DE102023100457A1 - Flexible printed circuit board, control device and method for producing a flexible printed circuit board - Google Patents

Abstract

The invention relates to a flexible circuit board with 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 circuit board (12) is formed by a surface of the first carrier film (16) facing away from the conductor track unit (14). The flexible 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 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 smaller thickness (40) than the second adhesive layer (28). Furthermore, the invention relates to a control device with such a circuit board (12) and to a method for producing a flexible circuit board (12).

Description

The invention relates to a flexible 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 first outer side of the flexible circuit board is formed by a surface of the first carrier film facing away from the conductor track unit. The invention further relates to a control device with at least one such circuit board and a method for producing a flexible circuit board.

The JP 2018041961 A describes a laminate for a flexible circuit board, which has a copper foil. The copper foil is connected to an insulating film of the laminate by means of an adhesive layer.

Furthermore, US 2021/0084768 A1 a method of manufacturing a substrate for a flexible printed circuit board.

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 producing a flexible printed circuit board.

This object is achieved by a flexible circuit board with the features of patent claim 1, a control device with the features of patent claim 9 and by a method with 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.

The flexible 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 circuit board is formed by a surface of the first carrier film facing away from the conductor track unit. The flexible 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 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.

This is based on the knowledge 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 is because adhesive from the second adhesive layer can then penetrate into these areas when the flexible circuit board is manufactured and ensure that components of the flexible circuit board, in particular those designed as respective laminates and comprising the respective carrier films and the respective adhesive layers, are held together well. This is advantageous.

However, because the first adhesive layer is thinner than the second adhesive layer, the circuit board unit is particularly cost-effective to manufacture. This is because the adhesive used for the adhesive layers or adhesive layers of the flexible circuit board is usually 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 therefore makes a significant contribution to the overall costs of the flexible circuit board. By making the first adhesive layer thinner than the second adhesive layer, the flexible circuit board can be manufactured particularly cost-effectively.

Preferably, the conductor track unit has a plurality of through-openings which are formed by removing conductor track material from the conductor track unit. In this case, 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.

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

The removal of the conductor material can be done, for example, by etching and/or milling and/or the other method causing removal of the conductor track material. Those areas of the conductor track unit in which conductor track material remains then provide the conductor tracks which are formed in the flexible circuit board.

Preferably, the through-openings are completely filled with adhesive, which is at least predominantly provided by the second adhesive layer. By completely filling the through-openings or gaps with the adhesive, it can be achieved that the individual conductor tracks of the conductor track unit are very well covered 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, by means of which the through-openings can be completely filled.

However, this does not rule out the possibility that adhesive from the first adhesive layer may enter the through-openings during the manufacture of the flexible circuit board, for example as a result of pressure being applied to the laminates of the flexible circuit board comprising the carrier films and the respective adhesive layer. However, due to the smaller thickness of the first adhesive layer, this is possible to a much lesser extent than is the case for the adhesive provided by the second adhesive layer.

Preferably, a thickness of the second adhesive layer is greater than a thickness of the conductor track unit. This makes it particularly easy to ensure that free spaces or gaps formed by removing conductor track material from the conductor track unit, in particular in the form of through-openings, are filled with adhesive from the second adhesive layers during the manufacture of the flexible circuit board. This is advantageous for ensuring that the laminates of the flexible circuit board comprising the respective carrier films and the respective adhesive layers hold together well. Furthermore, a structure of the flexible circuit board that is free of undesirable 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 circuit board.

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. The advantages that the greater thickness of the second adhesive layer brings with it then apply to a particularly high degree. In addition, the second adhesive layer can thus particularly easily fulfill its function, which includes holding the laminates together and filling as much as possible of undesirable cavities in the conductor track unit.

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 how good the electromagnetic compatibility of the flexible circuit board is. This is because both the respective adhesive layer and the respective carrier film provide shielding for the conductor track unit. This applies on the one hand with regard to the ability of the conductor track unit to be influenced by electromagnetic fields and on the other hand to a possible influence of electrical or electronic devices external to the circuit board by electromagnetic fields that occur during operation of the flexible circuit board.

Since the first adhesive layer has a comparatively small thickness, losses in terms of the electromagnetic compatibility of the flexible circuit board can be compensated for very easily and with little effort by increasing the thickness of the first carrier film. Accordingly, it can be advantageous to make the thickness of the first carrier film greater than the thickness of the second carrier film.

