High frequency module, board equipped with antenna, and high frequency circuit board

Abstract

A first board includes a first ground plane, a first ground land, a first transmission line, and a first signal land connected to the first transmission line, wherein the first ground land and the first signal land are formed on the same surface. A second board includes a second ground plane, a second ground land, a second transmission line, and a second signal land connected to the second transmission line, wherein the second ground land and the second signal land are formed on a surface opposing the first board. The second ground land and the second signal land oppose the first ground land and the first signal land, respectively. A conduction member connects the first ground land and the second ground land. The first signal land and the second signal land are connected by capacitance coupling without using any conductor.

Claims

1. A high frequency module comprising: a first board having a first ground plane, a first ground land connected to the first ground plane, a first transmission line, and a first signal land connected to the first transmission line, wherein the first ground land and the first signal land are located on a same surface; a second board having a second ground plane, a second ground land connected to the second ground plane, a second transmission line, and a second signal land connected to the second transmission line, wherein the second ground land and the second signal land are located on a surface opposing to the first board and are respectively opposed to the first ground land and the first signal land; and a conduction member for connecting the first ground land to the second ground land, wherein the first signal land and the second signal land are connected by capacitance coupling without using any conductor, wherein the first board further includes a radiation element connected to the first signal land with the first transmission line interposed between the radiation element and the first signal land, and a high frequency circuit element is mounted on the second board and is connected to the second signal land with the second transmission line interposed between the high frequency circuit element and the second signal land, wherein areas of the first signal land and the second signal land opposing each other are different from each other, and one of the first signal land and the second signal land is encompassed in another one of the first signal land and seconds signal land in a plan view, and wherein, when a positional shift between the first board and the second board occurs, the capacitance generated between the first signal land and the second signal land is maintained to be constant.

2. The high frequency module according to claim 1, wherein the first board includes a first stub provided on a connection portion between the first transmission line and the first signal land.

3. The high frequency module according to claim 2, wherein the second board includes a second stub provided on a connection portion between the second transmission line and the second signal land.

4. The high frequency module according to claim 2, wherein the first board includes a first protection film provided on a surface opposing to the second board, exposing the first ground land, and covering the first signal land, and the second board includes a second protection film provided on a surface opposing to the first board, exposing the second ground land, and covering the second signal land.

5. The high frequency module according to claim 1, wherein the second board includes a second stub provided on a connection portion between the second transmission line and the second signal land.

6. The high frequency module according to claim 5, wherein the first board includes a first protection film provided on a surface opposing to the second board, exposing the first ground land, and covering the first signal land, and the second board includes a second protection film provided on a surface opposing to the first board, exposing the second ground land, and covering the second signal land.

7. The high frequency module according to claim 1, wherein the first board includes a first protection film provided on a surface opposing to the second board, exposing the first ground land, and covering the first signal land, and the second board includes a second protection film provided on a surface opposing to the first board, exposing the second ground land, and covering the second signal land.

8. The high frequency module according to claim 1, wherein the first board includes a first protection film provided on a surface opposing to the second board, exposing the first ground land, and covering the first signal land, and the second board includes a second protection film provided on a surface opposing to the first board, exposing the second ground land, and covering the second signal land.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view of a high frequency module according to a first embodiment;

(2) FIG. 2A and FIG. 2B are views each illustrating planar arrangement of parts of signal lands and ground lands of a board equipped with an antenna as well as parts of ground lands and signal lands of a high frequency circuit board according to a second embodiment;

(3) FIG. 3A and FIG. 3B are respectively a perspective view and a cross-sectional view of a high frequency signal transmission path connecting an RFIC and a radiation element of a high frequency module according to a third embodiment;

(4) FIG. 4 is a graph indicating a simulation result of transmittance characteristics from an RFIC land to a leading end of a transmission line;

(5) FIG. 5 is a graph indicating a simulation result of transmittance characteristics from an RFIC land to a leading end of a transmission line according to a fourth embodiment; and

(6) FIG. 6A and FIG. 6B are respectively a perspective view and a cross-sectional view of a high frequency signal transmission path connecting an RFIC and a radiation element of a high frequency module according to a fifth embodiment.

