Contact arrangement having a welded flexible circuit board

Abstract

The invention relates to a contact arrangement. The contact arrangement has at least one electrically conductive substrate, in particular a circuit carrier. The contact arrangement also has an in particular flexible circuit board, wherein the flexible circuit board has at least one - in particular reversibly bendable - electrically insulating foil and at least one or only one electrically conductive layer. The electrically conductive layer of the flexible circuit board is electrically conductively connected to the substrate. The contact arrangement has an electrically conductive connecting element which is arranged on the electrically conductive layer of the flexible circuit board, such that the connecting element and the substrate enclose the flexible circuit board between them. The connecting element is welded to the electrically conductive layer of the flexible circuit board and to the substrate such that a welded connection extends from the connecting element, through the electrically conductive layer of the flexible circuit board, in particular transversely with respect to a flat extent of the flexible circuit board, into the substrate.

Description

[0001] Description

[0002] title

[0003] Contact arrangement with a welded flexible circuit board

[0004] State of the art

[0005] The invention relates to a contact arrangement. The contact arrangement comprises at least one electrically conductive substrate, in particular a circuit carrier. The contact arrangement also comprises a particularly flexible printed circuit board, wherein the flexible printed circuit board comprises at least one—in particular reversibly flexible—electrically insulating film, and at least one or only one electrically conductive layer. The electrically conductive layer of the flexible printed circuit board is electrically conductively connected to the substrate—in particular resting on the substrate.

[0006] From DE 10 2019 128 634 B3, a bonded self-supporting conductor connection between two bonding points is known, at each of which a material connection of the self-supporting conductor with a bonding surface is created in a bonding step and between which the conductor runs in a bonding loop.

[0007] Disclosure of the invention

[0008] According to the invention, the contact arrangement has an electrically conductive connecting element which is arranged on the electrically conductive layer of the flexible printed circuit board, such that the connecting element and the substrate enclose the flexible printed circuit board between one another. The connecting element is welded to the electrically conductive layer of the flexible printed circuit board and to the substrate in such a way that a welded connection extends from the connecting element, in particular transversely to a flat extension of the flexible printed circuit board, through the electrically conductive layer of the flexible printed circuit board, and into the substrate. Advantageously, a low-resistance and in particular solder-free electrical connection can thus be formed 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 A MB substrate (AMB = Active Metal Brazed).

[0009] It was recognized that the connecting element can reinforce the electrically conductive layer of the flexible circuit board in such a way that the electrically conductive layer of the flexible circuit board cannot advantageously burn away during laser welding.

[0010] The flexible printed circuit board is preferably designed to be bent transversely to its flat extension without breaking. The flexible printed circuit board preferably has a polyimide layer, a polyamide layer, a PET layer (PET = polyethylene terephthalate), a PVB layer (polyvinyl butyral), a PVF layer (PVF = polyvinyl fluoride), or an EVA layer (EVA = ethylene vinyl acetate) as an electrically insulating layer or film. The electrically conductive layer of the flexible printed circuit board is preferably a copper layer or a metal layer made of a copper alloy.

[0011] The connecting element is preferably designed to at least partially absorb heat generated during welding. Advantageously, the connecting element can thus form both a heat reservoir for excess process heat during welding and a material reservoir that can advantageously reinforce the electrically conductive layer in the region of the welded joint when the flexible printed circuit board is welded to the substrate.

[0012] In a preferred embodiment of the contact arrangement, the welded connection is a laser welded connection. Advantageously, a circuit carrier, in particular a ceramic circuit carrier, can thus be welded to the flexible printed circuit board from only one side. In another embodiment, the substrate is formed by a stamped grid, in particular a piece of sheet metal, or a lead frame. In this embodiment, the welded connection is, for example, a resistance spot welded connection. Advantageously, during resistance welding, an additional welding material can be formed by means of the connecting element to form an electrical contact bridge between the flexible printed circuit board and the substrate.

