Electrically conductive paste

Abstract

To provide electrically conductive paste which is excellent in electrical conductivity and heat-resistant bondability.SOLUTION: In a cured film 10 formed of electrically conductive paste, the electrically conductive paste contains silver particles, and a thermosetting epoxy resin 3 which is liquid at room temperature (25°C). The silver particles are composed of flaky silver particles 1 and spherical silver particles 2, and each of the flaky silver particles 1 has an average particle diameter of 2.0 μm or more and 3.5 μm or less, a specific surface area of 0.3 m2 / g or more and 1.0 m2 / g or less, and TAP density of 4.5 g / cm3 or more. Each of the spherical silver particles 2 has an average particle diameter of 0.1 μm or more and 1.0 μm or less, a specific surface area of 1.5 m2 / g or more, and TAP density of 2.0 g / cm3 or less. A mass mixture ratio (flaky silver particles / spherical silver particles) of each of the flaky silver particles 1 to the spherical silver particles 2 is within the range of 90 / 10 to 98 / 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a conductive paste. [Background technology]

[0002] Electronic components mounted on electronic devices such as personal computers and mobile phones are bonded to predetermined positions using conductive bonding materials, and it is preferable that such bonding materials have low electrical resistance. Examples of this type of bonding material include a bonding material that contains a conductive component such as metal particles and a thermosetting resin component such as an epoxy resin, and is prepared in a paste form (hereinafter, this type of bonding material will also be simply referred to as a "conductive paste"). As prior art of bonding materials (conductive pastes) containing such thermosetting resin components, for example, Patent Documents 1 to 3 disclose conductive pastes in which the particle size of the conductive components in the conductive paste is adjusted to increase the contact area between the conductive components, thereby reducing the electrical resistance of the cured film (bonding film) formed after thermal curing of the bonding material. Furthermore, Patent Document 4 discloses a conductive paste in which a sublimable organic compound is added to the conductive paste, and a dense cured film is formed by volatilization of the volatile components, thereby reducing the electrical resistance of the cured film. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7375249 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-147378 [Patent Document 3] Patent No. 5257574 [Patent Document 4] Japanese Patent Application Laid-Open No. 2004-179101 Summary of the Invention [Problem to be solved by the invention]

[0004] However, from the viewpoints of the cost of the conductive paste, miscibility of the conductive component in a product with a relatively high viscosity, etc., a conductive paste that achieves the low electrical resistance required for bonding electronic devices even with a low content of the conductive component is preferred. Therefore, further improvements in the content of the conductive component in the conductive paste and the electrical resistance of the cured film are required. On the other hand, when using electronic devices, there are concerns about an increase in thermal resistance due to miniaturization of components, an increase in heat generation due to an increase in the processing speed of semiconductor elements, etc. Therefore, it is preferable that this type of bonding material also has high bonding properties in a high-temperature environment after forming a cured film.

[0005] The present disclosure has been made in view of the above circumstances, and a main object thereof is to provide a paste-like bonding material (conductive paste) that is excellent in electrical conductivity and heat-resistant bonding. [Means for solving the problem]

[0006] To solve the above problems, the conductive paste disclosed herein contains silver particles and a thermosetting epoxy resin that is liquid at room temperature (25°C). The silver particles consist of flaky silver particles and spherical silver particles, and the flaky silver particles have an average particle diameter of 2.0 μm or more and 3.5 μm or less and a specific surface area of ​​0.3 m. 2 / g or more 1.0m 2 / g or less, TAP density 4.5g / cm 3 The spherical silver particles have an average particle diameter of 0.1 μm or more and 1.0 μm or less, and a specific surface area of ​​1.5 m 2 / g or more, TAP density 2.0g / cm 3 The mass mixing ratio of the flaky silver particles to the spherical silver particles (flaky silver particles / spherical silver particles) is in the range of 90 / 10 to 98 / 2.

