JP2005136318A - Flexible wiring board and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible wiring board whose thinning is possible, whose flexibility is excellent, which can be used for connection of components and part members having inadequate heat-resistance property, and whose alignment is easy. <P>SOLUTION: The flexible wiring board comprises a flexible transparent resin substrate 14 having total beam transmittance of 70% or more and wiring 12 embedded in the transparent resin substrate so as to expose on the surface of the transparent substrate. The flexible wiring board is thin, superior in bending resistance, capable of low-temperature compression bonding with a photo-curing anisotropically-conductive adhesive taking advantage that the substrate is transparent, easy in alignment, and superior in productivity. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

  The present invention relates to a flexible wiring board and a method for manufacturing the same.

As a flexible wiring board conventionally used, a flexible copper-clad laminate having a three-layer structure in which a copper foil is bonded to a polyimide film with an adhesive is known (for example, see Patent Document 1).
However, since such a three-layer laminate has an adhesive layer, there is a limit to reducing the thickness. Moreover, although the polyimide film is excellent in characteristics such as heat resistance, electrical characteristics, and mechanical strength, since an adhesive having inferior these characteristics is used, there is a problem that the characteristics of the polyimide film are not fully utilized.
In order to compensate for the disadvantages of such a three-layer laminate, a two-layer laminate (consisting of a copper foil layer and a polyimide film layer) having no adhesive layer has been developed. Since the laminate of this two-layer structure does not have an adhesive layer, it can make full use of the characteristics of the polyimide film and can be made thinner than the flexible copper-clad laminate of the three-layer structure, It is possible to improve heat resistance and electrical characteristics along with weight reduction.
As a method for producing such a two-layer laminate, for example, after applying a polyimide acid varnish, which is a polyimide precursor, on one or both sides of a copper foil, a cast method (for example, imidizing by heat treatment) Patent Document 2), evaporation method in which a copper piece is heated and evaporated in a high vacuum to form a thin copper layer on the polyimide film surface (for example, see Patent Document 3), or chemical reduction in a plating solution Examples include an electroless plating method in which copper is deposited on the surface of the polyimide film by a reaction to form a copper layer.
JP-A-5-048264 JP-A-5-129774 JP-A-5-183266

However, in recent years, further weight reduction of electronic devices and miniaturization of wiring have progressed, and further reduction in thickness is desired for both the polyimide film layer and the copper foil layer.
However, in manufacturing a flexible copper-clad laminate having a two-layer structure, if further thinning is performed by the method described in Patent Documents 2, 3, etc., the handling property of the material (polyimide film or copper foil) is poor. Therefore, it has been difficult to reduce the thickness.
In addition, in the method of laminating a metal on a polyimide film by vapor deposition or plating, there is a problem that peeling is likely to occur at the interface between the polyimide film and the metal, that is, adhesion is poor, and this causes bending resistance. I was inferior.

In addition, when polyimide is used as a base material for connection between a wiring board and various electronic components (objects to be connected) connected thereto, thermosetting anisotropic conductive adhesion is utilized by utilizing its excellent heat resistance. It is common to use an agent.
However, if the heat resistance of the object to be connected, such as a film liquid crystal, is low, or if the thermal dimensional stability is not sufficient, the use of a thermosetting anisotropic conductive adhesive reduces the connection reliability due to the high temperature during heating. There is a risk. Therefore, in such a case, it is desirable to use a photo-curing anisotropic conductive adhesive that can be connected at a low temperature.
However, polyimides and polyamideimides used for the substrate generally have a low total light transmittance in the ultraviolet to visible light region, and the appearance is dark yellow or brown. Therefore, in order to obtain good connection characteristics with a photo-curing anisotropic conductive adhesive, a long pressing time is required or high light energy is required. Also, depending on the substrate, a photo-curing anisotropic conductive adhesive could not be used at all.

