JP2006179589A - Multilayer flexible wiring board, its manufacturing method, and connection method of multilayer flexible wiring with circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent problems such as peeling of an interlayer adhesive layer when connecting a multilayer flexible wiring board having a structure where a plurality of circuit boards are stuck with an interlayer adhesive to another circuit board via an anisotropic conductive film. <P>SOLUTION: A multilayer flexible wiring board is made ino a structure not providing the interlayer adhesive layer 30 (i.e., a structure providing a portion 29 where the interlayer adhesive layer is not provided) on a connection part (connection area with another circuit board 50) 40 of the multilayer flexible wiring board. There is hereby eliminated the possibility that the interlayer adhesive layer 30 is peeled owing to heat upon bonding to realize highly reliable connection. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a multilayer flexible wiring board, a manufacturing method thereof, and a method of connecting a multilayer flexible wiring to a circuit board.

  As a method of connecting a flexible substrate (a wiring substrate in which a wiring pattern is formed on a flexible material such as a polyimide film) mounted on a small and lightweight device such as a mobile phone terminal to another substrate, A method of connecting using a connector is widely used (see, for example, Patent Document 1).

  Use of the connector has an advantage that the board can be easily replaced. However, the connector housing is thick and has a predetermined weight, which hinders the thickness and weight of the wiring board from being reduced.

  Therefore, recently, there is a tendency to use a method of directly connecting terminals on two substrates (a flexible substrate and another flexible substrate, a printed wiring substrate, or a rigid substrate) without using a connector.

  As a method for connecting terminals without using a connector, recently, a method using an anisotropic conductive adhesive (anisotropic conductive film) as a thermocompression bonding adhesive is used.

  An anisotropic conductive adhesive has a dual function of functioning as a conductor in the vertical direction (crimping direction) and functioning as an insulator in the horizontal direction, and also functions as an adhesive for connecting substrates together. I also have.

  By using this anisotropic conductive adhesive, electrical connection between wirings and bonding between substrates can be realized at once, and the connection process is simplified. An example using an anisotropic conductive adhesive is described in Patent Document 2.

  A multilayer flexible wiring board formed by laminating a plurality of flexible wiring boards with an adhesive (interlayer adhesive) and laminating each flexible circuit board has also been proposed (Patent Document 3).

JP 2002-298958 A

JP 2000-68624 A

JP 2002-43750 A

  As electronic devices become smaller and lighter, it becomes necessary to mount electronic components at a higher density, and in the future, the need for multilayer flexible wiring boards will increase, and many layers such as four layers, six layers, and eight layers will be formed. The appearance of a multilayer flexible wiring board is expected.

  When this multilayer flexible wiring board is connected to another circuit board (flexible board, printed wiring board, or rigid wiring board) via an anisotropic conductive adhesive, the connection portion (the outermost part) with the other circuit board is used. The area where the external connection terminals on the back surface of the lower circuit board are arranged is locally and vertically pressed while being heated (that is, located on the opposite side of the above-mentioned connection portion of the uppermost circuit board) It is necessary to heat and press the bonding tool from the surface.

  As the number of circuit board layers of the multilayer flexible wiring board increases, it is necessary to apply a stronger pressure at a higher temperature so that sufficient heat and pressure reach the connection portion. In other words, the heating temperature in the connection process is determined by the material of the connection part (material of the external connection terminal), etc., but the bonding tool is on the opposite side of the connection part (position away from the connection part). As a result, higher temperature and pressure than usual are applied to the interlayer adhesive on the connecting portion.

  There is a limit to the heat resistance temperature of the interlayer adhesive, and the interlayer adhesive may be weakened by moisture absorption. That is, there is a characteristic deterioration factor due to heat resistance and hygroscopicity.

  Therefore, the interlayer adhesive may be peeled off from the surface of the circuit board of each layer or partly damaged (crack generation) due to heat at the time of bonding. In some cases, the connection (adhesiveness) between circuit boards may be reduced.

  In addition, there are not a few problems of a decrease in connection strength due to the fact that vertical pressure and sufficient heat are not transmitted to the connection part with other circuit boards.

  That is, when the number of layers of the multilayer flexible wiring board is increased, the heat resistance of the interlayer adhesive is low, and thus, for example, the adhesive peels off due to heat at the time of bonding. There is a concern that this may decrease or the bonding strength with other circuit boards may decrease. In particular, when moisture is absorbed, a popcorn phenomenon occurs at the time of heating and pressurization, and the connection portion 40 is affected.