[0007] In the conductive paste having the above-described configuration, the use of flake-shaped and spherical silver particles having an average particle size, etc., within a predetermined range increases the contact area between the silver particles, thereby reducing the electrical resistance of the cured film even when only a small amount of silver particles is added.

[0008] In a preferred embodiment of the conductive paste disclosed herein, the paste does not contain a solvent, which can prevent voids from forming on the cured film of the conductive paste due to evaporation of the solvent.

[0009] In a preferred embodiment of the conductive paste disclosed herein, the content of the epoxy resin is 10% by mass or more and 20% by mass or less of the entire conductive paste, which allows the conductive paste to achieve suitable heat-resistant bonding properties.

[0010] In a preferred embodiment of the conductive paste disclosed herein, the spherical silver particles have an average particle size of 0.2 μm or more and 0.8 μm or less, which more preferably reduces the electrical resistance of the cured film of the conductive paste.

[0011] In a preferred embodiment of the conductive paste disclosed herein, the spherical silver particles have a specific surface area of ​​3.0 m 2 / g or more, the electrical resistance of the cured film of the conductive paste can be more suitably reduced.

[0012] In a preferred embodiment of the conductive paste disclosed herein, when a cured film measuring 2 cm in length, 2 cm in width, and 30 μm in thickness is formed on a glass plate, the volume resistivity of the cured film is 9.0×10 -4 This makes it suitable for use as a conductive paste.

[0013] In a preferred embodiment of the conductive paste disclosed herein, a copper substrate measuring 3 cm in length, 1 cm in width, and 0.15 cm in thickness and a silicon carbide substrate measuring 0.1 cm in length, 0.1 cm in width, and 300 μm in thickness are bonded together via a cured film measuring 0.11 cm in length, 0.11 cm in width, and 100 μm in thickness, and the shear strength after being held in an environment of 175°C or 200°C for a predetermined time is 30 N / mm 2 As a result, the conductive paste can be suitably used at high temperatures. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating the configuration of a cured film 10 formed from a conductive paste according to one embodiment. [Figure 2] FIG. 2 is a graph showing the measurement results of volume resistivity. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the technology disclosed herein are described below. Matters necessary for implementing the technology disclosed herein, other than those specifically mentioned in this specification, can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. Furthermore, in the drawings described in this specification, components and parts that perform the same function are denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not necessarily reflect the actual dimensional relationships.

[0016] <Conductive paste> The main constituent materials of the conductive paste according to the present disclosure will be described below. Note that, for additive materials of the conductive paste not described here, conventionally known materials that can be used for this type of paste-like joining material can be used.

[0017] 1 is a cross-sectional view schematically illustrating the configuration of a cured film 10 formed from a conductive paste according to one embodiment. The conductive paste according to one embodiment disclosed herein contains flaky silver particles 1, spherical silver particles 2, and a thermosetting epoxy resin (resin matrix component 3 constituting cured film 10) that is liquid at room temperature (25°C). In this specification, when the volume resistivity of the cured film is measured, it is at least 1.0 × 10 -2 When the volume resistivity is Ωcm or less, the conductive paste is deemed to have the conductivity required for the paste.

[0018] 1. Silver particles The metal filler contained in the conductive paste according to one embodiment includes flaky silver particles 1 and spherical silver particles 2. This will be explained in detail below.

[0019] 1.1 Flake-shaped silver particles 1 The flaky silver particles 1 have an aspect ratio of 1.5 or more. The aspect ratio is a value calculated based on observation with an electron microscope, and is the ratio a / b of the length of the long side b to the length of the short side a when a rectangle is drawn circumscribing the particles constituting the metal filler. The average aspect ratio refers to the arithmetic mean value of the aspect ratios obtained for 100 particles. The flaky silver particles 1 used may have an average aspect ratio of 1.5 or more, but a ratio of 1.5 to 3.5 is particularly preferred. The shape may be an irregular flake shape that includes a mixture of flakes (scales), strips, rods, fibers, etc. The size of each particle may be approximately uniform or random. Silver powder (particles) prepared into flakes by impacting non-flake-shaped silver powder can also be used.

