Conductive composition and method for manufacturing the same, as well as conductor and laminated structure using the conductive composition.

Abstract

To provide a conductive composition capable of forming a conductive body having an extremely small change in resistance value compared with that before exposure to high-temperature conditions such as solder reflow, even after being repeatedly exposed to such high-temperature conditions.MEANS: In a conductive composition comprising a binder resin and a silver powder, the number average particle diameter of the silver powder in the conductive composition, as measured by a laser diffraction scattering method, is adjusted to be more than 3.7 μm and less than 4.8 μm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a conductive composition, a method for producing the same, a conductor obtained by solidifying the conductive composition, and a laminated structure having a layer of the conductor. Furthermore, the present invention also relates to an electronic component including the conductor or the laminated structure.

Background Art

[0002] Conventionally, as a material for forming a patterned conductor such as a wiring circuit of a printed wiring board, a paste-like conductive composition in which metal powder is mixed with a binder resin is known. By applying such a conductive composition onto a substrate and then solidifying it, a desired pattern wiring, electrode, or the like can be formed. In recent years, with the high performance of electronic devices, the pattern wiring, electrodes, etc. formed using the conductive composition are required to have a lower resistance value and higher reliability.

[0003] Incidentally, when mounting electronic components on printed circuit boards used in electronic devices, a soldering method called solder reflow (reflow soldering) is sometimes employed. In this solder reflow process, the printed circuit board is usually exposed to high temperatures of around 260°C, so the conductive materials such as pattern wiring and electrodes formed by solidifying the conductive composition on the printed circuit board are also exposed to high temperatures. When a conductive material is used to form a conductor, the high temperature during solder reflow causes a hardening reaction to some components in the conductor, resulting in the conductor shrinking. As a result, the conductive powder in the conductor aggregates, and the resistance value of the conductor may decrease. On the other hand, if there is a large difference in the coefficient of thermal expansion between the conductive composition and the substrate, cracks may occur in the conductor formed by solidifying the conductive composition, resulting in an increase in the resistance value of the conductor or even a break in the conductor. Thus, in printed circuit boards equipped with conductors formed by solidifying a conductive composition, solder reflow impairs the performance of the conductor, leading to the problem that it cannot perform to the high performance required for conductors in modern electronic devices. Furthermore, solder reflow may be performed multiple times, in which case the conductor is repeatedly exposed to high-temperature conditions, causing the resistance of the conductor to increase even further, resulting in a significant deterioration of the conductor's performance. For example, Patent Document 1 proposes suppressing the formation of pores in silver powder, which is a conductive particle contained in the conductor, in order to suppress the increase in its resistance, and proposes using silver powder having specific physical properties, namely specific ignition loss, tap density, maximum aspect ratio, and BET specific surface area.

[0004] However, in this case, the physical properties of the silver powder incorporated into the conductive composition are limited, and in some cases, it becomes impossible to obtain a conductor with the desired physical properties. Furthermore, providing a conductive composition that can form a conductor with a small range of resistance change not only after a single exposure to high-temperature conditions, but also after repeated exposure, remains an ongoing technical challenge. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2017 / 110255 Brochure [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, an object of the present invention is to provide a conductive composition and a method for producing the same that can form a conductor in which the change in resistance value is extremely small even after repeated exposure to high-temperature conditions such as solder reflow, compared to before exposure to high-temperature conditions. Another object of the present invention is to provide a conductor obtained by solidifying the above conductive composition, a laminated structure having a layer of the conductor, and an electronic component comprising the conductor or the laminated structure. [Means for solving the problem]

[0007] The present inventors have found that, in a conductive composition containing a binder resin and silver powder, by adjusting the number-average particle size of the silver powder in the conductive composition to more than 3.7 μm and less than 4.8 μm, the change in resistance value of the conductor obtained by solidifying the conductive composition can be significantly suppressed even after repeated exposure to high-temperature conditions such as solder reflow, compared to the conductor before exposure to high-temperature conditions. The present invention is based on this finding. In other words, the gist of the present invention is as follows.

[0008] [1] A conductive composition comprising a binder resin and silver powder, A conductive composition characterized in that the number-average particle size of the silver powder in the conductive composition, as measured by laser diffraction scattering, is greater than 3.7 μm and less than 4.8 μm. [2] The conductive composition according to [1], wherein the silver powder comprises a first silver powder and a second silver powder having different number-average particle sizes. [3] The conductive composition according to [2], wherein the number average particle size of the first silver powder is 3.0 μm or more, and the number average particle size of the second silver powder is less than 3.0 μm. [4] The conductive composition according to [2], wherein the number average particle size of the first silver powder in the conductive composition is 4.5 μm or more, and the number average particle size of the second silver powder in the conductive composition is less than 4.5 μm. [5] The conductive composition according to [1], wherein the silver powder is contained in an amount of 55 to 95% by mass relative to the total mass of solids in the conductive composition. [6] The conductive composition according to [1], wherein the silver powder is surface-treated silver powder. [7] The conductive composition according to [1], further comprising a thermosetting component. [8] The conductive composition according to [7], wherein the thermosetting component is an epoxy resin. A conductor obtained by solidifying the conductive composition described in [9][1].

[10] A laminated structure having a base material and a layer of the conductive material described in [9] provided on the base material. An electronic component comprising a conductor as described in

[11] [9] or a laminated structure as described in

[10] .

[12] A method for producing a conductive composition comprising a binder resin and silver powder, The process includes a step of mixing the binder resin and silver powder, The number-average particle size of the silver powder in the conductive composition, as measured by laser diffraction scattering, is greater than 3.7 μm and less than 4.8 μm. A manufacturing method characterized by the following features. [Effects of the Invention]

[0009] According to the present invention, in a conductive composition containing a binder resin and silver powder, by adjusting the number-average particle size of the silver powder in the conductive composition to more than 3.7 μm and less than 4.8 μm, it is possible to realize a conductive composition that can form a conductor in which the change in resistance value is extremely small even after repeated exposure to high-temperature conditions such as solder reflow, compared to before exposure to high-temperature conditions. [Modes for carrying out the invention]

[0010] [Conductive composition] The conductive composition of the present invention contains a binder resin and silver powder as essential components. The components contained in the conductive composition of the present invention will be described in detail below.

