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 has at least one conductive substrate, in particular a circuit carrier. The contact structure also has, in particular, a flexible printed circuit board, which has at least one - in particular 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 Art

[0002] From German Patent Invention No. 102019128634, a bonded self-supporting conductor connection between two bonding locations is known, where at each of these two bonding locations, a connection by material bonding between the self-supporting conductor and the bonding surface is generated in one bonding step, and between these two bonding locations, the conductor extends in a bonding loop.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Means for Solving the Problems

[0004] Disclosure of the Invention According to the present invention, the contact structure has a conductive connecting element, which is positioned on the conductive layer of a flexible printed circuit board, so that the connecting element and the substrate sandwich the flexible printed circuit board between them. The connecting element is welded to the conductive layer of the flexible printed circuit board and the substrate such that the welded connection extends from the connecting element, particularly across the flat extension of the flexible printed circuit board, through the conductive layer of the flexible printed circuit board and into the substrate. This advantageously makes it possible to form a low-ohm resistance, particularly solder-free, electrical connection between the flexible printed circuit board and the substrate, particularly a circuit support, such as a DCB substrate (DCB = Direct-Copper-Bonded) or an AMB substrate (AMB = Active-Metal-Brazed).

[0005] Advantageously, it was found that the conductive layer of a flexible printed circuit board can be reinforced with connecting elements to prevent it from being incinerated during laser welding.

[0006] A flexible printed circuit board is preferably configured to be bent without breaking in a direction traversing the flat extension of the flexible printed circuit board. Preferably, the flexible printed circuit board has an electrically insulating layer or film consisting of 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). 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 absorb at least partially the heat generated during welding. This advantageously allows the connecting element to constitute a heat accumulator for excess process heat during welding, as well as a material storage area that can advantageously reinforce the conductive layer in the area of ​​the weld connection when the flexible printed circuit board is welded to the substrate.

[0008] In one preferred embodiment of the contact structure, the welded connection is a laser-welded connection. This advantageously allows the circuit support, particularly the ceramic circuit support, to be welded to the flexible printed circuit board from only one side.

[0009] In other embodiments, the substrate is formed from a punched grid, particularly from thin metal sheets or lead frames. The welded connection in this embodiment is, for example, a resistance spot weld connection. This is advantageous because, during resistance welding, the connecting element can be used to provide additional welding material for forming an electrical contact bridge between the flexible printed circuit board and the substrate.

[0010] In one preferred embodiment, the connecting element has a surface-extending portion that extends radially outward—particularly on the plane of the flexible printed circuit board—beyond the spatial extension length of the welded connection, and the connecting element covers the flexible printed circuit board outside the welded connection. This advantageously allows for mechanical reinforcement and a holding function by shape coupling, particularly the formation of a kind of collar portion centered on 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 welded connection is formed by a weld bead that extends flatly on the substrate plane, particularly in the longitudinal direction. The weld bead extends into the connecting element, into the flexible printed circuit board, and into the substrate. Preferably, the weld bead is formed to completely penetrate the connecting element and the flexible printed circuit board, particularly at least one conductive layer of the flexible printed circuit board. This advantageously allows for the formation of a conductive connection between the joining partners by material bonding.

[0012] In one preferred embodiment, the welded joint is formed only partially along the thickness-direction extension of the substrate, particularly along the conductive layer of the substrate, especially the wiring layer. Advantageously, the conductive layer of the substrate, particularly the ceramic substrate, is not mechanically deformable by thermal input.

[0013] In one preferred embodiment of the contact structure, the substrate comprises at least one electrically insulating ceramic layer and at least one conductive layer. The substrate is, 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 allows for the connection of flexible printed circuit boards to a ceramic substrate, particularly without the use of solder. The flexible printed circuit board is also advantageously protected by the connection element from unintended delamination, insofar as the connecting element forms a collar that extends laterally beyond the welded connection and this collar is formed to hold and / or press the flexible printed circuit board onto the substrate.

[0015] In one preferred embodiment, the connecting element has a thickness extension greater than the conductive layer of the flexible printed circuit board. This advantageously allows for the formation of not only a material addition portion during welding, but also a mechanical collar portion for fixing the flexible printed circuit board onto the substrate.