[0020] The average particle size of the flaky silver particles 1 (50% cumulative particle size on a volume basis based on a laser diffraction / scattering method) is suitably approximately 2.0 μm or more, and may be 2.5 μm or more, 2.7 μm or more, or 2.9 μm or more. On the other hand, if the average particle size of the flaky silver particles 1 is excessively large, it is undesirable because it increases the contact area with the spherical silver particles 2 described below, potentially reducing the effect of suitably reducing the electrical resistance of the cured film 10. For example, a particle size of 3.5 μm or less is suitable, and 3.0 μm or less is preferable.

[0021] The specific surface area of ​​the flake silver particles 1 (specific surface area based on the BET method) is approximately 1.0 m 2 / g or less is appropriate, and 0.90m 2 / g or less, 0.80m 2 / g or less, or 0.70m 2 / g or less. On the other hand, if the specific surface area of ​​the flaky silver particles 1 is excessively small, the contact area with the spherical silver particles 2 (described later) increases, which is undesirable because it may reduce the effect of suitably reducing the electrical resistance of the cured film 10. For example, 2 / g or more is appropriate, and 0.40m 2 / g or more is more preferable, and 0.50m 2 / g or more is particularly preferred.

[0022] The tap density (the density obtained after mechanically tapping the measuring vessel containing the powder sample) of flake silver particles is approximately 7.0 m 2 / g or less is appropriate, and 6.5m 2 / g or less, or 6.0m 2 On the other hand, if the TAP density of the flaky silver particles 1 is excessively low, the contact area with the spherical silver particles 2 (described later) increases, which is undesirable as it may reduce the effect of suitably reducing the electrical resistance of the cured film 10. For example, 3 The above is appropriate, and 5.0m 2 / g or more is preferred.

[0023] 1.2 Spherical silver particles 2 The spherical silver particles 2 have an aspect ratio of 1.0 or more and less than 1.5 and are spherical in shape. The size of each particle may be approximately uniform or may be random.

[0024] The average particle size of the spherical silver particles 2 is suitably approximately 0.10 μm or more, and may be 0.20 μm or more, 0.30 μm or more, or 0.40 μm or more. On the other hand, if the average particle size of the spherical silver particles 2 is excessively large, it is undesirable because it increases the contact area with the above-mentioned flaky silver particles 1 and may reduce the effect of suitably reducing the electrical resistance of the cured film 10. For example, a size of 1.0 μm or less is suitable, and 0.8 μm or less is preferable.

[0025] The specific surface area of ​​spherical silver particles 2 is approximately 4.5 m 2 / g or less is appropriate, and 4.0m 2 / g or less, or 3.5m 2 / g or less. On the other hand, if the specific surface area of ​​the spherical silver particles 2 is excessively small, the contact area with the flaky silver particles 1 increases, which is undesirable because it may reduce the effect of suitably reducing the electrical resistance of the cured film 10. For example, 2 / g or more is appropriate, and 2.0m 2 / g or more is preferred.

[0026] The TAP density of spherical silver particles 2 is approximately 5.0 m 2 / g or less is appropriate, and 4.5m 2 / g or less, 4.0m 2 / g or less, or 3.5m 2 / g or less. On the other hand, if the TAP density of the spherical silver particles 2 is excessively low, the contact area with the flaky silver particles 1 described above increases, which is undesirable because it may reduce the effect of suitably reducing the electrical resistance of the cured film 10. For example, 3 The above is appropriate, and 2.5m 2 / g or more is preferred.

