JP2010146734A - Method of manufacturing copper film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for sintering copper particulates in low temperatures and in a short time, and to manufacture the copper film on a base material by this method. <P>SOLUTION: This method of manufacturing the copper film includes a process to form a paint film by applying a composition containing the copper particulates onto the base material, and a process to sinter the copper particulates by disposing a shield having shape followability on the upper part of the paint film and applying hot press to the paint film to sinter the copper particulates. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a copper film, which includes a step of applying a composition containing copper fine particles on a substrate and a step of heat-pressing the composition.

  Wiring boards used in the electronics field in recent years have been miniaturized for the purpose of improving the degree of integration. Conventionally, vacuum processes such as sputtering and vacuum deposition have been mainly used for the production of wiring patterns, and it has become possible to produce a fine pattern of several tens of nanometers using these processes. However, the vacuum process can produce a thin film with high accuracy, but the deposition rate is slow and the process cost is high.

  In recent years, printed wiring technology has attracted attention as an alternative to these vacuum processes. This technique is a technique in which a paste in which metal particles are dispersed is printed on a base material, heat-treated, and wired on a substrate. Although it is inferior in terms of fine wiring as compared with a vacuum process, pattern formation on the order of several microns has become possible with the recent development of printing technology, and is expected as a low-cost process wiring technology.

  However, in the printed wiring technology, since it is necessary to perform heat treatment at a very high temperature in order to sinter the metal, the polymer substrate or the like may be damaged. On the other hand, in order to make an inexpensive printed wiring board, it is desirable to use a highly versatile film substrate such as a polyester film. For example, when a polyethylene terephthalate film, which is the most versatile polyester film, is used, it is desirable that the substrate can be sintered by a heat treatment at 200 ° C. or less because of the durability of the substrate.

  In general, a technique for reducing the firing temperature of a metal paste by reducing the particle size of the metal particles is known. For example, a technique that can be sintered at a relatively low temperature by using metal fine particles having a particle diameter of 100 nm or less is disclosed (Patent Document 1). In addition, the fact that the particles are minute is advantageous in that the pattern accuracy is improved even in fine printed wiring.

  Regarding the method of forming fine wiring patterns using metal fine particles, for example, silver fine particles have already established a methodology, and silver fine particle pastes that can be printed by the screen printing method have been commercialized (manufactured by Fujikura Kasei Co., Ltd.). : Dotite, manufactured by Harima Kasei Co., Ltd .: conductive silver paste, manufactured by Namics Co., Ltd .: HIMEC). However, if silver fine particles are used, the material silver itself is expensive, so the cost of producing the paste is also expensive, and there is a limit to the cost reduction that is the merit of printed wiring, which is a major obstacle to widespread use as a general-purpose product. It has become.

  In addition, as the fine silver particles become narrower in wiring width and inter-wiring space, disconnection due to electromigration becomes a problem. It is known that it is effective to use copper fine particles as the metal fine particles in order to avoid the disconnection due to the electromigration phenomenon. Copper has electrical conductivity equivalent to that of gold and silver, has much less electromigration, and has a lower material unit price than silver. Therefore, application of copper fine particles to printed wiring technology is highly expected.

  Silver, which is a noble metal, has characteristics that make it difficult to undergo oxidation, and it is easy to maintain it in an unoxidized state even when stored in a paste form. On the other hand, copper fine particles, which are base metals, have a characteristic of being easily oxidized, and particularly when heated for sintering, they easily react with surrounding oxygen and are oxidized. Once the copper fine particles are oxidized, the surface is stabilized and the sintering phenomenon is less likely to occur. For this reason, in order to sinter the copper fine particles, it is necessary to perform the atmosphere control in a reducing gas atmosphere or an inert gas atmosphere.

  In the known examples, sintering is performed by heating in a nitrogen gas atmosphere at 350 ° C. for 1 hour to obtain a resistivity of 5.0 μΩ · cm (Patent Document 2), or an organic reducing gas vapor atmosphere at 250 ° C. In which a thin film having a resistivity of 6.6 μΩ · cm is obtained by heating for 40 minutes or more (Patent Document 3), after being heated and fired at 250 ° C. in a nitrogen gas atmosphere, then 300 ° C. in a hydrogen gas atmosphere There is an example in which 3 μΩ · cm is obtained by heating and baking for 1 hour. In these examples, since the atmosphere must be controlled during the process, the process cost is high, the heating temperature is high, and the substrates that can be used are limited.

  There are other examples in which the degree of sintering is increased not only by heating but also by devising the process. An example in which plasma reduction is performed at 150 ° C. in an argon / hydrogen mixed gas (Patent Document 5), an example in which sintering is performed by electron beam irradiation although being an example of silver particle sintering (Patent Document 6), Examples of firing using a laser (Patent Literature 7) and examples of pressing and firing during heating (Non-Patent Literature 1 and Patent Literature 8) are known examples. These examples are different from calcination by simple heating and may enable the use of polymer substrates. However, plasma reduction uses hydrogen gas, resulting in higher costs and new electron beam irradiation and lasers. The problem of cost is great in that a simple apparatus must be used.

  The sintering method using a hot press, which is superior in terms of cost, can be easily sintered with silver. This is because when the silver is heated, the reduction reaction proceeds naturally, and the silver oxide becomes silver. However, in the copper particle film, the oxidation reaction proceeds easily by reacting with external oxygen during hot pressing, and the thick oxide film on the particle surface inhibits the sintering, so that a film having uniform conductivity cannot be obtained.

  In addition, there is an example (Patent Document 8) in which a film made of silver particles is coated with a resist agent, which may prevent oxidation. However, when the conductive film is contacted with another wiring, a process of peeling the coated layer again is required. This is necessary and the process becomes complicated, leading to an increase in cost.