[0011] (Binder resin) The conductive composition of the present invention includes a binder resin to promote contact between silver powders contained in the conductive composition. The binder resin is not particularly limited as long as it has the function of promoting contact between silver powders, especially as an organic binder, and examples include thermoplastic resins and elastomers. The binder resin may be used alone or in combination of two or more types.

[0012] The binder resin content in the conductive composition of the present invention is not particularly limited, but is preferably 5 to 50% by mass, more preferably 5 to 40% by mass, and even more preferably 5 to 20% by mass, relative to the total mass of solids contained in the conductive composition. When the binder resin includes a block copolymer as described later, the amount of block copolymer relative to the total mass of binder resin is preferably 85 to 100% by mass. When the binder resin content is within the above range, the elasticity of the coating film formed by the conductive composition of the present invention is good.

[0013] Examples of thermoplastic resins include polyester resins, polyether resins, polyamide resins, polyamide-imide resins, polyimide resins, butyral resins, polyvinyl formal resins, phenoxy resins, polyhydroxypolyether resins, acrylic resins, polystyrene resins, butadiene resins, acrylonitrile-butadiene copolymers, acrylonitrile-butadiene-styrene copolymers, styrene-butadiene copolymers, and acrylic acid copolymers. These thermoplastic resins may be saturated or unsaturated. Furthermore, from the viewpoint of adhesion between the substrate and the conductive composition, phenoxy resins and butyral resins are preferably used.

[0014] As the elastomer, any elastomer having rubber elasticity at room temperature can be used without particular limitation. Examples thereof include rubber, thermoplastic elastomer, functional group-containing elastomer, block copolymer, and the like.

[0015] As the rubber, either diene rubber or non-diene rubber may be used, and known and commonly used rubbers can be employed.

[0016] Examples of the thermoplastic elastomer include styrene-based elastomer, olefin-based elastomer, urethane-based elastomer, polyester-based elastomer, polyamide-based elastomer, acrylic-based elastomer, silicone-based elastomer, and the like.

[0017] Examples of the functional group-containing elastomer include thermoplastic elastomers having functional groups, and the types of thermoplastic elastomers can be the same as those described above. Among the functional group-containing elastomers, from the viewpoint of stretchability, preferably functional group-containing urethane-based elastomers and functional group-containing olefin-based elastomers are used.

[0018] From the viewpoint of solvent resistance, the functional groups possessed by the functional group-containing elastomer are preferably (meth)acryloyl group, acid anhydride group, carboxyl group, and epoxy group. From the fact that the solvent resistance is more excellent, functional group-containing elastomers having a (meth)acryloyl group are more preferable, and it is particularly preferable to have a plurality of (meth)acryloyl groups.

[0019] Specific examples of urethane elastomers having (meth)acryloyl groups include, commercially available (bifunctional) urethane elastomers having two (meth)acryloyl groups, such as U-108A, UA-112P, UA-5201, UA-512, UA-412A, UA-4200, UA-4400, UA-340P, UA-2235PE, UA-160TM, UA-122P, UA-512, UA-W2, UA-7000, UA-7100 from Shin Nakamura Chemical Industry Co., Ltd.; and CN962, CN963, CN964, CN965, CN980, CN981, CN982, CN983, CN996, CN9001, CN9002 from Sartomer. Examples include CN9788, CN9893, CN978, CN9782, CN9783; Arronix (registered trademark) M-1100, M-1200, M-1210, M-1310, M-1600 manufactured by Toagosei Chemical Industry Co., Ltd.; UN-9000PEP, UN-9200A, UN-7600, UN-333, UN-1255, UN-6060PTM, UN-6060P, SH-500B manufactured by Negami Kogyo Co., Ltd.; AH-600, AT-600 manufactured by Kyoeisha Chemical Co., Ltd.; and Evecryl 280, Evecryl 284, Evecryl 402, Evecryl 8402, Evecryl 8411, Evecryl 8807, Evecryl 9270 manufactured by Daicel Ornex Co., Ltd. Furthermore, commercially available (trifunctional) urethane elastomers having three (meth)acryloyl groups include, for example, CN929, CN944B85, CN989, and CN9008 from Sartomer Corporation; and Evecryl 264, Evecryl 265, Evecryl 1259, Evecryl 8201, KRM8296, Evecryl 294 / 25HD, and Evecryl 4820 from Daicel Ornex Corporation.In addition, examples of commercially available (tetrafunctional or higher) urethane-based elastomers having four or more (meth)acryloyl groups include, for example, U-6HA, U-6H, U-15HA, UA-32P, U-324A, UA-7200 manufactured by Shin-Nakamura Chemical Co., Ltd.; CN968, CN9006, CN9010 manufactured by Sartomer Co., Ltd.; UN-3320HA, UN-3320HB, UN-3320HC, UN-3320HS, UN-904, UN-901T, UN-905, UN-952 manufactured by Negami Kogyo Co., Ltd.; Ebercryl 1290, Ebercryl 1290K, KRM8200, Ebercryl 5129, Ebercryl 8210, Ebercryl 8301, Ebercryl 8405 manufactured by Daicel Ornex Co., Ltd., and the like.

