JP7640489B2 - Thermosetting Paste - Google Patents

Description

The technology disclosed herein relates to a thermosetting paste.

Electrodes of electronic components (such as terminal electrodes of solar cell cells) are formed, for example, by printing a conductive paste on a substrate and then curing the paste. One example of this type of conductive paste is a thermosetting paste. This thermosetting paste contains conductive particles such as silver particles (Ag particles) and a thermosetting component such as an epoxy resin. This thermosetting paste is cured by heating at a relatively low temperature (for example, 400°C or less) and does not require a high-temperature firing process. For this reason, thermosetting pastes are suitable for use in the manufacture of electronic components that use substrates with low heat resistance (such as resin substrates). Patent documents 1 and 2 are examples of this type of thermosetting paste.

Patent No. 5281529 Patent No. 6092754

Electrodes made from hardened thermosetting pastes are required to have various properties. First, from the viewpoint of the electrical performance of electronic components, the electrodes are required to have low electrical resistance after the paste is hardened. In addition, the electrodes are required to have excellent high-temperature reliability so that they do not deform or denature even when exposed to high-temperature environments. Next, in consideration of the durability of electronic components, the electrodes are required to have excellent adhesion to the substrate. The technology disclosed herein aims to improve these properties and provide a thermosetting paste that can form high-quality electrodes.

To achieve the above-mentioned objectives, the technology disclosed herein provides a thermosetting paste having the following configuration:

The thermosetting paste disclosed herein includes at least (A) scaly Ag particles, (B) spherical Ag particles, (C) a thermosetting component, (D) a silane coupling agent, and (E) an organic solvent. The (A) scaly Ag particles of this thermosetting paste have a _D50 particle size of 4 μm to 10 μm, which corresponds to a cumulative 50% from the smallest particle size, in a volume-based particle size distribution based on a laser diffraction/scattering method, and a content of 30 parts by weight to 80 parts by weight when the total weight of the Ag particles is 100 parts by weight. The (B) spherical Ag particles have a _D50 particle size of 1.5 μm to 2.5 μm, and a BET specific surface area of 0.5 m ² /g or less. Furthermore, the (C) thermosetting component contains a novolac type epoxy resin that is solid at 25° C., a curing agent, and a curing accelerator, and the content is 10 parts by weight or more and 15 parts by weight or less when the total weight of the Ag particles is 100 parts by weight. And the (D) silane coupling agent is a silane coupling agent having a polysulfide group, and the content is 0.1 parts by weight or more and 0.6 parts by weight or less when the total weight of the Ag particles is 100 parts by weight.

First, the thermosetting paste disclosed herein contains two types of Ag particles, namely, scaly Ag particles and spherical Ag particles. When this thermosetting paste is thermally cured, the scaly Ag particles are densely arranged on the surface side of the electrode after curing, and the Ag particles are easily in contact with each other in the electrode after curing. In the thermosetting paste disclosed herein, the _D50 particle size of the scaly Ag particles is set to 4 μm or more and 10 μm or less. Since the scaly Ag particles having such a particle size are easily able to form contacts between the Ag particles in the electrode after curing, they can form a suitable conductive path in the electrode and contribute to reducing electrical resistance. In the thermosetting paste disclosed herein, the content of the scaly Ag particles is set to 30 parts by weight or more when the total weight of the Ag particles is 100 parts by weight. This allows the resistance reducing effect of the scaly Ag particles to be properly exhibited.

On the other hand, the bottom side of the electrode after curing is mainly composed of a mixture of spherical Ag particles and a thermosetting component. This can improve the adhesion of the electrode to the substrate. Furthermore, in the thermosetting paste disclosed herein, the _D50 particle size of the spherical Ag particles is set to 1.5 μm or more, and the BET specific surface area is set to 0.5 m ² /g or less. This can prevent a plurality of spherical Ag particles from agglomerating with each other, and the contact area between the spherical Ag particles and the thermosetting component from decreasing. As a result, the adhesion of the electrode can be further improved. Furthermore, in the thermosetting paste disclosed herein, the content of the scaly Ag particles relative to the total weight of the Ag particles is set to 80 parts by weight or less. This can make it possible to make the content of the spherical Ag particles 20 parts by weight or more, so that the effect of improving the adhesion by the spherical Ag particles is appropriately exhibited.

Next, the thermosetting component of the thermosetting paste disclosed herein contains a novolac type epoxy resin that is solid at 25°C. It has been confirmed through experiments that a paste containing an epoxy resin of this composition exhibits a high glass transition point after thermal curing. This suppresses deformation of the electrode in a high-temperature environment, thereby improving the high-temperature reliability of the electrode. In addition, in the thermosetting paste disclosed herein, the content of the thermosetting component (total content of the epoxy resin, curing agent, and curing accelerator) relative to the total weight of the Ag particles is set to 10 parts by weight or more. This makes it possible to prevent a decrease in adhesion due to a shortage of the thermosetting component. On the other hand, in the thermosetting paste disclosed herein, the content of the thermosetting component is set to 15 parts by weight or less. This makes it possible to suppress an increase in electrical resistance due to the excessive addition of the thermosetting component.

The thermosetting paste disclosed herein uses a silane coupling agent (sulfide-based silane coupling agent) having a polysulfide group. A typical silane coupling agent bonds to both inorganic particles (Ag particles) and thermosetting resin (epoxy resin), and contributes to improving the adhesion of the electrode after curing. However, according to the inventor's experiments, it has been confirmed that the sulfide-based silane coupling agent has a different effect that other silane coupling agents do not have, that is, reducing the resistance of the electrode after curing. Although it is not intended to limit the technology disclosed herein, it is expected that the resistance reduction effect of this sulfide-based silane coupling agent is due to the action of increasing the contact points between Ag particles during the curing process. And, in the thermosetting paste disclosed herein, the content of the silane coupling agent is set to 0.1 parts by weight or more. This allows the resistance reduction effect and adhesion improvement effect of the sulfide-based silane coupling agent to be properly exhibited. On the other hand, from the viewpoint of suppressing the increase in resistance caused by the relative decrease in the Ag particle content, the content of the silane coupling agent in the thermosetting paste disclosed herein is set to 0.6 parts by weight or less.

As described above, the thermosetting paste disclosed herein can form high-performance electrodes that are excellent in electrical resistance, high-temperature reliability, and adhesion.

In one embodiment of the thermosetting paste disclosed herein, the (A) scaly Ag particles have an average aspect ratio of more than 1.5 and not more than 10. Scaly Ag particles of this configuration are easily arranged on the surface side of the electrode after curing, and therefore the electrical resistance of the electrode can be more suitably reduced.