Furthermore, the carrier films and the adhesive layers made of 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 therefore 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.

Preferably, the thickness of the first adhesive layer is less than 15 µm. This is based on the knowledge that this can result in significant cost savings compared to a possible thickness of the first adhesive layer of, for example, 50 µm. This is particularly true if the thickness of the first adhesive layer is less than 10 µm.

In particular, the first adhesive layer can have a thickness of approximately 5 µm. In comparison to a thickness of the first adhesive layer of approximately 50 µm, which is possible in principle, a particularly large saving in costs for the adhesive of the first adhesive layer can be achieved in this way. This contributes to the cost-effective manufacturability of the flexible circuit board.

The flexible 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 type of structure makes it possible to achieve a particularly high level of flexibility or bendability of the flexible circuit board. In addition, the single-layer circuit board is characterized by its advantageously small installation space requirement.

Alternatively, the flexible circuit board can be designed as a multilayer circuit board. In this case, the conductor track unit has a plurality of conductor track layers. In this way, very complex interconnections of electronic components of the flexible circuit board equipped with these electronic components or similar electronic components can advantageously be achieved. The circuits can therefore be particularly complex if the flexible circuit board is designed as a multilayer circuit board. Consequently, the design of the flexible circuit board as a multilayer circuit board brings advantages.

If the conductor track unit in the multilayer circuit board comprises a plurality of conductor track layers, these separate conductor track layers can be connected to one another by additional adhesive layers. It is also possible to provide additional films made of an electrically insulating material between the individual conductor track layers, particularly in the manner of carrier films. This makes it easier to handle components or laminates of the flexible circuit board during the manufacture or production of the flexible circuit board.

Preferably, the first carrier film and/or the second carrier film are made of 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 circuit board with electronic components or similar electronic components, whereby soldering processes can be used to connect the electronic components 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.

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 circuit board to be populated with electronic components or electronic modules in a soldering process.

Additionally or alternatively, the first carrier film and/or the second carrier film can be made of polyethylene terephthalate (PET), for example. Such a plastic material is admittedly less heat-resistant than polyimide or polyethylene naphthalate. Nevertheless, an electrically conductive connection to the conductor tracks of the conductor track unit can be produced in a simple manner by using an electrically conductive adhesive if the first carrier film and/or the second carrier film is made of PET.

The control device according to the invention has at least one flexible circuit board according to the invention. By using the flexible circuit board in the control device, the costs for providing the control device can be reduced.

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 when the control device is arranged in the motor vehicle. Accordingly, the use of the control device equipped with the least one inexpensively manufactured flexible circuit board in the motor vehicle is advantageous.

In the method according to the invention for producing a flexible 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 first outer side of the flexible circuit board is formed by a surface of the first carrier film facing away from the conductor track unit. To produce the flexible 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 second outer side of the flexible circuit board is formed by a surface of the second carrier film facing away from the conductor track unit. The first adhesive layer is formed with a smaller thickness than the second adhesive layer.

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

The advantages and preferred embodiments described for the flexible printed circuit board according to the invention also apply to the appropriate control device and the method according to the invention and vice versa.

The invention therefore also includes further developments of the method according to the invention which have features as have already been described in connection with the further developments of the flexible printed circuit board according to the invention and the control device. For this reason, the corresponding further developments of the method according to the invention are not described again here.

The invention also includes combinations of the features of the described embodiments. The invention therefore also includes implementations that each have a combination of the features of several of the described embodiments, provided that the embodiments have not been described as mutually exclusive.

• 1 schematisch ein erstes Laminat für eine einlagige flexible Leiterplatte, wobei das erste Laminat eine erste Trägerfolie und eine erste Klebstofflage aufweist, und wobei eine durch genau eine Leiterbahnenlage gebildete Leiterbahneneinheit mittels der ersten Klebstofflage mit der ersten Trägerfolie verbunden ist;
• 2 schematisch ein zweites Laminat für die einlagige flexible Leiterplatte, wobei das zweite Laminat eine zweite Trägerfolie und eine zweite Klebstofflage aufweist, und wobei die zweite Klebstofflage dicker ist als die erste Klebstofflage des ersten Laminats gemäß 1;
• 3 das erste Laminat gemäß 1, wobei in der Leiterbahnenlage des ersten Laminats Leiterbahnen erstellt sind, indem Leiterbahnmaterial aus der Leiterbahnenlage entfernt wurde;
• 4 schematisch die einlagige flexible Leiterplatte, bei welcher das erste Laminat gemäß 3 und das zweite Laminat gemäß 2 mittels der zweiten Klebstofflage miteinander verbunden sind;
• 5 eine Variante des ersten Laminats gemäß 1, bei welcher die erste Trägerfolie eine größere Dicke aufweist als bei der Variante gemäß 1;
• 6 eine Variante der einlagigen flexiblen Leiterplatte, bei welcher das erste Laminat gemäß 5 und das zweite Laminat gemäß 2 mittels der zweiten Klebstofflage miteinander verbunden sind; und
• 7 stark schematisiert eine Steuerungseinrichtung eines Kraftfahrzeugs, wobei die Steuerungseinrichtung die flexible Leiterplatte gemäß 4 aufweist.