In general, when the flexible wiring board and the connection object are connected, the electrodes facing each other are aligned and then connected via an anisotropic conductive adhesive. That is, it is performed by directly aligning the electrodes facing each other, or by previously providing alignment markings on the outer edges of the electrodes, and overlapping or combining the alignment markings. In the actual manufacturing process, alignment is performed by superimposing a flexible wiring board as an upper layer and an object to be connected as a lower layer, and seeing and recognizing an electrode or marking from the upper layer side with an image recognition device.
However, since the base material of the wiring board is opaque, the recognizability of the electrode of the connection object that is the lower layer or the marking for alignment is low, and as a result, a strong light source is separately prepared to increase the recognition degree, A through hole is provided in the wiring board in a separate process only for alignment, which hinders productivity improvement.

  The present invention has been made in order to solve the above-mentioned problems, and can be thinned, has excellent flexibility, and can be used for connecting parts and members having insufficient heat resistance, and can be easily aligned. Intended for wiring boards.

The flexible wiring board of the present invention includes a flexible transparent resin substrate having a total light transmittance of 70% or more, and a wiring embedded in the transparent resin substrate so as to be exposed on the surface of the transparent resin substrate. It is characterized by having.
Here, it is desirable that the resin constituting the transparent resin base material penetrates into the wiring.
One of the manufacturing methods of the flexible wiring board of the present invention is:
Applying a conductive paste containing metal particles on a substrate and drying to form an unsintered wiring, sintering the unsintered wiring to form a wiring; and
A transparent resin solution in which a transparent resin is dissolved is applied and dried so as to cover the unsintered wiring or the sintered wiring, and a flexible transparent resin base material having a total light transmittance of 70% or more is formed. Laminating process to make a laminated body,
And a peeling step for peeling the substrate from the laminate.
Here, the substrate is preferably made of an inorganic material.
Another one of the manufacturing methods of the flexible wiring board of the present invention is:
A wiring forming step of applying a conductive paste containing a metal compound on a substrate and drying to form a wiring; and
A laminating step of applying a transparent resin solution in which a transparent resin is dissolved so as to cover the wiring and drying to form a flexible transparent resin base material having a total light transmittance of 70% or more to form a laminate,
And a peeling step for peeling the substrate from the laminate.

  The flexible wiring board according to the present invention is thin, excellent in bending resistance and transparent in base material, so it can be cold-pressed with a photo-curing anisotropic conductive adhesive, and can be easily aligned. Excellent in properties.

The flexible wiring board of the present invention has a transparent resin base material 14 and wirings 12, 12,... Embedded in the transparent resin base material 14, as shown in FIGS. .
The transparent resin base material 14 has a flat plate shape, and has an appropriate size and shape as a flexible wiring board. For example, the thickness is preferably 3 to 50 μm, and more preferably 5 to 30 μm. If the thickness is less than 3 μm, the strength of the transparent resin base material is insufficient and is easily damaged during handling, and if it is thicker than 50 μm, there is a concern that the thinning of the device using the flexible wiring board may be hindered.
This transparent resin base material is made of a material having predetermined physical properties as a flexible wiring board such as flexibility, heat resistance, mechanical properties, etc. in addition to electrical insulation. In particular, the present invention is characterized in that the total light transmittance is 70% or more. 80% or more is more preferable.
When considering a manufacturing method in which an organic solvent is dissolved and applied and dried as described later, a material soluble in the organic solvent is applied.
Examples of such transparent resins include polyester, polyurethane, polycarbonate, polyarylate, polyetherimide, polysulfone, and polyethersulfone. In addition, aromatic polyimide obtained by the reaction of a general tetracarboxylic dianhydride and diamine is not preferable because it has a low total light transmittance, but it is almost colorless and transparent, and is a modified polyimide soluble in an organic solvent, for example, Aliphatic polyimides and fluorinated polyimides can be used.
Among the resins, polyethersulfone, polyetherimide, aliphatic polyimide, and fluorinated polyimide are more preferable because they are excellent in heat resistance and electrical characteristics.
These transparent resin materials may be used alone or in combination of two or more.
Furthermore, as long as predetermined transparency is obtained, a resin having a low total light transmittance such as aromatic polyimide, polyamideimide, amide resin, and a resin having a high total light transmittance may be mixed and used. it can.
As a modified polyimide that is soluble in organic solvents and excellent in transparency, a conventional polyimide resin that is soluble in organic solvents before ring closure of polyamic acid and insoluble in organic solvents after ring closure of polyamic acid is used. There are polyimide resins that are soluble in organic solvents even after ring closure and those after polyamic acid ring closure, but both can be used.
Furthermore, in order to improve the adhesiveness to wiring and to have better heat resistance, the transparent resin may further contain alkoxysilane and / or alkoxytitanium. As a result, the transparent resin base material can be a so-called hybrid resin of inorganic silane, inorganic titanium and flexible resin.

