JP2016167558A - Method for manufacturing base material for printed-wiring board, base material for printed-wiring board, and printed-wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a base material for a printed-wiring board capable of easily and surely manufacturing a via hole, and reducing the number of manufacturing processes.SOLUTION: A method for manufacturing a base material for a printed-wiring board, comprises the steps of: forming one or more through holes in a base film with insulation properties; coating an ink containing metal particles on at least one surface of the base film; and burning the coated ink. An average particle size of the metal particles is not less than 1 nm and not more than 500 nm. The coating step preferably includes a first step of coating the ink on one surface of the base film, and a second step of coating the ink on the other surface of the base film. A mean diameter of a through hole of the base film is preferably not less than 10 μm and not more than 100 μm. The content of metal particles in the ink is preferably not less than 5 mass% and not more than 50 mass%.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing a printed wiring board substrate, a printed wiring board substrate, and a printed wiring board.

  There is known a flexible printed wiring board in which conductive patterns are arranged on both surfaces of a flexible base film. In such a flexible printed wiring board 101, as shown in FIG. 8, conductive layers 103 and 104 having conductive patterns are laminated on both surfaces of a base film 102, and the base film 102 and one of the conductive layers 103 are penetrated. A hole 105 is formed. In the conventional flexible printed wiring board 101, a conductive material is filled in a recess formed by the through hole 105 and the other conductive layer 104, and the conductive material is cured to form a via hole 106. As a result, the pair of conductive layers 103 and 104 are electrically connected.

  Moreover, as a conductive material in such a conventional printed wiring board, a conductive paste containing conductive particles and a binder resin is used (see JP 2013-254910 A). That is, the conventional via hole is formed by fixing the conductive particles with the binder resin.

JP2013-254910A

  As described above, the conventional printed wiring board is formed by laminating a pair of conductive layers on both surfaces of a base film and electrically connecting the conductive layers by via holes. That is, in the conventional printed wiring board, a via hole is formed after forming a conductive layer. Therefore, in order to form the via hole, a separate via hole forming step is required in addition to the step of forming the conductive pattern. Therefore, the conventional printed wiring board is not sufficiently promoted to simplify the manufacturing process.

  The present invention has been made on the basis of the circumstances as described above, and provides a method for manufacturing a substrate for a printed wiring board capable of easily and reliably manufacturing a via hole and reducing the number of manufacturing steps. The purpose is to provide. Moreover, an object of this invention is to provide the base material for printed wiring boards and a printed wiring board which can suppress the increase in a manufacturing process.

  A method for manufacturing a printed wiring board substrate according to an aspect of the present invention, which has been made to solve the above problems, includes a step of forming one or a plurality of through holes in a base film having insulation properties, The method includes a step of applying an ink containing metal particles on at least one surface and a step of baking the applied ink, and the average particle diameter of the metal particles is 1 nm or more and 500 nm or less.

  A printed wiring board substrate according to another aspect of the present invention, which has been made to solve the above-described problems, has a base film having one or a plurality of through-holes and having an insulating property, and at least one of the base films A substrate for a printed wiring board comprising a sintered layer of metal particles formed on the surface of the substrate, and formed of a sintered body of metal particles similar to the sintered layer formed in the through hole. A via hole is further provided, and the average particle diameter of the metal particles is 1 nm or more and 500 nm or less.

  A printed wiring board according to another embodiment of the present invention made to solve the above problems is formed by a subtractive method or a semi-additive method using the printed wiring board substrate.

  The method for producing a printed wiring board substrate of the present invention can produce a via hole easily and reliably, and can reduce the number of production steps. Moreover, the base material for printed wiring boards and the printed wiring board of this invention can suppress the increase in a manufacturing process.

It is typical sectional drawing which shows the base film used with the manufacturing method of the base material for printed wiring boards which concerns on one Embodiment of this invention. It is typical sectional drawing explaining the through-hole formation process of the manufacturing method of the base material for printed wiring boards which concerns on one Embodiment of this invention. It is typical sectional drawing explaining the 1st process of the coating process of the manufacturing method of the base material for printed wiring boards which concerns on one Embodiment of this invention. It is typical sectional drawing explaining the 2nd process of the coating process of the manufacturing method of the base material for printed wiring boards which concerns on one Embodiment of this invention. It is typical sectional drawing explaining the baking process of the manufacturing method of the base material for printed wiring boards which concerns on one Embodiment of this invention. It is typical sectional drawing explaining the electroless-plating process of the manufacturing method of the base material for printed wiring boards which concerns on one Embodiment of this invention. It is typical sectional drawing explaining the electroplating process of the manufacturing method of the base material for printed wiring boards which concerns on one Embodiment of this invention. It is a typical sectional view showing the substrate for printed wiring boards concerning one embodiment of the present invention. It is a typical partial enlarged view which shows the via hole of the base material for printed wiring boards of FIG. It is typical sectional drawing which shows the base material for printed wiring boards which concerns on embodiment different from the base material for printed wiring boards of FIG. It is typical sectional drawing which shows the base material for printed wiring boards which concerns on embodiment different from the base material for printed wiring boards of FIG.2 and FIG.4. It is a typical sectional view showing the printed wiring board concerning one embodiment of the present invention. It is typical sectional drawing explaining the coating process of the manufacturing method of the base material for printed wiring boards which concerns on other embodiment of this invention. It is typical sectional drawing which shows the conventional printed wiring board.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.

  The manufacturing method of the base material for printed wiring boards which concerns on 1 aspect of this invention contains the metal particle in the process of forming 1 or several through-hole in the base film which has insulation, and the said base film at least one surface A step of applying the ink to be applied and a step of baking the applied ink, wherein the metal particles have an average particle diameter of 1 nm to 500 nm.

  The printed wiring board substrate manufacturing method includes forming a through hole in a base film, and applying an ink containing metal particles having an average particle diameter in the above range on one surface of the base film. The ink can be filled into the through-hole while covering one surface of the base film. Moreover, the manufacturing method of the said base material for printed wiring boards is a sintered compact formed with the said metal particle by baking the ink with which one side of the said base film was coat | covered, and the said through-hole was filled. Thus, a sintered layer serving as a base of the conductive pattern can be formed on one surface of the base film, and a via hole can be formed in the through hole. Thus, since the said manufacturing method of the base material for printed wiring boards can manufacture the said via hole easily and reliably simultaneously with the said sintered layer, compared with the manufacturing method of the conventional base material for printed wiring boards. Manufacturing processes can be reduced, and efficiency and cost reduction can be promoted.