[0020] Specific examples of other functional group-containing elastomers include, as commercially available products of elastomers having an acid anhydride group, for example, Rycon (registered trademark) 130MA-8, Rycon (registered trademark) 130MA-13, Rycon (registered trademark) 130MA-20, Rycon (registered trademark) 131MA-5, Rycon (registered trademark) 131MA-10, Rycon (registered trademark) 131MA-17, Rycon (registered trademark) 131MA-20, Rycon (registered trademark) 184MA-6, Rycon (registered trademark) 156MA-17, etc. manufactured by Sartomer Co., Ltd.; US102 manufactured by Kuraray Co., Ltd., CN301, CN307 manufactured by Sartomer Co., Ltd., BAC-45 manufactured by Osaka Organic Chemical Industry Co., Ltd., and the like as commercially available products of elastomers having a (meth)acryloyl group. Examples of elastomers having a carboxyl group include carboxyl group-terminated butadiene-acrylonitrile copolymers and the like. Examples of elastomers having an epoxy group and a carboxyl group include elastomers obtained by modifying part or all of the epoxy groups of epoxy resins having various skeletons with carboxyl group-terminated butadiene-acrylonitrile copolymers, and the like.

[0021] When the above-mentioned rubber or functional group-containing elastomer is used as the elastomer, sulfur-based and / or non-sulfur-based vulcanizing agents are added to the elastomer as needed. In a conductive composition containing silver powder as in the present invention, it is preferable to use a non-sulfur-based vulcanizing agent from the viewpoint of preventing corrosion of the silver powder in the conductive composition by oxidation or sulfidation due to the sulfur contained in the vulcanizing agent.

[0022] As a block copolymer, any block copolymer of a hard segment and a soft segment can be used without particular limitations. Block copolymers have low crystallinity and weak intermolecular forces, resulting in a relatively low glass transition temperature (Tg), and when mixed with silver powder, they have the advantage of being flexible and elongated. Preferably, a block copolymer of a hard segment with a Tg of less than 150°C and a soft segment with a Tg of less than 0°C is used. In this invention, Tg can be measured by differential scanning calorimetry (DSC).

[0023] The ratio of hard segments to soft segments in the block copolymer is not particularly limited, but is preferably adjusted to a range of 20:80 to 50:50, and more preferably 25:75 to 40:60.

[0024] Examples of units constituting the hard segment in a block copolymer include methyl (meth)acrylate units and styrene units. Examples of units constituting the soft segment include n-butyl acrylate units and butadiene units. In this specification, "(meth)acrylate" is a general term for acrylate and methacrylate, and the same applies to other similar expressions.

[0025] Commercially available block copolymers include, for example, acrylic triblock copolymers manufactured by Arkema using living polymerization. More specifically, SBM types, represented by polystyrene-polybutadiene-polymethyl methacrylate copolymers, MAM types, represented by polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate copolymers, and MAM N or MAM A types that have undergone carboxylic acid modification or hydrophilic group modification are used. Examples of SBM types include E41, E40, E21, and E20. Examples of MAM types include M51, M52, M53, and M22. Examples of MAM N types include 52N and 22N. Examples of MAM A types include SM4032XM10. Another example of a commercially available block copolymer is Clarity®, manufactured by Kuraray Co., Ltd. Clarity® is a block copolymer derived from methyl methacrylate and butyl acrylate.

[0026] The weight-average molecular weight of the block copolymer can be set as appropriate, for example, to 10,000-500,000, 20,000-400,000, 50,000-300,000, etc.

[0027] The tensile elongation at break of the block copolymer can be set as appropriate, for example, to 100-600%, 200-600%, 300-500%, etc. In this invention, the tensile elongation at break is expressed by the following formula and can be measured by a method compliant with the International Organization for Standardization's international standard ISO 37.

number

[0028] The elastomer described above may contain known additives such as softeners and plasticizers as needed. Examples of softeners include mineral oil-based softeners and vegetable oil-based softeners. Examples of mineral oil-based softeners include paraffinic process oils, naphthenic process oils, and aromatic process oils. Examples of vegetable oil-based softeners include castor oil, linseed oil, flaxseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, pine oil, and tall oil. A single softener may be used, or two or more may be used in combination. The rubber elasticity and stretchability of the elastomer can be adjusted by changing the amount of softener added.

[0029] (Silver powder) The conductive composition of the present invention contains silver powder as conductive particles. The silver powder imparts conductivity to the cured product formed using the conductive composition of the present invention.

[0030] The conductive composition of the present invention, by adjusting the number-average particle size of the silver powder in the conductive composition to a specific range described later, can significantly suppress changes in resistance value even after the hardened product (conductor) obtained by solidifying the conductive composition has been repeatedly exposed to high-temperature conditions such as solder reflow, compared to the conductor before exposure to high-temperature conditions.

[0031] The silver powder in the conductive composition of the present invention has a number-average particle diameter (hereinafter also simply referred to as "number-average particle diameter of silver powder") greater than 3.7 μm and less than 4.8 μm, as measured by laser diffraction scattering. Here, "silver powder in the conductive composition" means silver powder in the state in which it is contained in the conductive composition. That is, in this specification, the number-average particle diameter for silver powder in the conductive composition means the number-average particle diameter of silver powder in the state in which it is contained in the conductive composition after mixing. Similarly, for silver powder, "number-average particle diameter in the conductive composition" means the number-average particle diameter of silver powder in the state in which it is contained in the conductive composition. The number-average particle diameter of silver powder in the conductive composition is preferably 3.8 to 4.7 μm, more preferably 3.9 to 4.6 μm, and even more preferably 4.0 to 4.6 μm. In the present invention, the number-average particle size of silver powder in the conductive composition can be measured by laser diffraction scattering using, for example, the Microtrac MT3300EX particle size distribution analyzer manufactured by Nikkiso Co., Ltd. Specifically, it can be measured under the following conditions and procedures.

