JP2014120382A - Conductive resin paste and electronic element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive resin paste capable of being cured in short time at lower temperature than conventional ones, having low resistance as for an internal electrode such as a solid electrolytic capacitor or a conductive aluminum electrolytic capacitor, excellent in a high adhesive property, storage stability, and having low silver content, and to provide an electronic element using the same.SOLUTION: A conductive resin paste contains a conductive powder consisting of a silver powder (A) and an inorganic powder (B), a thermoplastic resin (C) and a solvent (D) as essential components, the inorganic powder (B) has a specific gravity of 4 or more and an average particle diameter of 1 μm or less, the thermoplastic resin (C) is a solid epoxy resin having an average molecular weight of 900 or more and contains no curing agent, the silver powder (A) is blended at 10 to 50 wt.% and the inorganic powder (C) is blended at 60 wt.% or less based on the whole weight so that a weight ratio between the conductive powder and the thermoplastic resin (C), (A+B):(C) is in a range of 80:20 to 98:2, and the weight ratio between the total amount of the conductive powder and the thermoplastic resin (C) and the solvent (D), (A+B+C):(D) is in the range of 90:10 to 30:70, and viscosity at 25°C is 0.2 to 100 Pa s.

Description

  The present invention relates to a conductive resin paste and an electronic device using the conductive resin paste, and more specifically, can be cured in a short time at a lower temperature than conventional, with low resistance for internal electrodes such as solid electrolytic capacitors and conductive aluminum solid electrolytic capacitors, The present invention relates to a conductive resin paste excellent in high adhesion and storage stability and having a low silver content, and an electronic device using the same.

  For the connection of electronic parts and the formation of electrodes and circuits, conductive resin paste containing silver powder, resin component, curing agent component and solvent is used, for example, silver powder of conductive material and epoxy of resin component A conductive resin paste containing a resin, a phenol resin-based curing agent, and a solvent has been proposed (Patent Document 1). By using this, excellent conductivity was obtained such that the volume resistance value after heat curing was less than 10 μΩcm. However, since the conductive resin paste needs to be sintered at a high temperature of 180 ° C. or higher when in use, it is difficult to use it on an organic material having low heat resistance. In addition, since the resin and the curing agent are mixed, there is also a problem that it cannot be stored at room temperature.

  In order to avoid this problem, a conductive resin paste that uses a thermoplastic resin and can be stored at room temperature has been proposed (Patent Document 2). This enables storage at room temperature by selecting acrylic, butyral, polyester or the like as the resin component. However, since a specific amount of Na ions is contained in the Ag powder for the purpose of reducing the resistance, there is a concern about an increase in leakage current of the electronic device.

Until now, as in Patent Document 3, Patent Document 4 and Patent Document 5, it has been studied to maintain various characteristics such as volume resistivity and strength during heat by using only silver powder as a conductive material.
That is, in patent document 3, it is comprised with a metal powder, an epoxy resin, bisalkenyl substituted nadiimide, and a hardening | curing agent, and while the said metal powder is mix | blended in the range of 60 to 90 weight%, silica, titania, A powder selected from alumina, a curing accelerator, and a conductive agent that acts as a diluent for an epoxy resin and the bisalkenyl-substituted nadiimide, and at least one organic compound that does not exist as a liquid during curing is added as an additive component Adhesives have been proposed.

Further, JP at 4, to improve the Patent Document 3, but is contained 80 to 95 wt% of silver powder with respect to the total amount, this time, 8.0 g / cm ³ tap density of 3.5 g / cm ³ or more The following silver powder (a) is 40 to 95% by weight based on the total amount, and the silver powder (b) having a tap density of 0.1 g / cm ³ or more and less than 3.5 g / cm ^{3 is set} to 50% by weight or less. Conductive adhesives have been proposed.

  In Patent Document 5, the conductive filler is 50 to 95% by weight, the resin binder is 5 to 50% by weight, and the conductive filler and a specific diluent. The resin binder is epoxy resin, dicyandiamide, curing acceleration. A product obtained by reacting an epoxy compound with a dialkylamine as a curing accelerator and treating the powder surface of a compound having a specific functional group in the molecule with an acidic substance. A conductive resin composition to be used has been proposed.

In addition, chip parts such as electronic elements have been reduced in size and performance, and a low silver content is required from the viewpoint of short-time curing and cost merit from the viewpoint of production efficiency. Therefore, there is a demand for a paste that has a low silver content, can be cured for a short time, and can be stored at room temperature with low resistance after curing.
However, although Patent Documents 3 to 5 can maintain various properties such as volume resistivity and strength at heat, the silver content is 50% by weight or more, leading to an increase in cost to the conductive adhesive composition. End up. Further, since a curing agent is added, it is difficult to store at room temperature.

Therefore, as a general method for reducing the silver content, a method of using only a metal powder obtained by coating a base metal with silver, or a method of using it in combination with silver powder has been selected. For example, in Patent Document 6, the volume resistivity is reduced by using a metal powder obtained by coating copper powder with silver and silver powder.
That is, in Patent Document 6, silver coated copper powder having an average particle diameter of 5 to 60 μm, silver powder having an average particle diameter of 0.5 to 15 μm, and an epoxy resin which is liquid at room temperature are essential components, and silver is contained in the components. A conductive resin paste containing 10 to 90% by weight of coated copper powder, 5 to 85% by weight of silver powder, and 75 to 97% by weight of the total amount of silver coated copper powder and silver powder is described.

