JP2012169558A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance connection reliability by stabilizing the sectional shape of wiring.SOLUTION: The printed wiring board comprises an insulating film, and wiring which includes an inner lead and an outer lead formed on the insulating film. The wiring consists of an etching formation wiring part formed by etching a copper foil layer on the insulating film, and a direct drawing formation wiring part formed by directly drawing the insulating film with a conductive ink containing metal nanoparticles as a main component. At least the inner lead is the direct drawing formation wiring part.

Description

  The present invention relates to a printed wiring board, and more particularly to a printed wiring board in which a part of wiring is formed by direct drawing.

  The printed wiring board is used, for example, in a driver IC package for driving a liquid crystal display (LCD) mounted on an electronic device such as a personal computer display or a liquid crystal television. In recent years, due to the miniaturization of LCDs and the accompanying fine wiring, the demand for fine wiring is also increasing in TCP (Tape Carrier Package) packages for LCD driver ICs.

  TCP consists of a three-layer structure of polyimide tape (for example, thickness 12 to 100 μm), adhesive, and copper foil (for example, thickness 18 μm) as an insulating film, and protrudes from a device hole provided in the insulating film. Since the flying lead is liable to be deformed, the miniaturization of the wiring pitch is limited to about 40 μm. In contrast, COF (Chip On Film) has a two-layer structure of polyimide tape as an insulating film and copper foil (for example, a thickness of 8 to 35 μm), has no device holes, and the inner leads are insulative. The structure is in close contact with the film. For this reason, fine wiring can be achieved as compared with TCP.

In general, the COF wiring (lead) for LCD is connected to the liquid crystal panel and PCB (Printed Circuit Board) from the input / output side inner leads connected to the liquid crystal driver chip on the insulating film surface. It is formed by being routed to the output side outer lead.
The wiring pitch on the input / output side inner leads has been reduced to a fine pitch, and is currently a narrow pitch of about 25 μm. On the other hand, the wiring pitch in the outer lead is about 35 to 50 μm for the output side outer lead and about 200 μm to 300 μm for the input side outer lead, which is a rough pitch having a wider wiring pitch than the inner lead. That is, in the COF wiring, fine pitch (narrow pitch) inner leads and rough pitch (wide pitch) outer leads are mixed in a narrow region.

The COF wiring is generally formed by a subtractive method. In the subtractive method, a desired resist pattern is formed by exposure and development on a resist film formed on a copper foil on an insulating film, and the copper foil is selectively removed by etching using the resist pattern as a mask. In this way, a predetermined pattern of wiring is obtained.
As another wiring pattern forming method, there is a method of directly forming (direct drawing) a wiring pattern on an insulating film. For example, Patent Document 1 proposes a lithographic printing plate precursor for forming a pattern having a uniform line width. By using this original plate and printing conductive ink on a substrate such as a film, a pattern having a uniform line width can be directly drawn.

  In addition, as the conductive ink used in the pattern direct drawing method, there is a conductive ink or a conductive paste containing metal nanoparticles. For example, Patent Document 2 proposes a conductive ink to which metal nanoparticles having an average particle diameter of 1 to 10 nm, metal particles having an average particle diameter of 0.5 to 10 μm, and a protective agent or a dispersion medium are added. This conductive ink contains metal particles, and the conductive component in the conductive ink increases, so that it is possible to suppress a decrease in wiring reliability due to shrinkage when sintering metal particles and metal nanoparticles. Has been.

