Abstract:
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.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    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. 
         [0003]    2. Description of the Related Art 
         [0004]    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. 
         [0005]    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 
       [0006]    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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    These general and specific aspects may be implemented using a device, a system, and any combination of devices and systems. 
         [0010]    According to the present disclosure, impedance matching can be obtained with a simple configuration without an increase in circuit scale. 
         [0011]    It should be noted that general or specific embodiments may be implemented as a system, a method, an integrated circuit, a computer program, a storage medium, or any selective combination thereof. 
         [0012]    Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a cross sectional view schematically illustrating a typical configuration of a radio-frequency module  1  using a BGA package; 
           [0014]      FIG. 2  is a cross sectional view schematically illustrating an example configuration of the typical radio-frequency module; 
           [0015]      FIG. 3  is an enlarged view illustrating a configuration of a main portion of the typical radio-frequency module; 
           [0016]      FIG. 4  is a Smith chart showing reflectance characteristics of a signal in a land of the typical radio-frequency module; 
           [0017]      FIG. 5  shows pass characteristics of a signal in the land of the typical radio-frequency module; 
           [0018]      FIG. 6  shows reflectance characteristics of a signal in the land of the typical radio-frequency module; 
           [0019]      FIG. 7  is a cross-sectional view schematically illustrating an example configuration of a radio-frequency module according to an embodiment of the present disclosure; 
           [0020]      FIG. 8  is an enlarged view illustrating a configuration of a main portion of the radio-frequency module according to the embodiment of the present disclosure; 
           [0021]      FIG. 9  is a Smith chart showing reflectance characteristics of a signal in a land of the radio-frequency module according to the embodiment of the present disclosure; 
           [0022]      FIG. 10  shows pass characteristics of a signal in the land of the radio-frequency module according to the embodiment of the present disclosure; 
           [0023]      FIG. 11  shows reflectance characteristics of a signal in the land of the radio-frequency module according to the embodiment of the present disclosure; 
           [0024]      FIG. 12  illustrates signal transmission in the typical radio-frequency module; 
           [0025]      FIG. 13  illustrates signal transmission in the radio-frequency module according to the embodiment of the present disclosure; 
           [0026]      FIG. 14  is an enlarged view illustrating a configuration of a main portion of a radio-frequency module according to Variation 1 of the embodiment; 
           [0027]      FIG. 15  is an enlarged view illustrating a configuration of a main portion of a radio-frequency module according to Variation 2 of the embodiment; 
           [0028]      FIG. 16  is an enlarged view illustrating a configuration of a main portion of a radio-frequency module according to Variation 3 of the embodiment; 
           [0029]      FIG. 17  illustrates states of a current transmitted through an interconnect part and a current flowing in a ground conductor; 
           [0030]      FIG. 18A  illustrates a current path in the configuration of  FIG. 15 ; 
           [0031]      FIG. 18B  illustrates a current path in the configuration of  FIG. 8 ; 
           [0032]      FIG. 18C  illustrates a current path in the configuration of  FIG. 14 ; 
           [0033]      FIG. 19A  illustrates an example of the location of a coupling part in the embodiment of the present disclosure; 
           [0034]      FIG. 19B  illustrates an example of the location of the coupling part in the embodiment of the present disclosure; 
           [0035]      FIG. 19C  illustrates an example of the location of the coupling part in the embodiment of the present disclosure; and 
           [0036]      FIG. 19D  illustrates an example of the location of the coupling part in the embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]    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. 
         [0038]      FIG. 1  is a cross sectional view schematically illustrating a typical configuration of a radio-frequency module  1  using a BGA package. The radio-frequency module  1  illustrated in  FIG. 1  includes a BGA package  11  and a printed circuit board  12 , and is connected to an RF chip  10  for a millimeter wave band. 
         [0039]    A surface of the BGA package  11  at one side is connected to the RF chip  10 . Another surface of the BGA package  11  at the other side is provided with a signal transmission ball  111  and a grounding ball  112 , and is connected to the printed circuit board  12  through the signal transmission ball  111 . The signal transmission ball  111  is a transmission unit for allowing a signal to be transmitted between the BGA package  11  and the printed circuit board  12 . The grounding ball  112  is disposed adjacent to the signal transmission ball  111 , and has a zero potential. 
         [0040]    The configuration of the radio-frequency module  1  will now be more specifically described.  FIG. 2  is a cross sectional view schematically illustrating the configuration of the typical radio-frequency module  1 . 