In one embodiment of the thermosetting paste disclosed herein, the (A) scaly Ag particles have an ignition loss (Ig-loss) of 0.5 wt% or less when heated from room temperature to 600°C. This improves the moldability of the paste, making it easy to form electrodes with smooth surfaces.

In one embodiment of the thermosetting paste disclosed herein, the (A) scaly Ag particles have a tap density of 4 g/ml or more and 7 g/ml or less. This improves the moldability of the paste, making it easy to form electrodes with smooth surfaces.

In one embodiment of the thermosetting paste disclosed herein, the spherical Ag particles (B) have an average aspect ratio of 1 or more and 1.5 or less. Spherical Ag particles of this configuration are likely to be arranged on the bottom side of the electrode after curing, and therefore can more suitably reduce the adhesiveness of the electrode.

In one embodiment of the thermosetting paste disclosed herein, the spherical Ag particles (B) have a tap density of 5 g/ml or more and 7 g/ml or less. This can further improve the adhesion of the electrode after curing.

In one embodiment of the thermosetting paste disclosed herein, the novolac type epoxy resin includes one or more selected from phenol novolac type epoxy resin, cresol novolac type epoxy resin, naphthol novolac type epoxy resin, naphthol-phenol co-condensed novolac type epoxy resin, and naphthol-cresol co-condensed novolac type epoxy resin. This allows the formation of electrodes with even better high-temperature reliability.

In one embodiment of the thermosetting paste disclosed herein, the silane coupling agent (D) is bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)tetrasulfide, The sulfide-based silane coupling agent contains at least one selected from the group consisting of bis(2-triethoxysilylpropyl) disulfide, bis(2-triethoxysilylethyl) disulfide, bis(4-triethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl) disulfide, bis(2-trimethoxysilylethyl) disulfide, bis(4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide. These sulfide-based silane coupling agents can effectively exert both the resistance reducing effect and the adhesion improving effect.

In one embodiment of the thermosetting paste disclosed herein, the Casson yield value at 25°C is 120 Pa or less. This improves the moldability of the thermosetting paste, making it easy to form electrodes with smooth surfaces.

One embodiment of the technology disclosed herein is described below. Note that matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein (e.g., means for preparing the paste, means for printing the paste on the substrate, etc.) can be implemented based on the technical content taught by this specification and the general technical common sense of those skilled in the art in this field. Note that the notation "A to B" indicating a numerical range in this specification means greater than or equal to A and less than or equal to B.

1. Thermosetting paste The thermosetting paste is cured by heat treatment to form a film-like body (electrode) that exhibits electrical conductivity. The thermosetting paste disclosed herein contains at least (A) scaly Ag particles, (B) spherical Ag particles, (C) a thermosetting component, (D) a silane coupling agent, and (E) an organic solvent. The components of the thermosetting paste are described below.

(A) Scaly Ag Particles The thermosetting paste disclosed herein contains at least two types of Ag particles, namely, scaly Ag particles and spherical Ag particles. These Ag particles become conductive components in the electrode after the paste is cured. In addition, the "Ag particles" in this specification are particles containing silver (Ag) element as a main component. That is, the Ag particles may contain a small amount of metal elements other than silver as long as it does not significantly impede the technology disclosed herein. The "metal elements other than silver" here are unavoidable impurities that may be mixed in during the production process of the Ag particles, and are not limited to specific metal elements. For example, the purity of the Ag particles (content of silver element) is preferably 95% or more, more preferably 97% or more, and particularly preferably 99% or more. As the purity of the Ag particles increases, the electrical resistance of the electrode after curing tends to decrease.

The scaly Ag particles are flat Ag particles with a thin thickness overall. When the thermosetting paste containing the scaly Ag particles is heated, the scaly Ag particles are densely arranged on the surface side of the electrode after thermal curing. The electrode with the scaly Ag particles densely arranged on the surface side has the advantage that the silver exposure rate on the surface is high, making it easy to plate the electrode surface. In addition, when the scaly Ag particles are used, the Ag particles are more likely to come into contact with each other in the electrode after curing. This makes it easier to form a conductive path in the electrode, which can contribute to reducing the electrical resistance. The average aspect ratio of the scaly Ag particles is preferably more than 1.5, more preferably 2 or more, even more preferably 2.5 or more, and particularly preferably 3 or more. Since the scaly Ag particles with such a large aspect ratio are particularly likely to be arranged on the surface side of the electrode after thermal curing, the electrical resistance can be more suitably reduced. On the other hand, the upper limit of the average aspect ratio of the scaly Ag particles is preferably 10, and more preferably 7.5 or less. The "average aspect ratio" here is the average value of the ratio between the thickness and the major axis of a plurality of Ag particles. This average aspect ratio can be measured according to the following procedure. First, a rectangular parallelepiped is drawn circumscribing the Ag particle in a scanning electron microscope photograph (SEM photograph) of the Ag particle to be measured. Next, the aspect ratio is calculated by dividing the long side of this rectangular parallelepiped by the thickness (shortest side) (long side/thickness). The average value of the aspect ratios of 50 Ag particles is then taken as the average aspect ratio. This average aspect ratio can be calculated using conventionally known image analysis software (such as WinROOF by Mitani Shoji Co., Ltd.).

Next, in the thermosetting paste disclosed herein, the _D50 particle size of the scaly Ag particles is set to 4 μm or more. Scaly Ag particles with a small _D50 particle size are difficult to obtain contact points between Ag particles and are difficult to float to the electrode surface during heating, so they tend to be difficult to exhibit the resistance reduction effect. From the viewpoint of more suitably reducing the electrical resistance of the electrode, the _D50 particle size of the scaly Ag particles is preferably 4.2 μm or more, more preferably 4.5 μm or more, even more preferably 4.7 μm or more, and particularly preferably 4.9 μm or more. On the other hand, scaly Ag particles having an excessively large _D50 particle size also tend to be difficult to float to the electrode surface, so they tend to be difficult to exhibit the resistance reduction effect. For this reason, in the thermosetting paste disclosed herein, the _D50 particle size of the scaly Ag particles is set to 10 μm or less. From the viewpoint of more suitably reducing the electrical resistance of the electrode, the _D50 particle size of the scaly Ag particles is preferably 9.7 μm or less, more preferably 9.5 μm or less, even more preferably 9 μm or less, and particularly preferably 8.9 μm or less. In this specification, the " _D50 particle size" is the particle size corresponding to the cumulative 50% from the smallest particle size in the volume-based particle size distribution based on the laser diffraction/scattering method.

