JP2007234454A - Connection structure of coaxial cable to circuit board - Google Patents

Abstract

To provide a connection structure of a coaxial cable to a circuit board for preventing a noise current induced in a shield conductor due to noise from the outside from flowing into a signal transmission / reception circuit.
A terminal portion 20a of a shield conductor 20 of a coaxial cable 12 is connected to a first ground conductor 28, and a metal member 36 having a plate thickness larger than the thickness of the shield conductor 20 is connected to the shield conductor 20 at the end of the shield conductor 20. A two-point grounding connection structure 10 is obtained in which the legs 36c of the metal member 36 are connected to the second ground conductor 30 by being electrically connected and wound.
[Selection] Figure 1

Description

  The present invention relates to a structure for connecting a coaxial cable to a circuit board, and more particularly to a structure for connecting a coaxial cable to a circuit board that is suitably used as an electric wire for transmitting a high-frequency signal.

  In recent years, high frequency signals have been used in electronic and electrical equipment such as car navigation systems mounted on automobiles, and coaxial cables have been used to transmit such high frequency signals.

  The coaxial cable has a center conductor and a shield conductor. The shield conductor serves as a return current path for signals transmitted to the center conductor, and noise is mixed into the center conductor from the outside. It has a function of shielding the influence of noise on the transmitted signal. Therefore, the shield conductor is usually grounded at both ends.

  For example, Patent Document 1 shows a structure in which a shield conductor is grounded using a terminal. Referring to FIG. 3, the shield conductor 48 of the coaxial cable 40 is caulked by the barrel portion 46 of the terminal 44 that attaches the tip of the coaxial cable 40 to the printed circuit board 42, and the shield conductor 48 is electrically connected to the terminal 44. Yes. A cover portion 50 is continuously provided on the barrel portion 46 of the terminal 44, and a leg portion 52 extending to the cover portion 50 is attached to the attachment hole 54 of the printed circuit board 42. A contact portion 56 connected to a circuit (not shown) is provided in the vicinity of the hole edge of the attachment hole 54, and the shield conductor 48 is grounded by soldering 58 the contact portion 56 and the leg portion 52.

  At this time, if a noise current flows through the shield conductor 48 by being induced by noise from the outside, the noise current is induced by the shield conductor 48, and the noise current also flows through the center conductor 60. Inductive noise may occur in the transmitted signal. The noise current induced in the shield conductor 48 due to the skin effect of the current flows on the outer peripheral surface of the shield conductor 48 and is induced in the shield conductor 48. The coaxial cable 40 having a thickness of the shield conductor 48 to such an extent that the noise current is not induced in the central conductor 60 by the noise current may be selected.

JP 2000-323213 A

  However, even if the coaxial cable 40 in which the noise current is not induced in the center conductor 60 due to the noise current induced in the shield conductor 48, the shield conductor 48 functions as a return current path for signals transmitted to the center conductor 60. Therefore, in the grounding structure shown in Patent Document 1, the noise current induced in the shield conductor 48 is superimposed on the signal return current and flows in the signal transmission / reception circuit, so that the induction noise affects the transmitted / received signal. There was a problem.

  In order to solve such a problem, for example, as shown in FIG. 4, two shield conductors are provided via an insulating layer 62, the inner shield conductor 64 is used as a signal return current path, and the outer shield conductor 66 is used. There is also a grounding structure that uses as a shield for external noise. However, in the structure shown in FIG. 4, since the coaxial cable 68 is thick, the coaxial cable 68 is difficult to bend, and it is difficult to arrange the wiring in an electric device with dense wiring. Further, since the number of constituent members of the coaxial cable 68 increases, the cost increases.

  SUMMARY OF THE INVENTION Accordingly, the problem to be solved by the present invention is to provide a connection structure of a coaxial cable to a circuit board that prevents a noise current induced in a shield conductor due to external noise from flowing into a signal transmission / reception circuit. .

  In the connection structure of the coaxial cable to the circuit board according to the present invention, the inner peripheral side of the shield conductor end of the coaxial cable is connected to the first ground conductor of the circuit board, and the outer peripheral side of the shield conductor end is the circuit board. The gist is to be connected to the second ground conductor.

