JP2017228362A - Conductive paste - Google Patents

Abstract

Disclosed is a conductive paste excellent in applicability and sinterability.
The conductive paste of the present invention includes conductive particles, a resin, and a dispersion medium, and is 1 [1 / s] or more and 100 [1] in a temperature environment of 25 ° C. / S] or less, there is a region where the viscosity increases as the shear rate increases.
[Selection figure] None

Description

  The present invention relates to a conductive paste.

  Until now, conductive pastes have been used for various purposes. One of them is the use for electronic devices such as solar cells in which electrodes and wirings are formed.

  Patent Document 1 describes an example in which a conductive paste is used for a solar battery cell. According to this document, it is described that the light receiving surface electrode and the back surface silver electrode in the solar battery cell are formed by wiring made of silver paste.

  As a method for forming the wiring described in this document, the following method using a silver paste is used. That is, a silver paste containing silver particles, a glass component, an organic binder, and an organic solvent is applied by screen printing, dried, and then sintered at a temperature of 800 ° C. to 900 ° C. for the purpose of melting the glass component. It is described that the molten glass component enhances the adhesion between the sintered silver particles and the substrate. On the other hand, the organic binder and organic solvent in the silver paste are volatilized during sintering.

JP 2014-33175 A

  As a result of investigation by the inventors, the conductive paste described in the above literature has room for improvement in terms of both low-temperature sinterability and applicability.

Hereinafter, the results studied by the present inventors will be described. First, since the conductive paste described in the above literature contains a glass component, a sintering process at a high temperature is required. For this reason, the fire-through property is required for the substrate surface in the solar battery cell. Therefore, the base material which can form the wiring which consists of an electroconductive paste of the said literature was limited.
Therefore, in order to enhance the versatility of the base material, studies were made on conductive paste that does not require a high-temperature sintering process.
As a result of intensive studies by the inventor, the following further findings were obtained.
(1) Based on the premise that the glass component is not included, a resin that has characteristics that remain after sintering (sintering) of conductive particles and that assists in sintering of the conductive particles is appropriately selected. By doing so, it was found that good sinterability can be realized under low temperature conditions.
(2) Further, when the conductive paste is used for wiring or the like, the present inventor considered that it is necessary to improve the form retention of the coated film of the conductive paste from the viewpoint of manufacturing stability. From various experiments, it was found that there is a relationship between the viscosity characteristics of the conductive paste and the form retention of the coating film.
(3) Detailed investigations were made on the viscosity characteristics of the conductive paste having the resin. As a result, in a predetermined shear rate region, according to the increase in the shear rate, by controlling so that there is a region where the viscosity increases, the form retention of the coating film made of conductive paste can be highly realized, It has been found that the applicability can be improved.

  As a result of more specific investigation based on the findings of (1) to (3), the conductive paste having the resin has a value of 1 [1 / s] or more and 100 [1 / s] or less. When there is a region where the viscosity increases in accordance with an increase in the shear rate in a predetermined shear rate region, it becomes possible to achieve both low-temperature sinterability and applicability, thereby completing the present invention. It came.

That is, according to the present invention,
Conductive particles;
Resin,
A conductive paste containing a dispersion medium,
Provided is a conductive paste in which in a shear rate region of 1 [1 / s] or more and 100 [1 / s] or less in a temperature environment of 25 ° C., there is a region where the viscosity increases as the shear rate increases. Is done.

  ADVANTAGE OF THE INVENTION According to this invention, the electrically conductive paste excellent in low temperature sintering property and applicability | paintability is provided.

It is sectional drawing which shows the structure of the photovoltaic cell of this embodiment.

<Conductive paste>
An outline of the conductive paste according to this embodiment will be described.
The conductive paste according to the present embodiment includes conductive particles, a resin, and a dispersion medium. In the conductive paste, in a temperature range of 25 ° C., in a shear rate region of 1 [1 / s] or more and 100 [1 / s] or less, there is a region where the viscosity increases as the shear rate increases. Can exist.

  The present inventor has come to consider that it is important to achieve both sinterability and applicability when a wiring is formed using a conductive paste by an application method such as screen printing. The applicability in the present embodiment can be improved by increasing the form retainability. Such form retainability means, for example, that a predetermined form can be retained in the wiring on which the conductive paste is printed, and there is little variation in the form. Moreover, manufacturing stability can also be improved by improving the form retainability of an electrically conductive paste.

As a result of the study of the sinterability and applicability by the present inventors, the following knowledge was obtained.
First, good sintering under low temperature conditions by appropriately selecting a resin that remains after sintering (sintering) of the conductive particles and has a characteristic that assists the sintering of the conductive particles. It has been found that sex can be realized.

  Further, as a result of investigation by the present inventor, it has been found from various experiments that there is a relationship between the viscosity characteristics of the conductive paste and the form retention of the coating film.

  Based on these findings, detailed investigation was made on the viscosity characteristics of the conductive paste having the resin. As a result of diligent research, we have achieved high form retention of the coating film made of conductive paste by controlling so that there is a region where the viscosity increases as the shear rate increases in a given shear rate region. It was found that it was possible.

Although the detailed mechanism is not clear, it can be considered as follows.
First, a range corresponding to the shear rate of the coating film during the coating process is specified and set as a predetermined shear rate region. By using the viscosity in a predetermined shear rate region as an index, it is considered that the state (for example, viscosity characteristics) of the coating film of the conductive paste at the time of coating can be evaluated.
And knowledge which shows the relation between the viscosity behavior of the conductive paste including the resin and the state of the coating film (for example, the form) in the predetermined shear rate region by using such a new evaluation index. Can be obtained.
In other words, by using an index that can be used as an alternative to evaluating the viscosity characteristics of conductive paste at the time of application, the viscosity characteristics that viscosity increases in a predetermined shear rate region are adjusted based on experimental results that show the relationship between viscosity behavior and morphology. By doing so, it is considered that the shape retention of the coating film can be realized to a high degree.

  In such viscosity control, for example, by increasing dispersibility in the conductive paste, it is possible to stably control the viscosity characteristics of the conductive paste. For example, in the present embodiment, the viscosity increasing behavior of the conductive paste can be stably controlled by employing a composition that enhances dispersibility and using conductive particles having a high filling rate described later.

  As described above, the conductive paste of this embodiment can appropriately select a resin remaining after sintering and can form a region where the viscosity increases in a predetermined shear rate region. Coexistence can be realized.

In the conductive paste of the present embodiment, since a resin having a characteristic that assists the sintering of the conductive particles is appropriately selected, it is possible to further reduce the resistance.
Although the detailed mechanism is not clear, by selecting an appropriate resin, the conductive particles can be easily moved because (i) the melt viscosity of the resin is kept low when sintering the conductive particles. Or (ii) It can be considered that sintering can be promoted because a shrinking resin can create a state of pressing metal particles against each other.

  Therefore, the conductive particles of this embodiment cause sintering by heat treatment to form a particle connection structure. That is, the specific resistance of the cured body of the conductive paste of the present embodiment can be kept low. In other words, in the present embodiment, the specific resistance of the cured body of the conductive paste is within the following range means that the sintering of the conductive particles proceeds sufficiently to obtain a desired low resistance. means. In the present embodiment, the lower limit value of the specific resistance of the cured body may be, for example, 1 μΩ · cm or more, 2 μΩ · cm or more, or 4 μΩ · cm or more. Thereby, the electrically conductive paste excellent in low resistance is obtained. Further, the upper limit value of the specific resistance of the cured body is, for example, preferably 20 μΩ · cm or less, more preferably 15 μΩ · cm or less, and further preferably 11 μΩ · cm or less. Thereby, the yield of an electrically conductive paste can be raised.

  Hereinafter, each component of the conductive paste according to the present embodiment will be described.

(Conductive particles)
The conductive particles according to this embodiment will be described.
The conductive particles of the present embodiment cause sintering by heat treatment to form a particle connection structure.

  In the present embodiment, the conductive particles mean metal particles composed of one or more metal atoms selected from the group consisting of Ag (silver), Au (gold), and Cu (copper), for example. . Among these, the conductive particles are preferably silver particles or copper particles, and more preferably silver particles, from the viewpoint of low resistance.