JP 2007-148386 A JP 2005-174828 A

  By the way, when a pattern in which a narrow pitch inner lead portion and a rough pitch outer lead portion are mixed in a narrow region is formed by the subtractive method, the etching conditions are adjusted according to the formation of the inner lead portion which is usually a narrow pitch. Is done. For this reason, a difference occurs in the etching shape between the inner lead portion having a narrow pitch and the outer lead portion having a rough pitch. This will be described with reference to FIG. 3A showing a cross-sectional view of wiring in a narrow pitch region and FIG. 3B showing a cross-sectional view of wiring in a rough pitch region. Etching is appropriately performed on the inner lead 6 having a narrow pitch on the insulating film 2, and as shown in FIG. 3A, the cross-sectional shape of the wiring in the inner lead 6 is rectangular or trapezoidal (mesa). Become. On the other hand, in the rough-pitch input / output-side outer leads 7a and 7b, as shown in FIG. 3B, the etching solution stays 20 between the patterns before the etching of the narrow-pitch inner leads 6 is completed. As a result, the etching proceeds excessively. Due to excessive etching 30, the cross-sectional shape of the wiring in the input / output side outer leads 7 a, 7 b with rough pitch becomes an inverted mesa shape. The inverted mesa shape is a structure in which the top width is wider than the bottom width of the wiring and is brittle. For this reason, when the terminals of the PCB and the liquid crystal panel are electrically connected to the input / output side outer leads 7a and 7b having the reverse mesa shape, the strength against the bonding pressure is weak and the connection reliability is low. As described above, when a high-definition pattern is formed by etching, there is a problem that connection reliability tends to be lowered in the outer lead portion having a relatively rough pitch.

  In this regard, according to Patent Document 1 and Patent Document 2 which are directly drawn, since etching is not performed, it is considered that a pattern in which the cross-sectional shape of the wiring is relatively stable can be formed. However, in the above-mentioned Patent Document 1, since a conductive ink containing a metal powder having a large particle is used for direct drawing, a fine wiring is required, and a printed wiring board such as a COF having a fine pattern width has a In particular, it is difficult to form inner lead portions with a narrow wiring pitch.

  Currently, there are conductive inks containing metal nanoparticles as the main component, but the metal nanoparticles contained are generally Ag nanoparticles. An Ag wiring formed using a conductive ink mainly composed of Ag nanoparticles has a problem that it is inferior in electrical conductivity and migration resistance as compared to a Cu wiring formed by etching.

  An object of the present invention is to provide a printed wiring board that is excellent in wiring connection reliability and suitable for miniaturization.

  According to a first aspect of the present invention, in a printed wiring board comprising: an insulating film; and a wiring including an inner lead portion and an outer lead portion formed on the insulating film, the wiring is the insulating film. Etching formation wiring part formed by etching the copper foil layer on the conductive film, and direct drawing formation formed by directly drawing conductive ink mainly composed of metal nanoparticles on the insulating film And a printed wiring board in which at least the inner lead portion is the direct drawing formation wiring portion.

In the printed wiring board, on the insulating film in the formation region of the direct drawing formation wiring portion, a resin layer including a conductive expression agent that acts on the metal nanoparticles to express conductivity is provided, and the resin It is preferable that the direct drawing formation wiring portion is formed on the layer.

  In the printed wiring board, it is preferable that a porous layer is interposed between the insulating film and the resin layer.

  In the printed wiring board, the insulating film includes a conductive enhancer that acts on the metal nanoparticles to develop conductivity, and the direct drawing wiring portion is formed on the insulating film. Is preferred.

  In the printed wiring board, the metal nanoparticles are preferably made of Ag or Cu.

  ADVANTAGE OF THE INVENTION According to this invention, the printed wiring board suitable for miniaturization which is excellent in the connection reliability of wiring is obtained.

(A) is a schematic plan view of the printed wiring board concerning one Embodiment of this invention, (b) is the principal part enlarged view in (a). It is a top view which shows 1 process of the manufacturing method which manufactures the printed wiring board concerning one Embodiment of this invention. It is a top view which shows 1 process of the manufacturing method which manufactures the printed wiring board concerning one Embodiment of this invention. It is a top view which shows 1 process of the manufacturing method which manufactures the printed wiring board concerning one Embodiment of this invention. (A) is sectional drawing of the wiring in a narrow pitch area | region, (b) is sectional drawing of the wiring in a rough pitch area | region.

  A printed wiring board according to an embodiment of the present invention will be described with reference to the drawings. The printed wiring board of this embodiment is a COF type printed wiring board for a liquid crystal display. A schematic plan view of the printed wiring board according to the present embodiment is shown in FIG.

