JP4236607B2 - Circuit board - Google Patents

Description

  The present invention relates to a circuit board equipped with a high-frequency semiconductor element and including a waveguide connected to the transmission line. In particular, transmission loss of a high-frequency signal from the microstrip line to the waveguide can be suppressed. At the same time, it relates to a circuit board suitable for high yield and inexpensive mass production.

In-vehicle radars that are considered to be applied to subscriber wireless access systems (FWA), satellite communications, home links, ultra-high speed wireless LANs, collision prevention, etc. that transmit high-speed and large-capacity information are high-frequency signals of several to 100 GHz. Is transmitted and received with an antenna. Among them, many antennas used in a frequency band of 40 GHz or more have a structure in which a waveguide having a small transmission loss is used as a feeding part.
On the other hand, a semiconductor device that generates or amplifies a high-frequency signal of 40 GHz or more is usually used by being mounted on a planar circuit board such as a microstrip line. Therefore, it is important how to connect the planar line to the waveguide while suppressing loss.

First, a conventionally used circuit board will be described with reference to FIG. FIG. 9A is a cross-sectional view showing the prior art of a circuit board, and FIG. 9B is an arrow view seen from the direction indicated by the reference numeral B in FIG. In FIG. 9, a circuit board 21 has a semiconductor element 22 mounted on a dielectric substrate 24, and a microstrip line 23 connected to the semiconductor element 22 is wired on the dielectric substrate 24.
On the other hand, a ground pattern 25 in which a slot 26 is formed is provided on the side of the dielectric substrate 24 opposite to the side where the microstrip line 23 is wired, and a waveguide 27 is connected to the ground pattern 25. Has been. The slot 26 is formed so as to fit inside the waveguide 27.
In such a conventional circuit board 21, when a high frequency signal is transmitted between the microstrip line 23 and the waveguide 27, conversion is possible only through the slot 26, and excitation is performed only in the slot 26. Yes. Further, the impedance can be adjusted according to the size of the slot 26. However, there is a limit to the impedance adjustment possible with the size of one slot 26. Due to the reflection of a high-frequency signal due to mismatching, the transmission loss may increase and the circuit board characteristics may be insufficient.
Therefore, conventionally, such a connection structure has been improved in technology for reducing transmission loss.

  For example, in Patent Document 1, the name of the invention is “connection structure with wiring board and its waveguide”, “dielectric substrate, signal transmission line formed on one surface of the dielectric substrate, A wiring board having a connection portion for connecting the signal transmission line and the waveguide, wherein the connection portion is formed on the other surface of the dielectric substrate and faces the end of the signal transmission line. A first ground layer having a first slot hole, a dielectric part formed on at least the first slot hole forming surface of the first ground layer, and a surface of the dielectric part, A second ground layer having a second slot hole at a position facing the first slot hole and maintained at the same potential as the first ground layer when connected to the waveguide. A wiring board ”is disclosed.

Hereinafter, the prior art disclosed in Patent Document 1 will be described with reference to FIG. In FIG. 10, a wiring board connects a waveguide 32 to a high frequency package 31, a high frequency element 33 is mounted on a dielectric substrate 30, and a first slot hole is formed on the lower surface of the dielectric substrate 30. A first ground layer 35 forming 34 is provided. In addition, a dielectric portion 36 is provided inside the waveguide 32 connected to the first ground layer 35, and the second ground layer 38 forming the second slot portion 37 is connected to the inner wall of the waveguide 32. The size is the same as or smaller than the size.
In this way, by providing the second slot hole in addition to the first slot hole, the high-frequency signal that has passed through the first slot hole can be further excited by the second slot hole, and thus the signal transmission line. And the connectivity of the waveguide can be improved. In addition, it is possible to make the magnetic field distribution horizontal at the interface between the second slot portion 37 and the waveguide 32. Further, it is possible to suppress the electromagnetic field distribution in the air at the connection portion and suppress the conversion loss due to radiation. As a result, a connection structure with a small transmission loss of high-frequency signals can be realized.