  However, when metal powder coated with silver is used, if the pressure is high during the kneading with the three rolls, the silver coat part may be peeled off or cracks may occur. In addition, after application to an electronic device, cracks progress with time and the resistance value can be changed by exposing internal metal, making it difficult to apply. Further, when the pressure is low, the dispersion state is not sufficient, so that the variation tends to increase. Even with a revolving mixer or a mixer with stirring blades, the dispersion is insufficient and the performance is not exhibited. Furthermore, since a curing agent is added, room temperature storage is difficult.

On the other hand, in order to realize a low volume resistivity with a low silver content, Patent Document 7 has an average particle diameter of 0.5 to 2 μm and a tap density of ³ to 7 g / cm ³ , A conductive paste for plasma display has been proposed which contains a conductive powder having a specific surface area of 0.4 to 1.5 m ² / g and a specific organic component as essential components and contains glass frit.
According to Patent Document 7, a low silver content and cost reduction can be realized, but the glass frit is melted by holding at 590 ° C. for 15 minutes, and an adhesive force is expressed by re-solidification. At that time, the glass frit functions as a sintering aid for silver to reduce the volume resistivity. In general, organic substances such as resins are decomposed and evaporated at a high temperature of 590 ° C.

Such a conductive paste is applied when a peripheral member is not affected even when heat-treated at a high temperature such as a plasma display. In some applications, heat treatment must be performed at a temperature of 300 ° C. or lower in consideration of deterioration of peripheral members due to high-temperature heat treatment.
For example, it is a case where internal electrodes and end face electrodes of various electronic elements such as tantalum capacitors and aluminum solid electrolytic capacitors are bonded. Even after heat treatment at a temperature of 300 ° C. or less, organic substances such as resins exist, and the adhesive force is the resin. It is expressed by.
However, the fired silver paste as in Patent Document 7 requires heat treatment at a high temperature. Therefore, when heat treatment is performed at 300 ° C. or lower, the resin remains but cannot undergo a curing reaction, and the glass frit does not melt. Therefore, the adhesive strength is weak and not practical.

  Under such circumstances, there has been a strong demand for a conductive adhesive composition that can be cured at a low temperature for a short time and has low resistance, high adhesive strength, low silver content, and room temperature storage, which is used for chip parts such as semiconductors. .

JP 2011-129335 A JP 2007-284497 A Japanese Patent No. 3484957 Japanese Patent No. 3975728 JP 2001-192437 A Japanese Patent No. 3526183 Japanese Patent No. 3520798

  An object of the present invention is to provide a conductive resin paste that can be cured at a low temperature for a short time and has low resistance, high adhesion, and excellent storage stability, and an electronic device using the same, in view of the problems of the prior art described above. It is in.

  As a result of intensive studies to solve the above problems, the present inventor has found that a conductive resin paste containing silver powder, inorganic powder, thermoplastic resin, and solvent as essential components is an epoxy that is solid at room temperature as a thermoplastic resin. The weight ratio of the amount of the resin combined with the silver powder (A) and the inorganic powder (B) having a specific gravity of 4 or more and the amount of the thermoplastic resin (C) is 80:20 to 98. : The weight ratio of the amount of the total amount of the silver powder (A), the inorganic powder (B) having a specific gravity of 4 or more and the thermoplastic resin (C) to the amount of the solvent (D) is 90:10. It was found that when mixed so as to be in the range of ˜30: 70, a conductive resin paste having a specific viscosity can be solidified at a low temperature for a short time, and low resistance, high adhesion, and excellent storage stability can be obtained. It came to be completed.

That is, according to the first invention of the present invention, the conductive resin comprising the conductive powder comprising the silver powder (A) and the inorganic powder (B), the thermoplastic resin (C), and the solvent (D) as essential components. Paste,
The inorganic powder (B) has a specific gravity of 4 or more and an average particle diameter of 1 μm or less, and the thermoplastic resin (C) is a solid epoxy resin having an average molecular weight of 900 or more, does not contain a curing agent, and contains silver powder ( A) is blended in an amount of 10 to 50% by weight based on the total amount, and the inorganic powder (B) is blended in an amount of 60% by weight or less based on the total amount, and the weight ratio (A + B) of the conductive powder and the thermoplastic resin (C): ( C) is in the range of 80:20 to 98: 2, and the weight ratio (A + B + C) :( D) of the total amount of conductive powder and thermoplastic resin (C) to the amount of solvent (D) is 90: A conductive resin paste is provided which is mixed so as to be in the range of 10 to 30:70 and has a viscosity at 25 ° C. of 0.2 to 100 Pas.

According to a second aspect of the present invention, there is provided the conductive resin paste according to the first aspect, wherein the silver powder (A) has a tap density of ³ to 8 g / cm ^3. The

  According to a third aspect of the present invention, there is provided the conductive resin paste according to the first aspect, wherein the silver powder (A) has a flake shape.

  According to the fourth invention of the present invention, in the first invention, the inorganic powder (B) is selected from Ni, Cu, Bi, Co, Mn, Sn, Fe, Cr, Ti, or Zr. There is provided a conductive resin paste characterized by being a metal powder or an oxide powder thereof.