[0032] <Condition Settings> Enter the measurement conditions according to the following procedure. Launch the software included with the Microtrac MT3300EX ("Particle Size Distribution Measurement"), proceed from the SET UP screen, and set the time from the measurement condition setting options. Set the Setzero time to 30 sec, the measurement to 30 sec, and the number of measurements to 2. Next, enter the analysis conditions according to the following procedure. In the particle information tab of the analysis conditions, set the particle characteristics to reflectance. Also, in the solvent information, select PMA (propylene glycol monomethyl ether acetate) and set the solvent refractive index to 1.4. Next, enter the scale settings according to the following procedure. In the particle size range, set the minimum particle size to 0.021 μm and the maximum particle size to 995.61 μm. Next, enter the sampling system according to the following procedure. Set the number of washes of the circulation device ASVR to 4, the flow rate to 50%, the ultrasonic output to 40 W, and the ultrasonic time to 60 sec. After entering all conditions, press Save to close the measurement condition settings.

[0033] <Sample Preparation> Prepare the sample using the following procedure: Weigh 1.0 g of the conductive composition into a screw-top bottle, gradually add 20 g of PMA (propylene glycol monomethyl ether acetate) using a dropper, and shake the bottle to disperse the silver powder and prepare the sample. None of the samples should be subjected to external dispersion or pre-dispersion.

[0034] <Measurement of the number-average particle size of a sample> The number-average particle size of silver powder in the sample is measured using the following procedure. First, click on "Particle Size Distribution Measurement" in the software included with the Microtrac MT3300EX to open the sample loading screen. Next, drop a few drops of sample into the sample inlet of the main unit using the dropper. Then, when a red indicator bar appears on the sample loading screen, drop more sample into the sample inlet until the indicator bar moves from red to green. Once the indicator bar is in the green range, press the ultrasonic stirring button to start ultrasonic stirring of the sample. After ultrasonic stirring is complete, press the ultrasonic stirring button again to perform ultrasonic stirring a total of two times. After the two ultrasonic stirring cycles are complete, start measuring the number-average particle size of the silver powder within 3 minutes.

[0035] The reason why adjusting the number-average particle size of silver powder in the conductive composition to the specific range described above significantly suppresses changes in the resistance value of the conductor before and after exposure to high-temperature conditions is not entirely clear, but it can be inferred as follows. First, it is presumed that the following two phenomena occur simultaneously under high-temperature conditions such as solder reflow. As the first phenomenon, the hardening reaction of some components (especially organic components) in the conductor proceeds, causing the conductor to shrink. As a result, the silver powder in the conductor aggregates, increasing its density and lowering the resistance value of the conductor. Furthermore, as the second phenomenon, oxidation of the silver powder in the conductor and thermal decomposition of some components (especially organic components) occur, increasing the resistance value of the conductor. In the conductive composition of the present invention, by controlling the number-average particle size of the silver powder to be greater than 3.7 μm and less than 4.8 μm, the decrease in resistance value due to the first phenomenon described above and the increase in resistance value due to the second phenomenon become roughly equal in the formed conductor. As a result, it is inferred that the resistance value of the conductor will remain stable even when repeatedly exposed to high-temperature conditions such as solder reflow.

[0036] To adjust the number-average particle size of the silver powder in the conductive composition to the range described above, one or more types of silver powder having a number-average particle size within the range described above in the conductive composition (in the state after being blended into the conductive composition) may be used alone or in combination, or two or more types of silver powder with different number-average particle sizes may be used in combination. Preferably, two or more types of silver powder with different number-average particle sizes in the conductive composition (number-average particle size in the state after being blended into the conductive composition) are used in combination, and particularly preferably, a first silver powder having a number-average particle size of 4.5 μm or more in the conductive composition is used in combination with a second silver powder having a number-average particle size of less than 4.5 μm in the conductive composition.

[0037] The number-average particle diameter of the silver powder itself, that is, the number-average particle diameter of the silver powder before it is incorporated into the conductive composition, is not particularly limited and can be set appropriately depending on the shape of the silver powder used. For example, when spherical, approximately spherical, spheroidal, or approximately spheroidal silver powders described later are used, the number-average particle diameter of the silver powder can be 0.1 to 20 μm, 0.5 to 15 μm, 0.7 to 10 μm, etc. In order to adjust the number-average particle diameter of the silver powder in the conductive composition to the above range, it is preferable to use a combination of two or more types of silver powder with different number-average particle diameters before they are incorporated into the conductive composition, and it is particularly preferable to use a combination of silver powder with a number-average particle diameter of 3.0 μm or more before it is incorporated into the conductive composition and silver powder with a number-average particle diameter of less than 3.0 μm before it is incorporated into the conductive composition. The number-average particle diameter of the silver powder itself can be measured by the laser diffraction scattering method described above. When measuring the number-average particle size of the silver powder itself, the sample for measurement shall be prepared according to the following method.

[0038] To measure the number-average particle size of the silver powder itself, a sample can be prepared by weighing 0.5 g of silver powder into a screw-top bottle, gradually adding 20 g of PMA (propylene glycol monomethyl ether acetate) using a dropper, and shaking the bottle to disperse the silver powder. In this case, no external dispersion or pre-dispersion of the sample should be performed.

[0039] The shape of the silver powder is not particularly limited, and various shapes of silver powder can be used, such as spherical, approximately spherical, ellipsoidal, approximately ellipsoidal, approximately ellipsoidal, flake-shaped, and dendritic-shaped. Preferably, two or more types of silver powder with different shapes are used in combination, and particularly preferably, spherical, approximately spherical, ellipsoidal, and approximately ellipsoidal silver powders are used in combination with flake-shaped silver powders. Generally, when printing a conductive composition onto a substrate or the like, in order to ensure good edge cutting of the printed pattern, the conductive composition needs to have both appropriate viscosity and thixotropy (thixo property). If the silver powder blended into the conductive composition consists only of spherical, approximately spherical, ellipsoidal, and approximately ellipsoidal silver powders, the thixo property of the conductive composition is often not sufficiently obtained, and the viscosity needs to be increased in order to ensure good edge cutting of the printed pattern when printed. However, if the goal is to achieve good edge breakage in the printed pattern, the viscosity becomes too high, leading to streaking when printing the conductive composition and a decrease in the quality of the printed pattern. On the other hand, flake-shaped silver powder tends to increase thixotropy. Therefore, if the conductive composition contains only flake-shaped silver powder, the thixotropy of the conductive composition often becomes too high, resulting in poor printability. Thus, by combining spherical, nearly spherical, ellipsoidal, and nearly ellipsoidal silver powder with flake-shaped silver powder in the conductive composition, it is possible to sufficiently increase the thixotropy with a small amount of flake-shaped silver powder, resulting in a conductive composition that possesses both appropriate viscosity and thixotropy. Furthermore, since flake-shaped silver powder tends to have lower resistance values ​​compared to spherical, nearly spherical, ellipsoidal, and nearly ellipsoidal silver powders, increasing the proportion of flake-shaped silver powder in the mixture allows for achieving the desired conductivity in a conductive composition with less silver powder.

