A radio-frequency module includes: boards; interconnect parts that are conductor layers on the individual boards, at least one of the conductor layers being connected to an RF chip; a land that is a conductor layer connected to one of the interconnect parts; a transmission unit disposed between the boards, connected to the boards through the land to transmit a signal; a ground conductor disposed around the land and the interconnect part connected to the land; an isolation part disposed between the interconnect layer connected to the land and the ground conductor to isolate the interconnect layer connected to the land from the ground conductor; and a coupling part disposed between the land and the ground conductor to short-circuit the land and the ground conductor.

BACKGROUND

1. Technical Field

The present disclosure relates to a radio-frequency module connected to a radio frequency (RF) chip for a millimeter wave band and configured to transfer a radio-frequency signal.

2. Description of the Related Art

As a known radio-frequency module for transmitting a signal in a radio-frequency band such as a millimeter wave band, a module using, for example, a ball grid array (BGA) package has been used. To suppress degradation of pass characteristics of signals, a module for transmitting radio-frequency signals needs to match impedance.

For example, Japanese Unexamined Patent Application Publication No. 2001-308547 discloses a configuration in which a matching circuit whose line width and line length is adjusted to obtain matching between a via connecting a plurality of circuit layers and a signal line connected to the via is provided in part of the signal line.

SUMMARY

In the known technique of Japanese Unexamined Patent Application Publication No. 2001-308547, however, since the matching circuit needs to be provided in part of the signal line, an increase in the circuit scale needs to be handled.

One non-limiting and exemplary embodiment provides a radio-frequency module that can obtain impedance matching with a simple configuration without an increase in circuit scale.

In one general aspect, the techniques disclosed here feature a radio-frequency module including: a plurality of boards; a plurality of interconnect parts that are a plurality of conductor layers, each conductor layer of the plurality of conductor layers being provided on a corresponding one of the plurality of boards, at least one of the plurality of conductor layers being connected to an RF chip; a land that is a conductor layer connected to an interconnect part of the plurality of interconnect parts; a transmission circuitry disposed between two of the plurality of boards, and connected to the plurality of boards through the land to transmit a signal; a ground conductor disposed around the land and the interconnect part to which the land is connected; an isolation part disposed between the land and the ground conductor to isolate the land and the ground conductor from each other, and disposed between the interconnect part to which the land is connected and the ground conductor to isolate the interconnect part to which the land is connected and the ground conductor from each other; and a coupling part disposed between the land and the ground conductor to short-circuit the land and the ground conductor.

These general and specific aspects may be implemented using a device, a system, and any combination of devices and systems.

According to the present disclosure, impedance matching can be obtained with a simple configuration without an increase in circuit scale.

DETAILED DESCRIPTION

First, a typical configuration of a radio-frequency module using a ball grid array (BGA) package in the present disclosure and possible problems thereof will be described with reference to the drawings.

FIG. 1is a cross sectional view schematically illustrating a typical configuration of a radio-frequency module1using a BGA package. The radio-frequency module1illustrated inFIG. 1includes a BGA package11and a printed circuit board12, and is connected to an RF chip10for a millimeter wave band.

A surface of the BGA package11at one side is connected to the RF chip10. Another surface of the BGA package11at the other side is provided with a signal transmission ball111and a grounding ball112, and is connected to the printed circuit board12through the signal transmission ball111. The signal transmission ball111is a transmission unit for allowing a signal to be transmitted between the BGA package11and the printed circuit board12. The grounding ball112is disposed adjacent to the signal transmission ball111, and has a zero potential.

The configuration of the radio-frequency module1will now be more specifically described.FIG. 2is a cross sectional view schematically illustrating the configuration of the typical radio-frequency module1.

As illustrated inFIG. 2, a plurality of interconnect parts113are formed on either surface of the BGA package11and used for signal transmission. A land114is provided on a surface of the BGA package11not connected to the RF chip2(seeFIG. 1) and is connected to the interconnect parts113. The interconnect parts113and the land114are conductor layers provided on the surfaces.

A ground conductor115is a conductor layer disposed around the interconnect parts113and the land114, and is connected to the grounding ball112to have a zero potential. An isolation part116is a notch formed on a plane and isolates the land114and the ground conductor115from each other.