In this way, the conventional technology requires high-cost processes such as atmosphere control and high-temperature heating in order to sinter the copper fine particles, and there are problems in terms of process cost and versatility of the board, so the copper fine particle paste It was difficult to put it into practical use as a wiring material for printed wiring boards.
Japanese Patent No. 2561537 International Publication No. 2004/050559 Pamphlet International Publication No. 2004/103043 Pamphlet Japanese Patent Application Laid-Open No. 2004-164876 JP 2004-247572 A JP 2006-26602 A JP 2006-38999 A JP 2005-177710 A AIST "TODAY" 2006-01

  The present invention has been made to solve the above-described problems, and provides a method capable of sintering copper fine particles at a lower temperature and in a shorter time than before, and an object of the present invention is to produce a copper film on a substrate. To do.

  As a result of diligent studies to solve the above problems, the inventors of the present invention manufactured a copper film by sintering at a lower temperature than before by placing a shielding object immediately above the coating film containing copper fine particles and performing a heat press treatment. Found that it is possible to do.

That is, the present invention is characterized by the following configurations (1) to (8).
(1) A step of applying a composition containing copper fine particles on a substrate to form a coating film, and a shielding object having a shape following property above the coating film, and heating the coating film And a step of sintering the copper fine particles.
(2) The manufacturing method of the copper film as described in (1) which contains a copper nanoparticle as said copper microparticle, and the number average particle diameter of this copper nanoparticle is 1 nm or more and 200 nm or less.
(3) The manufacturing method of the copper film as described in (1) or (2) whose heating temperature is 50 degreeC or more and 300 degrees C or less in the process of heat-pressing the said coating film.
(4) The method for producing a copper film according to any one of (1) to (3), wherein the press pressure is 1 MPa or more in the step of heat-pressing the coating film.
(5) The manufacturing method of the copper film in any one of (1)-(4) whose bending strength of the said shield is 100 GPa * mm < ² > or less.
(6) The manufacturing method according to any one of (1) to (5), wherein the shielding object includes at least one selected from the group consisting of a fluorine resin, a metal foil, a thermoplastic resin, and a silicone resin.
(7) Between the step of forming the coating film and the step of heating and pressing the coating film to sinter the copper fine particles, including the step of sintering the copper fine particles by heating and / or plasma (1) to ( 6) The manufacturing method of the copper film in any one.

  According to the present invention, a copper film can be manufactured by sintering copper fine particles in a short time by heat-pressing the copper fine particles at a low temperature.

  The method for producing a copper film of the present invention comprises a step of applying a composition containing copper fine particles on a substrate to form a coating film, and a shielding object having shape following property is disposed immediately above the composition. A method for producing a copper film, comprising a step of heat-pressing a coating film.

Copper fine particles:
The copper fine particles used in the present invention preferably contain copper nanoparticles having a particle diameter of less than 1 μm, but may contain copper microparticles of 1 μm or more and 10 μm or less. Of the copper fine particles used in the present invention, when the weight fraction of the copper nanoparticles is Ma and the weight fraction of the copper microparticles is Mb, the value of Ma / (Ma + Mb) may be 0.7 or more. Preferably, it is 0.8 or more and 1 or less. Copper microparticles are harder to sinter than copper nanoparticles, but are present in a small amount in the copper fine particles, so that they can be used as a conductive path and may become more conductive. However, when the value of Ma / (Ma + Mb) is smaller than 0.7, the entire film is adversely affected to sinter, which causes a problem.
It is preferable that the average particle diameter of the copper nanoparticle contained in the copper fine particle used for this invention is 200 nm or less, More preferably, it is 100 nm or less, More preferably, it is 50 nm or less. If it is 200 nm or less, the surface energy is increased, the melting point is lowered, the metal particles are fused at a low temperature, and a copper thin film is easily formed, which is preferable. Moreover, it is preferable that the particle diameter is small also for printed wiring, and in order to perform printing with a width of several microns and intervals, the particle diameter of the copper nanoparticles is more preferably 100 nm or less. In addition, it is preferable that the minimum of the particle diameter of a copper nanoparticle is 1 nm. This is because from the relationship with the surface oxide film of the copper nanoparticles, if the thickness is less than 1 nm, all the nanoparticles become copper oxide.

  Here, the particle diameter refers to the primary particle diameter and can be measured by morphological observation with an electron microscope. The calculation of the average particle diameter is based on the number average, and is obtained by selecting arbitrary 100 particles from the range of particles that can be observed with an electron microscope, and averaging the particle diameter by the number of particles. It is done.

  It is preferable that the copper fine particles are not oxidized. However, in order to contain a reducing substance in the coating film, it is not always essential that the particles are not oxidized. good. There are cuprous oxide and cupric oxide as copper oxide, and there is no limitation on the oxidation state of copper, but cuprous oxide is preferred from the viewpoint of easy reduction to metallic copper.

  The surface of the copper fine particles includes those covered with organic components and particle oxides. In addition to the effect of suppressing the oxidation reaction on the surface of the copper fine particles, the present invention has an effect on a coating method utilizing the charging effect of particles represented by electrophotographic printing described later.

  The copper fine particles used in the present invention can be obtained, for example, from Aldrich, which contains copper nanoparticles having a particle size of 50 nm and 100 nm, respectively, and from Alfa Aesar, which contains copper nanoparticles having a particle size of 200 nm. Further, as the particles whose surface is covered with an organic substance, for example, copper fine particles covered with gelatin can be obtained from Ishihara Sangyo. Moreover, it can synthesize | combine by the well-known method as described in Unexamined-Japanese-Patent No. 1-259108. The copper microparticles used in the present invention can be obtained, for example, from Kishida Chemical Co., Ltd. with a particle size of 1 μm, and from Aldrich, with a particle size of 10 μm. Moreover, copper microparticles can be produced using an atomizing method, which is a common production method for producing metal powder.

