Contact structure with welded flexible printed circuit board

Abstract

The invention relates to a contact structure. The contact structure has at least one electrically conductive substrate, in particular a circuit carrier. The contact structure also has a flexible printed circuit board, in particular a flexible printed circuit board, which has at least one - in particular a reversibly bendable - electrically insulating film and at least one or only one conductive layer. The conductive layer of the flexible printed circuit board is conductively connected to the substrate. The contact structure has an electrically conductive connection element, which is arranged on the conductive layer of the flexible printed circuit board, so that the connection element and the substrate sandwich the flexible printed circuit board between them. The connection element is welded to the conductive layer of the flexible printed circuit board and to the substrate in such a way that a welded connection extends from the connection element into the substrate, in particular in a direction transverse to the planar extension of the flexible printed circuit board, through the conductive layer of the flexible printed circuit board.

Description

[Technical field]

[0001] Prior Art The present invention relates to a contact structure. The contact structure comprises at least one electrically conductive substrate, in particular a circuit carrier. The contact structure also comprises a particularly flexible printed circuit board, which comprises at least one - in particular a reversibly bendable - electrically insulating film and at least one or only one conductive layer. The conductive layer of the flexible printed circuit board - in particular placed on the substrate - is conductively connected to the substrate. [Background technology]

[0002] From DE 10 2019 128 634 C1 a bonded self-supporting conductor connection is known between two bonding points, at which a material-bonded connection between the self-supporting conductor and the bonding surface is produced in each case in one bonding step, and between these two bonding points the conductor runs in a bonding loop. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] German Patent No. 102019128634 Summary of the Invention [Means for solving the problem]

[0004] Disclosure of the Invention According to the invention, the contact structure has an electrically conductive connection element which is arranged on a conductive layer of the flexible printed circuit board, so that the connection element and the substrate sandwich the flexible printed circuit board. The connection element is welded to the conductive layer of the flexible printed circuit board and to the substrate in such a way that a welded connection extends from the connection element, in particular transversely to the planar extension of the flexible printed circuit board, through the conductive layer of the flexible printed circuit board into the substrate. This advantageously makes it possible to produce a low-ohmic resistance, in particular solder-free, electrical connection between the flexible printed circuit board and the substrate, in particular a circuit carrier, for example a DCB substrate (DCB=Direct-Copper-Bonded) or an AMB substrate (AMB=Active-Metal-Brazed).

[0005] Advantageously, it has been found that the conductive layer of the flexible printed circuit board can be reinforced by the connection element so that there is no risk of the conductive layer of the flexible printed circuit board being burned off during laser welding.

[0006] The flexible printed circuit board is preferably configured to be bent in a direction transverse to the planar extension of the flexible printed circuit board without breaking. Preferably, the flexible printed circuit board comprises a polyimide layer, a polyamide layer, a PET layer (PET=polyethylene terephthalate), a PVB layer (PVB=polyvinyl butyral), a PVF layer (PVF=polyvinyl fluoride) or an EVA layer (EVA=ethylene vinyl acetate) as an electrically insulating layer or an electrically insulating film. The conductive layer of the flexible printed circuit board is preferably a copper layer or a metal layer made of a copper alloy.

[0007] Preferably, the connecting element is configured to at least partially absorb the heat generated during welding, which advantageously allows the connecting element to constitute a heat accumulator for excess process heat during welding and also a material reservoir which can advantageously reinforce the conductive layer in the region of the weld connection when the flexible printed circuit board is welded to the base body.

[0008] In a preferred embodiment of the contact structure, the welded connection is a laser welded connection, which advantageously makes it possible to weld the circuit carrier, in particular the ceramic circuit carrier, to the flexible printed circuit board from only one side.

[0009] In another embodiment, the base body is formed by a stamped grid, in particular a metal sheet strip or a lead frame. The welded connection is in this embodiment, for example, a resistance spot welded connection. This advantageously makes it possible to configure additional weld material for forming an electrical contact bridge between the flexible printed circuit board and the base body with the connection element during resistance welding.

