JP6484026B2 - Printed wiring board substrate, printed wiring board, and printed wiring board manufacturing method - Google Patents

Description

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

  For example, a metal layer made of metal or the like is laminated on the surface of an insulating base film made of resin or the like, and a conductive pattern is formed by etching the metal layer to obtain a printed wiring board. Printed wiring board substrates are widely used.

  Printed wiring with high peel strength between the base film and the metal layer so that the metal layer does not peel from the base film when bending bending force is applied to the printed wiring board formed using such a printed wiring board substrate There is a need for board substrates.

  In recent years, with the miniaturization and high performance of electronic devices, it has been required to increase the density of printed wiring boards. As a printed wiring board substrate that satisfies such a demand for higher density, a printed wiring board substrate having a reduced metal layer thickness is required.

  In response to the demand for improvement in peel strength and thinning, a printed wiring board substrate in which a copper thin layer is laminated on a heat-resistant insulating base film without an adhesive layer has been proposed (see Japanese Patent No. 3570802). . In this conventional printed wiring board substrate, a copper thin film layer (first conductive layer) having a thickness of 0.25 to 0.30 μm is formed on both surfaces of a heat-resistant insulating base film using a sputtering method, and an electric layer is formed on the copper thin film layer. A copper thick film layer (second conductive layer) is formed using a plating method.

Japanese Patent No. 3570802

  The printed wiring board substrate described in the above publication can be said to be a substrate that meets the demands for improving the peel strength and reducing the thickness in that a thin metal layer having a large peel strength can be formed. However, the printed wiring board substrate described in the above publication requires a vacuum facility to construct and maintain the facility because the first conductive layer is formed using a sputtering method in order to adhere the metal layer to the base film. , Driving costs and the like are high. Also, supply of the base film to be used, formation of the metal layer, storage of the base film, etc. must all be handled in a vacuum. Further, in terms of equipment, there is a limit to increasing the size of the substrate.

  The present invention has been made based on the circumstances as described above, and provides an inexpensive printed wiring board substrate and printed wiring board having a metal layer with high peel strength, and a method for manufacturing such a printed wiring board substrate. The issue is to provide.

  A printed wiring board substrate according to an aspect of the present invention made to solve the above-described problem is a printed board including an insulating base film and a metal layer laminated on at least one surface side of the base film. A wiring board substrate having a dispersed portion in which palladium is dispersed in the base film.

  Moreover, the printed wiring board which concerns on another aspect of this invention made | formed in order to solve the said subject is a printed wiring board which has a conductive pattern, Comprising: The said conductive pattern is a metal layer of the said board | substrate for printed wiring boards. It is formed by using a subtractive method or a semi-additive method.

  Moreover, the manufacturing method of the printed wiring board board | substrate which concerns on another aspect of this invention made | formed in order to solve the said subject is the conductive ink which contains a metal particle in the at least one surface side of the base film which has insulation. A step of applying and baking the conductive ink, a step of applying electroless plating using palladium as a catalyst on one side of the conductive ink, and a step of performing a heat treatment after the electroless plating step. The palladium is dispersed in the heat treatment step.

  The printed wiring board substrate according to one aspect of the present invention and the printed wiring board according to another aspect include a metal layer having high peel strength and are inexpensive. The printed wiring board substrate manufacturing method according to still another aspect of the present invention can inexpensively manufacture a printed wiring board substrate including a metal layer having high peel strength.

FIG. 1 is a schematic cross-sectional view of a printed wiring board substrate according to an embodiment of the present invention. FIG. 2 is a cross-sectional electron micrograph of an example of the printed wiring board substrate of FIG. FIG. 3 is a diagram in which the palladium content in the cross section of the printed wiring board substrate in FIG. 2 is mapped. FIG. 4 is a flowchart showing a manufacturing procedure of the printed wiring board substrate of FIG.

[Description of Embodiment of the Present Invention]
A printed wiring board substrate according to an aspect of the present invention is a printed wiring board substrate comprising a base film having insulating properties and a metal layer laminated on at least one surface side of the base film, It has a dispersed portion in which palladium is dispersed in the base film.

  The printed wiring board substrate has a dispersed portion in which palladium is dispersed in the base film, thereby improving the adhesion of the base film to the metal layer and increasing the peel strength of the metal layer. . In addition, since the printed wiring board substrate has improved adhesion by dispersing palladium in this way, a vacuum facility or the like is not required for its manufacture, and can be provided at low cost.

  Palladium is preferably present in the dispersed portion so that the content is 1% by mass or more as determined by EDX. Thus, in the said dispersion | distribution part, the adhesive improvement effect with respect to the metal layer of a base film is acquired more reliably by palladium existing so that a content rate may become 1 mass% or more by fixed_quantity | quantitative_assay by EDX.

  It is preferable that the dispersed portion includes a region having an average of 500 nm or more from the interface with the metal layer. Thus, when the said dispersion | distribution part contains the area | region of an average 500 nm or more from the interface with a metal layer, the adhesiveness of the interface with respect to the metal layer of a base film can be improved more.

  The palladium content of the A layer of 1 μm or less in the thickness direction from the interface with the metal layer in the base film is larger than the palladium content of the B layer of 500 nm or less in the thickness direction from the interface with the base film in the metal layer. Good. Thus, the palladium content of the A layer of 1 μm or less in the thickness direction from the interface with the metal layer in the base film is 500 nm or less in the thickness direction from the interface with the base film in the metal layer. By being larger than the rate, the effect of improving the adhesion of the base film to the metal layer becomes more reliable.

  The ratio of the palladium content at a position of 500 nm to the palladium content at a position of 1 μm in the thickness direction from the interface with the metal layer in the base film is preferably 0.7 or more and 1.1 or less. Thus, when the ratio of the palladium content at the position of 500 nm to the palladium content at the position of 1 μm in the thickness direction from the interface with the metal layer in the base film is within the above range, the base film enters the base film. Sufficient dispersion of palladium is ensured, and the effect of improving the adhesion of the base film to the metal layer is more certain.