         [0041]    As illustrated in  FIG. 2 , a plurality of interconnect parts  113  are formed on either surface of the BGA package  11  and used for signal transmission. A land  114  is provided on a surface of the BGA package  11  not connected to the RF chip  2  (see  FIG. 1 ) and is connected to the interconnect parts  113 . The interconnect parts  113  and the land  114  are conductor layers provided on the surfaces. 
         [0042]    A ground conductor  115  is a conductor layer disposed around the interconnect parts  113  and the land  114 , and is connected to the grounding ball  112  to have a zero potential. An isolation part  116  is a notch formed on a plane and isolates the land  114  and the ground conductor  115  from each other. 
         [0043]    Each of the signal transmission ball  111  and the grounding ball  112  is disposed in a location where the land  114  is formed. Each of the signal transmission ball  111  and the grounding ball  112  is formed by soldering, and has a substantially spherical shape due to surface tension. Locations of the signal transmission ball  111 , the interconnect parts  113 , and the land  114  will be described later. 
         [0044]    The printed circuit board  12  includes interconnect parts  121 , vias  122 , lands  123 , ground conductors  124 , and isolation parts  125 , and is constituted by a plurality of layers. The interconnect parts  121  are constituted by a plurality of layers, and serves as interconnections among circuits provided in a front layer  12   a , an inner layer  12   b , and a back layer  12   c  of the printed circuit board  12 . Each of the vias  122  is a transmission unit for transmitting a signal among the layers of the printed circuit board  12 . 
         [0045]    The land  123  is provided in a portion where the signal transmission ball  111  is connected to the front layer  12   a  of the printed circuit board  12 . The land  123  is a conductor layer similar to the interconnect parts  121 , and is connected to the interconnect part  121 . 
         [0046]    The land  123  is disposed between the via  122  and the corresponding interconnect parts  121 . The via  122  is connected to the interconnect part  121  through the land  123 . 
         [0047]    The ground conductors  124  are conductor layers disposed around the interconnect parts  121  and the land  123 , and have a zero potential. Each of the isolation parts  125  is a notch formed on a plane between a set of the interconnect part  121  and the land  123 , and the ground conductor  124 , and isolates the set of the interconnect part  121  and the land  123  from the ground conductor  124 . 
         [0048]    Configurations of the signal transmission ball  111 , the interconnect part  113 , and the land  114  will be described.  FIG. 3  is an enlarged view illustrating a configuration of a main portion of the typical radio-frequency module  1 .  FIG. 3  is an enlarged view of a region indicated by arrow X in  FIG. 2  and viewed in a direction of arrow III in  FIG. 2 . 
         [0049]    In  FIG. 3 , the signal transmission ball  111  is connected to the interconnect part  113  through the land  114 . The ground conductor  115  is a conductor layer provided around the interconnect part  113  and the land  114 , and has a zero potential when connected to the grounding ball  112  (see  FIG. 2 ). The isolation part  116  is a notch formed in a plane between a set of the interconnect part  113  and the land  114 , and the ground conductor  115 , and isolates the set of the interconnect part  113  and the land  114  from the ground conductor  115 . 
         [0050]    In the radio-frequency module  1  using the typical BGA package as illustrated in  FIGS. 1 and 2 , the ground conductor  115  having a zero potential is generally formed outside the interconnect part  113  and the land  114 . 
         [0051]    In the case of the configuration constituted by the signal transmission ball  111 , the interconnect part  113 , and the land  114  illustrated in  FIG. 3 , an impedance is discontinuous due to the capacitance of the land  114 , and thus, it is difficult to obtain impedance matching. The impedance matching will now be described. 
         [0052]      FIG. 4  is a Smith chart showing reflectance characteristics of a signal in the land  114  of the typical radio-frequency module  1 .  FIG. 4  shows paths of changes from 0 Hz to 100 GHz in S-parameters S 11  and S 22  in the land  114 . 
         [0053]    Under the influence of capacitance of the land  114 , the paths of the S-parameters S 11  and S 22  move in a direction indicated by arrow Z, i.e., downward in a clockwise direction. The paths of the S-parameters S 11  and S 22  move 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 land  114  will be specifically described. 
         [0054]      FIG. 5  shows pass characteristics of a signal in the land  114  of the typical radio-frequency module  1 .  FIG. 6  shows reflectance characteristics of a signal in the land  114  of the typical radio-frequency module  1 . 
         [0055]    In  FIG. 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 land  114 . In  FIG. 5 , as the value on the ordinate increases, pass characteristics of the signal improve. In  FIG. 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 land  114 . In  FIG. 5 , as the value on the ordinate increases, the degree of reflection of the signal increases. 