DETAILED DESCRIPTION OF THE DISCLOSURE

First Embodiment

(7) A high frequency module 1 according to a first embodiment will be described with reference to FIG. 1. The high frequency module 1 according to the first embodiment includes a board equipped with an antenna 10 and a high frequency circuit board 30 mounted on the board equipped with an antenna 10.

(8) FIG. 1 is a cross-sectional view of the high frequency module 1 according to the first embodiment. The board equipped with an antenna 10 includes a dielectric substrate 11. On one surface (hereinafter, referred to as an upper surface) of the dielectric substrate 11, there are provided a plurality of signal lands 21, a plurality of ground lands 22, a power supply land 23, and a connector 25. On the other surface (hereinafter, referred to as a lower surface) of the dielectric substrate 11, a plurality of radiation elements 13 are provided. An operation frequency band of the radiation element 13 is a millimeter wave band, for example. A ground plane 14 is disposed on a surface or at the inside of the dielectric substrate 11. The signal land 21 is provided corresponding to the radiation element 13, and a transmission line 15 provided inside the dielectric substrate 11 connects the signal land 21 and the radiation element 13 that correspond to each other. The ground plane 14 is connected to the ground land 22.

(9) A coaxial cable serving as both a signal line and a power supply line is connected to the connector 25. A DC power supply, a local signal, an intermediate frequency signal, and the like are supplied to the board equipped with an antenna 10 through the coaxial cable. A shield conductor of the coaxial cable is connected to the ground plane 14 via the connector 25. The center conductor of the coaxial cable is connected to the power supply land 23 via the wiring inside the dielectric substrate 11.

(10) The upper surface of the dielectric substrate 11 is covered with an insulative protection film 26 that is formed of solder resist or the like. The protection film 26 covers the signal land 21, but exposes the ground land 22 and the power supply land 23. For example, openings are provided in the protection film 26 at the positions corresponding to the ground land 22 and the power supply land 23.

(11) The high frequency circuit board 30 includes a dielectric substrate 31. On one surface (hereinafter, referred to as a lower surface) of the dielectric substrate 31, there are provided a plurality of signal lands 41, a plurality of ground lands 42, and a power supply land 43. On the other surface (hereinafter, referred to as an upper surface) of the dielectric substrate 31, a high frequency integrated circuit element (RFIC) 32 and a high frequency component 33 are mounted. A ground plane 34 is disposed on a surface or at the inside of the dielectric substrate 31. The ground plane 34 is connected to the ground land 42 and is also connected to a ground terminal of the RFIC 32. Transmission lines 35 provided inside the dielectric substrate 31 respectively connect the plurality of signal lands 41 and a plurality of signal terminals of the RFIC 32.

(12) The lower surface of the dielectric substrate 31 is covered with an insulative protection film 46 that is formed of solder resist or the like. The protection film 46 covers the signal lands 41, but exposes the ground lands 42 and the power supply land 43. For example, openings are provided in the protection film 46 at the positions corresponding to the ground lands 42 and the power supply land 43.

(13) The high frequency circuit board 30 is mounted on the board equipped with an antenna 10 in a posture such that its lower surface opposes the board equipped with an antenna 10. The power supply land 23 of the board equipped with an antenna 10 and the power supply land 43 of the high frequency circuit board 30 are connected with a conduction member 50 such as a solder bump or the like, and the ground land 22 of the board equipped with an antenna 10 and the ground land 42 of the high frequency circuit board 30 are connected with the conduction member 50 such as a solder bump or the like.

(14) The plurality of signal lands 21 of the board equipped with an antenna 10 oppose the plurality of signal lands 41 of the high frequency circuit board 30 so that the mutually corresponding signal lands 21 and 41 oppose each other while being distanced from each other, whereby the signal lands 21 and signal lands 41 are connected by capacitance coupling without using any conductor. The stated capacitance is determined by the size of the signal lands 21 and 41, an interval therebetween, and a dielectric constant of a space between the signal lands 21 and 41. An underfill material, for example, is filled into between the board equipped with an antenna 10 and the high frequency circuit board 30.

