Circuit carrier assembly consisting of at least two stacked circuit carriers

Abstract

Circuit carrier assembly (1) consisting of at least two stacked circuit carriers (10) which are connected to each other to form a unit, wherein each of the circuit carriers (10) has a dielectric substrate (11) and an electrically conductive conductive layer (12) arranged thereon, which forms conductive structures (13) created by a mechanical manufacturing process, wherein in at least one of the circuit carriers (10) a breakthrough (16) connecting at least two adjacent conductive layers (12) is formed, in which a bridge (21) electrically connecting the conductive structures (13) of the two nearest adjacent conductive layers (12) is arranged.

Description

[0001] The invention relates to a circuit carrier assembly consisting of at least two stacked circuit carriers.

[0002] A variety of circuit carriers and methods for their fabrication are known from the prior art, particularly for applications in electronics, where flexible or rigid substrates are provided with electrically conductive structures, i.e., conductor tracks. Such circuit carriers are frequently implemented as printed circuit boards, flexible conductive films, or multilayer substrates and serve for the electrical connection and mechanical mounting of electronic components.

[0003] A common method for fabricating conductive structures on substrates is chemical etching, in which a conductive layer, for example made of copper, is deposited onto a dielectric support material and then selectively removed. However, this method is associated with several disadvantages, such as a high number of process steps, limited speed in continuous processing, and environmental problems due to the use and disposal of chemical substances.

[0004] It is also already known to form a circuit carrier assembly from several layered circuit carriers, in which the conductive structures, i.e., the conductor tracks, are produced by electroplating processes. However, the possibilities for recycling valuable and rare materials such as copper are severely limited in this case.

[0005] In addition to better environmental compatibility, it can also be advantageous for small series production, for example, not to have to produce the guide structures using the comparatively complex etching or other chemical processes.

[0006] To overcome these disadvantages, mechanical methods have been developed in which the conductive layers are structured by milling or similar subtractive machining processes. For example, WO 2022 / 223539 A1 discloses a method in which a circuit carrier, consisting of a substrate and a conductive layer, is guided through a gap between a milling unit and a structured die roller. In this process, specific areas of the conductive layer are removed to create the desired conductive structures, i.e., the conductor tracks. This method enables the continuous and rapid fabrication of conductive structures on flexible or rigid substrate materials and eliminates the need for etching chemicals.

[0007] US patent 2007 / 0184743 A1 also discloses a method for manufacturing electrical components on flexible carrier materials by mechanical processing, in which a conductive layer is applied to a dielectric substrate and subsequently structured by mechanical removal, in particular milling.

[0008] Compared to, for example, electroplating methods, the aforementioned writings have the disadvantage that only single-layer circuit carriers with a correspondingly single conductive layer can be provided.

[0009] The limitation to only one layer represents a significant disadvantage, as it results in severe restrictions, for example regarding design freedom and process reliability.

[0010] In particular, with single-layer circuit carriers it is not possible to route conductive structures on different levels and thus realize intersections or complex interconnections.

[0011] The invention is therefore based on the objective of overcoming the aforementioned disadvantages and providing an environmentally friendly and process-reliable as well as easy-to-manufacture circuit carrier assembly.

[0012] This problem is solved by the combination of features according to claim 1.