  The coating step may include a first step of applying the ink to one surface of the base film and a second step of applying the ink to the other surface of the base film. Thus, by coating the ink on both sides of the base film in the coating step, for example, a substrate for a double-sided printed wiring board can be manufactured efficiently and at a low cost using the same equipment and materials. Can do.

  The average diameter of the through holes of the base film is preferably 10 μm or more and 100 μm or less. Thus, when the average diameter of the through holes of the base film is within the above range, the ink can be easily held in the through holes by the surface tension, and the manufacture of the printed wiring board substrate is facilitated. The

  The content of the metal particles in the ink is preferably 5% by mass or more and 50% by mass or less. Thus, since the content of the metal particles in the ink is within the above range, the viscosity can be adjusted so that the ink can be easily held in the through hole. Is done.

  It is preferable to further include a step of performing electroless plating on the outer surface of the sintered layer formed by the firing step. Thus, by providing a step of performing electroless plating on the outer surface of the sintered layer formed by the firing step, the space between the metal particles forming the sintered layer is filled with plating by electroless plating, The peel strength between the sintered layer and the base film can be improved and conductivity can be increased.

  It is preferable to further include a step of performing electroplating on the outer surface side of the sintered layer formed by the firing step. Thus, the thickness of plating can be adjusted easily and reliably by providing the process of electroplating the outer surface side of the sintered layer formed by the said baking process.

  The metal particles of the ink are preferably composed mainly of copper or a copper alloy. Thus, when the metal particles of the ink contain copper or a copper alloy as a main component, the conductivity can be improved while suppressing the manufacturing cost.

  A printed wiring board substrate according to another aspect of the present invention, which has been made to solve the above-described problems, has a base film having one or a plurality of through-holes and having an insulating property, and at least one of the base films A substrate for a printed wiring board comprising a sintered layer of metal particles formed on the surface of the substrate, and formed of a sintered body of metal particles similar to the sintered layer formed in the through hole. A via hole is further provided, and the average particle diameter of the metal particles is 1 nm or more and 500 nm or less.

  Since the substrate for a printed wiring board includes a via hole formed of a sintered body of metal particles similar to the sintered layer in the through hole, the insulating layer is further formed as in the conventional printed wiring board. It is not necessary to form the via hole by a separate process. Therefore, the said printed wiring board base material can aim at reduction of a manufacturing process compared with the conventional printed wiring board.

  The upper limit of the ratio of the maximum unevenness height of the via hole surface to the average diameter of the through-holes with respect to the average position of the outer surface of the sintered layer is preferably 1/10. Thus, by setting the ratio of the maximum unevenness height of the via hole surface to the average diameter of the through holes in the above range, planarization of the via hole surface is promoted, and for example, a cover coat is applied to the surface of the via hole without bubbles. Can do.

  A sintered layer may be provided on both sides of the base film. Thus, by providing a sintered layer on both surfaces of the base film, it is possible to promote manufacturing efficiency and cost reduction.

  The average diameter of the through holes of the base film is preferably 10 μm or more and 100 μm or less. Thus, when the average diameter of the through-holes of the base film is within the above range, the via hole can be accurately formed and the conductivity can be enhanced.

  It is good to have the plating metal formed in the outer surface of the said sintered layer. Thus, by having a plating metal on the outer surface of the sintered layer, the peel strength between the sintered layer and the base film is improved and the conductivity is enhanced.

  It is good to have a metal plating layer in the outer surface of the layer formed with the said sintered layer and plating metal. Thus, by having a metal plating layer on the outer surface of the sintered layer and the layer formed by the plating metal, the thickness of the metal layer formed by these can be easily and reliably adjusted.

  The metal particles are preferably composed mainly of copper or a copper alloy. As described above, when the metal particles contain copper or a copper alloy as a main component, the conductivity can be improved while suppressing the manufacturing cost.

  The porosity of the via hole is preferably 0.1% or more and 50% or less. Thus, when the porosity of the via hole is within the above range, the conductivity can be sufficiently increased.

  A printed wiring board according to another embodiment of the present invention made to solve the above problems is formed by a subtractive method or a semi-additive method using the printed wiring board substrate.

  Since the printed wiring board uses the substrate for the printed wiring board, the number of manufacturing steps can be reduced as compared with the conventional printed wiring board.

  In the present invention, the “average particle diameter” refers to the average particle diameter represented by the center diameter D50 of the volume particle size distribution of the metal particles in the dispersion. “Average diameter” means the diameter when converted to a perfect circle of the same area. “Via porosity” refers to the ratio of voids in the sintered body inside the through hole forming the via hole, and can be determined by measuring the density of the via hole in accordance with ASTM-D-792. In addition, regarding the parameters of the fine regions such as “maximum unevenness height of via hole surface”, “average particle diameter”, “average diameter”, “via hole porosity”, the cross section of the via hole is enlarged and observed with an electron microscope. It can also be measured.

[Details of the embodiment of the present invention]
Hereinafter, a printed wiring board substrate manufacturing method, a printed wiring board substrate, and a printed wiring board according to an embodiment of the present invention will be described with reference to the drawings.

[First embodiment]
<Method for producing substrate for printed wiring board>
With reference to FIG. 1A thru | or FIG. 1G, the manufacturing method of the said base material for printed wiring boards is demonstrated. The method for manufacturing a printed wiring board substrate is used for manufacturing a flexible printed wiring board substrate having flexibility. The method for producing a substrate for a printed wiring board includes a step of forming one or a plurality of through holes in an insulating base film, a step of applying an ink containing metal particles on both sides of the base film, And a step of baking the coated ink. The printed wiring board substrate manufacturing method includes the steps of electroless plating on the outer surface of the sintered layer formed by the firing step, and the electric surface on the outer surface side of the sintered layer formed by the firing step. And a step of performing plating.