  In this case, a metal member electrically connected to the outer peripheral surface is provided on the outer peripheral surface of the shield conductor end, and the outer peripheral side of the shield conductor end is connected to the second ground of the circuit board via the metal member. It is desirable to be connected to a conductor.

  And it is desirable to make the thickness of the metal member thicker than the thickness of the shield conductor.

  According to the connection structure of the coaxial cable to the circuit board according to the present invention, due to the skin effect of the current, the return current of the signal flows on the inner peripheral surface of the shield conductor, and the noise current induced from the outside to the shield conductor Therefore, at the shield conductor end, the return current of the signal flows to the first ground conductor of the circuit board connected to the inner peripheral side of the shield conductor, and the second of the circuit board connected to the outer peripheral side. Since the noise current flows to the ground conductor, the signal return current and the noise current can be separated. As a result, the noise current is prevented from flowing into the signal transmission / reception circuit by being superimposed on the signal return current.

  In this case, if a metal member that is electrically connected to the outer peripheral surface is provided on the outer peripheral surface of the shield conductor end, the conductor through which signal return current and noise current flow becomes thicker at the shield conductor end. The return current and the noise current can be effectively separated. In addition, since the metal member is connected to the ground conductor, the coaxial cable is securely fixed to the circuit board.

  When the metal member is thicker than the shield conductor, the signal return current and the noise current can be more effectively separated.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of a structure for connecting a coaxial cable to a circuit board according to the present invention. FIG. 2 is a cross-sectional view of the connection structure shown in FIG.

  As shown in FIG. 1, the connection structure 10 of the coaxial cable to the circuit board according to this embodiment is a structure in which the end of the coaxial cable 12 is electrically connected to the circuit board 14.

  The coaxial cable 12 includes a central conductor 16 that transmits a signal, an insulating layer 18 that covers and insulates the outer periphery of the central conductor 16, a shield conductor 20 that is provided on the outer periphery of the insulating layer 18, and an outer periphery of the shield conductor 20. And a sheath 22 covering the. The shield conductor 20 is formed of a braid having a shape in which a plurality of strands are juxtaposed in a strip shape and these are knitted up and down. The shield conductor 20 is disposed so as to cover the outer periphery of the center conductor 16 in order to shield noise from entering the center conductor 16 from the outside.

  The coaxial cable 12 is peeled off step by step so as to be electrically connected to the circuit board 14. That is, the central conductor 16 and the shield conductor 20 are exposed so as to be electrically connected to the circuit board 14, and the shield conductor 20 is twisted together at the terminal (hereinafter referred to as the terminal part 20a).

  The circuit board 14 includes an insulating base 24 made of glass epoxy resin and the like, and a wiring conductor 26, a first ground conductor 28, and a second ground conductor 30 made of copper foil or the like formed on the insulating base 24. Has been. The first ground conductor 28 and the second ground conductor 30 are both ground conductors, but are separate conductors and are connected to a ground (not shown).

  The central conductor 16 of the coaxial cable 12 is electrically connected to the wiring conductor 26 of the circuit board 14 by soldering 32, and the terminal portion 20 a to which the shield conductor 20 is twisted is similarly connected to the first of the circuit board 14 by soldering 34. Are electrically connected to the ground conductor 28.

  A metal member 36 is wound around the exposed end of the shield conductor 20 of the coaxial cable 12 so as to cover the outer periphery of the shield conductor 20. The metal member 36 has a substantially cylindrical cylindrical portion 36a having an inner diameter slightly larger than the outer diameter of the shield conductor 20, and the cylindrical portion 36a has a notched portion 36b in which a lower portion is notched. A leg portion 36c extends outward from the cutout portion 36b. Then, after the metal member 36 is wound around the outer periphery of the shield conductor 20, the metal member 36 is caulked to sufficiently connect the metal member 36 and the shield conductor 20.

  Thus, since the metal member 36 is electrically connected to the outer peripheral surface of the shield conductor 20, the conductor through which a signal return current or noise current flows is thicker at the end of the shield conductor 20 by the thickness of the metal member 36. It has become.

