CIRCUIT MODULE AND METHOD FOR MANUFACTURING A CIRCUIT MODULE

Abstract

A circuit module (100) in which an inner conductor (1) of a coaxial cable (200) is connected by a solder (30) to a circuit body (20) of a circuit board (300), wherein the circuit board (300) comprises: a dielectric body (21); the circuit body (20) formed on a surface of the dielectric body (21); and a grounding body (22) formed on a rear surface of the dielectric body (21), and wherein the coaxial cable (200) comprises: the inner conductor (1); an insulator (2) provided to surround the inner conductor (1); an outer conductor (3) provided to surround the insulator (1); and a sheath (4) provided to surround the outer conductor (3), wherein the inner conductor (1) has a connecting portion (5) connected to the circuit body (20) and a non-exposed portion (6) within the sheath (4), and a thickness (h1) of the connecting portion (5) is equal to or less than 35% of a thickness (h2) of the non-exposed portion (6) and the cross-sectional area of ​​the connecting portion (5) is the same as the cross-sectional area of ​​the non-exposed portion (6).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a circuit module and a method for manufacturing the circuit module. 2. Description of related technology

[0002] JP H05-235613 A discloses a circuit module in which an inner conductor of a coaxial cable is connected to a circuit body of a circuit board, the coaxial cable including an inner conductor; an insulator provided to surround the inner conductor; and an outer conductor provided to surround the insulator.

[0003] Conventionally, Japanese Patent Application Laid-Open No. JP 2009-218085 A discloses, as a technique for connecting a coaxial cable to a circuit board, maintaining impedance matching by using, for example, an adapter 10 for connecting a high-frequency cable 20 to wiring 32 of a PWB 30.

[0004] Furthermore, Japanese Patent Application Laid-Open No. JP 2018-063894 A discloses easy matching of impedance by using a coaxial connector 10 for connecting a coaxial cable Cb to a printed circuit board 9q.

[0005] However, in the case of the foregoing connection techniques disclosed in Japanese Patent Application Laid-Open No. JP 2009-218085 A and Japanese Patent Application Laid-Open No. JP 2018-063894 A described above, although impedance mismatch is suppressed by using the adapter 10 or the coaxial connector 10, a component such as the adapter 10 or the coaxial connector 10 is required to suppress impedance mismatch. SUMMARY OF THE INVENTION

[0006] The present invention has been conceived in view of the foregoing, and the purpose of the present invention is to provide a circuit module and a method of manufacturing the circuit module that enable impedance mismatch suppression without using an impedance mismatch suppression component.

[0007] To achieve the above-mentioned object, a circuit module in which an inner conductor of a coaxial cable is connected to a circuit body of a circuit board by a solder includes the circuit board including: a dielectric body; the circuit body formed on a surface of the dielectric body; and a grounding body formed on a back surface of the dielectric body, and the coaxial cable including: the inner conductor; an insulator provided to surround the inner conductor; an outer conductor provided to surround the insulator;and a sheath provided to surround the outer conductor, wherein the inner conductor has a connecting portion connected to the circuit body and an unexposed portion within the sheath, and a thickness of the connecting portion is equal to or less than 35% of a thickness of the unexposed portion, and the cross-sectional area of ​​the connecting portion is the same as the cross-sectional area of ​​the unexposed portion.;

[0008] To achieve the above-mentioned object, a method for manufacturing a circuit module in which an inner conductor of a coaxial cable is connected to a circuit body of a circuit board by solder according to another aspect of the present invention includes the circuit board including: a dielectric body; the circuit body formed on a surface of the dielectric body; and a grounding body formed on a back surface of the dielectric body, and the coaxial cable including: the inner conductor; an insulator provided to surround the inner conductor; an outer conductor provided to surround the insulator;and a sheath provided to surround the outer conductor, the inner conductor having a connecting portion connected to the circuit body and an unexposed portion within the sheath, the method including: an exposing step in which the insulator, the outer conductor, and the sheath of the coaxial cable are peeled off to expose the connecting portion to the outside; a compressing step in which compression is performed to make a thickness of the connecting portion equal to or less than 35% of a thickness of the unexposed portion and to make the cross-sectional area of ​​the connecting portion the same as the cross-sectional area of ​​the unexposed portion; and a joining step in which the connecting portion is joined to the circuit body by the solder.