(Base film)
First, the base film used with the manufacturing method of the said base material for printed wiring boards is demonstrated. The base film 1 of FIG. 1A has insulation and flexibility. Examples of the main component of the base film 1 include synthetic resins such as polyimide, polyethylene terephthalate, fluororesin, and liquid crystal polymer. Among these, polyimide that is excellent in insulation, flexibility, heat resistance, and the like is preferable.

  As a minimum of average thickness of base film 1, 10 micrometers is preferred, 15 micrometers is more preferred, and 25 micrometers is still more preferred. On the other hand, the upper limit of the average thickness of the base film 1 is preferably 100 μm, more preferably 60 μm, and even more preferably 40 μm. If the average thickness of the base film 1 is less than the above lower limit, the insulation and mechanical strength may be insufficient. Further, a through-hole 2 to be described later is provided in the base film 1, and when the through-hole 2 is filled with ink, the ink film thickness cannot be sufficiently obtained, and the surface of the via hole 5 obtained by baking this ink is flattened. There is a risk of becoming difficult. Conversely, if the average thickness of the base film 1 exceeds the upper limit, the amount of the ink used may increase unnecessarily and increase the cost. The “average thickness” refers to the distance between the average line of the front-side interface and the average line of the back-side interface within the measured length in the cross section cut in the thickness direction of the object. Here, the “average line” is an imaginary line drawn along the interface, and the total area of the mountain (total area above the imaginary line) and the total of the valleys partitioned by the interface and the imaginary line. A line whose area (total area below the imaginary line) is equal.

  Moreover, it is preferable to perform a hydrophilic treatment on the surface (fixed surface) on which sintered layers 4a and 4b, which will be described later, of the base film 1 are laminated. As the hydrophilization treatment, for example, plasma treatment for irradiating plasma to hydrophilize the fixing surface or alkali treatment for hydrophilizing the fixing surface with an alkaline solution can be employed. By applying a hydrophilic treatment to the fixed surface, the surface tension of the ink with respect to the fixed surface is reduced, so that the ink can be uniformly applied to the fixed surface.

<Through hole formation process>
In the through hole forming step, as shown in FIG. 1B, one or a plurality of through holes 2 are formed in the insulating base film. The through hole 2 is formed in a direction perpendicular to the planar direction of the base film 1. The method for forming the through hole 2 is not particularly limited, and examples thereof include etching processing, laser processing, punching processing, and the like.

  The lower limit of the average diameter of the through holes 2 is preferably 10 μm, more preferably 20 μm, and even more preferably 30 μm. On the other hand, the upper limit of the average diameter of the through holes 2 is preferably 100 μm, more preferably 70 μm, and even more preferably 50 μm. When the average diameter of the through-holes 2 is less than the above lower limit, there is a possibility that sufficient conductivity cannot be obtained when the via holes 5 are formed. On the other hand, if the average diameter of the through holes 2 exceeds the upper limit, the ink cannot be properly held in the through holes 2 when the ink is filled in the through holes 2, which may cause liquid leakage.

<Coating process>
In the coating process, ink containing metal particles is applied to both surfaces of the base film 1. The coating process includes a first process in which the ink is applied to one surface of the base film 1 and a second process in which the ink is applied to the other surface of the base film 1.

(First step)
In the first step, as shown in FIG. 1C, an ink containing metal particles is applied to one surface of the base film 1. The ink applied in the first step covers one surface of the base film 1 and fills the through hole 2 to form a coating film 3a. Hereinafter, the first step will be described in detail.

(Metal particles)
The metal particles dispersed in the ink can be produced by a high temperature treatment method, a liquid phase reduction method, a gas phase method, or the like. Especially, according to the liquid phase reduction method, the manufacturing cost can be further reduced, and the particle diameter of the metal particles can be easily made uniform by stirring in an aqueous solution.

In order to produce metal particles by the liquid phase reduction method, for example, a water-soluble metal compound that is a source of metal ions that form metal particles in water and a dispersant are dissolved, and a constant is added by adding a reducing agent. What is necessary is just to carry out the reduction reaction of a metal ion for a time. The metal particles produced by the liquid phase reduction method have a spherical or granular shape and can be made into fine particles. Examples of the water-soluble metal compounds underlying the metal ions, if for example a copper, copper nitrate _{(II) (Cu (NO 3} ) 2), copper (II) sulfate pentahydrate (CuSO ₄ · 5H ₂ O) and the like. In the case of silver, silver nitrate (I) (AgNO ₃ ), silver methanesulfonate (CH ₃ SO ₃ Ag), etc. In the case of gold, tetrachloroauric (III) acid tetrahydrate (HAuCl ₄ · 4H ₂ O) In the case of nickel, nickel chloride (II) hexahydrate (NiCl ₂ · 6H ₂ O), nickel nitrate (II) hexahydrate (Ni (NO ₃ ) ₂ · 6H ₂ O) and the like can be mentioned. it can. For other metal particles, water-soluble compounds such as chlorides, nitric acid compounds and sulfuric acid compounds can be used. Among these, the metal particles preferably include copper or a copper alloy as a main component. Thus, when the metal particles of the ink contain copper or a copper alloy as a main component, the conductivity can be improved while suppressing the manufacturing cost.

  As the reducing agent, various reducing agents capable of reducing and precipitating metal ions in a liquid phase (aqueous solution) reaction system can be used. Examples of the reducing agent include sodium borohydride, sodium hypophosphite, hydrazine, transition metal ions such as trivalent titanium ions and divalent cobalt ions, reducing sugars such as ascorbic acid, glucose and fructose, Examples include polyhydric alcohols such as ethylene glycol and glycerin. Among these, a trivalent titanium ion is preferable as the reducing agent. The liquid phase reduction method using trivalent titanium ions as a reducing agent is referred to as a titanium redox method. In this titanium redox method, metal ions are reduced by the redox action when trivalent titanium ions are oxidized to tetravalent, thereby depositing metal particles. Since the metal particles obtained by the titanium redox method have small and uniform particle diameters, the metal particles are filled with higher density, and the coating film 3a can be formed into a denser film.