  Further, as a technology before Patent Document 1, the same applicant as Patent Document 1 in Patent Document 2 is connected to a high-frequency element housed in the cavity of the high-frequency package under the name of “high-frequency package and its connection structure”. A ground layer having an opening is formed on the surface of the dielectric substrate opposite to the surface on which the high-frequency transmission line is formed, and functions as a terminating wall of the waveguide connecting the ground layer, and the high-frequency transmission line is electromagnetically By coupling to the opening by coupling and exciting the waveguide connected using this opening, it is possible to directly connect to the waveguide having an open end, and to seal the high-frequency element in the cavity. An invention that can be surely stopped is disclosed.

JP 2001-217618 A JP 11-112209 A

However, since the conventional technique described in Patent Document 2 has only one slot hole for exciting a high-frequency signal, there is a limit to improving the connectivity between the signal transmission line and the waveguide. was there.
Further, in the conventional technique described in Patent Document 1, slot holes are added in the waveguide to provide first and second slot holes, and the transmission loss is more effectively reduced. A dielectric is provided between the first slot hole and the second slot hole. This dielectric is intended to match the impedance of the slot hole and the impedance of the waveguide. This is also described in the prior art disclosed in Patent Document 2.
However, this dielectric must be housed inside the waveguide, and of course, the dielectric member is required, and the processing and housing processes are necessary, which affects the cost and yield. Given that, there was a problem in terms of mass productivity.
Moreover, when processing the dielectric, the effective wavelength in the dielectric varies due to variations in the dielectric constant of the material, and the distance between the first slot hole and the second slot varies due to variations in the thickness of the dielectric. For this reason, in order to adjust the impedance, it is necessary to adjust both the material and the shape element, which has been a big problem for mass production.

  The present invention has been made in response to such a conventional situation, and it is possible to transmit high-speed and large-capacity information by suppressing transmission loss associated with passage of a high-frequency signal through a waveguide, and at the same time, high yield and inexpensive mass production. It also provides a circuit board suitable for the above.

To achieve the above object, the circuit board is a first aspect of the present invention, a ground pattern microstrip line connected to the device and elements on one surface to form a first slot-hole on the other surface is wire A circuit board having a first dielectric substrate comprising: and a waveguide connected to the other surface of the first dielectric substrate, on a ground pattern provided on the first dielectric substrate A metal layer that forms a cavity having a larger horizontal cross-sectional area than the first slot hole is provided at a position coincident with the first slot hole, and the metal layer is cut horizontally through the cavity at a position coincident with the first slot hole. A metal plate for forming a second slot hole having a small area is provided on the metal layer, and a waveguide having a horizontal cross-sectional area larger than that of the second slot hole is connected to the metal plate .

Furthermore, a circuit board according to a second aspect of the present invention is the circuit board according to the first aspect , wherein instead of the metal layer, a cavity is formed and a side surface ground pattern is provided on the inner peripheral surface of the cavity, and at the same time A second dielectric substrate having a ground via connected to the first dielectric substrate is provided, and a waveguide is connected to the second dielectric substrate.

In the circuit board according to claim 1 and claim 2, via the first slot-hole and the cavity, the metal plate or metal cap with a second slot holes at positions coincident with the first slot-hole Therefore, the high-frequency signal passing through the waveguide is excited by the second slot hole in addition to the first slot hole, and impedance mismatch can be reduced, so that transmission loss can be reduced. is there. In addition, since the first slot hole and the second slot hole are formed at positions that coincide with each other through the cavity, no dielectric material is required, and the process is more effective than housing and manufacturing the dielectric. The number is small, and low-cost productivity and high mass productivity can be exhibited.

  Further, when the dielectric is accommodated inside the waveguide, it is necessary to match the impedance in consideration of the dielectric constant of the dielectric and the shape factor, which is described in claims 1 to 5. In the circuit board, air having a relative dielectric constant of 1 exists in the formed cavity, and a stable dielectric constant is ensured as compared with the case where a separate dielectric is accommodated inside the waveguide. Can do. Therefore, only the shape element needs to be considered for the impedance adjustment, and the shape can be easily processed because it is a cavity.