[0016] In a preferred embodiment, the welded joint, particularly the weld bead, has a widthwise extension equal to the thicknesswise extension of the connecting element. For example, the weld bead has a widthwise extension between 100 and 300 micrometers, preferably between 180 and 220 micrometers, or 200 micrometers. The exemplary thickness of the connecting element is between 150 and 250 micrometers, preferably between 180 and 220 micrometers. This advantageously allows for the formation of a stable and electrically conductive welded joint.

[0017] In one preferred embodiment of the contact structure, the connecting element is a longitudinal section of bonding tape, more preferably made of copper or a copper alloy. This is advantageous as it allows the connecting element to be bonded to a flexible printed circuit board at low cost by a bonding device. This is even more advantageous as it allows the connecting element to be unwound from a bonding tape storage unit, particularly from a bonding tape roll, and the longitudinal section to be welded onto a circuit support and then cut.

[0018] In one preferred embodiment, the connecting element is a metal plate. This is advantageous as it allows the connecting element to be placed on a circuit support, particularly on a flexible printed circuit board, in the area of ​​the electrical connection, using a vacuum mounting machine, and especially an automatic mounting machine. The metal plate is, for example, self-adhesive and has an adhesive on the side facing the flexible printed circuit board, at least on a portion of the surface that should not be welded, or only on a portion of the surface that should not be welded.

[0019] For example, a connecting element, particularly a metal plate, such as a copper plate, can be set on a circuit support by an automated mounting machine, which is configured to fix the metal plate by vacuum force, to place the metal plate on the circuit support, to press the circuit support, particularly 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 substrate. This advantageously allows the welded connection to be incorporated into an automated mounting process during the mounting of the circuit support.

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

[0021] The present invention also relates to a contact system comprising at least one contact structure in the form described above. The contact structure has at least one further substrate, the substrates being electrically connected to each other using a flexible printed circuit board. Preferably, the electrical connection between the flexible printed circuit board and the substrate is created by a connecting element mounted on the flexible printed circuit board and a welded connection by material bonding that penetrates the connecting element and the flexible printed circuit board and extends into the substrate. This advantageously allows different substrates, particularly circuit supports, to be electrically connected to each other at low cost using a flexible printed circuit board.

[0022] In a preferred embodiment, the flexible printed circuit board has a plug for electrically connecting the substrate. This plug can be connected to the flexible printed circuit board in addition to, or instead of, the aforementioned further substrate. Thereby, advantageously, the electrical connection between the substrate, particularly the ceramic circuit carrier, and the plug connector can be configured to be held continuously, with low cost and in a reliable process.

[0023] In a preferred embodiment, the flexible printed circuit board can be formed on the circuit carrier as a further mounted wiring layer, and electronic components, such as sensors, can be arranged on this wiring layer. Advantageously, the flexible printed circuit board can be welded to the circuit carrier without using a solder material, so that the layer composite including the circuit carrier and the flexible printed circuit board can be put into a soldering furnace for reflow soldering of electronic components to this layer composite. At this time, it is not necessary to dissociate the layer composite formed without using a solder material again.

[0024] The present invention also relates to a method for connecting a flexible printed circuit board to a substrate by material bonding. In this method, the surface area of the flexible printed circuit board is conductively connected to the substrate by material bonding.

[0025] Preferably, a flatly extending connecting element is placed on the surface area of the flexible printed circuit board, and the resulting three-layer structure including the substrate, the flexible printed circuit board, and the flatly extending connecting element is welded using a laser beam to form a three-layer composite. In this three-layer composite, the joining partners are preferably stacked one above the other and connected to each other by material bonding.

[0026] Preferably, the three-layer composite is welded using a laser beam from the side of the connecting element. Thereby, advantageously, it becomes possible to generate an electrically conductive connection that can be held and has a low ohmic resistance between the flexible printed circuit board and the substrate.

[0027] In the following, the invention will be described based on the drawings and further examples. Further advantageous embodiments can be obtained from the combinations of features described in the dependent claims and the drawings.

Brief Description of the Drawings

[0028] [Figure 1] It is a diagram showing a welding apparatus and a method for welding a flexible printed circuit board to a circuit support. Here, a connecting element formed by a bonding tape longitudinal section is disposed on the flexible printed circuit board, the connecting element is welded using a laser beam together with the flexible printed circuit board and the circuit support, and the bonding tape longitudinal section is cut from the remaining bonding tape after welding. [Figure 2] It is a diagram showing an example of a contact structure generated using the welding apparatus shown in FIG. 1 and the method. [Figure 3] It is a diagram showing a modification of the method shown in FIG. 1, where a metal plate is placed on the flexible printed circuit board and welded to the flexible printed circuit board and the circuit support to form a three-layer connection.

