TWI781528B - Wiring board and method of manufacturing the same - Google Patents

Abstract

The present invention provides a novel wiring substrate, which has both the flexibility brought by the resin substrate and the high conductivity brought by the metal wiring, and the adhesion between the metal wiring and the insulating resin substrate is high, and the present invention provides A method of manufacturing such a wiring board without using a photolithography step. The wiring board of the present invention has a resin substrate and metal wiring, and the metal wiring includes a sintered body of metal particles, the sintered body has a plurality of voids, the voids have openings facing the resin substrate, and a part of the resin substrate is formed from The opening part enters into the gap.

Description

Wiring substrate and manufacturing method thereof

The present invention relates to a wiring substrate and its manufacturing method.

A flexible wiring board is a substrate made of a flexible organic insulating film, and metal wiring is formed on the insulating film.

As a method of forming metal wiring on a board|substrate, three types, the subtractive method, the semi-additive method, and the additive method, are mentioned.

Specifically, in the subtractive method, a metal foil is attached to a substrate, and wiring is formed through a photolithography step. Also, in the semi-additive method, a thin film serving as a seed layer is deposited on a substrate by sputtering or the like, and then electroplated to form wiring (for example, refer to Patent Documents 1 and 2). However, since both the subtractive method and the semi-additive method require photolithography steps, the number of steps is relatively large. In addition, waste liquid treatment and the like are required, and the cost is high and the burden on the environment is large.

On the other hand, the additive method is a method of forming metal wirings by directly writing metal wirings on the substrate by inkjet or screen printing, which has the advantage of not requiring photolithography steps. However, if the metal wiring is only directly formed on the substrate, there is a problem that the metal wiring is easy to peel off because the adhesion strength between the metal wiring and the substrate is weak. Therefore, in order to increase the adhesion strength between metal wiring and the substrate, a method is known in which a Ni-Cr alloy thin film is previously formed on the substrate as an adhesion layer, and then the metal wiring is formed (see, for example, Non-Patent Document 1). However, in this method, a photolithography step is required in order to etch the Ni-Cr alloy thin film as the adhesion layer into the wiring shape. Therefore, in the method of forming the adhesive layer, there are the same problems as the subtractive method and the semi-additive method: the number of steps is large, and waste liquid treatment is required, so the cost is high and the environmental burden is large. [Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 62-72200 [Patent Document 2] Japanese Patent Laid-Open No. 5-136547 [Non-patent literature]

[Non-Patent Document 1] Y.Cao, J.Tian, and X.Hu, This Solid Films, Vol.365(1), pp.49-52(2000)

[Problem to be solved by the invention]

The present invention is made in view of the above-mentioned actual situation, and its object is to provide a wiring board that has both the flexibility brought by the resin substrate and the high conductivity brought by the metal wiring, and the metal wiring and the insulation The adhesiveness between resin substrates is high, and a method of manufacturing such a wiring substrate without using photolithography steps is provided. [Technical means to solve the problem]

The inventors of the present invention have intensively studied in order to solve the above-mentioned problems. As a result, it was found that a wiring board having the intended function can be obtained by having a structure in which, in a wiring board comprising a resin substrate and a sintered body of metal particles, the sintered body has a plurality of voids, and a part of the resin substrate emerges from the voids. and found that such a wiring board can be manufactured by forming a sintered body of metal particles and a resin substrate; thereby completing the present invention. Specifically, the present invention provides the following embodiments.

(1) A wiring board having a resin substrate and metal wiring, and The metal wiring includes a sintered body of metal particles, the sintered body has a plurality of voids, the voids have openings facing the resin substrate, and a part of the resin substrate enters the voids through the openings.

(2) The wiring board as described in said (1) whose said metal particle contains 1 or more types selected from the group which consists of copper, silver, and nickel.

(3) The wiring board as described in said (1) or (2) whose ratio of the said void is 1 volume % or more and 30 volume % or less.

(4) The wiring board described in any one of (1) to (3) above, wherein a part of the void is connected to a part of the resin substrate entering from the opening.

(5) The wiring board described in any one of the above (1) to (4), wherein in the above-mentioned sintered body, a resin surface layer is formed on the surface opposite to the interface with the above-mentioned resin substrate. .

(6) A method of manufacturing a wiring board, which is a method of manufacturing a wiring board having a resin substrate and metal wiring including a sintered body of metal particles, comprising: a sintered body forming step of forming the above-mentioned sintered body on a member for sintering; The coating step is to apply a solution containing a resin component on the surface of the above-mentioned sintered body and the periphery of the above-mentioned sintered body on the above-mentioned sintering member; the curing step is to harden the above-mentioned resin component to form a resin substrate; and the peeling step, The above-mentioned sintered body and the above-mentioned resin substrate are separated from the above-mentioned member for sintering.

(7) The method for producing a wiring board as described in (6) above, wherein the solution contains a resin precursor material or a polymerizable monomer of the resin.

(8) A method of manufacturing a wiring board, which is a method of manufacturing a wiring board having a resin substrate and metal wiring including a sintered body of metal particles, comprising: a step of preparing a resin substrate; and a step of forming a sintered body, bonded to the above resin The above-mentioned sintered body is formed on the substrate.

(9) The method of manufacturing a wiring board as described in the above (8), which includes the steps of applying a solution containing a resin component on the above-mentioned resin substrate, and curing the above-mentioned resin component to form an interface resin layer; and the above-mentioned sintered body is formed The step includes forming the above-mentioned sintered body on the above-mentioned interface resin layer.