         [0056]    In the configuration of  FIG. 3 , the intensity of a signal passing through the land  114  is small in a millimeter wave band (a frequency band of 30 GHz or more), as shown in  FIG. 5 . As shown in  FIG. 6 , a signal in a millimeter wave band greatly reflects on the land  114 . That is, as shown in  FIGS. 5 and 6 , under the influence of discontinuity of impedance due to the capacitance of the land  114 , pass characteristics of a signal in a millimeter wave band degrades. 
         [0057]    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. 
         [0058]    The present disclosure focused on the configuration of a land. 
       Embodiment 
       [0059]    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. 
         [0060]    A configuration of a radio-frequency module according to an embodiment of the present disclosure will be described with reference to  FIG. 7 . 
         [0061]      FIG. 7  is a cross-sectional view schematically illustrating an example configuration of a radio-frequency module  2  according to an embodiment of the present disclosure. The radio-frequency module  2  illustrated in  FIG. 7  includes a BGA package  21  and a printed circuit board  22 . In  FIG. 7 , components of the configuration also shown in  FIG. 2  are denoted by the same reference characters as those used in  FIG. 2 , and detailed description thereof is not repeated. The radio-frequency module  2  illustrated in  FIG. 7  includes a land  214  different from the land  114  illustrated in  FIG. 2 , and a coupling part  217  is added to the configuration illustrated in  FIG. 2 . Although not shown in  FIG. 7 , the radio-frequency module  2  of this embodiment includes an isolation part  216  different from the isolation part  116  illustrated in  FIGS. 2 and 3 . The land  214 , the isolation part  216 , and the coupling part  217  will now be described with reference to  FIG. 8 . 
         [0062]      FIG. 8  is an enlarged view illustrating a configuration of a main portion of the radio-frequency module  2  according to the embodiment of the present disclosure.  FIG. 8  is an enlarged view of a region indicated by arrow X′ in  FIG. 7  and viewed in a direction of arrow VIII in  FIG. 7 . 
         [0063]    In  FIG. 8 , the signal transmission ball  111  is a transmission unit for transmitting a signal between a BGA package  21  (see  FIG. 7 ) and a printed circuit board  22  (see  FIG. 7 ), and is connected to an interconnect part  113  through the land  214 . A ground conductor  115  is a conductor layer provided around the interconnect part  113  and the land  214 , and has a zero potential when connected to a grounding ball  112  (see  FIG. 7 ). The isolation part  216  is a notch formed on a plane between a set of the interconnect part  113  and the land  214 , and the ground conductor  115 , and isolates the set of the interconnect part  113  and the land  214  from the ground conductor  115 . 
         [0064]    The land  214  is a circular conductor layer, and is connected to the interconnect part  113  at a point P. 
         [0065]    In the land  214 , the coupling part  217  is 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 part  113 . The coupling part  217  couples the land  214  and the ground conductor  115  to each other, and partially short-circuits the land  214 . 
         [0066]    The configuration illustrated in  FIG. 8  can obtain impedance matching of the radio-frequency module  2  according to this embodiment. Characteristics of the radio-frequency module  2  of this embodiment will now be described. 
         [0067]      FIG. 9  is a Smith chart showing reflectance characteristics of a signal in the land  214  of the radio-frequency module  2  according to the embodiment of the present disclosure. In a manner similar to  FIG. 4 ,  FIG. 9  shows paths of changes from 0 Hz to 100 GHz in S-parameters S 11  and S 22  in the land  214 . 
         [0068]    Since the land  214  is partially short-circuited, the paths of the S-parameters S 11  and S 22  start from the left end of a horizontal line in the Smith chart. Under the influence of capacitance of the land  214 , the S-parameters S 11  and S 22  moves in a direction indicated by arrow Z′, i.e., downward in a clockwise direction. The paths of the S-parameters S 11  and S 22  approach 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 land  214  will now be described in detail. 
         [0069]      FIG. 10  shows pass characteristics of a signal in the land  214  of the radio-frequency module  2  according to the embodiment of the present disclosure.  FIG. 11  shows reflectance characteristics of a signal in the land  214  of the radio-frequency module  2  according to the embodiment of the present disclosure. 
         [0070]    In  FIG. 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 land  214 .  FIG. 10  shows that as the value on the ordinate increases, pass characteristics of the signal improves. In  FIG. 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 land  214 .  FIG. 11  shows that as the value on the ordinate increases, the degree of reflection of the signal increases. 