Embodiments of the invention are described below.

• 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;
• 2 schematically a second laminate for the single-layer flexible printed circuit board, wherein the second laminate comprises 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 1 ;
• 3 the first laminate according to 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;
• 4 schematically the single-layer flexible printed circuit board, in which the first laminate according to 3 and the second laminate according to 2 are connected to each other by means of the second adhesive layer;
• 5 a variant of the first laminate according to 1 , in which the first carrier film has a greater thickness than in the variant according to 1 ;
• 6 a variant of the single-layer flexible printed circuit board, in which the first laminate is 5 and the second laminate according to 2 are connected to each other by means of the second adhesive layer; and
• 7 highly schematically a control device of a motor vehicle, wherein the control device comprises the flexible circuit board according to 4 having.

The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the components of the embodiments described each represent individual features of the invention that are to be considered independently of one another and which also develop the invention independently of one another. Therefore, the disclosure should also include combinations of the features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by other features of the invention already described.

In the figures, identical reference symbols designate functionally identical elements.

In 1 is schematically a first laminate 10 for providing or producing a flexible printed circuit board 12 (see 4 ) is shown. For the sake of simplicity, the following illustration will be based on the 4 shown flexible circuit board 12, which is designed as a single-layer circuit board. Accordingly, a conductor track unit of the single-layer flexible circuit board 12 is formed by exactly one conductor track layer 14. With regard to the flexible and single-layer circuit board 12 shown here (compare for example 4 and 6 ), the terms conductor track unit and conductor track layer 14 can therefore be used synonymously.

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 several conductor track layers.

The flexible circuit board 12 can be bent or twisted without any problem, without such bending of the circuit board 12 causing damage to the circuit board 12. This allows for a particularly high degree of freedom in the design and use of the flexible or bendable circuit board 12. In particular, the flexible circuit board 12 is therefore suitable for arrangement in limited installation spaces, which presents greater difficulties with rigid, i.e. non-flexible circuit boards.

For reasons of simplicity, the flexible printed circuit board 12 can also be referred to simply as printed circuit board 12. The terms flexible printed circuit board 12 and circuit board 12 are therefore to be understood as synonymous in this case.

According to 1 In addition to the conductor track unit provided in this case by exactly one conductor track layer 14, the first laminate 10 comprises a first carrier film 16 which is made of an electrically insulating material. A first adhesive layer 18, which is part of 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 connected to the first carrier film 16 by means of the first adhesive layer 18.

In the finished flexible printed circuit board 12 (compare approximately 4 ), a first outer side 20 of the flexible 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 circuit board 12 faces an environment 22 of the circuit board 12.

As from 4 As can be seen, the flexible circuit board 12 comprises a second laminate 24, which in 2 shown schematically. 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 2 ). According to 2 the second laminate 24 is formed by the second carrier film 26 and the second adhesive layer 28.

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 4 ).

According to 4 Thus, the second adhesive layer 28, which is associated with the second laminate 24, ensures a connection of the first laminate 10 to the second laminate 24. The conductor track layer 14 is arranged in a sandwich-like manner between the first adhesive layer 18 and the second adhesive layer 28.

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 4 ). Accordingly, the second outer side 34 faces the environment 22 of the flexible circuit board 12 in the same way as the first outer side 20 of the flexible circuit board 12.

For the production of 4 In the flexible printed circuit board 12 shown, the first laminate 10 is processed in order 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 formed, for example, from copper and/or aluminum. The conductor tracks 36 produced are shown schematically in 3 illustrated, whereby for reasons of clarity only some of the conductor tracks 36 are provided with a reference number.

