JP2005303274A - Flexible substrate, multilayer flexible substrate, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-density, thin flexible substrate that is excellent in terms of the flexing life. <P>SOLUTION: A method of manufacturing a flexible substrate comprises: a process (a) of forming an insulating resin layer on the front face of a film and the rear face opposite to the front face, wherein each insulating resin layer is thicker than the film; a process (b) of forming a through hole in the film and the insulating resin layers; a process (c) of filling the through hole with a conductive resin composition; and a process (d) of embedding a wiring pattern into each of the insulating resin layers in such a manner that the wiring pattern is electrically connected to the conductive resin composition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flexible substrate, and more particularly to a flexible substrate and a multilayer flexible substrate suitable for mounting, and a method for manufacturing the same.

  A flexible substrate (FPC: Flexible Printed Circuit) has a basic structure of a combination of a conductor and a heat-resistant polymer film. A flexible substrate in which a conductor is provided only on one side of a heat-resistant polymer film is called a single-sided flexible substrate, and a flexible substrate in which conductors are provided on both sides of a heat-resistant polymer film is called a double-sided flexible substrate. ing.

  A copper clad laminate (CCL: Copper Clad Laminate) is generally used for manufacturing a single-sided flexible substrate. There are two types of copper-clad laminates, one is a three-layer CCL in which a copper foil is bonded to a heat-resistant polymer film via an adhesive, and the other is without an adhesive, A two-layer CCL in which a copper foil is bonded to a heat-resistant polymer film. Such a two-layer CCL or three-layer CCL is manufactured by, for example, a laminating method, a casting method, or a sputter plating method. By applying the subtractive method to the two-layer CCL or the three-layer CCL, a wiring pattern is formed, and a single-sided flexible substrate is manufactured.

  A multilayer flexible substrate is a substrate obtained by coating a single-sided flexible substrate or a double-sided flexible substrate with a film and an insulating resin layer. In a multilayer flexible board, a metal is provided on the inner wall of the through-hole hole by a plating method to form a through-hole conductor (ie, via), and the wiring patterns of each layer of the multilayer flexible board are electrically connected. Yes.

Since such a flexible substrate or a multilayer flexible substrate is foldable, it is effectively used for a spatially narrow mounting region. For example, a flexible substrate or a multilayer flexible substrate is mounted not only around a small liquid crystal such as a camera, a mobile phone, or a portable PC, but also in a narrow space such as a PC peripheral device such as a printer or HDD. In recent years, as electronic devices are further reduced in size, weight, and thickness, semiconductors are required to have higher density and higher functionality. Accordingly, there is a demand for further reduction in thickness and density of a flexible substrate on which a semiconductor or a passive element is mounted. For example, with the increase in color and high definition of liquid crystal displays, an increase in the number of output terminals and a reduction in the pad pitch of driver ICs are required.
JP 11-157002 A (page 3) JP 2004-31588 A (page 2) JP-A-4-107896 (page 1-2) Japanese Patent Laid-Open No. 2-180679 (first page) JP 10-256700 A (page 2-3) JP 2000-77800 A (first page) JP2003-224366

  The conventional flexible substrate (or multilayer flexible substrate) and the manufacturing method thereof have the following problems (I) to (VII).

  (I) In order to further reduce the thickness and density of the flexible substrate, it is important to make the wiring pattern finer. However, the thickness of the copper foil used for the flexible substrate is usually 18 to 35 μm, and the subtractive method has a limit in miniaturizing the line width of the wiring pattern. That is, in a subtractive method such as chemical etching, it is difficult to form a wiring pattern having a line width of 75 μm or less from a copper foil having a thickness of about 18 to 35 μm. Foil must be used.

  (II) If a subtractive method such as chemical etching is used to form the wiring pattern, the etching solution remains between the wiring patterns, which may adversely affect the insulation reliability. Further, in the subtractive method, the resulting wiring pattern protrudes from the substrate surface, and the flatness of the substrate is reduced. Accordingly, not only is it difficult to mount the bumps formed on the semiconductor chip on the wiring pattern, but there is a possibility that the bumps move between the wiring patterns after mounting to cause a short circuit. Furthermore, the protruding structure of the wiring pattern itself can be a factor that hinders the resin sealing performed later.

  (III) A through-hole conductor is generally used for wiring connection between layers. In such wiring connection, if the number of stacked layers increases and the number of through holes increases, it becomes difficult to secure a sufficient space for wiring. For this reason, multilayering is generally performed by laminating a single-sided flexible substrate or a double-sided flexible substrate with through-hole conductors. In this case, the through-hole conductor is filled with a metal paste, but the metal paste inevitably contains a liquid resin or solvent in order to improve the fillability and printability in the through-hole. The resistance value is higher than that of a circuit formed by copper plating. Since the through-hole filled with the metal paste becomes difficult to fill with the metal paste as its diameter decreases, it is necessary to adjust the viscosity and fluidity of the metal paste by adding a large amount of solvent. Then, since the solvent in the metal paste evaporates after filling, pores are generated in the evaporated portion. Therefore, due to such pores, the resistance of the through-hole conductor itself increases.

  (IV) In forming the through-hole conductor, holes are formed in the adhesive layer and the film by laser processing. Although the adhesive layer can be easily laser processed, it is difficult to perform laser processing on a thick film used in a conventional flexible substrate. Specifically, in the conventional organic film, the shape of the processed hole is not circular due to the processing heat generated by the laser, and burrs may occur. Further, since the emission diameter is smaller than the laser incident diameter, there is a problem that it is difficult to fill the obtained hole with a metal paste.

  (V) In order to make the flexible substrate thinner and higher in density, it is important not only to make the wiring pattern and through-hole conductor fine, but also to make the circuit components connected to the wiring pattern thinner. However, in general, passive elements such as inductors, capacitors, and resistors are mounted in a state of protruding on the substrate surface, and there is a problem that the substrate becomes thick as a whole.

  (VI) In the conventional flexible substrate, the passive element or the active element is generally formed on the exposed surface of the flexible substrate, and the passive element or the active element is not built in the flexible substrate. Therefore, in a multilayer flexible substrate formed from such a flexible substrate, the passive element or active element on the exposed surface is multilayered, and the passive element or active element is placed between the wiring patterns between the layers. It is the structure formed. For this reason, such a multilayer flexible substrate has a problem that a wiring allowable region is narrow.

  (VII) Since a flexible substrate is used by being bent in a narrow space, it is required to have a good bending life (or sliding flexibility). Therefore, for example, the two-layer CCL needs to have a sufficient bending life, and the adhesion strength between the polyimide film and the copper foil is required to be high. The three-layer CCL is required to have not only high adhesion strength between the polyimide film and the copper foil but also high adhesion strength between them and the adhesive composition.