         [0071]    In the configuration of  FIG. 8 , the intensity of a signal passing through the land  214  can be increased in a millimeter wave band, as shown in  FIG. 10 . As shown in  FIG. 11 , the intensity a signal reflected in the land  214  is reduced in a millimeter wave band. 
         [0072]    That is, in the configuration of  FIG. 8 , the coupling part  217  couples the land  214  and the ground conductor  115  to each other and partially short-circuits the land  214  so that impedance matching can be obtained. As a result of impedance matching, as shown in  FIGS. 10 and 11 , reflection of a signal in a millimeter wave band can be reduced so that pass characteristics can be enhanced. 
         [0073]    Signal transmission in the radio-frequency module  2  of this embodiment will be described in comparison with signal transmission in the typical radio-frequency module  1  illustrated in  FIG. 2 . 
         [0074]      FIG. 12  is a schematic illustration of signal transmission in the typical radio-frequency module  1 .  FIG. 13  is a schematic illustration of signal transmission in the radio-frequency module  2  according to this embodiment of the present disclosure.  FIGS. 12 and 13  illustrate 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. In  FIGS. 12 and 13 , a lighter region indicates a location where the signal intensity is higher. 
         [0075]    In the typical radio-frequency module  1 , as illustrated in a region P 1  in  FIG. 12 , a signal in a millimeter wave band is emitted from the land  114  connected to the signal transmission ball  111  to the outside of the board. Consequently, as illustrated in a region P 2 , the intensity of the signal transmitted to the printed circuit board  12  decreases. 
         [0076]    On the other hand, in the radio-frequency module  2  of this embodiment, as illustrated in a region P 3  in  FIG. 13 , a signal in a millimeter wave band is not emitted from the land  214  connected to the signal transmission ball  111  to the outside of the board. This is because the land  214  is connected to the ground conductor  115  through the coupling part  217  and is short-circuited so that the potential at the region P 3  is zero. Since the signal is not emitted to the outside of the board, the intensity of a signal transmitted to the printed circuit board  22  can be increased, as illustrated in a region P 4 . 
         [0077]    As described above, in this embodiment, the land  214  is partially short-circuited by connecting the land  214  to the ground conductor  115  through the coupling part  217 . Thus, excellent pass characteristics of a signal can be achieved, and impedance matching can be obtained. 
       (Other Configurations of Embodiment) 
       [0078]    In the embodiment described above, in the configuration illustrated in  FIG. 8 , i.e., in the land  214 , the coupling part  217  is disposed at the side of the center Q opposite to the point P. Alternatively, the embodiment may employ a configuration except the configuration illustrated in  FIG. 8 . Another configuration except the configuration illustrated in  FIG. 8  will now be described. 
       (Variation 1) 
       [0079]    In Variation 1 of the embodiment, the location of the coupling part  217  provided in the land  214  is different from that in the configuration illustrated in  FIG. 8 . 
         [0080]      FIG. 14  is an enlarged view illustrating a configuration of a main portion of a radio-frequency module  2  according to Variation 1 of this embodiment. As illustrated in  FIG. 14 , the coupling part  217  is disposed to form an angle θ with respect to a straight line connecting the center Q and the point P. 
       (Variation 2) 
       [0081]    In Variation 2 of the embodiment, the shape of the isolation part  216  provided outside the coupling part  217  is different from that in the configuration illustrated in  FIG. 8 . 
         [0082]      FIG. 15  is an enlarged view illustrating a configuration of a main portion of a radio-frequency module  2  according to Variation 2 of the embodiment. As illustrated in  FIG. 15 , the isolation part  216  is disposed outside the coupling part  217  and extends substantially in parallel with a straight line connecting the center Q and the point P in a direction away from the center Q. 
       (Variation 3) 
       [0083]    In Variation 3 of this embodiment, the location of the coupling part  217  provided in the land  214  and the number of the coupling parts  217  are different from those in the configuration illustrated in  FIG. 8 . 
         [0084]      FIG. 16  is an enlarged view illustrating a configuration of a main portion of a radio-frequency module  2  according to Variation 3 of this embodiment. As illustrated in  FIG. 16 , the coupling parts  217  are disposed in directions that form angles θ 1  and θ 2  with respect to the straight line connecting the center Q and the point P. 
         [0085]    Differences among the configurations illustrated in  FIGS. 8, 14, and 15  will now be described. 
         [0086]    As described above, in the typical radio-frequency module  1 , the ground conductor  115  is disposed outside the interconnect part  113  and is isolated by the isolation part  116 . In this configuration, a current flowing in a direction opposite to the direction of a radio-frequency current transmitted through the interconnect part  113  flows in the ground conductor  115 . 