(15) A shield 48 for covering the RFIC 32 and the high frequency component 33 is disposed on the upper surface of the dielectric substrate 31. For example, it is possible to seal the RFIC 32 as well as the high frequency component 33 with resin and form the shield 48 on a surface of the sealing resin. A shield cap made of metal may be used as the shield 48.

(16) The signal terminals of the RFIC 32 are each connected to the radiation element 13 with the transmission line 35 inside the dielectric substrate 31, the capacitor generated between the signal lands 21 and 41, and the transmission line 15 inside the dielectric substrate 11 interposed therebetween.

Effect of First Embodiment

(17) Next, an excellent effect of the high frequency module according to the first embodiment will be described.

(18) In general, a thinned microstrip line with a thickness of about 50 m is used as a transmission line of a millimeter wave band (wave length is no less than about 1 mm and no more than about 10 mm; frequency is no less than about 30 GHz and no more than about 300 GHz). In contrast, the signal lands 21 and 41, ground lands 22 and 42, and power supply lands 23 and 43 have a dimension of about several hundred m. These lands are each formed in a substantially circular shape with a diameter of about 300 m, for example. It is not preferable to make these lands further smaller from the standpoint of mechanical strength of bonding between the board equipped with an antenna 10 and the high frequency circuit board 30.

(19) In a case of the signal lands 21 and 41 being connected to each other with a solder bump or the like, a difference between the width of the transmission line and the dimension of the land, solder bump, or the like cannot be ignored in the transmission of millimeter wave band. For example, a difference in dimension causes discontinuity in the characteristic impedance. The transmission characteristics are degraded due to the occurrence of reflection of the millimeter wave signal at a discontinuity point of the characteristic impedance.

(20) In the first embodiment, the transmission line 15 inside the board equipped with an antenna 10 and the transmission line 35 inside the high frequency circuit board 30 are connected by capacitance coupling, whereby the degradation in the transmission characteristics due to a dimensional discontinuity of joint portions can be lessened.

(21) Although the high frequency circuit board 30 is shielded by the shield 48, a power supply signal to drive the RFIC 32, DC noise, a local signal having a lower frequency than the millimeter wave band (in general, no less than about 1 GHz and no more than about 7.5 GHz), an intermediate frequency signal (in general, no less than about 10 GHz and no more than about 15 GHz), or the like are superposed on the transmission line 35 of the millimeter wave band. In a configuration in which the signal lands 21 and 41 are connected with a solder bump or the like, the above-mentioned signals superposed on the transmission line 35 undesirably are leaked as noise to the board equipped with an antenna 10.

(22) In the first embodiment, because the transmission line 35 inside the high frequency circuit board 30 and the transmission line inside the board equipped with an antenna 10 are connected by capacitance coupling, the leakage of low frequency noise from the high frequency circuit board 30 to the board equipped with an antenna 10 can be suppressed. This makes it possible to suppress the radiation of low frequency noise from the radiation element 13.

(23) In a case of employing the configuration in which the signal lands 21 and 41 are connected with a solder bump or the like, the signal lands 21 and 41 need to be exposed. In the first embodiment, the signal lands 21 of the board equipped with an antenna 10 are covered with the protection film 26, and the signal lands 41 of the high frequency circuit board 30 are covered with the protection film 46. With this, the signal lands 21 and 41 can be also protected during a processing stage after having formed the protection films 26 and 46.

Variation on First Embodiment

(24) Next, a variation on the first embodiment will be described. In the first embodiment, although the high frequency circuit board 30 is bonded to the board equipped with an antenna 10 using solder bumps or the like, other two high frequency circuit boards may be bonded. Also in this case, it is sufficient that a ground land and a power supply land of one board are respectively connected to a ground land and a power supply land of the other board with solder bumps or the like interposed therebetween, and signal lands of the respective boards are connected to each other by capacitance coupling without using any conductor.