Modes for Carrying Out the Invention

[0029] FIG. 1 schematically shows an example of a method 1 for generating a connection structure using a welding apparatus 9. The connection structure includes a circuit support 2, a flexible printed circuit board 3, and a connecting element 6 configured to be conductive. In this embodiment, the connecting element 6 is formed by a bonding tape longitudinal section of a bonding tape 7.

[0030] In this method, a welding apparatus 9 having a pressing unit 10 and a laser 12 configured to generate a laser beam 11 is placed on a three-layer structure including a circuit support 2, a flexible printed circuit board 3, and a connecting element 6 formed by a longitudinal section of bonding tape. The pressing unit 10 is configured to press the connecting element 6 in a direction traversing the flat extension 40 of the circuit support 2, pressing the connecting element 6 against the flexible printed circuit board 3, and consequently against the substrate formed by the circuit support 2. The pressing unit 10 is shown in a pressing position 10' supported on the connecting element 6.

[0031] The flexible printed circuit board 3 has an electrically insulating film 5 and a conductive layer 4, particularly a copper layer, extending on the plane of the flexible film. The laser beam 11 is configured to specifically weld the longitudinal section 6 of the bonding tape, the conductive layer 4, and the conductive wiring layer 17 of the circuit support 2 to each other by shape coupling.

[0032] For this purpose, the region of the connecting element 6 formed by the longitudinal section of the bonding tape that is irradiated by the laser beam 11 can be evaporated and / or melted by the laser beam 11. In this process, the metal region located adjacent to the evaporated zone can be melted into the evaporated zone, thereby forming liquefied metal in the crucible created in the region of the laser beam 11. The zone of liquefied metal extends through the connecting element 6, particularly the bonding tape section, and further through the conductive layer 4, and even into the conductive layer 17 of the circuit support 2, particularly into the wiring layer. In this way, the molten zone formed at the depth of the stacked laminate formed by the bonding tape section 6, the conductive layer 4, and the circuit support 2 can, after solidification, create a welded connection between the conductive layer of the flexible printed circuit board 3 and the circuit support 2, particularly the conductive layer 17, through shape bonding.

[0033] Therefore, the welded connection portion 8 formed along the widthwise extension length 15 on the flat extension portion 40 of the circuit support 2 has a widthwise extension length smaller than the widthwise extension length 14 of the connection element 6. In this embodiment, the connection element 6 is separated from the bonding tape 7 using a cutting cutter 13 moved by a cutting device 45 after the welded connection portion 8 is formed. In this example, the cutting device 45 is a component of the welding device and is arranged and configured to reciprocate the cutting cutter 13 and to separate the longitudinal section of the bonding tape 7 that extends along the widthwise extension length 14 from the bonding tape 7, thereby generating individualized connection elements 6.

[0034] In this way, a collar portion 19 can be formed around the welded joint 8, and this collar portion 19 can cover the flexible printed circuit board 3, particularly the conductive layer 4 surrounding the welded joint 8, in particular in the form of a nail head or rivet head, and in this embodiment, it can also cover the area of ​​the electrically insulating layer 5, thereby enabling tightening between the circuit support 2 and the connecting element 6.

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

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

[0037] Flexible printed circuit boards are designed to be flexible enough to be bent into convex or concave shapes in a direction that traverses the flat extension of the flexible printed circuit board without being damaged.

[0038] Figure 2 schematically shows a connection structure 20 produced using Method 1 shown in Figure 1. The connection structure 20 includes a substrate 2, in this embodiment, a ceramic circuit support, the ceramic circuit support including an electrically insulating ceramic layer 18 and a conductive wiring layer 17, particularly a copper layer, as shown in Figure 1. In addition to the wiring layer 17, the circuit support 2 further has a conductive back layer 46, which, together with the conductive wiring layer 17, sandwiches the electrically insulating layer 18. The connection structure 20 also includes a flexible printed circuit board 3 and a connection element 6.

