Flexible printed circuit board, control device, and method for manufacturing a flexible printed circuit board

Abstract

The invention relates to a flexible printed circuit board comprising a conductor track unit (14). A first side (30) of the conductor track unit (14) is connected to a first carrier film (16) by means of a first adhesive layer (18). A first outer side (20) of the flexible printed circuit board (12) is formed by a surface of the first carrier foil (16) facing away from the conductor track unit (14). The flexible printed circuit board (12) comprises a second carrier film (26) which is connected to a second side (32) of the conductor track unit (14) by means of a second adhesive layer (28). A second outer side (34) of the flexible printed circuit board (12) is formed by a surface of the second carrier film (26) facing away from the conductor track unit (14). The first adhesive layer (18) has a lower thickness (40) than the second adhesive layer (28). The invention also relates to a control device comprising such a printed circuit board (12) and to a method for manufacturing a flexible printed circuit board (12).

Description

[0001] AUDI AG

[0002] Flexible printed circuit board, control device and method for producing a flexible printed circuit board

[0003] DESCRIPTION:

[0004] The invention relates to a flexible printed circuit board with a conductor track unit, wherein a first side of the conductor track unit is connected to a first carrier film by means of a first adhesive layer. A surface of the first carrier film facing away from the conductor track unit forms a first outer side of the flexible printed circuit board. Furthermore, the invention relates to a control device with at least one such printed circuit board and a method for producing a flexible printed circuit board.

[0005] JP 2018041961 A describes a laminate for a flexible printed circuit board comprising a copper foil. The copper foil is bonded to an insulating film of the laminate by means of an adhesive layer.

[0006] Furthermore, US 2021 / 0084768 A1 describes a method for producing a substrate for a flexible printed circuit board.

[0007] The object of the present invention is to provide a flexible printed circuit board of the type mentioned at the outset which is particularly cost-effective to manufacture, as well as to provide a control device with such a printed circuit board and a corresponding method for manufacturing a flexible printed circuit board.

[0008] This object is achieved by a flexible printed circuit board having the features of patent claim 1, a control device having the features of patent claim 9, and a method having the features of patent claim 10. Advantageous embodiments with expedient further developments of the invention are specified in the dependent patent claims and in the following description.

[0009] The flexible printed circuit board according to the invention comprises a conductor track unit, wherein a first side of the conductor track unit is connected to a first carrier film by means of a first adhesive layer. A first outer side of the flexible printed circuit board is formed by a surface of the first carrier film facing away from the conductor track unit. The flexible printed circuit board comprises a second carrier film, which is connected to a second side of the conductor track unit by means of a second adhesive layer. A second outer side of the flexible printed circuit board is formed by a surface of the second carrier film facing away from the conductor track unit. The first adhesive layer has a smaller thickness than the second adhesive layer.

[0010] This is based on the realization that the first adhesive layer only needs to fulfill the purpose of connecting the conductor track unit to the first carrier film. Accordingly, a particularly small thickness is sufficient for the first adhesive layer to fulfill this function. The conductor track unit usually has areas in which a conductor track material of the conductor track unit has been removed in order to create the actual conductor tracks in the conductor track unit. It is therefore sensible for the second adhesive layer to be thicker than the first adhesive layer. This allows the adhesive from the second adhesive layer to penetrate into these areas during production of the flexible circuit board and ensure good cohesion of components of the flexible circuit board, in particular those designed as respective laminates and comprising the respective carrier films and the respective adhesive layers. This is advantageous.

[0011] However, because the first adhesive layer is thinner than the second adhesive layer, the printed circuit board unit is particularly cost-effective to manufacture. Typically, the adhesive used for the adhesive layers of the flexible printed circuit board is comparatively expensive, in particular significantly more expensive than a material that can be used for the carrier film. In addition to the conductor track material used for the conductor track unit, the adhesive of the adhesive layers contributes significantly to the overall cost of the flexible printed circuit board. By forming the first adhesive layer with a thinner thickness than the second adhesive layer, the flexible printed circuit board can be manufactured particularly cost-effectively.

[0012] Preferably, the conductor track unit has a plurality of through-openings formed by removing conductor track material from the conductor track unit. Adhesive from the second adhesive layer is introduced into the through-openings. The removal of the conductor track material serves to provide conductor tracks in the conductor track unit.