(10) The method for producing a wiring board according to (9), wherein the solution contains a resin precursor material or a polymerizable monomer of the resin. [Effect of Invention]

According to the present invention, it is possible to provide a wiring board having both the flexibility provided by the resin substrate and the high conductivity provided by the metal wiring, and the adhesion between the metal wiring and the insulating resin substrate is improved. Also, according to the method of manufacturing a wiring board of the present invention, such a wiring board can be manufactured without using a photolithography step.

Hereinafter, specific embodiments of the present invention will be described in detail. The present invention is not limited by the following embodiments, and can be implemented with appropriate changes within the scope of the purpose of the present invention.

1. Wiring substrate Hereinafter, the wiring board of this embodiment is demonstrated in detail using FIG. 1. FIG. FIG. 1 is a vertical cross-sectional view of a portion including a sintered body in a wiring board according to the present embodiment.

The wiring board 1 of the present embodiment has a resin substrate 2 and metal wiring, and the metal wiring includes a sintered body 3 of metal particles. In addition, the sintered body 3 has a plurality of voids 4a, 4b, 4c, and 4d. In this specification, the voids 4a, 4b, 4c, and 4d may be collectively described as voids 4 in some cases. At least a part of the cavity 4 has openings 41a, 41b, 41c, 41d facing the resin substrate 2, and a part 21a, 21b, 21c of the resin substrate 2 enters the cavity 4 through the openings 41a, 41b, 41c. As shown in FIG. 1, one part 21a, 21b, 21c of the resin substrate bends into the gap 4a, 4b, 4c. By having such a form, the number of contact portions between the insulating resin substrate and the sintered body is increased. Furthermore, when the sintered body and the resin substrate are peeled off, it is necessary to deform the resin entering the void, so that the peeling of the sintered body and the resin substrate can be suppressed. Therefore, by providing the structure of this embodiment, the adhesiveness between a sintered body and a resin substrate can be improved.

In addition, it is preferable that the parts 21a, 21b of the resin substrate 2 that enter from the openings 41a, 41b are connected to each other in the gap 4 . By having such a connection structure, the contact portion between the sintered body and the resin substrate is increased. Furthermore, when the sintered body and the resin substrate are separated, it is necessary to cut the resin substrate connected in the gap, so that the separation of the sintered body and the resin substrate can be suppressed. Therefore, by providing the structure of this embodiment, the adhesiveness between a sintered body and a resin substrate can be improved.

The wiring board of this embodiment also includes the form in which the interface resin layer was interposed between the resin substrate and the sintered body.

[porosity] In addition, the ratio of voids in the sintered body is preferably from 1 volume % to 30 volume % in total. In this specification, the ratio of this void is called "porosity". By setting the porosity to 1% by volume or more, there is an opening that allows a part of the resin substrate to enter the void. The ratio of the voids having openings facing the resin substrate increases, and a part of the resin substrate easily enters the voids. As a result, the adhesiveness between the resin substrate and the sintered body can be improved. Therefore, the porosity is preferably at least 1% by volume, more preferably at least 7% by volume, and more than 10% by volume.

On the other hand, if the porosity exceeds 30% by volume, there is a possibility that the sintered body may be broken and the electrical conductivity of the sintered body may be lowered. In order to improve the fracture resistance and electrical conductivity of the sintered body, the porosity is preferably 30% by volume or less, more preferably 27% by volume or less, and 25% by volume or less.

The ratio of the voids in this embodiment, that is, the "void ratio" can be calculated as follows. That is, the cross-section of the sintered body was observed with a scanning electron microscope, the internal area bounded by the outer periphery of the cross-section was obtained as the "total cross-sectional area", and the area of voids distributed in the interior was obtained as the "void area". Then, the value obtained by averaging the values obtained by the formula (1) shown below for 10 cross-sections was the porosity. Porosity (%) = (void area/total cross-sectional area) × 100 ・・・Formula (1)

In addition, the porosity of the present embodiment is calculated under the following conditions: In the observation image of the scanning electron microscope, a region not including the end of the sintered body (the surface of the sintered body and the interface with the resin substrate) is selected, and the selected The image area of the region is in the range of 1/3 to 2/3 of the total cross-sectional area of the sintered body.

[Resin substrate] The resin substrate 2 is a substrate mainly composed of resin, and the sintered body 3 of metal particles is formed on the resin substrate 2 to constitute the wiring substrate 1 .

The resin constituting the resin substrate is not particularly limited. Flexible resins such as polyimide, liquid crystal polymer, fluororesin, polyethylene terephthalate, and polyethylene naphthalate can be used.

The resin substrate may contain an antioxidant, a flame retardant, a filler containing inorganic particles, etc., in addition to the resin, depending on the application of the wiring substrate.

The thickness of the resin substrate is not particularly limited. For example, if the thickness of the resin substrate is 5 μm or more, the substrate can be prevented from breaking due to bending or tensile deformation. Therefore, it is preferably 5 μm or more, and more preferably 10 μm or more, or 15 μm or more. On the other hand, if the thickness of the resin substrate is too large, the flexibility provided by the resin material decreases. Therefore, the thickness of the resin substrate is preferably 100 μm or less, more preferably 75 μm or less, or 50 μm or less.

Moreover, the resin substrate of this embodiment includes the form in which the interface resin layer was provided in the interface contacting with a sintered compact.

[sintered body] The sintered body in the wiring board of this embodiment contains metal particles, the metal particles include one or more selected from the group consisting of copper, silver, and nickel, and the sintered body functions as a metal wiring as a conductive path in the wiring board role.

By using copper as the metal particles in the sintered body, metal wiring showing lower resistance can be provided at lower cost. In addition, by using silver as the metal particles, the wiring is not oxidized even during high-temperature sintering. Furthermore, by using nickel as the metal particles, it is possible to suppress poor electromigration that occurs under a load state with a high current density.

