The present invention relates to a base board module provided with a printed circuit board on which a coaxial connector is mounted.
Conventionally, a coaxial connector is often used to keep a good transmission characteristic in transmission of a high frequency signal a frequency of which exceeds GHz.
As a usage mode of the coaxial connector, there is a base board module in which the coaxial connector is attached to an edge of a printed circuit board. In this base board module, when an electrode structure is different between the coaxial connector and the printed circuit board, the transmission characteristic is degraded due to unmatched reflection in a high frequency domain.
For example, an attachment disclosed in Patent Literature 1 is a base board module in which a coaxial connector is covered with a conductive cover, and a quasi-coaxial transmission line is provided on a surface layer of a circuit board on which the coaxial connector is mounted. The quasi-coaxial transmission line is a transmission line obtained by covering a central conductor with a dielectric layer. A thickness of the dielectric layer is changed so that a position of the central conductor of the quasi-coaxial transmission line matches a position of a central conductor of the coaxial connector.
Patent Literature 1: JP 2003-208950 A
In the base board module disclosed in Patent Literature 1, in order to match characteristic impedances in transmission from the coaxial connector to the transmission line of the circuit board, it is necessary to appropriately design the thickness of the dielectric layer of the quasi-coaxial transmission line. Such design of a wiring layer of a printed circuit board generally requires a detailed study using three-dimensional electromagnetic field analysis. Thus, it is up to technical skill of a designer whether a base board module with a good transmission characteristic can be obtained. For example, when changing the printed circuit board in the conventional base board module, in order to keep the transmission characteristic good, it is necessary to redesign the wiring layer of the printed circuit board, which may cause a difference in the transmission characteristic due to a difference in designer.
The present invention solves the above-described problem, and an object thereof is to obtain a base board module capable of omitting detailed design of a printed circuit board and keeping the transmission characteristic good.
A base board module according to the present invention is provided with a coaxial connector and a printed circuit board.
The coaxial connector includes a first ground conductor portion which is a cylindrical conductor member and an inside of which is provided with a core wire for a coaxial cable and a second ground conductor portion which is a semi-cylindrical conductor member extending in an axial direction of the first ground conductor portion from the first ground conductor portion and covers an end of the core wire. The printed circuit board includes a signal pad, a signal wire electrically connected to the signal pad, and a conductor-less area in which a conductor is excluded over an entire edge on a side to which the coaxial connector is attached.
In this configuration, the coaxial connector is attached to the conductor-less area, and the end of the core wire is brought into contact with the signal pad in a state of being covered with the second ground conductor portion of the coaxial connector attached to the conductor-less area.
According to the present invention, since the coaxial connector is attached to the area in which the conductor is excluded over the entire edge of the printed circuit board, detailed design of the printed circuit board in consideration of an effect of the conductor of the edge on a characteristic of the signal wire can be omitted. Furthermore, the transmission characteristic can be kept good because signal transmission in which characteristic impedances of the coaxial cable, the coaxial connector, and the printed circuit board are matched can be achieved just by design of the coaxial connector.
Modes for carrying out the present invention are hereinafter described with reference to the attached drawings in order to describe the present invention in more detail.
In the coaxial connector 2, the first ground conductor portion 20 is a cylindrical conductor member with the core wire 22 provided inside thereof, and is electrically connected to a shield member (not illustrated) of a coaxial cable to have ground potential. The shield member of the coaxial cable is an outer conductor provided around the core wire 22 which is a central conductor. The second ground conductor portion 21 is a semi-cylindrical conductor member which extends in an axial direction of the first ground conductor portion 20 from the first ground conductor portion 20 to cover the core wire 22 and has the ground potential. An end of the core wire 22 protrudes from the first ground conductor portion 20 and is covered with the second ground conductor portion 21.
In the printed circuit board 3, as illustrated in
The ground pads 34 are provided on the first layer of the printed circuit board 3, and bond with the second ground conductor portion 21. The signal pad 35 is provided on the first layer of the printed circuit board 3 and is electrically connected to one end of the signal wire 32.
Furthermore, as illustrated in
As indicated by dashed arrows in
The lower surfaces of the second ground conductor portion 21 are bonding surfaces bonded to the ground pads 34, and are bonded to the ground pads 34 by soldering, for example. The core wire 22 is also bonded to the signal pad 35 by soldering.