[0013] If adhesive from the second adhesive layer is introduced into the openings or gaps formed in this way, unwanted penetration of dirt and / or water or the like into those areas where the conductor track material of the conductor track unit has been removed can be largely prevented. Accordingly, impairment of the conductor tracks due to such contamination and / or corrosion or the like can be advantageously avoided. This is beneficial for the long-term functionality of the flexible printed circuit board during use.

[0014] The removal of the conductor track material can be achieved, for example, by etching and / or milling and / or other processes that remove the conductor track material. Those areas of the conductor track unit in which conductor track material remains then provide the conductor tracks formed in the flexible printed circuit board.

[0015] Preferably, the through-openings are completely filled with adhesive, which is provided at least predominantly by the second adhesive layer. By completely filling the through-openings or gaps with the adhesive, the individual conductor tracks of the conductor track unit can be very well enveloped or enclosed by the adhesive. And since the second adhesive layer is thicker than the first adhesive layer, the second adhesive layer provides a particularly large amount of adhesive, which allows the through-openings to be completely filled.

[0016] However, this does not rule out the possibility that during the manufacture of the flexible printed circuit board, for example, due to pressure being applied to the laminates of the flexible printed circuit board comprising the carrier films and the respective adhesive layer, adhesive from the first adhesive layer may penetrate into the through-holes. However, due to the smaller thickness of the first adhesive layer, this is possible to a significantly lesser extent than is the case for the adhesive provided by the second adhesive layer.

[0017] Preferably, the thickness of the second adhesive layer is greater than the thickness of the conductor track unit. This makes it particularly easy to ensure that any free spaces or gaps formed by removing conductor track material from the conductor track unit, particularly in the form of through-openings, are filled with adhesive from the second adhesive layers during production of the flexible printed circuit board. This is advantageous for ensuring good cohesion between the laminates of the flexible printed circuit board comprising the respective carrier films and the respective adhesive layers. Furthermore, a structure of the flexible printed circuit board free of unwanted cavities in the conductor track unit can be achieved particularly reliably. Accordingly, this ensures a particularly advantageous, robust structure or layer structure of the flexible printed circuit board.

[0018] Preferably, the thickness of the second adhesive layer is greater than the sum of the respective thicknesses of the conductor track unit and the first adhesive layer. In this case, the advantages associated with the greater thickness of the second adhesive layer are particularly significant. Furthermore, the second adhesive layer can thus fulfill its function, which includes holding the laminates together and filling unwanted cavities in the conductor track unit as extensively as possible, with particular ease.

[0019] Preferably, the thickness of the first carrier film is greater than the thickness of the second carrier film. This is based on the knowledge that both the respective adhesive layers and the carrier films are responsible for the electromagnetic compatibility of the flexible printed circuit board. This is because both the respective adhesive layer and the respective carrier film provide shielding for the conductor track unit. This applies both with regard to the susceptibility of the conductor track unit to electromagnetic fields and to the potential influence of electrical or electronic devices external to the printed circuit board by electromagnetic fields occurring during operation of the flexible printed circuit board.

[0020] Since the first adhesive layer is comparatively thin, any compromises in the electromagnetic compatibility of the flexible circuit board can be easily and inexpensively compensated for by increasing the thickness of the first carrier film. Accordingly, it may be advantageous to make the thickness of the first carrier film greater than that of the second carrier film.

[0021] Furthermore, the carrier films and the adhesive layers formed from an electrically insulating material are important for the electrical safety of the flexible circuit board and for the dielectric strength of the flexible circuit board. In this respect, too, it is advantageous if the thickness of the first carrier film is greater than the thickness of the second carrier film. This is because losses in terms of electrical safety and / or dielectric strength, which are caused by the small thickness of the first adhesive layer, can be compensated for to a particularly large extent by increasing the thickness of the first carrier film. This is advantageous. The thickness of the first adhesive layer is preferably less than 15 μm. This is based on the knowledge that this allows significant cost savings to be achieved compared to a possible thickness of the first adhesive layer of, for example, 50 μm.This applies in particular if the thickness of the first adhesive layer is less than 10 pm.