  In order to adjust the particle size of the metal particles, the types and blending ratios of the metal compound, the dispersant and the reducing agent are adjusted, and the stirring speed, temperature, time, pH, etc. are adjusted when the metal compound is reduced. That's fine. The lower limit of the pH of the reaction system is preferably 7, and the upper limit of the pH of the reaction system is preferably 13. By setting the pH of the reaction system within the above range, metal particles having a minute particle diameter can be obtained. At this time, the pH of the reaction system can be easily adjusted to the above range by using a pH adjuster. As this pH adjuster, common acids or alkalis such as hydrochloric acid, sulfuric acid, nitric acid, sodium hydroxide, sodium carbonate, ammonia and the like can be used. In particular, alkali metals, alkaline earths are used to prevent deterioration of peripheral members. Nitric acid and ammonia which do not contain impurities such as metals, halogen elements, sulfur, phosphorus and boron are preferred.

  The lower limit of the average particle diameter of the metal particles is 1 nm, more preferably 10 nm, and even more preferably 30 nm. On the other hand, the upper limit of the average particle diameter of the metal particles is 500 nm, more preferably 300 nm, and even more preferably 100 nm. If the average particle diameter of the metal particles is less than the above lower limit, the dispersibility and stability of the metal particles in the ink may be reduced. Conversely, if the average particle diameter of the metal particles exceeds the above upper limit, the metal particles may be easily precipitated and the density of the metal particles may be non-uniform when the ink is applied.

  The lower limit of the content ratio of the metal particles in the ink is preferably 5% by mass, more preferably 10% by mass, and still more preferably 20% by mass. Moreover, as an upper limit of the content rate of the metal particle in ink, 50 mass% is preferable, 40 mass% is more preferable, and 30 mass% is further more preferable. When the content ratio of the metal particles is less than the lower limit, the viscosity of the ink is lowered, and there is a possibility that liquid leakage occurs when the ink is filled in the through hole 2. On the contrary, when the content ratio of the metal particles exceeds the upper limit, the viscosity increases, and the surface of the via hole 5 obtained by filling the through hole 2 with the ink and baking the ink may be difficult to flatten. .

(Other ingredients)
The ink may contain a dispersant in addition to the metal particles. The dispersant is not particularly limited, and various dispersants that can favorably disperse the metal particles can be used. The lower limit of the molecular weight of the dispersant is preferably 2,000, and the upper limit of the molecular weight of the dispersant is preferably 30,000. By using a dispersant having a molecular weight in the above range, the metal particles can be favorably dispersed in the ink, and the film quality of the coating film 3a can be made dense and defect-free. If the molecular weight of the dispersant is less than the lower limit, the effect of preventing the aggregation of the metal particles and maintaining the dispersion may not be sufficiently obtained. On the other hand, if the molecular weight of the dispersant exceeds the above upper limit, the volume of the dispersant is too large, and there is a possibility that voids are generated by inhibiting the sintering of the metal particles during firing of the coating film 3a. Moreover, when the volume of a dispersing agent is too large, there exists a possibility that the compactness of the coating film 3a may fall or the decomposition | disassembly residue of a dispersing agent may reduce electroconductivity.

  From the viewpoint of preventing deterioration of peripheral members, the dispersant preferably does not contain sulfur, phosphorus, boron, halogen and alkali. Preferred dispersants are those having a molecular weight in the above-mentioned range, such as amine-based polymer dispersants such as polyethyleneimine and polyvinylpyrrolidone, polyacrylic acid, and hydrocarbon-based polymers having a carboxy group in the molecule such as carboxymethylcellulose. High molecular weight dispersants such as molecular dispersants, poval (polyvinyl alcohol), styrene-maleic acid copolymers, olefin-maleic acid copolymers, copolymers having a polyethyleneimine moiety and a polyethylene oxide moiety in one molecule Examples thereof include molecular dispersants.

  The dispersant can also be added to the ink in the form of a solution dissolved in water or a water-soluble organic solvent. When a dispersant is added to the ink, the lower limit of the content of the dispersant is preferably 1 part by mass with respect to 100 parts by mass of metal particles. Moreover, as an upper limit of the content rate of a dispersing agent, 60 mass parts is preferable with respect to 100 mass parts metal particles. There exists a possibility that the aggregation prevention effect of a metal particle may become inadequate that the content rate of the said dispersing agent is less than the said minimum. On the other hand, if the content ratio of the dispersant exceeds the upper limit, excessive dispersant may inhibit the sintering of the metal particles during firing of the coating film 3a, and voids may be generated. May remain in the sintered layer 3 to be described later as an impurity and lower the electrical conductivity.

  As a dispersion medium in the ink, for example, water can be used. When water is used as a dispersion medium, the lower limit of the water content is preferably 20 parts by mass with respect to 100 parts by mass of metal particles. Moreover, as an upper limit of the content rate of water, 1,900 mass parts is preferable with respect to 100 mass parts metal particles. Water as a dispersion medium, for example, sufficiently swells the dispersant and serves to satisfactorily disperse the metal particles surrounded by the dispersant, but when the content ratio of the water is less than the lower limit, the dispersant The swelling effect may be insufficient. On the other hand, when the content ratio of the water exceeds the upper limit, the content ratio of the metal particles in the ink is decreased, and there is a possibility that a good sintered layer 3 having a necessary thickness and density cannot be formed.

  The ink may contain an organic solvent as necessary for viscosity adjustment, vapor pressure adjustment and the like. As such an organic solvent, various organic solvents that are water-soluble can be used. Specific examples thereof include alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol and tert-butyl alcohol; ketones such as acetone and methyl ethyl ketone; Examples include polyhydric alcohols such as ethylene glycol and glycerin and other esters; glycol ethers such as ethylene glycol monoethyl ether and diethylene glycol monobutyl ether.

  When the organic solvent is blended in the ink, the lower limit of the organic solvent content is preferably 30 parts by mass with respect to 100 parts by mass of the metal particles. Moreover, as an upper limit of the content rate of an organic solvent, 900 mass parts is preferable with respect to 100 mass parts metal particles. If the content ratio of the organic solvent is less than the lower limit, the effects of ink viscosity adjustment and vapor pressure adjustment may not be sufficiently obtained. On the other hand, when the content ratio of the organic solvent exceeds the above upper limit, for example, the swelling effect of the dispersant by water becomes insufficient, and the metal particles may be aggregated in the ink.