In the flexible wiring board of the present invention, as shown in FIG. 2, the wiring 12 is embedded in the transparent resin base material 14. That is, recesses 16, 16,... Are formed at predetermined positions of the transparent resin base material 14, the wirings 12 are located in the recesses 16, and the surface of the wirings is on the surface 18 of the transparent resin base material 14. It is exposed and forms substantially the same plane.
The wiring 12 has conductivity as a wiring board, and is usually made of metal and has a volume resistance of about 1 × 10 ⁻⁶ to 1 × 10 ⁻² Ω · cm.
The thickness of the wiring 12 is preferably 0.01 to 50 μm, and more preferably 1 to 20 μm. If the thickness is less than 0.01 μm, sufficient conductivity may not be obtained when a fine wiring is formed. On the other hand, when the thickness is larger than 50 μm, the circuit is not reduced in thickness and weight and tends to be a circuit having poor bending resistance.

In such a flexible wiring board of the present invention, since the wiring 12 is embedded in the transparent resin base material 14, the adhesiveness and holding power between the wiring 12 and the transparent resin base material 14 are high, and the bending resistance is improved. It will be excellent.
Further, since the wiring 12 is embedded in the transparent resin base material 14, further reduction in thickness can be realized.
In addition, since the flexible wiring board of the present invention has high transparency, even if a photo-curing anisotropic conductive adhesive is used, a large amount of pressure bonding time and light energy are not required. Therefore, it becomes possible to connect with high reliability to a connection object having low heat resistance and thermal dimensional stability such as film liquid crystal.
In addition, when connecting the flexible wiring board and the connection object, even if the flexible wiring board and the connection object are overlapped, it is easy to see and recognize each electrode and marking with an image recognition device. This eliminates the need for a strong light source for increasing the degree of recognition and a through-hole forming process for positioning, and is excellent in productivity.

  In the flexible wiring board 10 of the present invention, it is desirable that the resin constituting the transparent resin base material 14 penetrates into at least a part of the wiring 12. When the transparent resin penetrates into the wiring 12, the adhesion between the wiring 12 and the transparent resin base material 14 becomes stronger, it becomes difficult to peel off, and the bending resistance is further improved.

A method suitable for producing the flexible wiring board of the present invention will be described below.
Manufacturing example 1
First, a flat substrate is prepared. As this substrate, for example, an inorganic substrate made of an inorganic material such as a glass plate, a metal plate, a ceramic plate; polyester, polyurethane, polyamide, polyetherimide, polyamideimide, polyethersulfone, polyetheretherketone, polyimide, fluororesin, etc. An organic substrate such as a plastic sheet or a plastic film can be used.
Various bases may be selected in consideration of the wiring formation method, manufacturing efficiency, and the like. For example, when the wiring is formed by high-temperature sintering as described below, it is desirable to use an inorganic substrate having excellent heat resistance. Further, if an organic substrate that can be continuously supplied and wound in a film state is used as the substrate, the production efficiency can be improved.
It is desirable that the substrate has excellent handling properties. By using a substrate having excellent handling properties, each layer of the two-layer structure can be thinned. The thickness of the substrate is preferably 20 μm to 10 mm.
As will be described later, this substrate is used in the manufacturing process, and finally peeled off and removed. Accordingly, it is preferable to provide a release material on the surface of the substrate in order to make the substrate easier to peel. As the release material, an organic release material made of silicone resin or fluorine resin, or an inorganic release material such as a releasable ceramic such as a diamond-like carbon (DLC) thin film or a zirconium oxide thin film can be used. In particular, it is desirable to use an inorganic release material excellent in heat resistance and durability.