[0022] In particular, the first adhesive layer can have a thickness of approximately 5 μm. Compared to a theoretically possible thickness of approximately 50 μm for the first adhesive layer, this allows for particularly significant cost savings for the adhesive in the first adhesive layer. This contributes to the cost-effective manufacture of the flexible printed circuit board.

[0023] The flexible printed circuit board can be designed as a single-layer circuit board. In this case, the conductor track unit is formed by exactly one conductor track layer. This design allows for particularly high flexibility or bendability of the flexible circuit board. Furthermore, the single-layer circuit board is characterized by its advantageously small installation space requirement.

[0024] Alternatively, the flexible printed circuit board can be designed as a multilayer printed circuit board. In this case, the conductor track unit has a plurality of conductor track layers. This advantageously allows for very complex interconnections of electronic components on the flexible printed circuit board equipped with these electronic components or similar electronic components. The circuits can therefore be particularly complex if the flexible printed circuit board is designed as a multilayer printed circuit board. Consequently, designing the flexible printed circuit board as a multilayer printed circuit board offers advantages.

[0025] If the conductor track unit in a multilayer printed circuit board comprises a plurality of conductor track layers, these separate conductor track layers can be connected to each other by additional adhesive layers. Furthermore, it is possible to provide additional foils made of an electrically insulating material between the individual conductor track layers, particularly in the form of carrier foils. This facilitates the handling of components or laminates of the flexible printed circuit board during the manufacture or production of the flexible printed circuit board.

[0026] Preferably, the first carrier film and / or the second carrier film are formed from a polyimide (PI). Such an electrically insulating carrier film is particularly heat-resistant. This makes it possible to equip at least one of the outer sides of the flexible printed circuit board with electronic modules or similar electronic components, whereby soldering processes can be used to connect the electronic modules to the conductor tracks of the conductor track unit. This is advantageous for a reliable and secure electrically conductive connection of the electronic components to the conductor tracks of the conductor track unit.

[0027] Additionally or alternatively, the first carrier film and / or the second carrier film can be made of polyethylene naphthalate (PEN). Such an electrically insulating plastic material is also characterized by high heat resistance, which advantageously enables the flexible printed circuit board to be populated with electronic components or electronic modules in a soldering process.

[0028] Additionally or alternatively, the first carrier film and / or the second carrier film can be formed, for example, from polyethylene terephthalate (PET). Although such a plastic material is less heat-resistant than polyimide or polyethylene naphthalate, an electrically conductive connection to the conductor tracks of the conductor track unit can nevertheless be easily established by using an electrically conductive adhesive if the first carrier film and / or the second carrier film is formed from PET.

[0029] The control device according to the invention comprises at least one flexible printed circuit board according to the invention. The use of the flexible printed circuit board in the control device allows the costs of providing the control device to be reduced.

[0030] In particular, the control device can be provided for a motor vehicle or used in a motor vehicle. The advantages associated with the reduced costs of the control device apply analogously to the motor vehicle if the control device is arranged in the motor vehicle. Accordingly, the use of the control device equipped with the fewest cost-effectively manufactured flexible printed circuit boards in the motor vehicle is advantageous.

[0031] In the method according to the invention for producing a flexible printed circuit board with a conductor track unit, a first side of the conductor track unit is connected to a first carrier film by means of a first adhesive layer. A surface of the first carrier film facing away from the conductor track unit forms a first outer side of the flexible printed circuit board. To produce the flexible printed circuit board, a second carrier film is used, which is connected to a second side of the conductor track unit by means of a second adhesive layer. A surface of the second carrier film facing away from the conductor track unit forms a second outer side of the flexible printed circuit board. The first adhesive layer is formed with a smaller thickness than the second adhesive layer.

[0032] Such a process enables particularly cost-effective production or manufacturing of the flexible printed circuit board.

[0033] The advantages and preferred embodiments described for the flexible printed circuit board according to the invention also apply to the control device according to the invention and the method according to the invention, and vice versa. Accordingly, the invention also includes further developments of the method according to the invention that have features already described in connection with the further developments of the flexible printed circuit board according to the invention and the control device according to the invention. For this reason, the corresponding further developments of the method according to the invention are not described again here.

[0034] The invention also encompasses combinations of the features of the described embodiments. The invention therefore also encompasses implementations that each comprise a combination of the features of several of the described embodiments, unless the embodiments are described as mutually exclusive.