Each of the ground pads 34 and 34A has an area equal to or smaller than that of the bonding surface (lower surface) of the second ground conductor portion 21. As a result of this configuration, a substantial distance between the second ground conductor portion 21 and the core wire 22 does not change, so that the coaxial connector 2 can be attached to the printed circuit board 3 without a change in a transmission characteristic of the base board module 1.
Herein, a case where the coaxial cable is connected to the coaxial connector 2 and the base board module 1 is used in communication of high frequency signals is described. It is assumed that a characteristic impedance of the coaxial cable matches a characteristic impedance of the signal wire 32 of the printed circuit board 3.
First, in order for reflection of the high frequency signal transmitted through the coaxial cable not to increase at the base board module 1, a characteristic impedance of the core wire 22 provided inside the first ground conductor portion 20 is designed so that the characteristic impedance matches the characteristic impedance of the coaxial cable.
The characteristic impedance of the core wire 22 provided inside the first ground conductor portion 20 is determined by a diameter of the core wire 22 and a distance between the first ground conductor portion 20 and the core wire 22.
The characteristic impedance of the coaxial cable is similarly determined by a diameter of a core wire of the coaxial cable and a distance between the core wire and an outer conductor provided around the core wire.
In a case of embedding a dielectric between the first ground conductor portion 20 and the core wire 22, a relative permittivity of the dielectric also affects the characteristic impedance, so that it is necessary to design in consideration of this.
A characteristic impedance of a portion of the core wire 22 is designed so that the characteristic impedance matches the characteristic impedance of the coaxial cable, the portion being covered with the second ground conductor portion 21.
Note that, when a dielectric is embedded inside the second ground conductor portion 21, a relative permittivity of the dielectric is also one of parameters in the design of the coaxial connector 2.
The characteristic impedance of the portion of the core wire 22, which is covered with the second ground conductor portion 21, is obtained, for example, by performing electromagnetic field analysis on cross-sectional structure of the second ground conductor portion 21 and the core wire 22 by using a two-dimensional electromagnetic field analysis tool.
In this manner, a characteristic impedance of the coaxial connector 2 is designed so that the characteristic impedance matches the characteristic impedance of the coaxial cable and the characteristic impedance of the signal wire 32 of the printed circuit board 3. As a result, it becomes possible to perform signal transmission without deterioration in an RF characteristic of the signal in the communication using the base board module 1.
As described above, in the base board module 1 according to the first embodiment, the printed circuit board 3 includes the conductor-less area 30 in which the conductor is excluded over the entire edge on a side to which the coaxial connector 2 is attached. The end of the core wire 22 is brought into contact with the signal pad 35 in a state of being covered with the second ground conductor portion 21 of the coaxial connector 2 attached to the conductor-less area 30.
By configuring in this manner, detailed design of the printed circuit board 3 in consideration of an effect of the conductor of the edge of the printed circuit board 3 on the characteristic of the signal wire 32 can be omitted. For example, it is not required to design, on the printed circuit board 3, a structure for insulating a signal wire from a conductor in an edge area as in a dielectric layer of a quasi-coaxial transmission line disclosed in Patent Literature 1.
Furthermore, since signal transmission in which characteristic impedances of the coaxial cable, the coaxial connector 2, and the printed circuit board 3 are matched can be achieved just by design of the coaxial connector 2, the transmission characteristic can be kept good.
The base board module 1 according to the first embodiment is provided with the ground pads 34 or 34A which are provided on the first layer of the printed circuit board 3 and to which the second ground conductor portion 21 is bonded. Each of the ground pads 34 and 34A has an area equal to or smaller than that of the bonding surface of the second ground conductor portion 21.
As a result of this configuration, a substantial distance between the second ground conductor portion 21 and the core wire 22 does not change, so that the coaxial connector 2 can be attached to the printed circuit board 3 without a change in the transmission characteristic of the base board module 1.
Similar to the first embodiment, the coaxial connector 2A has a structure in which a conductor member including a first ground conductor portion 20 and a second ground conductor portion 21 surrounds a core wire 22, but a first dielectric portion 23 is provided inside the second ground conductor portion 21.
As illustrated in
The dielectrics 230 to 232 are stacked (in two layers) in an arrow C direction orthogonal to the printed circuit board 3 inside the second ground conductor portion 21.
Furthermore, in a layer facing the printed circuit board 3 being a lowermost layer, the dielectrics 230 to 232 are provided in the axial direction. The dielectrics 230 to 232 are provided so that the relative permittivity gradually increases toward a tip end of an end of the core wire 22 as indicated by an arrow D.