[0010] In a preferred embodiment, the connecting element has an area extension which - in particular in the plane of the flexible printed circuit board - extends radially outwards beyond the spatial extent of the welded connection, the connecting element covering the flexible printed circuit board outside the welded connection, which advantageously allows a mechanical reinforcement and a form-locking holding function, in particular the formation of a kind of collar around the welded connection, which can mechanically fix and stabilize the flexible printed circuit board in the area of ​​the welded connection.

[0011] In a preferred embodiment of the contact structure, the weld connection is formed by a weld bead that extends flat on the plane of the substrate, in particular in the longitudinal direction. The weld bead extends into the connection element, into the flexible printed circuit board and into the substrate. Preferably, the weld bead is formed so as to completely penetrate the connection element and the flexible printed circuit board, in particular at least one conductive layer of the flexible printed circuit board. This advantageously makes it possible to form a material-bonded, electrically conductive connection between the joining partners.

[0012] In a preferred embodiment, the welded connection is formed only partially along the thickness-wise extension of the substrate, in particular of the conductive layer of the substrate, in particular of the wiring layer. Advantageously, the substrate, in particular the conductive layer of the ceramic substrate, is mechanically indeformable by heat input.

[0013] In a preferred embodiment of the contact structure, the substrate comprises at least one electrically insulating ceramic layer and at least one electrically conductive layer, for example a DCB substrate (DCB=Direct-Copper-Bonded), an AMB substrate (AMB=Active-Metal-Brazed), an IMS substrate (IMS=Insulated-Metal-Substrate), an LTCC substrate (LTCC=Low-Temperature-Cofired-Ceramic) or an HTCC substrate (HTCC=High-Temperature-Cofired-Ceramic).

[0014] This advantageously makes it possible to connect the flexible printed circuit board to the ceramic substrate, in particular without the use of soldering metal. Insofar as the connecting element forms a laterally extending collar beyond the welded connection, which collar is designed to hold and / or press the flexible printed circuit board onto the substrate, the flexible printed circuit board is advantageously also protected by the connecting element from unintentional detachment.

[0015] In a preferred embodiment, the connection element has a thickness extension greater than the conductive layer of the flexible printed circuit board, which advantageously allows the formation of not only a material add-on during welding, but also a mechanical collar for fastening the flexible printed circuit board on the base body.

[0016] In a preferred embodiment, the weld connection, in particular the weld bead, has a widthwise extension that is comparable to the thicknesswise extension of the connection element. For example, the weld bead has a widthwise extension of between 100 and 300 micrometers, preferably between 180 and 220 micrometers or even 200 micrometers. Exemplary thicknesses of the connection element are between 150 and 250 micrometers, preferably between 180 and 220 micrometers. This advantageously allows the formation of a stable and electrically conductive weld connection.

[0017] In a preferred embodiment of the contact structure, the connection element is a bonding tape longitudinal section, preferably made of copper or a copper alloy, which advantageously allows the connection element to be applied cost-effectively to a flexible printed circuit board by means of a bonding device, which further advantageously allows the connection element to be unwound from a bonding tape supply, in particular from a bonding tape roll, and the longitudinal section to be welded onto the circuit carrier and cut off.

[0018] In a preferred embodiment, the connection element is a metal plate, which advantageously allows the connection element to be placed on the circuit carrier, in particular on the flexible printed circuit board, in the region of the electrical connection point using a vacuum mounting machine, in particular an automatic mounting machine. The metal plate is, for example, designed in a self-adhesive manner and has adhesive on the side facing the flexible printed circuit board, at least or only on the partial surface areas that are not to be welded.

[0019] For example, the connection element, in particular a metal plate, for example a copper plate, can be set on the circuit carrier by an automatic mounting machine, which is configured to fix the metal plate by vacuum force, to place the metal plate on the circuit carrier, to press the circuit carrier, in particular a flexible printed circuit board, to deliver a laser beam to the metal plate in the area of ​​the pressing element during pressing, and to weld the metal plate to the flexible printed circuit board and to the substrate, which advantageously allows the welded connection to be integrated into an automated mounting process during mounting of the circuit carrier.