[0013] According to the invention, a circuit carrier assembly is proposed, consisting of at least two superimposed or stacked circuit carriers, which are connected to each other to form a unit, preferably a single piece. Each of the circuit carriers has a dielectric substrate, and preferably exactly one dielectric substrate, i.e., exclusively one dielectric substrate, on which one, and preferably exactly one, electrically conductive layer, i.e., exclusively one electrically conductive layer, for example a foil made of copper or a copper-aluminum alloy, is arranged. The conductive layer may also comprise or be formed by other elements and compounds, provided that these form a conductive layer in the overall assembly and can be applied to the substrate as a planar layer.The conductive layer forms conductive structures, such as conductor tracks, through a mechanical manufacturing process. Because these conductive structures are formed mechanically, the recesses in the conductive layer that define the conductive structures can extend to a predetermined and intended depth in the substrate. It is also possible for the recesses to pass entirely through the conductive layer without, or without significantly penetrating, the substrate. Compared to chemical manufacturing processes, a further advantage is that the mechanically produced recesses in the conductive layer, which define and define the conductive structures, are sharply delineated.Furthermore, the mechanically removed material, and in particular the material of the conductive layer, can be collected directly and easily recycled without requiring complex processing or further separation from a solution, for example. At least one of the circuit carriers, and especially the one located on a mounting side of the circuit carrier assembly, has a through-hole connecting at least two adjacent, and in particular two nearest, conductive layers. A bridge is arranged in this through-hole, electrically connecting the conductive structures of the two nearest conductive layers.

[0014] The ability to stack multiple circuit carriers on top of each other allows conductive structures to be routed on different levels and electrically connected at any desired point. This significantly increases design freedom and enables the realization of complex circuits, such as those required for LED matrix arrangements or other high-density electronic assemblies.

[0015] If more than two circuit carriers are stacked on top of each other, the breakthrough can extend from the circuit carrier located on the mounting side of the circuit carrier assembly, i.e., the first, to the conductive layer of the circuit carrier located on a rear side facing away from the mounting side, i.e., the last, so that all or at least some of the conductive layers can be contacted from the first circuit carrier to the last circuit carrier.

[0016] By forming a circuit carrier assembly with multiple stacked circuit carriers, a compact and reliable electrical connection between different levels is enabled. The integration of through-holes and electrically conductive bridges allows for flexible design of the electrical interconnection and increases design freedom.

[0017] In an advantageous embodiment, the conductive structures are produced by milling. Milling, as a mechanical manufacturing process, enables precise and clean structuring of the conductive layers. This allows for the creation of fine and complex conductive structures without the need for chemical or etching processes. This results in both high environmental compatibility and high cost-efficiency, even for small production runs and special applications.

[0018] In particular, milling allows for the quick and flexible implementation of individual designs and prototypes without the need for costly masks or etching chemicals.

[0019] Furthermore, the breakthrough can be produced mechanically, for example by milling, drilling, laser processing, punching, or waterjet cutting, or chemically, whereby the breakthrough can also be produced at least partially integrally with the guide structures. The possibility of producing the breakthrough both mechanically and chemically offers flexibility in the choice of manufacturing process. Depending on the material and requirements, the most suitable process can be used to ensure high quality and reliability of the connection.

[0020] If the breakthrough is to be produced integrally with the conductive structures in sections, the conductive layer of the circuit carrier, or the conductive layers of the circuit carriers through which the breakthrough is to extend, can be mechanically penetrated integrally at a position predetermined for the breakthrough during the production of the conductive structures, and corresponding recesses can be provided in the conductive layer. If the circuit carriers were subsequently stacked on top of each other, the breakthrough can be produced, for example, using a laser, by piercing only the substrates of the circuit carriers with the laser and thereby connecting the recesses corresponding to the breakthrough.

[0021] If the bridge is to be produced by milling, this can be done after stacking the circuit carriers, after connecting the stacked circuit carriers, or already integrally during the production of the guide structures of the individual circuit carriers.

[0022] Preferably, the circuit carrier assembly can have a mounting side formed by one of the conductive layers or by the conductive layer of the circuit carrier arranged on the mounting side, i.e., the first, and a back side facing away from it and preferably formed by a substrate, wherein the conductive layers of the circuit carriers are each facing the mounting side.

[0023] Alternatively, it can be provided that the conductive layer of the last circuit carrier faces away from the mounting side and towards the back, whereby, for example, a heat dissipation area, which will be explained further below, can be formed on the conductive layer of the last circuit carrier.