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 processing can be achieved, for example, by etching, milling or other abrasive processes.

In 3 It is schematically illustrated that gaps or through-openings 38 are formed by removing the conductor track material in the conductor track layer 14. These through-openings 38, which extend to the first adhesive layer 18, are also shown in 3 For reasons of clarity, only some are provided with a reference symbol.

In a 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 made 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 borne in mind that the adhesive used for the adhesive layers 18, 28 or adhesive layers is comparatively expensive.

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

The second adhesive layer 28, which is associated with the second laminate 24, serves according to 4 in particular the joining of the two laminates 10, 24. Accordingly, the second adhesive layer 28 ensures that in the finished flexible printed circuit board 12 (see 4 ) hold the two laminates 10, 24 together well. The second adhesive layer 28 also serves to fill the gaps or openings 38, which result from the fact that parts of the previously continuous conductor layer 14 (see 1 ) removed or removed to form the conductor tracks 36 (see 3 ).

Depending on the thickness of the conductor track unit, in this case just the 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.

In the present case, however, the first adhesive layer 18 has a significantly reduced thickness 40. For example, it can be provided that the thickness 40 of the first adhesive layer 18 is only about 5 µm instead of 50 µm.

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, savings of EUR 3 to EUR 5 per square meter of the first laminate 10 are possible by reducing the thickness 40 of the first adhesive layer 18 in this way. This is advantageous in order to realize a particularly cost-effective production of the flexible printed circuit board 12.

In 4 It is shown how the two laminates 10, 24 are connected to each other by means of the second adhesive layer 28. Adhesive of the second adhesive layer 28 is introduced into the through-openings 38, which are in 3 In particular, the through-openings 38 are completely filled with adhesive (see 4 ). The adhesive present in the area 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 through-openings 38 is at least predominantly provided by the second adhesive layer 28.

Filling the through-openings 38 with the adhesive without gaps is particularly advantageous in order to prevent dirt and/or water, in particular water containing at least one electrolyte, from entering the area of the conductor track layer 14. It is therefore advantageous to make the thickness 42 of the second adhesive layer 28 greater than a thickness 44 of the conductor track layer 14. This is because it is 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.

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

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

When designing the flexible circuit board 12 according to 4 a distance from the first side 30 of the conductor track layer 14 to the first outer side 20 of the circuit board 12 is smaller 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 smaller than is the case for the thicker second adhesive layer 28 and the second carrier film 26.

This can in principle be counteracted when using the circuit board 12 by arranging or aligning the circuit board 12 in a suitable manner. For example, the flexible circuit board 12 can be rotated in such a way that the side which is to have a higher resistance with regard to electromagnetic compatibility and/or with regard to electrical safety faces the side on which a higher load in this regard is to be expected.

However, it can also be advantageous that the flexible printed circuit board 12 has essentially equally good resistance with regard to electromagnetic compatibility and/or electrical safety both towards the first outer side 20 and towards the second outer side 34. For this purpose, as shown in 6 As shown schematically, the first carrier film 16 is formed with the greater thickness 46 than the second carrier film 26.

If in addition in the direction of the second outer side 34 of the 6 shown circuit board 12, an even higher resistance with regard to electromagnetic compatibility and/or an even further improved electrical insulation is to be achieved (for example in order to achieve a correspondingly high electrical safety and/or high voltage voltage 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.

According to the variant 5 and 6 is further based on the knowledge that the respective carrier film 16, 26 is significantly cheaper 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).

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.

In 7 A control device 50 is shown in a highly schematic manner, which has the at least one flexible circuit board 12.

In 7 For reasons of clarity, it is not shown separately how the flexible 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 circuit board 12.

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

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

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. 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

• JP 2018041961 A [0002]
• US 20210084768 A1 [0003]

Claims (10)

Flexible 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 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 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 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). 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). Flexible printed circuit board according to Claim 2 , characterized in that the passage openings (38) are completely filled with adhesive which is at least predominantly provided by the second adhesive layer (28). 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). 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). 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 µm, in particular less than 10 µm, wherein the first adhesive layer (18) in particular has a thickness (40) of approximately 5 µm. 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. 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. Control device, in particular for a motor vehicle, with at least one flexible circuit board (12) according to one of the preceding claims. Method for producing a flexible 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 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 a second carrier film (26) is used to produce the flexible circuit board (12), 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 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 (28).