More specifically, in the lowermost layer, the dielectric 230, the dielectric 232, and the dielectric 231 are provided in this order in an arrow D direction.
By adopting a structure in which the first dielectric portion 23 is provided inside the second ground conductor portion 21, electromagnetic field distribution of a signal transmitted from the coaxial connector 2A to the printed circuit board 3 is concentrated to the lowermost layer of each dielectric in the arrow D direction. As a result, a drastic change in electromagnetic field distribution from the second ground conductor portion 21 to the printed circuit board 3 is alleviated, and thus an RF characteristic of the connector more stable than that in the configuration of the first embodiment can be achieved.
Note that, although
Although a structure in which the dielectrics 230 to 232 are stacked in the arrow C direction orthogonal to the printed circuit board 3 is illustrated, a structure in which the dielectrics 230 to 232 are stacked in a radial direction centered on the core wire 22 is also possible.
As described above, the base board module 1A according to the second embodiment is provided with the first dielectric portion 23.
The first dielectric portion 23 is configured so that the dielectrics 230 to 232 having different relative permittivities are stacked inside the second ground conductor portion 21 and the dielectrics 230 to 232 are provided in the axial direction in the lowermost layer. Especially, the dielectrics 230 to 232 are provided in the lowermost layer so that the relative permittivity gradually increases toward the tip end of the end of the core wire 22.
By configuring in this manner, a drastic change in electromagnetic field distribution from the second ground conductor portion 21 to the printed circuit board 3 is alleviated, and thus the RF characteristic of the connector more stable than that in the configuration of the first embodiment can be achieved.
Similar to the first embodiment, the coaxial connector 2B has a structure in which a conductor member including a first ground conductor portion 20 and a second ground conductor portion 21 surrounds a core wire 22, but a second dielectric portion 24 is provided inside the first ground conductor portion 20.
As illustrated in
The dielectrics 240 to 242 are stacked (in two layers) in an arrow C direction orthogonal to the printed circuit board 3. Furthermore, in an uppermost layer, the dielectrics 240 to 242 are provided in the axial direction.
The dielectrics 240 to 242 are provided so that the relative permittivity gradually increases toward a tip end of an end of the core wire 22 as indicated by an arrow D. More specifically, in the uppermost layer, the dielectric 240, the dielectric 242, and the dielectric 241 are provided in this order in an arrow D direction.
By adopting a structure in which the second dielectric portion 24 is provided inside the first ground conductor portion 20, electromagnetic field distribution of a signal transmitted from a coaxial cable to the coaxial connector 2B is concentrated to the uppermost layer of each dielectric in the arrow D direction.
As a result, a drastic change in electromagnetic field distribution from the first ground conductor portion 20 to the second ground conductor portion 21 is alleviated, and thus an RF characteristic of the connector more stable than that in the configuration of the first embodiment can be achieved.
Note that, although
Although a structure in which the dielectrics 240 to 242 are stacked in the arrow C direction orthogonal to the printed circuit board 3 is illustrated, a structure in which the dielectrics 240 to 242 are stacked in a radial direction centered on the core wire 22 is also possible.
As described above, the base board module 1B according to the third embodiment is provided with the second dielectric portion 24.
The second dielectric portion 24 is configured so that the dielectrics 240 to 242 having different relative permittivities are stacked inside the first ground conductor portion 20 and the dielectrics 240 to 242 are provided in the axial direction in the uppermost layer. Especially, the dielectrics 240 to 242 are provided in the uppermost layer so that the relative permittivity gradually increases toward the tip end of the end of the core wire 22.
By configuring in this manner, a drastic change in electromagnetic field distribution from the first ground conductor portion 20 to the second ground conductor portion 21 is alleviated, and thus the RF characteristic of the connector more stable than that in the configuration of the first embodiment can be achieved.
Note that although the configuration in which one of the first dielectric portion 23 and the second dielectric portion 24 is provided is heretofore described, a configuration in which both the first dielectric portion 23 and the second dielectric portion 24 are provided is also possible.
By configuring in this manner, the effects described in the second embodiment and the third embodiment can be obtained.
Note that, in the present invention, the embodiments may be freely combined, any component of each embodiment may be modified, or any component may be omitted in each embodiment without departing from the scope of the invention.
The base board module according to the present invention is suitable for, for example, transmission of a high frequency signal because the structure of the printed circuit board can be simplified and the transmission characteristic can be kept good.
Filing Document | Filing Date | Country | Kind |
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PCT/JP2017/009226 | 3/8/2017 | WO | 00 |