  According to a fifth aspect of the present invention, there is provided the conductive resin paste according to the first aspect, wherein the thermoplastic resin (C) has an average molecular weight of 1000 to 100,000. The

  According to a sixth aspect of the present invention, there is provided the conductive resin paste according to the first aspect, wherein the thermoplastic resin (C) is a linear bifunctional epoxy polymer compound. Is provided.

  According to a seventh aspect of the present invention, there is provided the conductive resin paste according to the first aspect, wherein the solvent (D) is a solvent having a vapor pressure at 20 ° C. of 0.7 hPa or less. Is provided.

  On the other hand, according to the eighth invention of the present invention, there is provided an electronic device using the conductive resin paste of any one of the first to seventh inventions.

  According to a ninth aspect of the present invention, there is provided an electronic device according to the eighth aspect, wherein the internal electrode of the solid electrolytic capacitor is formed from a conductive resin paste.

In the present invention, since a solid epoxy resin is used as a resin component and a curing agent is not blended by dissolving in a solvent, by volatilizing the solvent at a predetermined temperature during use, a thermoplastic resin such as polyester or acrylic resin can be used. Similar drying and solidification can be realized.
Since a liquid epoxy resin containing a curing agent is not used as in the past, even when the resin is applied to the gap between the electrodes, it does not harden before the gap is filled, so a stable coatability is obtained. It is done.

  Hereinafter, embodiments of the present invention will be described in detail.

1. Conductive resin paste The conductive resin paste of the present invention uses a solid epoxy resin having an average molecular weight of 900 or more as a thermoplastic resin in a conductive resin paste in which silver powder and inorganic powder, a thermoplastic resin, and a solvent are blended. Including silver powder in an amount necessary for imparting conductivity without adding a curing agent, and adding inorganic powder with a specific gravity of 4 or more in order to express cost merit. It is adjusted to a specific viscosity.

(A) Silver powder In the present invention, silver powder (hereinafter also referred to as Ag powder) is a conductive component of a conductive resin paste, and is usually pure that does not contain elements (such as Pb) that are harmful to electronic elements and the human body. Ag is used.
However, Sn, Bi, In, Ni, Cu, Fe, Zn, Ru, Au, Pt, Pd, and the like are coated with powder coated with Ag on the surface thereof, and the like within the range not impairing the object of the present invention. The mixed powder may be used.

In the present invention, the silver powder is not particularly limited by the tap density, shape, particle size, and the like.
However, since Ag powder has different characteristics depending on the tap density and the particle size, it may be preferable to use an Ag powder having a tap density of 3 to 8 / cm ³ depending on the type of electronic device.

Here, the tap density is a bulk density of a powder such as metal powder, and is a numerical value measured under the conditions of cylinder capacity: 20 mm, tap stroke: 20 mm, and stroke number: 50 in accordance with JIS Z2500. Silver powder having a tap density of 2 to 8 g / cm ³ has excellent dispersibility in the resin component.
On the other hand, if it is less than 2 g / cm ³ , the dispersibility is inferior, so the resin adhesive composition may not be highly filled, and silver-coated metal powder having a tap density of 8 g / cm ³ or more is currently available. It is difficult and preparation is not easy. A preferable tap density is 2.5 to 7 g / cm ³ , and a more preferable tap density is ³ to 6 g / cm ³ .
The shape of the silver powder may be any of flakes, spheres, needles, or a mixture thereof. Preferred in the present invention is a flake shape. The average particle size is preferably 15 μm or less, and more preferably 10 μm or less. This value shows the value when measured with a microtrack. If the above conditions are satisfied, two or more types of Ag powder may be mixed.

  Moreover, the ratio of Ag powder is set to the range of 10-50 weight% with respect to the total amount. Preferably it is 25 to 50% by weight. If it is less than 10% by weight, the volume resistivity may increase, and if it exceeds 50% by weight, the cost merit may be lost.

(B) Inorganic powder An inorganic powder is mix | blended as electroconductivity, in order to reduce silver content rate. However, since the main conductivity is expressed by silver powder, it is necessary to use an inorganic powder having a specific gravity of 4 or more so as not to inhibit it.

The inorganic powder is not particularly _{limited, WO 3, SnO 2, ZrO} 2, ZnO, TiO 2, NiO, ceramic powder and Ni, such as ZrC, Cu, Bi, Co, Mn, Sn, Fe, Cr, Ti, Examples thereof include metal powders such as Zr. In the case of ceramic powder, metal oxides are easily available, but metal carbides and metal sulfides can also be used. These are all inorganic powders having a specific gravity of 4 or more. Inorganic powders with a specific gravity of less than 4, such as Al ₂ O ₃ , Al, MgO and Mg, because the volume is large even with the same blending amount, the conductivity of the silver powder is hindered and the volume resistivity is increased. This is not preferable. The specific gravity of the inorganic powder is more preferably 5 or more.
The average particle size is 1 μm or less, preferably 0.8 μm or less, and more preferably 0.5 μm or less. This value shows the value when measured with a microtrack. If the above is satisfied, two or more kinds of inorganic powders may be mixed.