Then, as shown in FIG. 3A, a wiring having a predetermined thickness and a predetermined pattern is formed on the substrate 20 (wiring forming step).
This wiring can be formed by firing metal particles. That is, it is obtained by sintering a conductive paste in which a metal powder and an inorganic binder are dispersed in an organic vehicle.
In this case, the metal is preferably one or more selected from gold, silver and copper.
Examples of the inorganic binder include zinc borosilicate low-melting glass.
Examples of the organic vehicle include those obtained by dissolving a resin such as ethyl cellulose, methyl cellulose, polyvinyl alcohol, and polyvinyl butyral in a solvent such as tervineol and butyl carbitol.
As a firing method, in addition to a method in which the conductive paste is sintered at a high temperature to burn the organic vehicle, metal particles having a nanosize particle size of 1 to 500 nm are sintered at a temperature below the melting point of the metal and at a temperature near room temperature. A method of forming a low resistance wiring can be applied.
As a method of forming a predetermined thickness and a predetermined pattern, a known printing method such as screen printing or gravure printing can be applied.
By using such a printing method, a predetermined pattern of wiring can be directly formed on the substrate 20 in one step.
After firing the wiring 12 having a predetermined pattern on the substrate 20, a transparent resin base material 14 is formed so as to cover the wiring 12, as shown in FIG.
The transparent resin base material 14 can be formed by applying and drying the above-described transparent resin solution containing the predetermined transparent resin and the organic solvent.
Any organic solvent may be used as long as it can dissolve the transparent resin to be used, and any organic solvent such as an alcohol, ketone, ester, hydrocarbon, or aromatic solvent can be used.
The application of the transparent resin solution can be performed by a known application method such as bar coating, comma coating, gravure coating, or screen printing.
Drying can be performed, for example, by heating at about 100 to 250 ° C. using a hot air furnace, an IR furnace, or the like.
And after removing an organic solvent by drying and a transparent resin base material fully solidified, as shown in FIG.3 (c) as a peeling process, the base | substrate 20 is peeled and a transparent resin base material is peeled off. The flexible wiring board 10 in which the wiring 12 is embedded in the wiring 14 is manufactured.

According to such a manufacturing method, the flexible wiring board of the present invention described above can be easily manufactured, and the thickness can be reduced without impairing handling.
Furthermore, fine voids are generated by the evaporation of the solvent and organic vehicle components contained in the conductive paste before sintering, and by applying a solution containing a transparent resin substrate, the transparent resin is infiltrated. Since the wiring 12 is formed, the adhesion between the wiring 12 and the transparent resin base material 14 becomes strong.
The sintering of the unsintered wiring can be performed by drying the solvent before applying the transparent resin, but may be performed after providing the transparent resin base material. Like the latter, by applying a transparent resin before sintering, and simultaneously performing sintering and drying of the transparent resin, the adhesion between the wiring and the transparent resin substrate is further improved, and the flex resistance is more excellent become.
Further, the unsintered wiring may be sintered a plurality of times, for example, twice before and after the application of the transparent resin.
Moreover, as described above, by using an inorganic substrate having high heat resistance as a substrate used during production, it can be sintered using a high-temperature type conductive paste that requires a high temperature of about 400 to 800 ° C., Wiring can be formed on the resin base material while eliminating restrictions on the material selection of the conductive paste.