  In addition, when producing metal particles by the liquid phase reduction method, the metal particles deposited in the liquid phase (aqueous solution) reaction system are once powdered through steps such as filtration, washing, drying, and crushing. An ink can be prepared using the above. In this case, an ink containing metal particles can be obtained by blending powdered metal particles, a dispersion medium such as water, and, if necessary, a dispersant, an organic solvent, and the like at a predetermined ratio. At this time, it is preferable to prepare an ink using a liquid phase (aqueous solution) in which metal particles are deposited as a starting material. Specifically, the liquid phase (aqueous solution) containing the precipitated metal particles is subjected to treatment such as ultrafiltration, centrifugation, washing with water, and electrodialysis to remove impurities, and if necessary, concentrated to remove water. . Or conversely, after adding water and adjusting the density | concentration of a metal particle, the ink containing a metal particle is prepared by mix | blending an organic solvent in a predetermined | prescribed ratio further as needed. In this method, generation of coarse and irregular particles due to aggregation of the metal particles during drying can be prevented, and a dense and uniform sintered layer 4a can be easily formed.

(Ink coating method)
Examples of methods for applying the ink in which metal particles are dispersed on one surface of the base film 1 include spin coating, spray coating, bar coating, die coating, slit coating, roll coating, and dip coating. The conventionally known coating method can be used. Further, ink may be applied to only a part of one surface of the base film 1 by screen printing, a dispenser or the like.

(Second step)
In the second step, an ink containing metal particles is applied to the other surface of the base film 1. In the second step, first, the base film 1 after the first step is turned upside down. Then, as shown in FIG. 1D, the ink is applied to the other surface of the base film 1. The ink used in the second step is not particularly limited, but it is preferable to use the same ink as in the first coating step. The ink application method is not particularly limited, but can be the same as in the first step. By this second step, the coating film 3 b is formed on the other surface of the base film 1.

<Baking process>
In the firing step, as shown in FIG. 1E, the coating films 3a and 3b formed by the coated ink are fired. Specifically, in the baking step, the ink applied on both sides of the base film is dried and then heat-treated. In the firing step, the metal particles are sintered to form a sintered body, and the sintered body is fixed to the base film 1. As a result, the sintered layers 4 a and 4 b are formed on both surfaces of the base film 1, and the via hole 5 that conducts the sintered layers 4 a and 4 b is formed in the through hole 2. The dispersant and other organic substances that can be contained in the ink are volatilized or decomposed by baking. Further, in the vicinity of the interface between the sintered layers 4a and 4b and the base film 1, the metal particles are oxidized by firing, so that the generation of metal hydroxides based on the metal particles and groups derived from the metal hydroxides is suppressed. On the other hand, metal oxides based on metal particles and groups derived from the metal oxides (hereinafter collectively referred to as “metal oxides”) are generated. Since the metal oxide or the like generated in the vicinity of the interface between the sintered layers 4a and 4b and the base film 1 is strongly bonded to a resin such as polyimide constituting the base film 1, the base film 1 and the sintered layers 4a and 4b. Adhesion between the two increases.

  In order to promote the oxidation of the metal particles in the vicinity of the interface between the sintered layers 4a and 4b and the base film 1, the firing is preferably performed in an atmosphere containing a certain amount of oxygen. In this case, the lower limit of the oxygen concentration in the firing atmosphere is preferably 1 volume ppm, and more preferably 10 volume ppm. Moreover, as an upper limit of the said oxygen concentration, 10,000 volume ppm is preferable and 1,000 volume ppm is more preferable. When the oxygen concentration is less than the lower limit, the amount of metal oxide or the like generated in the vicinity of the interface between the sintered layers 4a and 4b and the base film 1 is reduced, and between the base film 1 and the sintered layers 4a and 4b. There is a possibility that it becomes impossible to improve the adhesive strength of. On the other hand, if the oxygen concentration exceeds the upper limit, the conductivity of the sintered layers 4a and 4b may be reduced due to excessive oxidation of the metal particles.

  The drying can be performed at room temperature, for example.

  As a minimum of the above-mentioned heat treatment temperature, 150 ° C is preferred and 200 ° C is more preferred. On the other hand, the upper limit of the temperature of the heat treatment is preferably 500 ° C, more preferably 400 ° C. When the heat treatment temperature is less than the lower limit, the amount of metal oxide or the like generated in the vicinity of the interface between the sintered layers 4a and 4b and the base film 1 is reduced, and between the base film 1 and the sintered layers 4a and 4b. There is a possibility that it becomes impossible to improve the adhesive strength of. On the other hand, when the heat treatment temperature exceeds the upper limit, the base film 1 may be deformed. In addition, although it does not specifically limit about heat processing time, For example, what is necessary is just to be the range of 30 minutes or more and 400 minutes or less.

  The lower limit of the average thickness of the sintered layers 4a and 4b is preferably 10 nm, more preferably 50 nm, and even more preferably 100 nm. On the other hand, the upper limit of the average thickness of the sintered layers 4a and 4b is preferably 1 μm, more preferably 700 nm, and further preferably 500 nm. If the average thickness of the sintered layers 4a and 4b is less than the above lower limit, the sintered layers 4a and 4b may be cut in plan view and the conductivity may be lowered. On the other hand, if the average thickness of the sintered layers 4a and 4b exceeds the above upper limit, the time required for the plating step to be described later becomes long and the productivity may be lowered.

<Plating process>
The printed wiring board substrate 11 (see FIG. 2), which will be described later, is obtained by the firing step. However, if voids remain in the sintered layers 4a and 4b, the voids become firing points for firing. The binding layers 4a and 4b are easily peeled from the base film 1. On the other hand, as shown in FIG. 1F, by filling the gaps with the plating metals 6a and 6b, the plating metals 6a and 6b can be used not only for the outer surfaces of the sintered layers 4a and 4b but also for the sintered layers 4a and 4b. The inside (the space between the metal particles constituting the sintered layers 4a and 4b) enters, and peeling of the sintered layers 4a and 4b from the base film 1 is prevented.