  A first conductive layer formed by applying and firing a conductive ink containing metal particles, and a second conductive layer formed by electroless plating on one surface side of the first conductive layer. It is good to have. As described above, the metal layer has the first conductive layer formed by applying and baking the conductive ink containing the metal particles, so that the second conductive layer is efficiently formed using the first conductive layer as a base. be able to. In addition, by forming the second conductive layer by electroless plating with the first conductive layer as a base, the thickness of the metal layer can be increased, and the gap between the first conductive layers can be filled and densified. it can. Thereby, the electroconductivity of a metal layer and the adhesiveness with respect to a base film can be improved.

  The average particle diameter of the metal particles is preferably 1 nm to 500 nm. Thus, when the average particle diameter of the metal particles is within the above range, a thin conductive film can be formed on the surface of the base film, and the gaps between the metal particles can be reliably filled by plating.

  The metal layer may further include a third conductive layer formed by electroplating on one surface side of the second conductive layer. Thus, when the metal layer further includes the third conductive layer formed by electroplating on one surface side of the second conductive layer, the metal layer can be further thickened easily and with high accuracy. .

  Moreover, the printed wiring board which concerns on another aspect of this invention is a printed wiring board which has a conductive pattern, Comprising: The said conductive pattern uses a subtractive method or a semiadditive method for the metal layer of the said board | substrate for printed wiring boards. It is formed by that.

  The printed wiring board is inexpensive because the conductive pattern is formed on the metal layer of the printed wiring board substrate by using a subtractive method or a semi-additive method, and the conductive pattern is fine and has a base film. Difficult to peel from.

  Moreover, the method for manufacturing a printed wiring board substrate according to still another aspect of the present invention includes a step of applying and baking a conductive ink containing metal particles on at least one surface side of an insulating base film; After the conductive ink is applied and baked, the method includes a step of performing electroless plating on one side using palladium as a catalyst, and a step of performing a heat treatment after the electroless plating step, wherein the palladium is dispersed in the heat treatment step.

  The printed wiring board manufacturing method can easily form a thin conductive film on the surface of the base film by applying and baking a conductive ink containing metal particles. A metal layer can be formed easily. In addition, since the method for manufacturing a printed wiring board substrate includes a step of performing electroless plating using palladium as a catalyst, gaps between layers formed by firing metal particles can be filled with metal, and the metal layer can be densely formed. To strengthen the bonding to the base film. Furthermore, since the manufacturing method of the printed wiring board substrate includes a heat treatment step for dispersing the palladium, the palladium that can lower the adhesion from between the base film and the metal layer is excluded. A printed wiring board substrate having a high peel strength from the layer can be produced. Moreover, the manufacturing method of the said printed wiring board board | substrate does not require a vacuum installation, and can manufacture the printed wiring board board | substrate cheaply.

  Here, “EDX” is an abbreviation for Energy Dispersive X-ray Spectrometry. The “average particle size” means a particle size at which the volume integrated value is 50% in the particle size distribution measured by the laser diffraction method. For example, it is measured with a Nikkiso Co., Ltd. Microtrac particle size distribution analyzer “UPA-150EX”. Can do.

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

[PCB board]
The printed wiring board substrate of FIGS. 1 and 2 includes an insulating base film 1 and a metal layer 2 laminated on at least one surface side of the base film 1.

<Base film>
The base film 1 is a sheet-like member that serves as a base material for the printed wiring board substrate. The base film 1 serves as a base material that supports a conductive pattern in a printed wiring board formed using the printed wiring board substrate.

  The base film 1 has a dispersed portion 3 in which palladium is dispersed. FIG. 3 is a map in which the palladium content in the same cross-sectional area as in FIG. 2 is quantitatively determined by EDX. Note that “presently dispersed” means that the diameter of a perfect circle that can be drawn in a region where no significant palladium is detected by quantification by EDX, preferably in a region where the palladium content is less than 1% by mass, is 20 nm or less. Say something. That is, it is preferable that palladium exists in the base film 1 so that the content is 1% by mass or more as determined by EDX in the dispersed portion 3.

  As a material of the base film 1, for example, a flexible resin such as polyimide, liquid crystal polymer, fluororesin, polyethylene terephthalate, polyethylene naphthalate, paper phenol, paper epoxy, glass composite, glass epoxy, Teflon (registered trademark), It is possible to use a rigid material such as a glass substrate, or a rigid flexible material in which a hard material and a soft material are combined. Among these, polyimide is particularly preferable because it has a high bonding force with a metal oxide or the like formed on the surface of the metal layer 2.

  The thickness of the base film 1 is set by a printed wiring board using the printed wiring board substrate and is not particularly limited. For example, the lower limit of the average thickness of the base film 1 is preferably 5 μm, and 12 μm. Is more preferable. On the other hand, the upper limit of the average thickness of the base film 1 is preferably 2 mm, and more preferably 1.6 mm. When the average thickness of the base film 1 is less than the above lower limit, the strength of the base film 1 may be insufficient. Conversely, when the average thickness of the base film 1 exceeds the above upper limit, it may be difficult to make the printed wiring board thinner.

  The base film 1 is preferably subjected to a hydrophilic treatment on the surface on which the metal layer 2 is laminated. As the hydrophilic treatment, for example, plasma treatment for irradiating plasma to make the surface hydrophilic, alkali treatment for making the surface hydrophilic with an alkaline solution, or the like can be employed. By subjecting the base film 1 to the hydrophilic treatment, the surface tension of the conductive ink with respect to the base film 1 is reduced, so that it becomes easy to uniformly apply the conductive ink to the base film 1.

(Distributed part)
The dispersion portion 3 is formed by introducing and dispersing palladium from the surface of the base film 1 into the base film 1. In this dispersed portion 3, palladium is introduced and dispersed substantially evenly from the interface with the metal layer 2 of the base film 1, and part or all of the base film 1 is formed in the thickness direction with the interface with the metal layer 2 as the base. In order to occupy, it is preferably formed in a layer shape having a substantially constant thickness. That is, the dispersed portion 3 preferably includes a region from the interface with the metal layer 2 of the base film 1 to a certain depth.