  And the plate | board thickness of the cylinder part 36a of this metal member 36 is thicker than the thickness of the shield conductor 20. FIG. At this time, the plate thickness of the cylindrical portion 36a is preferably set to be twice or more the thickness of the shield conductor 20.

  The metal member 36 has a leg portion 36 c electrically connected to the second ground conductor 30 of the circuit board 14 by soldering 38. Thereby, the coaxial cable 12 is reliably fixed to the circuit board 14.

  As described above, in the connection structure 10 of the coaxial cable according to the present embodiment, the center conductor 16 is connected to the wiring conductor 26 of the circuit board 14 and the shield conductor 20 is the first ground conductor 28. And a connection structure in which two grounding conductors 30 are grounded (two-point grounding). Then, the inner peripheral side of the end portion of the shield conductor 20 is connected to the first ground conductor 28 of the circuit board 14 by the terminal portion 20a of the shield conductor 20, and the leg portion 36c of the metal member 36 wound around the outer periphery of the shield conductor ( In this structure, the outer peripheral side of the end of the shield conductor 20 is connected to the second ground conductor 30 of the circuit board 14 (via the metal member 36).

  And the connection structure 10 to the circuit board of the coaxial cable which concerns on this embodiment is formed as follows.

  First, the sheath 22 of the end of the coaxial cable 12 is peeled off to expose the shield conductor (braid) 20. Then, the exposed shield conductor (braid) 20 is twisted (terminally processed) at the terminal to form the terminal portion 20a, and the wiring is connected to the first ground conductor 28 of the circuit board 14. Next, the insulator layer 18 exposed by the terminal treatment of the shield conductor (braid) 20 is peeled off to expose the center conductor 16. The exposed center conductor 16 is electrically connected to the wiring conductor 26 of the circuit board 14 and the terminal portion 20a of the shield conductor (braid) 20 is electrically connected to the first ground conductor 28 by soldering 32 and 34, respectively. Next, after the metal member 36 is wound around the end portion of the exposed shield conductor (braid) 20 that has not been subjected to terminal treatment, the leg portion 36c of the metal member 36 is soldered 38 to the second ground conductor 30. Electrically connect to

  Next, the effect of the connection structure 10 to the circuit board of the coaxial cable according to the present embodiment will be described with reference to FIG.

  The coaxial cable is a communication cable formed by a pair of conductors of a center conductor and a shield conductor, and serves as a forward path for a current communicated by the center conductor and as a return path for a current communicated by the shield conductor. Therefore, when a signal current flows through the central conductor of the coaxial cable, a signal return current flows through the shield conductor.

  In such a transmission / reception circuit, when a high-frequency signal is transmitted, the signal current A flows on the outer peripheral surface of the center conductor 16 due to the skin effect of the current, and the signal return current B is transmitted through the shield conductor 20 as shown in FIG. Flows on the inner surface. At this time, when the noise current C is induced in the shield conductor 20 due to external noise, the noise current C flows in the shield conductor 20. Since this noise current C is also a high-frequency current, it flows on the outer peripheral surface of the shield conductor 20 due to the skin effect of the current.

  Therefore, if the inner peripheral side of the shield conductor 20 is connected to the first ground conductor 28 and the outer peripheral side is connected to the second ground conductor 30 (two-point grounding), the return current B is supplied to the first ground conductor 28. The noise current C can be separated to the second ground conductor 30.

  Here, the skin effect of the current flowing through the electric wire is affected by the magnitude of the signal frequency, and the higher the frequency, the shallower the current path from the surface of the electric wire, and the deeper the frequency decreases. And depending on the magnitude of the frequency of the return current and noise current, the current path of the return current in the shield conductor and the current path of the noise current partially overlap. May not be sufficiently separated.

  At this time, in the connection structure 10 of the coaxial cable to the circuit board according to the present embodiment, the metal member 36 is wound around the exposed end portion of the shield conductor 20 so as to cover the outer periphery of the shield conductor 20. At the end of the conductor 20, the conductor through which the signal return current and noise current flow is thick. Then, the inner peripheral side of the end portion of the shield conductor 20 is connected to the first ground conductor 28 by the terminal portion 20a, and the outer peripheral side of the end portion of the shield conductor 20 is connected to the first ground conductor 28 (via the metal member 36) by the leg portion 36c of the metal member 36. Two ground conductors 30 are connected.