Compositions containing copper particulates:
In the present invention, examples of the form of the composition applied onto the substrate include powder and paste.

  In the case of powder, the composition may contain a binder, a reducing agent, and other additives, which will be described later, as necessary. The weight of the copper nanoparticles is 50% by weight or more, preferably 80% by weight or more, based on the total weight of the powder. When it is lower than 50% by weight, the components other than the copper fine particles prevent the copper fine particles from contacting the base material, and sintering becomes difficult.

  The binder is a resin that adheres between particles or between particles and a substrate, and when added, it becomes easy to form a dense film. It can be roughly divided into curable resins and plastic resins. Examples of the thermosetting resin that can be used as the binder include epoxy resins, phenol resins, resol resins, polyimides, polyurethanes, melamine resins, urea resins, polyimide resins, and the like, and these resin monomers, oligomers, and derivatives are also included. Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, (cresol) novolac type epoxy resin, halogenated bisphenol resin, reso, glycerin triether, polyolefin, epoxidized soybean oil, cyclopentadiene dioxide, vinyl. And cyclohexene dioxide. Liquid epoxy resins are preferred because of their low viscosity. Specifically, phenoxyalkyl monoglycidyl ether, bisphenol A diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, hexanediol diglycidyl ether, hydrogenated bisphenol A di Glycidyl ether, neopentyl glycol diglycidyl ether, glycerin diglycidyl ether, N, N-diglycidyl aniline, N, N-diglycidyl toluidine, trimethylolpropane triglycidyl ether, glycerin toglycidyl ether and various liquid polysiloxane di Examples thereof include glycidyl ether. Examples of the thermoplastic resin include polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, polygrillamide resin, and polyamide resin.

As the reducing agent, an action that prevents oxidation of copper fine particles at room temperature, that is, a substance having an anti-oxidation action, an anti-oxidation action when heated in a step of sintering copper fine particles, and an action of reducing oxides in copper fine particles Either a substance exhibiting the above or a substance having both properties can be used. The form of the reducing agent can be either liquid or solid. Examples of the method of adding a liquid reducing agent to the powdery composition include a method in which the reducing agent is dropped into the powdery composition and stirred, and dried in a room or vacuum at a temperature lower than the boiling point of the reducing agent. . When dried at a temperature lower than the boiling point, the reducing agent is adsorbed on the surface of the copper fine particles. The reducing agent that can be used is not particularly limited, and may be an inorganic reducing agent or an organic reducing agent. Examples of the inorganic reducing agent include hydrogen compounds such as sodium borohydride and lithium borohydride, sulfur compounds such as sulfur dioxide, salts of lower oxides such as sulfites, hydrogen iodide, and carbon.
Examples of the organic reducing agent include polyhydric alcohols, saccharides, aldehydes, hydrazine and derivatives thereof, diimides, oxalic acid, phenols, and ascorbic acid. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, and 2-butene-1. , 4-diol, 2,3-butanediol, pentanediol, hexanediol, octanediol, 1,1,1-trishydroxymethylethane, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 1, Examples include 2,6-hexanetriol, 1,2,3-hexanetriol, 1,2,4-butanetriol, and the like. Sugar alcohols such as glycerol, threitol, erythritol, pentaerythritol, pentitol, hexitol can also be used, and pentitol includes xylitol, ribitol, and arabitol. Hexitol includes mannitol, sorbitol, dulcitol and the like. Sugars include glyceraldehyde, dioxyacetone, threose, erythrulose, erythrose, arabinose, ribose, ribulose, xylose, xylulose, lyxose, glucose, fructose, mannose, idose, sorbose, gulose, talose, tagatose, galactose, allose, alt Examples are loose, lactose, xylose and trehalose. Aldehydes include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobitylaldehyde, pareraldehyde, isovaleraldehyde, pivalinaldehyde, capronaldehyde, heptaldehyde, caprylaldehyde, peragonaldehyde, undecylaldehyde, laurinaldehyde , Aliphatic saturated aldehydes such as tridecyl aldehyde, myristic aldehyde, pentadecyl aldehyde, palmitic aldehyde, margarine aldehyde, stearaldehyde, aliphatic dialdehydes such as glyoxal, succinaldehyde, acrolein, crotonaldehyde, propiol aldehyde, etc. Aliphatic unsaturated aldehyde, benzaldehyde, o-tolualdehyde, m-tolualdehyde, p-to Aldehyde, salicylaldehyde, cinnamaldehyde, alpha-naphthaldehyde can be exemplified β- naphthaldehyde aromatic aldehydes such as, a heterocyclic aldehyde such as furfural and the like. Examples of phenols include phenol, catechol, pyrogallol, t-butylcatechol, resorcinol and the like. Examples of hydrazine derivatives include N-aminomorpholine, oxalohydrazide, 4,4, -dimethyl-1-phenyl-3-pyrazolidinone and the like. Diimides can be obtained, for example, by thermally decomposing azodicarboxylate, hydroxylamine-O-sulfonic acid, N-arenesulfonyl hydrazide or N-acylsulfonyl hydrazide. Examples of N-arenesulfonyl hydrazide or N-acylsulfonyl hydrazide include p-toluenesulfonyl hydrazide, benzenesulfonyl hydrazide, 2,4,6-trisisopropylbenzenesulfonyl hydrazide, chloroacetyl hydrazide, o-nitrobenzenesulfonyl hydrazide, m-nitrobenzenesulfonyl Examples thereof include hydrazide and p-nitrobenzenesulfonyl hydrazide.

  Examples of the other additives include metal salt compounds. Since the metal precipitates when the metal salt compound is reduced, the precipitated metal may serve to connect the sintered copper fine particles, and may be able to be sintered more densely. Specifically, copper formate, copper acetate, copper trifluoroacetate, copper nitrate, copper methoxide, copper neodecanoate, copper ketimine, copper 2-ethylhexanoate, copper thiosulfate, copper pentafluoropropionate, copper octoate, etc. Is mentioned.