  Note that the conventional wiring pattern formed by etching exposes the wiring pattern on the substrate surface, and micro-cracks tend to occur in the wiring pattern due to the bending of the flexible substrate, which is not always satisfactory in terms of the bending life. It wasn't.

  In view of the above problems or problems (I) to (VII) of the prior art, an object of the present invention is to provide a highly reliable and high-density thin flexible substrate, which is excellent in terms of flex life. Is to provide. Moreover, the objective of this invention also includes providing the manufacturing method of such a flexible substrate.

The present invention
(I) film,
(Ii) an insulating resin layer formed on the front surface of the film (i.e., the “front” surface) and the back surface facing the surface;
(Iii) a wiring pattern embedded in the insulating resin layer; and (iv) disposed between the front surface wiring pattern and the back surface wiring pattern, and electrically connecting the front surface wiring pattern and the back surface wiring pattern. Having vias to
Provided is a flexible substrate characterized in that the insulating resin layer on the front surface and the insulating resin layer on the back surface are thicker than the film.

In order to obtain such a flexible substrate,
(A) forming an insulating resin layer thicker than the film on the front surface of the film and the back surface facing the surface;
(B) forming a through hole in the film and the insulating resin layer;
(C) a step of filling the through hole with a conductive resin composition; and (d) a flexible substrate comprising a step of embedding a wiring pattern in an insulating resin layer and electrically connecting the wiring pattern to the conductive resin composition. A manufacturing method is provided.

  In the flexible substrate of the present invention, the wiring pattern is embedded in the insulating resin layer, and preferably the wiring pattern is embedded in the insulating resin layer so as to be flush with or substantially flush with the insulating resin layer. Further, in the flexible substrate of the present invention, since the via is provided between the wiring pattern on the front surface side and the wiring pattern on the back surface side, the via does not penetrate the entire substrate (therefore, the via in this specification is Also called “inner via”.

  The flexible substrate of the present invention is excellent in flatness because the wiring pattern is flush (or substantially flush) with the insulating resin layer, and can be mounted with high precision when mounting a semiconductor chip. In addition, the wiring pattern embedded in the insulating resin layer maintains the adhesion strength with the insulating resin layer, and the stress applied to the wiring pattern is dispersed, so that the flexible substrate has sufficient flexibility ( That is, the bending life is good). Furthermore, since the wiring pattern is formed by being embedded in the insulating resin layer by a transfer method, a clean substrate surface can be obtained without the presence of residues such as an etching solution, and the insulation reliability is excellent.

  In addition, when manufacturing a flexible substrate, the position of the via can be arbitrarily selected, so that conduction can be achieved at a desired location in the wiring pattern, and wiring design is easy. Since the wiring pattern is embedded in the insulating resin layer, the distance between the wiring pattern on the front surface and the wiring pattern on the back surface is narrow, and the via can be reduced in size.

  Furthermore, in the multilayer flexible substrate manufactured from the flexible substrate of the present invention, since passive elements or active elements are formed on the film, the passive elements and the active elements are densely arranged so as to shorten the wiring length. Can be implemented. Therefore, it is possible to obtain a flexible substrate including a higher-performance electronic circuit by combining various passive elements and active elements. In addition, since passive elements and active elements can be mounted with high density as described above, the influence of parasitic capacitance and inductance between wirings accompanying high-speed processing of electronic circuits can be suppressed to a minimum. Furthermore, since various passive elements and active elements are arranged inside the substrate, the area and the number of components used for surface mounting can be minimized, and further miniaturization and thinning can be achieved. .

BEST MODE FOR CARRYING OUT THE INVENTION

  Hereinafter, the flexible substrate and the manufacturing method thereof of the present invention will be specifically described.

  In FIG. 1, the structure of the flexible substrate 100 of this invention is shown with a cross section. As shown in FIG. 1, the flexible substrate 100 of the present invention has insulating resin layers 2a and 2b thicker than the film 1 formed on both surfaces of the film 1, and the wiring pattern 3a is formed on the insulating resin layers 2a and 2b. , 3b are embedded. In particular, the wiring patterns 3a and 3b are embedded in the insulating resin layers 2a and 2b so that the substrate surface becomes flat. The via 4 is provided between the wiring pattern 3a formed on the insulating resin layer 2a on the front surface side and the wiring pattern 3b formed on the insulating resin layer 2b on the back surface side, and the wiring patterns 3a and 3b are mutually connected. It has a function of electrical connection.

  In the flexible substrate 100 of the present invention, the insulating resin layers 2 a and 2 b are formed to be thicker than the film 1. For example, the thickness ratio of the insulating resin layer (2a or 2b) / the thickness of the film is preferably 1.1 to 8, more preferably 1.2 to 6. Here, “the thickness of the insulating resin layer” means the thickness of the insulating resin layer formed on one surface of the film. As specific thicknesses, for example, the thickness of the insulating resin layers 2a and 2b is 3 to 80 μm, and the thickness of the film 1 is 2 to 16 μm. As described above, when the insulating resin layers 2a and 2b are configured to be thicker than the film 1, the flexibility or sliding flexibility of the flexible substrate is improved. This is because when the flexible substrate is bent, the stress applied to the film and the embedded wiring pattern is relaxed by the insulating resin layer having a low elastic modulus.

  In the embodiment in which the wiring patterns 3a and 3b are embedded in the insulating resin layers 2a and 2b, the thickness of the wiring patterns 3a and 3b is preferably 40% to 100% of the thickness of the insulating resin layers 2a and 2b. More preferably, it is 80% to 95%. When the wiring pattern is embedded in the insulating resin layer at such a ratio, an effect of reducing the via resistance is brought about. In addition, since the distance between the wiring pattern 3a on the front surface and the wiring pattern 3b on the back surface is reduced, downsizing of the via is realized.

  The film 1 used for the flexible substrate 100 of the present invention is generally an insulating film, and is preferably an organic film such as a resin film. However, the film 1 is not particularly limited as long as the film 1 has heat resistance, flexibility, smoothness, low water absorption, and the like. For example, polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyimide (PI), polyamide (PA), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide (PEI), polyarylate ( PAR), polysulfone (PS), amorphous polyolefin (PO), polyamideimide (PAI), liquid crystal polymer (LCP), modified polyphenylene ether (PPE), polybutylene terephthalate (PBT), polycarbonate (PC), and polyether The film 1 is preferably formed from a material selected from the group consisting of ether ketone (PEEK). When such a material is used, a film particularly excellent in heat resistance and flexibility can be obtained. For this reason, when a film formed from such a material is used for a flexible substrate, a flexible substrate that can be folded and mounted in a spatially narrow space is obtained, further reducing the size and weight of electronic devices. This will contribute to the realization of thinning.