Each of the signal transmission ball111and the grounding ball112is disposed in a location where the land114is formed. Each of the signal transmission ball111and the grounding ball112is formed by soldering, and has a substantially spherical shape due to surface tension. Locations of the signal transmission ball111, the interconnect parts113, and the land114will be described later.

The printed circuit board12includes interconnect parts121, vias122, lands123, ground conductors124, and isolation parts125, and is constituted by a plurality of layers. The interconnect parts121are constituted by a plurality of layers, and serves as interconnections among circuits provided in a front layer12a, an inner layer12b, and a back layer12cof the printed circuit board12. Each of the vias122is a transmission unit for transmitting a signal among the layers of the printed circuit board12.

The land123is provided in a portion where the signal transmission ball111is connected to the front layer12aof the printed circuit board12. The land123is a conductor layer similar to the interconnect parts121, and is connected to the interconnect part121.

The land123is disposed between the via122and the corresponding interconnect parts121. The via122is connected to the interconnect part121through the land123.

The ground conductors124are conductor layers disposed around the interconnect parts121and the land123, and have a zero potential. Each of the isolation parts125is a notch formed on a plane between a set of the interconnect part121and the land123, and the ground conductor124, and isolates the set of the interconnect part121and the land123from the ground conductor124.

Configurations of the signal transmission ball111, the interconnect part113, and the land114will be described.FIG. 3is an enlarged view illustrating a configuration of a main portion of the typical radio-frequency module1.FIG. 3is an enlarged view of a region indicated by arrow X inFIG. 2and viewed in a direction of arrow III inFIG. 2.

InFIG. 3, the signal transmission ball111is connected to the interconnect part113through the land114. The ground conductor115is a conductor layer provided around the interconnect part113and the land114, and has a zero potential when connected to the grounding ball112(seeFIG. 2). The isolation part116is a notch formed in a plane between a set of the interconnect part113and the land114, and the ground conductor115, and isolates the set of the interconnect part113and the land114from the ground conductor115.

In the radio-frequency module1using the typical BGA package as illustrated inFIGS. 1 and 2, the ground conductor115having a zero potential is generally formed outside the interconnect part113and the land114.

In the case of the configuration constituted by the signal transmission ball111, the interconnect part113, and the land114illustrated inFIG. 3, an impedance is discontinuous due to the capacitance of the land114, and thus, it is difficult to obtain impedance matching. The impedance matching will now be described.

FIG. 4is a Smith chart showing reflectance characteristics of a signal in the land114of the typical radio-frequency module1.FIG. 4shows paths of changes from 0 Hz to 100 GHz in S-parameters S11and S22in the land114.

Under the influence of capacitance of the land114, the paths of the S-parameters S11and S22move in a direction indicated by arrow Z, i.e., downward in a clockwise direction. The paths of the S-parameters S11and S22move away from the center of the Smith chart as the frequency increases. That is, as the frequency increases, discontinuity of impedance increases. Next, pass characteristics and reflectance characteristics of a signal in the land114will be specifically described.

FIG. 5shows pass characteristics of a signal in the land114of the typical radio-frequency module1.FIG. 6shows reflectance characteristics of a signal in the land114of the typical radio-frequency module1.

InFIG. 5, the abscissa represents the frequency of a signal, and the ordinate represents a relative gain indicating the intensity of a signal passing through the land114. InFIG. 5, as the value on the ordinate increases, pass characteristics of the signal improve. InFIG. 6, the abscissa represents the frequency of a signal, and the ordinate represents a relative gain indicating the intensity of a signal reflected on the land114. InFIG. 5, as the value on the ordinate increases, the degree of reflection of the signal increases.

In the configuration ofFIG. 3, the intensity of a signal passing through the land114is small in a millimeter wave band (a frequency band of 30 GHz or more), as shown inFIG. 5. As shown inFIG. 6, a signal in a millimeter wave band greatly reflects on the land114. That is, as shown inFIGS. 5 and 6, under the influence of discontinuity of impedance due to the capacitance of the land114, pass characteristics of a signal in a millimeter wave band degrades.