  In the case of a paste, the composition may contain the above-described binder, reducing agent, other additives, and a dispersion medium described later, if necessary.

  The weight of the copper nanoparticles is 3% to 95% by weight, preferably 10% to 90% by weight, based on the total weight of the coating film. When it is less than 3% by weight, the amount of the copper sintered body obtained by one firing is reduced, and it becomes difficult to function as a conductive thin film. On the other hand, if it exceeds 95% by weight, the coating film does not become a paste but becomes a powder, making application to a substrate difficult.

In order to disperse the copper fine particles in the coating film formed on the base material,
It is preferable that an appropriate amount of liquid is contained as a dispersion medium. Examples of the dispersion medium that can be used in the present invention include an organic solvent and / or water. Examples of the organic solvent used as the dispersion medium include liquid alcohol solvents, ketone solvents, amide solvents, ester solvents, and ether solvents. Further, when the reducing substance is a liquid, it may be used as a dispersion medium.

  Alcohol solvents used as a dispersion medium include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, t-butanol, n-pentanol, isopentanol, 2-methylbutanol, sec -Pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol, sec-heptanol, 3-heptanol, n-octanol, 2-ethylhexanol, monoalcohol solvents such as sec-octanol, n-nonyl alcohol, 2,6-dimethyl-4-heptanol, n-decanol, ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, 1, -Pentanediol, 2-methylpentane-2,4-diol, 2,5-hexanediol, 2,4-heptanediol, 2-ethylhexane-1,3-diol, diethylene glycol, dipropylene glycol, 1,2- Polyhydric alcohol solvents such as hexanediol, 1,2-octanediol, triethylene glycol, tripropylene glycol, glycerol, and ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, Ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, ethylene glycol mono-2-ethylbutyl ether, diethylene glycol monomethyl ether Diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol Examples thereof include polyhydric alcohol partial ether solvents such as monoethyl ether and dipropylene glycol monopropyl ether. These alcohol solvents may be used alone or in combination of two or more.

  Examples of the ketone solvent used as the dispersion medium include acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl-n-butyl ketone, diethyl ketone, methyl isobutyl ketone, methyl-n-pentyl ketone, ethyl-n-butyl ketone, and methyl-n. -Hexyl ketone, diisobutyl ketone, cyclohexanone, 2-hexanone, 2-methylcyclohexanone, 2,4-pentanedione, acetonylacetone, acetophenone, acetylacetone, 2,4-hexanedione, 2,4-heptanedione, 3,5-heptanedione, 2,4-octanedione, 3,5-octanedione, 2,4-nonanedione, 3,5-nonanedione, 5-methyl-2,4-hexanedione, 2,2,6, 6-tetramethyl-3,5-heptanedio , Like β- diketones such as 1,1,1,5,5,5-hexafluoro-2,4-heptanedione.

  Examples of the amide solvent used as a dispersion medium include formamide, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, acetamide, N-methylacetamide, N, N-dimethylacetamide, N-ethylacetamide, N, N-diethylacetamide, N-methylpropionamide, N-methylpyrrolidone, N-formylmorpholine, N-formylpiperidine, N-formylpyrrolidine, N-acetylmorpholine, N-acetylpiperidine, N- Examples include acetylpyrrolidine. As ester solvents, diethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, methyl acetate, ethyl acetate, γ-butyrolactone, γ-valerolactone, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, acetic acid sec-butyl, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, benzyl acetate, cyclohexyl acetate, methyl cyclohexyl acetate, ethyl propionate, propionic acid Examples include n-butyl, isoamyl propionate, diethyl oxalate, di-n-butyl oxalate, methyl lactate, ethyl lactate, and n-butyl lactate. These ester solvents may be used alone or in combination of two or more.

  Ether solvents used as dispersion media include dipropyl ether, diisopropyl ether, dioxane, tetrahydrofuran, tetrahydropyran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol Examples include dipropyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and diethylene glycol dipropyl ether.

  These dispersion media may be used alone or as a mixture of two or more dispersion media.

  In sintering copper fine particles, considering the denseness of the film state after sintering and handling in the printing process, the copper fine particles are well dispersed in the composition or in the coating film after application to the substrate. It is preferable. The state of being well dispersed means a state in which the copper fine particle aggregates in the coating film are few and the fluidity of the copper fine particles in the coating film is high. In order to satisfactorily disperse the copper fine particles in the composition, there are a method of assisting the dispersion state chemically by adding a dispersant, a method of physically dispersing, and a method of combining them.

  Examples of the dispersant suitable for dispersing the copper fine particles include low molecular compounds, oligomers, and polymers having a polar group such as a hydroxyl group, an amino group, and a carboxyl group. Examples of the low molecular weight compound having a polar group include alcohol compounds, amine compounds, amide compounds, ammonium compounds, and phosphorus compounds. Examples of the polymer having a polar group include polyvinyl pyrrolidone, polyvinyl alcohol, polymethyl vinyl ether, and polyethylene glycol. Further, a surfactant may be used as a dispersant. Examples of the surfactant include a cationic surfactant, an anionic surfactant, and a nonpolar surfactant. Examples of the polymer having a polar group include polyvinyl pyrrolidone, polyvinyl alcohol, polymethyl vinyl ether, and polyethylene glycol.

  As a method of dispersing copper fine particles using a dispersing agent, when synthesizing copper fine particles, a method of synthesizing in the presence of a dispersant and coordinating on the surface of the copper fine particles, or a time of dispersing copper fine particles A method of coordinating on the surface of the copper fine particles by performing in the presence of a dispersant may be considered. A distributed processing method will be described later.