  Of the materials listed above, polyamide is particularly preferable. This is because polyamide has high rigidity and high heat resistance. In particular, aramid which is an aromatic polyamide is preferable. This is because aramid has a strong film even when it is thinned, has excellent handling properties, and contributes to the realization of a thinner flexible substrate. By the way, among aromatic polyamides, para-aromatic polyamides have a linear structure in the main chain, so that high rigidity appears more remarkably than meta-aromatic polyamides. Furthermore, it can be made thin. When the film is thinned in such a manner, the film can be easily laser processed, and a fine via can be formed.

  The insulating resin layers 2a and 2b formed on both surfaces of the film 1 have a function of accommodating the wiring patterns 3a and 3b. In order to improve the adhesion to the wiring patterns 3a and 3b, or to improve the adhesion between the substrates in the case of multilayering, it is preferable that the insulating resin layers 2a and 2b have adhesiveness. Therefore, the material of the insulating resin layers 2a and 2b is preferably at least one resin selected from the group consisting of epoxy resins, polyimide resins, acrylic resins, and resins obtained by modifying them.

  The wiring patterns 3a and 3b may be formed of any material as long as it has conductivity. For example, the wiring patterns 3a and 3b may be formed of a metal material selected from the group consisting of copper, nickel, gold, and silver. preferable. Although the thickness of the wiring patterns 3a and 3b is changed according to the application, it is preferably about 3 to 18 μm, and the wiring patterns 3a and 3b are preferably formed in a film shape. More preferably, in order to achieve a thinner and flexible substrate having high-density wiring, the wiring patterns 3a and 3b are formed to have a thickness of 3 to 12 μm.

  The flexible substrate 100 of the present invention is characterized in that the wiring patterns 3a and 3b are embedded in the insulating resin layers 2a and 2b. It is preferable to use a transfer method to obtain such wiring patterns 3a and 3b. Specifically, first, a carrier sheet provided with wiring patterns 3a and 3b in advance and a film 1 having insulating resin layers 2a and 2b on both surfaces are prepared. The carrier sheet itself is preferably a sheet material made of an organic film such as PET or a metal foil such as copper foil, and having a thickness of about 25 to 200 μm. Next, the carrier sheet and the film 1 are stacked and pressed so that the wiring patterns 3a, 3b and the insulating resin layers 2a, 2b are in contact with each other. By this pressing, the wiring patterns 3 a and 3 b on the carrier sheet are embedded in the insulating resin layers 2 a and 2 b of the film 1. When the insulating resin layers 2a and 2b are made of a thermosetting resin, it is preferable that the insulating resin layers 2a and 2b be in a semi-cured state at the time of embedding. Finally, by removing the carrier sheet, a sheet substrate in which the wiring patterns 3a and 3b are embedded in the insulating resin layers 2a and 2b is obtained. In this case, the wiring patterns 3a and 3b are preferably embedded in the insulating resin layers 2a and 2b so as to be flush with or substantially flush with the insulating resin layers 2a and 2b. Thereby, the flatness of the flexible substrate is excellent, which is advantageous when multilayered. Such a transfer method can form a wiring pattern with a finer pitch than a wiring pattern formed by wet etching. For example, the line / space (L / S) of the wiring pattern formed by wet etching is about 40 μm / 40 μm, whereas the L / S of the wiring pattern using the transfer method is 15 μm / 15 μm (30 μm pitch). ).

  The via 4 configured in the flexible substrate 100 of the present invention is provided between the wiring pattern 3a on the front surface and the wiring pattern 3b on the back surface, and is provided in contact with the wiring patterns 3a and 3b. Therefore, the via 4 has a function of electrically connecting the wiring pattern 3a on the front surface and the wiring pattern 3b on the back surface. For this reason, the via 4 is preferably formed from a conductive resin composition containing a metal selected from the group consisting of copper, nickel, and silver.

  Next, preferred embodiments (I) to (V) of the flexible substrate of the present invention will be described below.

  In a preferred embodiment (I), at least one passive element and / or active element and wiring electrically connected to the passive element and / or active element are at least one of the front surface and the back surface of the film. Provided on the surface, the wiring and the via are electrically connected.

  FIG. 2 shows a configuration of the flexible substrate 110 of the present invention including passive elements. 2, the same elements as those in FIG. 1 are denoted by the same reference numerals. 2 is different from FIG. 1 in that a capacitor 5, a wiring 6 and a resistor 7 are provided on one surface of the film 1, and the wiring patterns 3a and 3b on the front or back surface and the wiring 6 are electrically connected. The vias 4 are formed so as to be connected to each other. In this embodiment, the capacitor 5 is electrically connected to the via 4 via the wiring 6, and the resistor 7 is connected to the via 4 via the wiring 6. Note that the wiring 6 may be an electrode wiring.

  In such an embodiment, an electronic circuit can be formed inside the substrate by combining various active elements and passive elements. In addition, since various passive elements and active elements can be mounted with high density and a short wiring length, the influence of parasitic capacitance and inductance between the wirings on the circuit can be suppressed. Furthermore, since the passive element and / or the active element and the wiring are covered with the insulating resin layer, the adhesive strength with the film is maintained, and the flexible substrate 110 has sufficient flexibility. In addition, since the passive element and / or active element and the wiring are embedded in the insulating resin layer without appearing on the surface of the substrate, the surface of the substrate is flat and can be stacked without causing an obstacle to wiring. A dense multilayer flexible substrate can be obtained.

  In a preferred embodiment (II), passive elements and / or active elements are formed in a film shape. “Film-like” as used herein means that the thickness of the passive element and / or active element is about 0.01 to 70 μm. Thus, by forming the passive element and / or the active element in a film shape, a thin flexible substrate is realized, and sufficient flexibility is obtained.

  Furthermore, in a preferred embodiment (III), further further passive elements and / or active elements are formed.

  FIG. 3 is a cross-sectional view showing the configuration of the flexible substrate 120 of the present invention in which another passive element and / or active element is incorporated. 3, the same elements as those in FIG. 2 are denoted by the same reference numerals. 3 differs from FIG. 2 in that the resistor 8 is formed between the wiring patterns 3b in a state of being embedded in the insulating resin layer 2b.

  In such an embodiment, it is possible to form a more sophisticated electronic circuit inside the substrate by combining various active elements and passive elements. Also in such an embodiment, the flexible substrate can be mounted at a high density so as to shorten the wiring length, so that the influence of parasitic capacitance, inductance, etc. between the wirings on the circuit can be suppressed.

  Here, the passive element is preferably an element selected from the group consisting of a capacitor, a resistor, an inductor, and combinations thereof made of an inorganic dielectric. Accordingly, the passive element can be incorporated into the flexible substrate as an element having a function such as a filter.