[0040] The silver powder is preferably in the form of elemental silver, but it may also be in the form of a silver alloy, a multilayer body with silver as the core or coating layer, or a silver oxide, and two or more of these may be used in combination.

[0041] To adjust the affinity between the silver powder and the binder resin described above, surface-treated silver powder may be used. Methods for surface-treating the silver powder include a wet method in which the silver powder is added to a solution containing a dispersion and stirred, and a dry method in which the solution containing the dispersion is sprayed while stirring the silver powder. Surface treatment may also be performed using a surfactant in combination.

[0042] Examples of dispersants used in the surface treatment of silver powder include organic acids such as fatty acids, organometallic acids, and protective colloids such as gelatin. Dispersants may be used individually or in combination of two or more. From the viewpoint of suppressing the inclusion of impurities and improving adsorption to hydrophobic groups, fatty acids or their salts are preferably used as dispersants. Alternatively, a dispersant may be an emulsion of fatty acids or their salts with a surfactant. Preferred dispersants include fatty acids having 6 to 24 carbon atoms, specifically stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and linolenic acid. These fatty acids are preferred because they are considered to have little adverse effect on wiring layers and electrodes using conductive compositions.

[0043] The surface treatment of the silver powder may be applied to the entire surface of each silver powder particle, or to only a portion of the surface. When the surface treatment is applied to only a portion of the surface of the silver powder particles, the area of ​​the treated surface can be, for example, 10-90%, 20-80%, 30-70%, 40-60%, etc., of the total surface area of ​​the silver powder.

[0044] The content of silver powder in the conductive composition of the present invention is not particularly limited, but is preferably 55 to 95% by mass, more preferably 65 to 95% by mass, and even more preferably 75 to 95% by mass, relative to the total mass of solids contained in the conductive composition. In a preferred embodiment, when the conductive composition contains a first silver powder having a number average particle diameter of 4.5 μm or more in the conductive composition, and a second silver powder having a number average particle diameter of less than 4.5 μm in the conductive composition, the mass ratio of the first silver powder to the second silver powder in the conductive composition (mass of the first silver powder:mass of the second silver powder) is preferably 3:7 to 7:3, more preferably 4:6 to 6:4, and even more preferably 5:5.

[0045] As described above, the conductive composition of the present invention can significantly suppress changes in resistance value compared to the conductor before exposure to high-temperature conditions, even after the conductor obtained by solidifying the conductive composition has been repeatedly exposed to high-temperature conditions. In this specification, the "high-temperature conditions" to which the cured product (conductor) obtained by solidifying the conductive composition of the present invention is exposed are not particularly limited, but can be, for example, 150°C or higher, 180°C or higher, 200°C or higher, or 300°C or lower, 280°C or lower, 250°C or lower. More specifically, the high-temperature conditions can be, for example, 150~300°C, 180~280°C, 200~250°C, etc. The time of exposure to high-temperature conditions is also not particularly limited, but can be, for example, 10 seconds or more, 30 seconds or more, 60 seconds or more, or 300 seconds or less, 240 seconds or less, 180 seconds or less, etc. More specifically, the time exposed to high-temperature conditions can be, for example, 10-300 seconds, 30-240 seconds, 60-180 seconds, etc.

[0046] In this specification, "repeatedly" exposing a conductor obtained by solidifying the conductive composition of the present invention to high-temperature conditions means exposing the conductor to high-temperature conditions intermittently multiple times. The number of times the conductor is exposed to high-temperature conditions is not particularly limited, but for example, it can be two or more times, five or more times, seven or more times, ten or more times, fifteen or more times, etc.

[0047] The rate of change in resistance after exposure to high-temperature conditions (hereinafter also simply referred to as "rate of change in resistance"), compared to the resistance value before exposure to high-temperature conditions, is expressed by the following formula.

number

[0048] In the present invention, the resistance value of a conductor obtained by solidifying a conductive composition can be measured using a milliohmmeter by a four-terminal measurement method. Specifically, an evaluation line pattern with a width of 1 mm and a length of 400 mm, having 5 mm x 5 mm pads at both ends, is pattern printed on a copper substrate of FR-4 substrate using a screen printing plate (150 mesh, made of Tetron) with the conductive composition, and after heat treatment at 80°C for 30 minutes, it is heat-cured at 180°C for 30 minutes. The resistance value of the heat-cured line pattern (conductor) is measured using a four-terminal measurement method with a probe applied to the 5 mm x 5 mm pad portion using a Hioki E.E. CORPORATION Milliohm HiTester 3540. A more specific example of the method is shown in the examples.

[0049] The conductor obtained by solidifying the conductive composition of the present invention preferably has a rate of change in the resistance value described above of less than ±5%, more preferably within ±4%, even more preferably within ±3.5%, and particularly preferably within ±3%. When the rate of change in the resistance value of the conductor before and after exposure to high-temperature conditions is within the above range, it can be said that the change in the resistance value of the conductivity is significantly suppressed. In this specification, "within ±X%" means the range of -N% to +N%. Also, "less than ±Y%" means the range of greater than -Y% to less than +Y%.