  Thus, since the conductor at the end of the shield conductor 20 is thick, the return current and the noise current are easily separated at the end of the shield conductor 20 even if the current path is deep. Therefore, the return current B flows from the inner peripheral surface of the shield conductor 20 through the terminal portion 20a of the shield conductor 20 to the first ground conductor 28, and the noise current C flows from the outer peripheral surface of the shield conductor 20 to the legs of the metal member 36. It becomes easy to flow to the second ground conductor 30 through the part 36c, and the effect of separating the return current B and the noise current C is high even if the current path is deep.

  Further, since the plate thickness of the cylindrical portion 36 a of the metal member 36 is thicker than the thickness of the shield conductor 20, the depth of the current path of the noise current C flowing through the shield conductor 20 is about the thickness of the shield conductor 20. Even if the current path is deeper as in some cases, the noise current C can be passed through the leg portion 36c of the metal member 36. Thereby, the separation performance between the return current B and the noise current C is further improved. In particular, if the thickness of the shield conductor 20 is set to be twice or more, the return current B and the noise current C are reliably separated.

  That is, according to the connection structure 10 to the circuit board of the coaxial cable according to the present embodiment, the return current B and the noise current C are more effectively without being particularly affected by the magnitude of the frequency of the signal flowing through the electric wire. Can be separated, and the separation effect is high. Then, the noise current C induced in the shield conductor 20 is prevented from flowing in the signal transmission / reception circuit in a superimposed manner with the signal return current B, thereby preventing the induction noise from affecting the transmitted / received signal.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  For example, in the above embodiment, the inner peripheral side of the shield conductor 20 is connected to the first ground conductor 28 without winding the metal member 36 around the outer periphery of the shield conductor 20, and the outer peripheral side is connected to the second ground conductor 30. Of course, it is possible to separate the return current B and the noise current C by utilizing the skin effect of the current even if they are connected to each other (two-point grounding). Of course, other methods may be used.

  The circuit board 14 has one insulating base 24 and a wiring conductor 26 and ground conductors 28 and 30 on the top surface of the insulating base 24. The circuit board 14 has a multilayer structure of two or more layers. A wiring conductor or a ground conductor may be formed in the space (inside the circuit board). At this time, if there is a pad connected to the wiring conductor or a pad connected to the ground conductor on the insulating substrate, the connection is facilitated.

  The structure for connecting a coaxial cable to a circuit board according to the present invention can be used in connection of a coaxial cable to a circuit board of an electronic / electrical device mounted on an automobile or the like.

It is a perspective view showing one Embodiment of the connection structure to the circuit board of the coaxial cable which concerns on this invention. It is sectional drawing of the connection structure shown by FIG. It is sectional drawing showing an example of the connection structure to the circuit board of the conventional coaxial cable. It is a schematic diagram showing an example of the connection structure to the circuit board of the conventional coaxial cable which made the shield conductor of the coaxial cable into two layers.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Connection structure of coaxial cable to circuit board 12 Coaxial cable 14 Circuit board 16 Center conductor 20 Shield conductor 20a End portion 26 of shield conductor Wiring conductor 28 First ground conductor 30 Second ground conductor 36 Metal member A Signal current B Return current C Noise current

Claims (3)

  The inner peripheral side of the shield conductor end of the coaxial cable is connected to the first ground conductor of the circuit board, and the outer peripheral side of the shield conductor end is connected to the second ground conductor of the circuit board. Connection structure of coaxial cable to circuit board.   A metal member electrically connected to the outer peripheral surface is provided on the outer peripheral surface of the shield conductor end, and the outer peripheral side of the shield conductor end is connected to the second ground conductor of the circuit board via the metal member. The structure for connecting a coaxial cable to a circuit board according to claim 1.   The structure for connecting a coaxial cable to a circuit board according to claim 2, wherein the thickness of the metal member is larger than the thickness of the shield conductor.

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