JP2007095502A - Conductive paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive paste sintered at a temperature lower than that of a conventional one, in particular, at a temperature around 200°C, and capable of reducing resistance. <P>SOLUTION: This conductive paste is prepared by dispersing metal ultrafine particles in an organic solvent. The metal ultrafine particles are synthesized by irradiating, with microwaves, a solution prepared by dissolving or dispersing, in a synthesizing organic solvent, a metal salt represented by (R-A)<SB>n</SB>-M (wherein R is a 10C or more hydrocarbon group; A is COO, OSO<SB>3</SB>, SO<SB>3</SB>or OPO<SB>3</SB>; M is silver, gold or platinum; and n is the valence of M). Each metal ultrafine particle has a metal core formed of a metal constituent derived from the metal salt and an organic constituent derived from the metal salt and covering the circumference of the metal core. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a conductive paste, and more particularly to a conductive paste using ultrafine metal particles.

  Conventionally, conductive paste using fine metal particles of μm size (hereinafter sometimes referred to as “micron size”) is used as, for example, a conductive material used for forming circuits such as electrodes and wiring on printed circuit boards and interlayer bonding. Widely used.

  In recent years, electronic devices in which printed boards are incorporated have become highly functional and miniaturized, and accordingly, wiring circuits have been narrowed. For this reason, general-purpose conductive pastes using micron-sized metal fine particles cannot cope with the narrow pitch sufficiently.

  Therefore, recently, various conductive pastes using ultrafine metal particles of nm size (hereinafter sometimes referred to as “nanosize”) have been proposed. Nano-sized ultrafine metal particles generally have properties different from bulk, such as sintering at a temperature lower than the original melting point of the metal. For this reason, this type of conductive paste is expected to reduce organic components contained in the sintered body by, for example, low-temperature firing, and to exhibit good conductive performance.

  For example, Patent Document 1 discloses a conductive paste in which silver ultrafine particles synthesized by a gas evaporation method are dispersed in an organic solvent. Patent Document 2 discloses a nanoparticle paste using a dispersion of ultrafine silver particles synthesized as a silver nanoparticle raw material by a gas evaporation method and having a surface coated with an amine compound.

Japanese Patent Laid-Open No. 3-34211 (Fourth Example) Japanese Unexamined Patent Publication No. 2004-273205 (Example 1)

  However, the conventionally known conductive paste does not sinter sufficiently at a temperature of about 200 ° C., and there is a problem that it is difficult to reduce the resistance of the sintered body.

  Therefore, for example, when a microcircuit having a low resistance is to be formed, it must be fired at a temperature greatly exceeding 200 ° C., which is cheaper than polyimide and has low heat resistance. Polyamideimide, polyethylene naphthalate (PEN) ) Or the like could not be used as a substrate material.

  Moreover, when the conventional conductive paste is sintered at a temperature of about 200 ° C., the protective agent component that constitutes a part of the ultrafine metal particles tends to remain. Therefore, when a conventional conductive paste is used as a conductive material for via holes, for example, outgas is likely to occur during a heat treatment process such as reflow (about 260 ° C.) or drying (about 60 to 100 ° C.) by solder bonding. There was a problem.

  These problems are considered to be mainly because the protective agent component constituting a part of the ultrafine metal particles does not decompose sufficiently at a temperature of about 200 ° C.

  Therefore, the problem to be solved by the present invention is to provide a conductive paste that can be sintered at a lower temperature than conventional ones, particularly at a temperature of about 200 ° C., and can be reduced in resistance.

In order to solve the above problems, the conductive paste according to the present invention is obtained by dispersing ultrafine metal particles in an organic solvent, and the ultrafine metal particles synthesize a metal salt represented by Chemical Formula 1 below. A metal core composed of a metal component derived from a metal salt, which is synthesized by irradiating microwaves to a solution dissolved or dispersed in an organic solvent for use, and a metal derived from a metal salt And having an organic component covering the periphery of the core.
(Chemical formula 1)
(R-A) _n -M
(However, R is a hydrocarbon group having 10 or more carbon atoms, A is COO, OSO ₃ , SO ₃ or OPO ₃ , M is silver, gold or white metal, and n is the valence of M.)

  Here, the said metal core is good in the average particle diameter being in the range of 2-30 nm.