The proportion of the inorganic powder is set to be 60% by weight or less. 1 to 55% by weight is preferred, and 5 to 50% by weight is more preferred. When it exceeds 60% by weight, the conductivity of the silver powder is hindered, so that the volume resistivity becomes high, which is not preferable. Also, if the proportion of the inorganic powder is too small, the amount of silver powder increases and the cost increases, which is not preferable.
The weight ratio (A + B) :( C) between the conductive powder made of silver powder and inorganic powder and the thermoplastic resin is set in the range of 80:20 to 98: 2. When the weight ratio is less than 80% by weight, the conductivity after solidification tends to be deteriorated, and when it exceeds 98% by weight, there is a concern that the adhesion to the adherend is lowered and the film is easily peeled off. More preferably, it is 85: 15-96: 4.

(C) Thermoplastic resin In the present invention, as the thermoplastic resin, a solid epoxy resin having an average molecular weight of 900 or more is used as an adhesive component of the conductive resin paste. The solid epoxy resin means a solid at room temperature among resins having an epoxy group.

  In the case of a conductive resin paste, an epoxy resin is generally used together with a curing agent, and is used as a one-component or two-component thermosetting conductive resin paste. That is, a liquid epoxy resin is selected as the epoxy resin. The liquid epoxy resin is an epoxy resin having a weight average molecular weight of 700 or less measured by the GPC method and exhibiting a liquid state at normal temperature, and usually having a polymerization degree (n) of 1 or less. When a solid epoxy is selected, it is usually used by dissolving it with a reactive diluent or solvent and adding a curing agent thereto.

The epoxy resin to which the curing agent has been added is further reduced in viscosity with the start of heating, and is mixed with the curing agent, so that the reaction can proceed rapidly. However, since the curing agent is contained, there is a problem that the viscosity increases due to the reaction between the epoxy resin and the curing agent when stored at room temperature.
For this reason, in the present invention, a solid epoxy resin is used to dissolve in a solvent, and a curing agent is not blended. In use, the solvent is volatilized at a predetermined temperature, so that a general heat such as polyester or acrylic resin is used. Drying and solidification similar to plastic resin can be realized. The dissolved solid epoxy resin is returned to the solid epoxy resin again by volatilizing only the solvent, and expresses remarkable adhesiveness as compared with polyester and acrylic resin.

  In addition, by using a solid epoxy resin having an average molecular weight of 900 or more with a degree of polymerization (n) of more than 1, the dispersibility with Ag powder and solvent is good, and the solvent separation is slower compared to polyester and acrylic resin, so that coating is stable. Excellent in properties. The solid epoxy resin used in the present invention preferably has a weight average molecular weight of 1000 to 100,000 as measured by GPC, more preferably 1000 to 80,000, and still more preferably 1000 to 60,000. .

  The solid epoxy resin is not limited by the type, and for example, bisphenol A type, bisphenol F type, bisphenol S type epoxy resin, phenoxy type, naphthalene type epoxy resin, novolac type epoxy resin, biphenyl type epoxy resin, cyclopentadiene type epoxy 1 type (s) or 2 or more types selected from resin can be used. These are usually straight-chain bifunctional epoxy polymer compounds, in which a part of the epoxy group is substituted with another functional group, alkoxy-containing silane-modified epoxy resin, fluorinated epoxy resin, rubber A modified epoxy resin such as a modified epoxy resin may be used.

  Solid epoxy resins having a softening point of 60 ° C to 150 ° C are known. In the present invention, all of these are used, and those of 65 ° C to 145 ° C are preferred. Those having a softening point of 60 ° C. or higher are easy to use because they become close to the behavior of a liquid epoxy resin when dissolved in a solvent. The higher the softening point, the lower the solubility in the solvent, and the more difficult the resin composition as a whole flows. On the other hand, as the softening point approaches 150 ° C., solidification drying during use becomes easier.

  The solid epoxy resin is blended so that the resin amount and the weight ratio (C) :( A + B) of the total of the silver powder and the inorganic powder are in the range of 20:80 to 2:98. If there is less solid epoxy resin and the weight ratio of Ag powder and inorganic powder is less than 2:98, fluidity will be insufficient, while there will be more solid epoxy resin and weight ratio of Ag powder and inorganic powder. When it is larger than 20:80, it is considered that the conductivity is insufficient. The range of 4:96 to 15:85 is preferable.

(D) Solvent In the present invention, since the thermoplastic resin is a solid epoxy resin, it must be dissolved in a solvent. The kind of solvent is not particularly limited as long as it can dissolve the thermoplastic resin. Polyhydric alcohols, hydrocarbons and esters can be used. For example, terpineol, dihydroterpinyl acetate (hydrogenated terpineol acetate), ethylene glycol monobutyl ether acetate, or dipropylene glycol methyl ether acetate, dihydroterpinyl acetate, Examples thereof include bornyl propionate, isobornyl butyrate, isobornyl isobutyrate and the like.

  However, when using a conductive resin paste, it is considered that the paste is exposed to air, and therefore a solvent having a vapor pressure at 20 ° C. of 0.7 hPa or less is preferable. More preferably, a solvent having a vapor pressure at 20 ° C. of 0.5 or less is preferred. Generally, 2- (2-n-butoxyethoxy) ethyl acetate, 2-n-butoxyethyl acetate, 2- (2-ethoxyethoxy) ethyl acetate, and the like can be given. These may be used alone or in combination of two or more.