[0009] The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a schematic diagram illustrating a circuit module in which an inner conductor of a coaxial cable is connected to a circuit body of a circuit board; Fig. Figure 1B is a cross-sectional view along AA in Fig. 1A; Fig. Figure 1C is a cross-sectional view along BB in Fig. 1A; Fig. 2 is a flowchart illustrating an overview of a method for manufacturing the circuit module; Fig. 3 is a cross-sectional view illustrating pressure processing of the inner conductor of the coaxial cable; Fig. 4 is a cross-sectional view illustrating variation in the thickness of the inner conductor of the coaxial cable; Fig. 5 is a graph illustrating the results of measuring the impedance of the circuit module; and Fig. Figure 6 is a graph illustrating the results of measuring the frequency and amount of attenuation of the circuit module. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment of a circuit module and a method for manufacturing the circuit module according to the present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to or by the present embodiment. Furthermore, the constituent elements of the following embodiment include constituent elements that can be easily conceived by a person skilled in the art or that are substantially the same. Furthermore, various omissions, substitutions, and modifications may be made to the constituent elements of the following embodiment without departing from the spirit of the invention.

[0011] Fig. 1A is a schematic diagram illustrating a circuit module 100 in which an inner conductor 1 of a coaxial cable 200 is connected to a circuit body 20 of a circuit board 300. Fig. Figure 1B is a cross-sectional view along AA in Fig. 1A. In addition, Fig. 1C a cross-sectional view along BB in Fig. 1A. The circuit module 100 according to the present embodiment includes a coaxial cable 200 that transmits a radio wave signal received by an antenna 50, and a circuit board 300 installed in a vehicle-mounted device. The configuration is such that the radio wave signal received by the antenna 50 is relayed through the coaxial cable 200 and transmitted to the circuit board 300 of the vehicle-mounted device. According to the present embodiment, the vicinity of the terminal of the coaxial cable 200 is stripped, thereby exposing an outer conductor 3 and the inner conductor 1 to the outside of the coaxial cable 200. The exposed inner conductor 1 is electrically connected to the circuit body 20 of the circuit board 300 by solder, and the exposed outer conductor 3 is electrically connected to a grounding body 22 of the circuit board 300 by solder 30.It should be noted that the peeling process is carried out by sequentially performing peeling treatments, which include, for example, cutting and peeling by laser radiation and cutting work or the like.

[0012] A method of electrically connecting the inner conductor 1 of the coaxial cable 200 to the circuit body 20 of the circuit board 300 through the solder 30 is performed, for example, by arranging the inner conductor 1 of the coaxial cable 200 to the circuit body 20 formed on a surface of a dielectric body 21 of the circuit board 300 and then performing soldering.

[0013] A method of electrically connecting the outer conductor 3 of the coaxial cable 200 to the grounding body 22 of the circuit board 300 through the solder 30 is performed, for example, by twisting braids that are the outer conductor 3 of the coaxial cable 200 together into a single cable, subsequently arranging the single twisted cable on the grounding body 22 formed on the back surface of the dielectric body 21, and then performing soldering.

[0014] As in Fig. 1 and Fig. As illustrated in FIG. 2, the coaxial cable 200 is provided with the inner conductor 1, an insulator 2 covering the outer periphery of the inner conductor 1, the outer conductor 3 covering the outer periphery of the insulator 2, and a cover 4 covering the outer periphery of the outer conductor 3. The coaxial cable 200 is formed from the center to the outside in a radial direction by the inner conductor 1, the insulator 2, the outer conductor 3, and the cover 4 in this order. The coaxial cable 200 according to the present embodiment has an impedance of 50 Ω.