  The purity of the metal of the conductive particles is not particularly limited, but a high purity is preferable, for example, 95% or more is more preferable, 98% or more is more preferable, and 99% or more is particularly preferable. For example, the conductive particles which are silver particles may contain a trace amount of metal other than silver which is the main component (showing the above purity) as long as the object of the present invention is not impaired. Examples of such metals include copper, iron, aluminum, zinc, tin, gold, nickel and the like. Further, the conductive particles can contain, for example, a non-metallic component for the purpose of promoting sintering or reducing the cost. In addition, the electroconductive particle of this embodiment accept | permits that the impurity mixed unavoidable in the manufacturing process is contained.

The electroconductive particle of this embodiment can contain carbon as a nonmetallic component, for example. The carbon contained in the conductive particles functions as a sintering aid when sintering occurs in the conductive particles. For this reason, it becomes possible to improve the sinterability of electroconductive particle. Here, the case where the conductive particles contain carbon includes the case where the conductive particles are contained inside the conductive particles and the case where the conductive particles are physically or chemically adsorbed on the surface of the conductive particles.
As an example of the case where the conductive particles contain carbon, a mode in which a lubricant containing carbon is attached to the conductive particles can be mentioned. Examples of such lubricants include higher fatty acids, higher fatty acid metal salts, higher fatty acid amides, and higher fatty acid esters. The content of the lubricant is preferably 0.01% by mass or more and 5% by mass or less with respect to the entire conductive particles. This makes it possible to suppress a decrease in thermal conductivity while effectively functioning carbon as a sintering aid.

  In the conductive particles of this embodiment, the particle connection structure formed by causing sintering by heat treatment may be determined from, for example, a cross-sectional view obtained with a scanning electron microscope, but a method using X-ray diffraction Can be determined. Specifically, a conductive film is prepared by using a paste in which metal powder is dispersed in an organic dispersion medium (butyl carbitol) at a concentration of 90 wt% and drying the dispersion medium at 100 ° C. for 10 minutes. The crystallite diameter is d1, and the crystallite diameter after heat-treating the coating film at 250 ° C. for 60 minutes is d2. When the ratio (d2 / d1) of these crystallite diameters is 1.1 or more and d1 is 15.0 nm or more, it can be determined that the conductive particles have the above-described particle connection structure. Here, the crystallite diameter can be evaluated using, for example, an X-ray diffractometer (XRD), and measured using a peak at 2Θ = 38 ° ± 0.2 of a diffraction chart derived from silver. Can do. Moreover, a slide glass can be used as a base material which forms a coating film.

For example, the lower limit value of the average particle diameter (D ₅₀ ) of the conductive particles of the present embodiment is preferably 0.5 μm or more, more preferably 0.6 μm or more, and further preferably 0.8 μm or more. Thereby, excessive thixotropy when applied can be prevented. The upper limit of the average particle diameter (D ₅₀ ) of the conductive particles is, for example, preferably 5.5 μm or less, more preferably 5 μm or less, and even more preferably 4.5 μm or less. Thereby, the sinterability between the conductive particles can be improved. In addition, the viscosity of the conductive paste can be stably controlled.
Further, from the viewpoint of improving the applicability of the conductive paste, the average particle diameter (D ₅₀ ) of the conductive particles is more preferably 0.6 μm or more and 7.0 μm or less, and 0.8 μm or more and 5.0 μm or less. Is particularly preferred.
In this embodiment, the conductive paste may have two or more kinds of conductive particles having different average particle diameters (D ₅₀ ).

Moreover, the said electroconductive particle is good also as an aspect which does not contain electroconductive nanoparticle.
The conductive nanoparticles, for example, may be an average particle diameter _{D 50} is not more 100nm or less, may be further 80nm or less. Thereby, since an excessive increase in viscosity can be suppressed in a predetermined shear rate region, the applicability of the conductive paste can be improved.

In the present embodiment, the average particle diameter (D ₅₀ ) of the conductive particles can be measured using, for example, a commercially available laser particle size distribution analyzer (for example, SALD-7000 manufactured by Shimadzu Corporation).

  In the present embodiment, the lower limit of the volume of the conductive particles is not particularly limited with respect to the total volume (100% by volume) of the solid content of the resin and the conductive particles, but is, for example, 40% by volume or more. Is preferable, and it is more preferable that it is 45 volume% or more. Thereby, it becomes possible to improve the sinterability of electroconductive particle and to contribute to the improvement of thermal conductivity and electroconductivity. On the other hand, the upper limit value of the volume of the conductive particles is preferably 95% by volume or less, and particularly preferably 90% by volume or less, with respect to the total volume. Thereby, it can contribute to the improvement of the workability | operativity etc. of the application | coating workability | operativity of an electrically conductive paste, and the electrically conductive paste after sintering.

  In this embodiment, the “solid content of the resin” refers to the non-volatile content in the resin and refers to the remaining portion excluding volatile components such as water and solvent. Moreover, in this embodiment, content with respect to the whole electrically conductive paste refers to the total value of solid content in resin, the solvent content in resin, electroconductive particle, and a dispersion medium, for example.

Although the shape of the electroconductive particle which concerns on this embodiment is not specifically limited, For example, spherical shape, polygonal shape (including the substantially spherical shape with rounded corners), flake shape, dendritic shape, scale shape, etc. can be mentioned. More preferably, the conductive particles include spherical particles, polygonal particles, or flaky particles.
Thereby, since the filling property of electroconductive particle can be adjusted moderately, applicability | paintability and sintering property can be improved. Moreover, it can contribute to the improvement of the uniformity of sintering. In addition, from the viewpoint of excellent sinterability and cost reduction, it is possible to employ an embodiment in which the conductive particles include flaky particles. Furthermore, from the viewpoint of improving the balance between cost reduction and sintering uniformity, the conductive particles may include both spherical particles or polygonal particles and flaky particles.

  The filling rate of the conductive particles according to the present embodiment can be calculated based on the following filling property evaluation method. For example, the upper limit of the filling rate is preferably 70% or less, more preferably 65% or less, further preferably 62.5% or less, and most preferably 60% or less. Thereby, it becomes easy to control the viscosity in the said shear rate area | region, and the applicability | paintability of an electrically conductive paste can be improved. The lower limit of the filling rate is not particularly limited, but may be 40% or more, 45% or more, or 50% or more, for example. Thereby, the viscosity increase behavior of the conductive paste can be controlled.

(Fillability evaluation method)
For example, the following method can be used as a method for measuring the filling rate of the conductive particles in the present embodiment. That is, it can be evaluated using a powder layer shear force measuring device NS-S500 manufactured by Nano Seeds. Specifically, an example in which the conductive particles that are powders are silver powder will be described. First, pre-weighed silver powder is put into a cylinder with an inner diameter of 4 mm (cylindrical cross-sectional area: 12.5 mm ² ), and a vertical load of 100 N is applied. With the longitudinal load applied, “powder layer height” and “silver powder weight (total weight)” formed by depositing silver powder are measured. Using these measured values, “silver powder density (g / cm ³ ) = (silver powder weight) / (powder layer height × cylindrical cross-sectional area)” when the silver powder is compressed by a load is calculated. The calculated “silver powder density (g / cm ³ )” is divided by “silver density (10.5 (g / cm ³ ))” at room temperature, and converted to volume density (%) as “filling rate ( %) ”. In addition, about other electroconductive particles other than silver powder, a filling rate can be measured similarly.
Filling rate (%) = (silver powder weight / silver density) / (powder layer height × cylindrical cross-sectional area) × 100

  In the present embodiment, the content of the conductive particles obtained by adding the spherical particles and the flaky particles is preferably 90% by weight or more, for example, 95% by weight or more with respect to 100% by weight of the entire conductive particles. It is preferable that Although the upper limit of this content is not specifically limited, For example, you may be 100 weight% or less. Thereby, the uniformity of sintering can be improved more effectively. Further, from the viewpoint of further improving the uniformity of sintering, the content of the conductive particles of the flaky particles is preferably 15% by weight or more, for example, with respect to 100% by mass of the entire conductive particles, It is preferably 50% by weight or more. Although the upper limit of this content is not specifically limited, For example, you may be 100 weight% or less.

(resin)
The resin according to this embodiment will be described.
The conductive paste of this embodiment can contain the following resin. The resin according to the present embodiment is preferably a resin that remains after sintering (however, a component that inevitably evaporates in the sintering process is allowed).

  In the present embodiment, the lower limit value of the solid content of the resin is preferably, for example, 1% by volume or more with respect to the total volume (100% by volume) of the solid content of the resin and the conductive particles. The volume is more preferably at least 5% by volume, and even more preferably at least 5% by volume. On the other hand, the upper limit of the volume of the solid content of the resin is not particularly limited, but is preferably 50% by volume or less, more preferably 45% by volume or less, and 40% by volume with respect to the total volume. More preferably, it is% or less.