  The present invention has been made in view of the above circumstances, and a multilayer flexible wiring board having a structure in which a plurality of flexible circuit boards are bonded together with an interlayer adhesive is replaced with another via a thermocompression-type conductive adhesive. An object of the present invention is to provide a multilayer flexible wiring board that can solve the problem that the interlayer adhesive layer is peeled off by heat when connecting to the circuit board, and can realize a highly reliable connection.

  In the multilayer flexible wiring board of the present invention, first and second circuit boards each having a predetermined wiring pattern formed on one or both sides of an insulating film-like substrate are bonded together via an interlayer adhesive layer. A multilayer flexible wiring board having a connection portion formed on one side of the first circuit board and provided with an external connection terminal for connection to another circuit board. The interlayer adhesive layer is provided so as not to overlap the connecting portion.

  In order to prevent problems such as peeling of the interlayer adhesive layer that occurs when connecting a multilayer flexible wiring board to another circuit board, the interlayer adhesion is avoided so as to avoid the connection part connected to the other circuit board. An agent layer is provided. Since there is no interlayer adhesive layer in the area where pressure is applied by the bonding tool, problems such as peeling of the interlayer adhesive layer do not occur, and the connection (adhesion) strength between the circuit boards of each layer does not decrease. Further, since sufficient pressure (and heat) is applied from the bonding tool to the connection area with other circuit boards, there is no problem of a decrease in bonding strength. Therefore, a multilayer flexible wiring board to which a large number of layers of circuit boards are bonded is easily connected to other circuit boards using a thermocompression-type conductive adhesive (anisotropic conductive adhesive). be able to. Therefore, it is possible to manufacture a high-density and ultra-small electronic component module that can be mounted on a device that is required to be small and light, such as a mobile phone terminal, without causing a reduction in reliability. be able to. Furthermore, by removing the interlayer adhesive around the circuit board, in the inspection process at the time of manufacture, the circuit board is visually inspected for the occurrence of misalignment (positional deviation) of each circuit board and the occurrence of foreign matter biting. There is also a secondary effect that it is possible.

  In the multilayer flexible wiring board of the present invention, the second circuit board also includes a circuit board provided so as not to overlap with the connection portion.

  In addition to the interlayer adhesive layer, the upper circuit board itself is disposed so as to avoid the connection and connection with other circuit boards. At the time of bonding, a bonding tool can be pressed against the surface on the lowermost circuit board, and pressure (and heat) can be applied directly to the connecting portion, so that stable bonding strength can be ensured.

  In the multilayer flexible wiring board of the present invention, in order to avoid a complete hollow state between the film-like base material of the first circuit board and the film-like base material of the second circuit board. In addition, the layer where the interlayer adhesive layer is left at a position having a partial overlap with the connection portion is included.

  If the interlayer adhesive is partially removed, a hollow structure is formed in the multilayer flexible wiring board as a result, and it cannot be said that the circuit board of each layer is likely to be deformed when handling the multilayer flexible wiring board. . Similarly, it cannot be said that deformation of the circuit board is likely to occur due to heat during reflow processing for surface mounting. Considering this point in particular, avoiding the part where the bonding tool comes into contact, partially leaving an interlayer adhesive layer, and by partially leaving the interlayer adhesive layer, the substrate of each circuit board (polyimide or epoxy) The film-like base material is supported, the structural stability is enhanced, and the deformation of the circuit board of each layer is suppressed.

  Moreover, in the multilayer flexible wiring board of this invention, the said film-form base material contains what is a polyimide base material.

  Using a polyimide base material with the characteristics of high heat resistance, low stress, and high elasticity, an electronic component module is formed using a thin multilayer flexible wiring board suitable for mounting on small and light equipment.

  In the method for producing a multilayer flexible substrate of the present invention, the first and second circuit boards having a predetermined wiring pattern formed on one side or both sides of an insulating film-like substrate are bonded to each other with an interlayer adhesive layer. And the interlayer adhesive layer is formed on the first circuit board, and external connection terminals for connection to other circuit boards are disposed. It is arranged in an area excluding the connection part. That is, a plurality of flexible boards are bonded together via an interlayer adhesive layer arranged so as to avoid overlapping with external connection terminals used for connection to other circuit boards.