[Printed wiring board]
As shown in FIG. 1A, the printed wiring board 1 according to the present embodiment includes an insulating film 2 and an inner lead portion 4 and an outer lead portion formed on at least one surface of the insulating film 2. And a wiring (lead) 3 having 5. The wiring 3 is formed by directly etching a conductive ink mainly composed of metal nanoparticles to form a direct drawing forming wiring portion 8 (gray-painted portion of the wiring 3) and a copper foil layer. And an etching-formed wiring portion 9 (a portion where the wiring 3 is not painted). In the present embodiment, the inner lead portion 4 is the direct drawing formation wiring portion 8. Sprocket holes 11 for conveying the insulating film 2 are provided at both ends of the printed wiring board 1.

The inner lead 6 of the inner lead portion 4 is formed in an IC chip mounting region located at the center in the width direction of the insulating film 2 on which a driver IC chip for driving a liquid crystal display is mounted. The outer lead portion 5 has an input-side outer lead 7a connected to the PCB terminal and an output-side outer lead 7b connected to the terminal of the liquid crystal panel. The wiring (lead) 3 between the inner lead 6 and the input / output side outer leads 7a, 7b is appropriately routed. In the present embodiment, the number of output terminals of the IC chip is larger than the number of input terminals, and as shown in FIG. 1A, the both ends of the insulating film 2 are not connected to the IC chip. Wiring 3 is also provided.

As described above, the wiring pitch D ₁ of the inner lead portion 4 composed of a plurality of inner leads 6 is about 25 [mu] m, and has a narrow pitch region. 35~50μm about in narrow wiring pitch _{D 2} of the plurality of output side outer leads 7b, the wiring pitch _{D 3} at the input side outer lead 7a is on the order of 200-300 [mu] m, the input-side outer leads 7a and the output side outer The outer lead portion 5 including the lead 7b is a rough pitch region having a wider wiring pitch than the inner lead portion 4. As described above, the wiring 3 has a mixture of various wiring pitch patterns.

  In this embodiment, as shown in FIG. 1A and FIG. 1B, the inner lead portion 4 of the wiring 3 is made of conductive ink mainly composed of metal nanoparticles on the insulating film 2. A direct drawing formation wiring portion 8 formed by direct drawing is formed, and a wiring excluding the inner lead portion 4 in the wiring 3 is an etching formation wiring portion 9 formed by etching.

  According to the above configuration, since the inner lead portion 4 with a narrow pitch is a direct drawing formation wiring portion formed by direct drawing, the cross-sectional shape of the wiring in the inner lead portion 4 is stable in a rectangular shape or a trapezoidal (mesa) shape. Formed. In addition, the wiring excluding the inner lead portion 4 is a rough pitch pattern and is an etching-formed wiring portion 9 formed by etching, but the etching conditions can be adjusted to a rough pitch region, so that the cross-sectional shape of the wiring is rectangular or It is stably formed in a trapezoidal (mesa) shape. In other words, by selectively forming a narrow pitch region by direct drawing even in high-definition wiring, the difference in etching shape between the narrow pitch region and the rough pitch region when the entire wiring region is formed by etching. This can be eliminated, and the cross-sectional shape of all wirings can be stabilized. And, by stabilizing the wiring shape, the connection reliability of the inner lead portion 4 and the outer lead portion 5 with the external terminals can be improved. In addition, since the etching conditions for forming the etching-formed wiring portion 9 can be adjusted as appropriate, the wiring width and shape of the etching-formed wiring portion can be appropriately formed, and the wiring shape due to excessive etching or insufficient etching The trouble can be avoided.

  Moreover, in this embodiment, although it has the direct drawing formation wiring part by the metal nanoparticle which is inferior in terms of electrical conductivity or migration resistance as compared with the copper wiring formed by etching the copper foil layer, the direct drawing Since the formed wiring portion is a part of the entire wiring (inner lead portion which is a narrow pitch region), it is possible to suppress a significant decrease in electrical conductivity and migration resistance as the entire wiring.

[Method for Forming Direct Drawing Formation Wiring Section]
Here, a method of forming the direct drawing formation wiring portion will be described. The direct drawing formation wiring part is formed of conductive ink (hereinafter referred to as conductive ink) mainly composed of metal nanoparticles. The conductive ink is not particularly limited as long as it can directly draw a high-definition pattern, and a known ink can be used. The conductive ink refers to an ink in which contained metal nanoparticles are coated with a dispersant and dispersed in a dispersion medium. Metal nanoparticles are metal fine particles having an average particle size of 100 nm or less and exhibiting high reactivity, and are coated with a dispersant and dispersed in a dispersion medium as a stable colloid. Any dispersing agent may be used as long as it can reduce and coat the metal nanoparticles. For example, citric acid or dextrin can be used. The dispersion medium is not particularly limited as long as it can disperse the metal nanoparticles, and is composed of water, an organic solvent, or a mixture thereof. The conductive ink can be used from a low viscosity solution state to a high viscosity paste state by adding a polymer binder.