The metal particles may also include a plurality of metal particles selected from the group consisting of copper, silver and nickel. In this case, part or all of the sintered body may be alloyed.

When there are voids inside the sintered body, there are parts with low mechanical strength. As such a portion, for example, a portion called a "neck" in which metal particles are sintered is formed thinner. By selecting a flexible resin substrate for the wiring substrate, when the wiring substrate is deformed along with the deformation in such an application that can be used as a flexible circuit, the force is concentrated on the neck and local damage is likely to occur .

Therefore, when the sintered body has a porous structure, it is preferable to include a conductive metal element in the gaps of the porous structure, and it is particularly preferable to include plating including the same metal element as the metal element constituting the sintered body. The metal element is preferably one or more selected from the group consisting of copper, silver, tin, and nickel. The existence of this metal plating can disperse the force concentrated on the neck during deformation, and improve the durability against deformation such as bending or stretching. Furthermore, since the voids are filled with a conductive metal element, the resistivity of the sintered body decreases.

Furthermore, depending on the kind of metal elements constituting the sintered body or the environment in which the wiring board is placed, the metal elements in the sintered body are inevitably oxidized. Therefore, in the sintered body, on the premise of ensuring the electrical conductivity, for example, a maximum of 20% or less of the metal atoms may be oxidized in terms of the number of atoms. In addition, the sintered body may contain various additives or unavoidable impurities other than copper, silver, tin, and nickel in an amount of about 30% by mass relative to the sintered body (100% by mass). Inevitable impurities also include oxygen in oxides.

[resin surface layer] In the wiring board of the present embodiment, it is preferable that the sintered body includes a resin surface layer on the surface opposite to the interface with the resin substrate. In this specification, the resin layer formed on the surface of the sintered body is referred to as "resin surface layer". In the sintered body, a plurality of voids are distributed with a void ratio above a certain level. Therefore, in the process of manufacturing the wiring board of this embodiment on the sintering member, the resin of the resin substrate wets and diffuses to the interface between the sintered body and the sintering member through the voids connected in the sintered body. As a result, a resin surface layer is formed on the surface of the sintered body opposite to the interface with the resin substrate. When a wiring board including such a resin surface layer is used in a heated environment in the air, the surface of the sintered body is covered with the resin surface layer, so oxidation of the surface can be suppressed, and it is preferable in terms of exhibiting good durability .

2. Manufacturing method of wiring board (1) Embodiment example 1 of the manufacturing method The method of manufacturing a wiring board according to this embodiment is a method of manufacturing a wiring board having a resin substrate and metal wiring including a sintered metal particle, and includes: a sintered body forming step of forming the above-mentioned sintered body on a member for sintering; and a coating step , on the above-mentioned member for sintering, coating a solution containing a resin component on the surface of the above-mentioned sintered body and the periphery of the above-mentioned sintered body; a resin layer forming step of hardening the above-mentioned resin component to form a resin layer; and a peeling step of forming a resin layer from the above-mentioned sintered The above-mentioned sintered body and the above-mentioned resin layer were peeled off with a member.

(2) Embodiment example 2 of the manufacturing method As another method of manufacturing the wiring board of this embodiment, there may also be a method of manufacturing a wiring board having a resin substrate and metal wiring including a metal particle sintered body including the steps of: preparing a resin substrate; A step of cloth containing a solution of a resin component; a hardening step of hardening the above resin component to form a resin interface layer; and a sintering step of forming the above sintered body on the above resin interface layer.

Prepare a resin substrate prefabricated into a film shape or a plate shape, apply a metal-containing paste on the resin substrate, and go through drying and firing steps to produce a sintered body of metal particles. At this time, the firing temperature of the metal-containing paste is a temperature at which the thermal deterioration of the resin substrate can be prevented. For example, in the case of a polyimide substrate, it needs to be approximately 450° C. or lower.

In addition, it may be a production method including the step of applying a solution containing a resin component on the above-mentioned resin substrate, curing the above-mentioned resin component to form an interface resin layer, and the above-mentioned sintering step includes forming the above-mentioned interface resin layer on the above-mentioned interface resin layer. Sintered body. In order to improve the adhesion between the resin substrate and the sintered body, the resin precursor or resin solution is coated on the resin substrate, and the interface resin layer is formed through specific heat treatment steps. Thereafter, a metal-containing paste can also be coated on the interface resin layer, and a sintered body of metal particles can be produced through drying and firing steps. As a resin precursor, for example, polyamic acid can be used. As the resin solution, for example, polyimide varnish can be used.

Furthermore, according to the manufacturing method of the wiring board as described in the above "(1) Embodiment 1 of the manufacturing method" and "(2) Embodiment 2 of the manufacturing method", it is possible to obtain the Features of the wiring board. That is, there can be obtained a wiring board having a resin substrate and metal wiring, wherein the metal wiring includes a sintered body of metal particles, the sintered body has a plurality of voids, the voids have openings facing the resin substrate, and the resin A part of the substrate enters the gap from the opening.

Hereinafter, the manufacturing method of the wiring board of this embodiment is demonstrated using FIG. 2. FIG. FIG. 2 is a schematic diagram for explaining the manufacturing method. Hereinafter, it demonstrates based on said "Example 1 of Embodiment of a manufacturing method". The production method of the present invention is not limited to Embodiment Example 1. A wiring board having the characteristics of the present invention can also be provided by the above-mentioned "Example 2 of embodiment of the manufacturing method".

[Sintered Body Formation Step] The steps of forming the sintered body of this embodiment are shown in (a) and (b) of FIG. 2 . The sintered body forming step is a step of forming the sintered body 6 of metal particles on the member 5 for sintering. As the metal particles, it is preferable to contain one or more types selected from the group consisting of copper, silver, and nickel.