  For example, a thermosetting sheet-like (film-like) interlayer adhesive is used as an interlayer adhesive, and after the interlayer adhesive is provided between the circuit boards of each layer, both circuit boards are pasted by heating and pressing. It is to match. By adjusting the position where the sheet-like interlayer adhesive is placed (or adjusting the size when processing the sheet), it is possible to prevent the interlayer adhesive layer from being present in the area where pressure is applied by the bonding tool. Easily possible. When an interlayer adhesive applied by spin coating is used, for example, the application position is adjusted, or a dam (damping portion) is formed at a predetermined position on the surface of the circuit board of each layer, and the interlayer adhesive is used. By devising such as preventing the outflow of the film, it is possible to intentionally create a region where the interlayer adhesive layer does not exist.

The method for connecting the multilayer flexible wiring board of the present invention to another circuit board includes a step of facing the external connection terminal of the multilayer flexible wiring board to an electrode terminal formed on the other circuit board, and heating. And applying a load with a bonding tool from the surface opposite to the connection portion of the multilayer flexible wiring board and connecting the external connection terminal to the electrode terminal on the other circuit board. Features.
In the connecting method of the present invention, the connecting step includes a method in which the step of connecting is thermocompression bonded through an anisotropic conductive material.

  According to the method of the present invention, the interlayer adhesive in the connection portion with the other circuit board in the multilayer flexible wiring board is intentionally removed in the production process of the multilayer flexible wiring board. Therefore, problems such as peeling of the interlayer adhesive layer from the circuit board do not occur, and connection failure between the circuit boards does not occur. In addition, a simple method using an anisotropic conductive adhesive can be used to connect to other circuit boards, reducing the thickness (miniaturization) of electronic component modules without worrying about lowering reliability. Can be realized.

  According to the present invention, during face-down bonding of a multilayer flexible wiring board, problems such as peeling of the interlayer adhesive layer from the circuit board due to heat and stress do not occur, and connection (adhesion) failures between the circuit boards do not occur. .

  In addition, a simple method using an anisotropic conductive adhesive can be used to connect to other circuit boards, reducing the thickness (miniaturization) of electronic component modules without worrying about lowering reliability. Can be realized.

  Furthermore, by removing the interlayer adhesive around the circuit board, in the inspection process at the time of manufacture, the circuit board is visually inspected for the occurrence of misalignment (positional deviation) of each circuit board and the occurrence of foreign matter biting. It is also possible.

  Before describing embodiments of the present invention, a basic structure of a multilayer printed wiring board and a method for connecting to another circuit board using a thermocompression-type interlayer adhesive (anisotropic conductive adhesive) will be described. To do.

  As shown in FIG. 6, in the multilayer printed wiring board used in the present invention, the first and second circuit boards A and B are made of an interlayer adhesive (for example, epoxy resin, polyimide resin, silicone resin, or cyanoate ester). It has a multilayer structure bonded (bonded) with a resin (adhesive mainly composed of resin) 30.

  The first circuit board A has a predetermined pattern made of copper foil on both surfaces of a base material 10 made of an organic insulating material such as a thin film-like polyimide resin (or epoxy resin) via an adhesive (12, 14). The conductor layers (18a, 18b and 16) are formed.

  Here, in particular, the polyimide base material has characteristics of high heat resistance, low stress, and high elasticity, and thus is useful for forming an electronic component module using a thin multilayer flexible wiring board that is suitable for mounting a small and lightweight device.

  In addition, a part of the conductor layer 18b provided on the lower surface of the first circuit board A (portion surrounded by a dotted line in FIG. 6) functions as an external connection terminal. That is, the external connection terminal is used for connection with the electrode terminal 52 provided on the surface of another circuit board 50.

  Further, in this specification, a part of the conductor layer 18b provided on the lower surface of the first circuit board A (portion 40 surrounded by a dotted line in FIG. 6) is referred to as “with other circuit board. This is referred to as a “connection section or connection area”.

  Similarly, the second circuit board B is formed of a thin film-like organic insulating material made of a thin film-like polyimide resin (or epoxy resin) on both surfaces of the base material 20 with an adhesive (22, 24) interposed therebetween. Thus, conductor layers (26 and 28) having a predetermined pattern made of copper foil are formed.

  Bonding (bonding) of the first circuit boards (A, B) is performed as follows.

  That is, a sheet-like uncured interlayer adhesive layer (thermosetting adhesive layer) 30 is attached to one of the first and second circuit boards (A, B), and then the first The first and second circuit boards (A, B) are bonded to each other and heated while being pressed to thermally cure the interlayer adhesive layer 30. Thereby, both the substrates (A, B) are bonded.