[0050] In one embodiment, the conductive composition of the present invention can significantly suppress the increase in resistance value compared to the conductor before exposure to solder reflow, even when the conductor obtained by solidifying the conductive composition is repeatedly exposed to solder reflow 10 times. Specifically, the rate of change in the resistance value of the conductor after exposure to solder reflow, compared to the conductor before exposure to solder reflow, is preferably less than ±5%, more preferably within ±4%, even more preferably within ±3.5%, and particularly preferably within ±3%.

[0051] (Organic solvents) The conductive composition of the present invention may contain organic solvents for purposes such as preparing the composition or adjusting its viscosity when applying it to a substrate or film. As organic solvents, for example, ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene; glycol ethers such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, diethylene glycol monomethyl ether acetate, and tripropylene glycol monomethyl ether; esters such as ethyl acetate, butyl acetate, butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and propylene carbonate; aliphatic hydrocarbons such as octane and decane; and petroleum-based solvents such as petroleum ether, petroleum naphtha, and solvent naphtha can be used. Among these, glycol ethers are preferred. These organic solvents may be used individually or in combination of two or more.

[0052] The volatilization drying of organic solvents can be carried out using a hot air circulation drying oven, an IR oven, a hot plate, a convection oven, etc. (using a heat source equipped with a steam-heated air heating method, either by bringing the hot air inside the dryer into countercurrent contact or by blowing it onto the support from a nozzle).

[0053] The content of the organic solvent in the conductive composition is preferably changed as appropriate depending on the materials constituting the conductive composition, but for example, it can be 5 to 30% by mass relative to the conductive composition.

[0054] (thermosetting component) The conductive composition of the present invention may further contain a thermosetting component. Examples of known and commonly used thermosetting components include isocyanate compounds, blocked isocyanate compounds, amino resins, maleimide compounds, benzoxazine resins, carbodiimide resins, cyclocarbonate compounds, epoxy compounds, oxetane compounds, and episulfide resins. The thermosetting component may be used alone or in combination of two or more. Of these, epoxy resins are preferably used as the thermosetting component.

[0055] Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, hydrogenated bisphenol A type epoxy resin, brominated bisphenol A type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolac type epoxy resin, biphenyl type epoxy resin, naphthalene type epoxy resin, dicyclopentadiene type epoxy resin, and triphenylmethane type epoxy resin.

[0056] Examples of commercially available epoxy resins include jER 828, 806, 807, YX8000, YX8034, 834 from Mitsubishi Chemical Corporation; YD-128, YDF-170, ZX-1059, ST-3000 from Nippon Steel Chemical & Material Corporation; EPICLON 830, 835, 840, 850, N-730A, N-695 from DIC Corporation; and RE-306 from Nippon Kayaku Co., Ltd.

[0057] (Thermosetting catalyst) The conductive composition of the present invention may contain a thermosetting catalyst. Examples of thermosetting catalysts include imidazole derivatives such as imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 4-phenylimidazole, 1-cyanoethyl-2-phenylimidazole, and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole; amine compounds such as dicyandiamide, benzyldimethylamine, 4-(dimethylamino)-N,N-dimethylbenzylamine, 4-methoxy-N,N-dimethylbenzylamine, and 4-methyl-N,N-dimethylbenzylamine; hydrazine compounds such as adipic acid dihydrazide and sebacate dihydrazide; and phosphorus compounds such as triphenylphosphine.

[0058] Examples of commercially available thermosetting catalysts include 2MZ-A, 2MZ-OK, 2PHZ, 2P4BHZ, and 2P4MHZ (all trade names for imidazole compounds) from Shikoku Chemicals, Inc., and U-CAT 3513N (trade name for a dimethylamine compound), DBU, DBN, and U-CAT SA 102 (all bicyclic amidine compounds and their salts) from Sunapro Co., Ltd. However, the catalyst is not limited to these; any thermosetting catalyst for epoxy resins or oxetane compounds, or one that promotes the reaction between an epoxy group and an oxetanyl group and a carboxyl group, may be used individually or in combination of two or more. Furthermore, S-triazine derivatives such as guanamine, acetoguanamine, benzoguanamine, melamine, 2,4-diamino-6-methacryloyloxyethyl-S-triazine, 2-vinyl-2,4-diamino-S-triazine, 2-vinyl-4,6-diamino-S-triazine isocyanuric acid adduct, and 2,4-diamino-6-methacryloyloxyethyl-S-triazine isocyanuric acid adduct can also be used, and preferably these compounds that also function as adhesion imparters are used in combination with a thermosetting catalyst.

[0059] (Other ingredients) The conductive composition of the present invention may optionally further contain components such as colorants, mercapto compounds, urethane catalysts, thixonating agents, adhesion promoters, chain transfer agents, polymerization inhibitors, copper damage inhibitors, antioxidants, rust inhibitors, thickeners such as organic bentonite and montmorillonite, defoaming agents and leveling agents such as silicone-based, fluorine-based, and polymer-based agents, silane coupling agents such as imidazole-based, thiazole-based, and triazole-based agents, and flame retardants such as phosphinates, phosphate ester derivatives, and phosphazene compounds. These components may be those known in the field of electronic materials.

[0060] The conductive composition of the present invention can be manufactured, for example, by kneading a binder resin dissolved in a solvent with silver powder. Examples of kneading methods include using a stirring and mixing device such as a roll mill. Specifically, a conductive composition can be obtained by dissolving the binder resin in an organic solvent to prepare a resin solution with a solid content of 50% by mass, adding silver powder to the resulting resin solution, pre-mixing it using a stirrer, and then kneading it using a three-roll mill. Depending on the binder resin, organic solvent, and their respective proportions, the conductive composition can be in liquid or paste (semi-solid) form. Preferably, the conductive composition of the present invention is a paste.