Second Embodiment

(25) Next, a high frequency module according to a second embodiment will be described with reference to FIG. 2A and FIG. 2B. Hereinafter, description of the same configurations as those of the high frequency module according to the first embodiment will be omitted.

(26) FIG. 2A is a view illustrating planar arrangement of parts of the signal lands 21 and ground lands 22 of the board equipped with an antenna 10 (FIG. 1) as well as parts of the signal lands 41 and ground lands 42 of the high frequency circuit board 30. For example, four ground lands 22 are so disposed as to surround the signal land 21. The signal land 21 is larger in size than the ground land 22. For example, the signal land 21 is formed in a substantially circular shape with a diameter of about 400 m, while the ground land 22 is formed in a substantially circular shape with a diameter of about 300 m.

(27) The signal lands 41 and ground lands 42 of the high frequency circuit board 30 (FIG. 1) are respectively disposed at the positions corresponding to the signal lands 21 and ground lands 22 of the board equipped with an antenna 10. The size and shape of the ground land 42 of the high frequency circuit board 30 are the same as those of the ground land 22 of the board equipped with an antenna 10. The signal land 41 of the high frequency circuit board 30 is smaller in size than the signal land 21 of the board equipped with an antenna 10. For example, the signal land 41 of the high frequency circuit board 30 is formed in a substantially circular shape with a diameter of about 300 m. This causes the signal land 41 of the high frequency circuit board 30 to be encompassed in the signal land 21 of the board equipped with an antenna 10 in a plan view.

(28) FIG. 2B illustrates a state in which the high frequency circuit board 30 is mounted as being shifted relative to the board equipped with an antenna 10. The center of the signal land 41 of the high frequency circuit board 30 is shifted relative to the center of the signal land 21 of the board equipped with an antenna 10. Note that, however, if the amount of shift falls within a tolerable range, the state in which the signal land 41 of the high frequency circuit board 30 is encompassed in the signal land 21 of the board equipped with an antenna 10 is maintained.

Effect of Second Embodiment

(29) Next, an excellent effect of the second embodiment will be described. Even in the case where the high frequency circuit board 30 is mounted as being shifted relative to the board equipped with an antenna 10, if the amount of shift falls within the tolerable range, an area of a portion where the signal lands 21 and 41 overlap with each other is unchanged. This makes it possible to maintain capacitance between the signal lands 21 and 41 to be constant. As a result, a variation in transmission characteristics among individual high frequency modules 1 can be lessened.

Variation on Second Embodiment

(30) Although each of FIGS. 2A and 2B describes an example in which the signal land 21 of the board equipped with an antenna 10 is larger than the signal land 41 of the high frequency circuit board 30, the signal land 41 may be larger than the signal land 21. For example, the signal land 21 of the board equipped with an antenna 10 may be formed in a substantially circular shape with a diameter of about 300 m, while the signal land 41 of the high frequency circuit board 30 may be formed in a substantially circular shape with a diameter of about 400 m.

Third Embodiment

(31) Next, a high frequency module according to a third embodiment will be described with reference to FIGS. 3A, 3B, and 4. Hereinafter, description of the same configurations as those of the first and second embodiments will be omitted.

(32) FIG. 3A and FIG. 3B are respectively a perspective view and a cross-sectional view of a high frequency signal transmission path connecting the RFIC 32 and the radiation element 13 (FIG. 1). Note that the upper side and lower side in FIG. 1 are inverted in the drawings of FIGS. 3A and 3B. That is, the high frequency circuit board 30 is illustrated on the lower side while the board equipped with an antenna 10 is illustrated on the upper side in each of the drawings. Further, the ground plane is not illustrated in FIG. 3A. The RFIC 32 is mounted on the high frequency circuit board 30 with solder bumps or the like interposed therebetween. An RFIC land 38 of the high frequency circuit board 30 is connected to a signal terminal of the RFIC with a solder bump interposed therebetween.