[0013] In a preferred embodiment, the connecting element has a surface extension that extends radially outward—particularly in a plane of the flexible printed circuit board—over the spatial extent of the welded joint, with the connecting element covering the flexible printed circuit board outside the welded joint. Advantageously, this can provide mechanical reinforcement and a positive-locking holding function, in particular a type of collar, around the welded joint, whereby the collar can mechanically hold and stabilize the flexible printed circuit board in the area of ​​the welded joint.

[0014] In a preferred embodiment of the contact arrangement, the welded connection is formed by means of a weld bead extending flatly in the substrate plane, in particular longitudinally. The weld bead extends into the connecting element, the flexible circuit board, and the substrate. The weld bead is preferably designed to completely penetrate the connecting element, the flexible circuit board, in particular the at least one electrically conductive layer of the flexible circuit board. This advantageously allows an electrically conductive, integral connection to be formed between the joining partners.

[0015] In a preferred embodiment, the welded connection is formed only partially along a thickness extension of the substrate, in particular an electrically conductive layer, in particular a rewiring layer, of the substrate. Advantageously, the electrically conductive layer of the substrate, in particular a ceramic substrate, cannot be mechanically deformed by heat input. In a preferred embodiment of the contact arrangement, the substrate has at least one electrically insulating ceramic layer and at least one electrically conductive layer. The substrate is, for example, a DCB substrate (DCB = Direct Copper Bonded), an AM B 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).

[0016] Advantageously, a flexible printed circuit board can be connected to a substrate, particularly a ceramic one, without the use of solder. The flexible printed circuit board is also advantageously protected from accidental tearing by the connecting element, insofar as the connecting element forms a collar extending laterally beyond the welded joint, which is designed to hold and / or press the flexible printed circuit board onto the substrate.

[0017] In a preferred embodiment, the connecting element has a greater thickness than the electrically conductive layer of the flexible circuit board. This advantageously allows for the formation of a material addition during welding, as well as a mechanical collar for securing the flexible circuit board to the substrate.

[0018] In a preferred embodiment, the welded joint, in particular the weld bead, has the same width as the thickness of the connecting element. For example, the weld bead has a width of between 100 and 300 micrometers, preferably between 180 and 220 micrometers, or 200 micrometers. An 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 highly electrically conductive welded joint.

[0019] In a preferred embodiment of the contact arrangement, the connecting element is a longitudinal section of bonding tape, more preferably made of copper or a copper alloy. Advantageously, the connecting element can thus be applied to the flexible printed circuit board in a cost-effective manner using a bonding device. Furthermore, the connecting element can be unrolled from a bonding tape supply, in particular a bonding tape roll, and the longitudinal section can be welded to the circuit carrier and cut off.

[0020] In a preferred embodiment, the connecting element is a metal plate. Advantageously, the connecting element can be placed onto the circuit carrier, in particular the flexible printed circuit board, in the region of the electrical connection point by means of vacuum placement, in particular using an automatic placement machine. The metal plate is designed, for example, to be self-adhesive and has an adhesive on a side facing the flexible printed circuit board, at least on a partial surface area that is not to be welded, or only on that surface area.

[0021] For example, the connecting element, in particular the metal plate, for example a copper plate, can be placed on the circuit carrier by an automatic assembly machine configured to hold the metal plate using vacuum force, deposit the metal plate on the circuit carrier, and press it onto the circuit carrier, in particular the flexible printed circuit board. During the pressing process, a laser beam is directed onto the metal plate in the region of a pressure element, thus welding the metal plate to the flexible printed circuit board and the substrate. The welding process can thus advantageously be integrated into an automated assembly process when assembling a circuit carrier.

[0022] Advantageously, a materially bonded three-layer composite can be produced from the aforementioned joining partners.