[0015] The inner conductor 1 transmits electrical power, signals, and the like, and in the present embodiment, is configured as a twisted wire made by twisting seven metal wires together with a wire diameter of 0.18±0.008 mm. Soft copper is used as the material of the metal wires. Note that, for example, tinned soft copper, a copper alloy, aluminum, an aluminum alloy, or the like may also be used. Furthermore, the inner conductor 1 has a part inside the sheath 4 as an unexposed portion 6. Within the inner conductor 1, the cross section of the unexposed portion 6 is formed into a circular shape.

[0016] The inner conductor 1 has a connecting portion 5 for connecting to the circuit body 20 of the circuit board 300. The connecting portion 5 is exposed to the outside of the coaxial cable 200 and is, as shown in Fig. 1 to 3, is formed with a rectangular cross-section. As shown in Fig. 3, the connecting portion 5 is formed with a thickness h1 equal to or less than 35% of a thickness h2 of the unexposed portion 6. Furthermore, the connecting portion 5 is formed with a cross-sectional area that is the same as the cross-sectional area of ​​the part of the inner conductor 1 that is inside the cover 4, that is, the unexposed portion 6. The thickness h1 of the connecting portion is preferably set to 30% to 35% of the thickness h2 of the unexposed portion 6 due to concern about the degrading strength of the connecting portion 5 when a load acts on the connecting portion 5 in the case of excessive compression. For the connecting portion 5 according to the present embodiment, the thickness h1 is 25% of h2.

[0017] The insulator 2 is arranged on the outer peripheral surface of the inner conductor 1 and is stacked on the outer side in a radial direction from the outer peripheral surface of the inner conductor 1. To adjust the impedance of the coaxial cable 200 to 50 Ω, the insulator 2 is made of cross-linked polyethylene and has a thickness of 0.555 mm. Note that a synthetic resin such as a thermoplastic elastomer or other rubber-like elastic body, a foam insulator obtained by foaming a polyethylene resin, or other synthetic resin or rubber-like elastic body can be used for the insulator 2.

[0018] The outer conductor 3 is arranged on the outer peripheral surface of the insulator 2 and is stacked on the outer side in a radial direction from the outer peripheral surface of the insulator 2. The outer conductor 3 is configured by braiding metal wires with a diameter of 0.10 mm into a braid. Note that, for example, either a metallic foil or both a metallic foil and a braid can be used. Tinned soft copper is used as the material of the metal wires. Note that, for example, soft copper, a copper alloy, aluminum, an aluminum alloy, or the like can also be used. Braids of the outer conductor 3 are twisted together into a single wire, which is electrically connected to the grounding body 22 of the circuit board 300 through the solder 30.By twisting braids together into a single wire that is electrically connected to the grounding body 22 of the circuit board 300 through the solder 30, a ground connection can be implemented without using a terminal or such an element.

[0019] The sheath 4 is arranged on the outer peripheral surface of the outer conductor 3 and is stacked on the outer side in a radial direction from the outer peripheral surface of the outer conductor 3. Polyvinyl chloride (PVC) is used for the sheath 4, which is permitted to have a thickness of 0.455 mm. Note that PE or PP or the like can also be used.

[0020] The antenna 50 receives radio waves from the outside. The antenna 50 is equipped with a variety of electronic components such as an amplifier and a filter. The antenna 50 is electrically connected to the circuit board 300 via the coaxial cable 200.

[0021] Circuit board 300 is a processing circuit for displaying a signal received by antenna 50 on a car navigation system or the like. Circuit board 300 includes circuit body 20 configured to sandwich dielectric body 21.

[0022] The circuit board 300 is configured by a dielectric body 21 (for example, a PET film) of a predetermined thickness (750 μm), a circuit body 20 formed on a surface of the dielectric body 21, a grounding body (not illustrated) on both sides of the circuit body 20, and a grounding body 22 formed on the back surface of the dielectric body 21. Note that the circuit body 20 and the grounding body 22 have a thickness on the order of 18 μm.