  The inorganic dielectric used for the capacitor is preferably a material composed of ATiO 3 type perovskite, and A in “ATiO 3” is strontium (Sr), calcium (Ca), magnesium (Mg), barium (Ba), and It is preferably at least one element selected from the group consisting of lead (Pb). When an inorganic dielectric is formed from such a material, a capacitor having a high dielectric constant can be obtained. As a result, the capacitance per unit area increases, leading to a reduction in the size of the flexible substrate.

Resistors used for the passive elements are tantalum (Ta), titanium (Ti), nichrome alloy (Ni—Cr), titanium-nickel alloy (Ti—Ni), tantalum nitride (TaN), chromium-silicon oxide (Cr—). Selected from the group consisting of SiO), tin-doped indium oxide (ITO), zinc oxide (ZnO), copper aluminum oxide (CuAlO ₂ ), strontium copper oxide (SrCu ₂ O ₂ ), and aluminum-doped zinc oxide (AZO). Preferably, it is formed from the material to be made. When a resistor is formed from such a material, a high-resistance resistor can be obtained. As a result, the resistance value per unit area increases, leading to a reduction in the size of the flexible substrate.

  In a preferred embodiment (IV), the active element is preferably an organic semiconductor. An active element formed from an organic semiconductor is excellent in that it is not only thin and light but also has flexibility. In addition, an organic semiconductor can be manufactured by a simple manufacturing method such as rotary printing or inkjet printer printing without going through a complicated manufacturing process, so that the manufacturing cost can be reduced as compared with a conventional inorganic semiconductor.

  In particular, the organic semiconductor is preferably a pn junction solar cell. This is because a solar cell can be formed inside the flexible substrate, so that highly functional electronic circuits can be provided at high density. For example, a module that does not require power supply can be realized. Furthermore, compared to conventional solar cells made of inorganic materials, pn-junction solar cells are inexpensive and do not require large-scale equipment for production. Furthermore, a manufacturing method such as applying an organic solution on a substrate is also applicable. Therefore, it is possible to manufacture a lightweight thin flexible substrate having flexibility at a low cost.

  Further, as a preferred embodiment (V), the flexible substrate of the present invention is laminated to produce a multilayer flexible substrate. In FIG. 4, the structure of the multilayer flexible substrate 200 of this invention is shown with sectional drawing. The illustrated multilayer flexible substrate 200 includes a first flexible substrate 101, a second flexible substrate 102, and a third flexible substrate 103. In such a multilayer flexible substrate 200, various passive elements can be arranged inside the multilayer flexible substrate, so that the area and the number of components required for surface mounting can be minimized, and as a result, the electronic It leads to miniaturization of equipment. In addition, since various passive elements can be mounted at high density so that the wiring length is shortened, the influence on the circuit due to the parasitic capacitance and inductance between the wirings can be minimized, and as a result Leads to the realization of a high-performance multilayer flexible substrate.

  Next, the manufacturing method of the flexible substrate of this invention is demonstrated below.

  The production method of the present invention includes (a) a step of forming an insulating resin layer thicker than the film on the surface of the film and the back surface facing the surface, (b) a step of forming a through hole in the film and the insulating resin layer, (C) a step of filling the through hole with the conductive resin composition, and (d) a step of embedding the wiring pattern in the insulating resin layer and electrically connecting the wiring pattern to the conductive resin composition. In the manufacturing method of the present invention, since the position where the via is provided can be arbitrarily selected, it is possible to establish conduction at a desired portion of the wiring pattern, and the wiring design is easy.

  In the step (a), an insulating resin layer thicker than the film is formed on the front surface of the film and the back surface facing the surface. Therefore, for example, an epoxy resin, a polyimide resin, an acrylic resin, or a resin obtained by modifying them is applied to the film surface. In applying, it is preferable to use a dip method, a roll coater method, a die coater, a spray method, a curtain method, or the like. After application, the insulating resin layer is dried, but it is preferably left in a semi-cured state. Therefore, it is preferable to attach the insulating resin layer at a temperature of 40 to 100 ° C. after the insulating resin layer is formed.

  Next, in a process (b), a through-hole is formed in a film and an insulating resin layer. The diameter of the through hole is preferably 5 to 100 μm, more preferably 10 to 50 μm. In order to form the through hole, means such as a laser, a punch, or a drill can be used.

  In the step (c), the conductive resin composition is filled in the through holes. Prior to filling, the conductive resin composition is preferably pasted. Therefore, the conductive resin composition preferably has a viscosity of 10 to 300 Pa · s at a temperature of 25 to 40 ° C. Note that the conductive resin composition may be filled using a screen printing method. Moreover, not only the aspect filled with a conductive resin composition but the aspect which implements through-hole plating etc. and forms a metal in the inner wall of a through-hole is also possible.

  In the step (d), the wiring pattern is embedded in the insulating resin layer, and the wiring pattern is electrically connected to the conductive resin composition. Therefore, the wiring pattern needs to be provided at a position in contact with the conductive resin composition filled in the through hole. In this step (d), it is preferable to use a transfer method, and it is possible to transfer the wiring pattern formed in advance on the carrier sheet to the insulating resin layer on the film obtained in steps (a) to (c). preferable. In the transfer method, it is preferable to press the carrier sheet against the insulating resin layer under a temperature of 40 to 120 ° C. and a pressure of 0.1 to 3 MPa. When the transfer method is used, since a wiring pattern is formed in advance on a carrier sheet, inspection is performed and only good wiring patterns can be embedded in the insulating resin layer, so that a flexible substrate can be manufactured with high yield. In addition, after embedding a wiring pattern, it is preferable to fully harden | cure an insulating resin layer on the conditions of the temperature of 100-200 degreeC, and the pressure of 0.1-3 MPa.

  In a preferred embodiment, the manufacturing method of the present invention includes at least one passive element and / or active element and wiring electrically connected to the passive element and / or active element. The method further includes providing on at least one of the above. Accordingly, in this case, the film used in the step (a) includes at least one passive element and / or active element and wiring electrically connected to the passive element and / or active element at least on the front surface and the back surface. It is a film formed on one side. When such a film is used, in step (c), the wiring provided on the film and the conductive resin composition filled in the through hole are electrically connected. When the wiring is electrically connected to the conductive resin composition, the wiring, the wiring pattern on the front surface, and the wiring pattern on the back surface are electrically connected. In such an embodiment, various active elements and passive elements can be combined to form an electronic circuit. In addition, since various passive elements and active elements can be mounted so that the wiring length is shortened with high density, the influence of parasitic capacitance and inductance between the wirings on the circuit can be suppressed. In the manufacturing method of the present invention, since the passive element and / or active element and the wiring electrically connected to the passive element and / or active element are covered with the insulating resin layer, the adhesion strength with the film is high. A flexible substrate that is maintained and excellent in flexibility is obtained.