[0023] The invention also relates to a contact system with at least one contact arrangement according to the type described above. The contact arrangement has at least one further substrate, wherein the substrate and the further substrate are electrically conductively connected to one another by means of the flexible printed circuit board. The electrical connection points between the flexible printed circuit board and the substrate are preferably created by means of the connecting element placed on the flexible printed circuit board and the integral welded connection penetrating the connecting element and the flexible printed circuit board and extending into the substrate. Advantageously, different substrates, in particular circuit carriers, can thus be electrically and cost-effectively connected to one another by means of a flexible printed circuit board.

[0024] In a preferred embodiment, the flexible circuit board has a connector for electrically connecting the substrate. The connector can be connected to the flexible circuit board in addition to the aforementioned additional substrate or instead of the additional substrate. Advantageously, an electrical connection of a substrate, in particular a ceramic circuit carrier, to a plug-in connection can be designed in a cost-effective, process-reliable, and durable manner.

[0025] In a preferred embodiment, the flexible printed circuit board can be formed on the circuit carrier as an additional rewiring layer on which electronic components, such as a sensor, can be arranged. Advantageously, the flexible printed circuit board can be welded to the circuit carrier without the use of solder, so that the layered composite comprising the circuit carrier and the flexible printed circuit board can be inserted into a soldering furnace for reflow soldering of electronic components onto the layered composite without the possibility of the solder-free layered composite disintegrating.

[0026] The invention also relates to a method for bonding a flexible printed circuit board to a substrate. In this method, a surface area of ​​the flexible printed circuit board is bonded to a substrate in an electrically conductive and bonded manner.

[0027] Preferably, a flatly extending connecting element is placed on the surface area of ​​the flexible printed circuit board, and the three-layer arrangement thus produced, comprising the substrate, the flexible printed circuit board and the flatly extending connecting element, is welded by means of a laser beam to form a three-layer composite in which the joining partners are preferably bonded to one another in a materially bonded manner.

[0028] Preferably, the three-layer composite is welded from the side of the connecting element using the laser beam. This advantageously creates a durable, low-resistance electrical connection between the flexible circuit board and the substrate.

[0029] The invention will now be explained below with reference to figures and further exemplary embodiments. Further advantageous embodiments will emerge from a combination of the features described in the dependent claims and in the figures.

[0030] Figure 1 shows a welding device and a method for welding a flexible printed circuit board to a circuit carrier, in which a connecting element formed by a bonding tape longitudinal section is arranged on the flexible printed circuit board, and the connecting element is welded together with the flexible printed circuit board and the circuit carrier by means of laser beams, and the bonding tape longitudinal section is cut off from the remaining bonding tape after welding;

[0031] Figure 2 shows an embodiment of a contact arrangement which has been produced with the welding device and method shown in Figure 1;

[0032] Figure 3 shows a variant of the process shown in Figure 1, in which a metal plate is placed on the flexible circuit board and welded to the flexible circuit board and the circuit carrier to form a three-layer connection.

[0033] Figure 1 shows - schematically - an embodiment of a method 1 for producing a connection arrangement by means of a welding device 9. The connection arrangement comprises a circuit carrier 2, a flexible printed circuit board 3, and an electrically conductive connecting element 6. The connecting element 6 in this embodiment is formed by a bonding band longitudinal section of a bonding band 7. In the method, a welding device 9, which has a hold-down device 10, and a laser 12, which is designed to generate a laser beam 11, are placed on a three-layer arrangement comprising the circuit carrier 2, the flexible printed circuit board 3, and the connecting element 6 formed by the bonding band longitudinal section.The hold-down device 10 is designed to press onto the connecting element 6 transversely to a flat extension 40 of the circuit carrier 2, pressing it against the flexible printed circuit board 3 and thus also against the substrate formed by the circuit carrier 2. The hold-down device 10 is shown in a holding position 10' supported on the connecting element 6.

