission loss is desired. It is rare.

[0006]

As one means for transmitting a high-frequency signal in the vertical direction of the substrate, it is conceivable to improve a via-hole conductor which has conventionally been frequently used in a package or a wiring substrate. (See IEICE Electronics Society Conference 1995, C-326). In this attempt, it has been proposed that a ground layer be provided around the via hole conductor to suppress the reflection due to the impedance mismatch at the via hole conductor, and to have a structure similar to a coaxial line.

[0007] However, the transmission characteristics thereof are such that the reflection loss is -18 dB and the loss is -2 dB at a signal frequency of 10 GHz, and the transmission loss is large. At a signal frequency of 10 GHz or more, the characteristics deteriorate more rapidly. This is presumably because, when a high-frequency signal is transmitted to the via-hole conductor, the electromagnetic field distribution differs greatly between the wiring portion and the via portion, and the electromagnetic field distribution changes rapidly at the connection portion between the wiring and the via.

That is, in the wiring portion, the magnetic field associated with the high-frequency signal is generated in a circular shape around the wiring in a plane perpendicular to the wiring. However, in the via-hole conductor, the high-frequency signal is transmitted in the same mode as the wiring part, and the magnetic field is generated in a circular shape around the via-hole conductor in a plane parallel to the substrate surface.
Magnetic field distribution is 90 ° at the connection between wiring and via-hole conductor
It turns.

In order to moderate the change in the electromagnetic field distribution at the connection portion between the wiring and the via-hole conductor, it is conceivable that the via-hole conductor is provided obliquely and the angle between the wiring and the via-hole conductor is made obtuse. It is difficult to form such a via-hole conductor, and there is a problem in workability and mass productivity.

On the other hand, it has been proposed to use electromagnetic coupling instead of the via-hole conductor. This electromagnetic coupling structure has a structure in which a microstrip line and another microstrip line face each other via a slot hole provided in a ground layer.

However, as for signal transmission with such an electromagnetic coupling structure, there has only been reported that transmission is possible at a low frequency in the microwave band. Is not applicable to the transmission of signals having a thickness close to the thickness of the dielectric, and no specific structure for reducing the insertion loss to a level that can be practically used even if the transmission is possible has not been reported.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to reduce the loss of high-frequency signals such as millimeter waves of 30 GHz or more in practical use, and to provide a high-frequency It is an object of the present invention to provide a coupling structure of a high-frequency transmission line capable of transmitting a signal in a direction perpendicular to a substrate.

[0013]

Means for Solving the Problems As a result of diligent studies on the above problems, the present inventors have found that when electromagnetic waves are coupled between microstrip lines via slot holes to transmit a millimeter wave signal, a high frequency signal to be transmitted is transmitted. In the case where various dimensions of the electromagnetic coupling portion satisfy a specific relationship according to the frequency and the dielectric constant of a dielectric used as a substrate, 30 GHz
It has been found that even if the millimeter wave is equal to or larger than z, the loss of the high-frequency signal is small enough to cause no practical problem, and a line coupling structure that does not allow transmission of a signal in the vertical direction can be realized.

That is, the coupling structure of the high-frequency transmission line according to the present invention includes a first microstrip line, a ground layer having a slot hole, a second microstrip line,
An end portion of the first microstrip line, the second microstrip line, and a dielectric disposed between the second microstrip line and the ground layer. In a coupling structure of a high-frequency transmission line formed by electromagnetically coupling the first microstrip line and the second microstrip line by facing an end of the microstrip line through the slot hole, The frequency of the high-frequency signal transmitted through the line is f (GHz), the relative permittivity of the dielectric is ε, and the distance from directly above the center of the slot hole of the first and second microstrip lines to the end of the line is M.
L (mm), the length of the slot hole is SL (mm), and the width of the slot hole is SW (mm).

[0015]

(Equation 1)

It is characterized by satisfying the following.

According to the coupling structure of the high-frequency transmission line of the present invention, as a means for transmitting a high-frequency signal perpendicularly to the substrate, the second micro-strip line is connected to the second micro-strip line via the slot hole formed in the ground layer. The frequency of the high-frequency signal to be transmitted, the relative permittivity of the substrate, the distance from directly above the center of the slot hole to the open end of the microstrip line, the length of the slot hole, and the width of the slot hole using electromagnetic coupling coupled to the microstrip line Is determined so as to satisfy the above-described conditions, a high-frequency signal can be transmitted with low loss in the vertical direction, and the characteristic change is small as long as each of the dimensions satisfies the above relationship, and the mass productivity is excellent. The coupling structure of the transmission line can be provided.