  The solvent content is such that the weight ratio (A + B + C) :( D) of the combined amount of silver powder, inorganic powder and thermoplastic resin is within the range of 90:10 to 30:70. . When the content of the solvent is less than 10% by weight, the viscosity of the conductive resin paste becomes too high, and when it exceeds 70% by weight, the Ag powder of the conductive resin paste, the inorganic powder, and the thermoplastic resin are combined. The concentration becomes low and it becomes difficult to form a uniform coating film. There is also a tendency for volume resistivity to increase. Preference is given to a range of 85:15 to 50:50.

  Further, since the content of the solvent is determined by the required viscosity characteristics of the electronic element, the optimum amount varies depending on the method for forming the coating film of the conductive resin paste. In coating film formation by screen printing or dispenser, etc., a conductive resin paste having a relatively high viscosity is required. Therefore, it is preferable to reduce the solvent content. In coating film formation by dipping, etc., low viscosity conductive Since a resin paste is required, it is preferable to increase the content of the solvent.

In the present invention, the viscosity of the conductive resin paste at 25 ° C. is set to 0.2 to 100 Pas. Within this viscosity range, it can be used regardless of the type of electronic element, but a great effect can be obtained particularly when applied to a solid electrolytic capacitor.
In addition, as for a viscosity, when it is left for a long time, a part of silver powder may settle. Therefore, the viscosity is a measured value after 60 seconds at 20 rpm using a HAT viscometer manufactured by Brookfield. In the present invention, a range of 0.3 to 50 Pas is preferable.

(E) Other optional components In the present invention, a dispersant, a stabilizer, a colorant, and the like can be added to the above essential components as long as the object of the present invention is not impaired.
Moreover, you may add thermoplastic resins, such as polyester and an acrylic resin, in the range which does not impair the objective of this invention. When a thermoplastic resin such as polyester or acrylic resin is added, it is 30% by weight or less, preferably 10% by weight or less based on the solid epoxy resin.

2. Electronic Element The conductive resin paste of the present invention can be applied to the formation and adhesion of internal electrodes and end face electrodes of various electronic elements such as tantalum capacitors, aluminum solid electrolytic capacitors, chip resistors, and multilayer ceramic capacitors. In particular, it is effective for manufacturing an internal electrode of a solid electrolytic capacitor in which a coating film is formed by dipping or the like of a conductive resin paste.

  The conductive resin paste is stable when the coating film is solidified on the object, for example, when heated at a temperature of 120 to 180 ° C. for 10 to 60 minutes, the solvent component is volatilized / evaporated or decomposed and scattered. It becomes a solidified film. The obtained electronic device has excellent conductivity because the solidified film uniformly disperses silver powder in the resin component.

  EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. The raw materials used are as follows. Moreover, each sample of Examples 1-17 and Comparative Examples 1-15 evaluated the following shown after kneading | mixing.

(A) Silver powder Flaked Ag powder A Ag powder having a tap density of 3.8 g / cm ³ Flaked Ag powder B Ag powder having a tap density of 2 g / cm ³ Spherical Ag powder C Tap density of 4.1 g / cm ³ Ag powder

(B) Inorganic powder Inorganic powder A Specific gravity of 7.16, WO ₃ powder having an average particle size of 0.3 μm Inorganic powder B Ni powder having a specific gravity of 8.90 and an average particle size of 0.5 μm Inorganic powder C Specific gravity Of SnO ₂ powder with an average particle diameter of 1.0 μm, an inorganic powder D, a specific gravity of 6.95, an SnO ₂ powder with an average particle diameter of 2.0 μm, an inorganic powder E, a specific gravity of 3.58, and an average particle size MgO powder with a diameter of 0.5 μm

(C) Resin Epoxy Resin Compound A Bisphenol A type solid epoxy resin (Mitsubishi Chemical Corporation: jER1256, average molecular weight: about 50,000)
Epoxy resin compound B bisphenol A type solid epoxy resin (Mitsubishi Chemical Corporation: jER1004, average molecular weight: about 1,650)
Epoxy resin compound C bisphenol A type liquid epoxy resin (Mitsubishi Chemical Corporation: jER828, average molecular weight: about 370)
Epoxy resin compound D Liquid epoxidized polybutadiene resin (Daicel Corporation: Epolide PB4700 average molecular weight: about 2,750)
Polyester resin compound A High molecular weight saturated polyester resin (Nippon Gosei Chemical Industry Co., Ltd .: Nichigo Polyester TP-220, average molecular weight: about 16,000)
Acrylic resin compound A Acrylic resin (Mitsubishi Rayon Co., Ltd .: BR-95, average molecular weight: about 320,000)

(D) Curing agent, curing accelerator Curing agent A Dicyandiamide (Mitsubishi Chemical Corporation: DICY7)
Curing Accelerator A 2-Phenyl-4-methyl-5-hydroxymethylimidazole (Shikoku Kasei Co., Ltd .: Curesol 2P4MHZ-PW)