[0027] The mass mixing ratio of the flaky silver particles 1 and the spherical silver particles 2 contained in the conductive paste is preferably 90 / 10 to 98 / 2, and particularly preferably 96 / 4 to 98 / 2, from the viewpoints of increasing the contact area therebetween and suitably reducing the electrical resistance of the cured film 10, as well as film-forming properties and handleability of the cured film 10.

[0028] 2. Epoxy resin The epoxy resin contained in the conductive paste according to one embodiment is liquid at room temperature (25°C). Epoxy resin is a general term for thermosetting resins that can be cured by crosslinking with epoxy groups contained in the polymer, and can contain an epoxy compound and a curing agent. In this case, the volume ratio of the epoxy compound to the curing agent can be 10:0.1 to 5:0.5.

[0029] Examples of the epoxy resins that are liquid at room temperature (25°C) include naphthalene-type epoxy resins, biphenyl-type epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, novolac-type epoxy resins, polyfunctional phenol-based epoxy resins, dicyclopentadiene-type epoxy resins, alicyclic and alcohol-based glycidyl amine-based resins, alicyclic and alcohol-based glycidyl ether-based resins, and alicyclic and alcohol-based glycidyl ester-based resins.

[0030] The curing agent may include at least one of an amine-based curing agent, a phenol-based curing agent, an acid anhydride-based curing agent, a polymercaptan-based curing agent, a polyaminoamide-based curing agent, an isocyanate-based curing agent, and a blocked isocyanate-based curing agent, and two or more types of curing agents may be mixed and used.

[0031] The epoxy resin may be any resin used in this type of bonding material without any particular limitation. Either one-component or two-component resins may be used, but one-component resins are preferred from the viewpoints of material stability, adjustment of curing temperature, etc.

[0032] The epoxy resin content of the conductive paste according to one embodiment is preferably relatively high from the viewpoint of improving the heat-resistant bonding property of the cured film, and is generally 10% by mass or more of the entire conductive paste, and may be 11% by mass or more, or even 12% by mass or more. On the other hand, if the amount of epoxy resin added is too excessive, the amount of silver particles added will be relatively small, which is not preferable. From this viewpoint, the epoxy resin content is, for example, appropriately 20% by mass or less, preferably 19% by mass or less, and more preferably 18% by mass or less.

[0033] 3. Other ingredients 3.1 Solvent As described above, the conductive paste disclosed herein preferably does not contain a solvent, but may contain a solvent as long as it does not contradict the objectives of the technology disclosed herein. Solvents that can be used are preferably those that dissolve the epoxy resin, are not reactive with the epoxy resin, and have a low vapor pressure. Examples of such solvents include alcohols, ethers, and ketones. Since the conductive paste does not contain the above-mentioned solvent, voids caused by evaporation of the solvent do not occur when a cured film is formed, and therefore the conductive paste can be suitably used.

[0034] If the conductive paste does not contain a solvent, the viscosity of the conductive paste increases depending on the viscosity of the epoxy resin, making it difficult to increase the content of the conductive component. Furthermore, since the solvent does not volatilize during curing of the conductive paste, the concentration of the conductive component in the cured film tends to be lower than in a conductive paste containing a solvent. However, in one embodiment, the conductive component, silver particles, is composed of flakes and spheres, and the physical quantities, such as particle diameter, are within a predetermined range that can suitably increase the contact area between the particles. Therefore, even if the amount of the conductive component added is small, the volume resistivity of the cured film can be suitably reduced.

[0035] 3.2 Dielectric powder The conductive paste disclosed herein may contain, in addition to the silver particles and epoxy resin described above, a dielectric powder as an optional component, within a range that does not significantly impair the essence of the present invention. The dielectric powder is a component that mainly constitutes the conductive film after firing. The dielectric powder is a component that, when disposed between particles that constitute the conductive powder, can, for example, suppress sintering of the conductive powder from a low temperature during firing of the conductive paste, and can adjust the thermal shrinkage rate, firing shrinkage history, and thermal expansion coefficient of the conductive film after firing.