  The plating method for forming the plated metals 6a and 6b is not particularly limited, and may be electroless plating or electroplating, but the voids between the metal particles forming the sintered layers 4a and 4b are formed. Electroless plating that can easily and surely improve the peel strength of the sintered layers 4a, 4b and the base film 1 by filling more accurately is preferable. Hereinafter, the electroless plating process will be described.

(Electroless plating process)
In the electroless plating step, electroless plating is performed on the outer surface of the sintered layer formed by the firing step. As the metal used for electroless plating, copper, nickel, silver or the like having good conductivity can be used. However, when copper is used for the metal particles, the adhesion to the sintered layers 4a and 4b is improved. Considering it, it is preferable to use copper or nickel. In addition, as for the plating solution used for electroless plating, when using metals other than nickel for electroless plating, it is preferable to use what contained nickel or the nickel compound in addition to the plating metal.

  The procedure of electroless plating is not particularly limited, and for example, well-known means together with processes such as a cleaner process, a water washing process, an acid treatment process, a water washing process, a pre-dip process, an activator process, a water washing process, a reduction process, and a water washing process Then, electroless copper plating may be performed.

  As a minimum of average thickness of plating metal 6a and 6b, 0.1 micrometer is preferred and 0.2 micrometer is more preferred. On the other hand, the upper limit of the average thickness of the plated metals 6a and 6b is preferably 1 μm, and more preferably 0.5 μm. If the average thickness of the plated metals 6a and 6b is less than the lower limit, the plated metals 6a and 6b may not be sufficiently filled in the voids in the sintered layers 4a and 4b. On the other hand, if the average thickness of the plated metals 6a and 6b exceeds the upper limit, the time required for electroless plating becomes long and the productivity may be lowered.

  Moreover, it is preferable to further heat-treat after filling the voids in the sintered layers 4a and 4b with the plated metals 6a and 6b. By this heat treatment, metal oxides and the like in the vicinity of the interface between the sintered layers 4a and 4b and the base film 1 are further increased, so that the adhesion between the base film 1 and the sintered layers 4a and 4b is further improved. Can do.

  A printed wiring board substrate 21 (see FIG. 4), which will be described later, is obtained by the formation of the plated metals 6a and 6b, but as shown in FIG. 1G, it is formed by the sintered layers 4a and 4b and the plated metals 6a and 6b. By laminating the metal plating layers 7a and 7b on the outer surface of the layer, for example, it can be easily applied to the printed wiring board substrate 31 (see FIG. 5) used in the subtractive method.

  The plating method of the metal plating layers 7a and 7b is not particularly limited, and may be electroless plating or electroplating, but the thickness can be adjusted easily and accurately and in a relatively short time. Electroplating capable of forming the metal plating layers 7a and 7b is preferable. Hereinafter, the electroplating process will be described.

(Electroplating process)
In the electroplating step, electroplating is performed on the outer surface side of the sintered layer formed by the firing step. The metal used for electroplating is not particularly limited, and examples thereof include copper, nickel, silver and the like having good conductivity. Also, the electroplating procedure is not particularly limited, and may be appropriately selected from known electroplating baths and plating conditions.

  The average thickness of the metal plating layers 7a and 7b is not particularly limited and is set depending on what kind of printed circuit is to be produced. For example, it can be set to 1 μm or more and 100 μm or less.

  When the plating metals 6a and 6b and the metal plating layers 7a and 7b are formed by the same plating method (electroless plating or electroplating), the plating metals 6a and 6b and the metal plating layers 7a and 7b are one They may be formed simultaneously in the process.

<Advantages>
The printed wiring board substrate manufacturing method includes forming through holes 2 in the base film 1 and applying ink containing metal particles having an average particle diameter in the above range on both surfaces of the base film 1. The through hole 2 can be filled with this ink while covering both sides of the base film 1. The printed wiring board base material is produced by firing the ink coated on both surfaces of the base film 1 and filling the through-holes 2 so that the base is formed by the sintered body formed of the metal particles. Sintered layers 4 a and 4 b serving as the base of the conductive pattern can be formed on both surfaces of the film 1, and via holes 5 can be formed in the through holes 2. Thus, since the manufacturing method of the said base material for printed wiring boards can manufacture via hole 5 easily and reliably simultaneously with sintered layer 4a, 4b, it is the conventional manufacturing method of the base material for printed wiring boards. Compared with this, the number of manufacturing processes can be reduced, and efficiency and cost reduction can be promoted.

  In the method for manufacturing the printed wiring board substrate, the average diameter of the through holes 2 and the viscosity of the ink are adjusted as described above, so that, for example, the base film 1 is kept in a horizontal state. When the ink is applied from above, the ink is held in the through hole 2 by surface tension. Therefore, when the sintered layers 4a and 4b are formed on both surfaces of the base film 1, the method for manufacturing the printed wiring board is a recess for receiving a conductive paste by a through hole and a conductive layer, as in a conventional printed wiring board. The via hole 5 can be formed without forming the hole. Therefore, the method for producing a printed wiring board substrate can facilitate the production of the printed wiring board substrate and can increase the degree of freedom in production.

  In the printed wiring board equipment manufacturing method, since the coating process includes the first and second processes, for example, the same equipment and materials are used to manufacture a printed wiring board substrate efficiently and at low cost. can do. Moreover, the manufacturing method of the said base material for printed wiring boards is that the said coating process has a 1st process and a 2nd process in this way, The ink coated on both surfaces of the base film 1 by the baking process is carried out simultaneously. It can bake and can further facilitate the simplification of the manufacturing process.

<Base material for printed wiring board>
[First embodiment of substrate for printed wiring board]
A printed wiring board substrate 11 of FIG. 2 includes a base film 1, sintered layers 4 a and 4 b, and via holes 5. The printed wiring board substrate 11 in FIG. 2 is a flexible printed wiring board substrate having flexibility.

(Base film)
The base film 1 has insulation and flexibility. The base film 1 has one or a plurality of through holes 2. The base film 1 is the same as the base film 1 shown in FIG.