  In the present embodiment, the adhesiveness of the conductive paste can be increased by setting the volume of the solid content of the resin to the above lower limit value or more. On the other hand, when the volume of the solid content of the resin is set to the upper limit value or less, hindering of sintering of the conductive particles can be suppressed, and the resistance of the conductive paste can be lowered. In the present embodiment, as the adhesion exhibited by the conductive paste, it is preferable to adhere not only to an inorganic material but also to an organic material.

  In this embodiment, as a method for measuring the volume of the resin, for example, it can be obtained from the blending weight and the specific gravity specific to the resin. On the other hand, as a method for measuring the volume of the conductive particles, for example, it can be calculated from the specific gravity of the conductive particles.

  Further, the lower limit value of the content of the resin of the present embodiment is, for example, preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and further preferably 1% by weight or more with respect to the entire conductive paste. preferable. Thereby, the adhesiveness of an electrically conductive paste can be improved. The upper limit value of the resin content is, for example, preferably 12% by weight or less, more preferably 10% by weight or less, and still more preferably 8% by weight or less with respect to the entire conductive paste. Thereby, the hindering of the sintering of the conductive particles can be suppressed, and the resistance of the conductive paste can be lowered.

  As the resin according to this embodiment, a thermosetting resin, a thermoplastic resin, a mixture of a thermoplastic resin and a thermosetting resin, or the like can be used. The resin of the present embodiment can be appropriately selected from these resins, but it is preferable to use a thermosetting resin.

  The thermosetting resin according to the present embodiment is a resin that forms a three-dimensional network structure by heating. The thermosetting resin is not particularly limited. For example, (meth) acrylic resin, phenolic resin, resin having a benzoxazine ring, epoxy resin, melamine resin, unsaturated polyester resin, maleimide resin, polyurethane resin, diallyl phthalate Examples thereof include resins, silicone resins, cyanate resins, and resins having a methacryloyl group. For example, the thermosetting resin may be a liquid resin that is liquid at room temperature. These can be used alone or in combination of two or more.

  Although it does not specifically limit as a thermoplastic resin which concerns on this embodiment, For example, an acrylic polymer, a butyral resin, a polystyrene resin, a polycarbonate resin, a polyamide resin, a polyamideimide resin etc. are mentioned. These can be used alone or in combination of two or more.

  Among these, the resin according to this embodiment preferably includes a resin having an appropriate polar group. Moreover, as said polar group, it is preferable to contain 1 or more types selected from the group which consists of a hydroxyl group, an amide group, an epoxy group, and an amino group, for example. Among these, it is preferable that at least an epoxy group is included. Thereby, since the dispersibility of an electrically conductive paste can be improved moderately, applicability | paintability can be improved.

Still, the lower limit of the weight average molecular weight (Mw) of the resin according to the present embodiment is preferably 10 ³ or more, more preferably 5.0 × 10 ³ or more, and further preferably 1.0 × 10 ⁴ or more. . The upper limit of the weight average molecular weight of the resin is not particularly limited, but is preferably 10 ⁶ or less, more preferably 7.0 × 10 ⁵ or less, further preferably 5.0 × 10 ⁵ or less, and 10 Most preferred is ⁵ or less. Thereby, since the dispersibility of an electrically conductive paste can be optimized, applicability | paintability can be improved.

  Among these, as a resin according to the present embodiment, from the viewpoint of having an appropriate polar group, a group consisting of an acrylic polymer not containing a carboxyl group, a resol type phenol resin, a resin having a benzoxazine ring, and a (meth) acrylate It is preferable that 1 or more types selected from are included. Among these, acrylic polymer, resol type phenol resin, or (meth) acrylate is preferable from the viewpoint of having an appropriate polar group and a high molecular weight.

  Examples of the acrylic polymer according to this embodiment include an epoxy group-containing acrylic polymer (SG-P3), an acrylic polymer having an epoxy group and an amide group (SG-80H), and an acrylic polymer having a hydroxyl group (SG-790). Is mentioned.

Moreover, as (meth) acrylate which is (meth) acrylic resin which concerns on this embodiment, trifunctional methacrylate monomers, such as a trimethylol propane trimethacrylate, bifunctional methacrylate monomers, such as ethoxylated bisphenol A diacrylate, etc., etc., for example. Is mentioned.
Examples of the acrylic resin according to this embodiment include monofunctional (meth) acrylate, bifunctional (meth) acrylate, trifunctional or higher polyfunctional (meth) acrylate, epoxy (meth) acrylate, urethane (meth) acrylate, 2 Examples thereof include polyester (meth) acrylates that are functional or higher.

  Examples of monofunctional (meth) acrylates include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, and s-butyl. (Meth) acrylate, t-butyl (meth) acrylate, butoxyethyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, heptyl (meth) acrylate, octyl heptyl (meth) ) Acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, undecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate Rate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, stearyl (meth) acrylate, behenyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-chloro-2- Aliphatic (meth) acrylates such as hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cyclopentyl (meth) acrylate, dicyclopentanyl (meth) Acrylate, dicyclopentenyl (meth) acrylate, isobornyl (meth) acrylate, 3-methyl-3-oxetanylmethyl (meth) acrylate, 1-adamantyl (meth) acrylate Cycloaliphatic (meth) acrylates such as salt, phenyl (meth) acrylate, nonylphenyl (meth) acrylate, p-cumylphenyl (meth) acrylate, o-biphenyl (meth) acrylate, 1-naphthyl (meth) acrylate, 2-naphthyl (meth) acrylate, benzyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2-hydroxy-3- (o-phenylphenoxy) propyl (meth) acrylate, 2-hydroxy-3 -(1-naphthoxy) propyl (meth) acrylate, aromatic (meth) acrylate such as 2-hydroxy-3- (2-naphthoxy) propyl (meth) acrylate, 2-tetrahydrofurfuryl (meth) acrylate, N- (Meth) acryloyloxye Examples include heterocyclic (meth) acrylates such as tilhexahydrophthalimide and 2- (meth) acryloyloxyethyl-N-carbazole.

  Examples of the bifunctional (meth) acrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, and polyethylene glycol di ( (Meth) acrylate, propylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetrapropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,3 -Butanediol di (meth) acrylate, 2-methyl-1,3-propanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, ne Pentyl glycol di (meth) acrylate, 3-methyl-1,5-pentanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 2-butyl-2-ethyl-1,3-propanediol Fats such as di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, glycerin di (meth) acrylate, tricyclodecane dimethanol (meth) acrylate Alicyclic (meth) acrylate, cyclohexanedimethanol (meth) acrylate, tricyclodecane dimethanol (meth) acrylate, hydrogenated bisphenol A di (meth) acrylate, hydrogenated bisphenol F di (meth) acrylate ( (Meth) acrylate, bispheno Aromatic (meth) acrylates such as di- (meth) acrylate, bisphenol F di (meth) acrylate, bisphenol AF di (meth) acrylate, ethoxylated bisphenol A di (meth) acrylate, fluorene-type di (meth) acrylate And heterocyclic (meth) acrylates such as isocyanuric acid di (meth) acrylate.

  Examples of the trifunctional or higher polyfunctional (meth) acrylates include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, and pentaerythritol tetra (meth) acrylate. , Dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, aliphatic (meth) acrylates such as ethoxylated glycerin tri (meth) acrylate, heterocyclic such as isocyanuric acid tri (meth) acrylate (Meth) acrylate is mentioned.

  Further, the phenol resin according to the present embodiment is not particularly limited. For example, a novolac type phenol resin such as a phenol novolak resin, a cresol novolak resin, a bisphenol A novolac resin, a resol type phenol resin, and an arylalkylene type phenol resin. Is mentioned. Among these, a resol type phenol resin is more preferable from the viewpoint of large thermosetting shrinkage and high adhesion. The resol type phenol resin is obtained, for example, by reacting phenols and aldehydes under an alkali catalyst.

The novolak-type phenol resin according to this embodiment can be obtained, for example, by reacting phenols and aldehydes under an acidic catalyst.
Examples of the phenols used in producing the novolak type phenol resin include phenol, cresol, xylenol, ethylphenol, p-phenylphenol, p-tert-butylphenol, p-tert-amylphenol, p-octylphenol, p- Nonylphenol, p-cumylphenol, bisphenol A, bisphenol F, resorcinol and the like can be mentioned. In addition, you may use these phenols individually or in combination of 2 or more types.