  The content of the organic component in the ultrafine metal particles is preferably in the range of 4 to 30% by weight.

  In the conductive paste according to the present invention, specific metal ultrafine particles are dispersed in an organic solvent. For this reason, it is sufficiently sintered at a lower temperature, particularly about 200 ° C., compared to the conventional conductive paste.

  Moreover, the organic component in the ultrafine metal particles is almost decomposed by firing at a temperature of about 200 ° C. Therefore, the residual amount of the organic component contained in the sintered body can be reduced, and resistance can be reduced by firing at a lower temperature than in the past.

  Therefore, for example, when this is used as a conductive material for a via hole, the amount of outgas generated during a heat treatment process such as reflow (about 260 ° C.) or drying (about 60 to 100 ° C.) can be reduced. it can. Further, it is possible to form a low-resistance fine circuit, an interlayer junction, or the like on a substrate made of a resin such as polyamide imide or polyethylene naphthalate (PEN) which is less expensive and has lower heat resistance than polyimide.

  In addition, since metal ultrafine particles synthesized by microwave heating are used, compared to the case of using metal ultrafine particles synthesized by a gas evaporation method, the productivity of the paste is excellent and the equipment is not likely to be large.

  At this time, when the average particle size of the metal core of the ultrafine metal particles is in the range of 2 to 30 nm and the content of the organic component in the ultrafine metal particles is in the range of 4 to 30% by weight, Excellent in the above effects.

  Hereinafter, the conductive paste according to the present embodiment (hereinafter referred to as “main paste”) will be described in detail.

1. This paste is made by dispersing specific metal ultrafine particles in an organic solvent. Hereinafter, each structure of this paste is demonstrated in order.

1.1 Metal Ultrafine Particles In this paste, the metal ultrafine particles are composed of a metal core mainly composed of a metal component derived from a specific metal salt, and an organic component derived from the specific metal salt and covering the periphery of the metal core. And have.

  The metal core may be composed of one or two or more metal components derived from one or more specific metal salts. Moreover, the said organic component may consist of 1 type, or 2 or more types of organic components derived from 1 type, or 2 or more types of specific metal salt.

Here, the specific metal salt specifically refers to the general formula (RA) _n -M (where R is a hydrocarbon group having 10 or more carbon atoms, A is COO, OSO ₃ , SO _3. Or OPO ₃ , M is silver, gold or white metal, and n is the same as the valence that the metal M can take and is an integer of 1 or more.

  Since the organic component derived from the metal salt is relatively easily decomposed at a low temperature of about 200 ° C., the resistance can be easily reduced by low-temperature firing. Moreover, since this metal salt is comparatively cheap, it is advantageous also in terms of cost. In addition, it is estimated that the organic component derived from this metal salt is mainly RA group.

In the general formula (RA) _n -M, the hydrocarbon group R may be a saturated hydrocarbon group such as an alkyl group or an unsaturated hydrocarbon group such as an alkenyl group. The molecular structure may be linear or branched. Further, a part of hydrogen in the hydrocarbon group may be substituted with another substituent such as a halogen element as long as it does not adversely affect the properties of the conductive paste.

  However, the hydrocarbon group R has 10 or more carbon atoms. The upper limit of the carbon number is not particularly limited. However, when the carbon number is relatively large, there is a tendency that the low-temperature sinterability of the conductive paste decreases. Therefore, specific examples of the preferable upper limit of the carbon number of the hydrocarbon group R include, for example, 40, 35, 30, 25, 20, 18 and the like.

In the general formula (R-A) _n -M, CO can be particularly preferably used as A.

In the general formula (RA) _n -M, silver, gold, or white metal is used for M. Which type of metal is used may be appropriately selected in consideration of the use of the conductive paste.

  Specific examples of such metal salts include, for example, fatty acid metal salts, alkylsulfonic acid metal salts, and the like.

  More specifically, for example, saturated fatty acid metal salts such as undecanoic acid metal salt, lauric acid metal salt, myristic acid metal salt, palmitic acid metal salt, stearic acid metal salt, oleic acid metal salt, linoleic acid metal salt, linolenic acid More preferable examples include unsaturated fatty acid metal salts such as acid metal salts, branched fatty acid metal salts such as neodecanoic acid metal salts, and cyclic fatty acid metal salts such as abietic acid metal salts.