(Sintered layer)
The sintered layers 4 a and 4 b are laminated on both surfaces of the base film 1. The sintered layers 4a and 4b are made of metal particles, and more specifically, a sintered body of metal particles. The metal particles constituting the sintered layers 4a and 4b are the same as the metal particles used in the coating step, and preferably contain copper or a copper alloy as a main component. The substrate 11 for printed wiring board can improve the conductivity while suppressing the manufacturing cost because the metal particles are mainly composed of copper or a copper alloy. Further, the printed wiring board substrate 11 has the sintered layers 4 a and 4 b laminated on both surfaces of the base film 1, thereby promoting the production efficiency and cost reduction.

  The lower limit of the peel strength between the base film 1 and the sintered layers 4a and 4b is preferably 1 N / cm, more preferably 1.5 N / cm, still more preferably 2 N / cm, and particularly preferably 5 N / cm. By setting the peel strength to be equal to or higher than the lower limit, a printed wiring board having high electrical connection reliability can be manufactured. On the other hand, the upper limit of the peel strength is not particularly limited, but is, for example, about 20 N / cm. The peel strength can be controlled by, for example, the amount of the sintered body fixed to the base film 1, the firing temperature and the firing time when the coating films 3a and 3b are fired.

(Via hole)
The via hole 5 is formed in the through hole 2 and conducts the sintered layers 4a and 4b. The via hole 5 is composed of a sintered body of metal particles similar to the sintered layers 4a and 4b. The average diameter of the through holes 2 is adjusted in the same manner as the through holes 2 formed in the above through hole forming step. When the average diameter of the through holes 2 is within the above range, the printed wiring board substrate 11 can accurately form the via holes 5 and enhance the conductivity.

The surface of the via hole 5 is substantially flat as shown in FIG. Specifically, the ratio (L ₁ / D, L) of the maximum unevenness height L ₁ , L ₂ on the surface of the via hole 5 with respect to the average diameter D of the through-hole 2 on the basis of the average position of the outer surface of the sintered layers 4a, 4b. The upper limit of ₂ / D) is preferably 1/10, more preferably 1/20, and even more preferably 1/30. As described above, when the ratio (L ₁ / D, L ₂ / D) is in the above range, planarization of the surface of the via hole 5 is promoted, and for example, a cover coat can be applied to the surface of the via hole 5 without bubbles. . Incidentally, the ratio _{(L 1 / D, L 2} / D) is preferable because it is being more flattened promoting small, the ratio _{(L 1 / D, L 2} / D) as the lower limit of 0 and can do. The surface of the via hole 5 can be flattened, for example, by keeping the viscosity of the ink below a certain level while keeping the thickness of the base film 1 at or above the lower limit. The “average position of the outer surface” refers to the average position in the thickness direction of the outer surface of the region excluding the via hole, and preferably the outer surface in a region within 1 to 2 times the radius of the via hole from the central axis of the via hole. The average position in the thickness direction.

  The upper limit of the porosity of the via hole 5 is preferably 50%, more preferably 40%, and even more preferably 30%. If the porosity of the via hole 5 exceeds the above upper limit, sufficient conductivity may not be obtained. The lower limit of the porosity of the via hole 5 is not particularly limited, but may be 0.1%, for example. If the porosity of the via hole 5 is less than the lower limit, it may be difficult to manufacture the via hole 5.

(advantage)
Since the substrate 11 for printed wiring board includes a via hole 5 formed of a sintered body of metal particles similar to the sintered layers 4a and 4b in the through hole 2, an insulating layer as in a conventional printed wiring board. In addition, it is not necessary to form a via hole by a separate process. Therefore, the printed wiring board substrate 11 can reduce the number of manufacturing steps compared to a conventional printed wiring board.

  Moreover, since the surface of the via hole 5 is integrally formed with the sintered layers 4a and 4b, the printed wiring board substrate 11 can easily and reliably form a conductive pattern at desired positions on both sides of the base film 1. can do. Therefore, the printed wiring board substrate 11 can dramatically increase the degree of freedom in manufacturing the conductive pattern.

[Second Embodiment of Substrate for Printed Wiring Board]
4 includes a base film 1, sintered layers 4a and 4b, via holes 5, and plated metals 6a and 6b formed on and outside the sintered layers 4a and 4b. Prepare. The printed wiring board substrate 21 in FIG. 4 is a flexible printed wiring board substrate having flexibility. The printed wiring board substrate 21 in FIG. 4 is formed by applying electroless plating or electroplating to the outer surface of the sintered layers 4a and 4b of the printed wiring board substrate 11 in FIG.

(advantage)
Since the printed wiring board substrate 21 has plated metals 6a and 6b on the outer surfaces and inside of the sintered layers 4a and 4b, the gap between the metal particles forming the sintered layers 4a and 4b is filled with metal by plating. Is done. Therefore, the printed wiring board substrate 21 can improve the peel strength between the sintered layers 4a and 4b and the base film 1, and can improve the conductivity.

[Third embodiment of substrate for printed wiring board]
5 is formed of the base film 1, the sintered layers 4a and 4b, the via holes 5, the plated metals 6a and 6b, the sintered layers 4a and 4b, and the plated metals 6a and 6b. Metal plating layers 7a and 7b stacked on the outer surface of the layer to be formed. The printed wiring board substrate 31 of FIG. 5 is a flexible printed wiring board substrate having flexibility. The printed wiring board substrate 31 of FIG. 5 has metal plating layers 7a and 7b on the outer surface of the layers formed of the sintered layers 4a and 4b and the plating metals 6a and 6b of the printed wiring board substrate 21 of FIG. It is formed by stacking. When the plating metals 6a and 6b and the metal plating layers 7a and 7b are formed by the same plating (electroless plating or electroplating), the plating metals 6a and 6b and the metal plating layers 7a and 7b are integrated in the same process. It may be formed automatically or may be formed in a separate process.

(advantage)
Since the printed wiring board substrate 31 has the metal plating layers 7a and 7b on the outer surface of the layer formed by the sintered layers 4a and 4b and the plated metals 6a and 6b, the sintered layers 4a and 4b and the plated metal 6a. , 6b and the thickness of the laminate formed by the metal plating layers 7a and 7b can be adjusted easily and reliably. Therefore, the printed wiring board substrate 31 can be easily applied to a printed wiring board substrate used in, for example, a subtractive method.