In addition, in the thermosetting paste disclosed herein, the content of the scaly Ag particles is set to 30 parts by weight or more when the total weight of the Ag particles is 100 parts by weight. This allows the resistance reduction effect of the scaly Ag particles to be properly exerted. From the viewpoint of further reducing the electrical resistance of the electrode after curing, the content of the scaly Ag particles is preferably 32 parts by weight or more, more preferably 35 parts by weight or more, even more preferably 37 parts by weight or more, and particularly preferably 40 parts by weight or more. On the other hand, in the thermosetting paste disclosed herein, the content of the scaly Ag particles relative to the total weight of the Ag particles is set to 80 parts by weight or less (preferably 79 parts by weight or less, more preferably 77 parts by weight or less, even more preferably 76 parts by weight or less, and particularly preferably 75 parts by weight or less). As will be described in detail later, this allows the adhesiveness improving effect of the spherical Ag particles to be properly exerted.

In addition, the scaly Ag particles preferably have an ignition loss (Ig-loss) of 0.5 wt% or less. This ignition loss is the mass loss ratio (%) when the Ag particles are heated from room temperature to 600 ° C., and can be measured in accordance with the weight loss and residue test method for chemical products specified in JIS K 0067: 1992. This ignition loss is an index showing the amount of organic components attached to the surface of the Ag particles. For example, the scaly Ag particles may have an organic dispersant applied to the particle surface to suppress the aggregation of the particles. However, this organic dispersant can be a factor that deteriorates the compatibility with the epoxy resin. In this case, the moldability of the paste is reduced, and the surface smoothness of the electrode after curing may be reduced. From this viewpoint, it is preferable that the ignition loss of the scaly Ag particles is 0.5 wt% or less (more preferably 0.48 wt% or less, even more preferably 0.44 wt% or less, and particularly preferably 0.42 wt% or less). On the other hand, the lower limit of the ignition loss of the scaly Ag particles is not particularly limited, and may be 0.1 wt% or more, 0.12 wt% or more, 0.15 wt% or more, or 0.17 wt% or more.

The tap density of the scaly Ag particles is preferably 3.6 g/ml or more, more preferably 3.8 g/ml or more, even more preferably 4 g/ml or more, and particularly preferably 4.2 g/ml or more. The tap density is an index indicating the bulk density in a state in which the voids formed in the powder naturally filled in the container are eliminated by tapping (light impact). It has been confirmed that when the tap density of the scaly Ag particles increases, the wettability between the Ag particles and the thermosetting component improves, improving the moldability of the paste. On the other hand, the upper limit of the tap density of the scaly Ag particles is not particularly limited, and may be 7 g/ml or less, 6 g/ml or less, or 5.7 g/ml or less. In this specification, the "tap density" is a measured value when the tapping conditions are tap height: 5 cm, tap speed: 100 times/min, and tapping number: 1000 times. This tap density can be measured in accordance with the metal powder tap density measurement method specified in JIS Z 2512:2012.

The specific surface area of the scaly Ag particles is preferably 0.3 m ² /g or more, more preferably 0.34 m ² /g or more, even more preferably 0.38 m ² /g or more, and particularly preferably 0.4 m ² /g or more. As the specific surface area of the scaly Ag particles increases, the contact area between the scaly Ag particles increases, so that the electrical resistance of the electrode after thermal curing tends to decrease. On the other hand, the specific surface area of the scaly Ag particles is preferably 0.65 m ² /g or less, more preferably 0.6 m ² /g or less, and particularly preferably 0.55 m ² /g or less. When the specific surface area of the scaly Ag particles is reduced, the aggregation of the scaly Ag particles in the paste before thermal curing can be suppressed. This can improve the moldability of the paste. In addition, the "BET specific surface area" in this specification is a value calculated based on the BET method in accordance with the "Method for measuring specific surface area of powder (solid) by gas adsorption" defined in JIS Z 8830:2013 (ISO9277:2010).

(B) Spherical Ag particles The spherical Ag particles are spherical or nearly spherical Ag particles. As described above, when the thermosetting paste disclosed herein is heated, the scale-like Ag particles float to the surface side of the electrode. At this time, the mixture of the spherical Ag particles and the thermosetting component becomes the main component on the bottom side of the electrode (the region on the side close to the substrate). This makes it easier for the Ag particles to be bonded to the substrate via the epoxy resin, thereby improving the adhesiveness of the electrode. The average aspect ratio of the spherical Ag particles is preferably 1.5 or less, more preferably 1.2 or less, and even more preferably 1.1 or less. This can further improve the adhesiveness of the electrode. On the other hand, the lower limit of the average aspect ratio of the spherical Ag particles is not particularly limited and may be 1 or more.

Next, in the thermosetting paste disclosed herein, the _D50 particle size of the spherical Ag particles is set to 1.5 μm or more. This prevents a plurality of spherical Ag particles from agglomerating with each other, and prevents a decrease in the contact area between the spherical Ag particles and the thermosetting component due to the formation of agglomerated particles. As a result, the adhesion of the electrode to the substrate can be further improved. From the viewpoint of further improving the adhesion of the electrode, the _D50 particle size of the spherical Ag particles is preferably 1.6 μm or more, more preferably 1.7 μm or more, even more preferably 1.8 μm or more, and particularly preferably 1.9 μm or more. On the other hand, the upper limit of the _D50 particle size of the spherical Ag particles is not particularly limited, and may be 2.5 μm or less, 2.4 μm or less, 2.3 μm or less, 2.2 μm or less, or 2.1 μm or less.

In addition, in the thermosetting paste disclosed herein, the BET specific surface area of the spherical Ag particles is set to 0.5 m ² /g or less. If the BET specific surface area of the spherical Ag particles becomes too large, the aggregation of the spherical Ag particles is promoted, and the fixing property of the electrode may be reduced. From the viewpoint of suppressing the aggregation of the spherical Ag particles, the BET specific surface area of the spherical Ag particles is preferably 0.48 m ² /g or less, more preferably 0.46 m ² /g or less, and particularly preferably 0.44 m ² /g or less. The lower limit of the BET specific surface area of the spherical Ag particles is not particularly limited. For example, the BET specific surface area of the spherical Ag particles may be 0.05 m ² /g or more, 0.1 m ² /g or more, 0.15 ^{m 2} /g or more, 0.2 m ² /g or more, 0.25 ^{m 2} /g or more, or 0.3 m ² /g or more.

In the thermosetting paste disclosed herein, as described above, the content of scaly Ag particles relative to the total weight of Ag particles is set to 80 parts by weight or less. That is, in the thermosetting paste disclosed herein, the content of spherical Ag particles relative to the total weight of Ag particles is 20 parts by weight or more. This allows the above-mentioned adhesiveness improving effect of the spherical Ag particles to be properly exhibited. The content of the spherical Ag particles is preferably 21 parts by weight or more, more preferably 23 parts by weight or more, even more preferably 24 parts by weight or more, and particularly preferably 25 parts by weight or more. This allows the adhesiveness improving effect of the spherical Ag particles to be properly exhibited.