[0039] In the case of the connection structure 20, the three layers of a three-layer composite formed by the circuit support 2, the flexible printed circuit board 3, and the connection element 6 are stacked on top of each other. The welded connection portion 8, which connects by material bonding, connects three bonding partners, namely 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 support 2, in particular the conductive layer 17 of the circuit support 2, to each other by material bonding, and penetrates these three bonding partners at least partially or completely in a direction that traverses the flat extension portion 40 of the circuit support 2. In this embodiment, the welded connection portion 8 penetrates the circuit support 2 with a depth extension length that is smaller than the thickness extension length 41 of the circuit support 2, and also with a depth extension length that is smaller than the thickness extension length 42 of the conductive layer 17, in particular the wiring layer.

[0040] The thickness-direction extension length 44 of the connecting element 6 is greater than the thickness-direction extension length 43 of the conductive layer 4 of the flexible printed circuit board 3, or the thickness-direction extension length 43 of the flexible printed circuit board itself. The thickness-direction extension length of the conductive layer 4 can correspond to the thickness-direction extension length of the electrically insulating layer 5. As a result, the flexible printed circuit board 3 can have an isotropic thickness.

[0041] The connecting structure 20 may, in other embodiments, have, instead of the ceramic circuit support 2, punched metal sheet pieces, also referred to as a punched grid or lead frame, as a base.

[0042] Figure 3 schematically shows one embodiment of a connection method 21 for electrically connecting a circuit support 31 to a flexible printed circuit board 30 by material bonding.

[0043] In the joining method shown in Figure 3, the laser welding apparatus 22 includes a laser 23 for generating a laser beam 24 and a pressing section formed by a tube 25. The laser 23 is positioned and configured to deliver the laser beam 24 through a cylindrical hollow chamber 26 surrounded by the tube 25, along the longitudinal extension of the hollow chamber 26.

[0044] The pipe 25 has an end face 37, which in this embodiment is placed on a connecting element 29 in order to transport the connecting element, which is made of a metal plate, a punched grid, a lead frame, or a thin metal sheet, to the welding location on the circuit support 31. The hollow chamber 26 adjacent to the connecting element 29 is then vacuumed by a vacuum pump 28, thereby enabling the connecting element 29 to be sucked up toward the end face 37 of the pipe 25.

[0045] The hollow chamber 26 is connected to the vacuum pump 28 by a suction passage 27. The laser welding apparatus 22 may be a component of the manufacturing apparatus and can move up and down in a direction traversing at least the flat extension 40 of the circuit support 31, as indicated by the arrow 38. In this way, after the connecting element 29, which is formed of a metal plate, is sucked up, the connecting element 29 can be placed on a flexible printed circuit board 30 placed on the circuit support 31 - in the direction 39 of the circuit support 31 - and there it can be pressed by the laser welding apparatus 22.

[0046] The laser welding apparatus 22 may be configured to press the pipe 25, particularly the end face 37 of the pipe 25, against the connecting element 29, thereby firmly fastening the flexible printed circuit board 30 between the connecting element 29 and the circuit support 31 in the area of ​​the end face 37.

[0047] Next, a welded joint 36 can be generated using the laser beam 24. This welded joint 36 melts the connecting 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 through material bonding.

[0048] After the welded joint 36 has cooled and solidified, the manufacturing apparatus 22 can stop the vacuum pump 28, which will lift the pipe 25 from the connecting element 29 and then release the connecting element 29.

[0049] In this embodiment, the circuit support 31 has an electrically insulating layer 32, particularly a ceramic layer, which is sandwiched between a conductive layer 33 and a further conductive back layer 34, particularly in a sandwich configuration.

[0050] In this embodiment, the flexible printed circuit board 30 exemplary has a plug 35, which allows an electrical or electronic circuit structure formed on the circuit support 31 to be electrically connected to further electronic components externally using the plug 35. Instead of a plug, the flexible printed circuit board 30 can be plugged, welded, or brazed to a further circuit support.