[0024] On the mounting side, the circuit carrier assembly can be populated with components and electrical components can be connected to the conductive layer that defines the mounting side and / or adjacent conductive layers. The orientation of the conductive layers towards the mounting side enables efficient arrangement and connection of the components, with the conductive layers being insulated from each other by the dielectric substrate of the circuit carriers.

[0025] This enables simple and automated assembly of the circuit carrier assembly with electronic components, which is particularly advantageous for industrial manufacturing.

[0026] In a further advantageous embodiment, the substrate can be designed as a particularly flexible and preferably single-layer film. Using a film as a substrate results in a lightweight, flexible, and thin design of the circuit carrier assembly. This is particularly advantageous for applications with limited installation space or for flexible electronics.

[0027] Furthermore, it can be provided that the stacked circuit carriers are each connected to at least the nearest adjacent circuit carrier(s) by bonding or lamination. Bonding or lamination achieves a stable, planar, and permanent connection between the individual circuit carriers, which increases the mechanical robustness and electrical reliability of the assembly.

[0028] Any intermediate layers used for laminating or bonding, or generally for the surface joining of the circuit carriers, such as an adhesive layer applied by spraying or an adhesive film laid on top, are not electrically conductive by design.

[0029] For clarification, the first circuit carrier is only connected to the circuit carrier that is in full contact with its rear-facing surface, and the last circuit carrier is only connected to the circuit carrier that is in full contact with its mounting-side surface, with further circuit carriers between the first and last circuit carriers being connected to the adjacent circuit carriers both towards the mounting side and towards the rear.

[0030] In a further advantageous embodiment, the conductive layer of at least one of the circuit carriers can form a shielding area designed to block electromagnetic emissions and / or electromagnetic interference. Additionally or alternatively, the conductive layer of at least one of the circuit carriers can form a heat dissipation area designed to dissipate heat. By forming specific areas within the conductive layer, additional functions such as electromagnetic shielding or improved heat dissipation can be achieved, thus expanding the application possibilities of the circuit carrier assembly. Both the shielding area and the heat dissipation area can be formed integrally with the conductive structure or separately from it.

[0031] In particular, optimal functionality and reliability of the assembly can be achieved by strategically positioning shielding or heat dissipation areas in close proximity to sensitive or heat-generating components.

[0032] Assuming that electrical components are arranged as functional elements on the conductive layer forming the mounting side, or that functional elements are formed by one of the conductive layers through its conductive structure, it can be provided, particularly for the shielding area, that it is arranged with functional elements orthogonally to a plane defined by the conductive layer or the circuit carrier, overlapping or covering it in a nearest conductive layer, so that the functional elements are optimally shielded.

[0033] To improve the heat dissipation properties of the heat dissipation area, such an area can be realized in particular by the conductive layer of the first circuit carrier or by the conductive layer of a circuit carrier that extends section by section beyond the adjacent circuit carriers, whereby in general a section of a conductive layer realizing a heat dissipation area can be designed to be free of adjacent circuit carriers.

[0034] By way of example, but not determining the scope of protection, a method for manufacturing a circuit carrier assembly according to the invention shall be explained, which includes at least the following steps and preferably in the given order: a) Providing the circuit carriers; b) independent production of the conductive structures in the conductive layers of the circuit carriers by a mechanical manufacturing process, in particular by milling; c) Stacking and connecting the circuit carriers over a surface to form a unit; d) Creating a breakthrough in at least one of the circuit carriers to connect two adjacent and, in particular, two nearest conductor layers in the circuit carrier assembly; e) Applying an electrically conductive material, for example solder, solder paste or soldering material in general, at least into the breakthrough to form a bridge electrically connecting the conductive structures of the conductive layers.

[0035] The described process enables efficient and reproducible manufacturing of the circuit carrier assembly with high process reliability and flexibility with regard to the materials and connection technologies used.

[0036] In parallel with the production of the guide structures, and optionally also during the production of the breakthrough, it can be provided that the material of the guide layer, which is removed particularly mechanically, is collected for recycling.