  The at least one passive element and / or active element and the wiring electrically connected to the passive element and / or active element may be formed by a sputtering method, a vacuum evaporation method, or an ion plating method. When such a method is used, it becomes possible to form a film from a high melting point material with good adhesion at a low temperature. Therefore, a passive element, an active element, or a wiring can be formed without damaging the film.

  Similarly, a screen printing method, a metal mask printing method, or a drawing method can be used. Even with such a method, it is possible to form a film at a low temperature and not only damage the film but also form a passive element, an active element or a wiring at a low cost.

  In the transfer method, not only the wiring pattern can be transferred to the insulating resin layer, but also the passive element and / or the active element can be transferred to the insulating resin layer. In that case, after previously forming a wiring pattern and passive elements and / or active elements on the carrier sheet, the wiring pattern and passive elements and / or active elements are embedded in insulating resin layers on both sides of the film. become.

  As mentioned above, although the manufacturing method of the flexible substrate of this invention was demonstrated, when such a manufacturing method of a flexible substrate is implemented repeatedly, the multilayer flexible substrate 200 as shown in FIG. 4 can be obtained.

  Next, an example of the manufacturing process of the flexible substrate 100 of the present invention will be described with reference to FIG.

  First, epoxy-based thermosetting in aromatic solvents such as toluene and xylene, ketone solvents such as methyl ethyl ketone and acetone, alcohol solvents such as methanol and ethanol, or polar solvents such as dimethylformamide and dimethylacetamide. An insulating material such as a mold resin composition is dissolved to form a varnish. Then, such an insulating material is applied to both surfaces of the organic film 1 such as aramid or polyimide by a coating means such as a dip method, a roll coater method, a die coater method, a spray method, or a curtain method, and the insulating resin layer 2a , 2b (see FIG. 5A). The formed insulating resin layers 2a and 2b are preferably in a semi-cured state.

  Next, the through-hole 13 is formed in the sheet material provided with the insulating resin layers 2a and 2b on both surfaces of the film 1 using a carbon dioxide gas laser or a UV laser (see FIG. 5B). Next, after filling the through holes with the conductive resin composition 14 by a printing method or the like (see FIG. 5C), the wiring patterns 3a and 3b are embedded in the insulating resin layers 2a and 2b by a transfer method. At this time, the wiring patterns 3a and 3b and the insulating resin layers 2a and 2b are preferably flush with each other. That is, it is preferable to embed the wiring patterns 3a and 3b in the insulating resin layers 2a and 2b so that the surface of the sheet material is smooth without a step. Further, by providing the wiring patterns 3a and 3b in the insulating resin layers 2a and 2b so that a part of the wiring pattern 3a on the front surface and a part of the wiring pattern 3b on the back surface are in contact with the conductive resin composition 14, the via 4 is formed. It forms (refer FIG.5 (d)). Finally, the flexible resin substrate 100 of the present invention is obtained by permanently curing the insulating resin layers 2a and 2b.

  Next, an example of a manufacturing process of the flexible substrate 110 incorporating a passive element will be described with reference to FIG.

  First, the capacitor 5 and the wiring 6 are formed on at least one of the front and back surfaces of the organic film 1 such as aramid or polyimide (see FIG. 6A). The wiring 6 is formed so that a part of the wiring 6 is located at a position of a via (that is, a through hole filled with a conductive resin composition) to be formed later. Capacitor 5 and wiring 6 are formed in a thin film (film thickness of about 0.01 to 1 μm) on at least one of the front and back surfaces of film 1 using sputtering, vacuum deposition, ion plating, or the like. May be. Further, the capacitor 5 and the wiring 6 may be formed in a thick film shape (film thickness of about 1 to 70 μm) by using a screen printing method, a metal mask printing method, a drawing method, or the like.

  Although the capacitor 5 is formed as a passive element in the manufacturing process shown in FIG. 6, the present invention is not limited to such an embodiment, and the active element may be formed on at least one surface of the film 1 and the back surface. In that case, the active element is preferably an organic semiconductor, and the organic semiconductor is preferably a pn junction solar cell.

  Next, use epoxy-based heat in an aromatic solvent such as toluene or xylene, a ketone solvent such as methyl ethyl ketone or acetone, an alcohol solvent such as methanol or ethanol, or a polar solvent such as dimethylformamide or dimethylacetamide. An insulating material such as a curable resin composition is dissolved to form a varnish. Next, the insulating material is applied to both surfaces of the film 1 on which the capacitor 5 and the wiring 6 are formed by an application means such as a dipping method, a roll coater method, a die coater method, a spray method, or a curtain method. 2a and 2b are formed (see FIG. 6B). The formed insulating resin layers 2a and 2b are preferably in a semi-cured state.

  Next, through holes 13 are formed in the sheet material provided with the insulating resin layers 2a and 2b on both surfaces of the film 1 by using a carbon dioxide gas laser, a UV laser, or the like (see FIG. 6C). Thereafter, the conductive resin composition 14 is filled in the through holes by a printing method or the like (see FIG. 6D). As a result, the conductive resin composition 14 is electrically connected to the wiring 6. Next, the wiring patterns 3a and 3b are embedded in the insulating resin layers 2a and 2b by a transfer method. At this time, the wiring patterns 3a and 3b and the insulating resin layers 2a and 2b are preferably flush with each other. That is, it is preferable to embed the wiring patterns 3a and 3b in the insulating resin layers 2a and 2b so that the surface of the sheet material is smooth without a step. Further, by providing the wiring patterns 3a and 3b in the insulating resin layers 2a and 2b so that a part of the wiring pattern 3a on the front surface and a part of the wiring pattern 3b on the back surface are in contact with the conductive resin composition 14, the via 4 is formed. It forms (refer FIG.6 (e)). Eventually, the insulating resin layers 2a and 2b are fully cured to obtain the flexible substrate 110 incorporating the passive elements.

  Next, an example of a method for producing the multilayer flexible substrate of the present invention will be described.