  Among the ultrafine metal particles, the type of the metal core can be confirmed by, for example, an X-ray diffraction method. The type of the organic component can be confirmed by, for example, NMR (nuclear magnetic resonance method), GC / MS (gas chromatography / mass spectrometry) or the like.

  The average particle diameter of the metal core may be adjusted as appropriate according to the use of the conductive paste. Specifically, 30 nm etc. can be illustrated as the preferable upper limit, for example. On the other hand, as a preferable lower limit value that can be combined with this preferable upper limit value, specifically, for example, 2 nm can be exemplified.

  The above average particle diameter is obtained by arbitrarily extracting 100 ultrafine metal particles (however, only a metal core can be observed by TEM) from a transmission electron microscope (TEM) photograph of ultrafine metal particles, and measuring the particle diameter. The value of the particle diameter (D50) when the number of particles is 50% when counted in order from the smallest diameter.

  Further, the particle size distribution of the ultrafine metal particles is not particularly limited, but is preferably relatively sharp. Specific examples of the sharpness ε = (D90−D10) / D50 of the particle size distribution include, for example, 2, 1.5, 1.3 and the like as preferable upper limit values. On the other hand, the lower limit value of ε is not particularly illustrated because ε is preferably as close to 0 as possible.

  D90 and D10 are values calculated in the same manner as D50, and are the particle size at which the number of particles is 90% and the particle size at which the number of particles is 10%.

  Further, the content of the organic component in the metal ultrafine particles is not particularly limited. Generally, when the content of the organic component is excessively increased, the low temperature sintering property tends to decrease. On the other hand, when the content of the organic component is excessively reduced, aggregation tends to occur, and the dispersion stability in the conductive paste tends to decrease. Therefore, it is good to pay attention to these when selecting the content of the organic component.

  Specific examples of the content of the organic component include, for example, 30% by weight as a preferable upper limit. On the other hand, 4 weight% etc. can be illustrated as a preferable lower limit which can be combined with this preferable upper limit.

  The content of the organic component is determined by performing thermogravimetric analysis on dried metal ultrafine particles in accordance with JIS K0129 “General Rules for Thermal Analysis” and JIS K7120 “Method for Thermogravimetric Measurement of Plastics”, and from room temperature to 600 ° C. The content of the organic component may be calculated from the weight loss rate.

  In addition, the content of the metal component in the paste is not particularly limited, and can be appropriately adjusted in consideration of the application. Generally, as a preferable upper limit, for example, 90% by weight, 85% by weight, 80% by weight and the like can be exemplified. On the other hand, examples of preferable lower limit values that can be combined with these preferable upper limit values include 1% by weight, 2% by weight, and 5% by weight.

  The ultrafine metal particles are synthesized by reducing the metal salt by irradiating a microwave to a solution obtained by dissolving or dispersing the specific metal salt in an organic solvent for synthesis. This synthesis method will be described later in the section of the preferred method for producing the paste.

1.2 Organic solvent Specific examples of the organic solvent include hexane, toluene, xylene, octane, decane, undecane, tetradecane, terpineol, decanol, methyl ethyl ketone (MEK), acetone, tetrahydrofuran (THF), hexanol, Examples include dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dipropylene glycol monomethyl ether, methanol, ethanol, ethyl acetate, ethyl carbitol, ethyl carbitol acetate, butyl carbitol, butyl carbitol acetate, etc. can do. These may be used alone or in combination.

  Moreover, the organic solvent for a synthesis | combination used at the time of the synthesis | combination of the metal ultrafine particle mentioned later may be contained 1 type, or 2 or more types.

1.3 Others In the present paste, one or more additives such as a dispersant for improving the dispersion stability of the ultrafine metal particles are added within the range not departing from the gist of the present invention. May be. Moreover, the reducing agent utilized at the time of the synthesis | combination of a metal ultrafine particle, an inevitable impurity, etc. may be contained.

  Next, a preferred method for producing the paste described above (hereinafter referred to as “the present production method”) will be exemplified.

2. This production method is basically a method in which a solution containing the above-mentioned specific metal salt is heated, the metal salt is reduced to synthesize the above-mentioned metal ultrafine particles, and the obtained metal ultrafine particles in an organic solvent. This is a method of dispersing and pasting.

2.1 Solution In this production method, a solution obtained by dissolving or dispersing the above-described specific metal salt in an organic solvent for synthesis is used.