In the conductive ink, since the metal nanoparticles are coated with a dispersant and dispersed in a dispersion medium, the conductive ink does not exhibit conductivity or is low even when applied. For this reason, it is necessary to develop conductivity by removing the dispersant and the dispersion medium and bringing the metal nanoparticles into contact with each other and fusing them.
Examples of a method for developing the conductivity of the conductive ink include the following methods. For example, as a method of heating (firing), a method of forming a conductive wiring by fusing and firing metal nanoparticles together by removing the dispersing agent and dispersion medium that coat and protect the metal nanoparticles by heating. There is. In addition, as a method of not firing, a conductive expression agent that develops conductivity by reducing and fusing metal nanoparticles mainly composed of silver (JP 2008-4375 A, JP 2008-235224 A, There is a method using Japanese Patent Application No. 2007-184064.

  Below, the case where it does not bake using a conductive expression agent is demonstrated concretely as a method of expressing electroconductivity.

The conductive ink in the present invention is an ink in which metal nanoparticles coated with a dispersant are dispersed in a dispersion medium as a colloid, and Cu, Ag, or the like can be used as a metal species. The average primary particle diameter of the dispersed metal nanoparticles is preferably 200 nm or less, more preferably 100 nm or less from the viewpoint of maintaining a stable dispersion state of the metal nanoparticles as a colloid. It is preferably 50 nm or less. Here, the average primary particle diameter is obtained by averaging the diameter of a circle equal to the projected area of each of 100 particles existing within a certain area by observation with an electron microscope of metal nanoparticles as the particle diameter.
The content of the metal nanoparticles contained in the conductive ink in the present invention is preferably 1% by mass to 95% by mass, more preferably 3% by mass to 90% by mass with respect to the total mass of the conductive ink. .

  The dispersion medium used for the conductive ink is water and / or an organic solvent, and examples thereof include water alone, a mixture of water and an organic solvent, and an organic solvent alone. As the mixture of water and the organic solvent, a water-soluble low-boiling point solvent such as methanol or a water-soluble high-boiling point organic solvent such as ethylene glycol can be used as the organic solvent. As organic solvents only, alcohol-based high boiling organic solvents such as ethylene glycol, ketone-based high boiling organic solvents such as diacetone alcohol, glycol ether-based high boiling organic solvents such as ethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, etc. An ester-based high-boiling organic solvent, an aprotic amide-based high-boiling organic solvent such as N, N-dimethylacetamide, mineral spirit, or the like can be used.

  Metal nanoparticles are vapor-evaporated in which the metal is evaporated in an inert gas, cooled and condensed by collision with the gas, recovered, a metal vapor synthesis method in which the metal is evaporated in vacuum and recovered with an organic solvent, laser irradiation Laser ablation method that evaporates and condenses in liquid by energy, chemical reduction method that reduces and generates and recovers metal ions in aqueous solution, method by pyrolysis of organometallic compound, metal chloride in gas phase Metal nanoparticles produced by various known methods such as a method by reduction, a method of reducing oxides in hydrogen, a method using energy such as ultraviolet rays, ultrasonic waves, and microwaves can be preferably used.

  Various additives such as thickeners, antistatic agents, UV absorbers, plasticizers, and polymer binders may be added to the conductive ink depending on the purpose. For example, by adding a UV curable resin component. Further, it is possible to provide characteristics (UV curing characteristics) suitable for pattern formation by UV printing or UV inkjet method.

In the present invention, the conductive ink is adjusted in any form from a low-viscosity solution state to a high-viscosity paste state. Specifically, the viscosity, the surface tension, the size / content rate of the metal nanoparticles, and the like suitable for the method of applying the metal nanoparticles on the conductive pattern forming substrate are adjusted. For example, when using an inkjet method, it is preferable to adjust a viscosity to the range of 1-100 mPa * s, and when using screen printing, it is preferable to adjust to the range of 1-500 Pa * s.