[0023] A method of manufacturing the circuit module 100 will be described next. Fig. 2 is a flowchart illustrating an overview of a method for manufacturing the circuit module. According to the method for manufacturing the circuit module 100, a circuit module is manufactured through an exposing step (step 1), a compressing step (step 2), and a connecting step (step 3), as shown in Fig. 2 illustrates, produced.

[0024] In the exposing step (step 1), in the vicinity of the terminal of the coaxial cable 200, for example, a coaxial cable stripper is used to remove the insulator 2, the outer conductor 3 and the sheath 4, so that the inner conductor 1 for connecting to the circuit body 20 of the circuit board 300 is exposed to the outside.

[0025] In the compression step (step 2), compression is performed to make the thickness h1 of the connecting portion 5 equal to or less than 35% of the thickness h2 of the non-exposed portion 6 and to make the cross-sectional area of ​​the connecting portion 5 the same as the cross-sectional area of ​​the non-exposed portion 6.

[0026] Here, the compression step (step 2), i.e., the method for compressing the inner conductor 1 of the coaxial cable 200, will be described. Fig. 3 is a cross-sectional view illustrating pressure processing of the inner conductor of the coaxial cable. Here in Fig. 3, (1) is a state diagram before a load is applied to dies, (2) is a state diagram when a load is applied to the dies, and (3) is a state diagram after a load has been applied to the dies.

[0027] First, inside the inner conductor 1, the part exposed to the outside is clamped between a pair of punches 40 ((1) in Fig. 3). Next, the punches 40 are moved in a direction toward each other and, by applying a load to the part of the inner conductor 1 exposed to the outside, the part of the inner conductor 1 exposed to the outside is subjected to compression molding ((2) in Fig. 3). By subjecting the part of the inner conductor 1 exposed to the outside to compression molding, this part is formed as the connecting portion 5 which is for connection to the circuit body 20 of the circuit board 300 ((3) in Fig. 3). Here, because the connecting portion 5 is subjected to compression molding by the punches 40, the connecting portion 5 has a width w2 wider than a width w1 of the non-exposed portion 6 and has a cross-sectional area the same as the cross-sectional area of ​​the non-exposed portion 6.

[0028] In the connecting step (step 3), the connecting portion 5 is arranged opposite to the circuit body 20 of the circuit board 300 and then by using the solder 30 as shown in Fig. 2. Furthermore, after the braids constituting the outer conductor 3 are twisted together into a single wire, the terminal of the outer conductor 3 resulting from this single wire is placed opposite the grounding body 22 and then connected using the solder 30. The circuit module 100 is manufactured accordingly.

[0029] Impedance matching of the circuit module 100 according to the present embodiment will be described next. Fig. Figure 4 is a cross-sectional view illustrating variation in the thickness of the inner conductor of the coaxial cable. Fig. 4 illustrates the thickness of the connecting portion 5 and the mass compressibility of the connecting portion 5 when the load on the punches 40 is 0N, 300N, and 1000N. The connecting portion 5 has a thickness h1 of 0.6 mm when no load is applied to the punches 40 (0N), a thickness h1 of 0.3 mm when the load on the punches 40 is 300N, and a thickness h1 of 0.15 mm when the load on the punches 40 is 1000N.

[0030] Here, the non-exposed portion 6 has the same thickness as a connecting portion 5 when no load is applied to the punches 40 (0 N), that is, the same thickness as the part of the inner conductor 1 exposed to the outside. Therefore, the connecting portion 5 has a mass compressibility of 50% when the load on the punches 40 is 300 N, and its thickness h1 is 50% of the thickness h2 of the non-exposed portion 6. In addition, the connecting portion 5 has a mass compressibility of 75% when the load on the punches 40 is 1000 N, and its thickness h1 is 25% of the thickness h2 of the non-exposed portion 6.