  The multilayer flexible substrate of the present invention has a flexible substrate obtained by the above-described method for producing a flexible substrate of the present invention as a structural unit. Therefore, first, in the method for manufacturing a flexible substrate according to the present invention, a plurality of substrates having a wiring pattern embedded in an insulating resin layer are prepared. At this stage, the insulating resin layer is not yet completely cured and is in a semi-cured state. Next, the prepared plurality of substrates are appropriately aligned and overlapped to obtain a precursor of the multilayer flexible substrate. Thereafter, the insulating resin layer of the precursor is collectively cured using, for example, a roller-type heat and pressure apparatus. The precursor of the multilayer flexible substrate is pressed when passing through the gaps between the rollers, and at the same time, the insulating resin layer is melted and cured, so that the precursor is integrated and the multilayer flexible as a result. A substrate is obtained. In such a manufacturing method, since a reel-to-reel process or a roll-to-roll process can be adopted, a multilayer flexible substrate can be manufactured more easily than in the case of using a conventional parallel plate heating and pressing machine. be able to. In the reel-to-reel process or roll-to-roll process, a flexible substrate can be continuously manufactured from a long base material, so that a multilayer flexible substrate can be manufactured at low cost, and in terms of manufacturing efficiency. preferable.

  Based on Examples 1-4, it tested about the flexible substrate of this invention, and its manufacturing method.

First, in Example 1 and Example 2, a test was performed on the flex life of the flexible substrate of the present invention.

[Example 1]
(Film material)
Table 1 shows the films (organic films) used in this example.

(Preparation of substrate used for flex life measurement)
A thermosetting epoxy resin was applied to both sides of the film by a roll coater method to form an insulating resin layer. Next, a wiring pattern was embedded in this insulating resin layer.

  Prior to embedding the wiring pattern, first, a thin release layer made of a nickel-phosphorus alloy is formed on the surface of an electrolytic copper foil having a thickness of 70 μm, which serves as a support substrate for the wiring pattern, and the thickness is electrolytically plated on the release layer. A 12 μm copper foil was formed. Then, a dry film resist was attached to the copper foil, and a wiring pattern was formed by sequentially performing exposure, development, etching, and resist film removal.

  Next, the support base material provided with the wiring pattern is aligned and superimposed on the insulating resin layers formed on the front side and the back side of the film, heated to 60 ° C., and a pressure of 3 MPa is applied for 5 minutes. Then, the wiring pattern of the supporting substrate was embedded in the insulating resin layer. Subsequently, after cooling, only the supporting base material was peeled off, and heated for 1 hour under conditions of 140 ° C. and 5 MPa to fully cure the insulating resin layer. The board | substrate used as the base of a flexible substrate was obtained by the above method. Table 2 shows the specifications of the substrate.

(Measurement of bending life)
The bending life of each of the obtained sample substrates was measured by a method based on IPC-240C and JIS-C5016.

  In measuring the bending life, first, the sample substrate was fixed between two flat plates facing each other at a constant interval in a state where the sample substrate was bent at 180 ° so as to have a constant curvature. By moving the flat plates in parallel at a determined speed and stroke, the sample substrate was slid and repeatedly reciprocated. At this time, the direct current resistance value of the wiring pattern located on the inner curved surface of the sample substrate was monitored, and the number of reciprocating motions when the initial resistance value was increased by 80% was defined as the flex life. As a comparative example, the bending life of a copper foil used for the wiring pattern (that is, a 12 μm copper foil formed by electrolytic plating) was examined by the same method.

(result)
The results of this example are shown in FIG. FIG. 7 is a graph of the number of bendings (= bending life) versus the film tensile modulus at room temperature. In the comparative example, breakage was observed after 800 reciprocations. In view of this, referring to FIG. 7, it can be seen that the substrate serving as the base of the flexible substrate of the present invention has a good flex life regardless of the elastic modulus of the film. The reason why the substrate has a good bending life is that the wiring pattern is embedded in the insulating resin layer, so that the wiring stress is dispersed by the insulating resin layer fixing the wiring surface, and the wiring pattern is caused by bending. This is probably because the progress of the obtained microcracks is suppressed.

[Example 2]
(Preparation of substrate used for flex life measurement)
In Example 2, by using the same method as in Example 1, the ratio of the insulating resin layer thickness to the film thickness was variously changed to prepare a substrate. Table 3 shows the specifications of the prepared substrate.

(Test conditions)
All films used were aramid films (“Mictron” manufactured by Toray Industries, Inc.). The sample substrates 2a to 2e have substantially the same substrate thickness, and the sample substrates 2c, 2f, and 2g have the same film thickness. Using such a sample substrate, the bending life was measured using the same method as in Example 1. The test conditions were a test speed of 25 Hz, a stroke of 25 mm, and a curvature radius of 2 mm, 4 mm, and 8 mm.

(result)
The results are shown in FIG. 8 and FIG. FIG. 8 is a graph of the number of bendings (= bending life) with respect to the bending radius. FIG. 9 is a graph of the ratio of the thickness of the insulating resin layer to the film thickness (= insulating resin layer thickness / film thickness) and the number of bendings (= flexing life). Referring to these graphs, it can be seen that the sample substrate having a thicker insulating resin layer than the film shows a better bending life, and the effect becomes particularly remarkable as the bending radius decreases. The reason why the flex life is improved in this way is considered to be that the stress applied to the wiring pattern and the film can be more relaxed by the insulating resin layer having a low elastic modulus.

  Next, in Examples 3 to 5 below, flexible substrates and multilayer flexible substrates were produced using the production method of the present invention.

[Example 3]
(Preparation of flexible substrate of the present invention)
As the film of Example 3, an aramid film having a thickness of 4 μm (manufactured by Toray Industries, Inc .: product name “Mictron”) was used. A thermosetting epoxy resin was applied to both surfaces of this film by a dip method to prepare an aramid sheet with an epoxy resin. In addition, it apply | coated so that the epoxy resin layer on a film might become predetermined thickness, and it was made to dry so that an epoxy resin layer might be in a semi-hardened state after application | coating. On the upper surface of this aramid sheet with an epoxy resin, a PEN film having a thickness of 9 μm was bonded using a hot press so that the epoxy resin would not be cured at a temperature of 40 ° C. and a pressure of 0.5 MPa. Subsequently, many 50-micrometer through-holes were formed in the aramid sheet | seat with an epoxy resin with which the PEN film was bonded together using UV-YAG laser. Subsequently, the through-hole was filled with the conductive resin composition by a printing method and subjected to a drying process. The conductive resin composition used for filling is 70% by weight of copper powder having an average particle diameter of 1 μm, 10% by weight of bisphenol A type epoxy resin as a resin component, and curing of the epoxy resin in consideration of filling properties for small-diameter holes. 3 wt% of an amine adduct curing agent as an agent and 17 wt% of butyl carbitol acetate were kneaded with a three roll to prepare a paste. At the time of filling, an existing screen printer was used with the PEN film on the aramid sheet with epoxy resin as a mask. That is, the conductive resin composition in a paste form was imprinted directly on the PEN film with a polyurethane squeegee and filled into the through holes from the substrate surface.