(33) The high frequency circuit board 30 includes the ground planes 34 that are respectively provided on the surfaces on both sides thereof, and four layers configured of the ground planes 34 that are disposed in an inner layer thereof. The high frequency circuit board 30 further includes the signal land 41 and the ground land 42 provided on a surface on the opposite side to the surface on which the RFIC 32 is mounted. The ground land 42 is configured by a part of the ground plane 34 formed on the surface.

(34) The signal land 41 is connected to the signal terminal of the RFIC 32 with a plurality of conductor vias 37 as well as a plurality of inner layer lands 36 disposed in the inner layer of the high frequency circuit board 30, and the RFIC land 38 interposed therebetween. The plurality of conductor vias 37 and the plurality of inner layer lands 36 function as the transmission line 35 (FIG. 1).

(35) The board equipped with an antenna 10 includes the signal land 21 provided on a surface opposing the high frequency circuit board 30, the transmission line 15 disposed in an inner layer thereof, and the ground plane 14 provided on the surface opposing the high frequency circuit board 30. A part of the ground plane 14 is used as the ground land 22. There are also provided the ground planes 14 on both sides of the transmission line 15 so that the transmission line 15 has a coplanar waveguide structure equipped with a ground. The radiation element 13 (FIG. 1) is connected to a leading end of the transmission line 15.

(36) The transmission line 15, at one end thereof, is connected to the signal land 21 with a conductor via 16 interposed therebetween. An open stub 17 is disposed on a connection portion between the transmission line 15 and the signal land 21. The open stub 17 is disposed, for example, in the same layer as the transmission line 15, and extends, taking the signal land 21 as a starting point, in a direction opposite to the side of the transmission line 15.

(37) A portion serving as the ground land 42 of the ground plane 34 provided on the surface of the high frequency circuit board 30 opposing the board equipped with an antenna 10 and a portion serving as the ground land 22 of the ground plane 14 provided on the surface of the board equipped with an antenna 10 opposing the high frequency circuit board 30 are connected to each other by each of a plurality of conduction members 50, for example, by four conduction members 50. The conduction members 50 are so disposed as to surround the signal lands 21 and 41 in a plan view. An underfill material 51 is filled into between the high frequency circuit board 30 and the board equipped with an antenna 10.

(38) FIG. 4 is a graph indicating a simulation result of transmittance characteristics S21 from the RFIC land 38 to the leading end of the transmission line 15 (FIGS. 3A and 3B). The horizontal axis represents the frequency in units of GHz, while the vertical axis represents the transmittance characteristics S21 in units of dB. A solid line in FIG. 4 indicates the transmittance characteristics S21 of the high frequency module according to the third embodiment shown in FIGS. 3A and 3B, and a broken line indicates transmittance characteristics S21 of a high frequency module according to a reference example. In the high frequency module according to the reference example, the signal lands 21 and 41 are connected with a conduction member, and the open stub 17 is not provided.

(39) Hereinafter, the configuration of the high frequency module according to the third embodiment, which was a simulation target, will be described. A desired electrostatic capacity of a capacitor configured by the signal lands 21 and 41 is about 50 fF. In order to meet this requirement, a planar shape of each of the signal lands 21 and 24 was made substantially circular having a diameter of about 300 m, a relative dielectric constant of a space between the signal lands 21 and 41 was set to be about four, an interval between the signal lands 21 and 41 was set to be about 50 m, impedance of the open stub was set to be about 50, and an electrical length of the open stub was set to be about 0.3 times the wave length of a signal of about 60 GHz.

Effect of Third Embodiment

(40) As shown in FIG. 4, it is understood that the high frequency module according to the third embodiment can obtain more favorable transmittance characteristics S21 than the high frequency module according to the reference example in a frequency band of no less than about 57 GHz and no more than about 66 GHz that is used in the communications of the Wigig standards. Further, the high frequency module according to the third embodiment exhibits rejection characteristics of no less than about 10 dB in a frequency region lower than about 50 GHz.