  The composition containing the copper fine particles used in the present invention or the coating film coated with the composition may contain metal particles other than the copper fine particles. Specific examples include gold, silver, platinum, zinc, and tin particles. Gold, silver, and platinum are less oxidized and have a higher electrical conductivity than copper, so a partially conductive sintered body can be obtained by mixing it partially in the composition or the coating film on which it is applied. There is an effect to be obtained. In addition, since zinc and tin have a lower melting point than copper, an effect of easily melting and assisting in sintering can be obtained. The content of the metal other than the copper fine particles in the composition is preferably 20% by weight or less, more preferably 10% by weight or less, and still more preferably 5% by weight or less, with respect to the copper fine particles.

Method for preparing composition (paste) containing copper fine particles:
The composition used in the present invention is formed as a paste by appropriately mixing the above-mentioned copper fine particles, a dispersion medium, and, if necessary, a coating composition such as a dispersant, a binder, a reducing substance, and other additives. It is preferable (hereinafter, the paste-like composition may be referred to as “paste”). A paste in which each component is well kneaded is preferable. In particular, it is preferable that the copper fine particles are well dispersed in the paste and are in a state of high agglomeration with little aggregation.

  As a method of dispersing the copper fine particles in the paste, a known method of dispersing powder in a liquid can be used. Examples thereof include an ultrasonic method, a mixer method, a three-roll method, a two-roll method, a planetary mixer, a kneader, a homogenizer, a ball mill, a sand mill, a jet mill, and crushing with a mortar. Usually, dispersion is performed by combining a plurality of these dispersion means. These dispersion treatments may be performed at room temperature, or may be performed by heating in order to reduce the viscosity of the solvent. Among these methods, in order to redisperse the aggregation of the copper fine particles in the paste, the three-roll method and crushing with a mortar are particularly preferable.

  When these treatments are performed in the presence of the above-described dispersant, the dispersion state may be further improved.

Base material:
The substrate used in the present invention is preferably a substrate or a film substrate. As the substrate, either an inorganic substrate made of an inorganic substance or an organic substrate made of an organic substance can be used. As the inorganic substrate, a semiconductor substrate such as silicon, germanium, or SiC, a glass substrate, or a ceramic substrate can be used. The organic substrate may be a substrate made of a material that is not damaged during the baking process, and a substrate such as a polyimide substrate, a polyester substrate, an epoxy substrate, an aramid substrate, or a fluororesin substrate can be used. Specific examples include polyimide (Kapton), polyetheretherimide (Ultem), polyphenylene sulfide (PPS), polyethersulfone (PES), polyethylene terephthalate (PET), and polycarbonate (PC). A porous substrate can also be used. For example, paper, green sheet, and the like. Moreover, the film-form base material which can be processed with a roll toe roll in a manufacture process can also be used preferably. When processing at a high temperature of 200 ° C. or higher, a Kapton film having high heat resistance is preferable, and when processing at a low temperature of 150 ° C. or lower, a PET film is preferable because it is easily available and the quality is stable.

The process of applying a composition on a substrate to form a coating film:
The application of the composition containing copper fine particles to the substrate is different depending on whether the composition is powdery or paste-like.

  In the case of powder, a known method of applying a powder to a substrate can be used, and examples thereof include an electrophotographic printing method using the chargeability of powder.

  In the case of a paste, a known method used when applying a paste to a substrate can be used, and for example, a coating method or a printing method can be applied. Examples of the coating method include a bar coating method, a dip coating method, a spray coating method, and a spin coating method. Examples of the printing method include screen printing, gravure printing, flexographic printing, offset printing, microcontact printing method, and inkjet method. Moreover, when the paste-like thing is apply | coated to the board | substrate, it is preferable to dry the liquid component in a paste before a subsequent heat press. An airtight state is formed at the time of hot pressing in order to block outside air. For this reason, if the coating contains a large amount of liquid components, a large volume change from liquid to gas occurs and there is a risk of explosion. The drying temperature is 30 ° C. or higher and 200 ° C. or lower, preferably 50 ° C. or higher and 120 ° C. or lower. This is because the copper fine particles are not oxidized during drying.

Shield with shape following:
In the present invention, a shielding object having a shape following property is disposed above a composition containing copper fine particles and a reducing agent to block oxygen contact in the outside air with the composition during pressing, and heat the coating film. And a step of sintering the copper fine particles. By heating the composition in a state in which the shield is disposed, it is possible to obtain a copper film by sintering the copper fine particles while preventing reaction with oxygen in the outside air. As shown in FIG. 1, the shape following property refers to, for example, covering a shielding object along an irregular surface shape such as a base material coated with a copper particle film, and shielding when applying pressure. It means the property that an object plastically deforms and follows the shape of the object, and the property that the shape can be maintained even after releasing the force that follows the shape. Specifically, it can be achieved by using a shield made of a material having a high flexibility.

  The shielding object having shape following property is not particularly limited as long as it does not cause melting or modification at a temperature lower than the heating temperature of the coating film, such as metal, ceramics, or resin. However, from the viewpoint of shape followability, a metal one is limited to a foil-like one such as an aluminum foil and a ceramic one such as a green sheet. In the case of resin, the form of the shielding object is not particularly limited. As the material for the shield, a thermoplastic resin, a fluorine resin, and a silicone resin are preferable. Thermoplastic resins include polyesters such as polyethylene terephthalate (PET), polystyrene (PS), acrylic resin (PMMA), polyphenylene sulfide (PPS), polyamide (PA), polyethersulfone (PES), polycarbonate (PC), heat Plastic polyimide (PI), polyetheretherketone (PEEK), polyetherimide (PEI) resin, and ABS resin are preferable.