  Since the specific metal salt has already been exemplified in the section of 1.1 ultrafine metal particles, detailed description thereof will be omitted.

  As the organic solvent for synthesis, any kind of organic solvent can be used as long as it can dissolve or disperse the metal salt. Specific examples include alcohols such as diols, glycols and polyols, amines, hydrocarbons, ketones, ethers, esters and the like. These may be used alone or in combination.

  Of these organic solvents for synthesis, it is preferable to use a reducing organic solvent that exhibits reducing properties with respect to the metal salt. Further, the reducing organic solvent preferably has a relatively low solubility in water.

  Specific examples of such a reducing organic solvent include monohydric alcohols having 3 or more carbon atoms such as propanol, butanol, pentanol, hexanol, heptanol, and octanol. In particular, a monohydric alcohol having 3 to 30 carbon atoms, preferably 3 to 20 carbon atoms, more preferably 3 to 10 carbon atoms, and most preferably 4 to 8 carbon atoms can be exemplified as a suitable example.

  This is because when the carbon number is within the above range, the metal salt is not easily reduced rapidly, and the metal salt is easily reduced with an appropriate reducing power.

  Whether the metal salt is dissolved or dispersed in the synthesis organic solvent depends on the combination of the selected metal salt and the synthesis organic solvent, the amount of the metal salt relative to the synthesis organic solvent, and the like. The amount of the metal salt may be appropriately adjusted in consideration of the amount of metal ultrafine particles to be contained in the conductive paste.

  In addition, for example, one or two or more additives such as a catalyst and a reducing agent may be appropriately added to the above solution within a range that does not adversely affect the formation of ultrafine metal particles.

2.2 Heating of solution In this production method, the solution is heated by irradiation with microwaves. Heating by microwave irradiation has advantages such that the solution can be heated uniformly and ultrafine metal particles can be synthesized in a short time. Further, the temperature raising time to the reaction temperature can be performed in a short time as compared with heating by an external heat source.

  At this time, the microwave irradiation is preferably performed in a state where the solution is present in an inert gas atmosphere such as nitrogen, helium, or argon in order not to oxidize the generated ultrafine metal particles.

  Here, the microwave used is not particularly limited. Specifically, for example, a microwave with a frequency of 2.45 GHz, which is usually used frequently in Japan, may be used. Hereinafter, the microwave irradiation conditions are based on the assumption that a microwave with a frequency of 2.45 GHz is selected. However, when other microwaves are selected, the irradiation conditions are appropriately set according to this. Change it.

  The irradiation intensity of microwaves generally varies depending on the metal salt in the solution, the type of organic solvent for synthesis, and the like. When the irradiation intensity of the microwave is excessively decreased, a tendency such as a longer heating time is observed. On the other hand, when the irradiation intensity of the microwave is excessively increased, the heating time is extremely shortened, and it tends to be difficult to control the particle size distribution of the generated ultrafine metal particles. Therefore, these should be taken into account when selecting the microwave irradiation intensity.

Usually, the irradiation intensity of the microwave, specifically, for example, as a preferable upper limit ^value, and the like can be exemplified ^{24W / cm 3, 18W / cm} 3, 12W / cm 3.

On the other hand, specific examples of preferable lower limit values that can be combined with these preferable upper limit values include 1 W / cm ³ , 2 W / cm ³ , 3 W / cm ³ , 4 W / cm ^{3, and the} like. The irradiation intensity of these microwaves is a value represented by microwave output (W) / volume of reaction solution (cm ³ ).

  The heating time generally varies depending on the metal salt in the solution, the type of organic solvent for synthesis, the reaction temperature, and the like. When the heating time is excessively short, there is a tendency that metal ultrafine particles are not sufficiently generated. On the other hand, when the heating time is excessively long, there is a tendency that productivity is lowered or purity of the metal ultrafine particles is lowered due to generation of a side reaction product. Therefore, these should be noted in selecting the heating time.

  Usually, as a heating time, specifically, as its preferable upper limit, for example, 2 hours or less, 1.5 hours or less, 1 hour or less can be exemplified.

  On the other hand, specific examples of preferable lower limit values that can be combined with these preferable upper limit values include 1 minute or more, 2 minutes or more, 3 minutes or more, 5 minutes or more, and the like.