Manufacturing method example 2
In the manufacturing method example 1 described above, firing is used to form the wiring 12, but the invention is not limited to this.
For example, the wiring 12 can be formed on the substrate 20 by applying a conductive paste containing a metal compound and, if necessary, a reducing agent instead of the conductive paste containing metal particles on the substrate and drying.
That is, the wiring can be formed by reduction of metal oxide, reduction of metal salt, or decomposition of organometallic compound.
For example, the wiring can be formed by reducing a colloidal solution (metal solution) containing metal oxide fine particles such as silver oxide and copper oxide by adding a reducing agent described later.
Similarly, a wiring can be formed by reducing a colloidal solution of an organic silver salt such as silver halide, silver nitrate or silver acetate, or an organic copper salt such as copper halide, copper nitrate or copper acetate with a reducing agent.
Moreover, wiring can be formed by decomposing | disassembling organic metal compounds, such as a metal carboxylic acid compound, a metal amine compound, a metal mercapto compound, and an acetylacetone metal complex, by heating.
The wiring can also be formed by combining these forming methods.
The solvent for the metal solution is not particularly limited, and examples thereof include water, alcohols, ketones, esters, hydrocarbons, and aromatic organic solvents.
Examples of the reducing agent include reducing resins such as ethyl cellulose and polyvinyl butyral, ascorbic acid, hydroquinone, benzoquinone, catechol, p-methoxyphenol, hydrazines, formaldehyde, glucose, amines, and tocophenol.
As a method for forming the wiring in a predetermined pattern, a known printing method such as screen printing or gravure printing can be applied, as in the case of Production Example 1.
And after wiring formation, a flexible wiring board is manufactured by passing through the same lamination process and peeling process as the above-mentioned manufacturing method example 1.
Also by this manufacturing method, the flexible wiring board of the present invention described above can be easily manufactured, and a reduction in thickness can be achieved without impairing handling.
Furthermore, fine voids are generated due to decomposition of organic components contained in the conductive paste, evaporation of the solvent, and the like. By applying a solution containing a transparent resin base material to this, the wiring 12 is in a state where the transparent resin has penetrated. Therefore, the adhesion between the wiring 12 and the transparent resin base material 14 becomes strong.

In the above description, the example in which the printing method is applied to the formation of the wiring is shown, but the present invention is not limited to this. For example, the wiring can be formed on the substrate by vapor deposition of metal and / or plating.
In this case, the metal is preferably one or more of gold, silver, copper, and nickel.
As a vapor deposition method, there are a physical vapor deposition method and a chemical vapor deposition method (CVD method), and either method can be used. Among these, the sputtering method, which is one of physical vapor deposition methods, is preferable because the formed circuit is dense and excellent in bending resistance, and the film thickness can be easily controlled.
Then, after forming a thin metal layer, when forming the metal layer into a desired pattern shape by an etching method, the surface of the metal layer is masked with a photoresist, and an unnecessary metal layer is removed with an etching solution. A predetermined pattern may be formed by a known etching method.
Even when formed by such a vapor deposition method or plating method, since the surface is complicatedly uneven, the transparent resin is infiltrated into the wiring through a process of applying a transparent resin solution so as to cover the wiring. It is possible to prevent peeling.

Hereinafter, the present invention will be described in more detail with reference to examples.
[Example 1]
A heat-resistant glass plate having a thickness of 5 mm was used as a substrate, and a DLC thin layer was provided thereon as a release layer to prepare a releasable substrate.
Silver is evaporated under a helium vacuum condition at a pressure of 0.6 Torr (80 Pa), and the resulting ultrafine silver particles are brought into contact with vapor of mineral spirit, cooled and recovered, and dispersed in a solvent (mineral spirit) in an independent state. A conductive paste containing 20% by mass of ultrafine silver particles having an average particle diameter of 0.01 μm was prepared.
This conductive paste is applied to the produced release substrate by a screen printing method to form a plurality of wiring lines having a line and space = 100 μm (lines with a width of 100 μm formed at intervals of 100 μm), and 250 Sintering was performed for 48 hours at 0 ° C. to obtain a circuit having a thickness of 2 μm.
On this circuit, a polyethersulfone solution (polyethersulfone (Sumika Excel G4800, manufactured by Sumitomo Chemical Co., Ltd.) was dissolved in N, N-dimethylacetamide so as to have a solid content of 30% by mass) using a comma coater. The film was coated at a thickness of 50 μm and dried at 180 ° C. for 10 minutes to form a transparent resin base material to obtain a laminate. The releasable substrate was peeled from the laminate thus obtained to produce a flexible wiring board.
The thickness, total light transmittance, and bending resistance of the obtained flexible wiring board were measured. The results are shown in Table 1.
(Thickness)
The value measured with an electric micrometer (ID-C112RB; Mitutoyo Corporation) according to JIS C 6471 is shown.
(Total light transmittance)
According to JIS K7361-1, a haze meter (NDH2000; manufactured by Nippon Denshoku Industries Co., Ltd.) was used for measurement.
(Flexibility)
A bending resistance test according to JIS C 6471 was performed, and the number of times until disconnection was measured.