  The lower limit of the average depth from the interface between the dispersed portion 3 and the metal layer 2 is preferably 500 nm, and more preferably 1 μm. On the other hand, the upper limit of the average depth of the dispersed portion 3 is preferably 100 μm, and more preferably 10 μm. When the average depth of the dispersed portion 3 is less than the lower limit, the effect of improving the peel strength between the base film 1 and the metal layer 2 due to the dispersion of palladium may be insufficient. When the average depth of the dispersion part 3 exceeds the upper limit, the cost for dispersing palladium, and thus the production cost of the printed wiring board substrate, may increase unnecessarily.

  The lower limit of the palladium content in the region La (hereinafter referred to as “A layer”) of 1 μm or less in the thickness direction from the interface with the metal layer 2 in the base film 1 is preferably 3% by mass as determined by EDX, and more preferably 5% by mass. Preferably, 10% by mass is more preferable. On the other hand, the upper limit of the palladium content of the A layer La is preferably 40% by mass, more preferably 25% by mass, and even more preferably 15% by mass. When the palladium content of the A layer La is less than the lower limit, the effect of improving the peel strength between the base film 1 and the metal layer 2 due to the dispersion of palladium may be insufficient. On the other hand, when the palladium content of the A layer La exceeds the above upper limit, the strength of the base film 1 may be insufficient.

  The palladium content of the A layer La is preferably larger than the palladium content of the region Lb (hereinafter referred to as B layer) of 500 nm or less in the thickness direction from the interface with the base film 1 in the metal layer 2. When the palladium content of the A layer La is less than the palladium content of the B layer Lb, the effect of improving the peel strength between the base film 1 and the metal layer 2 due to the dispersion of palladium may be insufficient.

  The lower limit of the ratio of the palladium content at the position of 500 nm to the palladium content at the position of 1 μm from the interface with the metal layer 2 in the base film 1 is preferably 0.7, more preferably 0.8. preferable. On the other hand, the upper limit of the palladium content ratio is preferably 1.1 and more preferably 1. When the ratio of the palladium content is less than the lower limit, the gradient of the palladium content in the base film 1 is large, and the effect of improving the peel strength between the base film 1 and the metal layer 2 may be insufficient. is there. On the other hand, when the ratio of the palladium content exceeds the upper limit, a large amount of palladium is dispersed in the deep part of the base film, which may unnecessarily increase the manufacturing cost.

<Metal layer>
The metal layer 2 includes a first conductive layer 4 formed by applying and firing a conductive ink containing metal particles, and electroless plating on one surface side (the side opposite to the base film 1) of the first conductive layer 4. And a third conductive layer 6 formed by electroplating on one surface side (the side opposite to the base film 1) of the second conductive layer 5.

  The thickness of the metal layer 2 is determined by what kind of printed circuit is created using the printed wiring board substrate. Although it does not specifically limit as a minimum of the average thickness of the metal layer 2, 1 micrometer is preferable and 2 micrometers is more preferable. On the other hand, the upper limit of the average thickness of the metal layer 2 is not particularly limited, but is preferably 100 μm and more preferably 50 μm. When the average thickness of the metal layer 2 is less than the lower limit, the metal layer 2 may be easily damaged. Conversely, if the average thickness of the metal layer 2 exceeds the upper limit, it may be difficult to make the printed wiring board thinner.

  The lower limit of the palladium content of the B layer Lb of the metal layer 2 is preferably 1% by mass as determined by EDX, more preferably 3% by mass, and even more preferably 5% by mass. On the other hand, the upper limit of the palladium content of the B layer Lb is preferably 20% by mass, more preferably 15% by mass, and still more preferably 10% by mass. When the palladium content rate of B layer Lb is less than the said minimum, there exists a possibility that the peeling strength improvement effect of the base film 1 and the metal layer 2 by dispersion | distribution of palladium may become inadequate. On the other hand, when the palladium content of the B layer Lb exceeds the above upper limit, the strength of the base film 1 may be insufficient.

(First conductive layer)
The first conductive layer 4 is laminated on one surface of the base film 1 by applying and baking conductive ink containing metal particles. In the printed wiring board substrate, since the first conductive layer 4 is formed by applying and baking conductive ink, one surface of the base film 1 can be easily covered with a conductive film. The first conductive layer 4 is formed by baking after the application of the conductive ink in order to remove unnecessary organic substances in the conductive ink and to securely fix the metal particles to one surface of the base film 1. Is done.

<Conductive ink>
The conductive ink forming the first conductive layer 4 contains metal particles as a conductive substance that provides conductivity. In this embodiment, the conductive ink includes metal particles, a dispersant that disperses the metal particles, and a dispersion medium. By applying using such conductive ink, the first conductive layer 4 made of fine metal particles is laminated on one surface of the base film 1.

  Although the metal which comprises the metal particle contained in the said conductive ink is not specifically limited, From a viewpoint of the adhesive force improvement between the 1st conductive layer 4 and the base film 1, the metal oxidation based on the metal is carried out. Preferred is one in which a group derived from a product or a metal oxide thereof and a metal hydroxide based on the metal or a group derived from the metal hydroxide are generated, for example, copper, nickel, aluminum, gold or silver Can be used. Among these, copper is preferably used as a metal having good conductivity and excellent adhesion to the base film 1.

  The lower limit of the average particle diameter of the metal particles contained in the conductive ink is preferably 1 nm, and more preferably 30 nm. On the other hand, the upper limit of the average particle diameter of the metal particles is preferably 500 nm, and more preferably 100 nm. When the average particle diameter of the metal particles is less than the lower limit, the dispersibility and stability of the metal particles in the conductive ink may be reduced. Conversely, when the average particle diameter of the metal particles exceeds the upper limit, the metal particles may be easily precipitated, or the density of the metal particles may not be uniform when the conductive ink is applied.