The tap density of the spherical Ag particles is preferably 5 g/ml or more, more preferably 5.2 g/ml or more, even more preferably 5.4 g/ml or more, and particularly preferably 5.6 g/ml or more. It has been confirmed that as the tap density of the spherical Ag particles increases, the adhesion of the electrode improves. On the other hand, the upper limit of the tap density of the spherical Ag particles is not particularly limited, and may be 7 g/ml or less, 6 g/ml or less, or 5.6 g/ml or less.

The ignition loss (Ig-loss) of the spherical Ag particles is preferably 0.7 wt% or less, more preferably 0.68 wt% or less, even more preferably 0.67 wt% or less, and particularly preferably 0.66 wt% or less. As with the scaly Ag particles described above, the moldability of the paste tends to improve as the ignition loss (amount of attached organic components) decreases. On the other hand, the lower limit of the ignition loss of the spherical Ag particles is not particularly limited, and may be 0.1 wt% or more, 0.12 wt% or more, 0.15 wt% or more, or 0.17 wt% or more.

(C) Thermosetting component In this specification, the term "thermosetting component" refers to a concept that includes a thermosetting resin, a curing agent, and a curing accelerator. This thermosetting component is an organic compound (excluding a silane coupling agent, which will be described later) that contributes to the thermosetting of the thermosetting paste and remains on the electrode after curing. Hereinafter, the thermosetting component of the thermosetting paste disclosed herein will be described.

(C-1) Thermosetting resin The thermosetting paste disclosed herein contains an epoxy resin as the thermosetting resin. The epoxy resin is a resin having an epoxy group. By heating this epoxy resin at a predetermined temperature (for example, 200°C or higher), a crosslinked network in which the epoxy groups are bonded to each other is generated. This causes the thermosetting paste to thermally cure, so that an electrode can be formed on a substrate. In the thermosetting paste disclosed herein, a novolac type epoxy resin is used. First, examples of the novolac type epoxy resin include phenol novolac type epoxy resin, cresol novolac type epoxy resin, naphthol novolac type epoxy resin, naphthol-phenol co-condensed novolac type epoxy resin, and naphthol-cresol co-condensed novolac type epoxy resin. The thermosetting paste may contain two or more of these novolac type epoxy resins. In addition, there are epoxy resins that are liquid at 25°C (liquid epoxy resins) and epoxy resins that are solid at 25°C (solid epoxy resins). According to the inventor's experiments, it has been confirmed that, among the above-mentioned novolac type epoxy resins, the novolac type epoxy resin that is solid at 25°C improves the glass transition point of the electrode after thermal curing. This makes it possible to suppress deformation of the electrode in a high-temperature environment, thereby improving the high-temperature reliability of the electrode. The content of the novolac type epoxy resin can be determined based on the number of epoxy groups contained in the novolac type epoxy resin and the contents of the curing agent and curing accelerator described below.

(C-2) Curing Agent The curing agent is an organic compound having a reactive group that reacts with the thermosetting resin. In the thermosetting paste disclosed herein, the thermosetting component contains a curing agent. This makes it possible to prevent a decrease in adhesion due to poor curing. As described above, in the thermosetting paste disclosed herein, an epoxy resin is contained as the thermosetting resin, and therefore a curing agent that reacts with the epoxy group of the epoxy resin is used. An example of a curing agent that reacts with this epoxy group is a phenol-based curing agent. Specific examples of such phenol-based curing agents include novolac-type phenolic resins such as phenol novolac resin, cresol novolac resin, bisphenol novolac resin, and phenol-biphenyl novolac resin. Another example of the curing agent is a urea-based curing agent. Specific examples of such urea-based curing agents include dimethyl urea, trimethyl urea, ethyl dimethyl urea, cyclohexyl dimethyl urea, dichlorophenyl dimethyl urea, chloromethylphenyl dimethyl urea, methylphenyl dimethyl urea, methylphenyl dimethyl urea, and dimethylphenyl dimethyl urea. The curing agent may contain two or more of the above-mentioned components.

In addition, the content of the curing agent is preferably adjusted in relation to the number of epoxy groups of the epoxy resin and the number of reactive groups of the curing agent. For example, in the case of a phenol-based curing agent, the hydroxyl group in the molecule becomes a reactive group and reacts with the epoxy group of the epoxy resin. For this reason, it is preferable to add 30 hydroxyl equivalent parts or more (more preferably 40 hydroxyl equivalent parts or more) of the phenol-based curing agent to the epoxy equivalent (100 epoxy groups) of the epoxy resin. This makes it easier to thermally cure the epoxy resin. On the other hand, considering the disadvantage of remaining curing agent that does not contribute to the curing reaction, it is preferable to add the phenol-based curing agent in a ratio of 100 hydroxyl equivalent parts or less to the epoxy equivalent of the epoxy resin.

(C-3) Curing Accelerator The curing accelerator is an additive that accelerates the reaction between the curing agent and the thermosetting resin. In the thermosetting paste disclosed herein, the thermosetting component contains a curing accelerator, so that it is possible to reliably prevent a decrease in adhesiveness due to poor curing. Specific examples of the curing accelerator include guanidine-based curing accelerators and amine-based curing accelerators. For example, guanidine-based curing accelerators include dicyandiamide, 1-methylguanidine, 1-ethylguanidine, 1-cyclohexylguanidine, 1-phenylguanidine, 1-(o-tolyl)guanidine, dimethylguanidine, diphenylguanidine, trimethylguanidine, tetramethylguanidine, pentamethylguanidine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1-methylbiguanide, 1-ethylbiguanide, 1-n-butylbiguanide, 1-n-octadecylbiguanide, 1,1-dimethylbiguanide, 1,1-diethylbiguanide, 1-cyclohexylbiguanide, 1-allylbiguanide, 1-phenylbiguanide, and 1-(o-tolyl)biguanide. Examples of the amine-based curing accelerator include trialkylamines such as triethylamine and tributylamine, 4-dimethylaminopyridine, benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, and 1,8-diazabicyclo(5,4,0)-undecene. The curing accelerator may contain two or more of the above-mentioned components. The content of the curing accelerator is preferably 0.14 to 0.8 parts by weight, and more preferably 0.2 to 0.5 parts by weight, based on the total amount (100 parts by weight) of the epoxy resin.