Hereinafter, a first embodiment of a circuit board according to the present invention will be described with reference to FIG.
FIG. 1A is a cross-sectional view of the circuit board according to the first embodiment, and FIG. 1B is a view as seen from the direction of the symbol A shown in FIG.
In FIG. 1, a circuit board 1 a has a semiconductor element 2 mounted on a dielectric substrate 4, and a microstrip line 3 is connected to the semiconductor element 2. A ground pattern 5 is provided on the lower surface of the dielectric substrate 4, and a slot 6 is formed in the ground pattern 5. The end 3a of the microstrip line 3 is provided in a so-called open stub state at a distance of about 1/4 wavelength of the high frequency signal frequency indicated by the symbol L from the center of the slot 6. Thus, the microstrip line 3 and the slot 6 are electromagnetically coupled.
A waveguide 7 is connected to the ground pattern 5, and a metal plate 8 in which an additional slot 10 is formed is accommodated inside the waveguide 7. The additional slot 10 is formed so as to coincide with the slot 6 through a cavity 9 formed inside the waveguide 7.

In the circuit board 1a according to the present embodiment thus formed, for example, a high-frequency signal generated by the semiconductor element 2 is excited from the microstrip line 3 to the slot 6 by electromagnetic coupling and transmitted. Further, it is excited by the additional slot 10 and transmitted into the waveguide 7.
During transmission of this high-frequency signal, transmission loss occurs due to reflection of the high-frequency signal due to the impedance mismatch between the microstrip line 3 and the waveguide 7, but the impedance mismatch is not limited to the slot 6, Further reduction is possible by the additional slot 10. In addition, the additional slot 10 is provided at a position coinciding with the slot 6 through the cavity 9, that is, immediately below the slot 6 in the waveguide 7. Since the cavity 9 is an air layer, the relative dielectric constant is stable at 1, and stable impedance matching can be performed by the additional slot, so that transmission loss of high-frequency signals can be stably reduced.

Next, a second embodiment of the circuit board according to the present invention will be described with reference to FIG.
FIG. 2 is a cross-sectional view of a circuit board according to the second embodiment. The arrow view used when explaining the first embodiment is omitted because it is substantially the same as that of the first embodiment in this embodiment.
2, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In the circuit board 1b according to the present embodiment, steps 11a and 11b are formed inside the waveguide 7a, and a metal plate 8 in which an additional slot 10 is formed is installed in the steps 11a and 11b. .
In the present embodiment, in addition to the effect of the first embodiment, the first embodiment is configured to install the metal plate 8 on the inner peripheral surface of the waveguide 7, while the step 11a. 11b can be installed with a larger installation area, so that it can be fixed more firmly. In addition, the metal plate 8 can be easily positioned by inserting it into the inside from the open end of the waveguide 7a and accommodating the steps 11a and 11b.

A third embodiment of the circuit board according to the present invention will be described with reference to FIG. (In particular, corresponding to claim 1 )
FIG. 3 is a cross-sectional view of a circuit board according to the third embodiment. The arrow view used when explaining the first embodiment is omitted because it is substantially the same as that of the first embodiment in this embodiment.
3, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In the circuit board 1c according to the present embodiment, a metal plate 12 in which a cavity 9 is formed is further provided on the lower surface of the ground pattern 5, and the slot 6 of the ground pattern 5 is denoted on the lower surface of the metal plate 12. A metal plate 8 having an additional slot 10 is installed. The waveguide 7 is connected to the lower surface of the metal plate 8.
In the present embodiment, the metal plate 8 is not housed in the waveguide 7 and is provided on the end surface of the waveguide 7. And the cavity 9 is formed similarly to 2nd Embodiment.
Also in the present embodiment, as in the first and second embodiments, impedance mismatch can be further reduced not only by the slot 6 but also by the additional slot 10. In addition, a dielectric substrate that transmits several tens of GHz, for example 77 GHz used in an on-vehicle radar, is very thin, easily broken, and needs to be handled with care. However, the use of a metal plate greatly increases the strength and provides excellent earthquake resistance.