  When adjusting to a high-viscosity paste state, it is difficult to obtain a desired viscosity only by increasing the concentration of metal nanoparticles, and therefore it is preferable to add a polymer binder or a thickener. As the polymer binder, various known polymer binders such as cellulose resin, phenol resin, epoxy resin, acrylic resin, polyester resin, and polyimide resin can be used. As the thickener, various known thickeners such as hydroxylpropylcellulose, carboxymethylcellulose, pectin, polystyrene sulfonates, and polyacrylic acid can be used.

  As the conductive ink used in the present invention, a conductive ink containing general metal nanoparticles can be used. In addition, it is preferable to use metal nanoparticles prepared using citric acid or dextrin because the production method is simple and the conductivity is excellent when the following conductivity enhancer is used.

The conductive ink is applied to a resin layer or an insulating film containing a conductive expression agent, and then the dispersion medium contained in the conductive ink is removed. The dispersion medium is removed by heating, drying, or absorption. After the dispersion medium is removed, the metal nanoparticles coated with the dispersant are reduced by the conductive enhancer, and the coating dispersant is removed. Along with the removal of the dispersant, the reduced and exposed metal nanoparticles come into contact with each other and are fused to form a conductive wiring. In other words, according to the conductive enhancer, since the dispersant is chemically removed by reduction, heating at a relatively low temperature that can remove the dispersion medium is not required when the metal nanoparticles are fused, and the dispersion medium can be removed. Thus, the metal nanoparticles can be fused to form a conductive wiring.
The conductive agent is not limited as long as it can reduce and fuse metal nanoparticles, for example, a compound having a halogen in the molecule by ionic bond, an alkali metal salt or alkaline earth metal salt of thiosulfuric acid. An ammonium salt. In addition, a plurality of these substances can be used in combination.

  In the printed wiring board according to the above-described embodiment, it is preferable to provide a resin layer containing a conductive expression agent on the direct drawing region of the insulating film. According to this configuration, when the metal nanoparticles are fused, the dispersant can be removed chemically by reduction, so that a high-temperature heating step for removing the dispersant can be omitted. And if it is the said structure, the selection range of an insulating film can be expanded. That is, when removing the dispersant and fusing the metal nanoparticles by high-temperature heating without using a conductive developer, an insulating film having a glass transition temperature lower than the heating temperature is selected because it will bend. Can not do it. On the other hand, according to the said structure, even if it heats, since it is the heating of the comparatively low temperature for removing a dispersion medium, the breadth of selection of an insulating film can be expanded.

  Moreover, the resin layer containing the conductive expression agent is preferably a resin that absorbs the dispersion medium and dissolves or swells. As this resin, for example, a water-soluble resin, an organic solvent-soluble resin, or organic fine particles can be used. This is because this configuration can absorb the dispersion medium contained in the applied conductive ink and improve the adhesion of the metal nanoparticles in the conductive ink to the insulating film.

Moreover, in the printed wiring board which concerns on the said embodiment, it is preferable to interpose a porous layer between the resin layer containing a conductive expression agent and an insulating film. As the porous layer, fine particles such as silica and alumina hydrate are contained in a resin, and any known material can be used as long as it can quickly absorb the dispersion medium. According to this configuration, the porous layer absorbs the dispersion medium in the conductive ink, and the heating and drying steps for removing the dispersion medium can be omitted. In other words, the combination of the resin layer containing the conductive enhancer and the porous layer makes it possible to absorb excess dispersant and dispersion medium and bring the metal nanoparticles into close proximity, and melt the metal nanoparticles at a relatively low temperature. Can be worn. In addition, since the absorption of the dispersion medium is promoted by the porous layer, it is possible to form a high-definition pattern by suppressing the bleeding of the conductive ink and improving the adhesion between the wiring and the resin layer. In addition, you may further add a conductive expression agent in a porous layer.