  Next, a wiring pattern was formed on an aramid sheet with an epoxy resin. Prior to that, first, a composite copper foil in which copper having a predetermined thickness was formed by electrolytic plating on one side of a copper foil having a thickness of 70 μm ( Furukawa Circuit Foil Co., Ltd. product: “Peelable copper foil”, copper plating thickness: 5 μm, 9 μm, 12 μm) were prepared. Next, a dry film resist was attached to the surface of the copper plating layer, and exposure, development, etching and resist film removal were sequentially performed to form a predetermined wiring pattern. At this time, the thickness of the wiring pattern was changed by half etching.

  Next, after peeling the PEN film from the aramid sheet with epoxy resin, the wiring pattern obtained from the copper foil was embedded in the epoxy resin layer at a pressure of 3 MPa. And after giving to the temperature of 80 degreeC for 5 minutes, it cooled and peeled the copper foil as a carrier sheet. Thereafter, the epoxy resin layer was fully cured by applying it for 1 hour under conditions of a temperature of 180 ° C. and a pressure of 5 MPa to obtain a flexible substrate.

(Measurement of specific resistance of via)
The specific resistance value of the via (that is, the inner via) formed on the flexible substrate was measured. In this measurement, first, a resistance value was measured by a four-terminal measurement method through a wiring pattern formed on a copper foil with 500 vias formed in series on the obtained flexible substrate in series. Next, the resistance of the copper foil was subtracted from the measured resistance value to obtain the resistance value of 500 vias. The specific resistance value was calculated from the filling volume obtained from the substrate thickness and the hole diameter.

As a criterion, in view of the fact that the specific resistance value of the metallic copper particles used in the examples was 1.7 × 10 ⁻⁶ Ωcm, the resistance value not more than 10 times the specific resistance value of copper was determined as “excellent”. A resistance value of 10 times or more and 100 times or less was set as “good”, and a resistance value of 100 times or more was set as “impossible”.

  The results are shown in Table 4. From the results in Table 4, it was confirmed that the vias of any condition were electrically connected. In particular, for a flexible substrate having a wiring pattern thickness of 80% or more with respect to the thickness of the insulating resin layer (that is, the epoxy resin layer), the via resistance may be 10 times or less the copper specific resistance value, and the resistance may be particularly low. It could be confirmed.

[Example 4]
(Preparation of flexible substrate with built-in passive element of the present invention)
As the film of Example 4, a 4 mm thick aramid film (manufactured by Toray Industries, Inc .: product name “Mikutron”) was used. Using a sputtering method, a Ti (titanium) film having a film thickness of 0.05 μm and a Pt (platinum) film having a film thickness of 0.2 μm were sequentially formed on the aramid film. Subsequently, patterning into a predetermined shape using a photolithography technique was performed to form a capacitor lower electrode. Next, an SrTiO ₃ (strontium titanate) film having a film thickness of 0.1 μm is formed using an RF sputtering method at 400 ° C., and patterned into a predetermined shape using a photolithography technique, thereby forming a dielectric material. A layer was formed. Next, an upper electrode was formed on the dielectric layer and a capacitor was formed on the aramid film in the same manner as the lower electrode. The intersection area of the upper electrode and the lower electrode was formed to be 100 μm × 100 μm, and each electrode was formed to extend outward from the end of the dielectric layer. This allows the via to pass through the electrode when forming the via in a later step. Further, a TiN (titanium nitride) film having a film thickness of 0.03 μm is formed on the aramid film by sputtering, and then patterned into a predetermined shape by using a photolithography technique to form a resistor film (100 μm × 100 μm). A pair of electrode wirings made of copper having a film thickness of 20 μm are formed on both ends thereof by sputtering and plating so as to overlap with the resistor film (specifically, overlap with a resistor film having a width of 100 μm and a length of 10 μm). Formed with. In this case as well, each electrode wiring is formed so as to extend outward from the end portion of the resistor film, and when the via is formed in a later process, the via can penetrate the electrode wiring.

  Thus, the thermosetting epoxy resin was apply | coated by the dipping method on both surfaces of the film in which the passive element was formed, and the aramid sheet with an epoxy resin in which the passive element was incorporated was produced. Therefore, first, a thermosetting epoxy resin was applied so that the epoxy resin layer on the film had a predetermined thickness (10 μm), and dried after application so that the epoxy resin layer was in a semi-cured state. On the upper surface of this aramid sheet with an epoxy resin, a PEN film having a thickness of 9 μm was bonded at a temperature of 40 ° C. under a pressure of 0.5 MPa so that the epoxy resin would not be cured using a hot press. Subsequently, many 50-micrometer through-holes were formed in the aramid sheet | seat with an epoxy resin with which the PEN film was bonded together using UV-YAG laser. Next, the conductive resin composition was filled in the through holes by a printing method and subjected to a drying step. The conductive resin composition has 70% by weight of copper powder having an average particle diameter of 1 μm, 10% by weight of bisphenol A type epoxy resin as a resin component, and an amine as a curing agent for the epoxy resin in consideration of the filling property for small diameter holes 3 wt% of adduct curing agent and 17 wt% of butyl carbitol acetate were kneaded with a three roll to prepare a paste. At the time of filling, an existing screen printer was used with the PEN film on the aramid sheet with epoxy resin as a mask. That is, the conductive resin composition in a paste form was imprinted directly on the PEN film with a polyurethane squeegee and filled into the through holes from the substrate surface.

  Next, a wiring pattern was formed on an aramid sheet with an epoxy resin with a built-in passive element. Prior to that, first, a composite in which copper having a predetermined thickness was further formed by electrolytic plating on one side of a copper foil having a thickness of 70 μm. Two copper foils (manufactured by Furukawa Circuit Foil Co., Ltd .: product name “Peelable Copper Foil”, copper plating thickness: 9 μm) were prepared. A dry film resist was attached to the surface of the copper plating layer, and exposure, development, etching, and resist film removal were sequentially performed to form a predetermined wiring pattern.

  Next, after peeling the PEN film from the aramid sheet with epoxy resin, the wiring pattern obtained from the copper foil was embedded in the epoxy resin layer at a pressure of 3 MPa. And after attaching | subjecting to the temperature of 80 degreeC for 5 minutes, it cooled and peeled the copper foil as a carrier sheet. Thereafter, the epoxy resin layer was fully cured by applying it for 1 hour under conditions of a temperature of 180 ° C. and a pressure of 5 MPa. By the above method, a flexible substrate with a built-in passive element could be obtained.