Furthermore, a fourth embodiment of the circuit board according to the present invention will be described with reference to FIG. (In particular, corresponding to claim 2 )
FIG. 4 is a cross-sectional view of a circuit board according to the fourth embodiment. The arrow view used when explaining the first embodiment is also omitted in this embodiment.
4, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In the circuit board 1d according to the present embodiment, instead of the metal plate 12 provided in the third embodiment, a dielectric 13 is provided on the lower surface of the ground pattern 5, and the metal plate is provided on the lower surface of the dielectric 13. 8 is installed. The metal plate 8 is connected to the ground pattern 5 by the ground via 14 and the side surface ground pattern 16. Then, the waveguide 7 is connected to the metal plate 8 as in the third embodiment.
The circuit board 1d configured as described above can achieve the same effects as those of the first to third embodiments described above.

Finally, a circuit board according to a fifth embodiment of the present invention will be described with reference to FIG.
FIG. 5 is a cross-sectional view of a circuit board according to the fifth embodiment. The arrow view is also omitted in the present embodiment.
5, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In the circuit board 1e according to the present embodiment, a metal cap 18 in which an additional slot 10 is formed is provided instead of the metal plate 8 provided in the first to fourth embodiments. In addition, a conductor 17 is interposed between the inner peripheral surface of the waveguide 7 and the outer peripheral surface of the metal cap 18.
In this embodiment configured as described above, since the metal cap 18 is provided so as to be connected to the ground pattern 5, the distance between the preset slot 6 and the additional slot 10 and the dimension of the cavity 9 to be formed are set. It can be adjusted easily, and the impedance can be adjusted more easily.
In addition, although the conductor 17 is required to be inserted, the metal cap 18 itself can be inserted relatively easily because the end face of the metal cap 18 is installed on the ground pattern 5, and a large load is applied to the assembly process. There is no.
In addition, the effects exhibited by the circuit boards according to the first and second embodiments can be similarly achieved.

Next, the simulation was implemented using the finite element method about the circuit board 1a which concerns on 1st Embodiment. The results will be described with reference to FIGS.
FIG. 6 shows the S11 (reflection) analysis result with the input side as a microstrip line, FIG. 7 shows the S21 (passing) analysis result, and FIG. 8 shows the radiation ratio analysis result. It is shown. In any of the figures, the analysis result of the circuit board 21 shown in FIG. 9 is added as a conventional structure.
In FIG. 6, the horizontal axis represents the frequency of the high-frequency signal transmitted from the microstrip line, and the vertical axis represents the absolute value of the reflection level of the high-frequency signal. The reflection analysis result of the circuit board 1a according to the first embodiment described as the present invention structure shows a lower reflection level at any frequency than the reflection analysis result of the circuit board 21 described as the conventional structure. ing. In particular, in the vicinity of 76.5 GHz, the level is dramatically lower than that of the conventional structure. Furthermore, for example, the frequency width of −15 dB or less is about double from the conventional 3 GHz to 6 GHz. Thus, it is understood that by adjusting to match the generated high frequency signal, the reflection of the high frequency signal can be improved to a significant level.

  In FIG. 7, the horizontal axis is the same as that in FIG. 6, and the vertical axis represents the absolute value of the pass level of the high-frequency signal. Also in FIG. 7, the passage analysis result of the circuit board 1 a according to the first embodiment shows excellent results at all frequencies compared to the passage analysis result of the circuit board 21 according to the conventional technique. In particular, while the conventional structure shows the characteristic that the pass characteristic deteriorates in the high frequency band, in the embodiment of the present invention, the degree of the deterioration is small and the characteristic persists even in the high frequency band, and the change of the characteristic as a whole I can understand that there are few.