<Printed wiring board>
A printed wiring board 41 in FIG. 6 includes a base film 1, a via hole 5, and conductive patterns 42a and 42b. It is formed using the printed wiring board substrate 31 of FIG. Specifically, the conductive patterns 42a and 42b of the printed wiring board 41 of FIG. 6 are formed by the sintered layers 4a and 4b, the plated metals 6a and 6b, and the metal plated layers 7a and 7b of the printed wiring board base 31. The laminated body is patterned and includes a part of the laminated body. As a patterning method at this time, for example, a method (subtractive method) in which the laminated body is masked with a resist pattern or the like and etched (subtractive method) can be employed.

(advantage)
Since the printed wiring board 41 uses the printed wiring board base 31, the number of manufacturing steps can be reduced as compared with the conventional printed wiring board. Moreover, since the surface of the via hole 5 is integrally formed with the sintered layers 4a and 4b as described above, the printed wiring board 41 can be easily and reliably provided with a conductive pattern at desired positions on both sides of the base film 1. 42a and 42b can be formed.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

  For example, in the method for producing a substrate for a printed wiring board, the ink may be applied to both sides of the base film as described above, and the above-described method is performed only on one side of the base film 51 as shown in FIG. Ink may be applied. As described above, even when the ink is applied only to one surface of the base film 51, the ink covers one surface of the base film 51 and fills the through hole 52 to form the coating film 53. In the method of manufacturing the printed wiring board substrate, when the ink is applied only to one surface of the base film 51, another metal layer 54 is laminated on the other surface of the base film 51. The metal layer 54 may be laminated on the other surface of the base film 51 after applying the ink, but is preferably laminated before applying the ink as shown in FIG. Thus, by laminating the metal layer before applying the ink, it is possible to easily and reliably prevent the ink from leaking from the through hole 52.

  The manufacturing method of the said base material for printed wiring boards may form two or more through-holes in a base film.

  The substrate for a printed wiring board does not necessarily need to be for a flexible printed wiring board, and may be for a rigid printed wiring board.

  The printed wiring board is not necessarily formed by a subtractive method, and may be formed by a semi-additive method.

  The method for producing a printed wiring board may include a step of applying a hydrophilic treatment to the surface on which the ink is applied by the coating step before the coating step. By applying a hydrophilic treatment to the base film, the surface tension of the ink with respect to the base film is reduced, so that it becomes easy to uniformly apply the ink to the base film.

  As mentioned above, since the manufacturing method of the base material for printed wiring boards of this invention can manufacture a via hole easily and reliably and can reduce a manufacturing process, it is used for various electronic devices etc. It is suitable for manufacturing printed circuit board substrates. Moreover, the base material for printed wiring boards and the printed wiring board of the present invention are suitably used for various electronic devices and the like.

DESCRIPTION OF SYMBOLS 1, 51 Base film 2, 52 Through-hole 3a, 3b, 53 Coating film 4a, 4b Sintered layer 5 Via hole 6a, 6b Metal plating layer 7a, 7b Metal plating layer 11, 21, 31 Base 41 for printed wiring boards Printed wiring Plates 42a and 42b Conductive pattern 54 Metal layer 101 Printed wiring board 102 Base films 103 and 104 Conductive layer 105 Through hole 106 Via hole

Claims (16)

Forming one or a plurality of through holes in the insulating base film;
Applying an ink containing metal particles on at least one surface of the base film;
And baking the coated ink.
The manufacturing method of the base material for printed wiring boards whose average particle diameter of the said metal particle is 1 nm or more and 500 nm or less. The coating process
A first step of applying the ink to one surface of the base film;
The method for producing a substrate for a printed wiring board according to claim 1, further comprising: a second step of applying the ink to the other surface of the base film.   The method for producing a substrate for a printed wiring board according to claim 1 or 2, wherein an average diameter of the through holes of the base film is 10 µm or more and 100 µm or less.   The method for producing a printed wiring board substrate according to claim 1, wherein the content of metal particles in the ink is 5% by mass or more and 50% by mass or less.   The manufacturing method of the base material for printed wiring boards of any one of Claims 1-4 further equipped with the process of performing electroless plating on the outer surface of the sintered layer formed by the said baking process.   The manufacturing method of the base material for printed wiring boards of any one of Claim 1 to 5 further equipped with the process of electroplating to the outer surface side of the sintered layer formed by the said baking process.   The method for producing a substrate for a printed wiring board according to any one of claims 1 to 6, wherein the metal particles of the ink contain copper or a copper alloy as a main component. A base film having one or more through-holes and having insulating properties;
A printed wiring board substrate comprising a sintered layer of metal particles formed on at least one surface of the base film,
Further comprising a via hole formed in the through hole and formed of a sintered body of metal particles similar to the sintered layer,
A substrate for a printed wiring board, wherein the metal particles have an average particle diameter of 1 nm to 500 nm.   The printed wiring board substrate according to claim 8, wherein a ratio of a maximum unevenness height of the via hole surface with respect to an average diameter of the through holes based on an average position of the outer surface of the sintered layer is 1/10 or less.   The printed wiring board substrate according to claim 8 or 9, wherein a sintered layer is provided on both sides of the base film.   The substrate for printed wiring boards according to claim 8, 9 or 10, wherein an average diameter of the through holes of the base film is 10 µm or more and 100 µm or less.   The base material for printed wiring boards of any one of Claims 8-11 which has the plating metal formed in the outer surface of the said sintered layer.   The base material for printed wiring boards of Claim 12 which has a metal plating layer in the outer surface of the layer formed with the said sintered layer and plating metal.   The printed wiring board substrate according to any one of claims 8 to 13, wherein the metal particles contain copper or a copper alloy as a main component.   The substrate for printed wiring boards according to any one of claims 8 to 14, wherein a porosity of the via hole is 0.1% or more and 50% or less.   The printed wiring board formed by the subtractive method or a semi-additive method using the base material for printed wiring boards of any one of Claims 8-15.

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