[0035] Exemplary embodiments of the invention are described below. Shown are:

[0036] Fig. 1 schematically shows a first laminate for a single-layer flexible printed circuit board, wherein the first laminate has a first carrier film and a first adhesive layer, and wherein a conductor track unit formed by exactly one conductor track layer is connected to the first carrier film by means of the first adhesive layer;

[0037] Fig. 2 schematically shows a second laminate for the single-layer flexible printed circuit board, wherein the second laminate has a second carrier film and a second adhesive layer, and wherein the second adhesive layer is thicker than the first adhesive layer of the first laminate according to Fig. 1;

[0038] Fig. 3 shows the first laminate according to Fig. 1, wherein conductor tracks are created in the conductor track layer of the first laminate by removing conductor track material from the conductor track layer; Fig. 4 shows a schematic of the single-layer flexible printed circuit board in which the first laminate according to Fig. 3 and the second laminate according to Fig. 2 are connected to one another by means of the second adhesive layer;

[0039] Fig. 5 shows a variant of the first laminate according to Fig. 1 , in which the first carrier film has a greater thickness than in the variant according to Fig. 1 ;

[0040] Fig. 6 shows a variant of the single-layer flexible printed circuit board in which the first laminate according to Fig. 5 and the second laminate according to Fig. 2 are connected to each other by means of the second adhesive layer; and

[0041] Fig. 7 shows a highly schematic view of a control device of a motor vehicle, wherein the control device comprises the flexible printed circuit board according to Fig. 4.

[0042] The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that can be considered independently of one another, each of which also develops the invention independently of one another. Therefore, the disclosure is intended to encompass combinations of the features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0043] In the figures, the same reference symbols designate elements with the same function.

[0044] Fig. 1 schematically shows a first laminate 10 for providing or producing a flexible printed circuit board 12 (see Fig. 4). For the sake of simplicity, reference will be made below to the flexible printed circuit board 12 shown in Fig. 4, which is designed as a single-layer printed circuit board. Accordingly, a conductor track unit of the single-layer flexible printed circuit board 12 is formed by precisely one conductor track layer 14. With reference to the flexible and single-layer printed circuit board 12 illustrated here (see, for example, Fig. 4 and Fig. 6), the terms conductor track unit and conductor track layer 14 can therefore be used synonymously.

[0045] If, on the other hand, the flexible printed circuit board 12 has a plurality of conductor track layers which are arranged one above the other in the vertical direction of the printed circuit board 12, i.e. in the direction of a thickness of the printed circuit board 12, the statements made here for exactly one conductor track layer 14 apply analogously to the conductor track unit which has a plurality of conductor track layers.

[0046] The flexible printed circuit board 12 can be easily bent or twisted without causing damage to the printed circuit board 12. This allows for a particularly high degree of freedom in the design and use of the flexible or bendable printed circuit board 12. In particular, the flexible printed circuit board 12 is therefore suitable for installation in confined spaces, which, in contrast, presents greater difficulties with rigid, i.e., non-flexible printed circuit boards.

[0047] For the sake of simplicity, the flexible printed circuit board 12 may also be referred to simply as printed circuit board 12. The terms flexible printed circuit board 12 and printed circuit board 12 are therefore to be understood as synonymous in this context.

[0048] According to Fig. 1, the first laminate 10 comprises, in addition to the conductor track unit provided in this case by precisely one conductor track layer 14, a first carrier film 16 formed from an electrically insulating material. A first adhesive layer 18, which is associated with the first laminate 10, ensures that the conductor track layer 14 and the first carrier film 16 are held together. A first side 30 of the conductor track layer 14 is bonded to the first carrier film 16 by means of the first adhesive layer 18.

[0049] In the finished flexible printed circuit board 12 (see, for example, Fig. 4), a first outer side 20 of the flexible printed circuit board 12 is formed by a surface of the first carrier film 16 facing away from the conductor track layer 14. Accordingly, this first outer side 20 of the printed circuit board 12 faces an environment 22 of the printed circuit board 12.