  As a method of forming the interlayer adhesive layer 30, instead of using a sheet-like thermosetting adhesive, a thermosetting fluid adhesive is spin-coated with a spinner, and then heat is applied. It is also possible to adopt a method of curing.

  Next, a method of connecting a multilayer printed wiring board (A, B, 30 etc.) with another circuit board (another flexible wiring board, printed wiring board or rigid board) 50 will be described.

  As shown in FIG. 6, the external connection terminal on the multilayer flexible wiring board side (that is, the part included in the connection part 42 surrounded by the dotted line in the conductor layer 18 b) and the other circuit board 50 are provided. The connection with the electrode terminal 52 is performed by so-called face-down bonding using an anisotropic conductive adhesive (anisotropic conductive film) 42 which is a thermocompression bonding adhesive.

  Strictly speaking, the external connection terminal on the multilayer flexible wiring board side is a portion included in the connection portion 42 surrounded by a dotted line in the conductor layer 18b as described above. Therefore, it is described as “external connection terminal 18b”.

  When connecting using the anisotropic conductive adhesive 42, as shown in the drawing, a buffer sheet (made of Teflon or the like) 62 is interposed on the surface of the second circuit board B located above the connection portion 42. Then, the bonding tool 60 is pressed to heat and pressurize.

  As a result, the anisotropic conductive adhesive 42 is crushed and conducted in the vertical direction, and is cured by heating, so that electrical conduction and connection between both substrates are performed simultaneously.

  However, since the heat resistant temperature of the interlayer adhesive 30 is low, the interlayer adhesive may be partially peeled off or damaged during the heating and pressurizing treatment by the bonding tool 60. This leads to a decrease in the reliability of the substrate. In particular, when moisture is absorbed, a popcorn phenomenon occurs at the time of heating and pressurization, and the connection portion 40 is affected.

  Therefore, in the present invention, the portion of the interlayer adhesive that is likely to be deteriorated in reliability is removed in advance (that is, the interlayer adhesive is not intentionally provided), thereby reducing the reliability. Is solved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)

  FIG. 1 is a cross-sectional view showing a configuration of a multilayer flexible wiring board according to Embodiment 1 of the present invention and a connection structure with another circuit board. In FIG. 1, parts common to those in FIG. 6 are denoted by common reference numerals.

  As shown in the drawing, in this embodiment, the interlayer adhesive layer 30 is not provided in a portion located immediately above the connection portion 40 (portion surrounded by a dotted line) of the multilayer flexible wiring board. In FIG. 1, a reference numeral 29 is attached to a portion where the interlayer adhesive layer 30 is not provided.

  As described above, the interlayer adhesive layer 30 is provided so as to avoid the area 40 connected to the other circuit board 50 (that is, the interlayer adhesive layer is previously formed on the connection area 40 with the other circuit board 50. By adopting a structure that is removed), when the multilayer flexible wiring board is connected to another circuit board 50, problems such as peeling of the interlayer adhesive layer 30 due to heat or bonding stress do not occur. . Therefore, the connection (adhesion) strength between the circuit boards (10, 20) of each layer does not decrease.

  FIG. 2 is a cross-sectional view for explaining a process of connecting the multilayer flexible wiring board of FIG. 1 to another circuit board using a bonding tool.

  As shown in FIG. 1, the base material (10, 20) made of an organic insulating material (polyimide or the like) is not supported by other members above and below the portion 29 where the interlayer adhesive layer 30 does not exist. It is in a floating state (hollow state).

  Therefore, when it is pressed by the bonding tool 60, it is crushed without being repelled, resulting in a state as shown in FIG. Then, it is uniformly and vertically pressurized through a buffer sheet 62 made of Teflon or the like, so that the external connection terminal 18b of the multilayer flexible wiring board becomes anisotropic with the electrode terminal 52 on the other circuit board 50. Connection is made via a conductive adhesive 42. At this time, since a sufficient load (and heat) is applied from the bonding tool 60, there is no problem of reduction in bonding strength.

  Therefore, a multilayer flexible wiring board to which a large number of layers of circuit boards are bonded can also be easily connected to other circuit boards 50 using a thermocompression-type conductive adhesive (anisotropic conductive adhesive) 42. Can be taken.

  Therefore, it is possible to manufacture a high-density and ultra-small electronic component module that can be mounted on a device that is required to be small and light, such as a mobile phone terminal, without causing a reduction in reliability. be able to.

