Circuit assembly comprising a printed circuit board and a connecting cable, and manufacturing process for producing a circuit assembly

Abstract

The invention relates to a circuit assembly (1) comprising a printed circuit board (10) with a connecting cable (20), wherein circuit structures are arranged on a surface of the printed circuit board (10), wherein the connecting cable (20) has one or more internal strands (L) and a cable sheath (M), the strands (L) protrude from the cable sheath (M) and are each stripped at their ends, wherein the printed circuit board (10) has at least two bores per strand (L), each bore extending from a top (11) to a bottom (12) of the printed circuit board (10), wherein the strands (L) are each individually passed through a first bore (B11) and then through a second bore (B12) and are soldered to the printed circuit board (10) on the top (11) and on the bottom (12), and a method for manufacturing a circuit assembly.

Description

[0001] The invention relates to a circuit assembly according to the features of the preamble of patent claim 1, as well as a method for producing such a circuit assembly.

[0002] Proximity switches are generally contactless and are used in large quantities, primarily in automation technology. They consist of an externally controlled sensor element connected to an electronic (evaluation) circuit that evaluates the influence of the sensor element's electrical properties, processes it, and outputs it as a signal. The (evaluation) circuit is mounted on a printed circuit board. The printed circuit board, together with the connecting cable, forms a circuit assembly.

[0003] Such circuit assemblies are used in non-contact proximity switches. Proximity switches can utilize various sensor principles. Optical, inductive, capacitive, magnetic, or ultrasonic proximity switches are known, some of which are manufactured and distributed by the applicant. In the vast majority of applications, they are connected to the load to be controlled or a higher-level evaluation unit via a connector or cable. Since they are used as mass products, their efficient production is of great importance.

[0004] For so-called cable devices, both reliable contact and effective strain relief of the connecting cable play an important role.

[0005] Circuit assemblies are also installed in cable connectors, which have a circuit and are used as a connecting plug between proximity switches with plug connection and control device.

[0006] The printed circuit board can be a flexible circuit board or a rigid electronic board. The base material of the circuit board consists of an electrically insulating material. Conductive tracks are applied to the board. Electronic components, such as SMD components, are typically mounted and soldered onto the board using SMT technology.

[0007] DE 10 2004 060 416 A1 shows an arrangement for connecting a coaxial cable, the fastening of which also serves to provide strain relief. For this purpose, the signal line and the shield are soldered separately to a contact pad each.

[0008] DE 102009046870 A1 discloses an electronic switching device in which the stranded wire ends of the connecting cable are soldered to a preferably vertically arranged additional circuit board element to improve strain relief. The expense of the additional circuit board element is considered disadvantageous.

[0009] An object of the invention is to overcome the aforementioned disadvantages and to provide an improved circuit assembly comprising a printed circuit board and a connecting cable, which has an alternative strain relief, is simple and cost-effective to manufacture, and is space-saving. The circuit assembly should be able to be implemented without additional components.

[0010] The object is achieved by the characterizing features of patent claim 1. Advantageous developments of the invention are specified in the subclaims.

[0011] A further object of the invention is to provide a method for producing such a circuit assembly. This object is achieved by the features of claim 8. Advantageous developments of the invention are specified in the subclaims.

[0012] Electrical devices connected by a power cable, so-called cable devices, require cable strain relief. The purpose of any strain relief is to prevent mechanical stress on the electronic connecting components when the cable is pulled.

[0013] Strain relief is usually achieved by gluing or clamping the cable.

[0014] The invention shows a very cost-effective and process-reliable solution for cable strain relief on a circuit assembly without the need for additional components such as adhesive, a clamp or the like.

[0015] For this purpose, the strands of a connecting cable are pushed through holes in a circuit board and firmly connected to the circuit board by soldering. On the circuit board, there are solder pads arranged directly around the drill holes on both the top and bottom. One of the strands is first guided through a first drill hole and then through a second drill hole and is firmly connected to the circuit board by soldering to the solder pads arranged on the top and bottom of each drill hole. Each strand is soldered four times, so that after the soldering process, a first solder connection is formed for each strand on the bottom, a second and third solder connection on the top, and a fourth solder connection on the bottom of the circuit board. The first and second solder connection ensure a firm fit and a secure connection between the connecting cable and the circuit board.Tensile forces acting on the connecting cable are fully compensated by the first and second solder joints. By looping the stranded wire through the first and then through the second holes, it is ensured that no tensile force acts on the solder joints connected to the second hole and the stranded wire (third and fourth solder joints). The third and fourth solder joints remain unaffected by tensile forces. The connection between the stranded wire and the circuit board is further strengthened by the stranded wire being deflected 180° as it loops through the holes. The third and fourth solder joints of each strand are for electrical contact with a circuit structure, and the first and second solder joints of the strand are for absorbing the tensile force, for strain relief.