[0050] As can be seen from Fig. 4, the flexible printed circuit board 12 comprises a second laminate 24, which is shown schematically in Fig. 2. The second laminate 24 has a second carrier film 26, which is also made of an electrically insulating material. A second adhesive layer 28 is arranged on the second carrier film 26 (see Fig. 2). According to Fig. 2, the second laminate 24 is formed by the second carrier film 26 and the second adhesive layer 28.

[0051] In the finished flexible printed circuit board 12, the second carrier film 26 is connected to a second side 32 of the conductor track layer 14 by means of the second adhesive layer 28 (see Fig. 4).

[0052] According to Fig. 4, the second adhesive layer 28, which is associated with the second laminate 24, thus ensures a connection of the first laminate 10 to the second laminate 24. In this case, the conductor track layer 14 is arranged in a sandwich-like manner between the first adhesive layer 18 and the second adhesive layer 28.

[0053] A surface of the second carrier film 26 facing away from the conductor track layer 14 forms a second outer side 34 of the flexible circuit board 12 in the finished flexible circuit board 12 (see Fig. 4). Accordingly, the second outer side 34 faces the surrounding area 22 of the flexible circuit board 12 in the same way as the first outer side 20 of the flexible circuit board 12. To produce the flexible circuit board 12 shown in Fig. 4, the first laminate 10 is processed to produce individual conductor tracks 36 from a conductor track material of the conductor track layer 14. The conductor track material of the conductor track layer 14 can be made of copper and / or aluminum, for example. The produced conductor tracks 36 are illustrated schematically in Fig. 3, wherein, for reasons of clarity, only some of the conductor tracks 36 are provided with a reference symbol.

[0054] For the purpose of producing the individual conductor tracks 36, the conductor track material of the previously continuous conductor track layer 14 is removed or ablated in certain areas. This removal process can be achieved, for example, by etching, milling, or other ablation processes.

[0055] Fig. 3 schematically illustrates that gaps or through-openings 38 are formed by removing the conductor track material in the conductor track layer 14. For reasons of clarity, only a few of these through-openings 38, which extend to the first adhesive layer 18, are provided with a reference symbol in Fig. 3.

[0056] In conventional production of flexible printed circuit boards, it can in principle be provided that the first adhesive layer 18 or first adhesive layer, which is associated with the first laminate 10, is of the same thickness as the second adhesive layer 28 or second adhesive layer, which is associated with the second laminate 24. In this regard, however, it should be noted that the adhesive used for the adhesive layers 18, 28 or adhesive layers is comparatively expensive.

[0057] Therefore, in the present case, the adhesive layers 18, 28 have different thicknesses. A thickness 40 of the first adhesive layer 18 (see Fig. 1) is less than a thickness 42 of the second adhesive layer 28 (see Fig. 2). This is based on the following consideration. In the first laminate 10, the first adhesive layer 18 serves merely to hold the conductor track layer 14 and the first carrier film 16 together. For this purpose, the comparatively small thickness 40 of the first adhesive layer 18 is sufficient.

[0058] The second adhesive layer 28, which belongs to the second laminate 24, serves, according to Fig. 4, in particular to join the two laminates 10, 24. Accordingly, the second adhesive layer 28 ensures that the two laminates 10, 24 hold together well in the finished flexible printed circuit board 12 (see Fig. 4). The second adhesive layer 28 also serves to fill the gaps or through-openings 38, which result from the fact that partial areas of the previously continuous conductor track layer 14 (see Fig. 1) were abraded or removed in order to form the conductor tracks 36 (see Fig. 3).

[0059] Depending on the thickness of the conductor track unit—in this case, only the exact one conductor track layer 14—different thicknesses 42 of the second adhesive layer 28 can be provided. For example, it should be assumed that the thickness 42 of the second adhesive layer 28 is approximately 50 μm. If the first adhesive layer 18 and the second adhesive layer 28 have the same thickness, the thickness 40 of the first adhesive layer 18 would also be approximately 50 μm.

[0060] In the present case, however, the first adhesive layer 18 has a significantly reduced thickness 40. For example, the thickness 40 of the first adhesive layer 18 can be only approximately 5 μm instead of 50 μm.