  Examples of the aldehydes used for producing the novolak type phenol resin include alkyl aldehydes such as formaldehyde, acetaldehyde, propyl aldehyde, and butyraldehyde, and aromatic aldehydes such as benzaldehyde and salicyl aldehyde. Examples of the formaldehyde source include formalin (aqueous solution), paraformaldehyde, hemi-formal with alcohols, and trioxane. In addition, you may use these aldehydes individually or in combination of 2 or more types.

  When synthesizing a novolak-type phenol resin, the reaction molar ratio of phenols and aldehydes is usually 0.3 to 1.0 mol, particularly 0.6 to 1 mol per mol of phenol. It is preferable to set it as 0.9 mol.

  Examples of the acidic catalyst used for producing the novolak type phenol resin include organic carboxylic acids such as oxalic acid and acetic acid, organic sulfonic acids such as benzenesulfonic acid, paratoluenesulfonic acid and methanesulfonic acid, and 1-hydroxyethylidene-1 , 1′-diphosphonic acid, organic phosphonic acids such as 2-phosphonobutane-1,2,4-tricarboxylic acid, and inorganic acids such as hydrochloric acid, sulfuric acid and phosphoric acid. In addition, you may use these acidic catalysts individually or in combination of 2 or more types.

  The resol type phenol resin can be obtained, for example, by reacting phenols and aldehydes in the presence of a catalyst such as an alkali metal, an amine, or a divalent metal salt.

  Examples of the phenols used in the production of the resol type phenol resin include cresols such as phenol, o-cresol, m-cresol, and p-cresol, 2,3-xylenol, 2,4-xylenol, and 2,5-xylenol. Xylenols such as 2,6-xylenol, 3,4-xylenol and 3,5-xylenol, ethylphenols such as o-ethylphenol, m-ethylphenol and p-ethylphenol, isopropylphenol, butylphenol, p- Butylphenols such as tert-butylphenol, p-tert-amylphenol, p-octylphenol, p-nonylphenol, alkylphenols such as p-cumylphenol, fluorophenol, chlorophenol, bromophenol, iodof Halogenated phenols such as diol, monovalent phenol substitutes such as p-phenylphenol, aminophenol, nitrophenol, dinitrophenol and trinitrophenol, and monovalent phenols such as 1-naphthol and 2-naphthol, Examples thereof include polyphenols such as resorcin, alkylresorcin, pyrogallol, catechol, alkylcatechol, hydroquinone, alkylhydroquinone, phloroglucin, bisphenol A, bisphenol F, bisphenol S, and dihydroxynaphthalene. In addition, you may use these phenols individually or in mixture of 2 or more types.

  Examples of aldehydes used in the production of resol-type phenol resins include formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, polyoxymethylene, chloral, hexamethylenetetramine, furfural, glyoxal, n-butyraldehyde, capro. Examples include aldehyde, allyl aldehyde, benzaldehyde, crotonaldehyde, acrolein, tetraoxymethylene, phenylacetaldehyde, o-tolualdehyde, salicylaldehyde and the like. These aldehydes may be used alone or in combination of two or more. Of these aldehydes, formaldehyde and paraformaldehyde are preferably selected and used from the viewpoint of excellent reactivity and low cost.

  Examples of the catalyst used in the production of the resol type phenolic resin include alkali metal hydroxides such as sodium hydroxide, lithium hydroxide and potassium hydroxide, alkaline earth metal oxides such as calcium, magnesium and barium, and the like. Examples thereof include hydroxides, sodium carbonate, aqueous ammonia, amines such as triethylamine and hexamethylenetetramine, and divalent metal salts such as magnesium acetate and zinc acetate. These catalysts may be used alone or in combination of two or more.

  When producing a resol type phenol resin, the reaction molar ratio of phenols to aldehydes is preferably 0.80 to 2.50 moles of aldehydes per mole of phenols, more preferably , Aldehydes 1.00-2.30 mol.

  An arylalkylene type phenol resin refers to a phenol resin having one or more arylalkylene groups in a repeating unit. Examples of such aryl alkylene type phenol resins include xylylene type phenol resins and biphenyl dimethylene type phenol resins.

  The benzoxazine-based resin (resin having a benzoxazine ring) according to this embodiment is a thermosetting resin having a structure in which an oxazine ring is adjacent to a benzene ring. Although it does not specifically limit as said benzoxazine-type resin, For example, it can manufacture by making a phenol compound, an amine compound, and an aldehyde compound react.

In this embodiment, from the viewpoint of improving the balance of sintering uniformity, thermal conductivity, conductivity, and the like, for example, an embodiment in which a curing agent is not included in the resin can be employed. The phrase “not containing a curing agent in the resin” refers to a case where the content of the curing agent is, for example, 0.01 parts by weight or less with respect to 100 parts by weight as the whole thermosetting resin.
The conductive paste of this embodiment may include a curing accelerator. The curing accelerator is not particularly limited, and examples thereof include imidazoles, triphenylphosphine or tetraphenylphosphine salts, amine compounds such as diazabicycloundecene, and salts thereof.

  Here, the conductive paste of this embodiment shall be comprised from electroconductive particle, resin, and a dispersion medium. In this case, the resin can be all remaining components obtained by removing the conductive particles and the dispersion medium from the conductive paste. However, when the dispersion medium is dried and removed, it is preferable that the dispersion medium is completely removed, but the dispersion medium inevitably remaining in the work process is acceptable. Moreover, when the said electrically conductive paste contains a filler, what remove | excluded this filler is made into the said resin for evaluation.

The dispersion medium according to the present embodiment is not particularly limited. For example, methyl carbitol, ethyl carbitol, butyl carbitol, methyl carbitol acetate, ethyl carbitol acetate, butyl carbitol acetate, acetylacetone, methyl isobutyl ketone ( MIBK), anone, diacetone alcohol, ethyl cellosolve, methyl cellosolve, butyl cellosolve, ethyl cellosolve acetate, methyl cellosolve acetate, butyl cellosolve acetate, ethyl alcohol, propyl alcohol, butyl alcohol, pentyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, nonyl Alcohol, decyl alcohol, ethylene glycol monomethyl ether, ethylene glycol mono Tyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, methyl methoxybutanol, α-terpineol, β-terpineol, hexylene glycol , Benzyl alcohol, 2-phenylethyl alcohol, isopalmityl alcohol, isostearyl alcohol, lauryl alcohol, alcohols such as ethylene glycol, propylene glycol or glycerin, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, diacetone alcohol (4- Hydroxy-4-methyl-2- Ntanone), 2-octanone, isophorone (3,5,5-trimethyl-2-cyclohexen-1-one) or diisobutyl ketone (2,6-dimethyl-4-heptanone), ethyl acetate, butyl acetate, Diethyl phthalate, dibutyl phthalate, acetoxyethane, methyl butyrate, methyl hexanoate, methyl octoate, methyl decanoate, methyl cellosolve acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, 1,2-diacetoxyethane, phosphoric acid Esters such as tributyl, tricresyl phosphate or tripentyl phosphate, tetrahydrofuran, dipropyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethyl Ethers such as N-glycol dibutyl ether, propylene glycol dimethyl ether, ethoxyethyl ether, 1,2-bis (2-diethoxy) ethane or 1,2-bis (2-methoxyethoxy) ethane, 2- (2-butoxyethoxy acetate) ) Ether ethers such as ethane, ether alcohols such as 2- (2-methoxyethoxy) ethanol, hydrocarbons such as toluene, xylene, n-paraffin, isoparaffin, dodecylbenzene, turpentine oil, kerosene or light oil, α- Terpineols such as terpineol, dihydroxyterpineol, dihydroterpineol acetate, nitriles such as acetonitrile or propionitrile, amides such as acetamide or N, N-dimethylformamide, low molecular weight Nonvolatile silicone oils or volatile organic modified silicone oil is used. Among these, from the viewpoint of workability and volatility, for example, methyl carbitol, ethyl carbitol, butyl carbitol, methyl carbitol acetate, ethyl carbitol acetate, butyl carbitol acetate, acetylacetone, methyl isobutyl ketone (MIBK), Anone, diacetone alcohol, α-terpineol, dihydroxy terpineol, dihydroxy terpineol acetate and the like are preferable. From the viewpoint of dispersibility, butyl carbitol, butyl carbitol acetate, α-terpineol, dihydroxy terpineol, or dihydroxy terpineol acetate is more preferable.
Moreover, these can also be used as a mixed dispersion medium which combined 2 or more types.