[0061] [Applications of conductive compositions] The conductive composition of the present invention can be solidified to form a conductor. For example, a conductive layer can be formed by forming a coating film made of the conductive composition on a substrate, drying it, and solidifying it. Solidification of the conductive composition can be carried out, for example, by drying and / or heat-treating the conductive composition. Examples of heat treatment include hot air drying and thermosetting. Molding may be performed prior to heat treatment. For example, a conductive layer can be obtained by coating the conductive composition of the present invention onto a substrate in a desired shape, molding it as necessary, and then solidifying it. The conductive layer can take on various shapes depending on the application, and can be, for example, a conductive circuit, wiring, an electrode, etc.

[0062] When forming a conductive circuit, the process includes a pattern forming step of printing or coating the conductive composition of the present invention onto a substrate to form a coating pattern, and a solidification step of solidifying the patterned coating. For example, methods such as masking or resist can be used to form the coating pattern.

[0063] Methods used in the pattern formation process include, for example, printing methods and dispensing methods. Examples of printing methods include gravure printing, offset printing, and screen printing, with screen printing being preferred when forming intricate circuits. Gravure printing and offset printing are preferred methods for coating large areas. Dispensing methods involve controlling the amount of conductive composition applied and extruding it from a needle to form a pattern, and are suitably used for forming partial patterns such as earth wiring or patterns on uneven surfaces.

[0064] The substrate to which the conductive composition is applied can be any electrically insulating material without particular limitations and can be appropriately selected according to the purpose. Examples of substrates include copper-clad laminates of all grades (e.g., FR-4, etc.) using composite materials such as paper-phenolic resin, paper-epoxy resin, glass cloth-epoxy resin, glass-polyimide, glass cloth / nonwoven fabric-epoxy resin, glass cloth / paper-epoxy resin, synthetic fiber-epoxy resin, fluororesin / polyethylene / polyphenyl ether, polyphenylene oxide / cyanate ester, etc., sheets or films made of plastics such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, etc., polyimide, polyphenylene sulfide, polyamide, etc., sheets or films made of thermoplastic elastomers such as polyester, polyurethane, polyolefin, styrene block copolymer, etc.

[0065] As described above, the conductive composition of the present invention can be solidified on a substrate to form a conductive layer. Therefore, the conductive composition of the present invention can also be used in the manufacture of laminated structures having a substrate and a conductive layer. Such conductors and laminated structures can then be used as components for various electronic devices. [Examples]

[0066] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0067] [Preparation of conductive compositions] Each component shown in Table 1 was mixed in the amounts shown in the table, pre-mixed using a stirrer, and then kneaded using a three-roll mill to prepare the conductive compositions for Examples 1-3 and Comparative Examples 1-6. The details of each component in Table 1 are as follows. The physical properties of silver powders 1-5 are those of the silver powder before it was incorporated into each conductive composition, and the number-average particle size is the value measured by the method described in the section [Measurement of Number-Average Particle Size of Silver Powder (Before Incorporation into Conductive Composition)] below. In Table 1, values ​​without units represent "parts by mass". Binder resin: Phenoxy resin (PKHC, manufactured by InChem) Thermosetting component: Bisphenol AD ​​type epoxy resin (R710, manufactured by Printec Co., Ltd.) Thermosetting catalyst: Adduct-type latent curing epoxy curing agent (CureDuct® P-0505, manufactured by Shikoku Chemicals Co., Ltd.) Solvent: Diethylene glycol monomethyl ether acetate Silver powder 1: Number-average particle size 3.3 μm, specific surface area 0.18, flake-like. Silver powder 2: Number-average particle size 4.1 μm, specific surface area 0.21, flake-like. Silver powder 3: Number-average particle size 3.8 μm, specific surface area 0.18, flake-like. Silver powder 4: Number-average particle size 0.9 μm, specific surface area 1.10, flake-like. Silver powder 5: Number-average particle size 2.6 μm, specific surface area 0.31, spherical

[0068] [Table 1]

[0069] [Measurement of the average particle size of silver powder (before blending into conductive composition)] Before preparing each conductive composition in the examples and comparative examples, the number-average particle size of each silver powder was measured by laser diffraction scattering using a Microtrac MT3300EX particle size distribution analyzer and an ASVR circulation system manufactured by Nikkiso Co., Ltd. Specifically, the measurements were performed under the following conditions and procedures.

[0070] <Condition Settings> The measurement conditions were entered according to the following procedure. The software included with the Microtrac MT3300EX ("Particle Size Distribution Measurement") was launched, and from the SET UP screen, the time settings were configured from the measurement condition settings options. The Setzero time was set to 30 sec, the measurement to 30 sec, and the number of measurements to 2. Next, the analysis conditions were entered according to the following procedure. In the particle information tab of the analysis conditions, the particle characteristic was set to reflectance. In the solvent information, PMA (propylene glycol monomethyl ether acetate) was selected, and the solvent refractive index was set to 1.4. Next, the scale settings were entered according to the following procedure. In the particle size range, the minimum particle size was set to 0.021 μm and the maximum particle size to 995.61 μm. Next, the sampling system was entered according to the following procedure. The number of washes for the circulation device ASVR was set to 4, the flow rate to 50%, the ultrasonic output to 40 W, and the ultrasonic time to 60 sec. After entering all the conditions, the measurement condition settings were saved and closed.

[0071] <Sample Preparation> Samples were prepared using the following procedure: 0.5 g of each silver powder was weighed into a screw-top bottle, and 20 g of PMA (propylene glycol monomethyl ether acetate) was gradually added using a dropper. The bottle was then shaken to disperse the silver powder and prepare the sample. None of the samples underwent external dispersion or pre-dispersion.

[0072] <Measurement of the number-average particle size of a sample> The number-average particle size of silver powder in the sample was measured using the following procedure. First, the particle size distribution measurement function in the software included with the Microtrac MT3300EX was clicked to open the sample loading screen. Next, a few drops of each sample were added to the sample inlet of the main unit using a dropper. Then, when a red indicator bar appeared on the sample loading screen, more of each sample was added to the sample inlet until the indicator bar moved from red to green. Once the indicator bar moved into the green range, the ultrasonic stirring button was pressed to start ultrasonic stirring of the sample. After ultrasonic stirring was completed, the ultrasonic stirring button was pressed again to perform ultrasonic stirring a total of two times. After the two ultrasonic stirring cycles were completed, the measurement of the number-average particle size of the silver powder was started within 3 minutes. The measurement results are shown in the section [Preparation of Conductive Composition] above.