In addition, an example of the method of forming the sintered body 6 on the member 5 for sintering is demonstrated below. The production method of the present invention is not limited to the following specific examples. As long as the effects of the present invention are not hindered, any known or unknown examples may be employed.

(Sintering components) The member for sintering is preferably selected from the following: the metal-containing paste containing metal particles coated on the member for sintering, its dried product, and the sintered body formed by sintering thereof are adhered to a certain extent, and thereafter Those who are not easy to peel off in the steps.

The material or type of the member for sintering is preferably a material that does not react with the metal when the metal-containing paste is sintered at high temperature. For example, an inorganic substrate including an inorganic material may be used, and any one of a carbide substrate, a nitride substrate, and an oxide substrate may be used. Specifically, examples of inorganic materials include silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), boron nitride (BN), silicate glass (SiO ₂ ), magnesium oxide (MgO), oxide Aluminum (Al ₂ O ₃ ), mullite (Al ₂ O ₃ +SiO ₂ ), silicon (Si), etc. Furthermore, metals such as molybdenum and tungsten, which can be formed into a sheet shape and do not react with the metal in the paste, can be used. Magnesium oxide (MgO) or silicic acid glass (SiO ₂ ) material is preferable in terms of good peelability when peeling the wiring board including the sintered body and the resin substrate from the member for sintering.

In addition, a graphite substrate can also be used as a member for sintering. In the case of using a graphite substrate as a member for sintering, graphite particles may adhere to the resin layer in the wiring substrate, depending on the use of the wiring substrate, and the function of the resin layer (such as electrical insulation) is impaired situation. In this case, the surface of the member for sintering can also be used by covering the surface of the member for sintering with an insulator such as carbide, nitride, or oxide.

As shown in this example, regarding the member for sintering, the surface of the member for sintering may be modified or covered in consideration of the adhesiveness with the metal-containing paste, its dried product, and the sintered body, or the use of the obtained wiring board. Furthermore, the modification or covering can be either organic or inorganic.

The average roughness (Ra) of the surface of the member for sintering is preferably 25 μm or less. By setting the average roughness (Ra) to 25 μm or less, the surface smoothness of the resin layer formed on the surface of the sintering member can be ensured, and the origin of fracture due to tensile deformation or bending deformation of the resin layer can be prevented.

(with metal paste) The metal-containing paste is used to form a sintered body containing one or more metals selected from the group consisting of copper, silver, and nickel. Specifically, the metal-containing paste includes at least metal particles or metal oxide particles, a binder resin, and a solvent, for example.

(metal particles or metal oxide particles) Metal particles may also contain metal elements other than copper, silver or nickel. As for the content of metal elements other than copper, silver, and nickel, regardless of their state, in terms of metal conversion, it is preferably 30% by mass or less, or 20% by mass, relative to all the metal elements contained in the metal sintered body the following.

The content of glass components such as glass frit in the metal-containing paste is not particularly limited. Regardless of the state, in terms of metal, it is preferably at most 5% by mass, more preferably at most 1% by mass, at most 0.5% by mass, or at most 0.1% by mass relative to all the metal elements contained in the metal-containing paste. If the content of the glass component in the metal-containing paste exceeds 5% by mass, the glass component excessively reacts with the member for sintering in the sintering step of forming the sintered body from the metal-containing paste. Therefore, when the resin layer is peeled off from the member for sintering, a sintered body may remain on the surface of the member for sintering, which is not preferable. Moreover, by making content of a glass component into 0.5 mass % or less, or 0.1 mass % or less, the increase of the resistivity of a sintered compact can be suppressed.

The average particle diameter (D ₅₀ ) of the metal particles or metal oxide particles is not particularly limited. The average particle diameter (D ₅₀ ) is preferably not less than 0.1 μm and not more than 20 μm. By setting the average particle diameter (D ₅₀ ) to 0.1 μm or more, it is possible to prevent disconnection from being generated due to the influence of the unevenness of the surface of the member 5 for sintering, thereby impairing the function as wiring, or preventing voids in openings from being damaged. The size is as small as the particle size, so it is difficult for a part of the resin substrate to enter. By setting the average particle diameter (D ₅₀ ) to 20 μm or less, curved portions of voids can be formed. Furthermore, the average particle diameter (D ₅₀ ) of the metal particles or metal oxide particles in this embodiment refers to the 50% volume particle diameter, and refers to the particle diameter measured by the laser diffraction method.

There is no particular limitation on the content of metal particles or metal oxide particles. For example, it is preferably at least 80% by mass and at most 95% by mass relative to 100% by mass of the metal-containing paste.

(Binder resin) The binder resin compounded in the metal-containing paste is not particularly limited as long as it is a resin material that can be decomposed by sintering. For example, cellulose resins such as methylcellulose, ethylcellulose, and carboxymethylcellulose, acrylic resins, butyral resins, alkyd resins, epoxy resins, and phenol resins may be mentioned. Preferably, it is a cellulose-based resin that tends to disappear from the paste by reacting with oxygen or carbon monoxide. Among cellulose-based resins, ethyl cellulose is preferred.

The content of the binder resin is not particularly limited. For example, it is preferably at least 0.1% by mass and at most 5% by mass relative to 100% by mass of the metal-containing paste. If the binder resin remains in the sintered body, the resistivity will increase. In the case of sintering in the atmosphere, the binder resin reacts with oxygen in the atmosphere and burns, thereby reducing the amount of binder resin remaining in the sintered body and reducing the resistivity of the sintered body. Therefore, the content of the binder resin is preferably 5% by mass or less. , by making the content of the binder resin 5% by mass or less, the binder resin component can be suppressed from remaining in the sintered body, and the influence on the electrical resistivity of the sintered body can be ignored. On the other hand, by making the binder resin in the metal-containing paste 0.1% by mass or more, the viscosity of the metal-containing paste can be increased, and the coatability or printability of the paste can be improved. Therefore, the content of the binder resin is preferably at least 0.1% by mass.