[0061] At a price of, for example, approximately EUR 6 to approximately EUR 8 per square meter for the adhesive of the adhesive layers 18, 28, such a reduction in the thickness 40 of the first adhesive layer 18 enables savings of EUR 3 to EUR 5 per square meter of the first laminate 10. This is advantageous for achieving particularly cost-effective production of the flexible printed circuit board 12. Fig. 4 shows how the two laminates 10, 24 are joined to one another by means of the second adhesive layer 28. Adhesive from the second adhesive layer 28 is introduced into the through-openings 38, which are shown in Fig. 3. In particular, the through-openings 38 are completely filled with adhesive (see Fig. 4). The adhesive present in the region of the through-openings 38 or free spaces or gaps in the conductor track layer 14 originates at least predominantly from the second adhesive layer 28.In other words, this adhesive present in the passage openings 38 is at least predominantly provided by the second adhesive layer 28.

[0062] Filling the through-openings 38 completely with the adhesive is particularly advantageous for preventing contamination and / or water, in particular water containing at least one electrolyte, from entering the area of ​​the conductor track layer 14. Therefore, it is advantageous to make the thickness 42 of the second adhesive layer 28 greater than the thickness 44 of the conductor track layer 14. This makes it particularly easy to ensure that the second adhesive layer 28 provides a sufficient amount of adhesive to completely fill the through-openings 38 or gaps.

[0063] In Fig. 5, a variant of the first laminate 10 is shown, as in Fig. 1, before processing the conductor track layer 14 and the associated production of the individual conductor tracks 36.

[0064] In the variant of the first laminate 10 shown in Fig. 5, a thickness 46 of the first carrier film 16 is greater than a thickness 48 of the second carrier film 26 (see Fig. 2 and Fig. 6). The design of the first laminate 10 according to Fig. 5 or of the flexible printed circuit board 12 produced using this first laminate 10 according to Fig. 6 is based on the finding explained below.

[0065] In the design of the flexible printed circuit board 12 according to Fig. 4, a

[0066] Distance from the first side 30 of the conductor track layer 14 to the first outer side 20 of the printed circuit board 12 is less than a distance from the second side 32 of the conductor track layer 14 to the second outer side 34. Accordingly, both an electrical insulation effect provided by the first adhesive layer 18 and the first carrier film 16 and a shielding effect of these components of the first laminate 10 with regard to electromagnetic compatibility are less than is the case for the thicker second adhesive layer 28 and the second carrier film 26.

[0067] This can, in principle, be counteracted when using the printed circuit board 12 by arranging or aligning the printed circuit board 12 appropriately. For example, the flexible printed circuit board 12 can be rotated such that the side that is expected to exhibit greater resistance with regard to electromagnetic compatibility and / or electrical safety faces the side where a higher load in this regard is expected.

[0068] However, it may also be advantageous for the flexible printed circuit board 12 to have substantially equally good resistance with regard to electromagnetic compatibility and / or electrical safety both toward the first outer side 20 and toward the second outer side 34. For this purpose, as shown schematically in Fig. 6, the first carrier film 16 can be formed with a greater thickness 46 than the second carrier film 26.

[0069] If, in addition, an even higher resistance with regard to electromagnetic compatibility and / or even further improved electrical insulation is to be achieved in the direction of the second outer side 34 of the circuit board 12 shown in Fig. 6 (for example, to ensure a correspondingly high electrical safety and / or high dielectric strength of the circuit board 12), it can be provided that the thickness 48 of the second carrier film 26 is increased. In particular, the thickness 48 of the second carrier film 26 can therefore essentially correspond to the thickness 46 of the first carrier film 16. The variant according to Fig. 5 and Fig. 6 is further based on the finding that the respective carrier film 16, 26 is significantly more advantageous than the respective adhesive layer 18, 28.For example, with a thickness 48 of the second carrier film 26 of, for example, 25 μm, the costs can be in the range of, for example, approximately EUR 0.70 to approximately EUR 1.30, for example, in the range of approximately EUR 1, per square meter. This is significantly less than the approximately EUR 6 per square meter to approximately EUR 8 per square meter for the respective adhesive layer 18, 28. The figures given as examples for a possible price of the carrier film 26 apply in particular when the carrier film 26 is made of polyethylene naphthalate (PEN).

[0070] However, even if the carrier films 16, 26 are made of polyimide, the costs for the carrier film 16, 26 are generally significantly lower than the costs for the adhesive of the adhesive layers 18, 28.