[0034] The flexible printed circuit board 3 has an electrically insulating film 5 and an electrically conductive layer 4, in particular a copper layer, extending in a plane of the flexible film. The laser beams 11 are designed to form-fit, in particular weld, the bonding band longitudinal section 6, the electrically conductive layer 4, and an electrically conductive rewiring layer 17 of the circuit carrier 2.

[0035] For this purpose, a region of the connecting element 6 struck by the laser beams 11, formed by the bonding band longitudinal section, can be vaporized and / or melted by the laser beams 11, wherein metal regions arranged adjacent to the vaporization zone can melt into the vaporization zone, thus forming a melting pot of liquefied metal created in the region of the laser beams 11. The zone of liquefied metal extends through the connecting element 6, in particular the bonding band section, and further through the electrically conductive layer 4 and further into the electrically conductive layer 17, in particular the rewiring layer of the circuit carrier 2.The melting zone thus formed in the depth of the superimposed layers, formed by the bonding band section 6, the electrically conductive layer 4, and the circuit carrier 2, can, after solidification, create a positive welded connection between the electrically conductive layer of the flexible printed circuit board 3 and the circuit carrier 2, in particular the electrically conductive layer 17. The welded connection 8 formed in the flat extension 40 of the circuit carrier 2 along a width extension 15 thus has a smaller width extension than a width extension 14 of the connecting element 6, which in this exemplary embodiment has been severed from the bonding band 7 after the welded connection 8 has been created by means of a cutting blade 13 moved by a cutting device 45.In this example, the cutting device 45 is a component of the welding device and is arranged and designed to move the cutting blade 13 back and forth and to separate from the bonding strip 7 a bonding strip longitudinal section extending along the width extension 14 and thus to produce the separated connecting element 6.

[0036] In this way, a collar 19 can be formed around the welded joint 8, which - in particular in the manner of a nail head or a rivet head - can cover the flexible printed circuit board 3, in particular the electrically conductive layer 4 surrounding the welded joint 8, and in this exemplary embodiment also a region of the electrically insulating layer 5, and can thus clamp it between the circuit carrier 2 and the connecting element 6.

[0037] In this exemplary embodiment, the width 14 of the connecting element 6 is larger than a width 16 of the electrically conductive layer 4 formed in the flexible circuit board 3. Along with the width 14 of the connecting element 6, a surface area on the flexible circuit board 3 corresponding to the width 14 is also covered by the connecting element 6, which extends radially outward via the welded connection 8. In this way, a type of collar is formed that can press and hold the flexible circuit board welded to the circuit board onto the circuit board.

[0038] The flexible circuit board 3 has a polyimide film, a polyamide film, a Mylar layer, in particular a polyethylene terephthalate layer, or an elastomer layer as the electrically insulating material 5. The flexible circuit board is designed to be flexible enough to be bent back and forth transversely to a flat extension of the flexible circuit board without breaking.

[0039] Figure 2 schematically shows a connection arrangement 20 produced by the method 1 shown in Figure 1. The connection arrangement 20 comprises the substrate 2, in this exemplary embodiment a ceramic circuit carrier, comprising the electrically insulating ceramic layer 18 shown in Figure 1, and an electrically conductive rewiring layer 17, in particular a copper layer. In addition to the rewiring layer 17, the circuit carrier 2 has an electrically conductive backside layer 46, which, together with the electrically conductive rewiring layer 17, encloses the electrically insulating layer 18 between them. The connection arrangement 20 also comprises the flexible printed circuit board 3 and the connecting element 6.

[0040] In the connection arrangement 20, the three layers of the three-layer composite, formed by the circuit carrier 2, the flexible printed circuit board 3, and the connecting element 6, rest on one another, wherein the integrally connecting welded connection 8 integrally connects the three joining partners, namely the connecting element 6, the flexible printed circuit board 3, in particular the electrically conductive layer 4 of the flexible printed circuit board 3, and the circuit carrier 2, in particular the electrically conductive layer 17 of the circuit carrier 2, and at least partially or completely penetrates them transversely to a flat extension 40 of the circuit carrier 2. In this exemplary embodiment, the welded connection 8 penetrates the circuit carrier 2 with a smaller depth extension than its thickness extension 41, and also with a smaller depth extension than the thickness extension 42 of the electrically conductive layer 17, in particular the rewiring layer.

