JP2023127192A - Wiring board and manufacturing method thereof - Google Patents

Abstract

To provide a method capable of manufacturing, without employing a photolithography step, a novel wiring board in which adhesiveness of a metal wire and an insulative resin substrate is improved and peeling or disconnection hardly occurs when the resin substrate is bent, while having flexibility derived from the resin substrate and high electric conductivity derived from the metal wire.SOLUTION: A manufacturing method of a wiring board includes the steps of: forming a polymer compound layer containing a thermoplastic resin having a glass transition temperature Tg on a heat resistant resin substrate; applying or printing metal containing paste in which an average particle diameter of primary particles is 150 nm or more and which contains metal particles selected from among copper, silver and nickel, on the polymer compound layer; performing heating at a temperature T1 of 150°C or higher and 450°C or lower under an oxidation atmosphere having an oxygen concentration of 500 ppm or higher; and performing heating at 150°C or higher and 450°C or lower under a reduction atmosphere, wherein Tg and T1 satisfy an inequality:Tg<T1.SELECTED DRAWING: Figure 2

Description

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

A flexible wiring board uses a flexible organic insulating film as a substrate, and metal wiring is formed on this film.

There are three types of methods for forming metal wiring: a subtractive method, a semi-additive method, and an additive method.

Specifically, in the subtractive method, metal foil is attached to a substrate and wiring is formed by a photolithography process. 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 electrolytic plating is performed to form wiring (for example, Patent Documents 1 and 2). However, both the subtractive method and the semi-additive method require a photolithography process, and in addition to the large number of steps, waste liquid treatment is required, resulting in large costs and environmental burdens.

On the other hand, in the additive method, metal wiring is drawn directly onto the substrate using inkjet or screen printing. This additive method has the advantage of not requiring a photolithography process. However, simply forming metal wiring on a substrate has a problem in that the metal wiring easily peels off because the adhesion strength of the metal wiring is weak. Therefore, in order to increase the adhesion strength between the metal wiring and the substrate, there is a method of forming a Ni--Cr alloy thin film as an adhesion layer on the substrate in advance, and then forming the metal wiring (for example, see Non-Patent Document 1). However, if this method is used, it is still necessary to etch the Ni--Cr alloy thin film into a wiring shape, and a photolithography process is required. Similar to the subtractive method and the semi-additive method, this method involves a large number of steps and requires waste liquid treatment, so it is expensive and has a large environmental impact.

Japanese Unexamined Patent Publication No. 62-72200 Japanese Patent Application Publication No. 5-136547

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

The present invention has been made in view of the above-mentioned circumstances, and has the flexibility derived from a resin substrate and the high electrical conductivity derived from a metal wiring, while also providing a structure that allows the connection between the metal wiring and the insulating resin substrate. An object of the present invention is to provide a method for manufacturing a new wiring board that has high adhesion and is less likely to peel or break when a resin board is bent, without using a photolithography process.

The present inventors have made extensive studies in order to solve the above-mentioned problems. As a result, a polymer compound layer containing a thermoplastic resin and a metal-containing paste containing metal particles are laminated on a heat-resistant resin substrate, the resulting laminate is heated in an oxidizing atmosphere, and then, By heating in a reducing atmosphere and performing these heat treatments under specific conditions, it is possible to combine metal wiring and insulating resin substrates with the flexibility derived from resin substrates and the high electrical conductivity derived from metal wiring. The present inventors have discovered that it is possible to manufacture a new wiring board that has high adhesion between resin substrates and is less prone to peeling or disconnection when the resin substrate is bent, and has completed the present invention. Specifically, the present invention provides the following embodiments.

(1) The method for manufacturing a wiring board includes at least a step of forming a polymer compound layer containing a thermoplastic resin having a glass transition temperature Tg on a heat-resistant resin substrate to obtain a laminate. , Coating or printing a metal-containing paste on the polymer compound layer, the average particle diameter of the primary particles being 150 nm or more, and containing at least one metal particle selected from the group consisting of copper, silver, and nickel. a paste coating or printing step, and a first heating temperature T in a range of 150°C or more and 450°C or less in an oxidizing atmosphere having an oxygen concentration of 500 ppm or more. a _second heating step of heating the laminate heated at the first heating temperature _T1 at a temperature of 150° C. or higher and 450° C. or lower in a reducing atmosphere; A method for manufacturing a wiring board, wherein the glass transition temperature Tg and the first heating temperature _T1 satisfy the following formula (I).
Tg<T ₁ ...Formula (I)

(2) In the polymer compound layer forming step, after applying a raw material solution onto the heat-resistant resin substrate, the heat-resistant resin substrate coated with the raw material solution is placed under an oxygen-containing atmosphere or an inert gas atmosphere. The method for manufacturing a wiring board according to (1) above, wherein the wiring board is heated at a layer forming heating temperature _T0 , and the layer forming heating temperature _T0 and the glass transition temperature Tg satisfy the following formula (II). .
T ₀ <Tg...Formula (II)

(3) The method for manufacturing a wiring board according to (1) or (2) above, wherein the reducing atmosphere contains a reducing gas of 1% by volume or more.