(E) Solvent Solvent A 2- (2-n-Butoxyethoxy) ethyl acetate (Kanto Chemical Co., Inc .: 2- (2-n-Butoxyethoxy) ethyl acetate, vapor pressure (20 ° C.): 0.01 hPa)
Solvent B 2-n-butoxyethyl acetate (Kanto Chemical Co., Inc .: 2-n-butoxyethyl acetate, vapor pressure (20 ° C.): 0.31 hPa)
Solvent C Butyl carbitol (Kanto Chemical Co., Inc .: 2- (2-n-butoxyethoxy, vapor pressure (20 ° C.): 0.013 hPa)
Solvent D N-methyl-2-pyrrolidone (Kanto Chemical Co., Inc .: N-methyl-2-pyrrolidinone, vapor pressure (20 ° C.): 0.32 hPa)
Solvent E 2-n-butoxyethanol (Kanto Chemical Co., Inc .: 2-n-butoxyethanol, vapor pressure (20 ° C.): 0.8 hPa)

(1) Viscosity of conductive resin paste Viscosity is a value measured after 60 seconds at 20 rpm using a HAT viscometer manufactured by Brookfield.

(2) Measurement of volume resistivity After printing a sample (conductive resin paste) in a rectangular shape having a width of 0.6 mm and a length of 60 mm on an alumina substrate and leaving it in an oven at 150 ° C. for 40 minutes to solidify, After cooling to room temperature, the resistance value was measured at both ends on the conductive resin paste. Subsequently, the film thickness of the printed and solidified conductive resin paste was measured, and the resistivity was determined from the resistance value and the film thickness.

(3) Measurement of adhesive strength A sample (conductive resin paste) was dropped on an alumina substrate, a 1.5 mm square silicon chip was placed, and allowed to solidify in an oven at 150 ° C. for 40 minutes. After cooling to room temperature, a force was applied to the silicon chip from the horizontal direction with respect to the substrate, and the force when the silicon chip was peeled was measured as the adhesive strength.

(4) Storage stability When the kneaded conductive resin paste is stored at 25 ° C., the viscosity is measured once / week, and the number of days until the initial viscosity is increased by 20% or more is 90 days or more. Is determined to be good (◯), and less than that is impossible (×).
Using a Brookfield HAT viscometer, the viscosity at 20 rpm was measured.

(5) Cost merit A case where the silver content is 50% by weight or less was judged as good (◯), and a case where the silver content was exceeded was judged as impossible (×).

(6) Comprehensive evaluation In the above five items, the viscosity is 0.2 to 100 Pa · s, the volume resistivity is 5 mΩ · cm or less, the adhesive strength is 20 N or more, the storage stability is good (◯), and the cost merit is Only those satisfying all the conditions of good (◯) were judged as good (◯), and when there was one that did not satisfy the conditions, it was judged as impossible (×).

Example 1
Flaked Ag powder A having a tap density of 3.8 g / cm ³ as Ag powder, WO ₃ powder A having a specific gravity of 7.16 and an average particle size of 0.3 μm as an inorganic powder, and epoxy resin as a resin component Compound A: bisphenol A type solid epoxy resin (Mitsubishi Chemical Corporation: jER1256), 2- (2-n-butoxyethoxy) ethyl acetate (Kanto Chemical Co., Ltd .: 2- (2-n-butoxyethoxy) acetate as a solvent component ) Ethyl) as a raw material, a conductive resin paste was prepared and kneaded using a three-roll kneader to obtain the conductive adhesive of the present invention.
Using this conductive resin paste, printing was performed on an alumina substrate, and the volume resistivity was measured under the above conditions. Moreover, it dropped on the alumina substrate, mounted a silicon chip, heated to 150 ° C. to evaporate the solvent for 40 minutes, and then measured the adhesive strength. Further, the storage stability was evaluated by measuring the viscosity while storing the conductive resin paste of the present invention at 25 ° C. The results are also shown in Table 1. In Table 1, the concentration of each component is shown in wt%.

(Examples 2 to 8)
A conductive resin paste was prepared in the same manner as in Example 1 except that the composition of Ag powder, inorganic powder, epoxy resin compound A, and solvent A described in Table 1 was changed, and a three-roll kneader was used. And kneaded to obtain the conductive resin paste of the present invention. Then, using this conductive resin paste, it printed on the alumina substrate and measured the volume resistivity on said conditions. Further, it was dropped on an alumina substrate, placed on a silicon chip, heated to 150 ° C. and the solvent was vaporized for 40 minutes, and then the adhesive strength was measured. While the conductive resin paste of the present invention was stored at 25 ° C., the viscosity was measured and storage stability was evaluated. The results are also shown in Table 1.