  The lower limit of the average thickness of the first conductive layer 4 is preferably 0.05 μm, and more preferably 0.1 μm. On the other hand, the upper limit of the average thickness of the first conductive layer 4 is preferably 2 μm, and more preferably 1.5 μm. When the average thickness of the first conductive layer 4 is less than the lower limit, the first conductive layer 4 may be cut and the conductivity may be lowered. On the other hand, if the average thickness of the first conductive layer 4 exceeds the upper limit, it may be difficult to reduce the thickness of the metal layer 2 or the second conductive layer 5 described later may be formed in the pores of the first conductive layer 4. Sometimes the metal cannot be filled, and the conductivity and strength of the first conductive layer 4 and thus the metal layer 2 may be insufficient.

(Second conductive layer)
The second conductive layer 5 is laminated on the surface of the first conductive layer 4, that is, the surface opposite to the base film 1 by electroless plating. Since the second conductive layer 5 is thus formed by electroless plating, the gap between the metal particles forming the first conductive layer 4 is filled with the metal of the second conductive layer 5. If voids remain in the first conductive layer 4, the void portion becomes a starting point of breakage and the first conductive layer 4 is easily peeled off from the base film 1. The second conductive layer 5 is formed in the void portion. The first conductive layer 4 is prevented from being peeled off by being filled with the metal to be used.

  As the metal used for the electroless plating, copper, nickel, silver or the like having good conductivity can be used. When copper is used for the metal particles forming the first conductive layer 4, the first conductive layer 4 is used. It is preferable to use copper or nickel in consideration of the adhesion to the substrate. In addition, when using metals other than nickel for electroless plating, it is preferable to use the plating solution used for electroless plating which contained nickel or the nickel compound in addition to the plating metal.

  The lower limit of the average thickness of the second conductive layer 5 formed by electroless plating is preferably 0.2 μm, and more preferably 0.3 μm. On the other hand, the upper limit of the average thickness of the second conductive layer 5 formed by electroless plating is preferably 1 μm, and more preferably 0.5 μm. When the average thickness of the second conductive layer 5 formed by the electroless plating is less than the lower limit, the second conductive layer 5 may not be sufficiently filled in the gap portion of the first conductive layer 4 and the conductivity may be lowered. There is. On the contrary, when the average thickness of the second conductive layer 5 formed by the electroless plating exceeds the upper limit, the time required for the electroless plating becomes long and the productivity may be lowered.

(Third conductive layer)
The third conductive layer 6 is formed by laminating by electroplating on the surface of the second conductive layer 5 formed by electroless plating. Thus, by laminating the third conductive layer 6 formed by electroplating on the surface of the second conductive layer 5, the thickness of the metal layer 2 can be adjusted easily and accurately, and in a relatively short time. A metal layer having a thickness necessary to form a printed wiring board can be formed.

  As a metal used for electroplating for forming the third conductive layer 6, copper, nickel, silver or the like having good conductivity can be used.

  The thickness of the third conductive layer 6 is determined according to the required thickness of the entire metal layer 2.

[Method of manufacturing printed circuit board]
The method for manufacturing the printed wiring board substrate in FIG. 4 is a method for manufacturing the printed wiring board substrate in FIG. 1.

  The printed wiring board substrate manufacturing method includes a step of preparing a conductive ink containing metal particles (step S1: conductive ink preparation step) and the above-described conduction to one surface side of the base film 1 having insulation. The step of forming the first conductive layer 4 by applying and baking the conductive ink (step S2: conductive ink applying and baking step), and after the first conductive layer forming step, palladium is formed on one surface side of the first conductive layer 4. The step of forming a second conductive layer by depositing metal on the surface of the first conductive layer 4 and the pores inside the first conductive layer 4 by performing electroless plating using as a catalyst (step S3: electroless) Plating step), a step of dispersing palladium in the base film 1 by heat treatment after this electroless plating step (step S4: heat treatment step), and a step of applying the second conductive layer 5 after this heat treatment step. Scan film 1 forming a third conductive layer 6 by electroplating on the surface opposite to the: and a (step S5 electroplating process).

<Preparation process>
In the preparation step of Step S1, a dispersant is dissolved in a dispersion medium, and the above-described metal particles are dispersed in the dispersion medium. That is, the dispersing agent surrounds the metal particles to prevent aggregation and to disperse the metal particles well in the dispersion medium. The dispersant can also be added to the reaction system in the form of a solution dissolved in water or a water-soluble organic solvent.

(Method for producing metal particles)
Here, a method for producing metal particles dispersed in the conductive ink will be described. The metal particles can be produced by a high-temperature treatment method, a liquid phase reduction method, a gas phase method, or the like, but preferably by a liquid phase reduction method that can produce particles having a uniform particle diameter at a relatively low cost.

In order to produce the above 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 reducing agent is added. What is necessary is just to make a metal ion reduce-react for a fixed time. In the case of the liquid phase reduction method, the metal particles to be produced have a spherical or granular shape and can be made into fine particles. For example, in the case of copper, copper (II) nitrate (Cu (NO ₃ ) ₂ ), copper (II) sulfate pentahydrate (CuSO ₄ .5H ₂ ) as the water-soluble metal compound that is the basis of the metal ions. 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. . For other metal particles, water-soluble compounds such as chlorides, nitric acid compounds and sulfuric acid compounds can be used.

  As a reducing agent when producing metal particles by a liquid phase reduction method, 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, ethylene Examples thereof include polyhydric alcohols such as glycol and glycerin. Among these, the titanium redox method is a method in which metal ions are reduced by a redox action when trivalent titanium ions are oxidized to tetravalent and metal particles are precipitated. The metal particles obtained by the titanium redox method have small and uniform particle diameters, and the titanium redox method can make the shape of the metal particles spherical or granular. Therefore, by using the titanium redox method, the metal particles are filled with higher density, and the first conductive layer 4 can be formed in a denser layer.