[0037] As already explained, it can also be provided that the breakthrough(s) are formed section by section and integrally with step b), in which the conductive layers of the circuit carriers are simultaneously penetrated at predetermined positions for the breakthrough during the production of the conductive structures, so that in step d) preferably only the substrates of the circuit carriers need to be penetrated, but that material of the conductive layers could already be removed and collected for recycling in step b).

[0038] In particular, when using a laser to create the breakthrough in step d), it is also advantageous that the laser does not have to remove material from an electrically conductive and possibly metallic material, so that a weaker laser can be used and / or a laser whose wavelength is matched to the material of the substrate can be used.

[0039] Furthermore, it can be provided that, after or during the application of the conductive material to form the bridge, further conductive material, i.e., again for example, solder, solder paste, or soldering material in general, is arranged for fixing and contacting electrical components at predetermined positions on a mounting side of the circuit carrier assembly formed by one of the conductive layers or by the conductive layer of the first circuit carrier, and that the mounting side is then populated with the electrical components at the predetermined positions. This enables simple and reliable assembly of the circuit carrier assembly with electronic components, which supports industrial manufacturing and automation.

[0040] Preferably, the bridges can then be formed by soldering, in particular by reflow soldering, and the electrical components can be fixed in the predetermined positions and electrically contacted. Soldering ensures a permanent, electrically and mechanically stable connection both between the layers and to the components.

[0041] By using standard soldering processes, the entire manufacturing process can be integrated into existing production lines, further improving the cost-effectiveness and scalability of production.

[0042] The features disclosed above can be combined in any way, provided that this is technically possible and they do not contradict each other.

[0043] Other advantageous embodiments of the invention are characterized in the dependent claims or are described in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. The figures show: Fig. 1 a circuit carrier assembly formed from three layered circuit carriers; Fig. 2 steps for manufacturing a circuit carrier assembly formed from two layered circuit carriers.

[0044] The figures are schematic examples. Identical reference symbols in the figures indicate identical functional and / or structural features.

[0045] In Fig. Figure 1 shows a first variant of a circuit carrier assembly 1 according to the invention, in which three circuit carriers 10 are stacked on top of each other and connected to each other to form a unit.

[0046] For this purpose, an intermediate layer 14 designed as an adhesive layer is arranged between the individual circuit carriers 10, so that the circuit carrier assembly 1 forms a single-piece and one-piece unit.

[0047] Each circuit carrier 10 consists of exactly one dielectric substrate 11, in this case designed as a flexible film, on which exactly one conductive layer 12 is applied, wherein conductive structures 13 formed by milling are created in the conductive layer 12 of each of the circuit carriers 10, which, however, cannot be seen in detail in the figures due to the chosen sectional representation.

[0048] As shown, the circuit carriers 10 are each arranged such that the conductive layers 12 face a mounting side M of the circuit carrier assembly 1 and the substrates 11 face a rear side R of the circuit carrier assembly 1.

[0049] This connects the mounting side M through the conductive layer 12 of a first and as shown in the illustration in Fig. 1 uppermost circuit carrier 10 and the back side R through the substrate 11 of a last and according to the representation in Fig. 1 bottom circuit carrier 10 formed.

[0050] In order to connect the conductive layers 12 of the various and here three circuit carriers 10 to each other, three openings 16 are formed by milling as an example, whereby these extend from conductive layer 12 of the first or uppermost circuit carrier 10 to a conductive layer 12 of an adjacent circuit carrier 10 in order to enable electrical contacting of the conductive layers 12 by means of a bridge 21.

[0051] If the breakthrough 16 does not extend from a conducting layer 12 merely to the nearest adjacent conducting layer 12, as is the case in the representation plane of the Fig. If the right-hand opening 16 is the case, the bridge 21 can contact all adjacent conductive layers 12, whereby an electrical connection to the conductive structure 13 formed by the respective conductive layer 12 can only optionally be formed. Consequently, the representation of the Fig. 1 right bridge 21, for example, also merely connects the conductive structure 13 formed by the conductive layer 12 of the first circuit carrier 10 with the conductive structure 13 of the conductive layer 12 of the last circuit carrier 10.