[0020] This advantageously makes it possible to produce a three-layer composite connected by a material bond from the aforementioned joining partners.

[0021] The invention also relates to a contact system with at least one contact structure of the above-mentioned type. The contact structure has at least one further substrate, which is electrically conductively connected to one another by means of a flexible printed circuit board. Preferably, the electrical connection between the flexible printed circuit board and the substrate is created by a connection element that is placed on the flexible printed circuit board and a welded connection by material bonding that passes through the connection element and the flexible printed circuit board into the substrate. This advantageously makes it possible to electrically connect different substrates, in particular circuit carriers, to one another by means of a flexible printed circuit board in a cost-effective manner.

[0022] In a preferred embodiment, the flexible printed circuit board has a plug for electrically connecting the substrate, which can be connected to the flexible printed circuit board in addition to or instead of the aforementioned further substrate, which advantageously allows the electrical connection between the substrate, in particular the ceramic circuit carrier, and the plug connector to be constructed at low cost, in a reliable process and in a durable manner.

[0023] In a preferred embodiment, a flexible printed circuit board can be formed on the circuit carrier as a further applied wiring layer, on which electronic components, for example sensors, can be arranged. Advantageously, the flexible printed circuit board can be welded to the circuit carrier without the use of solder, so that the layer composite comprising the circuit carrier and the flexible printed circuit board can be introduced into a brazing furnace for reflow soldering of electronic components to the layer composite, without the layer composite formed without the use of solder having to be disassembled again.

[0024] The invention also relates to a method for connecting a flexible printed circuit board to a substrate by a material bond, in which a surface area of ​​the flexible printed circuit board is electrically conductively connected to the substrate by a material bond.

[0025] Preferably, a flat-extending connecting element is placed on a surface area of ​​the flexible printed circuit board, and the resulting three-layer structure comprising a substrate, a flexible printed circuit board and a flat-extending connecting element is welded using a laser beam to form a three-layer composite in which the joining partners are preferably connected to one another by a material bond, overlapping one on top of the other.

[0026] Preferably, the three-layer composite is welded from the side of the connection element with a laser beam, which advantageously makes it possible to create a retainable, low-ohmic electrical connection between the flexible printed circuit board and the substrate.

[0027] In the following, the invention is explained on the basis of the drawings and further exemplary embodiments. Further advantageous implementation variants result from the feature combinations set forth in the dependent claims and in the drawings. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 shows a welding apparatus and a method for welding a flexible printed circuit board to a circuit carrier, in which a connection element formed by a longitudinal section of bonding tape is placed on the flexible printed circuit board, the connection element is welded together with the flexible printed circuit board and the circuit carrier using a laser beam, and the longitudinal section of bonding tape is cut from the remaining bonding tape after welding. [Diagram 2] 2 shows an example of a contact structure produced using the welding apparatus shown in FIG. 1 and the method. [Diagram 3] FIG. 2 illustrates a variation of the method shown in FIG. 1, in which a metal plate is placed on the flexible printed circuit board and welded to the flexible printed circuit board and the circuit carrier to form a three-layer connection. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] 1 shows -schematically- an embodiment of a method 1 for producing a connection structure by means of a welding device 9. The connection structure comprises a circuit carrier 2, a flexible printed circuit board 3 and an electrically conductively configured connection element 6. The connection element 6 is formed in this embodiment by a bonding tape longitudinal section of a bonding tape 7.

[0030] In this method, a welding device 9 having a pressing part 10 and a laser 12 configured to generate a laser beam 11 is placed on a three-layer structure including a circuit carrier 2, a flexible printed circuit board 3 and a connection element 6 formed by a longitudinal section of a bonding tape. The pressing part 10 is configured to press the connection element 6 in a direction transverse to a flat extension 40 of the circuit carrier 2, so as to press the connection element 6 against the flexible printed circuit board 3 and thus also against the substrate formed by the circuit carrier 2. The pressing part 10 is shown in a pressing position 10' supported on the connection element 6.