In addition, the lower limit value of the SP value that is the solubility parameter of the dispersion medium according to the present embodiment is preferably 6 ((cal / cm ³ ) ^1/2 ) or more, for example, 7 ((cal / cm ³ ) ^1/2. ) Or more is more preferable, and 8 ((cal / cm ³ ) ^1/2 ) or more is more preferable. Dispersibility can be improved by using a dispersion medium having a high SP value. Although the detailed mechanism is not clear, it is considered that the higher the polarity, the better the dispersibility due to repulsion due to the ζ potential.
The upper limit of the SP value is not particularly limited, but is preferably 11 ((cal / cm ³ ) ^1/2 ) or less, and more preferably 10.5 ((cal / cm ³ ) ^1/2 ) or less. Preferably, 10 ((cal / cm ³ ) ^1/2 ) or less is more preferable. By using a dispersion medium having a moderately high SP value, good resin solubility can be obtained, and an appropriate silver powder dispersibility can be obtained, thereby improving applicability.

  The solubility parameter (SP value) in the present embodiment follows Hansen's formula, and details are obtained based on “SP value basics / applications and calculation methods” (Hideki Yamamoto, published by Information Technology Corporation).

Moreover, content of the dispersion medium in this embodiment can be shown using the total value of content of the said electroconductive particle and the said resin with respect to the whole electroconductive paste. That is, a large total value of the conductive particles and the resin indicates that the content of the dispersion medium is low.
Here, the upper limit of the total content of the conductive particles and the resin is preferably, for example, 95% by weight or less, and more preferably 92.5% by weight or less with respect to the entire conductive paste of the present embodiment. 90% by weight or less is more preferable. Thereby, since a suitable quantity of a dispersion medium can be used, the applicability | paintability of an electrically conductive paste can be improved. The lower limit of the total content is not particularly limited, but is preferably 30% by weight or more, more preferably 40% by weight or more, and still more preferably 50% by weight or more. Thereby, the low resistance of an electrically conductive paste can be implement | achieved stably by reducing content of a dispersion medium.

(Other ingredients)
In the conductive paste according to this embodiment, an antioxidant, a dispersant, inorganic fillers such as silica and alumina, other elastomers such as silicone resin and butadiene rubber, coupling agents, antifoaming agents, Components such as a leveling agent and fine silica (thixo adjuster) can be added. The content of these components can be appropriately set according to the application to which the conductive paste is applied.

Further, the conductive paste of this embodiment includes Na ⁺ , NH ₄ ⁺ , K ⁺ , Ca ²⁺ , Mg ²⁺ , F ⁻ , Cl ⁻ , Br ⁻ , NO ₃ ⁻ , PO ₄ ³⁻ , PO ₃ ^3−. It is preferable not to contain ions (impurities) which are one type selected from the group consisting of SO ₄ ²⁻ and Zn ²⁺ . Ion consisting of Na ⁺ , NH ₄ ⁺ , K ⁺ , Ca ²⁺ , Mg ²⁺ , F ⁻ , Cl ⁻ , Br ⁻ , NO ₃ ⁻ , PO ₄ ³⁻ , PO ₃ ³⁻ , SO ₄ ²⁻ , and Zn ²⁺ The total amount of is preferably 300 ppm or less, more preferably 250 ppm or less, still more preferably 200 ppm or less, based on the entire conductive paste. Thereby, it can suppress that sintering of the silver powder in an electrically conductive paste is prevented. In addition, the lower limit of the total value of these ions is not particularly limited, but can be, for example, 0 ppm or more.

Next, the manufacturing method of the electrically conductive paste which concerns on this embodiment is demonstrated.
The conductive paste of this embodiment can be produced by kneading and mixing the above-described components. This mixing may be performed using, for example, a kneader such as a kneader, a three-roller, or a reiki machine, or various stirring devices. Further, the obtained kneaded mixture may be rolled by being compressed between two rolls.

  Moreover, the manufacturing method of the hardening body of the conductive paste of this embodiment mixes a conductive particle and resin, prepares the conductive paste which concerns on this embodiment, and heat-processes the said conductive paste. And forming a particle connection structure by causing sintering of the conductive particles.

  In this embodiment, by selecting a resin having a characteristic that assists sintering, it is possible to improve the manufacturing process characteristics such as lowering the sintering temperature and shortening the sintering time in the curing step. become. That is, even if low temperature or short-time sintering conditions are employed in the curing step, it is possible to achieve both low resistance and adhesion to the conductive paste. Moreover, in the manufacturing method of the electrically conductive paste of this embodiment, you may perform a drying process before a hardening process. The drying step is performed at a temperature lower than the sintering temperature, but may be, for example, 80 ° C. or higher and 150 ° C. or lower, or 90 ° C. or higher and 110 ° C. or lower. Thereby, since the dispersion medium in an electrically conductive paste can be evaporated appropriately, workability | operativity with respect to the coating film of an electrically conductive paste can be improved.

The conductive paste according to the present embodiment can be used in a sintering process by selecting a resin as described above by heat treatment at a low temperature of 200 degrees or less and 160 degrees or more. In the present embodiment, the upper limit value of the sintering temperature is not particularly limited, but is preferably 200 degrees or less, more preferably 190 degrees or less, and particularly preferably 180 degrees or less. Moreover, the lower limit value of the sintering temperature is not particularly limited, but is preferably, for example, 160 degrees or more, more preferably 165 degrees or more, and particularly preferably 170 degrees or more.
As the sintering temperature, for example, a temperature higher than 200 degrees such as 250 degrees or less or 230 degrees or less may be used.

  In the present embodiment, the lower limit of the sintering time is not particularly limited, but is preferably 15 minutes or longer, more preferably 18 minutes or longer, and even more preferably 20 minutes or longer. The upper limit of the sintering time is not particularly limited, but is preferably 60 minutes or less, more preferably 55 minutes or less, and particularly preferably 50 minutes or less.

[Partial sintering structure]
The hardened body of the conductive paste of this embodiment has a sintered part in which a particle connection structure of conductive particles (for example, silver particles) is formed, but further, a particle connection structure of conductive particles is formed. You may have the non-sintered part which is not carried out. In other words, the cured body of the present embodiment may have a whole sintering structure in which sintering is formed entirely, but has a partial sintering structure in which sintering is only partially formed. It may be. The resin of this embodiment remains in the non-sintered portion.

  In this embodiment, a sintered part and a non-sintered part can be confirmed by the following method. For example, the cross section of the cured conductive paste is observed with various microscopes such as a scanning electron microscope, and the sintered structure of conductive particles (for example, silver particles) is determined from the observed image.

  The step of forming the particle connection structure of the present embodiment may include a step of forming a sintered part in which the particle connection structure is formed and a non-sintered part in which the particle connection structure is not formed. In this embodiment, in order to form a partial sintering structure, for example, resin content, sintering temperature, time, and the like can be selected as appropriate.

  In the present embodiment, as the effect of partial sintering, it is possible to achieve both low resistance conductivity and high adhesion to the adherend. In addition, shortening of the manufacturing process and low-temperature curing can be mentioned. For example, even if the temperature required for a system capable of complete sintering is low or the time is short, partial sintering is not a practical problem when it is very close to a system capable of complete total sintering. It can be said that it is sintered to the level. Moreover, since various appropriate resin can be mix | blended, it becomes easy to adjust the viscosity characteristic as an appropriate paste by a use. Furthermore, since the resin remains, the brittleness of the cured body is improved. As a result, it is possible to increase the structural strength and improve the connection reliability.

  Hereinafter, the characteristics of the conductive paste according to the present embodiment will be described.

  In the conductive paste according to this embodiment, in a shear rate region I of 1 [1 / s] or more and 100 [1 / s] or less in a temperature environment of 25 ° C., the viscosity is increased according to the increase in the shear rate. It is preferred that there is a region in which the increase is.