(41) As can be understood from the simulation result shown in FIG. 4, the configuration in which the signal lands 21 and 41 are not connected with a conduction member makes it possible to improve the transmittance characteristics in the frequency band of no less than about 57 GHz and no more than about 66 GHz, and improve the rejection characteristics against low frequency noise in a frequency region lower than the above frequency band. Further, providing the open stub 17 makes it possible to obtain the impedance matching.

Fourth Embodiment

(42) Next, a high frequency module according to a fourth embodiment will be described with reference to FIG. 5. Hereinafter, description of the same configurations as those of the first through third embodiments will be omitted.

(43) In the high frequency module according to the fourth embodiment, a short stub is provided in place of the open stub 17 of the high frequency module according to the third embodiment (FIGS. 3A and 3B). Impedance of the short stub is about 50, and an electrical length thereof is about 0.75 times the wave length of a signal of about 60 GHz. Other configurations are the same as those of the high frequency module according to the third embodiment shown in FIGS. 3A and 3B.

(44) FIG. 5 is a graph indicating a simulation result of transmittance characteristics S21 from the RFIC land 38 to the leading end of the transmission line 15. The horizontal axis represents the frequency in units of GHz, while the vertical axis represents the transmittance characteristics S21 in units of dB. A solid line in FIG. 5 indicates the transmittance characteristics S21 of the high frequency module according to the fourth embodiment, and a broken line indicates transmittance characteristics S21 of a high frequency module according to a reference example. The transmittance characteristics S21 of the high frequency module according to the reference example are the same as those shown in FIG. 4.

(45) It is understood that the high frequency module according to the fourth embodiment can also obtain more favorable transmittance characteristics S21 than the high frequency module according to the reference example in the frequency band of no less than about 57 GHz and no more than about 66 GHz that is used in the communications of the Wigig standards. Further, the high frequency module according to the fourth embodiment also exhibits more favorable rejection characteristics than the high frequency module according to the reference example in a frequency region lower than about 50 GHz.

(46) In the fourth embodiment, because the short stub is used in place of the open stub, high electro-static discharge (ESD) resistance can be obtained.

(47) It can be understood, by comparing FIG. 4 with FIG. 5, that the employment of the short stub rather than the open stub is preferable in the case where the leakage of low frequency noise of about 50 GHz, which is slightly lower than the Wigig standards frequency band, needs to be suppressed. It can be understood that the employment of the open stub rather than the short stub is preferable so as to obtain an effect of noise leakage suppression across the entire frequency region lower than the Wigig standards frequency band.

Fifth Embodiment

(48) Next, a high frequency module according to a fifth embodiment will be described with reference to FIG. 6A and FIG. 6B. Hereinafter, description of the same configurations as those of the first through fourth embodiments will be omitted.

(49) FIG. 6A and FIG. 6B are respectively a perspective view and a cross-sectional view of a high frequency signal transmission path connecting the RFIC 32 and the radiation element 13. Although, in the third embodiment, the open stub 17 is provided to the transmission line 15 inside the board equipped with an antenna 10 (FIGS. 3A and 3B), an open stub 18 is provided on a connection portion between the transmission line 35 inside the high frequency circuit board 30 (FIG. 1) and the signal land 41 in the fifth embodiment. Further, like in the fourth embodiment, a short stub instead of the open stub 18 may be provided. The same effects as those of the third or fourth embodiment can be obtained in the fifth embodiment as well.

(50) It should be understood that the above-described embodiments are illustrative only, and that configurations described in different embodiments can partly replace each other or be combined as well. Same action effects brought by the same configurations in the plurality of embodiments are not successively described in each of the embodiments. Further, the present disclosure is not limited to the above-described embodiments. For example, it will be apparent to those skilled in the art that various kinds of changes, improvements, combinations, and so on can be carried out.

(51) While preferred embodiments of the disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The scope of the disclosure, therefore, is to be determined solely by the following claims.