  To adjust the particle size of the metal particles, adjust the type and blending ratio of the metal compound, dispersant, and reducing agent, and adjust the stirring speed, temperature, time, pH, etc. when reducing the metal compound. That's fine. For example, the pH of the reaction system is preferably 7 or more and 13 or less in order to obtain metal particles having a minute particle diameter. At this time, the pH of the reaction system can be adjusted to the above range by using a pH adjuster. As this pH adjuster, a general acid or alkali such as hydrochloric acid, sulfuric acid, sodium hydroxide, sodium carbonate or the like is used. In particular, in order to prevent deterioration of peripheral members, alkali metal or alkaline earth metal, Nitric acid and ammonia which do not contain halogen elements such as chlorine and impurity elements such as sulfur, phosphorus and boron are preferable.

  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. The conductive ink can be adjusted by using one. In this case, a powdered metal particle, water as a dispersion medium, a dispersant, and, if necessary, a water-soluble organic solvent are blended in a predetermined ratio to obtain a conductive ink containing metal particles. Can do. At this time, it is preferable to adjust the conductive 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 electroconductive ink containing a metal particle is adjusted by mix | blending a water-soluble organic solvent in a predetermined | prescribed ratio further as needed. In this method, generation of coarse and irregular particles due to agglomeration of metal particles during drying can be prevented, and the dense and uniform first conductive layer 4 can be easily formed.

(Dispersion medium)
As a dispersion medium for the conductive ink, water, a highly polar solvent, or a mixture of two or more of these can be used. What mixed the solvent is used suitably.

  As a minimum of the content rate of the water used as the main component of the dispersion medium in electroconductive ink, 20 mass parts is preferable per 100 mass parts of metal particles, and 50 mass parts is more preferable. On the other hand, the upper limit of the content ratio of water that is the main component of the dispersion medium in the conductive ink is preferably 1,900 parts by weight, more preferably 1,000 parts by weight per 100 parts by weight of the metal particles. The water of the dispersion medium sufficiently swells the dispersing agent to disperse the metal particles surrounded by the dispersing agent well, but when the content ratio of the water is less than the lower limit, the swelling effect of the dispersing agent by water May become insufficient. On the other hand, when the content ratio of the water exceeds the upper limit, the metal particle ratio in the conductive ink is reduced, and a good first conductive layer 4 having the necessary thickness and density is formed on the surface of the base film 1. It may not be possible.

  Various organic solvents that are water-soluble can be used as the organic solvent blended into the conductive ink as necessary. 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 thereof include polyhydric alcohols such as ethylene glycol and glycerin and other esters, and glycol ethers such as ethylene glycol monoethyl ether and diethylene glycol monobutyl ether.

  As a minimum of the content rate of a water-soluble organic solvent, 30 mass parts is preferable per 100 mass parts of metal particles, and 80 mass parts is more preferable. On the other hand, as an upper limit of the content rate of a water-soluble organic solvent, 900 mass parts is preferable per 100 mass parts of metal particles, and 500 mass parts is more preferable. When the content ratio of the water-soluble organic solvent is less than the lower limit, the effects of adjusting the viscosity and vapor pressure of the dispersion with the organic solvent may not be sufficiently obtained. On the other hand, when the content ratio of the water-soluble organic solvent exceeds the upper limit, the swelling effect of the dispersant due to water becomes insufficient, and the metal particles may be aggregated in the conductive ink.

(Dispersant)
The dispersant contained in the conductive ink is preferably one that does not contain sulfur, phosphorus, boron, halogen, and alkali from the viewpoint of preventing deterioration of the printed wiring board substrate. Such preferred dispersants include amine-based polymer dispersants such as polyethyleneimine and polyvinylpyrrolidone, hydrocarbon-based polymer dispersants having a carboxylic acid group in the molecule such as polyacrylic acid and carboxymethylcellulose, and poval. (Polyvinyl alcohol), styrene-maleic acid copolymer, olefin-maleic acid copolymer, polymer dispersant having a polar group such as a copolymer having a polyethyleneimine moiety and a polyethylene oxide moiety in one molecule, etc. Can be mentioned.

  The lower limit of the molecular weight of the dispersant is preferably 2,000, and more preferably 5,000. On the other hand, the upper limit of the molecular weight of the dispersant is preferably 300,000, more preferably 100,000. If the molecular weight of the dispersant is less than the lower limit, the effect of preventing the aggregation of metal particles and maintaining the dispersion may not be sufficiently obtained. As a result, the first conductive layer laminated on the base film 1 There is a possibility that 4 cannot be made dense with few defects. On the contrary, when the molecular weight of the dispersant exceeds the upper limit, the bulk of the dispersant is too large, and in the heat treatment performed after application of the conductive ink, the metal particles may be inhibited from sintering to generate voids. Thus, the denseness of the film quality of the first conductive layer 4 may be reduced, and the decomposition residue of the dispersant may decrease the conductivity.

  As a minimum of a content rate of a dispersing agent in conductive ink, 1 mass part is preferred per 100 mass parts of metal particles, and 5 mass parts is more preferred. On the other hand, the upper limit of the content ratio of the dispersant in the conductive ink is preferably 60 parts by mass and more preferably 40 parts by mass per 100 parts by mass of the metal particles. When the content ratio of the dispersant is less than the lower limit, the aggregation preventing effect may be insufficient. On the contrary, when the content ratio of the dispersant exceeds the upper limit, during the heat treatment after coating the conductive ink, excessive dispersant may inhibit firing including sintering of metal particles, and voids may be generated, There is a possibility that the decomposition residue of the polymer dispersant remains as an impurity in the first conductive layer 4 to lower the conductivity.

<Conductive ink application firing process>
In the conductive ink coating and baking process of step S2, the conductive ink prepared in step S1 is applied to the surface of the base film 1, dried, heated and baked.

(Applying conductive ink)
As a method of applying the conductive ink in which metal particles are dispersed on one surface of the base film 1, a spin coating method, a spray coating method, a bar coating method, a die coating method, a slit coating method, a roll coating method, a dip coating method. A conventionally known coating method such as the above can be used. Alternatively, the conductive ink may be applied to only a part of one surface of the base film 1 by screen printing, a dispenser, or the like.