  The temperature of the solution during the reaction (reaction temperature) is preferably controlled so as to be substantially constant. The reaction temperature is preferably set to a temperature near the boiling point of the organic solvent for synthesis to be used.

  Specific examples of the reaction temperature include 300 ° C., 275 ° C., and 250 ° C. as preferred upper limits. On the other hand, specific examples of preferable lower limit values that can be combined with these preferable upper limit values include 80 ° C., 100 ° C., 120 ° C., and the like.

  In addition, the reaction temperature can be controlled, for example, by immersing a temperature sensor in the above solution and repeating on / off of microwave irradiation so that the temperature of the solution becomes constant. Further, microwave irradiation may be performed using a known microwave irradiation apparatus.

2.3 Recovery of metal fine particles In this production method, after synthesizing metal ultrafine particles, the generated metal ultrafine particles are recovered from the synthesis solution. A general method may be used as the recovery method. Specifically, for example, techniques such as centrifugation, filtration, and solvent extraction can be exemplified. These may be used alone or in combination of two or more. These may be performed once or a plurality of times.

  As a more specific recovery method, for example, the supernatant of the synthesis solution is removed, and there is a cleaning property, and a poor solvent (such as methanol) is added to the metal ultrafine particles, A method of recovering ultrafine metal particles by repeating the precipitation treatment by washing and centrifuging and then drying the obtained precipitate under reduced pressure can be exemplified.

2.4 Pasting In this production method, the obtained ultrafine metal particles are dispersed in an organic solvent, thereby obtaining a conductive paste.

  Since the organic solvent has already been exemplified in the above section 1.2, a detailed description thereof will be omitted.

  In this production method, the metal ultrafine particles and the organic solvent are mixed together, and then the metal ultrafine particles may be dispersed, or the metal ultrafine particles may be dispersed during the mixing of the metal ultrafine particles and the organic solvent. You may do it.

  That is, the order of the mixing and dispersion treatment is not particularly limited as long as the ultrafine metal particles contained in the organic solvent are finally dispersed uniformly to obtain a paste.

  Moreover, the said mixing means is not specifically limited. Specific examples of the mixing means include a propeller type, a crushing type such as a mortar, a rotating type (rotation by rotation / revolution), a vibration type, etc., a three-roller, a bead mill, and the like. .

  On the other hand, as the dispersing means, any kind of dispersing means may be used as long as the ultrafine metal particles can be uniformly dispersed. Specific examples of the dispersing means include ultrasonic treatment, bead mill, and dispersion treatment in a supercritical state.

  In addition, the content of the metal component in the obtained conductive paste is not particularly limited, and can be appropriately adjusted in consideration of the application. In general, examples of preferable upper limit values include 90% by weight, 85% by weight, and 80% by weight. On the other hand, examples of preferable lower limit values that can be combined with these preferable upper limit values include 1% by weight, 2% by weight, and 5% by weight.

  Hereinafter, the present invention will be described in detail using examples.

(Conductive paste according to Example 1)
5 mmol of lauric acid silver salt (C ₁₁ H ₂₃ COOAg) was mixed in 25 ml of 1-hexanol as an organic solvent for synthesis, and then subjected to ultrasonic treatment to prepare a dispersion solution.

Next, using a microwave irradiation apparatus (manufactured by Micro Electronics Co., Ltd., 2,450 MHz microwave heating apparatus “MMG-213VP”), a microwave (frequency 2) with an irradiation intensity of 6 W / cm ^{3 in} a nitrogen atmosphere. .45 GHz) was irradiated to the dispersion solution and heated for 11 minutes while controlling the temperature of the solution at 157 ° C. (reaction temperature). The reaction temperature was controlled by immersing a temperature sensor in the solution and repeating on / off of microwave irradiation so that the temperature of the solution became constant.

  Next, a sample obtained by dispersing the synthetic solution after these operations in hexane and dripping and drying it on a carbon mesh was used as a transmission electron microscope (manufactured by Hitachi High-Technologies Corporation, “Hitachi Transmission Electron Microscope H- 9000 "). As a result, it was confirmed that nano-sized ultrafine particles were generated.

  Next, methanol was added to the synthetic solution after the above operation, ultrafine particles were precipitated by centrifugation, and the supernatant was removed. Subsequently, methanol was added again, and precipitation of ultrafine particles and removal of the supernatant were repeated. Next, the collected precipitate was vacuum-dried to dry-collect ultrafine particles.