As a result, by providing the coupling structure of the transmission line on a multilayered high-frequency wiring board or a package on which a high-frequency element is mounted, a highly reliable multilayer wiring board or package can be manufactured. Can be.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing a basic structure of a coupling structure of a high-frequency transmission line according to the present invention. In FIG.
1A and 1B are dielectrics, 2A is a center conductor of the first microstrip line, 2B is a center conductor of the second microstrip line, 3 is a ground layer, and 4 is a slot hole formed in the ground layer.

According to the coupling structure shown in FIG. 1, the center conductor 2A of the first microstrip line is provided on the upper surface of the dielectric 1A.
Is formed, a ground layer 3 is formed on the upper surface of the dielectric 1B, and a center conductor 2B of the second microstrip line is formed on the lower surface of the dielectric 1B. The slot hole 4 is formed in the ground layer 3.

According to the above structure, the first microstrip line A is formed by the interaction between the center conductor 2A and the ground layer 3, and similarly, the second microstrip line A is formed by the interaction between the center conductor 2B and the ground layer 3. A microstrip line B is formed.

The present invention relates to a structure for electromagnetically coupling microstrip lines A and B formed between different layers via dielectrics 1A and 1B. The ends of the conductors 2 </ b> A and 2 </ b> B are formed to face symmetric positions via the slot holes 4 provided in the ground layer 3.

In FIG. 1, the distance from directly above the center of the slot hole 4 of the first and second microstrip lines A, B to the line ends 5A, 5B is ML (mm), and the longitudinal direction of the slot hole 4 is Is defined as SL (mm), and the width of the slot hole 4 is defined as SW (mm).

According to the coupling structure shown in FIG. 1, the high-frequency signal supplied to the microstrip line A overlaps with the traveling wave traveling toward the end 5A and the backward wave reflected at the end 5A. Therefore, by adjusting the distance ML from just above the center of the slot hole 4 in the microstrip line A to the line end 5A, the current just above the slot hole 4 can be increased. The ML for maximizing the current immediately above the slot hole 4 varies depending on the frequency of the signal to be transmitted and the dielectric constant ε of the dielectric 1A constituting the microstrip line A.

When the current just above the slot hole 4 is increased, the magnetic field here is also increased, and an electromagnetic field accompanied by a strong magnetic field orbiting around the central conductor 2A of the microstrip line A is generated. When the length SL of the slot hole 4 is adjusted,
A strong electromagnetic field is also excited in the slot hole 4 by the magnetic field generated in the microstrip line A. Then, an electromagnetic field with a strong magnetic field orbiting around the center conductor 2B is also generated in the microstrip line B on the back surface, and the high-frequency signal supplied to the microstrip line A is
, And transmitted to the microstrip line B.

The magnetic field of the high-frequency signal from this transmission line is
Unlike the case where a via-hole conductor is used, it always has a circling shape in a plane perpendicular to the microstrip line, which is transferred to the microstrip line A, the slot hole 4 and the microstrip line B by coupling, and a high-frequency high frequency with a small loss It enables signal transmission.

The above-described electromagnetic coupling is the most basic form of coupling. In such a coupling structure, the ML has a length corresponding to a quarter wavelength of the signal wavelength, and the SL has
Although it is reported in part that the length is set to a half wavelength equivalent to the signal wavelength, in the case of millimeter wave signal transmission of 30 GHz or more, for example, the microstrip line portion becomes capacitive depending on the size of each portion, and the slot becomes It is found that the hole becomes inductive and resonates and couples as a whole, and by using this, even if the dimensions of each part of the electromagnetic coupling part slightly change due to manufacturing tolerances other than the above setting, the characteristic change is small. And transmission lines with low loss are realized.