(C-4) Total amount of thermosetting component And, the thermosetting paste disclosed herein contains 10 parts by weight or more of the above (C) thermosetting component with respect to the total weight (100 parts by weight) of the Ag particles. This can prevent a decrease in adhesiveness due to a shortage of the thermosetting component. From the viewpoint of further improving the fixation of the electrode, the content of the thermosetting component relative to the Ag particles is preferably 10.5 parts by weight or more, more preferably 11 parts by weight or more. On the other hand, if the content of the thermosetting component relative to the Ag particles is increased too much, the contact points between the Ag particles are reduced, making it difficult to form a conductive path in the electrode. From this viewpoint, in the thermosetting paste disclosed herein, the content of the thermosetting component relative to the Ag particles is set to 15 parts by weight or less. From the viewpoint of further reducing the electrical resistance of the electrode, the content of the thermosetting component is preferably 14.5 parts by weight or less, particularly preferably 14 parts by weight or less.

(D) Silane coupling agent The silane coupling agent is an additive that bonds to both Ag particles and epoxy resin, improving the adhesiveness of the electrode. Specifically, the silane coupling agent is an organosilicon compound having a functional group X that reacts and bonds with Ag particles, and a functional group Y that reacts and bonds with epoxy resin. The functional group X that bonds with Ag particles includes an alkoxy group, an acetoxy group, and the like. These functional groups X generate silanols by hydrolysis, and react and bond with Ag particles. Meanwhile, the thermosetting paste disclosed here uses a sulfide-based silane coupling agent. This sulfide-based silane coupling agent has a polysulfide group as the functional group Y that reacts and bonds with epoxy resin. According to the inventor's experiments, it has been confirmed that this sulfide-based silane coupling agent has a heterogeneous effect of reducing the resistance of the electrode after curing, in addition to the general effect of improving adhesiveness. It is expected that this resistance reduction effect occurs when the sulfide-based silane coupling agent increases the contact points between Ag particles.

Examples of sulfide-based silane coupling agents include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, and bis(3-triethoxysilylpropyl)tetrasulfide. Examples of the sulfide-based silane coupling agents include bis(2-triethoxysilylpropyl) disulfide, bis(4-triethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl) disulfide, bis(2-trimethoxysilylethyl) disulfide, bis(4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide. One of these sulfide-based silane coupling agents may be used alone, or two or more may be mixed. The silane coupling agent may contain a silane coupling agent other than the sulfide-based silane coupling agent, as long as it does not significantly impart the effects of the technology disclosed herein (particularly the reduction in potential resistance).

The thermosetting paste disclosed herein contains 0.1 parts by weight or more of a sulfide-based silane coupling agent relative to the total weight (100 parts by weight) of the Ag particles. This allows the resistance reduction effect and fixation improvement effect of the sulfide-based silane coupling agent to be appropriately generated. The content of the sulfide-based silane coupling agent relative to the total weight of the Ag particles is preferably 0.11 parts by weight or more, more preferably 0.12 parts by weight or more, even more preferably 0.13 parts by weight or more, and particularly preferably 0.15 parts by weight or more. This allows the formation of an electrode with lower electrical resistance and better adhesion to the substrate. On the other hand, if the content of the sulfide-based silane coupling agent is increased too much, the content of the Ag particles will relatively decrease, and there is a risk that the electrical resistance will increase instead. From this perspective, in the thermosetting paste disclosed herein, the content of the sulfide-based silane coupling agent relative to the Ag particles is set to 0.6 parts by weight or less. In addition, from the viewpoint of further reducing the electrical resistance of the electrode, the content of the sulfide-based silane coupling agent is preferably 0.5 parts by weight or less, more preferably 0.45 parts by weight or less, even more preferably 0.4 parts by weight or less, and particularly preferably 0.38 parts by weight or less.

(E) Organic Solvent The organic solvent is a liquid medium that disperses Ag particles and dissolves the thermosetting component and the silane coupling agent. The organic solvent can be any conventionally known organic solvent that can be used in a conductive paste (typically a thermosetting paste) without any particular restrictions, and is not a factor that limits the technology disclosed herein. Examples of this organic solvent include alcohol-based solvents such as terpineol, texanol, dihydroterpineol, and benzyl alcohol; glycol-based solvents such as ethylene glycol and diethylene glycol; glycol ether-based solvents such as diethylene glycol monoethyl ether and butyl carbitol (diethylene glycol monobutyl ether); ester-based solvents such as isobornyl acetate, ethyl diglycol acetate, butyl glycol acetate, butyl diglycol acetate, butyl cellosolve acetate, and butyl carbitol acetate (diethylene glycol monobutyl ether acetate); hydrocarbon-based solvents such as toluene and xylene; and mineral spirits. In consideration of the storage stability of the conductive paste, the boiling point of the organic solvent is preferably about 200° C. or higher.

As mentioned above, the organic solvent is a component that is removed by heat treatment. Therefore, from the viewpoint of improving the performance of the electrode after thermal curing (electrical resistance, adhesiveness, high-temperature reliability, etc.), the content ratio of the organic solvent in the thermosetting paste is not limited. It is preferable that the content ratio of the organic solvent is appropriately adjusted so that an electrode of the desired shape is formed, taking into consideration the means for printing (applying) the paste. For example, when the total weight of the paste is 100 parts by weight, the content of the organic solvent is preferably 2 parts by weight to 30 parts by weight, and more preferably 4 parts by weight to 20 parts by weight.

In addition, the thermosetting paste disclosed herein is preferably controlled in terms of paste moldability by controlling the Casson yield value. The Casson yield value is the shear stress when the shear rate is set to zero in viscosity measurement using a B-type viscometer. As the Casson yield value increases, the stress required when the shape of the paste begins to change increases. A paste with a small Casson yield value has excellent leveling properties after printing (application), and therefore can form an electrode with good dimensional properties. From this perspective, the Casson yield value of the thermosetting paste is preferably 120 Pa or less, more preferably 100 Pa or less, and even more preferably 80 Pa or less. On the other hand, the lower limit of the Casson yield value is not particularly limited, and may be 10 Pa or more, or may be 20 Pa or more. The Casson yield value (paste moldability) can be adjusted by the ignition loss of the Ag particles, the tap density of the scaly Ag particles, the content of the thermosetting component, the structure (type) of the thermosetting component (e.g., epoxy resin), the viscosity of the organic solvent, the content of the organic solvent, etc.

The above describes the thermosetting paste disclosed herein. Note that the thermosetting paste disclosed herein is not limited to one containing only the components described above. In other words, the thermosetting paste may further contain conventionally known additives that can be used in conductive pastes (typically, thermosetting pastes) to the extent that the effect of the technology disclosed herein is not significantly impaired.