(4) Metal particles comprising a thermoplastic resin layer on at least a portion of a heat-resistant resin substrate, and at least a portion of the thermoplastic resin layer containing one or more selected from the group consisting of copper, silver, and nickel. The sintered body has a plurality of voids having a total amount of 5% by volume or more and 40% by volume or less, and at least some of the voids have openings toward the thermoplastic resin layer. A wiring board, wherein a part of the thermoplastic resin layer is bent and entered from the opening.

According to the present invention, the flexibility derived from the resin substrate and the high electrical conductivity derived from the metal wiring are combined, and the adhesion between the metal wiring and the insulating resin substrate is high, and the resin substrate can be bent. It is possible to provide a new wiring board that is less prone to peeling and disconnection. According to the present invention, the wiring board can be manufactured without using a photolithography process.

FIG. 2 is a longitudinal cross-sectional view of a portion of the wiring board according to the present embodiment that includes a sintered body. FIG. 3 is a schematic diagram for explaining the method for manufacturing a wiring board according to the present embodiment, in which (a) and (b) show a polymer compound layer forming step, and (c) show a paste coating or printing step. , (d) shows the first heating process, and (e) shows the second heating process.

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

1. Wiring Board The wiring board according to this embodiment will be described in detail below with reference to FIG. FIG. 1 is a longitudinal cross-sectional view of a portion of the wiring board according to the present embodiment that includes a sintered body.

The wiring board 1 according to the present embodiment includes a thermoplastic resin layer 3 on at least a portion of a heat-resistant resin substrate 2, and at least a portion of the thermoplastic resin layer 3 is selected from the group consisting of copper, silver, and nickel. The present invention includes a sintered body 4 of metal particles containing one or more types of metal particles. The sintered body 4 has a plurality of voids 5 (5a, 5b, 5c, 5d) with a total amount of 5% by volume or more and 40% by volume or less, and at least a part of the voids 5 are formed in the thermoplastic resin layer 3. The thermoplastic resin layer 3 has openings 51a, 51b, 51c, and 51d, and parts 31a, 31b, and 31c of the thermoplastic resin layer 3 are bent into the openings 51a, 51b, and 51c. It is something to do. In this way, the parts 31a, 31b, 31c of the thermoplastic resin layer 3 are bent into the voids 5a, 5b, 5c, so that the insulating resin substrate enters the sintered body and The number of contact areas between the sintered body 4 and the thermoplastic resin layer 3 increases, and when the sintered body 4 and the thermoplastic resin layer 3 are peeled off, it is necessary to deform the resin that has been bent and entered. It is possible to improve the adhesion between the two.

Further, among the voids 5 (5a, 5b, 5c) having openings 51a, 51b, 51c toward the thermoplastic resin layer 3, a plurality of voids 5a, 5b are connected inside the sintered body 4, It is preferable that the portions 31a and 31b of the thermoplastic resin layer 3 entered through a plurality of different openings 51a and 51b are connected to each other. In this way, by connecting the parts 31a and 31b of the thermoplastic resin layer 3 that have entered through a plurality of different openings 51a and 51b, the contact area increases and the thermoplastic resin layers that have entered and are connected Since peeling will not occur unless parts 31a and 31b of 3 are cut, it is possible to improve the adhesion with the insulating resin substrate.

As described above, the sintered body 4 has voids of 5% by volume or more and 40% by volume or less in total. By having a porosity of 1% by volume or more, it is possible to have openings into which portions 31a, 31b, and 31c of the thermoplastic resin layer 3 can enter. Further, by having a porosity of 40% by volume or less, the fracture resistance of the sintered body 4 can be increased. Note that "porosity" refers to the area of the sintered body 4 observed with a scanning electron microscope. The void area is the average value given by the following formula (A) for 10 cross sections.
Porosity (%) = (void area/total cross-sectional area) x 100...Formula (A)

(Heat-resistant resin substrate)
The heat-resistant resin substrate 2 is a substrate mainly containing resin, and the thermoplastic resin 3 is formed on the heat-resistant resin substrate 2.

The resin constituting the heat-resistant resin substrate 2 is not particularly limited, but it can be constructed using a flexible resin such as polyimide, liquid crystal polymer, fluororesin, polyethylene terephthalate, polyethylene naphthalate, or the like.