[0016] When the connecting cable is subjected to stress (force acting on it, pulling on the cable), the tensile force is absorbed by the first and second soldered joints. The third and fourth soldered joints remain unstressed.

[0017] The essential idea of ​​the invention is to increase the mechanical strength of the electrical connection, which is achieved by providing multiple holes per stranded wire to provide better anchoring to the circuit board. According to the invention, this is achieved by passing the individual stranded wires through at least two holes and soldering the stranded wires to the feedthroughs.

[0018] According to the invention, a circuit assembly is specified which has a printed circuit board with a connecting cable. Circuit structures are arranged on a surface of the printed circuit board. The base material of the printed circuit board consists of an electrically insulating material. Circuit structures can be, for example, electronic components and conductor tracks of a circuit which are applied to the printed circuit board. The connecting cable has one or more internal strands. The strands are surrounded by a cable sheath. The strands protrude from the cable sheath towards the printed circuit board and are each stripped at their ends. Furthermore, the printed circuit board has at least two holes for each strand, each hole extending from a top side to a bottom side of the printed circuit board.According to the invention, the stranded wires are each individually passed through a first hole and then through a second hole and are soldered to the circuit board on the top and bottom.

[0019] An advantageous embodiment provides for four solder connections per stranded wire: a first solder connection on the underside, a second and third solder connection on the top, and a fourth solder connection on the underside. The third and fourth solder connections of each stranded wire are intended for electrical contact with a circuit, and the first and second solder connections of the stranded wire serve as strain relief, absorbing a tensile force when the cable is pulled.

[0020] One embodiment of the invention provides for the circuit board to be a flexible circuit board made of flexible, pliable material or an electronic board made of a more dimensionally stable material. By using a flexible circuit board, the shape of the circuit board can adapt to the installation conditions. For example, a flexible circuit board can be installed curved or bent. Furthermore, it is possible to fold a flexible circuit board. This allows for more space-saving installation.

[0021] One design provides for the circuit board to have circuit structures on both the underside and the top side. This is particularly advantageous when the installation space for the circuit on one side is too small. This allows both surfaces to be utilized.

[0022] An advantageous embodiment provides that the circuit assembly is a sensor circuit for wired sensors or a circuit for cable connectors, and is used in a proximity switch or connector to meet industrial requirements due to tensile forces on the cable.

[0023] The method according to the invention comprises the following steps: passing a stranded wire from an underside of the circuit board through a first hole; further passing this stranded wire from an upper side of the circuit board through a second hole, so that the end of this stranded wire projects beyond the underside of the circuit board; soldering the stranded wire to the feedthroughs, respectively on the underside and on the upper side, so that a first and fourth solder connection is formed on the underside and a second and third solder connection is formed on the upper side.

[0024] In a further advantageous embodiment, the process steps for further strands can take place in parallel or be carried out one after the other.

[0025] The invention is explained in more detail below using exemplary embodiments with reference to the drawings.

[0026] They show schematically: Fig. 1 a circuit assembly according to the invention in a sectional view.

[0027] In the following description of the preferred embodiments, like reference numerals designate like or comparable components.

[0028] Fig. Figure 1 shows a circuit assembly 1 according to the invention in a sectional view. The circuit assembly 1 comprises a printed circuit board 10 with a connecting cable 20. The printed circuit board 10 consists of an electrically insulating base material, with a top side 11 and a bottom side 12. The printed circuit board 10 has circuit structures in the form of conductor tracks and electronic components on the top side 11 and the bottom side 12, respectively, in Fig. 1, which together form a circuit. Circuit structures can also be applied on both sides, on the top side 11 as well as on the bottom side 12. This is the case, for example, if the installation space for the circuit structures on one side of the printed circuit board 10 is insufficient, or the circuit carrier should be designed to be more space-saving. The circuit structures form an electronic circuit. Fig. The circuit carrier 1 shown in Figure 1 has two through holes B11, B12. Each hole B11, B12 extends from the top side 11 to the bottom side 12 of the circuit carrier 10. A connecting cable 20 is connected to the circuit carrier 10. The connecting cable 20 has a cable sheath M and internal stranded wires L. The stranded wires L protrude from the cable sheath M and are each stripped at their ends. Fig.1, only one stranded wire L is shown in a simplified manner. The connecting cable 20 can have further stranded wires L. Typically, a connecting cable 20 has four strands L. Each stranded wire L is individually passed through a first hole B11 and then through a second hole B12 and soldered to the circuit board on the top side 11 and the bottom side 12. Each stranded wire L is connected to the circuit board with four solder connections V1, V2, V3, V4. A first solder connection V1 is provided on the bottom side 12, a second and a third solder connection V2, V3 on the top side 11, and finally a fourth solder connection on the bottom side 12. The third and fourth solder connections V3, V4 of a respective stranded wire L are provided for electrical contact with a circuit structure. The first and second solder connections V1, V2 of the stranded wire L are each provided for absorbing a tensile force F.