  Specifically, the viscosity function indicating the viscosity change in the shear rate region I is preferably an arbitrary continuous decrease function. The viscosity function of the present embodiment preferably has a maximum in the shear rate region I. In other words, in the conductive paste of this embodiment, in a shear rate region I of 1 [1 / s] or more and 100 [1 / s] or less in a temperature environment of 25 ° C., according to an increase in shear rate. It is preferable that an inflection point indicating an increase in viscosity exists. Moreover, when the viscosity function of this embodiment has the minimum and maximum in the shear rate area | region I, it is preferable to have one each. However, the viscosity function in the shear rate region I may partially include a region where the viscosity is substantially constant as long as the effect of the present invention is not impaired.

  In the conductive paste of this embodiment, an inflection point indicating an increase in viscosity exists in a shear rate region II of 1 [1 / s] or more and 10 [1 / s] or less in a temperature environment of 25 ° C. It is particularly preferable to do this. The conductive paste having such viscosity characteristics is very excellent in applicability in the application method.

In this embodiment, the type of each component contained in the conductive paste, the average particle size, shape and filling rate of the conductive particles, the polar group and weight average molecular weight of the resin, the solubility and content of the dispersion medium, the conductive paste By appropriately selecting factors such as the manufacturing conditions, the viscosity of the conductive paste in a predetermined shear rate region can be controlled. Among these, it is preferable that two or more elements be within the above-described preferable types and numerical ranges.
Here, in the present embodiment, the following (1) and (2) are listed as elements for controlling the viscosity behavior in a predetermined shear rate region.
(1) Examples of elements that enhance dispersibility include conductive pastes that do not contain glass particles (glass components) and conductive nanoparticles, high molecular weight resins having appropriate polar groups, and dispersion media having appropriate solubility. Is mentioned.
(2) As an element for adjusting the viscosity increasing behavior, the filling rate of the conductive particles is set to the above lower limit (for example, 40%) or more.
By using these elements in combination, the viscosity increasing behavior of the conductive paste can be stably controlled.

  In the viscosity function of the present embodiment, when viewed in the increasing direction of the shear rate, the upper limit of the range of viscosity rising from the minimum to the maximum (that is, the difference between the minimum value and the maximum value) is, for example, 20 Pa. · S or less is preferable, 15 Pa · s or less is more preferable, and 10 Pa · s or less is more preferable. The lower limit value of the increasing viscosity range is not particularly limited, and may be, for example, 0 Pa · s or more. By setting the range of increasing viscosity to the upper limit value or less, an excessive increase in viscosity can be suppressed, so that a conductive paste excellent in applicability can be realized.

When the conductive paste of the present embodiment has the above inflection point, the viscosity is 1 [1 / s] or more and 100 [1 / s] or less in a temperature environment of 25 ° C. The shear rate that starts increasing is defined as V1, and the shear rate at which the viscosity has increased is defined as V2. In this case, the upper limit value of the shear rate difference | V2-V1 | is not particularly limited, but is preferably 20 [1 / s] or less, more preferably 15 [1 / s] or less, and 10 [1 / s], for example. More preferred are: Thereby, it can be set as the electrically conductive paste excellent in manufacture stability. The lower limit value of the shear rate difference | V2-V1 | is, for example, preferably 1 [1 / s] or more, more preferably 2 [1 / s] or more, and further preferably 3 [1 / s] or more.
Thereby, since the viscosity increase in the shear rate region I can be moderated, a conductive paste having excellent coating properties can be obtained.

  In the conductive paste of this embodiment, the upper limit of the viscosity at a shear rate of 1 [1 / s] in a temperature environment of 25 ° C. is, for example, preferably 100 Pa · s or less, and 90 Pa · s or less. More preferred is 80 Pa · s or less. Thereby, the electrically conductive paste excellent in applicability | paintability can be obtained. The lower limit of the viscosity at a shear rate of 1 [1 / s] is not particularly limited, but is preferably 1 Pa · s or more, more preferably 2 Pa · s or more, and even more preferably 3 Pa · s or more. Thereby, the film-forming property of an electrically conductive paste can be improved.

  In the conductive paste of this embodiment, the upper limit of the viscosity at a shear rate of 100 [1 / s] in a temperature environment of 25 ° C. is preferably 20 Pa · s or less, for example, and 15 Pa · s or less. More preferred is 10 Pa · s or less. Thereby, the electrically conductive paste excellent in applicability | paintability can be obtained. The lower limit of the viscosity at a shear rate of 100 [1 / s] is not particularly limited. For example, it is preferably 0.1 Pa · s or more, more preferably 0.2 Pa · s or more, and further 0.3 Pa · s or more. preferable. Thereby, the film-forming property of an electrically conductive paste can be improved.

  Further, from the measurement result of the viscosity [Pa · s] corresponding to the shear rate [1 / s] at room temperature of 25 ° C. of the conductive paste of the present embodiment, the shear rate [1 / s] −viscosity [Pa · s] is obtained. A log-log plot curve is obtained.

The upper limit value of the average slope of the slope A indicating the increase in viscosity calculated from the logarithmic plot curve of the shear rate [1 / s] -viscosity [Pa · s] is, for example, smaller than 1, preferably 0.5. Or less, more preferably 0.4 or less. Thereby, an abrupt viscosity change can be suppressed and printability can be improved. On the other hand, the lower limit value of the average slope of the slope A is not particularly limited, but is, for example, greater than 0, preferably 0.05 or more, and more preferably 0.1 or more. The film formability of the conductive paste can be improved.
In the present embodiment, the average slope of the slope A is calculated from the above log-log plot curve, and can be made the average slope by connecting the above-mentioned minimum value and maximum value.

The lower limit value of the average slope of the slope B indicating the decrease in viscosity calculated from the logarithmic plot curve of the shear rate [1 / s] -viscosity [Pa · s] is, for example, larger than −1, preferably −0. 0.7 or more, more preferably -0.5 or more. Thereby, an abrupt viscosity change can be suppressed and printability can be improved. On the other hand, the upper limit value of the average inclination of the inclination B is not particularly limited, but is, for example, smaller than 0, preferably −0.05 or less, and more preferably −0.1 or less. The film formability of the conductive paste can be improved.
In this embodiment, the average slope of the slope B is calculated from the log-log plot curve, and the average slope can be obtained by connecting the viscosity at the shear rate of 1 [1 / s] and the minimum value. it can.

  In the present embodiment, the viscosity (Pa · s) according to the shear rate can be measured under the following conditions. For example, it can be measured by using a rheometer MCR301 manufactured by Anton Paar and setting the measurement temperature to 25 ° C. Then, the shear rate is increased from 0.01 [1 / s] to 1,000 [1 / s] and then decreased from 1,000 [1 / s] to 0.01 [1 / s]. At this time, the shear viscosity (Pa · s) in these shear rate regions is measured. From the measurement result of the obtained shear rate and viscosity, a logarithmic plot curve of shear rate [1 / s] −viscosity (shear viscosity) [Pa · s] can be created.

  The film thickness of the coating film formed by applying the conductive paste of this embodiment can be set to an appropriate thickness according to various applications. As an example, when used in an electronic device, the lower limit value of the thickness of the coating film may be, for example, 5 μm or more, 10 μm or more, or 100 μm or more. Further, the upper limit value of the film thickness of the coating film is not particularly limited, but may be, for example, 5 mm or less, 3 mm or less, or 1 mm or less.

<Semiconductor device>
Hereinafter, an example in which the conductive paste according to the present embodiment is applied to the solar battery cell 100 will be described.
FIG. 1 is a schematic diagram showing a solar battery cell 100. 1A is a light-receiving surface side, FIG. 1B is a back surface side, and FIG. 1C is a cross-sectional view along AA ′ in FIG.

The solar cell 100 of this embodiment includes a P-type silicon substrate 110, an N-type semiconductor layer 120, an antireflection film 130, a light-receiving surface electrode 140, a subgrid electrode 142, a back electrode plate 160, and a back electrode 170. On the light receiving surface side of the silicon substrate 110, an N-type semiconductor layer 120, an antireflection film 130, and an electrode are formed. The electrode on the light receiving surface side includes a subgrid electrode 142 for collecting carriers generated in the solar battery cell 100, and an interconnector (not shown) for further collecting the carriers collected by the subgrid electrode 142 and taking them out to the outside. The light receiving surface electrode 140 is used for connection. The plurality of electrodes are arranged in parallel, and the light receiving surface electrode 140 and the subgrid electrode 142 are arranged so as to intersect each other.
On the other hand, an electrode including a back electrode plate 160 and a back electrode 170 is formed on the back side of the silicon substrate 110.

  In the present embodiment, the silicon substrate 110 may be a glass substrate. Further, a double-sided power generation type structure may be adopted by forming a PN junction on the back side.