         [0087]      FIG. 17  illustrates states of a current transmitted through the interconnect part  113  and a current flowing in the ground conductor  115 . As illustrated in  FIG. 17 , a phase of a current d 1  transmitted through the interconnect part  113  and a phase of a current d 2  flowing in the ground conductor  115  are opposite to each other in a direction perpendicular to the direction of the current d 1  and d 2 . The same holds for the radio-frequency module  2  of this embodiment. 
         [0088]    On the other hand, in this embodiment, the land  214  includes the coupling part  217  connected to the ground conductor  115  so that a path of a current flowing in the ground conductor  115  is connected to the signal transmission ball  111  through the coupling part  217 . In this case, the phase of the current flowing in the ground conductor  115  coincides with a phase of a current flowing from the interconnect part  113  into the land  214 , in the signal transmission ball  111 . 
         [0089]    In the variations of this embodiment as illustrated in  FIGS. 8, 14, and 15 , the length of a path of a current flowing in the ground conductor  115  is adjusted in accordance with the frequency of a current so that impedance matching can be more effectively obtained. 
         [0090]      FIGS. 18A to 18C  illustrate paths of current in the configurations of  FIGS. 15, 8, 14 , respectively. 
         [0091]    As illustrated in  FIG. 18A , a phase (0° in  FIG. 18A ) of a current d 1  flowing in the interconnect part  113  at a point T 1  where the current d 1  reaches a signal transmission ball  111  is opposite to a phase (180° in  FIG. 18A ) of a current d 2  flowing in the ground conductor  115  at a point T 2  that is an intersection between a line passing through the point T 1  and perpendicular to the current d 1  and the current d 2 . On the other hand, the path of the current d 2  is connected to the signal transmission ball  111  through the coupling part  217  at a point T 3 . In this configuration, the phase (0° in  FIG. 18A ) of the current d 2  at the point T 3  coincides with the phase of the current d 1  at the point T 1  in the signal transmission ball  111 . The same holds for  FIGS. 18B and 18C . 
         [0092]    That is, in this embodiment, the path length from the point T 2  to the point T 3  of the current d 2  is approximately ½ wavelength of a current flowing. 
         [0093]    As illustrated in  FIGS. 18A to 18C , a path length form the point T 2  of the current d 2  to the point T 3  decreases in the order of  FIGS. 18A, 18B, and 18C . That is, in a case where the frequency of a current is relatively low, the configuration of  FIG. 15  corresponding to  FIG. 18A  may be employed. In a case where the frequency of a current is relatively high, the configuration of  FIG. 14  corresponding to  FIG. 18C  may be employed. In this case, in the configuration of  FIG. 14 , the angle θ formed by the coupling part  217  with respect to the straight line connecting the center Q and the point P may be set based on the frequency of a current. 
         [0094]    As described above, the shapes and locations of the land  214 , the isolation part  216 , and the coupling part  217  may 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. 
         [0095]    In this embodiment, the shapes and locations of the land  214 , the isolation part  216 , and the coupling part  217  are not necessarily adjusted based on the frequency of a current. In this embodiment, the configuration in which the land  214  is partially short-circuited when connected to the ground conductor  115  through the coupling part  217  can maintain excellent pass characteristics of a signal and obtain impedance matching. 
         [0096]    In the embodiment described above, as illustrated in  FIG. 7 , the coupling part  217  is provided in the land  214  connected to the signal transmission ball  111  in the BGA package  21 . However, the present disclosure is not limited to this example. 
         [0097]      FIGS. 19A to 19D  illustrate examples of locations of the coupling part  217  in this embodiment of the present disclosure.  FIG. 19A  illustrates a case where the coupling part  217  is disposed in the land  123  connected to the via  122  in the front layer  12   a  of the printed circuit board  22 .  FIG. 19B  illustrates a case where the coupling part  217  is disposed in the land  123  connected to the via  122  in the inner layer  12   b  of the printed circuit board  22 .  FIG. 19C  illustrates a case where the coupling parts  217  are disposed in the land  123  connected to the via  122  in the front layer  12   a  of the printed circuit board  22  and in the land  123  connected to the via  122  in the inner layer  12   b .  FIG. 19D  illustrates a case where the coupling parts  217  are disposed in both of the land  214  connected to the signal transmission ball  111  in the BGA package  21  and the land  123  connected to the signal transmission ball  111  in the front layer  12   a  of the printed circuit board  22 . 
         [0098]    In the configurations illustrated in  FIGS. 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. 
         [0099]    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.