  Next, X-ray diffraction was performed using the collected ultrafine particles. According to the result, it was confirmed that only silver was produced. Therefore, it was confirmed that the metal constituting the ultrafine particle core was silver.

  Next, GC / MS (gas chromatography / mass spectrometry) analysis was performed on the collected silver ultrafine particles. As a result, lauric acid was detected. Therefore, it was confirmed that the kind of the organic component covering the periphery of the silver core is a lauric acid group.

  Next, the collected silver ultrafine particles are subjected to thermogravimetric analysis in accordance with JIS K0129 “General Rules for Thermal Analysis” and JIS K7120 “Thermogravimetric Method for Plastics”. From the weight loss rate from room temperature to 600 ° C., the silver ultrafine particles are obtained. The content of organic components contained therein was determined. As a result, the content of the organic component was 14% by weight.

  Next, 100 silver ultrafine particles were arbitrarily extracted from the transmission electron microscope (TEM) photograph, and the average particle size (D50) of the silver core and the sharpness ε of the particle size distribution were analyzed. As a result, the average particle diameter of the silver core was 5.0 nm. Further, the sharpness ε of the particle size distribution was 0.33, and it was confirmed that the particle size distribution had a narrow particle size distribution.

  Next, 58.1 g of silver ultrafine particles collected by dry recovery and 108 g of hexanol were blended and mixed while being ground on a mortar. Then, in a state where this was put in a glass tube, the ultrafine silver particles were ultrasonically dispersed by an ultrasonic cleaner for 15 minutes. As a result, a conductive paste according to Example 1 was obtained.

  Next, the conductive paste according to Example 1 was coated on a glass substrate by a spin coating method (coating dimensions 38 mm × 26 mm), dried at 100 ° C. for 60 minutes to volatilize hexanol, and then in an atmospheric atmosphere. Baked at 200 ° C. for 30 minutes to obtain a fired film.

Next, after measuring the surface resistivity of the fired film using a low resistance measuring instrument (4-terminal 4-probe method, manufactured by Dia Instruments Co., Ltd., “Loresta GP MCP-T610 type”), a stylus type surface The film thickness difference was determined by measuring the film thickness step with a shape measuring instrument ("Dektak" manufactured by ULVAC, Inc.). The volume resistivity was calculated from the obtained surface resistivity and film thickness. As a result, the volume resistivity of the fired film was 4.0 × 10 ⁻⁶ Ω · cm.

  The measurement of the surface resistivity and the calculation of the volume resistivity were performed in accordance with JIS K7194 “Resistivity test method for conductive plastics by 4-probe method”. However, the area is 38 mm × 26 mm, and the measuring devices are (X, Y) = (10 mm, 15 mm), (30 mm, 15 mm), (20 mm, 10 mm), (10 mm, 5 mm), (30 mm, 5 mm). After calculating the correction coefficient at 5 points, the surface resistivity was measured and the volume resistivity was calculated.

  Next, thermogravimetric analysis was performed on the scraped fired film in the same manner as described above, and the content of residual organic components contained in the fired film was determined from the weight loss rate from room temperature to 600 ° C. As a result, the content of residual organic components was 0.20% by weight.

(Conductive paste according to Example 2)
In the production of the conductive paste according to Example 1 described above, silver stearate (C ₁₇ H ₃₅ COOAg) was used instead of silver laurate (C ₁₁ H ₂₃ COOAg), and the heating time was 11 minutes to 20 minutes. The electroconductive paste which concerns on Example 2 was obtained similarly except the point changed into minutes.

Next, the obtained conductive paste was tested in the same manner as in Example 1. As a result, stearic acid was detected by GC / MS (gas chromatography / mass spectrometry) analysis. The content of the organic component was 28% by weight. The average particle diameter of the silver core was 5.3 nm. Further, the sharpness ε of the particle size distribution was 0.625. The volume resistivity of the fired film was 5.6 × 10 ⁻⁶ Ω · cm. In addition, the content of residual organic components was 0.30% by weight.

(Conductive paste according to Example 3)
In the production of the conductive paste according to Example 1, Example 3 was carried out in the same manner except that silver oleate (C ₁₇ H ₃₃ COOAg) was used instead of silver laurate (C ₁₁ H ₂₃ COOAg). The electroconductive paste which concerns on was obtained.