  Moreover, in the printed wiring board which concerns on the said embodiment, it is preferable to make a conductive expression agent contain in an insulating film. According to this configuration, it is possible to omit the step of forming the resin layer containing the conductive expression agent. In addition, since a resin layer containing a conductive expression agent is not required, the heating temperature when heating is not affected by the glass transition temperature (Tg) of the resin used for the resin layer and the like, and is an insulating film. Heating at a temperature lower than the Tg of can be achieved. That is, the removal of the dispersion medium can be accelerated by heating without causing bending of the insulating film. Furthermore, since wiring can be formed directly on the insulating film, wiring with high adhesion can be formed.

  Moreover, in the printed wiring board which concerns on the said embodiment, it is preferable that a metal nanoparticle consists of Ag or Cu. In particular, Cu is more preferable because it is excellent in electric conductivity and migration resistance. Even in the case of using Ag, since only the direct drawing formation wiring portion that is a part of the wiring is formed of Ag, it is possible to suppress a decrease in electrical conductivity and migration resistance of the entire wiring.

  In the above-described embodiment, only the inner lead portion is used as the direct drawing formation wiring portion. However, in the present invention, not only the inner lead portion but also the direct drawing formation wiring portion can be appropriately selected. For example, a wiring (lead) routing portion in the vicinity of the inner lead can be directly used as a drawing formation wiring portion.

[Printed wiring board manufacturing method]
A method for manufacturing a printed wiring board according to an embodiment of the present invention will be described with reference to FIGS. 2A to 2C. The manufacturing method according to the present embodiment includes an etching step of etching the copper foil layer on the insulating film to form an etching formation wiring portion, and a porous layer on the formation region of the direct drawing formation wiring portion of the insulating film. A porous layer forming step to be formed; a resin layer forming step of providing a resin layer containing a conductive agent on the formed porous layer; and metal nanoparticles as a main component on the resin layer containing the conductive agent. A direct drawing step of directly drawing conductive ink to form a direct drawing forming wiring portion.

  First, a polyimide film is prepared as the insulating film 2, a Cr—Ni sputtering layer is formed on one surface of the insulating film 2 by sputtering, and a copper foil layer (copper plating layer) is plated on the sputtering layer. Form. In addition, the said copper foil layer is not limited to the copper plating layer formed above the sputter | spatter layer, For example, it is also possible to use a rolled copper foil, an electrolytic copper foil, etc. In this case, a rolled copper foil or the like can be bonded to the insulating film via an adhesive.

Next, a resist pattern is formed by applying a resist to the insulating film 2 on which the copper foil layer is formed, and exposing and developing. Thereafter, etching is performed with an etching solution to form a predetermined etching formation wiring portion 9. As shown in FIG. 2A, the etching-formed wiring portion 9 includes outer lead portions 5 having a rough pitch, and is a wiring excluding the inner lead portions having a narrow pitch. When forming the etching-formed wiring part 9, it is possible to focus on etching the etching-formed wiring part 9 including the outer lead part 5 having a relatively rough pitch by not etching the inner lead part having a narrow pitch. A difference in cross-sectional shape between wirings due to etching can be minimized. And the cross-sectional shape of the etching formation wiring part 9 can be stabilized, and the connection reliability in the outer lead part 5 can be improved. 2A is a region where a resin layer containing a conductive expression agent is formed, and the copper foil layer in the region S is etched and removed simultaneously with the etching process of the etching-formed wiring portion 9. Is done.

Next, as shown in FIG. 2B, a porous layer is formed by applying a resin containing silica as fine particles to the region where the inner lead portion of the insulating film 2 is formed. By this porous layer, the dispersion medium in the conductive ink drawn directly can be quickly absorbed, and the heating step for removing the dispersion medium can be omitted.
And resin containing an electroconductive expression agent is apply | coated on a porous layer, and the resin layer 10 containing an electroconductive expression agent is provided. By forming this resin layer 10, wiring can be formed by applying conductive ink mainly composed of metal nanoparticles in the formation of a direct drawing formation wiring portion described later, and excessive high-temperature heat treatment is omitted. can do. The total thickness of the porous layer and the resin layer 10 containing the conductive expression agent is approximately the same as the thickness of the etching formation wiring portion 9 as the sum of the thickness of the direct drawing formation wiring portion 8 provided on the resin layer 10. Each is adjusted to be equivalent. For example, the total thickness of the porous layer and the resin layer 10 can be about 1 to 5 μm.