  Furthermore, by removing the interlayer adhesive around the circuit board, in the inspection process at the time of manufacture, the circuit board is visually inspected for the occurrence of misalignment (positional deviation) of each circuit board and the occurrence of foreign matter biting. There is also a secondary effect that it is possible.

  FIG. 3 is a plan view (bottom view) showing an example of a layout pattern of external connection terminals in the connection portion 40 of the first circuit board (reference symbol A) shown in FIG.

  As shown in the figure, the connection portion (connection area) 40 is provided on the lower surface of the end portion of the first circuit board A. The connection portion (connection area) 40 has a plurality of external connections at predetermined intervals. A terminal (18b) is provided.

  When manufacturing the multilayer flexible substrate of the present invention, the interlayer adhesive layer 30 is provided so as to avoid overlapping with the connection portion 40 in which the external connection terminal 18b used for connection to the other circuit board 50 is disposed, A plurality of flexible circuit boards (A, B) are bonded together.

  For example, a thermosetting sheet-like (film-like) interlayer adhesive is used as the interlayer adhesive 30, and the sheet-like interlayer adhesive is provided between the circuit boards (A, B), and then heated. Pressure is applied to bond both circuit boards (A, B).

  At this time, by adjusting the position where the sheet-like interlayer adhesive 30 is arranged (or adjusting the size when processing the sheet), the interlayer adhesive layer does not exist in the region where the pressure is applied by the bonding tool. It is possible to

  Further, when using the interlayer adhesive 30 applied by spin coating, for example, the application position is adjusted, or a dam (damping portion) is formed at a predetermined position on the surface of the circuit board of each layer, and the interlayer adhesion is performed. A region where the interlayer adhesive layer 30 is not present can be intentionally created by a device such as preventing the outflow of the agent.

  Further, when the external connection terminal 18b is connected to another circuit board 50 via the anisotropic conductive adhesive 42, the interlayer adhesive layer 30 of the connection portion 40 is intentionally used in the production process of the multilayer flexible wiring board. Since it has been removed, there is no problem such as peeling of the interlayer adhesive layer from the circuit board due to heat or stress during bonding, and even if moisture is absorbed, the popcorn phenomenon can be prevented during heating and pressurization. 40 is not adversely affected, and the occurrence of poor connection between the circuit boards can be suppressed.

Further, a load (and heat) can be effectively applied from the bonding tool 60 to the connection portion 40, and the connection with the other circuit board 50 can be performed using a simple method using the anisotropic conductive adhesive 42. realizable. Since it is not necessary to use a connector, the electronic component module can be made thin (downsized).
(Embodiment 2)

  FIG. 4 is a cross-sectional view showing a configuration of a multilayer flexible wiring board according to Embodiment 2 of the present invention and a connection structure with another circuit board. In FIG. 4, the same reference numerals are given to portions common to the above-described drawings.

  In the present embodiment, not only the interlayer adhesive layer 30 but also the upper circuit board (B) itself is arranged so as to avoid the connection portion (connection area) 40 with the other circuit board 50. That is, the second circuit board (B) does not exist on the connection part 40.

  With such a structure, during bonding, the bonding tool 60 is pressed against the surface position corresponding to the connection portion 40 of the lowermost circuit board (A), and pressure (and heat) is directly applied to the connection portion 40. Therefore, stable bonding strength can be ensured. In particular, even if moisture is absorbed, the popcorn phenomenon does not occur during heating and pressurization, and the influence on the connecting portion 40 is reduced.

Further, when the bonding tool 60 is pressed, it is not necessary to bend the base materials 10 and 20 of the circuit board, so that the bonding tool 60 can be positioned accurately.
(Embodiment 3)

  FIG. 5: is sectional drawing which shows the structure of the multilayer flexible wiring board concerning Embodiment 3 of this invention, and a connection structure with another circuit board. In FIG. 5, the same reference numerals are given to the portions common to the above-mentioned drawings.

  When the interlayer adhesive layer 30 is partially removed, a hollow structure is formed in the multilayer flexible wiring board, and the circuit boards (A, B) of each layer are likely to be deformed when handling the multilayer flexible wiring board. It cannot be said that there will be no case. Similarly, it cannot be said that deformation of each circuit board (A, B) is likely to occur due to heat during reflow processing for surface mounting.

  In the present embodiment, in consideration of this point in particular, the interlayer adhesive layer 30 is partially left away from the portion where the bonding tool 60 contacts, and the circuit of each layer is formed by the partially left interlayer adhesive layer 30. The substrate base material (film base material made of polyimide or epoxy) 10 and 20 is supported to enhance the structural stability. Thereby, deformation of each circuit board (A, B) is suppressed.