Further, the shield is not necessarily required to be peeled off from the copper film after pressing. A form in which the copper film is laminated on the upper resin and sealed after the press treatment is also suitable. In this case, film-like polyester, polyphenylene sulfide (PPS), polyethersulfone (PES), polycarbonate (PC), polyimide (PI), polyetheretherketone (PEEK), and polyetherimide (PEI) resin are preferable. More preferred is polyester, especially polyethylene terephthalate (PET).
When the copper film is exposed after pressing, a thermoplastic resin having a high melting temperature, a fluorine resin, or a silicone resin that has been surface-treated so as to have good peelability is preferable. As thermoplastic resins having a high melting temperature, polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyamide (PA), polyethersulfone (PES), polycarbonate (PC), thermoplastic polyimide (PI), polyetheretherketone (PEEK), polyetherimide (PEI) resin, and polyamideimide (PAI) resin. More preferred is a fluororesin. This is because it has a relatively high melting temperature and is resistant to chemical modification, and is therefore excellent as a shielding material.
The bending strength is preferably 10 ⁻⁶ GPa · mm ² or more and 10 GPa · mm ² or less from the viewpoint of shape followability. More preferably, it is 10 ⁻⁵ GPa · mm ² or more and 5 GPa · mm ² or less. Here, the bending strength can be expressed as A × B ² (GPa · mm ² ) where the Young's modulus of the shielding material is A (GPa) and the thickness of the shielding material is B mm.
For example, when the Young's modulus of the aluminum foil is about 65 GPa and the thickness is 0.25 mm, the bending strength is about 4 GPa · mm ² . If the bending strength of the shield is too high, the shape following property is deteriorated under the same pressure condition. In addition, it takes time to transfer heat from the heating surface to the copper film, and as a result, shortening of the sintering time cannot be expected. If the bending strength of the shield is too small, the film will burst, so a certain thickness is required.

  In addition, it is preferable that the shield is in close contact with the copper film and the base material at the time of pressing, but a trace amount of oxygen may remain around the edge of the copper film. If it is a very small amount of oxygen, the oxide film on the particle surface will not inhibit the sintering.

  According to the production method of the present invention, since the contact between the outside air and the composition is blocked by using the shielding object, the condition of the outside air (outside atmosphere) is not particularly limited, and it is not necessary to control this. Therefore, a large-scale facility or the like for bringing the environment around the press machine into a nitrogen atmosphere not containing oxygen is not necessary, and a significant cut in facility cost can be expected. In addition, the contact between the shield and the coating film has an extremely high heat transfer rate as compared with heating by gas or steam, and it becomes possible to sinter the copper fine particles by firing in a short time.

Heat press process of coating film:
In the present invention, the heating press of the coating film is not particularly limited as long as the composition can be stably heated and pressed to sinter the copper fine particles. The heating and pressing steps are not necessarily simultaneous. It may be a separate process in which pressing is performed immediately before or after the heating process, or may be a process in which a preheated film is pressed while being heated. When the cross section of the film is compared with that before the process treatment, the conductive film can be obtained by coarsening (FIG. 3) or densifying (FIG. 4) the particles (FIG. 2) in the film before the treatment.

  Examples of the pressing method include a pressing method using a hydrostatic pressure and a roll press. Further, a pressing method with other energy such as an ultrasonic press may be used. The heating press method is one in which a heating mechanism is associated with these pressing methods. A preferable heating temperature is 50 ° C. or higher and 300 ° C. or lower, more preferably 100 ° C. or higher and 250 ° C. or lower, and further preferably 130 ° C. or higher and 200 ° C. or lower. If the heating temperature is too high, the copper fine particles are likely to be oxidized, and particularly when a polymer base material is used, there may be a problem in the heat resistance of the base material. If the heating temperature is too low, the sintering phenomenon due to the surface instability of the copper fine particles will not occur, or several hours or more will be required. A preferable pressing pressure is 0.1 to 1000 MPa, and more preferably 1 to 100 MPa. If the pressure is too high, the base material undergoes modification such as hardness change, and if it is too low, the sintering phenomenon due to the increased contact area of the copper fine particles does not occur. Moreover, preferable press time is 1 to 10 minutes, More preferably, it is 2 to 5 minutes. If the pressing time is too short, the sintering is not sufficient, and if the pressing time is too long, the production speed is lowered and the cost is increased. Specific examples of the heating press conditions include, for example, when the treatment target is a film coated with copper fine particles and dried, 50 to 100 MPa / 150 ° C. to 250 ° C./2 to 10 minutes, 25 MPa / 150 to 250 ° C./10 minutes, etc. In the case where the treatment target is a film obtained by applying copper fine particles and performing a reduction treatment, 2.5 to 7.5 MPa / 150 ° C. to 250 ° C./5 to 10 minutes may be used.

  Moreover, as a heating method not accompanied by a press, a method of heating using an oven, a hot plate, a heating furnace, or the like can be given. Further, heating by an electromagnetic wave such as a laser or a heating method using an activated gas such as plasma may be used.

  According to the manufacturing method of the present invention, the oxide film is destroyed by the press treatment, so that the clean surface of the copper is exposed and the copper fine particles are sintered. Moreover, since the area which the copper fine particle in a coating film contacts also increases, a sintering reaction rate becomes quick and the area which an electric current passes also increases. From the above, as shown in the examples, a higher-speed sintering reaction is possible compared to the conventional case. In the examples, the hydrostatic pressure hot press where the surface pressure is applied was used. However, a device capable of locally increasing the processing pressure by applying a linear pressure such as a roll press method can be expected to further shorten the time.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

(1) Structure of sintered body The structure of the sintered body was observed at a magnification of 10 kV and 20.0 k with a scanning electron microscope apparatus (S-4800) manufactured by Hitachi High-Technology Corporation.

(2) Resistivity of copper thin film The resistivity of the copper thin film was measured by a 4-terminal 4-probe method using Lorester GP manufactured by Dia Instruments Co., Ltd. The detection limit value is 1.0 × 10 ⁸ Ω · cm.