[0041] A thickness extension 44 of the connecting element 6 is larger than a thickness extension 43 of the electrically conductive layer 4 of the flexible printed circuit board 3 or of the flexible printed circuit board itself. The thickness extension of the electrically conductive layer 4 can correspond to a thickness extension of the electrically insulating layer 5. As a result, the flexible printed circuit board 3 can have an isotropic thickness.

[0042] In another embodiment, the connecting arrangement 20 can have a punched piece of sheet metal, also called a punched grid or leadframe, as a substrate instead of the ceramic circuit carrier 2.

[0043] Figure 3 shows - schematically - an embodiment of a connection method 21 for the materially bonded and electrically conductive connection of a circuit carrier 31 to a flexible printed circuit board 30.

[0044] In the joining method shown in Figure 3, a laser welding device 22 has a laser 23 for generating a laser beam 24, and a hold-down device formed by a tube 25, wherein the laser 23 is arranged and designed to transmit the laser beam 24 through a cylindrical cavity 26 enclosed by the tube 25 along the longitudinal extent of the cavity 26.

[0045] The tube 25 has an end face 37 which is designed to be placed on a connecting element 29, in this exemplary embodiment formed by a metal plate, a stamped grid, or a lead frame, or a piece of sheet metal, for transporting the connecting element up to the welding location on the circuit carrier 31, and to evacuate the cavity 26 bordering the connecting element 29 by means of a vacuum pump 28, so that the connecting element 29 can be sucked against the end face 37 of the tube 25.

[0046] A suction channel 27 connects the cavity 26 to the vacuum pump 28. The laser welding device 22 can be part of a manufacturing device and, as indicated by the arrow 38, can be moved up or down at least transversely to a flat extension 40 of the circuit carrier 31. In this way, after the connecting element 29, formed by the metal plate, has been sucked onto the circuit carrier 31, the laser welding device 22 can place the connecting element 29 onto the flexible printed circuit board 30 placed on the circuit carrier 31 in the direction 39 of the circuit carrier 31, where it can be pressed by the laser welding device 22.

[0047] The laser welding device 22 can be designed to press the tube 25, in particular the end face 37 of the tube 25, against the connecting element 29, so that the flexible printed circuit board 30 is firmly clamped between the connecting element 29 and the circuit carrier 31 in the region of the end face 37.

[0048] By means of the laser beam 24, the welded connection 36 can then be created, which can fuse the connecting element 29, the flexible printed circuit board 30 and the electrically conductive layer 33 of the circuit carrier 31 together and thus connect them to one another in a materially bonded manner.

[0049] After the welded joint 36 has cooled and solidified, the manufacturing device 22 can switch off the vacuum pump 28 so that after the pipe 25 is lifted off the connecting element 29, the connecting element 29 is released.

[0050] In this exemplary embodiment, the circuit carrier 31 comprises an electrically insulating layer 32, in particular a ceramic layer, which is enclosed between the electrically conductive layer 33 and a further electrically conductive rear layer 34 - in particular in the manner of a sandwich.

[0051] In this embodiment, the flexible printed circuit board 30 has, for example, a connector 35, so that an electrical or electronic circuit arrangement formed on the circuit carrier 31 can be electrically connected externally to other electronic components by means of the connector 35. Instead of the connector, the flexible printed circuit board 30 can be plugged, welded, or soldered to another circuit carrier.