2. Uses of Thermosetting Paste Next, a method for manufacturing an electronic component using the thermosetting paste disclosed herein will be described. In this method for manufacturing an electronic component, for example, the following steps S1 to S4 are performed.
Step S1: Preparation of substrate; Step S2: Preparation of thermosetting paste; Step S3: Printing step; Step S4: Heating step

(1) Preparation of Substrate In this step, a substrate on which the thermosetting paste is printed is prepared. The type of substrate is not particularly limited, and any conventionally known substrate for electronic components can be used without any particular restriction. The thermosetting paste disclosed herein is cured by heat treatment at a low temperature (200° C. or less) to form an electrode. In view of this, the manufacturing method disclosed herein is particularly suitable for use in the manufacture of electronic components that use substrates with low heat resistance. Examples of such substrates include substrates made of resin, paper, cloth, etc.

(2) Preparation of Thermosetting Paste In this step, the thermosetting paste having the above-mentioned configuration is prepared. The detailed configuration of the thermosetting paste is omitted because it is redundant. This step is not particularly limited as long as a thermosetting paste having the desired components can be prepared. That is, the thermosetting paste may be prepared by mixing the above-mentioned components, or a separately prepared thermosetting paste may be purchased.

(3) Printing Step In this step, the thermosetting paste disclosed herein is printed on a substrate. The specific printing method in this step is not particularly limited. For example, a conventionally known printing method such as screen printing or dip printing can be adopted without any particular limitation. The thickness of the paste printed in this step is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, and particularly preferably 20 μm or more. By printing a paste of a certain thickness or more in this way, an electrode with excellent conductivity can be formed. The printing thickness of the paste is preferably 150 μm or less, more preferably 100 μm or less, even more preferably 75 μm or less, and particularly preferably 50 μm or less. This makes it easy to volatilize the organic solvent and remove it from the paste in the heating step described later, thereby suppressing poor molding of the electrode.

(4) Heating Step In this step, the thermosetting paste printed on the substrate is heated. This causes the thermosetting paste to be thermally cured, and an electrode of a desired shape is formed on the substrate. In this step, it is preferable to carry out a first heating treatment (drying treatment) at a temperature at which the organic solvent volatilizes and the epoxy resin does not thermally cure, and a second heating treatment (thermal curing treatment) at a temperature at which the epoxy resin thermally cures, in stages. This allows the epoxy resin to be thermally cured after forming a high-density dry film in which the organic solvent has been sufficiently volatilized. As a result, the number of contact points between the Ag particles is further increased, and the electrical resistance of the electrode after curing can be further reduced. Specifically, the heating temperature in the first heating treatment (drying treatment) is preferably 80°C to 180°C, more preferably 100°C to 150°C. The heating time in the first heating treatment (drying treatment) is preferably 5 minutes to 60 minutes, more preferably 10 minutes to 30 minutes. On the other hand, the heating temperature in the second heating treatment (thermal curing treatment) is preferably 150° C. to 250° C., and more preferably 180° C. to 230° C. The heating time in the second heating treatment (thermal curing treatment) is preferably 15 minutes to 90 minutes, and more preferably 30 minutes to 60 minutes.

Here, when the thermosetting paste disclosed herein is used, the scaly Ag particles rise to the surface side of the paste in the heating process. As a result, the scaly Ag particles can be densely arranged on the surface side of the electrode after heat curing, thereby reducing the electrical resistance. In addition, in the thermosetting paste disclosed herein, the _D50 particle size of the scaly Ag particles is 4 μm or more, so that the scaly Ag particles are more likely to rise. As a result, the electrical resistance of the electrode after curing can be further reduced. As a result of the rise of the scaly Ag particles, the mixture of the spherical Ag particles and the thermosetting component becomes the main component on the bottom side of the electrode. As a result, the adhesion of the electrode to the substrate can be improved. In addition, the spherical Ag particles of the thermosetting paste disclosed herein have a _D50 particle size of 1.5 μm or more and a BET specific surface area of 0.5 m ² /g or less. As a result, the aggregation of the spherical Ag particles can be suppressed, so that the adhesion of the electrode to the substrate can be more appropriately improved. In the thermosetting paste disclosed herein, the content of the scaly Ag particles relative to the total weight of the Ag particles is set to 30 parts by weight or more and 80 parts by weight or less, thereby making it possible to achieve a high level of both the resistance reducing effect of the scaly Ag particles and the adhesiveness improving effect of the spherical Ag particles.

In addition, the thermosetting paste disclosed herein uses a novolac type epoxy resin that is solid at 25°C as the thermosetting resin. An electrode containing an epoxy resin of this configuration has a high glass transition point after thermal curing, and therefore has excellent high-temperature reliability. In the thermosetting paste disclosed herein, the content of the thermosetting component relative to the total weight of the Ag particles is set to 10 parts by weight or more and 15 parts by weight or less. This makes it possible to sufficiently improve the adhesiveness while suppressing an increase in electrical resistance. In addition, the thermosetting paste disclosed herein contains a sulfide-based silane coupling agent. The sulfide-based silane coupling agent not only improves the adhesiveness of the electrode after curing, but also contributes to reducing the electrical resistance. In the thermosetting paste disclosed herein, the content of the sulfide-based silane coupling agent relative to the total weight of the Ag particles is set to 0.1 parts by weight or more and 0.6 parts by weight or less. This makes it possible to achieve a well-balanced effect of reducing resistance and improving adhesiveness by the sulfide-based silane coupling agent.

As described above, the thermosetting paste disclosed herein makes it possible to manufacture high-performance electronic components that have excellent electrical resistance, high-temperature reliability, and adhesion properties.

[Test Example]
Test examples relating to the technology disclosed herein will be described below. Note that the technology disclosed herein is not limited to the test examples described below.

First Test
1. Components of Thermosetting Paste In this test example, 29 types of thermosetting pastes (Examples 1 to 12 and Comparative Examples 1 to 17) were prepared. Each of the thermosetting pastes prepared in this test contains scaly Ag particles, spherical Ag particles, a thermosetting component, a silane coupling agent, an organic solvent, a curing agent, and a curing accelerator. The specific components are described below.

(1) Scaly Ag Particles In this test, any one of the seven types of Ag particles shown in Table 1 was used as the scaly Ag particles. The type and content of the scaly Ag particles used in each example are shown in Tables 3 to 5 below.

(2) Spherical Ag particles In this test, one of the two types of Ag particles shown in Table 2 was used as the spherical Ag particles. The type and content of the spherical Ag particles used in each example are shown in Tables 3 to 5 below.