Next, the obtained conductive paste was tested in the same manner as in Example 1. As a result, oleic acid was detected by GC / MS (gas chromatography / mass spectrometry) analysis. The content of the organic component was 18% by weight. The average particle size of the silver core was 7.0 nm. Further, the sharpness ε of the particle size distribution was 0.52. The volume resistivity of the fired film was 4.9 × 10 ⁻⁶ Ω · cm. Further, the content of the residual organic component was 0.60% by weight.

(Conductive paste according to Example 4)
In the production of the conductive paste according to Example 1 above, Example 4 was carried out in the same manner except that silver linoleate (C ₁₇ H ₃₁ COOAg) was used instead of silver laurate (C ₁₁ H ₂₃ COOAg). The electroconductive paste which concerns on was obtained.

Subsequently, as a result of conducting the same test as Example 1 about the obtained electrically conductive paste, linoleic acid was detected by GC / MS (gas chromatography / mass spectrometry) analysis. The content of the organic component was 12% by weight. Moreover, the average particle diameter of the silver core was 7.3 nm. Further, the sharpness ε of the particle size distribution was 0.54. The volume resistivity of the fired film was 6.9 × 10 ⁻⁶ Ω · cm. The content of residual organic components was 0.90% by weight.

(Conductive paste according to Example 5)
In the production of the conductive paste according to Example 1, Example 5 was carried out in the same manner except that silver decanoate (C ₁₀ H ₂₁ COOAg) was used instead of silver laurate (C ₁₁ H ₂₃ COOAg). The electroconductive paste which concerns on was obtained.

Subsequently, as a result of conducting the same test as Example 1 about the obtained electrically conductive paste, undecanoic acid was detected by GC / MS (gas chromatography / mass spectrometry) analysis. The content of the organic component was 10% by weight. Moreover, the average particle diameter of the silver core was 6.5 nm. Further, the sharpness ε of the particle size distribution was 0.45. The volume resistivity of the fired film was 4.1 × 10 ⁻⁶ Ω · cm. Further, the content of residual organic components was 0.15% by weight.

(Conductive paste according to Example 6)
In the production of the conductive paste according to Example 1 above, Example 6 was similarly performed except that silver myristate (C ₁₃ H ₂₇ COOAg) was used instead of silver laurate (C ₁₁ H ₂₃ COOAg). The electroconductive paste which concerns on was obtained.

Next, the obtained conductive paste was tested in the same manner as in Example 1. As a result, myristic acid was detected by GC / MS (gas chromatography / mass spectrometry) analysis. The content of the organic component was 19% by weight. Moreover, the average particle diameter of the silver core was 5.5 nm. The sharpness ε of the particle size distribution was 0.55. The volume resistivity of the fired film was 4.5 × 10 ⁻⁶ Ω · cm. The content of residual organic components was 0.22% by weight.

(Conductive paste according to Example 7)
In the production of the conductive paste according to Example 1 above, Example 7 was carried out in the same manner except that silver palmitate (C ₁₅ H ₃₁ COOAg) was used instead of silver laurate (C ₁₁ H ₂₃ COOAg). The electroconductive paste which concerns on was obtained.

Subsequently, the obtained conductive paste was tested in the same manner as in Example 1. As a result, palmitic acid was detected by GC / MS (gas chromatography / mass spectrometry) analysis. The content of the organic component was 24% by weight. The average particle diameter of the silver core was 5.3 nm. Further, the sharpness ε of the particle size distribution was 0.60. The volume resistivity of the fired film was 4.9 × 10 ⁻⁶ Ω · cm. Further, the content of the residual organic component was 0.25% by weight.

(Conductive paste according to Comparative Example 1)
As a comparative example 1, a commercially available conductive paste (“Nano Metal Ink AgIT” manufactured by Vacuum Metallurgical Co., Ltd.) containing ultrafine silver particles produced by a gas evaporation method was used.

  Here, the conductive paste according to Comparative Example 1 was coated on a glass substrate, and the formed coating film was applied to a field emission scanning electron microscope (FE-SEM) (manufactured by Hitachi High-Technologies Corporation, “Hitachi Super High As a result of observation with a resolution field emission scanning electron microscope S-4800 "), it was confirmed that the contained silver ultrafine particles had a particle size distribution of 2 to 10 nm.