(Examples 9 to 17)
As described in Table 2, the Ag powder was used as flake Ag powder B having a tap density of 2 g / cm ³ (Example 9), or spherical Ag powder C having a tap density of 4.1 g / cm ³ was used (Example 10). The conductive resin paste was prepared in the same manner as in Example 1 except that, and kneaded using a three-roll type kneader to obtain the conductive resin paste of the present invention.
Also, the inorganic powder is changed to inorganic powder B: Ni powder having a specific gravity of 8.90 and an average particle diameter of 0.5 μm (Example 11), or the inorganic powder is inorganic powder C: specific gravity is 6.95, average A conductive resin paste was prepared in the same manner as in Example 1 except that the particle size was changed to SnO ₂ powder having a particle size of 1.0 μm (Example 12), and this was kneaded using a three-roll kneader. The conductive resin paste of the invention was obtained.
The resin component is changed to epoxy resin compound B: bisphenol A type solid epoxy resin (Mitsubishi Chemical Corporation: jER1004) (Example 13) or the solvent component is solvent B: 2-n-butoxyethyl acetate (Kanto Chemical Co., Inc .: 2-N-butoxyethyl acetate) (Example 14), or solvent C: butyl carbitol (Kanto Chemical Co., Inc .: 2- (2-n-butoxyethoxy) ethanol (Example 15), or solvent D: N-methyl-2-pyrrolidone (Kanto Chemical Co., Inc .: N-methyl-2-pyrrolidinone) (Example 16) or solvent E: 2-n-butoxyethanol (Kanto Chemical Co., Ltd .: 2-n-) A conductive resin paste was prepared in the same manner as in Example 1 except that (butoxyethanol) was changed to (Butoxyethanol), and kneaded using a three-roll kneader. To give a light conductive resin paste.
Then, using this conductive resin paste, it printed on the alumina substrate and measured the volume resistivity on said conditions. Further, it was dropped on an alumina substrate, placed on a silicon chip, heated to 150 ° C. and the solvent was vaporized for 40 minutes, and then the adhesive strength was measured. While the conductive resin paste of the present invention was stored at 25 ° C., the viscosity was measured and storage stability was evaluated. The results are also shown in Table 2.

(Comparative Examples 1-8)
As shown in Table 3, a conductive resin paste was prepared in the same manner as in Example 1 except that the blending amounts of the Ag powder component, the inorganic powder component, the resin component, and the solvent component were changed, and a three-roll kneader Was used for kneading to obtain a conductive resin paste for comparison.
Then, using this conductive resin paste, it printed on the alumina substrate and measured the volume resistivity on said conditions. Further, it was dropped on an alumina substrate, placed on a silicon chip, heated to 150 ° C. and the solvent was vaporized for 40 minutes, and then the adhesive strength was measured. The storage stability was evaluated by measuring the viscosity while storing this conductive resin paste at 25 ° C. The results are also shown in Table 3.

(Comparative Examples 9-15)
As described in Table 4, instead of inorganic powder A as an inorganic powder component, inorganic powder D: SnO ₂ powder having a specific gravity of 6.95 and an average particle size of 2.0 μm (Comparative Example 9), or inorganic powder E A conductive resin paste was prepared in the same manner as in Example 1 except that the specific gravity was changed to MgO powder having a specific gravity of 3.58 and an average particle diameter of 0.5 μm (Comparative Example 10), and a three-roll kneader Was used for kneading to obtain a conductive resin paste for comparison.
Moreover, instead of the epoxy resin compound A of the resin component, an epoxy resin compound C: a bisphenol A type liquid epoxy resin (Mitsubishi Chemical Corporation: jER828) is used (Comparative Example 11), or an epoxy resin compound D: an epoxidized polybutadiene resin ( (Comparative Example 12) or polyester resin compound A: high molecular weight saturated polyester resin (Nippon Gosei Chemical Co., Ltd .: Nichigo Polyester TP-220) (Comparative Example 13) or acrylic Resin Compound A: Conductive resin paste was prepared in the same manner as in Example 1 except that it was changed to acrylic resin (Mitsubishi Rayon Co., Ltd .: BR-95) (Comparative Example 14), and a three-roll kneader was used. And kneaded to obtain a conductive resin paste for comparison.
Curing agent A: dicyandiamide (Mitsubishi Chemical Corporation: DICY7) as a curing agent component, and curing accelerator A: 2-phenyl-4-methyl-5-hydroxymethylimidazole (Shikoku Kasei Co., Ltd .: Curesol 2P4MHZ- as an accelerator component) A conductive resin paste was prepared in the same manner as in Example 1 except that PW) was added, and kneaded using a three-roll kneader to obtain a conductive resin paste for comparison (Comparative Example 15). ).
Thereafter, these conductive resin pastes were used to print on an alumina substrate, and the volume resistivity was measured under the above conditions. Moreover, after dripping on an alumina substrate and mounting a silicon chip, it heated at 150 degreeC, and vaporized or hardened the solvent for 40 minutes, Then, the adhesive strength was measured. Next, the storage stability was evaluated by measuring the viscosity while storing this conductive resin paste at 25 ° C. The results are also shown in Table 4.

"Evaluation"
As is clear from Tables 1 and 2, the conductive resin pastes of Examples 1 to 17 use a solid epoxy resin having an average molecular weight of 900 or more according to the present invention, does not contain a curing agent, and contains silver powder (A) and heat. The weight ratio of the plastic resin (B) and the weight ratio of the amount of the silver powder (A) and the thermoplastic resin (B) combined with the amount of the solvent (C) are mixed in a predetermined range. Therefore, it turns out that all of electroconductivity, adhesiveness, and storage stability are excellent. In Examples 2, 7, and 8, the volume resistivity is slightly high, in Example 5, the viscosity is slightly high, and in Examples 7, 8, and 11, the adhesive strength is slightly weak, but there is no practical problem. .