[0031] The flexible printed circuit board 3 has an electrically insulating film 5 and a conductive layer 4, in particular a copper layer, extending in the plane of the flexible film. The laser beam 11 is configured in particular to weld the bonding tape longitudinal section 6, the conductive layer 4 and the conductive wiring layer 17 of the circuit carrier 2 to one another in a form-fitting manner.

[0032] For this purpose, the connection element 6 formed by the longitudinal section of the bonding tape can be evaporated and / or melted by the laser beam 11 in the region where it is struck, and the metal regions arranged adjacent to the region of the evaporation zone can be melted into the evaporation zone, so that a liquefied metal can be formed by the crucible generated in the region of the laser beam 11. The zone of liquefied metal extends through the connection element 6, in particular through the bonding tape section, and also through the conductive layer 4 and also into the conductive layer 17 of the circuit carrier 2, in particular into the wiring layer. The melted zone thus formed in the depth of the superimposed stack formed by the bonding tape section 6, the conductive layer 4 and the circuit carrier 2 can generate, after solidification, a form-locking welded connection between the conductive layer of the flexible printed circuit board 3 and the circuit carrier 2, in particular the conductive layer 17.

[0033] The welded connection 8 formed along the widthwise extension 15 on the flat extension 40 of the circuit carrier 2 thus has a widthwise extension that is smaller than the widthwise extension 14 of the connection element 6, which in this example is cut off from the bonding tape 7 after formation of the welded connection 8 by means of a cutting cutter 13 moved by a cutting device 45. The cutting device 45 is in this example a component part of the welding device and is arranged and configured to reciprocate the cutting cutter 13 and to cut off the bonding tape longitudinal section of the bonding tape 7 extending along the widthwise extension 14 from the bonding tape 7, thereby generating the individualized connection element 6.

[0034] In this way, a collar 19 can be formed around the welded connection 8, which can cover - particularly in the form of a nail head or rivet head - the flexible printed circuit board 3, in particular the conductive layer 4 surrounding the welded connection 8, and in this embodiment also the area of ​​the electrically insulating layer 5, so that fastening can be achieved between the circuit carrier 2 and the connection element 6.

[0035] In this embodiment, the widthwise extension 14 of the connection element 6 is configured to be greater than the widthwise extension 16 of the conductive layer 4 formed on the flexible printed circuit board 3. Due to the widthwise extension 14 of the connection element 6, the surface area on the flexible printed circuit board 3 corresponding to the widthwise extension 14 is also covered by the connection element 6 extending radially outward beyond the welded connection 8. In this way, a kind of collar is formed by which the flexible printed circuit board welded to the circuit carrier can be pressed and fixed to the circuit carrier.

[0036] The flexible printed circuit board 3 comprises as electrically insulating material 5 a polyimide film, a polyamide film, a Mylar layer, in particular a polyethylene terephthalate layer, or an elastomer layer.

[0037] The flexible printed circuit board is configured to be flexible such that it can be bent in both a convex and concave manner transverse to the planar extension of the flexible printed circuit board without breaking.

[0038] Figure 2 shows -schematically- a connection structure 20 produced using the method 1 shown in figure 1. The connection structure 20 comprises a substrate 2, in this embodiment a ceramic circuit carrier, which comprises an electrically insulating ceramic layer 18 as shown in figure 1, and an electrically conductive wiring layer 17, in particular a copper layer. In addition to the wiring layer 17, the circuit carrier 2 further comprises an electrically conductive backside layer 46, which together with the electrically conductive wiring layer 17 sandwiches the electrically insulating layer 18. The connection structure 20 also comprises a flexible printed circuit board 3 and a connection element 6.