  As described above, according to the present invention, during the face-down bonding of a multilayer flexible wiring board, problems such as peeling of the interlayer adhesive layer from the circuit board due to heat and stress do not occur, and the reliability of the flexible wiring board is maintained. Even when moisture is absorbed, the popcorn phenomenon does not occur during heating and pressurization, the connection part 40 can be maintained well, and the connection (adhesion) between the circuit boards of the connection part is generated. Can be prevented.

  In addition, a simple method using an anisotropic conductive adhesive can be used to connect to other circuit boards, reducing the thickness (miniaturization) of electronic component modules without worrying about lowering reliability. Can be realized.

  Furthermore, by removing the interlayer adhesive around the circuit board, in the inspection process at the time of manufacture, the circuit board is visually inspected for the occurrence of misalignment (positional deviation) of each circuit board and the occurrence of foreign matter biting. It is also possible.

  The present invention has an effect of reliably avoiding the problem that the interlayer adhesive layer is peeled off when the multilayer flexible wiring board is connected to another circuit board. It is useful for use in multilayer flexible wiring boards mounted on equipment.

Sectional drawing which shows the structure of the multilayer flexible wiring board concerning Embodiment 1 of this invention, and a connection structure with another circuit board Sectional drawing which shows the structure of the multilayer flexible wiring board concerning Embodiment 2 of this invention, and a connection structure with another circuit board The top view (bottom view) which shows the example of the layout pattern of the external connection terminal in the connection part 40 of the 1st circuit board (reference symbol A) shown by FIG. Sectional drawing which shows the structure of the multilayer flexible wiring board concerning Embodiment 2 of this invention, and a connection structure with another circuit board Sectional drawing which shows the structure of the multilayer flexible wiring board concerning Embodiment 3 of this invention, and a connection structure with another circuit board Diagram for explaining basic structure of multilayer printed wiring board and connection method to other circuit boards using thermo-compression type interlayer adhesive (anisotropic conductive adhesive)

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,20 Film-like base material 12,14,18,22,24,26 Conductor layer which consists of copper foil 18b External connection terminal 29 The part which an interlayer adhesive layer does not exist 30 Interlayer adhesive (interlayer adhesive layer)
40 Connection (connection area)
42 Anisotropic conductive adhesive (anisotropic conductive film)
50 Other circuit board 52 Electrode terminal 60 Bonding tool 62 Buffer sheet A 1st flexible circuit board B 2nd flexible circuit board

Claims (7)

The first and second circuit boards in which a predetermined wiring pattern is formed on one side or both sides of an insulating film-like base material are formed by bonding together via an interlayer adhesive layer,
A multilayer flexible wiring board having a connection portion formed on one side of the first circuit board and provided with an external connection terminal for connection to another circuit board,
The multilayer flexible wiring board, wherein the interlayer adhesive layer is provided so as not to overlap with the connection portion. The multilayer flexible wiring board according to claim 1,
The multilayer flexible wiring board, wherein the second circuit board is provided so as not to overlap with the connection portion. The multilayer flexible wiring board according to claim 1,
A position having a partial overlap with the connecting portion in order to avoid a complete hollow state between the film-like base material of the first circuit board and the film-like base material of the second circuit board A multilayer flexible wiring board, wherein the interlayer adhesive layer is left. A multilayer flexible wiring board according to any one of claims 1 to 3,
The multilayer flexible wiring board, wherein the film-like substrate is a polyimide substrate. Method of manufacturing a multilayer flexible wiring board by bonding together first and second circuit boards each having a predetermined wiring pattern formed on one or both sides of an insulating film-like substrate via an interlayer adhesive layer Because
The multi-layer flexible wiring, wherein the interlayer adhesive layer is disposed on a region excluding a connection portion formed on the first circuit board and provided with an external connection terminal for connection to another circuit board. A method for manufacturing a substrate. The step of causing the external connection terminal of the multilayer flexible wiring board according to any one of claims 1 to 4 to face an electrode terminal formed on another circuit board;
Applying a load by a bonding tool from the surface opposite to the connection portion of the multilayer flexible wiring board while heating, connecting the external connection terminal to the electrode terminal on the other circuit board,
A method for connecting a multilayer flexible wiring board to another circuit board, comprising: The connection method according to claim 6, comprising:
The connecting method is characterized in that the connecting step is thermocompression bonding through an anisotropic conductive material.

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