(solvent) The solvent contained in the metal-containing paste is not particularly limited as long as it has an appropriate boiling point, vapor pressure, and viscosity. For example, hydrocarbon-based solvents, chlorinated hydrocarbon-based solvents, cyclic ether-based solvents, amide-based solvents, ethylene-based solvents, ketone-based solvents, alcohol-based compounds, polyol ester solvents, and polyol ethers solvents, terpene-based solvents, and mixtures thereof. Among them, TEXANOL, butyl carbitol, butyl carbitol acetate, terpineol and the like having a boiling point of about 200° C. are preferable.

The content of the solvent contained in the metal-containing paste is not particularly limited. For example, it is preferably not less than 2% by mass and not more than 25% by mass relative to 100% by mass of the metal-containing paste. By making the content of the solvent 25% by mass or less, the viscosity of the metal-containing paste can be suppressed, and expansion beyond the desired printed shape can be suppressed. On the other hand, the printability of a metal-containing paste can be improved by making content of a solvent into 2 mass % or more.

The "organic vehicle" in this embodiment refers to a liquid obtained by mixing all binder resins, solvents, and other organic substances added as necessary. As an organic vehicle, the thing prepared by mixing a binder resin and a solvent normally can be used. Furthermore, a metal salt and a polyhydric alcohol can also be mixed with an organic vehicle.

The method for producing the metal-containing paste is not particularly limited. For example, the above-mentioned binder resin and a solvent may be mixed, and metal particles may be added thereto, followed by kneading using a device such as a planetary mixer. You can also use a three-roll mill as needed to improve the dispersion of metal particles.

Metal-containing paste is applied or printed on the sintering member to form a specific shape such as wiring or electrodes. Specifically, the method of coating or printing may, for example, be screen printing, dispenser printing, gravure printing, offset printing, or inkjet printing.

(sintering) After coating or printing the metal-containing paste on the sintering member, the sintering member is heated at a temperature of 600° C. to 800° C. to obtain a sintered body.

The sintering can be carried out in one stage under a nitrogen atmosphere or a reducing atmosphere, or can be carried out in two stages after heating under an oxidizing atmosphere and then heating under a reducing atmosphere. In addition, when heating is performed in two stages, the heating temperatures of the two stages are set to a temperature of 600° C. or more and 800° C. or less.

Hereinafter, the gas atmosphere in the case of heating in two stages will be described.

As the oxidizing gas in the oxidizing atmosphere, for example, oxygen or air can be used. Moreover, the gas other than an oxidizing gas can be mixed and used with an oxidizing gas. As a gas other than an oxidizing gas, an inert gas (such as nitrogen or argon) can be used.

The concentration of oxygen in the oxidizing atmosphere is not particularly limited. In terms of oxygen partial pressure, it is preferably 50 Pa or more, and more preferably 60 Pa or more or 70 Pa or more. When the pressure of the atmosphere is atmospheric pressure (10 ⁵ Pa), the oxygen partial pressure is converted into a volume ratio concentration, and the concentration is preferably 500 ppm or more, more preferably 600 ppm or more, or 700 ppm or more.

By making the oxygen concentration 500 ppm or more, the binder resin in the metal-containing paste can be fully burned and eliminated. On the other hand, if the concentration of the oxidizing gas exceeds 8000 ppm, there is a possibility that the reaction will rapidly occur only near the surface of the metal-containing paste. In order to fully sinter into the inside of the sintered body, the oxygen concentration is preferably 8000 ppm or less.

As the reducing gas, hydrogen, carbon monoxide, formic acid, ammonia, or the like can be used. Also, as the gas other than the reducing gas, an inert gas such as nitrogen or argon can be used.

The concentration of the reducing gas is not particularly limited. When the pressure of the reducing atmosphere is atmospheric pressure (10 ⁵ Pa), the concentration of the reducing gas is preferably 0.5% or more by volume, more preferably 1% or more, or 2% or more. If the volume ratio is less than 0.5%, the reduction of metal oxides such as copper, silver, or nickel in the sintered body cannot be sufficiently reduced, and metal oxides remain, so the metal wiring after firing has a high resistivity. risk.

In the case of using a paste containing metal particles, sintering may also be performed under a nitrogen atmosphere. Alternatively, when using a paste containing metal oxide particles, sintering may be performed under a reducing atmosphere. In any case, the sintering temperature is preferably not less than 600°C and not more than 850°C.

[Coating procedure] The coating step of this embodiment is shown in (c) of FIG. 2 . The coating step is a step of coating the solution 7 containing the resin component on the surface of the sintered body 6 and the periphery of the sintered body 6 on the member 5 for sintering.

The resin component in the coating step of this embodiment can use a resin precursor material or a polymerizable monomer of the resin. A resin hardened by a drying process to remove a solvent or a further process or a precursor material thereof may be used.

The polymerizable monomer is not particularly limited as long as it is a monomer of a resin cured by polymerization or further treatment. Examples thereof include monomers of flexible resins such as polyimide, liquid crystal polymer, fluororesin, polyethylene terephthalate, and polyethylene naphthalate.