(Measurement of resistance of passive elements)
The electrical characteristics of the capacitor and the resistor were measured before and after being built. Regarding the capacitor, a capacitance of 2.2 fF was measured with a measurement signal of 1 kHz before built-in. Similarly, with respect to the resistor, a resistance of 100Ω was measured with a measurement signal of 1 kHz before incorporation. On the other hand, for the capacitors and resistors after being incorporated in the insulating resin layer (that is, the epoxy resin layer), almost the same results as the characteristics obtained before incorporation were obtained. Therefore, even if passive elements such as capacitors and resistors are incorporated as in the flexible substrate of the present invention, it has been confirmed that the passive elements themselves are hardly affected electrically.

[Example 5]
(Preparation of multilayer flexible substrate of the present invention)
In Example 5, a multilayer flexible substrate was produced using the flexible substrate obtained in Example 1 or Example 2. First, three substrates were prepared in which wiring patterns were embedded in the insulating resin layers on both sides of the film by a transfer method. At this stage, the insulating resin layer was not completely cured yet and was in a semi-cured state. The three flexible substrates were appropriately aligned with each other and overlapped to form a multilayer flexible substrate precursor (ie, a flexible four-layer substrate). Thereafter, the precursor was cured in a lump using a roller-type heat and pressure apparatus. By adjusting the gap between the pair of rollers of this hot press apparatus, a nip pressure corresponding to 5 MPa applied by a conventional parallel plate press apparatus was applied to the precursor. The roller temperature was 200 ° C. When the precursor passes through the gap between the pair of rollers, the precursor is entirely pressed, and at the same time, the insulating resin layer is melted and cured by heating. As a result, it was possible to obtain a multilayer flexible substrate in which the precursors were integrated and three flexible substrates were laminated.

  The flexible substrate or multilayer flexible substrate of the present invention is excellent in terms of high density and high reliability despite being thin, and is also excellent in terms of bending life, so that further downsizing of electronic devices can be achieved.・ Contributes to weight reduction and thickness reduction.

Cross-reference of related applications

  This application is a priority under the Paris Convention based on Japanese Patent Application No. 2004-079847 (filing date: March 19, 2004, title of invention: “flexible substrate, flexible multilayer substrate and methods for producing them”). Insist. All the contents disclosed in the application are incorporated herein by this reference.

FIG. 1 is a cross-sectional view schematically showing the configuration of a flexible substrate 100 of the present invention. FIG. 2 is a cross-sectional view schematically showing the configuration of the flexible substrate 110 of the present invention including passive elements. FIG. 3 is a cross-sectional view schematically showing the configuration of another flexible substrate 120 of the present invention including passive elements. FIG. 4 is a cross-sectional view schematically showing the configuration of the multilayer flexible substrate 200 of the present invention. 5A to 5D are cross-sectional views schematically showing the manufacturing process of the flexible substrate 100. 6A to 6E are cross-sectional views schematically showing a manufacturing process of the flexible substrate 110 including passive elements. FIG. 7 is a graph showing the relationship between the film elastic modulus and the number of bendings. FIG. 8 is a graph showing the relationship between the radius of curvature and the number of bends. FIG. 9 is a graph showing the relationship between the insulating resin layer thickness / film thickness ratio and the number of bendings.

Explanation of symbols

1 Film 2a, 2b Insulating resin layer 3a, 3b Wiring pattern 4 Via 5 Capacitor 6 Wiring (electrode wiring)
7,8 Resistor 13 Through hole 14 Conductive resin composition 100 Flexible substrate 110,120 Flexible substrate including passive elements 200 Multilayer flexible substrate

Claims (18)

(I) film,
(Ii) an insulating resin layer formed on the front surface of the film and the back surface facing the surface;
(Iii) a wiring pattern embedded in the insulating resin layer; and (iv) disposed between the front surface wiring pattern and the back surface wiring pattern, and electrically connecting the front surface wiring pattern and the back surface wiring pattern. Having vias to connect,
A flexible substrate, wherein an insulating resin layer on a front surface and an insulating resin layer on a back surface are thicker than the film.   The flexible substrate according to claim 1, wherein a ratio of thickness of the insulating resin layer / thickness of the film is 1.2 to 6.   The flexible substrate according to claim 1, wherein a thickness of the wiring pattern is 80% to 95% of a thickness of the insulating resin layer.   The flexible substrate according to claim 1, wherein the via is formed from a conductive resin composition.   At least one passive element and / or active element and wiring electrically connected to the passive element and / or active element are provided on at least one of the front surface and the back surface of the film, The flexible substrate according to claim 1, wherein the via is electrically connected to the via.   The flexible substrate according to claim 5, wherein the passive element and / or the active element is formed in a film shape.   The flexible substrate according to claim 5 or 6, wherein the passive element is an element selected from the group consisting of a capacitor, a resistor, an inductor, or a combination thereof made of an inorganic dielectric.   The flexible substrate according to claim 1, wherein the film is made of aramid or polyimide.   The insulating resin layer is formed of at least one resin selected from the group consisting of epoxy resins, polyimide resins, acrylic resins, and resins obtained by modifying them. A flexible substrate according to any one of the above.   The flexible substrate according to claim 5, wherein the active element is an organic semiconductor.   The flexible substrate according to claim 10, wherein the organic semiconductor is a pn junction solar cell. A multilayer flexible substrate in which a plurality of flexible substrates are laminated,
A multilayer flexible substrate, wherein at least one of the flexible substrates is the flexible substrate according to claim 1. A method for producing a flexible substrate comprising a film, an insulating resin layer and a wiring pattern,
(A) forming an insulating resin layer thicker than the film on the front surface of the film and the back surface facing the surface;
(B) forming a through hole in the film and the insulating resin layer;
(C) filling the through hole with a conductive resin composition; and (d) embedding a wiring pattern in the insulating resin layer and electrically connecting the wiring pattern to the conductive resin composition. A method for producing a flexible substrate comprising:   The method for manufacturing a flexible substrate according to claim 13, wherein a ratio of thickness of the insulating resin layer / thickness of the film is 1.2 to 6. In the film used in the step (a), at least one passive element and / or active element and wiring electrically connected to the passive element and / or active element are formed on at least one of the front surface and the back surface. Is a film that
15. The method of manufacturing a flexible substrate according to claim 13, wherein the wiring and the conductive resin composition filled in the through hole are electrically connected by the step (c). .   The method for manufacturing a flexible substrate according to claim 15, wherein the passive element and / or the active element is formed by a sputtering method or a screen printing method.   The method for manufacturing a flexible substrate according to claim 13, wherein the wiring pattern is embedded in the insulating resin layer by transferring a previously formed wiring pattern to the insulating resin layer. The wiring pattern and the passive element and / or active element are embedded in the insulating resin layer by transferring a previously formed wiring pattern and passive element and / or active element to the insulating resin layer. Item 17. A method for producing a flexible substrate according to any one of Items 13 to 16.

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