  In FIG. 8, the horizontal axis is the same as in FIG. 6, and the vertical axis indicates the ratio of radiation loss in percentage. Also in this analysis result, the circuit board 1a according to the first embodiment shows excellent characteristics with less radiation loss than the circuit board 21 according to the prior art at all frequencies. It can be understood that the circuit board 1a is superior to the circuit board 21 in that the change in characteristics is smaller than that of the circuit board 21.

  The circuit board according to the present invention can be used as an electronic component of an electronic device such as a mobile phone or a portable information terminal that transmits a high-frequency signal at a high speed and a large capacity, and a high-speed wireless LAN, an inter-vehicle radar, or a personal computer.

(A) is sectional drawing of the circuit board based on the 1st Embodiment of this invention, (b) is the arrow line view seen from the direction of the code | symbol A shown in (a). It is sectional drawing of the circuit board based on the 2nd Embodiment of this invention. It is sectional drawing of the circuit board based on the 3rd Embodiment of this invention. It is sectional drawing of the circuit board based on the 4th Embodiment of this invention. It is sectional drawing of the circuit board based on the 5th Embodiment of this invention. FIG. 6 shows a (reflection) analysis result obtained by performing a simulation analysis while comparing the circuit board according to the first embodiment and a conventional circuit board. The circuit board which concerns on 1st Embodiment and the conventional circuit board are compared, and the simulation analysis (passing) analysis result is shown. The radiation ratio analysis result which carried out the simulation analysis while comparing the circuit board based on 1st Embodiment and the conventional circuit board is shown. (A) is sectional drawing which shows the prior art of a circuit board, (b) is the arrow line view seen from the direction of the code | symbol A shown in (a). It is sectional drawing which shows the prior art of a circuit board.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1a-1e ... Circuit board 2 ... Semiconductor element 3 ... Micro strip line 3a ... End part 4 ... Dielectric substrate 5 ... Ground pattern 6 ... Slot 7, 7a ... Waveguide 8 ... Metal plate 9 ... Cavity 10 ... Additional slot 11a , 11b ... Step 12 ... Metal plate 13 ... Dielectric 14 ... Ground via 15 ... Dielectric 16 ... Side surface ground pattern 17 ... Conductor 18 ... Metal cap 21 ... Circuit board 22 ... Semiconductor element 23 ... Microstrip line 24 ... Dielectric board 25 ... Ground pattern 26 ... Slot 27 ... Waveguide 30 ... Dielectric substrate 31 ... High frequency package 32 ... Waveguide 33 ... High frequency element 34 ... First slot hole 35 ... First ground layer 36 ... Dielectric part 37 ... second slot 38 ... second ground layer

Claims (2)

A first dielectric substrate having a ground pattern on one surface and a ground pattern forming a first slot hole on the other surface and a microstrip line connected to the device; and the first dielectric substrate A circuit board having a waveguide connected to the other surface, wherein the first slot is positioned at a position coinciding with the first slot hole on a ground pattern provided on the first dielectric substrate. A metal layer forming a cavity having a larger horizontal cross-sectional area than the hole is provided, and a second slot hole having a smaller horizontal cross-sectional area than the cavity is formed through the cavity at a position coinciding with the first slot hole. A circuit board, wherein a metal plate is provided on the metal layer, and the waveguide having a horizontal sectional area larger than that of the second slot hole is connected to the metal plate . Instead of the metal layer, a cavity having a horizontal cross-sectional area larger than that of the first slot hole is formed at a position coinciding with the first slot hole, and a side surface ground pattern is provided on the inner peripheral surface of the cavity. A second dielectric substrate having a ground via connected to the ground pattern is provided, and the second dielectric substrate is cut in a horizontal direction from the cavity through the cavity at a position coinciding with the first slot hole. a metal plate which forms a small second slot hole area provided, according to claim 1, wherein the connecting the waveguide big horizontal cross-sectional area than said second slot holes in the metal plate on Circuit board.