Claims

1. A contact structure (20) comprising a conductive substrate (2, 31) and a flexible printed circuit board (3, 30), The flexible printed circuit board (3, 30) has at least one electrically insulating film (5) and at least one conductive layer (4), The conductive layer (4) of the flexible printed circuit board (3, 30), which is placed on the substrate (2, 31), is electrically connected to the substrate. The substrate (2, 31) has at least one electrically insulating ceramic layer (18) and at least one conductive layer (17) disposed on the ceramic layer. In the contact structure (20), The contact structure has conductive connecting elements (6, 29), The conductive connecting elements (6, 29) are arranged on the conductive layer (4) of the flexible printed circuit board (3, 30), so that the connecting elements (6, 29) and the substrate (2, 31) sandwich the flexible printed circuit board (3, 30) between them. The connecting element (6, 29) is welded to the conductive layer (4) of the flexible printed circuit board (3, 30) and the substrate (2, 31) such that the welded connection portion (8, 36) extends from the connecting element (6, 29) in a direction that traverses the flat extending portion of the flexible printed circuit board (3, 30) and penetrates the conductive layer (4) of the flexible printed circuit board (3, 30) into the conductive layer (17) of the substrate (2, 31). A contact structure (20) characterized by the following.

2. The welded joint (8, 36) is a laser welded joint. The contact structure (20) according to claim 1.

3. The connecting elements (6, 29) extend radially outward from the welded connection portion (8, 36) to cover the flexible printed circuit board (3, 30). The contact structure (20) according to claim 1.

4. The welded joint (8, 36) is formed by a weld bead. The weld bead extends within the connecting element (6, 29), within the flexible printed circuit board (3, 30), and within the base body (2, 31). The weld bead is formed to completely penetrate the connecting element (6, 29) and the conductive layer (4) of the flexible printed circuit board (3, 30). The contact structure (20) according to claim 1.

5. The welded joint portion (8, 36) is formed only in a portion of the thickness-direction extension length (41) of the base body (2, 31). The contact structure (20) according to claim 1.

6. The connecting element (6) has a thickness-direction extension length (44) that is greater than the thickness-direction extension length (43) of the conductive layer (4) of the flexible printed circuit board (3, 30). The contact structure (20) according to claim 1.

7. The weld bead has a widthwise extension length (15) that is equivalent to the thicknesswise extension length (44) of the connecting element (6). The contact structure (20) according to claim 4.

8. The connecting element (6) is formed by the longitudinal sections (7, 14) of the bonding tape. The contact structure (20) according to claim 1.

9. The connecting element (29) is a metal plate. The contact structure (20) according to claim 1.

10. A contact system comprising at least one contact structure (20) according to any one of claims 1 to 9, The contact structure includes at least one further substrate, The substrate (2, 31) and the further substrate are electrically connected to each other using a flexible printed circuit board (3, 30). In the contact system, The electrical connection points between the flexible printed circuit board (3, 30) and the substrate (2, 31) are formed by a connecting element (6, 29) placed on the flexible printed circuit board (3, 30) and a welded connection portion (8, 36) formed by material bonding that penetrates the connecting element (6, 29) and the flexible printed circuit board (3, 30) and extends into the substrate (2, 31). A contact system characterized by the following features.

11. The flexible printed circuit board (3, 30) has a plug (35) for electrically connecting the substrate (2, 31). The contact system according to claim 10.

12. A method for connecting a flexible printed circuit board (3, 30) to a substrate (2, 31) by material bonding, In a method in which the planar region of the flexible printed circuit board (3, 30) is electrically connected to the substrate (2, 31) by material bonding, The flexible printed circuit board (3, 30) has at least one electrically insulating film (5) and at least one conductive layer (4), The substrate (2, 31) has at least one electrically insulating ceramic layer (18) and at least one conductive layer (17) disposed on the ceramic layer. A flat, extending conductive connecting element (6, 29) is placed on the surface region (14) of the flexible printed circuit board (3, 30). The conductive connecting elements (6, 29) are arranged on the conductive layer (4) of the flexible printed circuit board (3, 30), so that the connecting elements (6, 29) and the substrate (2, 31) sandwich the flexible printed circuit board (3, 30) between them. The connecting elements (6, 29) are welded to the conductive layer (4) of the flexible printed circuit board (3, 30) and the substrate (2, 31) such that the welded connection portion (8, 36) extends from the connecting elements (6, 29) in a direction that traverses the flat extending portion of the flexible printed circuit board (3, 30) and penetrates the conductive layer (4) of the flexible printed circuit board (3, 30) into the conductive layer (17) of the substrate (2, 31). The resulting three-layer structure is then welded together using a laser beam (11, 24) to form a three-layer composite. A method characterized by the following features.

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