The heat-resistant resin substrate 2 can contain, in addition to resin, an antioxidant, a flame retardant, a filler made of inorganic particles, etc., depending on the use of the wiring board 1.

The thickness of the heat-resistant resin substrate 2 is not particularly limited, but for example, it is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. On the other hand, the thickness of the heat-resistant resin substrate 2 is preferably 100 μm or less, more preferably 75 μm or less, and even more preferably 50 μm or less. In addition, when the heat-resistant resin substrate 2 is a PET base material, its thickness may be more than 100 μm. When the thickness of the heat-resistant resin substrate 2 is 5 μm or more, it is possible to more strongly prevent the substrate from breaking due to bending or tensile deformation. In addition, since the thickness of the heat-resistant resin substrate 2 is 100 μm or less, the wiring board 1 can be provided with excellent flexibility derived from the resin material.

(Thermoplastic resin layer)
Thermoplastic resin layer 3 mainly contains thermoplastic resin.

The resin constituting the thermoplastic resin layer 3 is not particularly limited, but it can be constructed using a flexible thermoplastic resin such as polyimide, polyamideimide, acrylic resin, cycloolefin resin, polycarbonate, or the like. Note that the heat-resistant resin substrate 2 and the thermoplastic resin layer 3 only need to be formed as two distinct layers. "Distinguishable" here means that the resin constituting the heat-resistant resin substrate 2 and the thermoplastic resin constituting the thermoplastic resin layer 3 are composed of different resins, or even if they are the same resin. , when the number average molecular weight or mass average molecular weight is different, or the orientation of the resin (as a layer) is different, the two layers are in a distinguishable state.

The thermoplastic resin layer 3 can contain, in addition to the thermoplastic resin, an antioxidant, a flame retardant, a filler made of inorganic particles, etc., depending on the use of the wiring board 1.

The thickness of the thermoplastic resin layer 3 is not particularly limited, but is preferably, for example, 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. On the other hand, the thickness of the thermoplastic resin layer 3 is preferably 5 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less. When the thickness of the thermoplastic resin layer 3 is 5 μm or more, it is possible to more strongly prevent the substrate from breaking due to bending or tensile deformation. Furthermore, by having the thickness of the thermoplastic resin layer 3 of 100 μm or less, the wiring board 1 can be provided with excellent flexibility derived from the resin material.

(sintered body)
The sintered body 4 is composed of a sintered body of metal particles containing one or more selected from the group consisting of copper, silver, and nickel, and acts as a conductive path in the wiring board 1. This sintered body is formed by sintering the metal particles.

By using copper particles as the sintered body 4, wiring exhibiting low resistance can be provided at low cost. Further, by using silver particles as the sintered body 4, the wiring does not oxidize even during high temperature sintering. Furthermore, by using nickel particles as the sintered body 4, it is possible to suppress electromigration failures that occur under a high current density load state.

The metal particles may be comprised of 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 4 may be alloyed.

The porosity of the sintered body 4 is not particularly limited as long as it is 5% by volume or more and 40% by volume or less in total. The porosity is preferably 6 vol% or more, more preferably 7 vol% or more, even more preferably 8 vol% or more, and particularly preferably 9 vol% or more. When the porosity is 5% by volume or more, the voids 5a, 5b, 5c, and 5d having the openings 51a, 51b, 51c, and 51d increase, making it easier for the thermoplastic resin layer 3 to enter. Adhesion between the plastic resin layer 3 and the sintered body 4 can be improved. On the other hand, the porosity of the sintered body 4 is preferably 37% by volume or less, more preferably 35% by volume or less. When the porosity is 40% by volume or less, the conductivity of the sintered body 4 can be improved in addition to the strength.

As the sintered body 4, those formed by sintering metal particles having a flake shape, a spherical shape, a polyhedral shape, an irregular shape, etc. can be used without particular limitation. It is preferable to use a material formed by sintering flaky metal particles and spherical metal particles. When using sintered flake metal particles and spherical metal particles, the ratio of flake metal particles to the total mass of flake metal particles and spherical metal particles is 20% or more. It is preferably 80% or less, and more preferably 30% or more and 70% or less. When the proportion of flaky metal particles is 20% or more and 80% or less, it becomes easier to form the sintered body 4 having the above-mentioned porosity.

In such a sintered body 4, since voids 5a, 5b, 5c, and 5d exist inside the sintered body 4, there are portions with low mechanical strength. An example of such a portion is a portion called a “neck,” which is a thin portion formed by sintering metal particles together. When the wiring board 1 is used as a flexible circuit, when the sintered body 4 is deformed as a result of the deformation depending on its use, force is concentrated on such necks, and local breakage is likely to occur.