[0039] In the case of the connection structure 20, the three layers of the three-layer composite formed by the circuit carrier 2, the flexible printed circuit board 3 and the connection element 6 are placed one on top of the other, and the welded connection 8, which establishes the connection by material bonding, connects the three connection partners, i.e. the connection element 6, the flexible printed circuit board 3, in particular the conductive layer 4 of the flexible printed circuit board 3, and the circuit carrier 2, in particular the conductive layer 17 of the circuit carrier 2, to one another by material bonding and penetrates at least partially or completely through these three connection partners in a direction transverse to the flat extension 40 of the circuit carrier 2. The welded connection 8 in this example also penetrates the circuit carrier 2 with a depth extension that is smaller than the thickness extension 41 of the circuit carrier 2 and also with a depth extension that is smaller than the thickness extension 42 of the conductive layer 17, in particular the wiring layer.

[0040] The thickness direction extension 44 of the connection element 6 is configured to be greater than the thickness direction extension 43 of the conductive layer 4 of the flexible printed circuit board 3 or the thickness direction extension 43 of the flexible printed circuit board itself. The thickness direction extension of the conductive layer 4 can correspond to the thickness direction extension of the electrically insulating layer 5. This allows the flexible printed circuit board 3 to have an isotropic thickness.

[0041] The connection structure 20 may in other embodiments have as a substrate, instead of the ceramic circuit carrier 2, a stamped sheet metal piece, also called a stamped grid or lead frame.

[0042] FIG. 3 shows -schematically- one embodiment of a connection method 21 for conductively connecting a circuit carrier 31 to a flexible printed circuit board 30 by material bonding.

[0043] In the joining method shown in FIG. 3, a laser welding device 22 has a laser 23 for generating a laser beam 24 and a pressing portion formed by a tube 25, the laser 23 being arranged and configured to deliver the laser beam 24 through a cylindrical cavity 26 surrounded by the tube 25 along the longitudinal extension of the cavity 26.

[0044] The tube 25 has an end face 37 which is configured so that in this embodiment, in order to transport a connection element 29 formed by a metal plate, a punched grid or a lead frame or a piece of sheet metal to a welding point on the circuit support 31, the hollow chamber 26 adjacent to the connection element 29 can be suctioned by a vacuum pump 28, thereby sucking the connection element 29 towards the end face 37 of the tube 25.

[0045] The cavity 26 is connected by a suction passage 27 to a vacuum pump 28. The laser welding device 22, which may be a component part of the production device, can move up and down, as indicated by the arrow 38, at least in a direction transverse to the flat extension 40 of the circuit carrier 31. After the connection element 29 formed by the metal plate has been sucked up in this way, it can be placed - in the direction 39 of the circuit carrier 31 - on a flexible printed circuit board 30 which is placed on the circuit carrier 31 and there can be pressed by the laser welding device 22.

[0046] The laser welding device 22 may be configured to press the tube 25, in particular the end face 37 of the tube 25, against the connection element 29, so that the flexible printed circuit board 30 is firmly clamped between the connection element 29 and the circuit support 31 in the area of ​​the end face 37.

[0047] The laser beam 24 can then be used to create a welded connection 36, which melts the connection element 29, the flexible printed circuit board 30 and the conductive layer 33 of the circuit support 31 together, thereby connecting them to each other by a material bond.

[0048] After the welded connection 36 cools and solidifies, the manufacturing device 22 can stop the vacuum pump 28, which will lift the tube 25 from the connection element 29 and then release the connection element 29.

[0049] The circuit support 31 in this embodiment has an electrically insulating layer 32, in particular a ceramic layer, which is sandwiched - in particular in the form of a sandwich - between a conductive layer 33 and a further conductive back layer 34.

[0050] The flexible printed circuit board 30 in this embodiment exemplarily has a plug 35, by means of which the electrical or electronic circuit structure formed on the circuit carrier 31 can be electrically connected to further electronic components towards the outside by means of the plug 35. Instead of a plug, the flexible printed circuit board 30 can also be plug-connected, welded or brazed to the further circuit carrier.