  Subsequently, the dispersion medium in the conductive ink applied to the base film 1 is evaporated, and the conductive ink is dried.

  As a method for drying the conductive ink, natural drying, drying by heating, drying by warm air, or the like can be applied. However, the method is such that the conductive ink before drying is not exposed to a strong wind that roughens the surface.

  Further, by heating the dried conductive ink, the dispersion medium in the conductive ink is thermally decomposed and the metal particles are baked to form the first conductive layer 4. By this firing, the metal particles are in a sintered state or a state before being sintered, and are brought into close contact with each other and solid joined. For this reason, the first conductive layer 4 after the conductive ink coating and baking step can have pores corresponding to the gaps between the metal particles.

  The firing is performed in an atmosphere containing a certain amount of oxygen. The lower limit of the oxygen concentration in the atmosphere during firing is 1 ppm by volume, and more preferably 10 ppm by volume. Moreover, as an upper limit of the said oxygen concentration, it is 10,000 volume ppm, and 1,000 volume ppm is more preferable. When the oxygen concentration is less than the lower limit, the amount of metal oxide generated in the vicinity of the interface of the first conductive layer 4 is reduced, and the effect of improving the adhesion between the first conductive layer 4 and the base film 1 due to the metal oxide. May not be sufficiently obtained. On the other hand, when the oxygen concentration exceeds the upper limit, the metal particles are excessively oxidized and the conductivity of the first conductive layer 4 may be lowered.

  As a minimum of the temperature of the said baking, 150 degreeC is preferable and 200 degreeC is more preferable. Moreover, as an upper limit of the temperature of the said baking, 500 degreeC is preferable and 400 degreeC is more preferable. When the firing temperature is less than the lower limit, the amount of metal oxide generated in the vicinity of the low interface peel strength of the first conductive layer 4 decreases, and the adhesion between the first conductive layer 4 and the base film 1 due to the metal oxide. There is a possibility that the improvement effect of the above is not sufficiently obtained. On the other hand, if the firing temperature exceeds the upper limit, the base film 1 may be deformed when the base film 1 is an organic resin such as polyimide.

<Electroless plating process>
In the electroless plating process of step S3, the base film 1 of the first conductive layer 4 is formed by performing electroless plating on the first conductive layer 4 laminated on the base film 1 in the conductive ink coating and baking process using palladium as a catalyst. The second conductive layer 5 is formed on the surface opposite to the first electrode, and a metal is deposited in the voids in the first conductive layer 4.

  In the electroless plating process, a catalyst adsorption process for adsorbing palladium on the first conductive layer 4 and a laminate of the first conductive layer 4 are immersed in an electroless plating solution, so that the surface and the inside of the first conductive layer 4 are immersed. A metal deposition step of depositing a metal. In addition to the catalyst adsorption step and the metal layer formation step, the electroless plating step may include known additional steps such as a cleaning step, a water washing step, an acid treatment step, a water washing step, a reduction step, and a drying step. Good.

(Catalyst adsorption process)
In the catalyst adsorption step, palladium ions are adsorbed by bringing the first conductive layer 4 into contact with a catalyst solution containing palladium, and the palladium ions are reduced to metallic palladium. As a palladium concentration of this catalyst solution, it can be 20 mass ppm or more and 1000 mass ppm or less, for example.

  As a minimum of the temperature of the catalyst solution at the time of immersion, although depending on immersion time, 30 degreeC is preferable and 40 degreeC is more preferable. On the other hand, as an upper limit of the temperature of the catalyst solution at the time of immersion, 70 degreeC is preferable and 60 degreeC is more preferable. When the temperature of the catalyst solution at the time of immersion is less than the said minimum, there exists a possibility that adsorption | suction of palladium may become inadequate. On the contrary, when the temperature of the catalyst solution at the time of immersion exceeds the above upper limit, the adjustment of the palladium adsorption amount may not be easy.

  The lower limit of the immersion time in the catalyst solution depends on the temperature of the catalyst solution, but is preferably 1 minute, more preferably 2 minutes, and even more preferably 3 minutes. On the other hand, the upper limit of the immersion time in the catalyst solution is preferably 10 minutes, more preferably 7 minutes, and even more preferably 5 minutes. If the immersion time in the catalyst solution is less than the above lower limit, the adsorption of palladium may be insufficient. On the other hand, when the immersion time in the catalyst solution exceeds the above upper limit, the palladium adsorption amount is too large and the first conductive layer 4 may not be densified.

(Metal deposition process)
Examples of the metal deposited in the metal deposition step include copper, nickel, and silver as described above. For example, when copper is deposited, a copper plating solution containing a small amount of nickel is used as a copper plating solution used in electroless plating. By using a copper plating solution containing nickel or a nickel compound, the low-stress second conductive layer 5 can be formed. As said copper plating solution, what contains 0.1 mol or more and 60 mol or less of nickel with respect to 100 mol copper is preferable, for example. Moreover, you may mix | blend other components, such as a complexing agent, a reducing agent, and a pH adjuster, with the said copper plating solution suitably.

  In this electroless plating step, the second conductive layer 5 is formed by depositing a metal on the surface of the first conductive layer 4, and at the same time, the metal also deposits in the pores inside the first conductive layer 4. The first conductive layer 4 is densified. The densification of the first conductive layer 4 not only improves the conductivity of the first conductive layer 4, but also increases the adhesion area of the first conductive layer 4 to the base film 1. As a result, the peel strength of the metal layer 2 from the base film 1 increases.

<Heat treatment process>
In the heat treatment step of step S4, palladium present in the vicinity of the interface between the metal layer 2 and the base film 1 is dispersed inside the base film 1 by heat treatment.