From this viewpoint, when the frequency of the high-frequency signal transmitted through the line is f (GHz) and the relative permittivity of the dielectrics 1A and 1B is ε, the ML (mm), SL (mm) and SW (mm) After examining the optimal conditions for

[0029]

(Equation 1)

When the above relationship is satisfied, coupling can be performed with the lowest loss. Specifically, as is apparent from the embodiment described later,
In a signal of a frequency of 30 to 60 GHz, an insertion loss of -4
Coupling can be achieved with a loss of less than dB, and if the above conditions are not satisfied, the insertion loss exceeds -4 dB and good coupling cannot be achieved.

The transmission characteristics of the electromagnetic coupling structure between the microstrip lines as shown in FIG. 1 tend to decrease as the resistance of each line or the conductor forming the ground layer decreases. As the type of conductor, W, Mo, Mo
-Mn, Cu, Au, Al, Pt, etc., among them, Cu, Au, Ag, Al
Etc. are most desirable.

As the dielectric, any of inorganic and organic substances conventionally used as an insulating substrate in a wiring board or a package can be used. In forming a laminated structure as shown in FIG. And the dielectric are preferably fired at the same time.

For example, when a metal having a high melting point such as W or Mo is used as the conductor, an alumina-based ceramic material is used as the dielectric, and when a metal such as Cu, Au or Ag is used, 900 is used. Ceramics that can be fired at ~ 1100 ° C, specifically, borosilicate glass, crystallized glass capable of precipitating a crystal phase in the sintering process, non-crystallized glass, or alumina, zirconia, Addition of boron oxide, alkali metal oxide, etc. as a sintering aid to so-called glass ceramic sinters, which are made by adding and firing cordierite, forsterite, silica, etc., and dielectrics such as magnesium titanate and calcium titanate Well-known materials such as fired ceramics are used.

In order to fabricate the coupling structure as shown in FIG. 1 using the above-described conductor material and dielectric material,
For example, a paste obtained by printing a paste containing various conductive metals on a surface of a green sheet formed of a sheet of the ceramic powder in the form of a central conductor and a ground layer having slot holes is laminated and integrated, and fired at a desired firing temperature. It can be manufactured by the following.

The coupling structure of the high-frequency transmission line according to the present invention is based on the structure shown in FIG. 1 and is applicable to a multilayer wiring board such as a high-frequency semiconductor package used for various high-frequency applications. It can be used as signal transmission wiring. In such a case, the coupling structure shown in FIG. 1 may be adopted in a portion of the multilayer wiring board where a high-frequency signal needs to be transmitted in the stacking direction of the wiring board.

[0036]

【Example】

Example 1 Crystalline borosilicate glass as a dielectric was added with 40% by weight of cordierite as a filler, and the dielectric constant was 5.6.
A wiring board for evaluation having a two-layer structure as shown in FIG. 2 by simultaneously firing at 940 ° C. in a nitrogen atmosphere using Cu as a conductor constituting a microstrip line and a ground layer using the glass ceramics described above. No. 6 was produced. FIG.
FIG. 4 is a cross-sectional view of a case where the evaluation wiring board 6 is joined to a metal block 7 for measuring transmission loss. According to FIG. 2, the evaluation wiring board 6 is placed inside the cavity portion 8.
Is placed on a metal block 7 having
Are electrically connected to the conversion board 9 for measurement by the ribbon 10. Therefore, the evaluation wiring board 6 includes two electromagnetic coupling portions for convenience of measurement, and is arranged such that the connection position with the measurement conversion board 9 is on the same plane.

The transmission loss measured by FIG. 2 is as follows: two electromagnetic coupling parts, two measurement conversion boards, two ribbons, two microstrip lines connecting the ribbon and the electromagnetic coupling parts,
This is the total loss of one microstrip line connecting the electromagnetic coupling parts.

The external dimensions of the wiring board for measurement 6 are 8.6 mm.
× 8.6 mm, the thickness is 0.4 mm, the thickness of each conductor layer is 0.015 mm, and the width of the microstrip line is 0.3 mm.
A substrate was prepared in which the distance ML (mm) from the position just above the center of the slot hole of the microstrip line to the line end, the length SL (mm) of the slot hole, and the width SW (mm) of the slot hole were varied. 60GHz and 30G
The insertion loss at Hz was measured. Table 1 (60
GHz) and Table 2 (30 GHz).