[0036] The dielectric constant of the dielectric powder is not particularly limited and can be appropriately selected depending on the intended application. For example, the dielectric constant of the dielectric powder used in this type of conductive paste is typically 100 or more, preferably 1000 or more, for example, approximately 1000 to 20000. The composition of such dielectric powder is not particularly limited, and one or more of various inorganic materials or amorphous materials can be appropriately used depending on the intended application. Typical examples of the dielectric powder include metal oxides having a perovskite structure represented by ABO3, such as barium titanate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, zirconium titanate, zinc titanate, barium magnesium niobate, and calcium zirconate, as well as other metal oxides such as titanium dioxide (rutile), titanium pentoxide, hafnium oxide, zirconium oxide, aluminum oxide, forsterite, niobium oxide, barium neodymium titanate, and rare earth element oxides. In the paste for the internal electrode layers, the dielectric powder can be suitably composed of, for example, barium titanate (BaTiO), strontium titanate, calcium zirconate (CaZrO), etc. However, it goes without saying that a dielectric material (and therefore an insulating material) having a relative dielectric constant of less than 100 may also be used.

[0037] The properties of the particles constituting the dielectric powder, such as particle size and shape, are not particularly limited. The average particle diameter of the dielectric powder can be appropriately selected depending on, for example, the application of the conductive paste and the dimensions (fineness) of the adherend. From the viewpoint of easily ensuring a predetermined conductivity for the target adherend, it is preferable that the average particle diameter of the dielectric powder is smaller than the average particle diameter of the metal filler. When the average particle diameter of the dielectric powder is D2 and the average particle diameter of the metal filler is D1, D1 and D2 are usually preferably D1 > D2, more preferably D2 ≦ 0.5 × D1, more preferably D2 ≦ 0.4 × D1, and may be, for example, D2 ≦ 0.3 × D1. Furthermore, if the average particle diameter D2 of the dielectric powder is too small, aggregation of the dielectric powder is likely to occur, which is undesirable. In this respect, as a rough guideline, 0.03 × D1 ≦ D2 is preferable, 0.05 × D1 ≦ D2 is more preferable, and for example, 0.1 × D1 ≦ D2 may be acceptable. For example, specifically, the average particle size of the dielectric powder is generally several nm or more, preferably 5 nm or more, and may be 10 nm or more. Also, the average particle size of the dielectric powder may be approximately several μm or less, for example, 1 μm or less, preferably 0.3 μm or less.

[0038] The content of the dielectric powder is not particularly limited. When the entire conductive paste is taken as 100% by mass, it is preferably about 0.2 to 20% by mass, for example, 1 to 15% by mass, 3 to 10% by mass, etc. Furthermore, the ratio of the dielectric powder to 100 parts by mass of silver is, for example, about 3 to 35 parts by mass, preferably 5 to 30 parts by mass, for example, 10 to 25 parts by mass. This appropriately suppresses the firing of the metal filler from a low temperature and improves the electrical conductivity, density, etc. of the conductor film after firing.

[0039] 3.3 Dispersants The conductive paste disclosed herein may contain a dispersant to the extent that the essence of the present invention is not significantly impaired. An anionic dispersant containing an acid value is suitable, and a carboxylic acid dispersant is particularly preferred in that it effectively suppresses the aggregation of the conductive powder in the conductive paste. For example, a carboxylic acid dispersant may contain one or more carbonyl groups (-C(=O)) in its molecular structure. - ) or its salt. This carbonyl group preferentially bonds to the surface of particles constituting the conductive powder or dielectric powder, imparting an electric charge to the particle surface and suppressing particle aggregation due to the electrical repulsion. Carboxylic acid-based dispersants are preferred because they contribute favorably to improving the uniform dispersion of the powder in the paste. Examples of carboxylic acid-based dispersants include, but are not limited to, dispersants based on fatty acid salts such as carboxylic acids or polycarboxylic acids, dispersants based on polycarboxylic acid partial alkyl ester compounds in which hydrogen atoms in some carboxylic acid groups are substituted with alkyl groups, dispersants based on polycarboxylic acid alkylamine salts, and dispersants based on polycarboxylic acid partial alkyl ester compounds in which a portion of the polycarboxylic acid has an alkyl ester bond. Examples of carboxylic acid salts include alkali metal salts (e.g., sodium salts and potassium salts) and alkaline earth metal salts (e.g., magnesium salts and calcium salts). These compounds may be used alone or in combination of two or more. The number average molecular weight of the carboxylic acid dispersant may be, for example, about 30,000 or less, preferably about 20,000 or less, for example, about 15,000 or less. The number average molecular weight of the carboxylic acid dispersant may be, for example, about 100 or more, about 200 or more, and preferably about 400 or more.