Therefore, when the sintered body has a porous structure, the sintered body 4 is filled with a metal element having conductivity, especially the same metal as the metal element constituting the sintered body 4 (copper), in the gaps of the porous structure. , silver, and nickel). In this way, the presence of metal plating in the gaps of the porous structure makes it possible to disperse the force that concentrates on the neck due to deformation, and improves durability against deformation such as bending and expansion/contraction. Furthermore, since the voids are filled with conductive metal, the electrical resistivity decreases.

Note that depending on the type of metal constituting the sintered body 4 and the environment in which the wiring board 1 is placed, the metal elements in the sintered body 4 may inevitably be oxidized. Therefore, in the sintered body 4, up to 20% or less of metal atoms in terms of the number of atoms may be oxidized, as long as the conductivity is ensured. In addition, the sintered body 4 contains various additives other than copper, silver, and nickel, and unavoidable impurities (including oxygen in oxides) at about 30% by mass based on the sintered body 4 (100% by mass). It's okay to stay.

2. Method for manufacturing a wiring board The method for manufacturing a wiring board according to the present embodiment includes forming at least a polymer compound layer containing a thermoplastic resin having a glass transition temperature Tg on a heat-resistant resin substrate to obtain a laminate. A polymer compound layer forming step, and a metal-containing paste whose primary particles have an average particle diameter of 150 nm or more and which contains at least one metal particle selected from the group consisting of copper, silver, and nickel, is formed into a polymer compound layer. A paste coating or printing step in which the metal-containing paste is coated or printed on the laminate is coated or printed on the metal-containing paste in an oxidizing atmosphere having an oxygen concentration of 500 ppm or more, and a temperature in the range of 150°C or more and 450°C or less. 1. A first heating step of heating at a heating temperature _T1 , and a second heating step of heating the laminate heated at a first heating temperature _T1 at a temperature of 150° C. or higher and 450° C. or lower in a reducing atmosphere. The glass transition temperature Tg and the first heating temperature _T1 satisfy the following formula (I).
Tg<T ₁ ...Formula (I)
According to such a method of manufacturing a wiring board, a wiring board having the above-mentioned characteristics can be obtained.

Hereinafter, a method for manufacturing a wiring board according to this embodiment will be described using FIG. 2. FIG. 2 is a schematic diagram for explaining the method for manufacturing a wiring board according to this embodiment.

(1) Polymer compound layer forming step The polymer compound layer forming step (FIGS. 2(a) and (b)) includes at least a thermoplastic resin having a glass transition temperature Tg on the heat-resistant resin substrate 6. This is a step of forming a polymer compound layer 7 to obtain a laminate.

(Heat-resistant resin substrate)
The heat-resistant resin substrate 6 is preferably one in which the glass transition temperature TG (° C.) of the resin constituting the heat-resistant resin substrate 6 satisfies the formula: TG+50° C.>first heating temperature _T1 . Although the resin constituting the heat-resistant resin substrate 6 starts to soften at the glass transition temperature TG, it can maintain almost the shape of the heat-resistant resin substrate up to a temperature 50° C. higher than TG. By setting the first heating temperature _T1 to a range lower than TG+50°C, it is possible to prevent deformation and deterioration of the heat-resistant resin substrate during heating in the first heating step.

As the heat-resistant resin substrate 6, one made of the above-mentioned resin can be used without particular limitation, as long as its glass transition temperature TG satisfies the above-mentioned formula.

(Method for forming a polymer compound layer)
A method for forming the polymer compound layer 7 includes, for example, a method of applying a solution of a thermoplastic resin or a solution of a precursor thereof onto the heat-resistant resin substrate 6. Here, the term "precursor substance" refers to a substance that can be cured to obtain a flexible resin through some treatment. Examples of the precursor substance include polyamic acid when polyimide is used as the resin. Although the details will be described later, this polyamic acid is converted into polyimide by imidization treatment, and can be said to be a precursor substance of polyimide.

The polymer compound solution is a solution in which the above-described polymer compound is dissolved in a solvent. The type of solvent and the concentration of the polymer compound may be appropriately selected in consideration of the solubility of the polymer compound, the ease of applying or printing a solution of the polymer compound, and the like.

The coating method is not particularly limited as long as it can uniformly form a film with a thickness of several μm, but spin coating, bar coating, slit coating, etc. can be used.

This polymer compound layer forming process involves applying a raw material solution onto a heat-resistant resin substrate, and then heating the heat-resistant resin substrate coated with the raw material solution under an oxygen-containing atmosphere or an inert gas atmosphere at a layer-forming temperature. It is preferable that the layer forming heating temperature T ₀ and the glass transition temperature Tg satisfy _the formula (II): T ₀ <Tg.