[0029] The advantages of the invention lie in particular in the arrangement and fastening of each stranded wire with two bores B11, B12. The connecting cable 20 is looped through the circuit board 10 through two bores. On both the underside 12 and the top side 11, there is a solder pad at each of the two bores B11, B12 for soldering a stranded wire L. The solder connections in the first bore B11 serve as cable strain relief; those in the second bore B12 provide electrical contact. When the cable is loaded (pulled with a tensile force F), the tensile force F is absorbed by the first bore B11 and the second bore B12 remains unloaded, which is particularly advantageous for meeting industrial requirements for tensile forces on the cable.

[0030] To increase the mechanical strength and for optimal electrical contact, the holes B11, B12 can also be designed as through-holes, whereby the through-hole connection of the hole B11 serves exclusively for strength, and the through-hole connection of the hole B12 remains unstressed by the tensile force F due to the inventive arrangement. List of reference symbols 1 circuit assembly 10 circuit board 11 Top 12 Bottom 20 connection cables B11 a continuous bore B12 second hole F traction force L strands M cable sheath V1 first solder connection V2 second solder connection V3 third solder connection V4 fourth solder connection QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2004 060 416 A1

[0007] DE 102009046870 A1

[0008]

Claims

[1] Circuit assembly (1) comprises a printed circuit board (10) with a connecting cable (20), wherein circuit structures are arranged on a surface of the printed circuit board (10), wherein the connecting cable (20) has one or more internal strands (L) and a cable sheath (M), the strands (L) protrude from the cable sheath (M) and are each stripped at their ends, wherein the printed circuit board (10) has at least two holes per strand (L), wherein each hole extends from a top side (11) to a bottom side (12) of the printed circuit board (10), characterized by , that the stranded wires (L) are each individually passed through a first hole (B11) and then through a second hole (B12) and are soldered to the circuit board (10) on the top side (11) and on the bottom side (12). [2] Circuit assembly (1) according to claim 1, characterized byin that four solder connections (V1, V2, V3, V4) are formed per stranded wire (L), a first solder connection (V1) on the underside (12), a second and a third solder connection (V2, V3) on the upper side (11) and a fourth solder connection (V4) on the underside (12), wherein the third and the fourth solder connection (V2) of a respective stranded wire (L) are provided for the electrical contact with a circuit structure and the first and second solder connection (V1) of the stranded wire (L) are each provided for absorbing a tensile force (F). [3] Circuit assembly (1) according to claim 1 to 2, wherein the printed circuit board (10) is a flexible printed circuit board or electronic board. [4] Circuit assembly (1) according to claims 1 to 3, characterized by that the holes (B11, B12) are designed as through-holes, whereby the hole B11 serves exclusively for strain relief and the hole (B12) is provided for electrical contact with a circuit. [5] Circuit assembly (1) according to claims 1 to 4, wherein the printed circuit board (10) has circuit structures on the underside (12) and on the top side (11). [6] Circuit assembly (1) according to claims 1 to 5, wherein the circuit structures are electronic components and conductor tracks applied to the circuit board (10). [7] Circuit assembly (1) according to claims 1 to 6, wherein the circuit assembly (1) is a sensor circuit for wired sensors or a circuit for cable connectors. [8] Method for producing a printed circuit board (1) according to one of claims 1 to 7 for the tensile connection of the printed circuit board (10) to a connecting cable (20), characterized by the following procedural features: a.) passing a stranded wire (L) from a bottom side (12) of the printed circuit board (10) through a first hole (B11); b.) further passing this stranded wire (L) from an upper side (11) of the printed circuit board (10) through a second bore (B12) so that the end of this stranded wire (L) projects beyond the underside (12) of the printed circuit board (10); c.) Soldering the stranded wire to the feedthroughs, respectively on the underside (12) and on the top side (12), so that a first and fourth solder connection (V1, V4) is formed on the underside (12) and a second and third solder connection (V2, V3) is formed on the top side (11). [9] Method according to claim 8, wherein the individual steps a.) to c.) are carried out for further strands (L) in parallel or successively.

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