[0031] As in Fig. As illustrated in Fig. 4, some of the plurality of wires 11 constituting the inner conductor 1 are in a state of point contact with the circuit body 20 when the thickness h1 of the connecting portion 5 is 0.6 mm and when the thickness h1 is 0.3 mm. On the other hand, when the thickness h1 of the connecting portion 5 is 0.15 mm, the plurality of wires 11 constituting the inner conductor 1 are deformed, and all the wires 11 of the connecting portion 5 are in a state of area contact with the circuit body 20. As a result of the connecting portion 5 changing from point contact with the circuit body 20 to area contact therewith, the area of ​​the connecting portion 5 in contact with the circuit body 20 increases. Due to the increase in the area of ​​contact, the resistance between the connecting portion 5 and the circuit body 20 decreases.

[0032] Fig. Figure 5 is a graph illustrating the results of measuring the impedance of the circuit module. Fig. Figure 5 illustrates the results of measuring the impedance of the circuit module 100 in which the inner conductor 1 is connected to a connecting portion 5 of each thickness h1 (each mass compressibility) in Fig. 4 is used. Specifically, the circuit module 100, in which the inner conductor 1 of the coaxial cable 200 is connected to the circuit body 20 of the circuit board 300, was connected to a port 1 and a port 2 of an N5222B PNA microwave network analyzer (10M to 26.5 GHz) via a coaxial cable for measurement (model number; N4419AK20) and an SMA (subminiature type A) compatible connector, and the impedance was measured using a rise time of 60 ps and a TDR function with a T11 or T22 parameter. As a result, the impedance was 59 Ω for a 0% mass compressibility (thickness h1 of 0.6 mm) of the connecting section 5, 57 Ω for a 50% mass compressibility (thickness h1 of 0.3 mm) of the connecting section 5, and 53 Ω for a 75% mass compressibility (thickness h1 of 0.15 mm) of the connecting section 5. Based on these results, an increase in impedance by increasing mass compressibility is suppressed.Here, in order to keep any increase in the impedance of the connecting portion 5 of the coaxial cable 200 connected to the circuit body 20 within ±5% of a reference impedance (for example, 50 Ω), the mass compressibility of the connecting portion 5 must be adjusted based on the results of . Fig. 5, should be set to 65% or more. Note that, due to concerns about the degradation of the strength of the connecting portion 5 when a load acts on the connecting portion in the event of excessive compression, the mass compressibility of the connecting portion 5 is preferably 65% ​​to 75%, which is optimal. The thickness h1 of the connecting portion 5, when the mass compressibility of the connecting portion 5 is equal to or more than 65%, is equal to or less than 35% of the thickness h2 of the non-exposed portion 6. Furthermore, when the mass compressibility of the connecting portion 5 is set to 75%, the thickness h1 of the connecting portion 5 is 25% of the thickness h2 of the non-exposed portion 6.

[0033] Fig. Figure 6 is a graph illustrating the results of measuring the frequency and amount of attenuation of the circuit module. Fig.Figure 6 illustrates the results of measuring the frequency attenuation of the circuit module 100, in which the inner conductor 1 of the coaxial cable 200 is connected to the circuit body 20 of the circuit board 300. Specifically, the circuit module 100, in which the inner conductor 1 of the coaxial cable 200 is connected to the circuit body 20 of the circuit board 300, was connected to a port 1 and a port 2 of an N5222B PNA microwave network analyzer (10M to 26.5 GHz) via a coaxial cable for measurement (model number; N4419AK20) and an SMA (Subminiature Type A) compatible connector, and S21 or S12 parameters were measured.When a comparative example in which the mass compressibility of the connecting portion 5 of the coaxial cable 200 is 0% is compared with an embodiment example in which the connecting portion 5 of the coaxial cable 200 is compressed at a mass compressibility of 75%, the embodiment example exhibits a minimal amount of attenuation compared with the comparative example, and therefore, the characteristics are improved. The above measurement results indicate a favorable effect in that impedance mismatch can be suppressed even when the inner conductor 1 of the coaxial cable 200, of which the connecting portion 5 has a mass compressibility of 65% to 75% (the thickness h1 of the connecting portion 5 is 35% to 25% of the thickness h2 of the non-exposed portion 6), is directly connected to the circuit body 20 of the circuit board 300.