Claims

1. A contact structure (20) comprising at least one electrically conductive substrate (2, 31) and in particular a flexible printed circuit board (3, 30), The flexible printed circuit board (3, 30) comprises at least one - in particular a reversibly bendable - electrically insulating film (5) and at least one or only one conductive layer (4), the conductive layer of the flexible printed circuit board (3, 30) - in particular placed on the substrate (2, 31) - is conductively connected to the substrate, In the contact structure (20), The contact structure has an electrically conductive connecting element (6, 29), the conductive connection element (6, 29) is disposed on the conductive layer of the flexible printed circuit board (3, 30), such that the connection element and the base (2, 31) sandwich the flexible printed circuit board (3, 30); The connection element (6, 29) is welded to the conductive layer of the flexible printed circuit board (3, 30) and to the base (2, 31) in such a way that a welded connection (8, 36) extends from the connection element (6, 29) - in particular in a direction transverse to the planar extension of the flexible printed circuit board (3, 30) - through the conductive layer (4) of the flexible printed circuit board (3, 30) and into the base (2, 31). A contact structure (20).

2. The welded connection (8, 36) is a laser welded connection. The contact structure (20) of claim 1.

3. The connection element (6, 29) extends radially outward from the welded connection portion (8, 36) so as to cover the flexible printed circuit board (3, 30). The contact structure (20) according to claim 1 or 2.

4. said welded connection (8, 36) being formed by a weld bead extending flatly on a base plane (40), in particular extending longitudinally, the weld bead extends into the connection element (6, 29), into the flexible printed circuit board (3, 30) and into the base (2, 31); the weld bead is formed so as to completely penetrate the connection element (6, 29) and the flexible printed circuit board (3, 30), in particular at least the conductive layer (4); A contact structure (20) according to any one of claims 1 to 3.

5. The welded connection (8, 36) is formed only partially along the thickness direction extension (41) of the base body (2, 31). A contact structure (20) according to any one of the preceding claims.

6. The substrate has at least one electrically insulating ceramic layer and at least one electrically conductive layer. A contact structure (20) according to any one of the preceding claims.

7. The connection element (6) has a thickness direction extension length (44) that is greater than a thickness direction extension length (43) of the conductive layer (17) of the flexible printed circuit board (3, 30). The contact structure (20) of any one of the preceding claims.

8. The weld bead has a widthwise extension (15) equal to the thicknesswise extension (44) of the connection element (6). A contact structure (20) according to any one of the preceding claims.

9. said connecting element (6) being formed by a bonding tape longitudinal section (7, 14); A contact structure (20) according to any one of the preceding claims.

10. The connecting element (29) is a metal plate. A contact structure (20) according to any one of the preceding claims.

11. A contact system comprising at least one contact structure (20) according to any one of claims 1 to 10, The contact structure includes at least one further substrate; the substrate (2, 31) and the further substrate are electrically conductively connected to each other by means of a flexible printed circuit board (3, 30); In the contact system, The electrical connection between the flexible printed circuit board (3, 30) and the base (2, 31) is created by a connection element (6, 29) placed on the flexible printed circuit board (3, 30) and a welded connection (8, 36) by material bonding that passes through the connection element (6, 29) and the flexible printed circuit board (3, 30) and extends into the base (2, 31). A contact system comprising:

12. The flexible printed circuit board (3, 30) has a plug (35) for electrically connecting the base body (2, 31). A contact system comprising at least one contact structure (20) according to any one of claims 1 to 11.

13. A method for connecting a flexible printed circuit board (3, 30) to a substrate (2, 31) by material bonding, comprising the steps of: A method in which a surface area of ​​the flexible printed circuit board (3, 30) is electrically conductively connected to the base body (2, 31) by material bonding, A flat extending connecting element (6, 29) is placed on the surface area (14) of the flexible printed circuit board (3, 30), The three-layer structure thereby produced is welded using a laser beam (11, 24) to form a three-layer composite. A method comprising:

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