The insertion loss shown in Tables 1 and 2 is a value obtained by subtracting the loss other than the electromagnetic coupling portion from the insertion loss value obtained from the measurement result in FIG.
Insertion loss per electromagnetic coupling). In addition, the loss other than the electromagnetic coupling portion is obtained by fabricating a substrate on which a single microstrip line having no electromagnetic coupling portion is formed in the same shape as the evaluation wiring substrate, and connecting both ends of the microstrip line with a ribbon. And measured.

[0040]

[Table 1]

[0041]

[Table 2]

According to the results shown in Tables 1 and 2, when the values of ML, SL, and SW satisfy the above-mentioned specific conditions, it is understood that the coupling with the insertion loss of -4 dB or less is realized. Moreover, the frequency of the signal to be transmitted is 30 GHz.
It can be seen that this relationship does not change even when changing from z to 60 GHz.

Example 2 In place of the glass ceramic having a low dielectric constant of Example 1 as a dielectric, magnesium titanate and calcium titanate were added, and the dielectric constant obtained by adding boron oxide and lithium oxide as sintering aids was changed. A wiring board for evaluation was produced in the same manner as in Example 1 by using Cu as the conductor material, and the insertion loss at a frequency of 60 GHz was measured.

Further, as a case where the conductor material is different, a humidifying reducing atmosphere (10% hydrogen, 90% nitrogen, 1500 ℃ with dew point 20 ℃)
At the same time to produce a wiring board (Sample No. 65)
The insertion loss was measured in the same manner as in Example 1. Table 3 shows the results
It was shown to.

[0045]

[Table 3]

From the results shown in Table 3, when ML, SL, and SW satisfy the conditions of the present invention, a coupling of -4 dB or less is realized, and when the conditions are not satisfied, the insertion loss is higher than -4 dB. It turned out to be bigger. It can also be seen that this relationship does not change even if the dielectric constant of the dielectric increases.

However, a comparison between Sample No. 59 and Sample No. 65 shows that the insertion loss is small even when tungsten is used as the conductor, but the insertion loss is further reduced when Cu having a small electric resistance is used. .

[0048]

As described above in detail, according to the high frequency transmission line coupling structure of the present invention, a signal is formed on a ground layer using a microstrip line as a means for transmitting a high frequency signal vertically to a substrate. Using electromagnetic coupling coupled to the microstrip line through the slot hole
Dimensions satisfying a specific relationship are defined as the frequency f of the high-frequency signal to be transmitted, the relative permittivity ε of the substrate, the distance ML from directly above the center of the slot hole of the microstrip line to the open end, the length SL of the slot hole, and the width SW of the slot hole. , The transmission loss of the high frequency signal is small, and ML, SL,
Even if the dimensions of the electromagnetic coupling part such as SW are slightly changed due to manufacturing tolerances, it is possible to realize a transmission line coupling structure that is small in characteristic change and excellent in mass productivity. As a result, it is possible to improve the reliability of a package or the like in which a multilayer wiring board or a high-frequency element having this coupling structure is mounted and housed.

[Brief description of the drawings]

1A and 1B are diagrams for explaining a basic structure of a coupling structure of a high-frequency transmission line according to the present invention, wherein FIG. 1A is a cross-sectional view, and FIG.
Is a plan view.

FIG. 2 is a diagram for explaining a method of measuring insertion loss in an example of the present invention.

[Explanation of symbols]

 Reference Signs List 1A, 1B Dielectric 2A, 2B Central conductor A First microstrip line B Second microstrip line 3 Ground layer 4 Slot hole 5A, 5B End 6 Evaluation wiring board 7 Metal block 8 Cavity 9 Conversion board for measurement 10 Ribbon

Claims (1)

[Claims] 1. A first microstrip line, a ground layer having a slot hole, a second microstrip line, the first microstrip line and the ground layer, and a second microstrip line and the ground. A dielectric disposed between the layers, wherein an end of the first microstrip line and an end of the second microstrip line face each other through the slot hole, thereby forming the second microstrip line. In a coupling structure of a high-frequency transmission line formed by electromagnetically coupling the first microstrip line and the second microstrip line, a frequency of a high-frequency signal transmitted through the line is f (GHz), and a relative permittivity of the dielectric is And ε, and the distance from directly above the center of the slot hole of the first and second microstrip lines to the end of the line is ML (mm The length of the slot hole SL (m
m), when the width of the slot hole is SW (mm), Structure of high frequency transmission line characterized by satisfying