In addition, the "precursor substance" of the resin refers to a substance that is hardened by any treatment to obtain a flexible resin. As a precursor material, the polyamic acid in the case of using polyimide as resin is mentioned, for example. The polyamic acid is a substance that becomes a polyimide by imidization treatment, and can be called a polyimide precursor substance. Furthermore, the precursor substance of this embodiment also includes monomers that are cured by any treatment after polymerization.

The solvent is not particularly limited. It can be appropriately selected in consideration of the solubility of the resin component, the viscosity corresponding to the coating method, and the like. For example, in the case of polyimide resin, N-methylpyrrolidone can be used as a solvent.

The viscosity of the solution containing the resin component is not particularly limited. For example, it is preferably at least 0.5 Pa·s, more preferably at least 2 Pa·s. On the other hand, it is preferably at most 50 Pa·s, more preferably at most 25 Pa·s. By setting the viscosity of the solution to 0.5 Pa·s or more and 50 Pa·s, a part of the resin substrate can enter the void of the sintered body. Furthermore, by setting the viscosity of the solution to 2 Pa·s or more and 25 Pa·s or less, parts of the resin substrates entering the voids of the sintered body can be connected to each other, thereby obtaining high adhesion strength and high elongation at break Rate.

The coating method is not particularly limited. For example, a slit coater, a bar coater, a spin coater, etc. can be used.

As described above, after coating the solution containing the resin component on the member for sintering, it is dried. The drying method is not particularly limited. For example, drying may be performed at normal temperature and atmospheric pressure, or at least any one of heating and reduced pressure may be performed.

The thickness of the dried resin component-containing layer was approximately equal to the thickness of the resin substrate. The thickness of the resin component-containing layer after drying is not particularly limited. For example, it is preferably 5 μm or more, and more preferably 10 μm or more, or 15 μm or more. On the other hand, it is preferably 100 μm or less, further preferably 75 μm or less, or 50 μm or less. By setting the thickness of the resin component-containing layer after drying to 5 m or more, it is possible to prevent the substrate from being broken due to bending or tensile deformation. On the other hand, by setting the thickness of the resin component-containing layer after drying to 100 m or less, excellent flexibility can be imparted.

[hardening step] The hardening step of this embodiment is shown in FIG. 2( d ). The hardening step is a step of converting resin components such as precursor substances or polymerizable monomers contained in the coated or printed resin component-containing solution into resin to form the resin substrate layer 8 in a state where the resin is cured.

The curing method is not particularly limited, and heating may be performed or various catalysts may be used according to the chemical species of each monomer. For example, in the case of using polyamic acid as a precursor material to form polyamide as a resin, dehydration reaction by heating can also be used.

In the manufacturing method of the wiring board of the present embodiment, in the hardening step, the resin of the resin substrate is wetted and diffused to the interface between the sintered body and the member for sintering through the gaps connected in the sintered body. As a result, a resin surface layer is formed on the surface of the sintered body opposite to the interface with the resin substrate.

[Peel off procedure] The peeling step of the present embodiment is shown in (e) of FIG. 2 . The peeling step is a step of peeling the sintered body 6 and the resin layer 8 from the member 5 for sintering. For example, the sintered body 6 and the resin layer 8 can be peeled from the member 5 for sintering by grasping the end of the resin layer 8 and pulling it in a peeling direction. [Example]

Examples are given below to further describe the present invention. The present invention is not limited by these Examples.

[Examples 1-4, Comparative Examples 1-2] (Preparation of samples) A magnesium oxide plate was used as a member for sintering. Copper paste was printed on the surface of the member for sintering by screen printing. As the copper paste, one containing 80% by mass of spherical particles with an average particle diameter of 1 μm and 20% by mass of a vehicle containing a mixture of a binder resin and a solvent was used. The printed copper paste was dried in the air at 100° C., then heat-treated and sintered in a nitrogen atmosphere, and then cooled to room temperature. As shown in Table 1, the heat treatment temperature was appropriately changed in the range of 600°C to 850°C, and the heat treatment time was appropriately changed in the range of 30 minutes to 60 minutes, thereby obtaining Examples 1-4 and Sintered bodies with different porosity in Comparative Examples 1-2. The approximate dimensions of the copper wiring of the obtained sintered body were a line width of 200 μm, a height of 13 μm, and a length of 6 cm.

For each sample of Examples 1 to 4 and Comparative Examples 1 to 2, polyimide varnish was coated on the surface of the member for sintering having the sintered body (copper wiring) with the amount of solvent adjusted so that the viscosity became 10 Pa·s ("UPIA", a product of Ube Industries, Ltd.). Next, heat treatment was carried out at 280° C. for 10 minutes in a nitrogen atmosphere, and then heat treatment was carried out at 350° C. for 30 minutes to harden the polyimide varnish and form a film-like polyimide resin substrate. The thickness of the resin substrate was 25 μm at the center portion in contact with the sintered body and 31 μm at the end portions. After cooling to room temperature, the laminate including the copper sintered body and the polyimide resin substrate was peeled off from the sintering member. Thereafter, the obtained laminate was subjected to ion beam processing using a cross section polisher (IB-19530CP manufactured by JEOL Ltd.) for obtaining a flat cross section.

(cross-sectional observation) The size of the obtained laminate including the copper sintered body and the polyimide resin substrate was about 20 mm×about 15 mm. In the longitudinal direction where the copper wiring was formed, it was cut vertically near the center to obtain a sample for cross-sectional observation. The cross-sectional structure of the laminate was observed using a field emission type scanning electron microscope (hereinafter referred to as "SEM"). The cross-sectional structure obtained by observing the sample of Example 2 is shown in FIG. 3A. The upper side of the copper sintered body 11 is a part in contact with the member for sintering. It can be confirmed that the entire copper sintered body is embedded in the resin substrate 12 . A portion of the image including only the copper wiring area surrounded by the frame indicated by the dotted line in FIG. 3A was cut out ( FIG. 3B ). Then, use image analysis software (Image J) to perform binarization to obtain a black and white image as shown in Figure 3C. The area ratio of the black part in Figure 3C was calculated by Image J to obtain the porosity (%).