For example, in Japanese Unexamined Patent Application Publication No. 2001-308547, matching circuits having different line widths and line lengths are provided between an interconnect part and a land to reduce discontinuity of impedance due to the capacitance of the land. However, the matching circuits of Japanese Unexamined Patent Application Publication No. 2001-308547 shows a variation in impedance depending on the accuracy of the line width and line length, and thus, it is difficult to reduce impedance discontinuity sufficiently.

The present disclosure focused on the configuration of a land.

Embodiment

An embodiment of the present disclosure will be described in detail with reference to the drawings. The following embodiment is merely an example, and is not intended to limit the present disclosure.

A configuration of a radio-frequency module according to an embodiment of the present disclosure will be described with reference toFIG. 7.

FIG. 7is a cross-sectional view schematically illustrating an example configuration of a radio-frequency module2according to an embodiment of the present disclosure. The radio-frequency module2illustrated inFIG. 7includes a BGA package21and a printed circuit board22. InFIG. 7, components of the configuration also shown inFIG. 2are denoted by the same reference characters as those used inFIG. 2, and detailed description thereof is not repeated. The radio-frequency module2illustrated inFIG. 7includes a land214different from the land114illustrated inFIG. 2, and a coupling part217is added to the configuration illustrated inFIG. 2. Although not shown inFIG. 7, the radio-frequency module2of this embodiment includes an isolation part216different from the isolation part116illustrated inFIGS. 2 and 3. The land214, the isolation part216, and the coupling part217will now be described with reference toFIG. 8.

FIG. 8is an enlarged view illustrating a configuration of a main portion of the radio-frequency module2according to the embodiment of the present disclosure.FIG. 8is an enlarged view of a region indicated by arrow X inFIG. 7and viewed in a direction of arrow III inFIG. 7.

InFIG. 8, the signal transmission ball111is a transmission unit for transmitting a signal between a BGA package21(seeFIG. 7) and a printed circuit board22(seeFIG. 7), and is connected to an interconnect part113through the land214. A ground conductor115is a conductor layer provided around the interconnect part113and the land214, and has a zero potential when connected to a grounding ball112(seeFIG. 7). The isolation part216is a notch formed on a plane between a set of the interconnect part113and the land214, and the ground conductor115, and isolates the set of the interconnect part113and the land214from the ground conductor115.

The land214is a circular conductor layer, and is connected to the interconnect part113at a point P.

In the land214, the coupling part217is disposed at the side of a center Q opposite to the point P, i.e., on a line extending from a line connecting a center Q and the interconnect part113. The coupling part217couples the land214and the ground conductor115to each other, and partially short-circuits the land214.

The configuration illustrated inFIG. 8can obtain impedance matching of the radio-frequency module2according to this embodiment. Characteristics of the radio-frequency module2of this embodiment will now be described.

FIG. 9is a Smith chart showing reflectance characteristics of a signal in the land214of the radio-frequency module2according to the embodiment of the present disclosure. In a manner similar toFIG. 4,FIG. 9shows paths of changes from 0 Hz to 100 GHz in S-parameters S11and S22in the land214.

Since the land214is partially short-circuited, the paths of the S-parameters S11and S22start from the left end of a horizontal line in the Smith chart. Under the influence of capacitance of the land214, the S-parameters S11and S22moves in a direction indicated by arrow Z′, i.e., downward in a clockwise direction. The paths of the S-parameters S11and S22approach the center of the Smith chart as the frequency increases. That is, as the frequency increases, impedance discontinuity is gradually canceled, and impedance matching can be obtained. Pass characteristics and reflectance characteristics of a signal in the land214will now be described in detail.

FIG. 10shows pass characteristics of a signal in the land214of the radio-frequency module2according to the embodiment of the present disclosure.FIG. 11shows reflectance characteristics of a signal in the land214of the radio-frequency module2according to the embodiment of the present disclosure.

InFIG. 10, the abscissa represents the frequency of a signal, and the ordinate represents a relative gain indicating the intensity of a signal passing through the land214.FIG. 10shows that as the value on the ordinate increases, pass characteristics of the signal improves. InFIG. 11, the abscissa represents the frequency of a signal, and the ordinate represents a relative gain indicating the intensity of a signal reflected on the land214.FIG. 11shows that as the value on the ordinate increases, the degree of reflection of the signal increases.