(3) Copper film heat press treatment / heating temperature The copper film heat press treatment was performed using a high-precision hot press SA401 manufactured by Tester Sangyo Co., Ltd. For the heating temperature, reference was made to the measured temperature display for hot press installation. When the temperature of the copper film part was measured by contacting a K-type thermocouple, it took about 55 to 65 seconds to raise the temperature until the temperature difference was less than 5 ° C. from the temperature of hot press installation.

(4) Uniformity of pressure and pressure distribution The pressure value and the uniformity of pressure distribution were confirmed using a pressure measurement film LW / MS type manufactured by Fujifilm.

(5) Thickness / Young (elastic) modulus of shielding object The thickness of the shielding object was measured using an upright gauge (7-547 series) manufactured by Mitutoyo Corporation. Moreover, about 10 samples extracted at random, the value was confirmed from the result of having observed the cross section with the scanning electron microscope (Hitachi High Technology S-4800). The Young (elasticity) modulus was determined based on ASTM D882-64T.

(6) Measuring method of average particle size of particles 100 particles out of the range that can be observed by scanning electron microscope (S-4800, manufactured by Hitachi High-Technology), and averaging the particle size by the number of particles Was determined by

(7) Number of measurements and sampling method The number of measurements was three times under each condition, and the average value was taken as the measured value.

[Example 1] Pressure change
30% by weight of polyvinylpyrrolidone (Mw = 10000) was dissolved in N-methyl-2-pyrrolidone (hereinafter referred to as NMP) (hereinafter referred to as PVP 30% NMP solution). After stirring 2.0 g of copper nanoparticles (Aldrich particle size: 50 nm) and 0.5 g of PVP 30% NMP solution for 3 minutes using a stirrer (ARV-100, manufactured by Sinky), three rolls (Exact Technologies) K-50 was used to make a paste. This paste was applied to a 3 cm square Kapton film (500V manufactured by Toray DuPont) using a bar coater (No. 5) to form a copper fine particle paste film on the film. The film with the copper fine particle film was dried for 2 hours while heating to 70 ° C. in a vacuum oven. At this time, the resistivity of the film was 1.0 × 10 ⁷ Ω · cm or more.

A film with a copper NMP dry film was sandwiched between “Teflon” (registered trademark) rubber sheets (thickness 1 mm) from above and below, heated from above and below at 200 ° C., and under pressures of 50, 75, and 100 MPa, respectively. Press processing was performed for 2 minutes. The resistivity of the thin film is as follows. The bending strength of the shield at this time was 0.5 GPa · mm ² .

[Example 2] Temperature change A dry film equivalent to Example 1 was sandwiched from above and below by a "Teflon" (registered trademark) rubber sheet, heated at 150 ° C, 200 ° C, and 250 ° C from above and below, and 100 MPa. Pressing was performed for 2 minutes under pressure. The resistivity of the thin film is as follows. The bending strength of the shield at this time was 0.5 GPa · mm ² .
[Example 3] Temperature change 2
A dry film equivalent to that in Example 1 is sandwiched between “Teflon” (registered trademark) rubber sheets from above and below, and heated at 150 ° C., 200 ° C., and 250 ° C. from above and below, and at a pressure of 25 MPa for 10 minutes. went. The resistivity of the thin film is as follows. The bending strength of the shield at this time was 0.5 GPa · mm ² .

[Example 4] Time change A copper NMP dry film equivalent to that in Example 1 was sandwiched between “Teflon” (registered trademark) rubber sheets from above and below, heated at 250 ° C. from above and below, and at a pressure of 100 MPa for 1 minute. Pressing was performed for 5 minutes. The resistivity of the thin film is as follows. The bending strength of the shield at this time was 0.5 GPa · mm ² .

[Example 5] Solvent change 30% by weight of polyvinylpyrrolidone (Mw = 10000) was dissolved in ethylene glycol known as a reducing agent (hereinafter referred to as PVP 30% ethylene glycol solution). After stirring 2.0 g of copper nanoparticles (Aldrich particle size: 50 nm) and 0.5 g of PVP 30% ethylene glycol solution for 3 minutes using a stirrer (ARV-100, manufactured by Sinky), three rolls (Exact. K-50 was used to make a paste. This paste was applied to a 3 cm square Kapton film using a bar coater (No. 5) to form a copper fine particle paste film on the film. The film with the copper fine particle film was dried for 2 hours while heating to 70 ° C. in a vacuum oven. The resistivity of the film at this time (hereinafter referred to as a copper EG dry film) was above the detection limit.

A film with a copper EG dry film is sandwiched from above and below by “Teflon” (registered trademark) rubber sheet (thickness 1 mm), heated at 200 ° C. from above and below, and under pressures of 50, 75, and 100 MPa, respectively. Press processing was performed for 2 minutes. The resistivity of the thin film is as follows. The bending strength of the shield at this time was 0.5 GPa · mm ² .

[Example 6] Sintering with particles Copper nanoparticles (Aldrich, particle size: 50 nm) were spread on a Kapton film and pressed with a film made of particles using a spatula to obtain a "Teflon" “(Registered trademark) rubber sheet (thickness: 1 mm) was sandwiched and heated at 200 ° C. and 250 ° C. from above and below for 2 minutes at a pressure of 100 MPa. The resistivity of the thin film is as follows. The bending strength of the shield at this time was 0.5 GPa · mm ² .

[Example 7] Shape follow-up shield The material of the shield covering the copper NMP dry film is aluminum foil (thickness 0.1 mm, bending strength 0.65 GPa · mm ² ), “Teflon” (registered trademark) (thickness 0.2) mm, bending strength 0.02 GPa · mm ² ), “Teflon” (registered trademark) (thickness 1 mm, bending strength 0.5 GPa · mm ² ), and heated and pressed at 200 ° C. and 100 MPa for 2 minutes. The resistivity of the thin film is as follows.