Claims

Claims 1. Contact arrangement (20) with at least one electrically conductive substrate (2, 31), a particularly flexible printed circuit board (3, 30), wherein the flexible printed circuit board (3, 30) has at least one - in particular reversibly flexible - electrically insulating film (5) and at least one or only one electrically conductive layer (4), and wherein the electrically conductive layer of the flexible printed circuit board (3, 30) - in particular resting on the substrate (2, 31) - is electrically conductively connected to the substrate, characterized in that the contact arrangement has an electrically conductive connecting element (6, 29) which is arranged on the electrically conductive layer of the flexible printed circuit board (3, 30), such that the connecting element and the substrate (2, 31) enclose the flexible printed circuit board (3, 30) between them, wherein the connecting element (6, 29) is in contact with the electrically conductive layer of the flexible printed circuit board (3, 30) and with the substrate (2, 31).31) is welded in such a way that a welded joint (8, 36) extends from the connecting element (6, 29), - in particular transversely to a flat extension of the flexible printed circuit board (3, 30), - through the electrically conductive layer (4) of the flexible printed circuit board (3, 30) into the substrate (2, 31).

2. Contact arrangement (20) according to claim 1 , characterized in that the welded joint (8, 36) is a laser welded joint.

3. Contact arrangement (20) according to claim 1 or 2, characterized in that the connecting element (6, 29) extends radially outwards from the welded joint (8, 36), covering the flexible printed circuit board (3, 30). Contact arrangement (20) according to one of the preceding claims, characterized in that the welded joint (8, 36) is formed by means of a contact element that lies flat in the substrate plane. (40) extending, in particular longitudinally extending, weld bead which extends into the connecting element (6, 29), the flexible printed circuit board (3, 30) and into the substrate (2, 31), wherein the weld bead is configured to completely penetrate the connecting element (6, 29) and the flexible printed circuit board (3, 30), in particular at least the electrically conductive layer (4). Contact arrangement (20) according to one of the preceding claims, characterized in that the weld joint (8, 36) extends only partially along a thickness extension. (41) of the substrate (2, 31). Contact arrangement (20) according to one of the preceding claims, characterized in that the substrate has at least one electrically insulating ceramic layer and at least one electrically conductive layer. Contact arrangement (20) according to one of the preceding claims, characterized in that the connecting element (6) has a greater thickness (44) than the thickness (43) of the electrically conductive layer (17) of the flexible printed circuit board (3, 30). Contact arrangement (20) according to one of the preceding claims, characterized in that the weld bead has the same width (15) as the thickness (44) of the connecting element (6). Contact arrangement (20) according to one of the preceding claims, characterized in that the connecting element (6) is formed by a bond strip longitudinal section (7, 14). Contact arrangement (20) according to one of the preceding claims, characterized in that the connecting element (29) is a metal plate.Contact system with at least one contact arrangement (20) according to one of the preceding claims, wherein the contact arrangement comprises at least one further substrate, and the substrate (2, 31) and the further substrate are electrically connected to each other by means of the flexible circuit board (3, 30), characterized in that. The electrical connection points of the flexible printed circuit board (3, 30) with the substrate (2, 31) are created by means of the connecting element (6, 29) placed on the flexible printed circuit board (3, 30) and the metallurgical weld connection (8, 36) penetrating the connecting element (6, 29) and the flexible printed circuit board (3, 30) and extending into the substrate (2, 31). A contact system with at least one contact arrangement according to one of the preceding claims, characterized in that the flexible printed circuit board (3, 30) has a connector (35) for electrically connecting the substrate (2, 31).Method for joining a flexible printed circuit board (3, 30) with a substrate (2, 31) in a materially bonded manner, in which an area of ​​the flexible printed circuit board (3, 30) is electrically conductive and materially bonded to a substrate (2, 31), characterized in that a flat extending connecting element (6, 29) is placed on the area (14) of the flexible printed circuit board (3, 30), and the three-layer arrangement thus produced is welded to form a three-layer composite by means of a laser beam (11, 24).

Images