[0034] As described hereinabove, for the circuit module 100 and the method of manufacturing the circuit module 100 according to the present embodiment, the thickness of the connecting portion 5 is equal to or less than 35% of the thickness of the non-exposed portion 6, and the cross-sectional area of ​​the connecting portion 5 is the same as the cross-sectional area of ​​the non-exposed portion 6, thereby making it possible to suppress impedance mismatch without using an impedance mismatch suppression component.

[0035] It should be noted that, although a twisted cable formed by twisting seven wires 11 together is used as the inner conductor 1 in the foregoing embodiments, a single wire could also be used.

[0036] The circuit module and the method for manufacturing the circuit module according to the present embodiment offers the advantageous effect of enabling impedance mismatch to be suppressed even when a coaxial cable is directly connected to a circuit board.

Claims

[1] A circuit module (100) in which an inner conductor (1) of a coaxial cable (200) is connected by a solder (30) to a circuit body (20) of a circuit board (300), wherein the circuit board (300) comprises: a dielectric body (21); the circuit body (20) formed on a surface of the dielectric body (21); and a grounding body (22) formed on a rear surface of the dielectric body (21), and wherein the coaxial cable (200) comprises: the inner conductor (1); an insulator (2) provided to surround the inner conductor (1); an outer conductor (3) provided to surround the insulator (1); and a sheath (4) provided to surround the outer conductor (3), wherein the inner conductor (1) has a connecting portion (5) connected to the circuit body (20) and a non-exposed portion (6) within the sheath (4), and a thickness (h1) of the connecting portion (5) is equal to or less than 35% of a thickness (h2) of the non-exposed portion (6) and the cross-sectional area of ​​the connecting portion (5) is the same as the cross-sectional area of ​​the non-exposed portion (6). [2] The circuit module (100) according to claim 1, wherein the thickness (h1) of the connecting portion (5) is 25% to 35% of the thickness (h2) of the non-exposed portion (6). [3] The circuit module (100) according to claim 1 or 2, wherein a width (W1) of the connecting portion (5) is greater than a width (W2) of the non-exposed portion (6). [4] The circuit module (100) according to any one of claims 1 to 3, wherein the outer conductor (3) is connected to the grounding body (22). [5] A method for manufacturing a circuit module (100) in which an inner conductor (1) of a coaxial cable (200) is connected to a circuit body (20) of a circuit board (300) by a solder (30), wherein the circuit board (300) includes: a dielectric body (21); the circuit body (20) formed on a surface of the dielectric body (21); and a grounding body (22) formed on a rear surface of the dielectric body (21), wherein the coaxial cable (200) includes: the inner conductor (1), an insulator (2) provided to surround the inner conductor (1), an outer conductor (3) provided to surround the insulator (2), and a sheath (4) provided to surround the outer conductor (3), and wherein the inner conductor (1) has a connecting portion (5) connected to the circuit body (20) and a non-exposed portion (6) within the sheath (4), the method comprising: an exposing step in which the insulator (2), the outer conductor (3) and the sheath (4) of the coaxial cable (200) are peeled off to expose the connecting portion (5) to the outside; a compression step in which compression is performed to make a thickness (h1) of the connecting portion (5) equal to or less than 35% of a thickness (h2) of the non-exposed portion (6) and to make the cross-sectional area of ​​the connecting portion (5) the same as the cross-sectional area of ​​the non-exposed portion (6); and a connecting step in which the connecting portion (5) is connected to the circuit body (20) by the solder (30).

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