  Next, the conductive ink which has Ag nanoparticle as a main component is drawn directly on the resin layer 10 containing a conductive expression agent by inkjet printing. The dispersion medium contained in the drawn conductive ink is absorbed and removed by the porous layer, and the dispersant covering the metal nanoparticles is reduced and chemically removed by the conductive developer in the resin layer 10. Will be. The exposed metal nanoparticles come into contact with each other and are fused by heating at a relatively low temperature. As a result, as shown in FIG. 2C, the direct drawing formation wiring portion 8 as the inner lead portion 4 is formed by being connected to the etching formation wiring portion 9. As described above, the thickness of the direct drawing formation wiring portion 8 is equal to the thickness of the copper foil layer of the etching formation wiring portion 9 as the sum of the thickness of the resin layer 10 containing the conductive agent and the porous layer. Formed to be. By this direct drawing, the inner lead portion 4 that was not formed by etching is formed, and all of the wiring 3 composed of the etching formed wiring portion 9 and the direct drawing wiring portion 8 is formed, and the printed wiring board according to the present embodiment Get one. Since the direct drawing formation wiring portion 8 has a rectangular or trapezoidal (mesa) cross-sectional shape, the connection reliability is high. In addition, although it does not specifically limit as a coating method of electroconductive ink, For example, inkjet printing and screen printing are preferable.

  In the above embodiment, the porous layer forming step and the resin layer forming step can be provided before the etching step. In this case, after removing the region for forming the resin layer containing the conductive expression agent from the copper foil layer on the insulating film in advance, a porous material is formed by applying a resin containing the conductive expression agent to the etched region. A layer and a resin layer are formed. Thereafter, an etching formation wiring portion excluding the inner lead portion is formed by etching. Next, a direct drawing formation wiring portion is formed on the resin layer by directly drawing conductive ink mainly composed of metal nanoparticles. According to this configuration, it is possible to reduce mistakes in the formation of the resin layer when applying the resin containing the conductive expression agent in the resin layer forming step.

  Moreover, although the porous layer was provided in the said embodiment, it is not necessary to form a porous layer. In this case, it is preferable to remove the dispersion medium by drying or heating the dispersion medium in the conductive ink at a temperature lower than the Tg of the insulating film.

A method for manufacturing a printed wiring board according to another embodiment will be described. In this embodiment, differences from the above embodiment will be described. This embodiment differs from the above-described embodiment in that an insulating film containing a conductive developer is used. By adding a conductive expression agent to the insulating film in advance, it is possible to omit the resin layer forming step and reduce the number of steps.

DESCRIPTION OF SYMBOLS 1 Printed wiring board 2 Insulating film 3 Wiring 4 Inner lead part 5 Outer lead part 6 Inner lead 7a Input side outer lead 7b Output side outer lead 8 Direct drawing formation wiring part 9 Etching formation wiring part 10 Resin containing conductive expression agent Layer 11 Sprocket hole 20 Retention of etching solution 30 Excessive etching

Claims (5)

In a printed wiring board comprising an insulating film, and a wiring including an inner lead portion and an outer lead portion formed on the insulating film,
The wiring is formed by directly drawing conductive ink mainly composed of metal nanoparticles on the insulating film and an etching-formed wiring portion formed by etching the copper foil layer on the insulating film. A direct drawing formation wiring portion to be formed, and
At least the inner lead part is the direct drawing formation wiring part.   2. The printed wiring board according to claim 1, wherein a resin layer including a conductive expression agent that acts on the metal nanoparticles and develops conductivity on the insulating film in the formation region of the direct drawing formation wiring portion. 3. A printed wiring board provided, wherein the direct drawing formation wiring portion is formed on the resin layer.   The printed wiring board according to claim 2, wherein a porous layer is interposed between the insulating film and the resin layer.   2. The printed wiring board according to claim 1, wherein the insulating film includes a conductive expression agent that acts on the metal nanoparticles to develop conductivity, and the direct-drawing wiring portion on the insulating film. A printed wiring board characterized in that is formed.   5. The printed wiring board according to claim 1, wherein the metal nanoparticles are made of Ag or Cu. 6.