In the configuration ofFIG. 8, the intensity of a signal passing through the land214can be increased in a millimeter wave band, as shown inFIG. 10. As shown inFIG. 11, the intensity a signal reflected in the land214is reduced in a millimeter wave band.

That is, in the configuration ofFIG. 8, the coupling part217couples the land214and the ground conductor115to each other and partially short-circuits the land214so that impedance matching can be obtained. As a result of impedance matching, as shown inFIGS. 10 and 11, reflection of a signal in a millimeter wave band can be reduced so that pass characteristics can be enhanced.

Signal transmission in the radio-frequency module2of this embodiment will be described in comparison with signal transmission in the typical radio-frequency module1illustrated inFIG. 2.

FIG. 12is a schematic illustration of signal transmission in the typical radio-frequency module1.FIG. 13is a schematic illustration of signal transmission in the radio-frequency module2according to this embodiment of the present disclosure.FIGS. 12 and 13illustrate locations where signal intensity is high in the case of transmission of a signal in a millimeter wave band, by using light and dark patterns. InFIGS. 12 and 13, a lighter region indicates a location where the signal intensity is higher.

In the typical radio-frequency module1, as illustrated in a region P1inFIG. 12, a signal in a millimeter wave band is emitted from the land114connected to the signal transmission ball111to the outside of the board. Consequently, as illustrated in a region P2, the intensity of the signal transmitted to the printed circuit board12decreases.

On the other hand, in the radio-frequency module2of this embodiment, as illustrated in a region P3inFIG. 13, a signal in a millimeter wave band is not emitted from the land214connected to the signal transmission ball111to the outside of the board. This is because the land214is connected to the ground conductor115through the coupling part217and is short-circuited so that the potential at the region P3is zero. Since the signal is not emitted to the outside of the board, the intensity of a signal transmitted to the printed circuit board22can be increased, as illustrated in a region P4.

As described above, in this embodiment, the land214is partially short-circuited by connecting the land214to the ground conductor115through the coupling part217. Thus, excellent pass characteristics of a signal can be achieved, and impedance matching can be obtained.

Other Configurations of Embodiment

In the embodiment described above, in the configuration illustrated inFIG. 8, i.e., in the land214, the coupling part217is disposed at the side of the center Q opposite to the point P. Alternatively, the embodiment may employ a configuration except the configuration illustrated inFIG. 8. Another configuration except the configuration illustrated inFIG. 8will now be described.

In Variation 1 of the embodiment, the location of the coupling part217provided in the land214is different from that in the configuration illustrated inFIG. 8.

FIG. 14is an enlarged view illustrating a configuration of a main portion of a radio-frequency module2according to Variation 1 of this embodiment. As illustrated inFIG. 14, the coupling part217is disposed to form an angle θ with respect to a straight line connecting the center Q and the point P.

In Variation 2 of the embodiment, the shape of the isolation part216provided outside the coupling part217is different from that in the configuration illustrated inFIG. 8.

FIG. 15is an enlarged view illustrating a configuration of a main portion of a radio-frequency module2according to Variation 2 of the embodiment. As illustrated inFIG. 15, the isolation part216is disposed outside the coupling part217and extends substantially in parallel with a straight line connecting the center Q and the point P in a direction away from the center Q.

In Variation 3 of this embodiment, the location of the coupling part217provided in the land214and the number of the coupling parts217are different from those in the configuration illustrated inFIG. 8.

FIG. 16is an enlarged view illustrating a configuration of a main portion of a radio-frequency module2according to Variation 3 of this embodiment. As illustrated inFIG. 16, the coupling parts217are disposed in directions that form angles θ1and θ2with respect to the straight line connecting the center Q and the point P.

Differences among the configurations illustrated inFIGS. 8, 14, and 15will now be described.

As described above, in the typical radio-frequency module1, the ground conductor115is disposed outside the interconnect part113and is isolated by the isolation part116. In this configuration, a current flowing in a direction opposite to the direction of a radio-frequency current transmitted through the interconnect part113flows in the ground conductor115.