[0073] [Measurement of the number-average particle size of silver powder in conductive compositions] After preparing each conductive composition in the examples and comparative examples, the number-average particle size of the silver powder in each conductive composition was measured by laser diffraction scattering using a Microtrac MT3300EX particle size distribution analyzer and an ASVR circulation system manufactured by Nikkiso Co., Ltd. Specifically, 1.0 g of each conductive composition from Examples 1-3 and Comparative Examples 1-6 was weighed into a screw-top bottle, 20 g of PMA (propylene glycol monomethyl ether acetate) was added little by little using a dropper, and the screw-top bottle was shaken to dissolve each conductive composition and prepare a sample. None of the samples underwent external dispersion or pre-dispersion. The number-average particle size of the silver powder in the samples was measured under the same conditions as the measurement of the number-average particle size of the silver powder before it was mixed into the conductive compositions as described above. The measurement results are shown in Table 1.

[0074] [Preparation of cured conductive materials (conductors)] FR-4 substrates were prepared by applying solder resist (PSR-4000D10ME, manufactured by Taiyo Ink Manufacturing Co., Ltd.) by screen printing, drying, exposing and curing with ultraviolet light, and post-curing in a hot air circulation drying oven. The thickness of the solder resist after post-curing was 20 μm. On the prepared FR-4 substrates, a line pattern for resistance evaluation, 1 mm wide and 400 mm long with 5 mm x 5 mm pads at both ends, was printed using a screen printing plate (150 mesh, made of Tetron) with each conductive composition from the examples and comparative examples to form a film of the conductive composition. After drying in a hot air circulation drying oven at 80°C for 30 minutes, the film was heat-cured in a hot air circulation drying oven at 180°C for 30 minutes to form cured products (conductors) of each conductive composition, and evaluation substrates were obtained.

[0075] [Measurement of the resistance value of a conductor before exposure to high-temperature conditions] The resistance values ​​of the conductors on each evaluation board were measured using the four-terminal measurement method with a Hioki E.E. CORPORATION Milliohm HiTester 3540, by placing a probe on a 5mm x 5mm pad area.

[0076] [Measurement of the resistance of a conductor after exposure to high-temperature conditions] After measuring the resistance of the conductors before exposure to high-temperature conditions, the resistance of the conductors on each evaluation substrate was subjected to high-temperature conditions by passing them through a reflow oven (NIS-20-82C, manufactured by Aitec Tectron Co., Ltd.) 10 times under the following conditions. Then, a probe was applied to a 5mm x 5mm pad area and measured using the four-terminal measurement method with a Hioki E.E. CORPORATION Milliohm HiTester 3540. Reflow conditions • Atmosphere: In the air • Profile: 30°C → 180°C (90 seconds) ·Furnace temperature*: Maintained at 180℃ (90 seconds) 180℃ → 265℃ (for 40 seconds) Maintain 265°C (for 10 seconds) 265℃ → 150℃ (for 40 seconds) *The furnace temperature is the actual measured value on the substrate.

[0077] [Calculation of the rate of change in the resistance value of a conductor before and after exposure to high-temperature conditions] For each conductive composition in the examples and comparative examples, the rate of change in the resistance value of the conductor before and after exposure to high-temperature conditions was calculated based on the following formula, using the resistance values ​​of the conductor measured using the evaluation substrates described above. The results are shown in Table 1.

number

[0078] The results shown in Table 1 indicate that in the conductive compositions of each example, where the number-average particle size of the silver powder in the conductive composition was adjusted to a predetermined range, the change in the resistance value of the formed cured product (conductor) was significantly suppressed before and after exposure to high-temperature conditions. On the other hand, in the conductive compositions of each comparative example, where the number-average particle size of the silver powder in the conductive composition was outside the predetermined range, the change in the resistance value of the formed cured product (conductor) was not sufficiently suppressed before and after exposure to high-temperature conditions.

Claims

1. A conductive composition comprising a binder resin and silver powder, A conductive composition characterized in that the number-average particle diameter of the silver powder in the conductive composition, as measured by laser diffraction scattering, is greater than 3.7 μm and less than 4.8 μm.

2. The conductive composition according to claim 1, wherein the silver powder comprises a first silver powder and a second silver powder having different number-average particle sizes.

3. The conductive composition according to claim 2, wherein the number-average particle diameter of the first silver powder is 3.0 μm or more, and the number-average particle diameter of the second silver powder is less than 3.0 μm.

4. The conductive composition according to claim 2, wherein the number average particle size of the first silver powder in the conductive composition is 4.5 μm or more, and the number average particle size of the second silver powder in the conductive composition is less than 4.5 μm.

5. The conductive composition according to claim 1, wherein the silver powder is contained in an amount of 55 to 95% by mass relative to the total mass of solids in the conductive composition.

6. The conductive composition according to claim 1, wherein the silver powder is surface-treated silver powder.

7. The conductive composition according to claim 1, further comprising a thermosetting component.

8. The conductive composition according to claim 7, wherein the thermosetting component is an epoxy resin.

9. A conductor obtained by solidifying the conductive composition described in claim 1.

10. A laminated structure comprising a base material and a layer of the conductive material described in claim 9 provided on the base material.

11. An electronic component comprising the conductor described in claim 9 or the laminated structure described in claim 10.

12. A method for producing a conductive composition, comprising a conductive composition containing a binder resin and silver powder, The process includes a step of mixing the binder resin and silver powder, The number-average particle size of the silver powder in the conductive composition, as measured by laser diffraction scattering, is greater than 3.7 μm and less than 4.8 μm. A manufacturing method characterized by the following features.

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