[Example 2]
A polyimide film (Kapton EN: manufactured by Toray DuPont) having a thickness of 50 μm was used as a substrate, and a silicone release material (KS839: manufactured by Shin-Etsu Chemical Co., Ltd.) was applied thereon to produce a releasable substrate.
A reduced silver conductive paste (XA-9024: manufactured by Fujikura Kasei Co., Ltd.) is applied to the releasable substrate prepared above by a screen printing method to form a plurality of wiring lines with a line and space = 100 μm. Time drying and sintering were performed to obtain a circuit having a thickness of 2 μm.
On this circuit, an aliphatic polyimide solution (aliphatic polyimide (PI-213: manufactured by Maruzen Petrochemical Co., Ltd.) was dissolved in N-methylpyrrolidone so as to have a solid content of 25% by mass) using a comma coater and a thickness of 50 μm. And dried at 250 ° C. for 10 minutes to form a transparent resin substrate. The substrate was peeled from the laminate thus obtained to produce a flexible wiring board.
The thickness, total light transmittance, and bending resistance of the obtained flexible wiring board were measured in the same manner as in Example 1. The results are shown in Table 1.

[Example 3]
A polyether ether ketone film (Sumilite FS-1100; Sumitomo Bakelite) having a thickness of 50 μm was used as the substrate.
A reduced silver conductive paste (XA-9024: manufactured by Fujikura Kasei Co., Ltd.) is applied to the releasable substrate prepared above by a screen printing method to form a plurality of wiring lines with a line and space = 100 μm. Time drying and sintering were performed to obtain a circuit having a thickness of 2 μm.
Fluoric acid dianhydride having a fluoroalkyl group introduced into the benzene ring of pyromellitic dianhydride, 1,4-ditrifluoromethylpyromellitic dianhydride, and 2,4,5,6-tetrafluoro-1 , 3-Phenylenediamine was dissolved in N, N-dimethylacetamide and stirred at room temperature for 48 hours in a nitrogen atmosphere to prepare an N, N-dimethylacetamide solution of polyamic acid so as to have a solid content of 25% by mass.
The N, N-dimethylacetamide solution was coated on the prepared circuit with a comma coater at a thickness of 50 μm and dried at 250 ° C. for 30 minutes in a nitrogen atmosphere to form a transparent resin substrate to obtain a laminate. . The substrate was peeled from the laminate thus obtained to produce a flexible wiring board.
The thickness, total light transmittance, and bending resistance of the obtained flexible wiring board were measured in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
A heat-resistant glass plate having a thickness of 5 mm was used as a substrate, and a DLC thin layer was provided thereon as a release layer to prepare a releasable substrate.
Silver is evaporated under a helium vacuum condition at a pressure of 0.6 Torr (80 Pa), and the resulting ultrafine silver particles are brought into contact with vapor of mineral spirit, cooled and recovered, and dispersed in a solvent (mineral spirit) in an independent state. A conductive paste containing 20% by mass of ultrafine silver particles having an average particle diameter of 0.01 μm was prepared.
This conductive paste is applied on the release substrate prepared above by a screen printing method to form a plurality of wiring lines of line & space = 100 μm (100 μm width formed at 100 μm intervals) at 250 ° C. And a circuit having a thickness of 2 μm was obtained.
On this circuit, a polyamideimide resin solution having a solid content of 30% by mass (Vilomax: manufactured by Toyobo Co., Ltd.) was coated with a comma coater at a thickness of 50 μm, dried at 180 ° C. for 10 minutes, and then a brown resin substrate Got. The substrate was peeled from the laminate thus obtained to produce a flexible wiring board.
The thickness, total light transmittance, and bending resistance of the obtained flexible wiring board were measured in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
Using a commercially available casting method two-layer copper-clad laminate (Espanex: manufactured by Nippon Steel Chemical Co., Ltd.), a patterned photoresist is formed on the copper foil, and an unnecessary copper foil portion is used with a ferric chloride solution. Etching was performed to form a circuit of line & space = 100 μm, and a flexible wiring board was manufactured.
The thickness, total light transmittance, and bending resistance of the obtained flexible wiring board were measured in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 3]
Using a commercially available two-layer copper-clad laminate (Metal Royal: manufactured by Toyobo Co., Ltd.), a patterned photoresist is formed on the copper foil, and an unnecessary copper foil portion is used with a ferric chloride solution. Etching was performed to form a circuit of line & space = 100 μm, and a flexible wiring board was manufactured.
The thickness, total light transmittance, and bending resistance of the obtained flexible wiring board were measured in the same manner as in Example 1. The results are shown in Table 1.