As the oxygen-containing atmosphere, for example, a gas containing oxygen or the atmosphere can be used. Further, a gas other than oxygen (for example, an inert gas) can be mixed with the oxygen gas. Examples of the inert gas atmosphere include nitrogen gas. Argon gas or the like can be used.

(When forming polyimide as a polymer compound layer)
Specifically, a method of forming polyimide as a polymer compound layer will be explained.

First, a solution of polyamic acid as a precursor of polyimide is applied onto the heat-resistant resin substrate 6 .

Solvents for forming the polyamic acid solution include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, γ-butyrolactone, cyclohexanone, methyl benzoate, ethyl benzoate, toluene, xylene, methyl ethyl ketone, water, etc. can be used.

Next, in order to remove the solvent on the heat-resistant resin substrate 6, it is dried in an atmospheric atmosphere. The drying method is not particularly limited, and operations such as heating and depressurization may be performed, or may be left standing.

Thereafter, for example, when the heat-resistant resin substrate 6 coated with the polyamic acid solution is heated at 150° C. or more and 300° C. or less in an air atmosphere, the imidization reaction proceeds and the thermoplastic resin is contained on the heat-resistant resin substrate 6. A layer of polyimide is formed as a polymer compound layer.

(2) Paste application or printing process The paste application or printing process (FIG. 2(c)) is a process of applying or printing the metal-containing paste 8 on the polymer compound layer 7.

(metal-containing paste)
The metal-containing paste is used to form a sintered body of metal containing one or more selected from the group consisting of copper, silver, and nickel. The metal-containing paste has primary particles having an average particle size of 150 nm or more, and contains at least one metal particle selected from the group consisting of copper, silver, and nickel. Further, the metal-containing paste contains, for example, a binder resin and a solvent.

The average particle diameter of the primary particles of the metal particles is not particularly limited as long as it is 150 nm or more, but it is preferably 250 nm or more, and more preferably 350 nm or more. Note that the average particle diameter of the primary particles of the metal particles refers to the median diameter measured using a laser diffraction particle size distribution meter after dissolving the metal-containing paste in a solvent, separating the metal particles with a filter, and drying the paste.

The metal particles may contain metal elements other than copper, silver or nickel. The content of metal elements other than copper, silver and nickel is from 0 (not contained) to 30% by mass or less in terms of metal, regardless of the state of all metal elements contained in the metal sintered body. The content is preferably from 0 (not contained) to 20% by mass or less.

The content of the metal particles is not particularly limited, but is preferably, for example, 80% by mass or more and 95% by mass or less based on 100% by mass of the metal-containing paste.

(binder resin)
The binder resin is not particularly limited as long as it is a resin that can be decomposed by sintering, and examples include cellulose resins such as methyl cellulose, ethyl cellulose, and carboxymethyl cellulose, acrylic resins, butyral resins, alkyd resins, epoxy resins, and phenol resins. It will be done.

The content of the binder resin is not particularly limited, but is preferably, for example, 0.1% by mass or more and 5% by mass or less based on 100% by mass of the metal-containing paste. When sintering is performed in the atmosphere, the binder resin reacts with oxygen in the atmosphere and burns, reducing the amount of resin remaining in the sintered body as much as possible, and reducing the electrical resistance of the sintered body due to the residual resin. rate can be reduced. In particular, by setting the binder resin content to 5% by mass or less, it is possible to suppress the binder resin component from remaining in the wiring and to make the effect on the electrical resistivity of the sintered body negligible. can. On the other hand, when the mass % of the binder resin in the organic vehicle is 0.1 or more, the viscosity of the conductive paste can be increased and the applicability or printability of the paste can be improved.

(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, but examples include hydrocarbon solvents, chlorinated hydrocarbon solvents, and cyclic solvents. Examples include ether solvents, amide solvents, sulfoxide solvents, ketone solvents, alcohol compounds, ester solvents of polyhydric alcohols, ether solvents of polyhydric alcohols, terpene solvents, and mixtures thereof. Among these, it is preferable to use texanol, butyl carbitol, butyl carbitol acetate, terpineol, etc. whose boiling point is around 200°C.

The content of the solvent is not particularly limited, but, for example, it is preferably 2% by mass or more and 25% by mass or less based on 100% by mass of the metal-containing paste. When the content of the solvent is 25% by mass or less, the viscosity of the metal-containing paste decreases, and it can be suppressed from expanding beyond the intended printed shape. On the other hand, when the content of the solvent is 2% by mass or more, the printability of the metal-containing paste can be improved.

(Other ingredients in organic vehicle)
The term "organic vehicle" refers to a liquid containing a binder resin, a solvent, and other organic substances added as necessary. As an organic vehicle, one obtained by mixing only a binder resin and a solvent can usually be used, but in addition to these components, a metal salt and a polyol can also be mixed with the organic vehicle.