[Example 8] Post-treatment 1 of conductive film
30% by weight of bisphenol A diglycidyl ether, which is an epoxy resin, was dissolved in ethylene glycol known as a reducing agent (hereinafter referred to as an epoxy 30% ethylene glycol solution). After stirring 2.0 g of copper nanoparticles (Aldrich particle size: 50 nm) and 0.5 g of an epoxy 30% ethylene glycol solution for 3 minutes using a stirrer (ARV-100, manufactured by Sinky), three rolls (Exact) -It knead | mixed using Technologies, Inc. M-50), and was made into the paste. Next, 0.01 g of undecylimidazole, which is a curing agent for the epoxy resin, was added and stirred for 1 minute using a stirrer. This paste was applied to a 3 cm square Kapton film using a bar coater (No. 5) to form a copper fine particle paste film on the film. When this paste film was reduced and fired at 200 ° C. under the vapor of ethylene glycol, it was 1.0 × 10 −3 Ω · cm (hereinafter referred to as a copper reduction treatment film). A Teflon (registered trademark) rubber sheet (thickness: 1 mm) was sandwiched between the copper reduction treatment films and pressures of 2.5, 5.0 and 7.5 MPa were applied for 5 minutes while heating at 150 ° C. The resistivity of the thin film is as follows. The bending strength of the shield at this time was 0.5 GPa · mm ² .

[Example 9] Post-treatment 2 of conductive film
The copper reduction treatment film was sandwiched between “Teflon” (registered trademark) rubber sheets (thickness 1 mm), and pressures of 2.5, 5.0 and 7.5 MPa were applied for 5 minutes while heating at 200 ° C. The resistivity of the thin film is as follows. The bending strength of the shield at this time was 0.5 GPa · mm ² .

[Example 10] Post-treatment 3 of conductive film
The copper reduction-treated film was sandwiched between “Teflon” (registered trademark) rubber sheets (thickness 1 mm), and pressures of 2.5, 5.0, and 7.5 MPa were applied while heating at 250 ° C. The resistivity of the thin film is as follows. The bending strength of the shield at this time was 0.5 GPa · mm ² .

[Comparative Example 1]
A copper NMP dry film equivalent to that of Example 1 was sandwiched between SUS304 iron plates (bending strength 20000 GPa · mm ² ) having a thickness of 1 cm from above and below, heated at 250 ° C. from above and below, and at a pressure of 75 MPa and 100 MPa for 2 minutes. Press processing was performed. At this time, the resistivity of the film was higher than the detection limit, and the film was changed to black.

[Comparative Example 2]
A copper NMP dry film equivalent to Example 1 was sandwiched between SUS304 iron plates (bending strength 20000 GPa · mm ² ) having a thickness of 1 cm from above and below, heated at 200 ° C. from above and below, and at a pressure of 100 MPa for 2 minutes and 5 minutes. Press processing was performed for a minute. Only in the case of 2 minutes, the conductivity of about 1.5 × 10 −3 Ω · cm was observed only in the central minute part of the film, but the resistivity of the film in the other part and other conditions was above the detection limit, Had turned black.

[Comparative Example 3]
A copper reduction treatment film equivalent to that in Example 8 was sandwiched between SUS304 (bending strength 20000 GPa · mm ² ) 1 cm thick SUS304 from above and below, heated at 250 ° C. from above and below, and 5.0 MPa and 7.5 MPa. Press processing was performed for 5 minutes under pressure. At this time, the resistivity of the film was higher than the detection limit, and the film was changed to black.

[Comparative Example 4]
A copper reduction treatment film equivalent to that in Example 8 was sandwiched between SUS304 (bending strength 20000 GPa · mm ² ) steel plates having a thickness of 1 cm from above and below, heated at 200 ° C. from above and below, and 5.0 MPa and 7.5 MPa. Press processing was performed for 5 minutes under pressure. At this time, the resistivity of the film was higher than the detection limit, and the film was changed to black.

  With respect to the back surface protective sheets obtained in Examples 1 to 10 and Comparative Examples 1 to 4, various properties were measured by the methods described above, and Table 1 and Table 2 show the respective physical properties.

FIG. 1 is a view showing that the shield is deformed to form an airtight structure when a press pressure is applied. FIG. 2 is a cross-sectional photograph of the film before heat pressing using the shielding sheet. FIG. 3 is a cross-sectional photograph of the film after heat pressing using a shielding sheet. Compared to FIG. 2, the particles are coarsened. FIG. 4 is a cross-sectional photograph of the film after heat pressing using a shielding sheet. Compared to FIG. 2, the film is densified.

Explanation of symbols

1 Shield 2 Copper particle film 3 Base material

Claims (7)

  A step of applying a composition containing copper fine particles on a substrate to form a coating film, and a shielding object having a shape following property is disposed above the coating film, and the coating film is heated and pressed. A method for producing a copper film, comprising a step of sintering copper fine particles.   2. The method for producing a copper film according to claim 1, comprising copper nanoparticles as the copper fine particles, wherein the number average particle diameter of the copper nanoparticles is 1 nm to 200 nm.   The manufacturing method of the copper film of Claim 1 or 2 whose heating temperature is 50 to 300 degreeC in the process of heat-pressing the said coating film.   The method for producing a copper film according to any one of claims 1 to 3, wherein in the step of heat-pressing the coating film, the pressing pressure is 1 MPa or more. The method for producing a copper film according to any one of claims 1 to 4, wherein a bending strength of the shield is 100 GPa · mm ² or less.   The manufacturing method according to any one of claims 1 to 5, wherein the shield is composed of at least one selected from the group consisting of a fluororesin, a metal foil, a thermoplastic resin, and a silicone resin.   7. The method of sintering copper fine particles by heating and / or plasma between the step of forming the coating film and the step of heating and pressing the coating film to sinter the copper fine particles. The manufacturing method of the copper film of description.