  On the other hand, as can be seen from Table 3, in Comparative Example 1, since the amount of Ag powder was smaller than that of the present invention, the resistance value could not be measured and became impossible. Since the comparative example 2 had more Ag powder than this invention, cost merit was not found but became impossible. In Comparative Example 3, since the total amount of Ag powder and inorganic powder was less than that of the present invention, the ratio between the total amount of Ag powder and inorganic powder and the amount of resin was changed, and the adhesive strength was weak and was impossible. In Comparative Example 4, the total amount of Ag powder and inorganic powder was larger than that of the present invention, and the amount of solvent was reduced. Therefore, the viscosity was high, and the ratio of the total amount of Ag powder and inorganic powder to the resin was changed. The strength was weak and was impossible. In Comparative Example 5, the ratio of the total amount of Ag powder and inorganic powder and the amount of resin was made lower than that of the present invention, so that the volume resistivity could not be measured and became impossible. In Comparative Example 6, since the ratio of the total amount of Ag powder and inorganic powder and the amount of resin was higher than that of the present invention, the adhesive strength was low and became impossible. In Comparative Example 7, the ratio of the total amount of the Ag powder, the inorganic powder, and the resin was made lower than that of the present invention, so that the adhesive strength was low and was impossible. In Comparative Example 8, since the ratio of the total amount of Ag powder, inorganic powder, resin, and solvent amount was higher than that of the present invention, the viscosity was high, and the resistance value could not be measured, which became impossible.

  As is clear from Table 4, Comparative Example 9 uses an inorganic powder D having a large particle size, and thus has a high volume resistivity and cannot be used. Moreover, since the comparative example 10 used the inorganic powder E with small specific gravity, the volume resistivity became high and became impossible. Since the comparative example 11 used the liquid epoxy resin compound C, the volume resistivity was high and the adhesive strength was weak and became impossible. Similarly, since Comparative Example 12 used a liquid epoxy resin compound D, the volume resistivity was high and the adhesive strength was weak, which was not possible. In Comparative Example 13, since the polyester compound A was used instead of the solid epoxy resin, the adhesive strength was weak and it was not possible. Since the comparative example 14 used the acrylic resin compound A instead of a solid epoxy resin, its adhesive strength was weak and became impossible. Since the comparative example 15 uses the hardening | curing agent A and the hardening accelerator A with respect to solid epoxy resin, its storage stability became bad and became impossible.

  According to the present invention, in a conductive resin paste containing silver powder (A), inorganic powder (B), thermoplastic resin (C), and solvent (D) as essential components, the specific gravity of silver powder (A) is 4 or more. The thermoplastic resin (B) is a solid epoxy resin having a molecular weight of 900 or more so that the total weight of the inorganic powder (B) and the weight ratio of the thermoplastic resin (B) and the weight ratio of these to the solvent are within a specific range. Since it was prepared without using a specific amount combination and a curing agent, the conductivity, adhesive strength and storage stability can be improved, and it can be applied to various electronic devices.

  The conductive resin paste of the present invention can be applied to internal electrodes and end face electrodes of various electronic elements such as tantalum capacitors, aluminum solid electrolytic capacitors, chip resistors, and adhesion thereof. In addition, since it can be cured at a low temperature, it can be handled well and a low resistance value can be realized with respect to wiring electrodes such as a touch panel and electronic elements using them.

Claims (9)

A conductive resin paste comprising silver powder (A) and inorganic powder (B) as conductive powder, thermoplastic resin (C), and solvent (D) as essential components,
The inorganic powder (B) has a specific gravity of 4 or more and an average particle diameter of 1 μm or less, and the thermoplastic resin (C) is a solid epoxy resin having an average molecular weight of 900 or more, does not contain a curing agent, and contains silver powder ( A) is blended in an amount of 10 to 50% by weight based on the total amount, and inorganic powder (B) is blended in an amount of 60% by weight or less based on the total amount, and the weight ratio (A + B) of the conductive powder and the thermoplastic resin (C): C) is in the range of 80:20 to 98: 2, and the weight ratio (A + B + C) :( D) of the total amount of conductive powder and thermoplastic resin (C) to the amount of solvent (D) is 90: A conductive resin paste, which is mixed so as to be in a range of 10 to 30:70, and has a viscosity at 25 ° C. of 0.2 to 100 Pas. 2. The conductive resin paste according to claim 1, wherein the silver powder (A) has a tap density of ³ to 8 g / cm ³ .   The conductive resin paste according to claim 1, wherein the silver powder (A) has a flake shape.   The inorganic powder (B) is a metal powder selected from Ni, Cu, Bi, Co, Mn, Sn, Fe, Cr, Ti, or Zr, or an oxide powder thereof. The conductive resin paste described in 1.   2. The conductive resin paste according to claim 1, wherein the thermoplastic resin (C) has an average molecular weight of 1000 to 100,000.   The conductive resin paste according to claim 1, wherein the thermoplastic resin (C) is a linear bifunctional epoxy polymer compound.   2. The conductive resin paste according to claim 1, wherein the solvent (D) is a solvent having a vapor pressure at 20 ° C. of 0.7 hPa or less.   An electronic device comprising the conductive resin paste according to claim 1.   The electronic device according to claim 8, wherein the internal electrode of the solid electrolytic capacitor is formed of a conductive resin paste.