(3) Thermosetting Component (3-1) Epoxy Resin In this test, the following eight types of epoxy resins were used as thermosetting resins. The types of epoxy resins used in each example are shown in Tables 3 to 5 below.
[Type of epoxy resin]
Resin 1: Cresol novolac type epoxy resin (solid at 25°C)
Epoxy equivalent: 214 g/eq.
Resin 2: Phenol novolac type epoxy resin (solid at 25°C)
Epoxy equivalent: 175 g/eq.
Resin 3: Phenol novolac type epoxy resin (liquid at 25°C)
Epoxy equivalent: 175 g/eq.
Resin 4: Bisphenol F type epoxy resin (liquid at 25°C)
Epoxy equivalent: 170 g/eq.
Resin 5: Bisphenol A type epoxy resin (solid at 25°C)
Epoxy equivalent: 2100 g/eq.
Resin 6: Bisphenol F type epoxy resin (solid at 25°C)
Epoxy equivalent: 2145 g/eq.
Resin 7: Dicyclopentadiene type epoxy resin (solid at 25°C)
Epoxy equivalent: 259 g/eq.
Resin 8: Naphthalene type epoxy resin (solid at 25°C)
Epoxy equivalent: 165 g/eq.

(3-2) Other thermosetting components In this test, a curing agent and a curing accelerator were used as the thermosetting components other than the epoxy resin. Novolac phenolic resin and dichlorophenyl dimethyl urea were used as the curing agents. The amount of novolac phenolic resin added was set to 3.2 parts by weight, and the amount of dichlorophenyl dimethyl urea added was set to 0.18 parts by weight when the total amount of Ag particles was 100 parts by weight. Dicyandiamide was used as the curing accelerator. The amount of the curing accelerator (dicyandiamide) added was set to 0.28 parts by weight when the total amount of Ag particles was 100 parts by weight. The content of the thermosetting components in each example (total content of epoxy resin, curing agent, and curing accelerator) is shown in Tables 3 to 5 below.

(4) Silane coupling agent In this test, the following four types of silane coupling agents were prepared as the silane coupling agents. The types and contents of the silane coupling agents used in each example are shown in Tables 3 to 5 below.
[Types of silane coupling agents]
SC1: Bis(3-triethoxysilylpropyl)tetrasulfide SC2: Bis(3-triethoxysilylpropyl)disulfide SC3: 3-glycidoxypropyltrimethoxysilane SC4: 3-aminopropyltriethoxysilane

(5) Organic Solvent In this test, butyl carbitol was used as the organic solvent. The content of the organic solvent (butyl carbitol) was set to 7.8 parts by weight when the total amount of Ag particles was 100 parts by weight.

2. Preparation procedure of paste In this test, first, an organic solvent, an epoxy resin, and a novolac type phenolic resin (hardening agent) were mixed. Then, this mixture was heated at 100°C for 24 hours and then cooled to room temperature. In this way, an organic vehicle in which the epoxy resin and the novolac type phenolic resin were dissolved in the organic solvent was obtained. Next, scaly Ag particles, spherical Ag particles, a silane coupling agent, dichlorophenyl dimethyl urea (hardening agent), and dicyandiamide (hardening accelerator) were added to this organic vehicle, and kneaded with a three-roll mill. In this way, the thermosetting paste of each example was prepared.

3. Evaluation Test In this test, electrodes were formed on a substrate using the thermosetting paste of each example, and then the electrical resistance, adhesiveness, and high-temperature reliability of the electrodes were evaluated. Specific explanations are given below.

(1) Evaluation of Electrical Resistance In this evaluation, first, the 29 types of thermosetting pastes described above were printed on the surface of a substrate by screen printing. The substrate used in this test was a glass substrate (Matsunami Glass Industry Co., Ltd.) with an upper surface area of 20 mm x 20 mm. In addition, in the screen printing, a metal mask with a thickness of 50 μm and an opening of 20 mm x 20 mm was used, and a metal squeegee was used, and the printing speed was set to 30 mm/sec. In this test, the printing thickness of the paste was set to about 25 μm, and a square-shaped printing film was formed in a plan view.

Next, the substrate after the paste printing was subjected to a first heating treatment (drying treatment) at 130°C for 15 minutes. This resulted in the formation of a dry film in which the organic solvent had been removed from the paste. Then, a second heating treatment (resin curing treatment) was performed at 180°C for 60 minutes to thermally cure the epoxy resin in the dry film.

In this evaluation, the electrical resistance of the electrode after thermal curing was evaluated. The specific evaluation procedure is as follows. First, the film thickness of the electrode was measured with a surface roughness meter (Surfcom manufactured by Tokyo Seimitsu Co., Ltd.). Next, the sheet resistance of the electrode after thermal curing was measured by a four-probe method using a resistivity meter (model: Loresta GX MCP-T700) manufactured by Mitsubishi Chemical Analytech Co., Ltd. Then, the electrical resistance (Ω·cm) of the electrode of each example was measured by multiplying the film thickness and the sheet resistance. In this test, examples in which the electrical resistance was 1×10 ⁻⁴ Ω·cm or less were evaluated as “◎”, examples in which the electrical resistance was more than 1×10 ⁻⁴ Ω·cm and less than 5×10 ⁻⁴ Ω·cm were evaluated as “○”, and examples in which the electrical resistance was 5×10 ⁻⁴ Ω·cm or more were evaluated as “×”.

(2) Evaluation of Adhesion In this evaluation, the adhesion of the electrode after thermal curing was evaluated. The specific evaluation procedure is as follows. First, the 29 types of thermosetting paste described above were printed on the surface of the substrate using screen printing. The printing conditions at this time were set to the same conditions as those in "(1) Evaluation of Electrical Resistance" above. Next, an alumina chip having a size of 2 mm x 2 mm was placed on the paste printed (applied) on the glass substrate, and a first heat treatment (drying treatment) was performed at 130°C for 15 minutes. Then, a second heat treatment (resin curing treatment) was performed at 180°C for 60 minutes to form a cured film (electrode) with the alumina chip adhered to the upper surface. Then, a load was applied to the alumina chip using a 4000 universal bond tester manufactured by Nordson DAGE, and the strength (peel strength) when the chip peeled off was measured. This measured the peel strength (N/mm ² ) of the electrode of each example. In this test, examples in which the peel strength was 20 N/mm2 or ^more were evaluated as "◎", examples in which the peel strength was less than 20 N/ ^mm2 and more than 10 N/ ^mm2 were evaluated as "○", and examples in which the peel strength was 10 N/mm2 or ^less were evaluated as "×".