As is apparent from Table 1, the flexible wiring boards of Examples 1 to 3 have a very thin thickness of 15 μm or less, excellent bending resistance of 50,000 times or more, and at the same time, a total light transmittance of 70% or more. And was very transparent.
On the other hand, Comparative Examples 1 to 3 have a total light transmittance of 70% or less and low transparency. In Comparative Examples 2 and 3, the thickness of the flexible wiring board was increased due to the manufacturing method, and Comparative Example 3 was inferior in bending resistance.

The flexible wiring board of the present invention is used, for example, for connecting circuit boards, circuit boards, etc., and a display body such as a liquid crystal display (LCD) or a plasma display (PDP). In particular, even when connecting to circuit boards equipped with film liquid crystal, electronic parts with poor heat resistance, members, etc., low temperature pressure bonding is possible with a photo-curing anisotropic conductive adhesive, thereby obtaining high connection reliability. .
In addition, the excellent total light transmittance of the transparent resin base material facilitates the alignment during the crimping process and improves the productivity.

It is a top view which shows an example of the flexible wiring board of this invention. It is II-II sectional drawing of FIG. It is process drawing which shows an example of the manufacturing process of the flexible wiring board of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Flexible wiring board 12 Wiring 14 Transparent resin base material 20 Base body 22 Laminated body

Claims (5)

  A flexible having a flexible transparent resin base material having a total light transmittance of 70% or more and wiring embedded in the transparent resin base material so as to be exposed on the surface of the transparent resin base material Wiring board.   The flexible wiring board according to claim 1, wherein a resin constituting the transparent resin base material penetrates into the wiring. Applying a conductive paste containing metal particles on a substrate and drying to form an unsintered wiring, sintering the unsintered wiring to form a wiring; and
A transparent resin solution in which a transparent resin is dissolved is applied and dried so as to cover the unsintered wiring or the sintered wiring, and a flexible transparent resin base material having a total light transmittance of 70% or more is formed. Laminating process to make a laminated body,
A method for producing a flexible wiring board, comprising: a peeling step of peeling the substrate from the laminate. A wiring forming step of applying a conductive paste containing a metal compound on a substrate and drying to form a wiring; and
A laminating step of applying a transparent resin solution in which a transparent resin is dissolved so as to cover the wiring and drying to form a flexible transparent resin base material having a total light transmittance of 70% or more to form a laminate,
A method for producing a flexible wiring board, comprising: a peeling step of peeling the substrate from the laminate. The method for manufacturing a flexible wiring board according to claim 3, wherein the substrate is made of an inorganic substance.

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