The method for producing the metal-containing paste is not particularly limited, but for example, the above-mentioned binder resin and solvent may be mixed, metal particles may be further added, and the mixture may be kneaded using a device such as a planetary mixer. Furthermore, if necessary, a three-roll mill can be used to improve the dispersibility of the metal particles.

(Coating or printing method)
A metal-containing paste is applied or printed on the polymer compound layer 7 to form the shapes of wiring, electrodes, and the like. Specifically, examples of the coating or printing method include screen printing, dispenser printing, gravure printing, offset printing, inkjet printing, and the like.

(3) First heating step In the first heating step (FIG. 2(d)), the laminate coated with or printed with the metal-containing paste is heated in an oxidizing atmosphere having an oxygen concentration of 500 ppm or more at 150°C or more and 450°C or less. This is a step of heating at a first heating temperature _T1 included in the range of. At this time, the glass transition temperature Tg of the thermoplastic resin before heating at the first heating temperature _T1 satisfies the formula: Tg< _T1 .

In this way, in the first heating step, the glass transition temperature Tg of the thermoplastic resin before heating at the first heating temperature _T1 satisfies the formula: Tg< _T1 , and is heated at the first heating temperature _T1 . By doing so, the polymer compound is softened. On the other hand, the metal particles are sintered in an oxidizing atmosphere to form a sintered body having a plurality of curved voids therein. The polymer compound in the polymer compound layer 7 softened by heating at the first heating temperature _T1 is partially bent along the gap from the opening on the polymer compound layer side of the gap in the sintered body. Get into it. In this way, a part of the polymer compound bends and enters along the gap from the opening on the polymer compound layer side of the gap in the sintered body, and the metal wiring and the insulating resin are bonded together. A wiring board that has high adhesion to the substrate and is less likely to peel or break when the resin substrate is bent can be obtained.

In addition, in the first heating step, by heating in an oxidizing atmosphere, the metal elements contained in the metal particles are oxidized, the volume of the metal particles expands, and the contact between the particles becomes strong in the obtained sintered body 8A. Become. The sintered body 8B obtained by reduction in the subsequent second heating step also becomes strong because the particles are in strong contact with each other.

Note that, as described above, when polyimide is formed from polyamic acid as a polymer compound, a small amount of polyamic acid may remain even after annealing alone. In such a case, the remaining polyamic acid is converted into polyamide by heating in the first heating step. Alternatively, in order to adjust the Tg of the polyimide, some unreacted polyamic acid may be intentionally left, and the remaining polyamic acid may be converted into polyamide by heating in the first heating step.

The first heating temperature _T1 is not particularly limited as long as it is 100°C or more and 500°C or less, but it is preferably 120°C or more and 400°C or less.

As the oxidizing gas in the oxidizing atmosphere, for example, oxygen, air, or the like can be used. Furthermore, a mixture of a gas other than the oxidizing gas and the oxidizing gas can be used. As the gas other than the oxidizing gas, an inert gas (for example, nitrogen gas, argon gas) can be used.

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

When the oxygen concentration is 500 ppm or more, the binder resin can be sufficiently burned. On the other hand, by setting the oxygen concentration to 8000 ppm or less, rapid reaction can be prevented from occurring only near the surface of the metal-containing paste, and sufficient sintering can be carried out to the inside of the sintered body.

In the first heating step, heating may be performed under at least one heating temperature and oxygen concentration condition, or heating may be performed under multiple heating temperatures and oxygen concentration conditions.

(4) Second heating step In the second heating step (FIG. 2(e)), the laminate heated at the first heating temperature _T1 is heated in a reducing atmosphere at a temperature of 150° C. or more and 450° C. or less (hereinafter referred to as “ This is a step of heating at a second heating temperature T ₂ ).

In the second heating step, the sintered body obtained as an oxide by sintering in an oxidizing atmosphere in the first heating step is reduced to obtain a conductive metal sintered body 8B.

The second heating temperature _T2 in the second heating step is not particularly limited as long as it is 150°C or more and 450°C or less, but is preferably 170°C or more and 450°C or less.

As the reducing gas constituting the reducing atmosphere, hydrogen, carbon monoxide, formic acid, ammonia, alcohol, etc. can be used. Further, as the gas other than the reducing gas, an inert gas such as nitrogen gas or argon gas can be used.

The concentration of the reducing gas is not particularly limited, but assuming that the pressure of the reducing atmosphere is atmospheric pressure (10 ⁵ Pa), it is preferably 1% by volume or more, more preferably 2% by volume or more. , more preferably 5% by volume or more. If the volume ratio is less than 1%, the reduction of copper, silver or nickel oxides in the sintered body will not be sufficient, the metal oxides will remain, and the metal wiring after firing will exhibit high electrical resistivity. There is a risk.