FIG. 17illustrates states of a current transmitted through the interconnect part113and a current flowing in the ground conductor115. As illustrated inFIG. 17, a phase of a current d1transmitted through the interconnect part113and a phase of a current d2flowing in the ground conductor115are opposite to each other in a direction perpendicular to the direction of the current d1and d2. The same holds for the radio-frequency module2of this embodiment.

On the other hand, in this embodiment, the land214includes the coupling part217connected to the ground conductor115so that a path of a current flowing in the ground conductor115is connected to the signal transmission ball111through the coupling part217. In this case, the phase of the current flowing in the ground conductor115coincides with a phase of a current flowing from the interconnect part113into the land214, in the signal transmission ball111.

In the variations of this embodiment as illustrated inFIGS. 8, 14, and 15, the length of a path of a current flowing in the ground conductor115is adjusted in accordance with the frequency of a current so that impedance matching can be more effectively obtained.

As illustrated inFIG. 18A, a phase (0° inFIG. 18A) of a current d1flowing in the interconnect part113at a point T1where the current d1reaches a signal transmission ball111is opposite to a phase (180° inFIG. 18A) of a current d2flowing in the ground conductor115at a point T2that is an intersection between a line passing through the point T1and perpendicular to the current d1and the current d2. On the other hand, the path of the current d2is connected to the signal transmission ball111through the coupling part217at a point T3. In this configuration, the phase (0° inFIG. 18A) of the current d2at the point T3coincides with the phase of the current d1at the point T1in the signal transmission ball111. The same holds forFIGS. 18B and 18C.

That is, in this embodiment, the path length from the point T2to the point T3of the current d2is approximately ½ wavelength of a current flowing.

As illustrated inFIGS. 18A to 18C, a path length form the point T2of the current d2to the point T3decreases in the order ofFIGS. 18A, 18B, and 18C. That is, in a case where the frequency of a current is relatively low, the configuration ofFIG. 15corresponding toFIG. 18Amay be employed. In a case where the frequency of a current is relatively high, the configuration ofFIG. 14corresponding toFIG. 18Cmay be employed. In this case, in the configuration ofFIG. 14, the angle θ formed by the coupling part217with respect to the straight line connecting the center Q and the point P may be set based on the frequency of a current.

As described above, the shapes and locations of the land214, the isolation part216, and the coupling part217may be adjusted based on the frequency of a current. In this embodiment, impedance matching can be more effectively obtained by performing adjustment based on the frequency of a current.

In this embodiment, the shapes and locations of the land214, the isolation part216, and the coupling part217are not necessarily adjusted based on the frequency of a current. In this embodiment, the configuration in which the land214is partially short-circuited when connected to the ground conductor115through the coupling part217can maintain excellent pass characteristics of a signal and obtain impedance matching.

In the embodiment described above, as illustrated inFIG. 7, the coupling part217is provided in the land214connected to the signal transmission ball111in the BGA package21. However, the present disclosure is not limited to this example.

FIGS. 19A to 19Dillustrate examples of locations of the coupling part217in this embodiment of the present disclosure.FIG. 19Aillustrates a case where the coupling part217is disposed in the land123connected to the via122in the front layer12aof the printed circuit board22.FIG. 19Billustrates a case where the coupling part217is disposed in the land123connected to the via122in the inner layer12bof the printed circuit board22.FIG. 19Cillustrates a case where the coupling parts217are disposed in the land123connected to the via122in the front layer12aof the printed circuit board22and in the land123connected to the via122in the inner layer12b.FIG. 19Dillustrates a case where the coupling parts217are disposed in both of the land214connected to the signal transmission ball111in the BGA package21and the land123connected to the signal transmission ball111in the front layer12aof the printed circuit board22.

In the configurations illustrated inFIGS. 19A to 19D, the land can be partially short-circuited when connected to the ground conductor through the coupling part(s). Thus, excellent pass characteristics of a signal can be maintained, and impedance matching can be obtained.

The radio-frequency module according to the present disclosure is preferable for use as a module connected to an RF chip for a millimeter wave band.