  Wirings such as the subgrid electrode 142, the light receiving surface electrode 140, and the back surface electrode 170 are formed using the conductive paste of the present embodiment. As a result, low resistance and good form retention are realized in these wirings.

  Further, the wiring formed using the conductive paste of the present embodiment can have a high aspect ratio wiring shape. That is, by using the conductive paste of this embodiment, a thick film and a thin wire can be formed.

Next, the manufacturing process of the photovoltaic cell 100 of this embodiment is demonstrated.
First, a single crystal or polycrystalline P type silicon substrate 110 is prepared. Next, the N-type semiconductor layer 120 and the antireflection film 130 which are silicon layers in which the N-type semiconductor is diffused by thermal diffusion are formed on the light receiving surface side of the silicon substrate 110. A PN junction is formed at the interface between the silicon substrate 110 and the N-type semiconductor layer 120.

  A subgrid electrode 142 and a light receiving surface electrode 140 are formed on the light receiving surface side of the silicon substrate 110. On the other hand, a back electrode plate 160 and a back electrode 170 are formed on the back side of the silicon substrate 110 (the side opposite to the light receiving surface). The subgrid electrode 142, the light receiving surface electrode 140, and the back surface electrode 170 have a wiring shape having a predetermined length in one direction. These wirings are thin wires from the viewpoint of space saving, and are preferably thick films from the viewpoint of low resistance.

  Here, these wirings can be formed using the conductive paste of the present embodiment. For example, the wiring can be formed by forming a conductive paste into a wiring shape by using a coating method such as screen printing, and then performing a sintering process by the above heat treatment. Since the conductive paste of the present embodiment is excellent in sinterability, it can be made into a low resistance wiring, and since it is excellent in applicability, a good form of wiring is maintained. As a result, it is possible to realize a high-speed and highly reliable wiring. Moreover, since the conductive paste of this embodiment can be sintered at a low temperature, an excessive heat history can be suppressed, so that the solar battery cell 100 excellent in connection reliability can be realized.

Thus, the solar battery cell 100 shown in FIG. 1 is obtained.
Moreover, after connecting the several photovoltaic cell 100 in series, a solar cell module can be formed by sealing with sealing resin. It is preferable that both surfaces of the solar cell module are protected by a protective member such as glass.

(Use of conductive paste)
The conductive paste of this embodiment can be used for various applications. For example, a die attach material or a conductive paste can be used. As the die attach material, for example, it may be used in an electronic device, and more preferably in a semiconductor device. Typical examples of conductive pastes include printed circuit board jumper circuits, through-hole conductors, additive circuits, touch panel conductor circuits, resistance terminals, solar cell electrodes, tantalum capacitor electrodes, and film capacitor electrodes. And formation of external electrodes and internal electrodes of chip-type ceramic electronic components, use as electromagnetic wave shields, and the like. Moreover, as an alternative to solder, in addition to the use as a conductive adhesive for mounting semiconductor elements and electronic components on a substrate, a grid electrode of a type that covers the surface of a high-temperature-baked silver electrode of a solar cell with solder, It can also be used as an alternative to the solder part.

The conductive paste of this embodiment can be made into a cured body (sintered body) by being cured by heat treatment. The cured body of this embodiment can be used for various purposes. For example, it is used for an electronic device. That is, the electronic device according to the present embodiment includes a cured body of the conductive paste according to the present embodiment and an electronic component to which the cured body is bonded.
Since the cured body of the present embodiment contains conductive particles in the cured body, it can be applied to various electronic device components in which electrodes and wirings are formed. Further, it can be preferably used for filling a through hole or a via hole of a printed wiring board.
Of course, the use mentioned here is an example of embodiment, and even if it is uses other than this, it can apply, adjusting the composition of an electrically conductive paste.

  It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.

(Preparation of conductive paste)
A conductive paste was prepared for each example and each comparative example. This preparation was performed by uniformly mixing each component (conductive particles, resin, and dispersion medium) according to the formulation shown in Table 1. The details of the components shown in Table 1 are as follows.

[Conductive particles]
Conductive particles 1: spherical silver powder (average particle size D ₅₀ = 0.98 μm, filling rate 59%)
Conductive particle 2: flaky silver powder (average particle size D ₅₀ = 4.74 μm, filling rate 44%)
Conductive particles 3: irregularly shaped silver powder (average particle size D ₅₀ = 5.88 μm, filling rate 39%)
The filling rate of the conductive particles was calculated using a powder bed shear force measuring device NS-S500 manufactured by Nano Seeds. First, conductive particles weighed in advance were put into a cylinder having an inner diameter of 4 mm (cylindrical cross-sectional area: 12.5 mm ² ), and a load of 100 N was applied. From the height of the powder layer and the weight of the conductive particles, the conductive particle density (g / cm ³ ) when the powder is compressed by the load is obtained, and the density of the conductive particles (in the case of silver powder, the silver density at room temperature) Was 10.5 (g / cm ³ ), and the volume density (%) was calculated as the filling rate (%).
Filling rate (%) = (weight of conductive particles / density of conductive particles) / (powder layer height × cylindrical cross-sectional area) × 100

[resin]
(Thermosetting resin)
Thermosetting resin 1: Resol type phenol resin (PR-54463, manufactured by Sumitomo Bakelite Co., Ltd., RC 55 wt% butyl carbitol solution)
Thermosetting resin 2: Trimethylolpropane trimethacrylate (NK ester TMPT, manufactured by Shin-Nakamura Chemical Co., Ltd., trifunctional methacrylate monomer)
Thermosetting resin 3: Ethoxylated bisphenol A diacrylate (NK ester ABE-300, manufactured by Shin-Nakamura Chemical Co., Ltd., bifunctional)
(Thermoplastic resin)
Thermoplastic resin 1: Acrylic polymer (SG80H BCA15, manufactured by Nagase ChemteX Corporation, RC15 wt% butyl carbitol acetate solution, functional group: epoxy group, amide group, Mw: 35 × 10 ⁴ )
Thermoplastic resin 2: acrylic polymer (SG-P3, manufactured by Nagase ChemteX Corporation, RC15 wt% MEK solution, functional group: epoxy group, Mw: 85 × 10 ⁴ )
Thermoplastic resin 3: acrylic polymer (SG-790, manufactured by Nagase ChemteX Corporation, RC 23 wt% toluene / ethyl acetate solution, functional group: hydroxyl group, Mw: 52 × 10 ⁴ )
Thermoplastic resin 4: acrylic polymer (SG-70L, manufactured by Nagase ChemteX Corporation, RC 13 wt% toluene MEK solution, functional group: hydroxyl group, carboxyl group, Mw: 80 × 10 ⁴ )
Thermoplastic resin 5: butyral resin (RC 10 wt% butyl carbitol solution of BH-9Z, manufactured by Sekisui Chemical Co., Ltd., Mw: 20 × 10 ⁴ )
Thermoplastic resin 6: Butyral resin (RC 20 wt% butyl carbitol solution of BH-3, manufactured by Sekisui Chemical Co., Ltd., Mw: 11 × 10 ⁴ )

[Dispersion medium]
Dispersion medium 1: Propylene glycol monomethyl ether acetate (manufactured by Tokyo Chemical Industry Co., Ltd., SP: 8.78 (cal / cm ³ ) ^1/2 )
Dispersion medium 2: Butyl carbitol (manufactured by Tokyo Chemical Industry Co., Ltd., SP: 9.61 (cal / cm ³ ) ^1/2 )
Dispersion medium 3: Terpineol (manufactured by Tokyo Chemical Industry Co., Ltd., SP (solubility): 11.09 (cal / cm ³ ) ^1/2 )

(Specific resistance)
About each Example and each comparative example, the specific resistance was measured as follows. First, after applying the obtained conductive paste, this was dried in air at 100 ° C. for 10 minutes, and subsequently heated under the curing conditions shown in Table 1 to obtain a sample (width 4 mm, long 40 mm in thickness and 40 μm in thickness). Subsequently, the resistance value in the planar direction of the sample was measured by a four-terminal method, and the specific resistance was calculated from the width and thickness of the coating film. Specific resistance In addition, a slide glass was used as a substrate for forming a coating film. The results are shown in Table 1.