In the second heating step, heating may be performed under at least one heating temperature and reducing gas concentration condition, or heating may be performed under a plurality of heating temperatures and reducing gas concentration conditions.

The present invention is not limited to the above-described specific embodiments, and can be modified as appropriate as long as the effects of the present invention are not impaired.

EXAMPLES The present invention will be explained in more detail with reference to Examples below. The present invention is not limited to these examples.

(Test 1) Effect of first heating temperature _T1 A polyimide substrate with a glass transition temperature of TG=413° C. was used as the heat-resistant resin substrate. Further, a polyimide varnish was prepared by dissolving a solvent-soluble polyimide made of a block copolymerized polyimide having a glass transition temperature T _g =225° C. in N-methyl-2-pyrrolidone. After applying polyimide varnish to a uniform thickness (approximately 6 μm) on a polyimide substrate using a bar coater, heat treatment was performed in a nitrogen gas atmosphere at a layer formation heating temperature T ₀ = 200°C for 20 minutes, and the solvent was removed to form a thermoplastic polymer compound layer with a thickness of 0.5 μm. Furthermore, after printing a copper paste containing copper particles with an average primary particle diameter of 0.6 μm on this polymer compound layer, heat treatment was performed for 10 minutes at T ₁ = 130 to 475°C in the atmosphere. Ta. Subsequently, heat treatment was performed at T ₂ =400° C. for 30 minutes in a reducing gas atmosphere of N ₂ +5% by volume H ₂ to form a copper electrode on the polymer compound layer, thereby producing a sample.

Using the obtained sample, the adhesion between the polymer compound layer and the copper electrode was examined by a tape test. Specifically, an adhesive tape with an adhesive force of 35 N/cm was attached to the surface of a sample copper electrode, and then the adhesive tape was peeled off to evaluate whether the adhesive tape was peeled off along with the adhesive tape. The results obtained are shown in Table 1. The evaluation criteria were based on ASTM D3359-79, and the highest level of 5 was considered a pass, which is indicated by "Y" in the table. On the other hand, if the test was less than level 5, it was judged as a failure and marked with "N". This level corresponds to the fact that the area to be peeled off together with the adhesive tape is small. The larger the numerical value of the level, the smaller the peeled area and the better the adhesion. Level 5 is a case where the area to be peeled off is zero.

Furthermore, the electrical resistivity (R) of the copper electrode in the sample was measured using a DC four-probe method. The results obtained are shown in Table 1. A case where R was 10 μΩ·cm or less was considered to be a pass, and was indicated by “Y” in the table. If R was larger than 10 μΩ·cm, it was judged as a failure and marked with “N”. In the overall judgment, the case where both the electrical resistivity and the tape test were passed (Y) was judged as a pass (Y), and the other cases were judged as a failure (N).

As shown in Table 1, it was found that when T ₁ was 150° C. or higher, the electrical resistivity was sufficiently low. Furthermore, it was found that when the formula: T ₁ >Tg was satisfied, the adhesion by tape test increased. However, it was found that at T ₁ =475° C., the polyimide substrate deteriorated in a high-temperature environment and the adhesion was impaired.

(Test 2) Effect of layer formation heating temperature T ₀ Same as Test 1, fixing Tg = 225°C, T ₁ = 300°C, T ₂ = 400°C, varying T ₀ in the range of 150 to 300°C. The test was conducted using the following procedure. The results are shown in Table 2.

It was found that since T ₁ is 300° C., the resistance is as low as 10 μΩ·cm or less regardless of the value of T ₀ . Furthermore, it was found that when the formula: Tg>To is satisfied, the adhesion as determined by the tape test increases.

(Test 3) Effect of average particle diameter of metal particles and porosity of sintered body Fixed at Tg = 285°C, T ₀ = 200°C, T ₁ = 300°C, T ₂ = 400°C, average particle size of copper particles Samples were prepared in the same manner as in Test 1, with the diameter varied in the range of 0.1 to 10 μm, and a tape test was conducted. Furthermore, the porosity of the copper electrode was measured. Observe the cross section of the sintered body of the copper electrode with a scanning electron microscope, measure the "total cross-sectional area" which is the internal area bordered by the outer periphery of the cross-section, and the "void area" inside it. "Porosity" was calculated using the formula "area/total cross-sectional area) x 100". The porosity of the sample was measured at 10 cross sections, and the average value was obtained. These results are shown in Table 3.

When the average particle diameter of the copper particles is 0.1 μm, sintering occurs rapidly during oxidation heating at a temperature of _T1 , forming a dense sintered structure with a volume fraction of voids smaller than 5%. ₁ >Tg, it was found that it became difficult for the thermoplastic resin to penetrate into the inside of the sintered body, and the adhesion deteriorated.