  As a minimum of processing temperature in this heat treatment process, 150 ° C is preferred and 200 ° C is more preferred. On the other hand, the upper limit of the treatment temperature in the heat treatment step is preferably 500 ° C, more preferably 400 ° C. When the treatment temperature in the heat treatment step is less than the lower limit, palladium in the first conductive layer 4 may not be sufficiently dispersed in the base film 1. Conversely, when the treatment temperature in the heat treatment step exceeds the above upper limit, the base film 1 or the like may be damaged.

  The lower limit of the heat treatment time in the heat treatment step is preferably 15 minutes, and more preferably 30 minutes. On the other hand, the upper limit of the heat treatment time in the heat treatment step is preferably 720 minutes, and more preferably 360 minutes. If the heat treatment time in the heat treatment step is less than the lower limit, palladium may not be sufficiently dispersed in the base film 1. Conversely, when the heat treatment time in the heat treatment step exceeds the above upper limit, the production cost of the printed wiring board substrate may be unnecessarily increased.

<Electroplating process>
In the electroplating step of step S5, the third conductive layer 6 is formed by further laminating a metal by electroplating on the surface of the second conductive layer 5 formed in the electroless plating step. At this time, vacancies remaining in the first conductive layer 4 after the electroless plating step and new vacancies formed by the diffusion of palladium into the base film in the heat treatment step are filled with metal by electroplating. Thus, the first conductive layer 4 is further densified, and the peel strength of the first conductive layer 4 from the base film 1 is further increased. That is, palladium that has a small contribution to improving the adhesion to the base film 1 in the metal layer 2 is dispersed in the base film 1, and instead of filling the metal that contributes to improving the adhesion by electroplating, the metal layer 2 The peel strength can be increased. In addition, by this electroplating step, the thickness of the metal layer 2 can be easily and reliably grown to a desired thickness.

  As a specific method of electroplating in this electroplating step, a known electroplating method can be applied.

[Printed wiring board]
The printed wiring board is manufactured by forming a conductive pattern on the printed wiring board substrate shown in FIG. The conductive pattern is formed on the metal layer 2 of the printed wiring board substrate using a subtractive method or a semi-additive method.

[Method of manufacturing printed wiring board]
The printed wiring board is manufactured by forming a conductive pattern on the printed wiring board substrate of FIG. The conductive pattern is formed by using a subtractive method or a semi-additive method based on the metal layer 2 of the printed wiring board substrate.

  In the subtractive method, a photosensitive resist is formed on one surface of the printed wiring board substrate, and patterning corresponding to the conductive pattern is performed on the resist by exposure, development, or the like. Subsequently, the metal layer 2 other than the conductive pattern is removed by etching using the patterned resist as a mask. Finally, the remaining resist is removed to obtain the printed wiring board having a conductive pattern formed from the remaining portion of the metal layer 2 of the printed wiring board substrate of FIG.

  In the semi-additive method, a photosensitive resist is formed on one surface of the printed wiring board substrate, and an opening corresponding to the conductive pattern is patterned on the resist by exposure, development, or the like. Subsequently, by plating using the patterned resist as a mask, a conductor layer is selectively laminated on the metal layer 2 exposed in the opening of the mask. Then, after removing the resist, the surface of the conductor layer and the metal layer 2 on which the conductor layer is not formed are removed by etching, so that the remaining metal layer 2 of the printed wiring board substrate in FIG. The printed wiring board having a conductive pattern formed by laminating further conductor layers is obtained.

〔advantage〕
The printed wiring board substrate has the dispersed portion 3 in which palladium is dispersed in the base film 1, thereby improving the adhesion of the base film 1 to the metal layer 2 and increasing the peel strength of the metal layer 2. can do. Furthermore, since the printed wiring board substrate has improved adhesion by dispersing palladium in this way, it does not require a vacuum facility or the like for its manufacture and can be provided at low cost.

  In addition, the printed wiring board substrate has the effect that the presence of palladium in the base film 1 by the presence of palladium so that the content is 1% by mass or more as determined by EDX in the dispersed portion, that is, the metal layer. 2 can be more reliably obtained.

  In addition, the printed wiring board has a fine conductive pattern and is peeled from the base film by forming a conductive pattern on the metal layer of the printed wiring board substrate by using a subtractive method or a semi-additive method. It is hard to do.

  Moreover, the manufacturing method of the said board | substrate for printed wiring boards can form the 1st conductive layer 4 on the surface of the base film 1 easily by providing the process of apply | coating and baking the conductive ink containing a metal particle. Moreover, since the manufacturing method of the said board | substrate for printed wiring boards is equipped with the process of performing electroless plating using palladium as a catalyst, the metal layer 2 is densified by filling the gap | interval of the 1st conductive layer 4 with a metal, and with respect to a base film. Bonding can be strengthened, and the metal layer 2 can be grown by laminating the second conductive layer 5. Moreover, the manufacturing method of the said board | substrate for printed wiring boards can grow the metal layer 2 to desired thickness cheaply and accurately by providing the process of forming a 3rd conductive layer by electroplating. Furthermore, since the manufacturing method of the printed wiring board substrate includes a heat treatment step for dispersing the palladium, it eliminates palladium that can reduce adhesion from between the base film 1 and the metal layer 2. The peel strength between 1 and the metal layer 2 is large.

[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

  In the said embodiment, although it was set as the structure which laminates | stacks a metal layer on one surface of the base film 1, it is good also as a board | substrate for double-sided printed wiring boards of the structure which laminates | stacks a metal layer on both surfaces of a base film with the same formation method. Moreover, you may form a metal layer by the other method on the other surface of the board | substrate for printed wiring boards obtained by the said embodiment. For example, a metal layer may be formed by bonding a metal foil to the other surface of the printed wiring board substrate.

  In addition, the metal layer in the printed wiring board substrate has a three-layer structure of a first conductive layer, a second conductive layer, and a third conductive layer. However, a single-layer structure, a two-layer structure, or a structure having four or more layers may be used. Good. Moreover, the formation method of each conductive layer is also arbitrary. As a specific example, electroless plating may be directly performed on the base film without forming a conductive layer by firing metal particles.