[0071] In Fig. 7, a control device 50 is shown in a highly schematic manner, which has at least one flexible printed circuit board 12.

[0072] For reasons of clarity, Fig. 7 does not separately show how the flexible printed circuit board 12 is equipped with electronic components or electronic modules. Such electronic components, which are electrically connected to the conductor tracks 36 of the conductor track layer 14, can be arranged on the first outer side 20 and / or on the second outer side 34 of the flexible printed circuit board 12.

[0073] The control device 50 according to Fig. 7 can be designed, in particular, as a control unit of a motor vehicle. Accordingly, cost advantages can be achieved in the provision of the control device 50 and thus also of the motor vehicle if the at least one flexible printed circuit board 12 is used for the control device 50.

[0074] Overall, the examples show how adhesive savings can be achieved in the production of flexible printed circuit boards 12.

Claims

PATENT CLAIMS:

1. A flexible printed circuit board with a conductor track unit (14), wherein a first side (30) of the conductor track unit (14) is connected to a first carrier film (16) by means of a first adhesive layer (18), wherein a first outer side (20) of the flexible printed circuit board (12) is formed by a surface of the first carrier film (16) facing away from the conductor track unit (14), characterized in that the flexible printed circuit board (12) comprises a second carrier film (26) which is connected to a second side (32) of the conductor track unit (14) by means of a second adhesive layer (28), wherein a second outer side (34) of the flexible printed circuit board (12) is formed by a surface of the second carrier film (26) facing away from the conductor track unit (14), and wherein the first adhesive layer (18) has a smaller thickness (40) than the second adhesive layer (28).

2. Flexible printed circuit board according to claim 1, characterized in that the conductor track unit (14) has a plurality of through-openings (38) which are formed by removing conductor track material from the conductor track unit (14), wherein adhesive of the second adhesive layer (28) is introduced into the through-openings (38).

3. Flexible printed circuit board according to claim 2, characterized in that the through-openings (38) are completely filled with adhesive, which is provided at least predominantly by the second adhesive layer (28).

4. Flexible printed circuit board according to one of the preceding claims, characterized in that a thickness (42) of the second adhesive layer (28) is greater than a thickness (44) of the conductor track unit (14), wherein the thickness (42) of the second Adhesive layer (28) is in particular greater than a sum of the respective thicknesses of the conductor track unit (14) and the first adhesive layer (18).

5. Flexible printed circuit board according to one of the preceding claims, characterized in that a thickness (46) of the first carrier film (16) is greater than a thickness (48) of the second carrier film (26).

6. Flexible printed circuit board according to one of the preceding claims, characterized in that the thickness (40) of the first adhesive layer (18) is less than 15 pm, in particular less than 10 pm, wherein the first adhesive layer (18) in particular has a thickness (40) of approximately 5 pm.

7. Flexible printed circuit board according to one of the preceding claims, characterized in that the flexible printed circuit board (12) is designed as a single-layer printed circuit board, wherein the conductor track unit is formed by exactly one conductor track layer (14), or the flexible printed circuit board (12) is designed as a multi-layer printed circuit board, wherein the conductor track unit has a plurality of conductor track layers.

8. Flexible printed circuit board according to one of the preceding claims, characterized in that the first carrier film (16) and / or the second carrier film (26) is formed from a polyimide and / or from polyethylene naphthalate.

9. Control device, in particular for a motor vehicle, with at least one flexible printed circuit board (12) according to one of the preceding claims.

10. A method for producing a flexible printed circuit board (12) with a conductor track unit (14), wherein a first side (30) of the Conductor track unit (14) is connected to a first carrier film (16) by means of a first adhesive layer (18), wherein a first outer side (20) of the flexible printed circuit board (12) is formed by a surface of the first carrier film (16) facing away from the conductor track unit (14), characterized in that for producing the flexible printed circuit board (12) a second carrier film (26) is used, which is connected to a second side (32) of the conductor track unit (14) by means of a second adhesive layer (28), wherein a second outer side (34) of the flexible printed circuit board (12) is formed by a surface of the second carrier film (26) facing away from the conductor track unit (14), and wherein the first adhesive layer (18) is formed with a smaller thickness (40) than the second adhesive layer

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