(Test 4) Effect of oxidizing atmosphere Tg = 285°C, T ₀ = 200°C, T ₁ = 300°C, T ₂ = 400°C, and the oxygen concentration in the heating furnace in the first heating step was changed from 100 ppm to atmospheric air ( 200,000 ppm), samples were prepared in the same manner as Test 1, and the electrical resistivity was measured. Furthermore, the porosity was measured using the same procedure as Test 5. These results are shown in Table 4.

If the oxygen concentration is lower than 500 ppm, oxidation will be insufficient, and the porosity in the first heating step at T ₁ = 300°C will exceed 40%, resulting in insufficient sintering, and as a result, the electrical resistivity after reduction will be 10 μΩ・It was found that it was larger than cm. Therefore, it was found that the oxygen concentration in the oxidizing atmosphere in the first heating step is preferably 500 ppm or more. Further, it was found that the porosity is preferably 40% or less.

(Test 5) Effect of second heating temperature T ₂ Fixing Tg = 285°C, T ₀ = 200°C, T ₁ = 300°C, changing T ₂ in the range of 120 to 475°C, heating time from 30 to A test was conducted using the same procedure as Test 1, with the time being changed within the range of 120 minutes. The results are shown in Table 5.

When T ₂ is 140°C or higher, the electrical resistivity is as low as 10 μΩ・cm or less, and the adhesion is good. On the other hand, when T ₂ is 475°C, the polyimide substrate may change in quality and the adhesion may deteriorate. Do you get it. Therefore, it was found that the reduction temperature _T2 is preferably 140°C or more and 450°C or less. Also, suitable heating time at 140°C is 90 minutes, and heating time at 450°C is 30 minutes.

(Test 6) Influence of reducing atmosphere In Test 5, the temperature _T2 of the second heating step was 300°C, the heating time was 30 minutes, and the reducing atmosphere was N ₂ + 3% H ₂ , N ₂ + 1% H ₂ , N ₂ The electrical resistivity was measured by changing the atmosphere to +0.5% H ₂ and N ₂ +0.1% H ₂ . According to the test results, a value of 10 μΩ·cm or less was shown when the hydrogen gas concentration was 1% or more. Therefore, it was found that the reducing gas concentration is preferably 1% by volume or more.

1 Wiring board 2 Heat-resistant resin substrate 3 Thermoplastic resin layer 31a, 31b, 31c Part of thermoplastic resin layer 4 Sintered body 5, 5a, 5b, 5c, 5d Gap 51a, 51b, 51c, 51d Opening 6 Heat resistant Polymer compound layer 8 Metal-containing paste 8A, 8B Sintered body

Claims (4)

In a method for manufacturing a wiring board,
A polymer compound layer forming step of forming at least a polymer compound layer containing a thermoplastic resin having a glass transition temperature Tg on a heat-resistant resin substrate to obtain a laminate;
Coating or printing on the polymer compound layer a metal-containing paste whose primary particles have an average particle diameter of 150 nm or more and which includes at least one metal particle selected from the group consisting of copper, silver, and nickel. paste application or printing process;
A first heating step of heating the laminate on which the metal-containing paste is applied or printed at a first heating temperature _T1 within a range of 150° C. or more and 450° C. or less in an oxidizing atmosphere having an oxygen concentration of 500 ppm or more. and,
a second heating step of heating the laminate heated at the first heating temperature T ₁ in a range of 150° C. or more and 450° C. or less in a reducing atmosphere;
The glass transition temperature Tg and the first heating temperature _T1 satisfy the following formula (I),
A method of manufacturing a wiring board.
Tg<T ₁ ...Formula (I) In the polymer compound layer forming step, a raw material solution is applied onto the heat-resistant resin substrate, and then the heat-resistant resin substrate coated with the raw material solution is layered under an oxygen-containing atmosphere or an inert gas atmosphere. Heating at a forming heating temperature T ₀ ,
The layer forming heating temperature _T0 and the glass transition temperature Tg satisfy the following formula (II),
The method for manufacturing a wiring board according to claim 1.
T ₀ <Tg...Formula (II) 3. The method for manufacturing a wiring board according to claim 1, wherein the reducing atmosphere contains a reducing gas of 1% by volume or more. A thermoplastic resin layer is provided on at least a portion of the heat-resistant resin substrate,
At least a part of the thermoplastic resin layer is provided with a sintered body of metal particles containing one or more selected from the group consisting of copper, silver and nickel,
The sintered body has a plurality of voids having a total amount of 5% by volume or more and 40% by volume or less, and at least a part of the voids has an opening toward the thermoplastic resin layer, and from the opening . A wiring board, in which a part of the thermoplastic resin layer is bent and inserted.

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