(3) Evaluation of Glass Transition Temperature In this evaluation, the glass transition temperature was measured. The specific evaluation procedure is as follows. First, the paste was applied onto a resin sheet made of PTFE (polytetrafluoroethylene) using an applicator with a gap set to 150 μm. Next, a first heat treatment (drying treatment) was performed at 130° C. for 15 minutes, and then a second heat treatment (resin curing treatment) was performed at 180° C. for 60 minutes to obtain a cured film. Next, the cured film after the heat treatment was peeled off from the resin sheet and cut into a size of 1 cm x 4 cm. Then, the glass transition temperature of the cured film was measured using a viscoelasticity measuring device (DMA7100) manufactured by Hitachi High-Tech Science Co., Ltd. In addition, in the measurement of the glass transition temperature, the temperature was raised to 300° C. at a heating rate of 1° C./min. And, the examples with a glass transition temperature of 200° C. or higher were evaluated as "◎" because it is understood that the durability against long-term environmental changes is improved when used in electrodes of electronic components. Moreover, examples in which the temperature was less than 200° C. and more than 150° C. were evaluated as "◯", and examples in which the temperature was 150° C. or less were evaluated as "×".

The results of each of the above evaluations are shown in Tables 3 to 5 below.

As shown in Tables 3 to 5, in Examples 1 to 12, electronic components were produced that were excellent in three performances: electrical resistance, adhesiveness, and high-temperature reliability. On the other hand, in Comparative Examples 1 to 17, it was confirmed that at least one of electrical resistance, adhesiveness, and high-temperature reliability was deteriorated. As a result of comparing and examining each example, it was confirmed that the _D50 particle size of the scaly Ag particles, the content of the scaly Ag particles, the structure of the silane coupling agent, the content of the silane coupling agent, and the content of the thermosetting component were affected by the electrical resistance of the electrode after curing. It was also confirmed that the _D50 particle size of the spherical Ag particles, the content of the spherical Ag particles, the content of the thermosetting component, the structure of the silane coupling agent, and the content of the silane coupling agent were affected by the adhesiveness of the electrode. It was also confirmed that the structure of the epoxy resin and the state of the epoxy resin at room temperature were affected by the high-temperature reliability of the electronic components.

<Second test>
In this test, the paste moldability and the silver exposure rate after thermal curing were evaluated for Examples 1 to 12 which showed excellent electrode performance in the first test.

(1) Evaluation of rheological properties In this evaluation, the Casson yield values of the pastes of Examples 1 to 12 were measured, and the paste moldability was evaluated based on the measurement results. In this test, examples in which the Casson yield value was 120 Pa or less were evaluated as "◎", and examples in which the Casson yield value was more than 120 Pa were evaluated as "×".

(2) Evaluation of Silver Exposure Rate In this evaluation, cured films (electrodes) were prepared using the pastes of Examples 1 to 12 according to the same procedure as in "(1) Evaluation of Electrical Resistance" of the first test. Then, the silver exposure rate on the surface of the prepared electrode was measured. The specific evaluation procedure is as follows. First, the surface of the electrode after thermal curing was observed (for example, at a magnification of 2,000 times) using a field emission scanning electron microscope (FE-SEM) to obtain an observation image. Next, the area of the silver particles in the observation image was calculated. Then, the silver exposure rate (%) on the surface of the electrode of each example was measured by dividing the area of the silver particles by the area of the observation range. Then, in this test, examples in which the silver exposure rate was 70% or more were evaluated as "◎", examples in which the silver exposure rate was less than 70% and more than 60% were evaluated as "○", and examples in which the silver exposure rate was 60% or less were evaluated as "×".

The results of each of the above evaluations are shown in Table 6 below.

As shown in Table 6, in addition to the above three performances, it was confirmed that Examples 1 to 10 have excellent paste moldability. As a result of comparing Examples 1 to 10 with Examples 11 and 12, it was found that the moldability (Casson's yield value) of the thermosetting paste is affected by the tap density and ignition loss (Ig-loss) of the scaly Ag particles. In addition, it was confirmed that Examples 1 to 12 all have excellent silver exposure rates. From this, it is expected that the silver exposure rate of the electrode is influenced by the _D50 particle size of the scaly Ag particles, the content of the scaly Ag particles, the structure of the silane coupling agent, the content of the silane coupling agent, and the content of the thermosetting component, as well as the electrical resistance measured in the first test.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples exemplified above.

Claims (9)

At least, the composition includes (A) scaly Ag particles, (B) spherical Ag particles, (C) a thermosetting component, (D) a silane coupling agent, and (E) an organic solvent;
The (A) scaly Ag particles are
In a volume-based particle size distribution based on a laser diffraction/scattering method, the _D50 particle size, which corresponds to a cumulative 50% from the smallest particle size, is 4 μm or more and 10 μm or less, and
The content of Ag particles is 30 parts by weight or more and 80 parts by weight or less when the total weight of the Ag particles is 100 parts by weight,
The (B) spherical Ag particles are
The _D50 particle size is 1.5 μm or more and 2.5 μm or less, and
The BET specific surface area is 0.5 m ² /g or less;
The (C) thermosetting component is
A novolac type epoxy resin that is solid at 25° C., a curing agent, and a curing accelerator,
the content of the Ag particles is 10 parts by weight or more and 15 parts by weight or less when the total weight of the Ag particles is 100 parts by weight,
The silane coupling agent (D) is
A silane coupling agent having a polysulfide group,
The content of the Ag particles is 0.1 parts by weight or more and 0.6 parts by weight or less when the total weight of the Ag particles is 100 parts by weight.
A thermosetting paste comprising: The thermosetting paste according to claim 1, wherein the (A) scaly Ag particles have an average aspect ratio of more than 1.5 and not more than 10. The thermosetting paste according to claim 1 or 2, wherein the (A) scaly Ag particles have an ignition loss (Ig-loss) of 0.5 wt% or less when heated from room temperature to 600°C. The thermosetting paste according to any one of claims 1 to 3, wherein the (A) scaly Ag particles have a tap density of 4 g/ml or more and 7 g/ml or less. The thermosetting paste according to any one of claims 1 to 4, wherein the spherical Ag particles (B) have an average aspect ratio of 1 or more and 1.5 or less. The thermosetting paste according to any one of claims 1 to 5, wherein the (B) spherical Ag particles have a tap density of 5 g/ml or more and 7 g/ml or less. The thermosetting paste according to any one of claims 1 to 6, wherein the novolac type epoxy resin includes at least one selected from the group consisting of phenol novolac type epoxy resin, cresol novolac type epoxy resin, naphthol novolac type epoxy resin, naphthol-phenol co-condensed novolac type epoxy resin, and naphthol-cresol co-condensed novolac type epoxy resin. The (D) silane coupling agent is, for example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(2 - triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)trisulfide, 8. The thermosetting paste according to claim 1, comprising at least one selected from the group consisting of bis(3-trimethoxysilylpropyl) disulfide, bis(2-trimethoxysilylethyl) disulfide, bis(4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide. The thermosetting paste according to any one of claims 1 to 8, having a Casson yield value of 120 Pa or less at 25°C.