When calculating the porosity, randomly select 10 parts in the cross-sectional structure of the sample, obtain their respective porosities, and use the average value as the porosity of the sintered body in this example.

FIG. 4 is an enlarged view showing the vicinity of the interface between copper sintered body 11 and resin substrate 12 in FIG. 3A . The dotted line shown in the interface 16 of FIG. 4 is drawn along the outer periphery of the cross-section of the copper sintered body, and represents the interface between the copper sintered body and the resin substrate. The region located further inside the boundary line and having no copper sintered portion corresponds to the void of the copper sintered body. In addition, when the SEM image was visually observed, when the resin was present on the inner side of the interface 16, it was determined that the resin had entered the void. For example, openings 9 and 10 facing the resin substrate 12 are provided inside the voids 13 and 14 that exist near the interface 16 in FIG. Furthermore, the void 13 and the void 14 are connected in the inside of a copper sintered body, and the resin 15 which penetrated into each void is also connected.

In this specification, when a part of the resin of the resin substrate enters the void of the copper sintered body, it can be said that the wiring substrate has "resin entry". In addition, when the resins in the plurality of voids in the sintered body are connected to each other, it can be said that the wiring board has "continuity of the resin".

(Determination of resistivity) The resistivity of the sample in Example 2 was measured by the DC four-probe method with a probe interval of 1 mm.

(Evaluation of adhesion) Prepare samples for evaluating adhesion. Copper paste was coated on a 10 mm square area on the magnesium oxide substrate, and then fired to obtain a flat copper sintered body. Thereafter, a polyimide varnish with a viscosity of 15 Pa·s was applied, heat-treated, cooled to room temperature, and peeled off from the sintering member. Using the sample obtained by laminating the copper sintered body and the resin substrate, a tape test was performed in accordance with ASTM D 3359-79, and the area of the peeled part of the copper sintered body peeled off from the resin substrate was measured to obtain the area ratio (%), and evaluated Adhesion between copper sintered body and resin substrate. Adhesiveness was evaluated on 6 scales of 0 to 5 from the area ratio (%) of the peeled part as shown below. Furthermore, 5 is the highest adhesion strength, and 0 is the lowest adhesion strength. 5:0 4: More than 0% and less than 5% 3: More than 5% and less than 15% 2: More than 15% and less than 35% More than 135% and less than 65% 0: more than 65%

(Determination of elongation at break) In addition, a tensile test was performed in the longitudinal direction of the copper sintered body to measure the change in electrical resistance as the elongation strain increases. As a result, the electrical resistance increased by 40% from the initial value when the elongation strain became 18%. When the elongation strain was further increased, the electrical resistance increased rapidly, and it was confirmed that the copper sintered body was broken. In this example, the elongation strain (%) at which a sharp increase in electrical resistance was observed was taken as the "elongation at break".

Table 1 shows the above evaluation results. The ideal result is that the electrical resistivity is 4 μΩ·cm or less, the adhesion evaluation is 3 or more, and the elongation at break is 8% or more. A more ideal result is that the resistivity is below 3 μΩ·cm, the adhesion evaluation is 5, and the elongation at break is above 13%.

[Table 1] Heat treatment temperature [°C] Heat treatment time [minutes] Porosity[%] entry of resin Resin Continuity Resistivity [μΩ・cm] Adhesion Evaluation Elongation at break[%] Example 1 850 30 3 have none 1.9 3 12 Example 2 800 30 12 have have 2.2 5 18 Example 3 700 30 twenty four have have 2.9 5 15 Example 4 650 30 28 have have 3.4 4 10 Comparative example 1 850 60 1 none none 1.8 2 5 Comparative example 2 600 30 33 have have 4 3 4

[Examples 5-8, Comparative Examples 3-4] In Examples 5-8 and Comparative Examples 3-4, sintered copper was obtained at 650°C for 30 minutes to obtain a copper sintered body with a porosity of 28%, and the viscosity of the polyimide varnish was set at 0.6 to 63 Pa·s Samples were produced under the same conditions as in Example 2, except that the range was changed. Furthermore, the viscosity of the polyimide varnish can be changed by adjusting the content of N-methylpyrrolidone (NMP) contained in the varnish (expressed in % relative to the mass of the varnish). For the obtained sample, the resin penetrated into the void, and the continuity, adhesiveness, and elongation at break of the resin in the void were evaluated. The results are shown in Table 2. The ideal result is that the adhesion evaluation is 3 or more, and the elongation at break is 8% or more. A more ideal result is that the adhesion evaluation is 5, and the elongation at break is more than 13%.

[Table 2] NMP concentration [mass%] Viscosity [Pa・s] entry of resin Resin Continuity Adhesion Evaluation Elongation at break[%] Example 5 80 0.6 have none 3 11 Example 6 75 3 have have 5 16 Example 7 67 twenty four have have 5 14 Example 8 50 47 have none 3 12 Comparative example 3 85 0.3 none none 2 7 Comparative example 4 40 63 none none 2 6

(Evaluation of Durability) [Example 9] A plurality of samples of the copper sintered body were produced in the same manner as in Example 2, and the cross-sectional structure of the copper sintered body was observed by SEM. FIG. 5 is an enlarged view showing the vicinity of the surface located on the opposite side of the interface 16 between the copper sintered body 11 and the resin substrate. A resin surface layer 17 is formed on the surface of the sintered body, and the thickness of the resin surface layer 17 is about 0.8 μm. These samples were heat-processed for 10 minutes at 200 degreeC, 250 degreeC, and 300 degreeC in air|atmosphere, and after cooling, the surface of the copper sintered body was visually observed. Before and after heat treatment, discoloration was not observed on the surface of the copper sintered body, and surface oxidation was suppressed. In this respect, it was confirmed that the wiring board of the present invention has good durability against the use environment.