(viscosity)
Using an Anton Paar rheometer MCR301, the measurement temperature was set to 25 ° C. and the measurement was performed. Specifically, the shear rate is increased from 0.01 [1 / s] to 1,000 [1 / s] and then decreased from 1,000 [1 / s] to 0.01 [1 / s]. At this time, the shear viscosity (Pa · s) when the pressure was lowered from 1,000 [1 / s] to 0.01 [1 / s] was measured.
Further, a logarithmic plot curve of shear rate [1 / s] −viscosity [Pa · s] was created from the measurement result of the viscosity [Pa · s] corresponding to the shear rate [1 / s] at 25 ° C.
Moreover, in the shear rate region I of 1 [1 / s] or more and 100 [1 / s] or less, when an inflection point exists in the viscosity behavior, the minimum value and the maximum value were calculated.
Further, in the shear rate region I of 1 [1 / s] or more and 100 [1 / s] or less, the shear rate at which the viscosity began to increase was defined as V1, and the shear rate at which the viscosity finished increasing was defined as V2. At this time, the shear rate difference | V2-V1 | was calculated.
In addition, the slope A calculated from the log-log plot curve is an average slope connecting the above-mentioned minimum value and maximum value.
The slope B calculated from the log-log plot curve was an average slope connecting the viscosity at the shear rate of 1 [1 / s] and the minimum value.
From the logarithmic plot curve results, it was found that the viscosity functions in the above examples and comparative examples are basically decreasing functions.

(Ion concentration)
The obtained conductive paste was dried at 150 ° C. for 10 minutes to remove the solvent, and then treated at 200 ° C. for 45 minutes to prepare a cured sample. Thereafter, the sample was freeze-ground. 40 mL of pure water was added to 2 g of the cured conductive paste that had been pulverized, and extracted with hot water at 125 ° C. for 20 hours to obtain extracted water.
This extraction water, Dionex ICS-3000 type, ICS-2000 type, ^Na _+, ^NH 4 ⁺ using DX-320 type ion ^{chromatograph, K +, Ca 2+, Mg} 2+, F -, Cl -, Br The total amount of ions of ⁻ , NO ₃ ⁻ , PO ₄ ³⁻ , PO ₃ ³⁻ , SO ₄ ²⁻ , and Zn ²⁺ was measured.
Here, a test solution and a standard solution were introduced into the ion chromatograph apparatus, each ion concentration was determined by a calibration curve method, and the amount of ions eluted from the sample was calculated.

(Sinterability)
Sinterability was judged using the specific resistance described above.
○: 20 μΩ · cm or less ×: More than 20 μΩ · cm For each example, the coating film obtained by applying the obtained conductive paste was dried at 100 ° C. for 10 minutes in an air atmosphere. Then, when it heat-processed on the hardening conditions shown in Table 1 continuously, the electroconductive particle in a coating film raise | generated the sintering and formed the particle | grain connection structure.

(Applicability (printability): aspect ratio, form retention)
The obtained conductive paste was screen-printed on a slide glass (manufactured by Matsunami Glass Industrial Co., Ltd., slide glass S1225) using a screen mask having an opening having a width of 50 μm and a length of 200 mm. The obtained printed matter was dried at 100 ° C. for 10 minutes using a box-type dryer. Thereafter, the printed material was cured at 200 ° C. for 45 minutes to obtain a cured product of the coating film. The thickness and width of this coating film were measured at 4 points on the coating film using a laser microscope VK9700 manufactured by Keyence Corporation, and the average value was taken. Aspect ratio = (thickness / width) × 100. The coating film was measured at four points of 20 mm, 60 mm, 100 mm, and 140 mm when the starting point was 0 mm.
When the aspect ratio was ◯: 10 or more, the shape retention was good. When the aspect ratio was less than 10: the shape retention was determined to be poor.

  In Table 1, the content of the resin (solid content of the resin calculated from the resin content (RC) in the resin solution) is the entire conductive paste (solid content of the resin, solvent content in the resin, conductive particles and dispersion). Content with respect to the medium). The resin (solid content of the resin calculated from the resin content (RC) in the resin solution) and the content of conductive particles indicate the content of the entire conductive paste. The solid content of the resin indicates the content relative to the total volume of the solid content of the resin and the conductive particles.

  As described above, the present invention has been described more specifically based on the embodiments. However, these are exemplifications of the present invention, and various configurations other than the above can be adopted.

DESCRIPTION OF SYMBOLS 100 Solar cell 110 Silicon substrate 120 N-type semiconductor layer 130 Antireflection film 140 Light-receiving surface electrode 142 Subgrid electrode 160 Back surface electrode plate 170 Back surface electrode

Claims (18)

Conductive particles;
Resin,
A conductive paste containing a dispersion medium,
A conductive paste having a region where the viscosity increases with an increase in shear rate in a shear rate region of 1 [1 / s] or more and 100 [1 / s] or less in a temperature environment of 25 ° C. The conductive paste according to claim 1,
Conductivity having an inflection point indicating an increase in viscosity with an increase in shear rate in a shear rate region of 1 [1 / s] or more and 100 [1 / s] or less in a temperature environment of 25 ° C. paste. The conductive paste according to claim 2,
The electroconductive paste whose difference between the minimum value and the maximum value in the viscosity is 20 Pa · s or less. The conductive paste according to claim 2 or 3,
In a shear rate region of 1 [1 / s] or more and 100 [1 / s] or less in a temperature environment of 25 ° C., the shear rate at which the viscosity starts to increase is defined as V1, and the shear rate at which the viscosity has been increased is defined as V1. A conductive paste in which | V2−V1 | is 1 [1 / s] or more and 20 [1 / s] or less when V2. The conductive paste according to any one of claims 1 to 4, wherein
A conductive paste having a viscosity at a shear rate of 1 [1 / s] in a temperature environment of 25 ° C. of 1 Pa · s or more and 100 Pa · s or less. The conductive paste according to any one of claims 1 to 5,
The electrically conductive paste whose specific resistance of the hardening body of the said electrically conductive paste is 1 microhm * cm or more and 20 microhm * cm or less. The conductive paste according to any one of claims 1 to 6,
The average particle diameter _{D 50} of the conductive particles, 0.5 [mu] m or more and 5.5μm or less, a conductive paste. The conductive paste according to any one of claims 1 to 7,
The resin includes a compound having a polar group,
The electrically conductive paste in which the said polar group contains 1 or more types selected from the group which consists of a hydroxyl group, an amide group, an epoxy group, and an amino group. The conductive paste according to any one of claims 1 to 8,
The electrically conductive paste whose weight average molecular weights of the said resin are 10 < ³ > or more and 10 < ⁶ > or less. The conductive paste according to any one of claims 1 to 9,
The electrically conductive paste whose content of the solid content of the said resin is 1 volume% or more and 50 volume% or less with respect to the total volume of the solid content of the said resin and the said electroconductive particle. The conductive paste according to any one of claims 1 to 10,
The conductive paste whose content of the said resin is 0.1 to 12 weight% with respect to the said whole conductive paste. The conductive paste according to any one of claims 1 to 11,
The electrically conductive paste in which the said resin contains 1 or more types selected from the group which consists of the acrylic polymer which does not contain a carboxyl group, a resole type phenol resin, the resin which has a benzoxazine ring, and (meth) acrylate. The conductive paste according to any one of claims 1 to 12,
A conductive paste comprising the conductive particles having a filling rate calculated using a powder layer shear force measuring apparatus of 40% or more and 70% or less. The conductive paste according to any one of claims 1 to 13,
A conductive paste, wherein the conductive particles include flaky particles. The conductive paste according to any one of claims 1 to 14,
A conductive paste, wherein the conductive particles include silver particles or copper particles. The conductive paste according to any one of claims 1 to 15,
The average particle diameter _{D 50} does not include the following conductive nanoparticles 100 nm, the conductive paste. The conductive paste according to any one of claims 1 to 16, wherein
The solubility parameter of the dispersing medium (SP value) ^{6 ((cal / cm 3)} 1/2) or ^{11 ((cal / cm 3)} 1/2) or less, a conductive paste. The conductive paste according to any one of claims 1 to 17,
Ions consisting of Na ⁺ , NH ₄ ⁺ , K ⁺ , Ca ²⁺ , Mg ²⁺ , F ⁻ , Cl ⁻ , Br ⁻ , NO ₃ ⁻ , PO ₄ ³⁻ , PO ₃ ³⁻ , SO ₄ ²⁻ , and Zn ²⁺ The electroconductive paste whose total amount of is 300 ppm or less with respect to the whole electroconductive paste.

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