[0052] As shown, electrical components 22 are arranged on the mounting side M on contact pads formed by the conductive structure 13 of the conductive layer 12 of the first circuit carrier 10 and are connected to the conductive structure 13 by conductive material 20, which is solder material.

[0053] Additionally, in Fig. It can be seen that the openings 16 are arranged in such a way that flexible contacting between any layers of the composite is possible, thereby further increasing the freedom of interconnection. Furthermore, the intermediate layer 14 can be selected to have specific dielectric or thermally conductive properties in order to optimize the functionality of the composite.

[0054] Fig. Figure 2 shows steps for producing a circuit carrier assembly 1 according to the invention with exactly two stacked or layered circuit carriers 10.

[0055] Following step a), which is not shown in detail, in which the two circuit carriers 10 are provided, step b) involves the independent production of the conductive structures 13 in the conductive layers 12 of the circuit carriers 10 by milling. At the predetermined positions for the openings 16, recesses 15 are simultaneously created in the conductive layers 12 of the circuit carriers 10 by milling. These recesses are intended to be traversed by the openings 16. Since the openings 16 are only intended to pass through the first circuit carrier 10, the recesses 15 at the predetermined positions are produced only in the first circuit carrier 10, or in the uppermost circuit carrier 10 in the representation plane, as can be seen in the figure corresponding to step c).

[0056] For illustrative purposes, a milling head 31 machining the respective circuit carrier 10 is shown in each case as a purely exemplary example, whereby the production of the guide structures 13 can be carried out in parallel to each other using several milling stations or one after the other on a milling station.

[0057] Subsequently, the circuit carriers 10 are stacked on top of each other according to step c), and the carrier layers 10 are bonded together to form a single unit. For this purpose, when stacking the circuit carriers 10, adhesive is placed between each pair of circuit carriers 10 as an intermediate layer 14, which bonds the circuit carriers 10 together permanently and over a single area.

[0058] After the assembly of the two circuit carriers 10 has been formed in step c), the openings 16 are created or completed in step d) by a laser 32, whereby the laser 32 only has to penetrate the substrate 11 of the first or, in the representation plane, uppermost circuit carrier 10 as well as the intermediate layer 14, so that these extend from the conductive layer 12 which determines the mounting side M to an adjacent and, in this case, nearest conductive layer 12.

[0059] Although the formation of breakthroughs 16 in the case of the Fig.Since the process shown in the two illustrated exemplary methods could be carried out not only partially, but also completely integrally in step b), the separate formation of the openings 16 according to step c) has the advantage that the openings formed by means of the laser 32 of the openings 16 in the individual circuit carriers 10 overlap congruently and have no offset to each other.

[0060] According to step e) described below, electrically conductive material 20, specifically a solder paste, is placed both in the openings 16 and at predetermined positions of the conductive layer 12 that defines the mounting side M. As already mentioned in the introduction, contact pads or surfaces of the conductive structure 13 are provided at the predetermined positions, at which electrical components 22 are to be contacted with the conductive structure 13.

[0061] After applying the material 20, in the following step f) the mounting side M is fitted with the electrical components 22 and a soldering process, in particular reflow soldering, is carried out, whereby the bridges 21 are produced and the electrical components 22 are fixed and electrically connected to the mounting side M. Reference symbol list: 1 circuit carrier assembly 10 circuit carriers 11 Substrat 12 Conductive layer 13 guiding structures 14 Intermediate shift 15 Exclusion 16 Breakthrough 20 Conductive Material 21 Bridge 22 Electrical components 31 milling head 32 lasers M Assembly side R Back QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] WO 2022 / 223539 A1

[0006] US 2007 / 0184743 A1

[0007]

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