In the copper sintered body of Example 9, a plurality of voids are distributed with the same porosity as that of Example 2. Therefore, it can be speculated that when the polyimide varnish is heated and hardened, the resin of the resin substrate wets and diffuses to the interface between the copper sintered body and the member for sintering through the connection gap in the copper sintered body, thereby forming a sintered body The resin surface layer.

[Comparative Example 5] A plurality of samples of the copper sintered body were produced in the same manner as in Comparative Example 1, and in the same order as in Example 9, the cross-sectional structure near the surface of the copper sintered body was observed by SEM, and then heat treatment was performed, and the copper sintered body was visually observed the surface. As a result, no resin surface layer was observed on the surface of the copper sintered body. Furthermore, the surface of the copper sintered body heat-processed at each temperature of 200 degreeC, 250 degreeC, and 300 degreeC was dark gray, and the surface was oxidized.

Since the copper sintered body of Comparative Example 5 was more sintered than that of Example 9, the distribution ratio of the voids was small as in Comparative Example 1. Therefore, it is presumed that in this copper sintered body, there are no interconnected voids to the extent that the resin of the resin substrate can pass, and no resin surface layer is formed.

1: Wiring board 2: Resin substrate 3: Sintered body 4: Gap 4a: Void 4b: Void 4c: Void 4d: Void 5: Components for sintering 6: Sintered body 7: Solution 8: Resin substrate layer 9: Opening 10: Opening 11: copper sintered body 12: Resin substrate 13: Gap 14: Gap 15: Resin 16: Interface (dotted line) 17: Resin surface layer 21a: Part of the resin substrate 21b: Part of the resin substrate 21c: Part of the resin substrate 41a: opening 41b: opening 41c: opening 41d: opening

FIG. 1 is a schematic diagram showing a cross section of a wiring board according to this embodiment. 2 is a schematic diagram for explaining the manufacturing method of the wiring board of this embodiment, (a) and (b) are diagrams showing steps of forming a sintered body, (c) is a diagram showing a resin coating step, (d ) is a diagram showing the hardening step of the resin, and (e) is a diagram showing the peeling step. 3A is a diagram showing a scanning electron micrograph of a cross-section of a resin substrate and a sintered body in a sample of Example 2. FIG. Fig. 3B is an enlarged view of the cross-sectional structure of the sintered body in Fig. 3A. FIG. 3C is a diagram showing a structure subjected to binarization processing with respect to FIG. 3B . FIG. 4 is a view showing a cross section near the boundary between the resin substrate and the sintered body in the sample of Example 2. FIG. FIG. 5 is a view showing a resin surface layer of a sintered body in a sample of Example 2. FIG.

1: Wiring board 2: Resin substrate 3: Sintered body 4a: Void 4b: Void 4c: Void 4d: Void 21a: Part of the resin substrate 21b: Part of the resin substrate 21c: Part of the resin substrate 41a: opening 41b: opening 41c: opening 41d: opening

Claims (10)

A wiring substrate having a resin substrate and metal wiring, wherein the metal wiring includes a sintered body of metal particles, the sintered body has a plurality of voids, the voids have openings facing the resin substrate, and a part of the resin substrate is formed from The opening enters into the void, and in the sintered body, the resin surface layer covers the surface on the opposite side to the interface with the resin substrate. The wiring board according to claim 1, wherein the metal particles include one or more selected from the group consisting of copper, silver, and nickel. The wiring board according to claim 1 or 2, wherein the ratio of the voids is 1% by volume or more and 30% by volume or less. The wiring board according to claim 1 or 2, wherein a part of the above-mentioned gap is connected, and a part of the above-mentioned resin substrate entering from the above-mentioned opening is connected. The wiring board according to claim 1 or 2, wherein the voids of the sintered body contain a metal element having conductivity. A method of manufacturing a wiring substrate, which is to manufacture the wiring according to any one of claims 1 to 5 A method for a substrate, the wiring substrate having a resin substrate and metal wiring including a sintered body of metal particles, comprising: a sintered body forming step of forming the sintered body on a member for sintering; a coating step of forming the sintered body on the member for sintering , coating a solution containing a resin component on the surface of the above-mentioned sintered body and the periphery of the above-mentioned sintered body; a hardening step of curing the above-mentioned resin component to form a resin substrate; and a peeling step of peeling the above-mentioned sintered body and The aforementioned resin substrate. The method of manufacturing a wiring board according to claim 6, wherein the solution contains a resin precursor material or a polymerizable monomer of the resin. A method of manufacturing a wiring board, which is a method of manufacturing a wiring board according to any one of claims 1 to 5, the wiring board having a resin substrate and metal wiring including a sintered metal particle, comprising: a step of preparing the resin substrate and a sintered body forming step, forming the above-mentioned sintered body on the above-mentioned resin substrate. The method of manufacturing a wiring board according to Claim 8, which includes the steps of applying a solution containing a resin component on the above-mentioned resin substrate, curing the above-mentioned resin component to form an interface resin layer, and the above-mentioned step of forming the sintered body is included in the above-mentioned interface resin. The above-mentioned sintered body is formed on the layer. The method of manufacturing a wiring board according to claim 9, wherein the solution contains a resin precursor material or a polymerizable monomer of the resin.

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