  Further, methanol was added to the conductive paste, and ultrafine silver particles were precipitated by centrifugation, and the supernatant was removed. Subsequently, methanol was added again, and precipitation of ultrafine silver particles and removal of the supernatant were repeated. Next, the collected precipitate was vacuum-dried to dry-collect silver ultrafine particles.

  Next, GC / MS (gas chromatography / mass spectrometry) analysis was performed on the collected silver ultrafine particles. As a result, dodecylamine was detected. Therefore, it was confirmed that the kind of the organic component covering the periphery of the silver core is at least a dodecylamine group.

Further, when the volume resistivity of the fired film and the content of residual organic components in the fired film were measured in the same manner as in the examples, the former was 8.0 × 10 ⁻⁶ Ω · cm, and the latter was 1.10. The weight percentage was clearly different from the examples.

  Table 1 summarizes the above examples and comparative examples.

In Table 1, the volume resistivity of each fired film is determined to be acceptable if it is 7.5 × 10 ⁻⁶ Ω · cm or less. In the table, those in the range of 5.0 × 10 ⁻⁶ Ω · cm to 7.5 × 10 ⁻⁶ Ω · cm are shown as good circles, and 5.0 × 10 ⁻⁶ Ω・ Those that were less than cm are marked as very good by double circles. On the other hand, the case where it is a value exceeding 7.5 × 10 ⁻⁶ Ω · cm is determined to be unacceptable, and is indicated by a cross mark.

  Moreover, about content of the residual organic component which occupies in a baking film, the case where it is 1.0 weight% or less is determined to be a pass. In the table, those in the range of 0.5 wt% or more and 1.0 wt% or less are shown as good circles, and those less than 0.5 wt% are shown as double circles as very good. Is shown. On the other hand, the case where the value is higher than 1.0% by weight is determined to be unacceptable and indicated by a cross mark.

  From the above results, the following can be understood. That is, it can be seen that Comparative Example 1 has a relatively high volume resistivity of the sintered film and is not sufficiently sintered by low-temperature firing at about 200 ° C. This is considered to be mainly due to the poor decomposability of the protective agent component covering the silver core. Moreover, since sintering is not sufficient, many residual organic components remain in the fired film. Therefore, it can be seen that if this is used as a conductive material for via holes, outgas is likely to occur during reflow. Also, since silver ultrafine particles produced by the gas evaporation method are used, it can be said that the productivity of the paste is low and the equipment tends to be large.

  On the other hand, in Examples 1-7, since specific silver ultrafine particles are used, it is possible to sufficiently sinter at a low temperature firing of about 200 ° C. and to achieve a lower resistance than in the past. It could be confirmed. Therefore, when this is used, for example, as a conductive material for via holes, the amount of outgas generated during reflow can be reduced. In addition, since a heating method using microwave irradiation is used when synthesizing silver ultrafine particles by the solution reduction method, the productivity of the paste is excellent, and the equipment is not likely to be large.

  Although the embodiments and examples have been described above, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention.

2 is a TEM photograph of ultrafine silver particles contained in a conductive paste according to Example 1; It is a TEM photograph of silver ultrafine particles contained in the conductive paste according to Example 2. It is a TEM photograph of silver ultrafine particles contained in the conductive paste according to Example 3. It is a TEM photograph of silver ultrafine particles contained in the conductive paste according to Example 4. It is a FE-SEM photograph of silver ultrafine particles contained in the conductive paste according to Comparative Example 1.

Claims (3)

A conductive paste in which ultrafine metal particles are dispersed in an organic solvent,
The ultrafine metal particles are synthesized by irradiating a solution obtained by dissolving or dispersing a metal salt represented by the following chemical formula 1 in an organic solvent for synthesis,
A conductive paste comprising: a metal core composed of a metal component derived from the metal salt; and an organic component derived from the metal salt and covering the periphery of the metal core.
(Chemical formula 1)
(R-A) _n -M
(However, R is a hydrocarbon group having 10 or more carbon atoms, A is COO, OSO ₃ , SO ₃ or OPO ₃ , M is silver, gold or white metal, and n is the valence of M.)   The metal core has an average particle size in the range of 2 to 30 nm.   The conductive paste according to claim 1 or 2, wherein the content of the organic component in the ultrafine metal particles is in the range of 4 to 30% by weight.