  Hereinafter, the present invention will be described in detail based on the results of trial production of a printed wiring board substrate, but the present invention is not limitedly interpreted based on the description of the prototype.

<Prototype>
Nine types of printed wiring boards of prototypes 1 to 8 with varying palladium concentration of electroless plating catalyst solution (activator solution) for forming the second conductive layer and heat treatment conditions after forming the second conductive layer A prototype board was made.

(Prototype 1)
Prototype 1 of the printed wiring board substrate was prototyped as follows. First, copper particles having an average particle diameter of 60 nm were dispersed in solvent water to prepare a conductive ink having a copper concentration of 26% by mass. Next, a polyimide film having an average thickness of 25 μm (Kapton “EN-S” manufactured by Toray DuPont Co., Ltd.) is used as an insulating base film, and the conductive ink is applied to one surface of the polyimide film, After drying in the air, the copper particles in the conductive ink are baked by heating at 350 ° C. for 30 minutes in a nitrogen atmosphere having an oxygen concentration of 100 ppm by volume, thereby the first conductive layer having an average thickness of 0.15 μm. Formed. Next, electroless plating of copper was performed on one surface of the first conductive layer to form a second conductive layer having an average thickness of 0.4 μm by electroless plating. In this electroless plating, a catalyst solution containing 50 ppm by mass of palladium was used, and the palladium was adsorbed on the first conductive layer by immersing it at a liquid temperature of 40 ° C. for 120 seconds. Moreover, as the electroless copper plating solution used for this electroless plating, the thing containing 0.1 mol of nickel with respect to 100 mol of copper was used. After the electroless plating, a heat treatment was performed at a heat treatment temperature of 350 ° C. and a treatment time of 120 minutes to disperse the palladium in the base film. Thereafter, copper electroplating was further performed to form a third conductive layer, and the total average thickness of the metal layers was set to 18 μm, thereby obtaining a prototype 1 of a printed wiring board substrate.

(Prototypes 2-9)
As shown in Table 1, prototypes 2 to 8 of the printed wiring board substrate were produced under the same conditions as the prototype 1 except that the palladium concentration of the catalyst solution, the liquid temperature during immersion, and the immersion time were different. Note that the prototype 6 does not use a catalyst solution.

<Peel strength>
For the printed wiring board substrates of Prototypes 1 to 8, the peel strength between the polyimide film and the metal layer is peeled off in a 180 ° direction with respect to the polyimide film in accordance with JIS-C6471 (1995). It was measured. The measurement results are also shown in Table 1.

<Measurement of palladium content>
About the cross section of the printed wiring board substrate of the prototypes 1-8, using an energy dispersive X-ray analyzer (scanning electron microscope “SU8020” of Hitachi High-Technologies Corporation), the A layer (base film) The palladium content of the B layer (region from the interface of the metal layer to 500 nm) was measured. The measurement results are also shown in Table 1.

[Evaluation results]
From the results shown in Table 1, the printed wiring board substrates of prototypes 1 to 5 have sufficient peel strength in which palladium is sufficiently dispersed in the A layer. On the other hand, the prototypes 6 to 8 have a small palladium content in the A layer and a small peel strength. From this result, it is understood that the peel strength of the metal layer can be improved by dispersing palladium in the base film.

  Since the printed wiring board substrate and printed wiring board of the present invention are inexpensive and have high peel strength of the metal layer, they can be suitably used for flexible printed wiring boards and the like. Moreover, the manufacturing method of the printed wiring board board | substrate of this invention can be utilized suitably in order to manufacture the printed wiring board board | substrate suitable for forming a flexible printed wiring board etc.

DESCRIPTION OF SYMBOLS 1 Base film 2 Metal layer 3 Dispersion part 4 1st conductive layer 5 2nd conductive layer 6 3rd conductive layer La A layer Lb B layer S1 Conductive ink preparation process S2 Conductive ink application | coating baking process S3 Electroless plating process S4 Heat treatment Process S5 electroplating process

Claims (9)

An insulating base film;
A printed wiring board substrate comprising a metal layer laminated on at least one surface side of the base film,
Having a dispersed portion in which palladium is dispersed in the base film;
The metal layer is
A first conductive layer formed by applying and firing a conductive ink containing copper particles;
Have a second conductive layer formed by electroless plating on one surface of the first conductive layer,
The palladium is derived from the electroless plating catalyst,
The dispersed portion is a printed wiring board substrate formed by a heat treatment after the electroless plating .   The printed wiring board substrate according to claim 1, wherein palladium is present in the dispersed portion so that the content is 1% by mass or more as determined by EDX.   The printed wiring board substrate according to claim 2, wherein the dispersed portion includes a region having an average of 500 nm or more from the interface with the metal layer.   The palladium content of the A layer of 1 μm or less in the thickness direction from the interface with the metal layer in the base film is larger than the palladium content of the B layer of 500 nm or less in the thickness direction from the interface with the base film in the metal layer. The printed wiring board substrate according to claim 1, claim 2, or claim 3.   The ratio of the palladium content at a position of 500 nm to the palladium content at a position of 1 µm in the thickness direction from the interface with the metal layer in the base film is 0.7 or more and 1.1 or less. 5. The printed wiring board substrate according to any one of 4 above.   The printed wiring board substrate according to any one of claims 1 to 5, wherein an average particle diameter of the copper particles is 1 nm or more and 500 nm or less.   The printed wiring board substrate according to any one of claims 1 to 6, wherein the metal layer further includes a third conductive layer formed by electroplating on one surface side of the second conductive layer. A printed wiring board having a conductive pattern,
The printed wiring board by which the said conductive pattern is formed by using a subtractive method or a semi-additive method in the metal layer of the board | substrate for printed wiring boards of any one of Claims 1-7. Applying and baking a conductive ink containing metal particles on at least one surface side of an insulating base film; and
After applying and baking the conductive ink, a step of performing electroless plating on one surface side using palladium as a catalyst;
And after the electroless plating step, a heat treatment step,
A method for producing a printed wiring board substrate, wherein the palladium is dispersed in the heat treatment step.

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