[0040] The action of such carboxylic acid dispersants is more effective than that of other anionic dispersants (e.g., sulfonic acid dispersants, phosphate dispersants, etc.), and a predetermined dispersing effect can be achieved with a small amount added compared to other anionic dispersants. The amount of carboxylic acid dispersant added may be 0.05% by mass or more, and preferably, for example, 0.1% by mass or more. The amount of carboxylic acid dispersant added may be 1.5% by mass or less, and preferably, for example, 1% by mass or less.

[0041] 3.4 Other additives The conductive paste disclosed herein may contain various organic additives known to be useful in general conductive pastes, provided that the essential features of the present invention are not significantly impaired. Examples of such organic additives include thickeners, plasticizers, pH adjusters, stabilizers, leveling agents, antifoaming agents, antioxidants, preservatives, and colorants (pigments, dyes, etc.). These organic additives may be contained alone or in combination. The content of the organic additives may be adjusted as needed to the extent that the properties of the conductive paste disclosed herein are not significantly impaired. For example, the organic additives may be contained in an appropriate proportion depending on the properties and purpose of the additive. For example, the additives are generally contained in an amount of about 5% by mass or less, e.g., 3% by mass or less, typically 1% by mass or less, and preferably about 0.01% by mass or more, based on the total mass of the powder components. It is not desirable to contain components that inhibit the sinterability of silver, or additives in amounts that would inhibit this. From this viewpoint, when organic additives are contained, the total content of these components is preferably about 5 mass % or less of the entire conductive paste agent, more preferably 3 mass % or less, and particularly preferably 2 mass % or less.

[0042] 4. Conductive paste performance 4.1 viscosity The viscosity of the conductive paste according to the present disclosure is not particularly limited, but a lower viscosity is preferable from the viewpoint of dispersibility of silver particles. On the other hand, if the viscosity of the conductive paste is too low, it is not preferable from the viewpoint of workability (for example, film formation). From the above viewpoints, the viscosity of the conductive paste is preferably 100 Pa·s to 650 Pa·s, more preferably 200 Pa·s to 600 Pa·s, and particularly preferably 250 Pa·s to 500 Pa·s.

[0043] 4.2 Volume resistivity From the viewpoint of suitable use as a conductive paste, when a cured film of 2 cm length x 2 cm width x 30 μm thickness is formed on a glass plate using the conductive paste, the volume resistivity of the cured film (1 cm of the test piece) is 3 The volume resistivity per -4 Ω·cm or less is preferable, 8.0×10- 4 Ω·cm or less is more preferable, 7.0×10- 4 A value of Ω·cm or less is particularly preferable.

[0044] 4.3 Heat resistant bondability When the conductive paste is used for electronic devices, the cured film of the conductive paste may be exposed to a high-temperature environment for a long time due to the manner of use. From this perspective, the conductive paste is used to bond a copper substrate measuring 3 cm in length, 1 cm in width, and 0.15 cm in thickness to a silicon carbide substrate measuring 0.1 cm in length, 0.1 cm in width, and 300 μm in thickness via a cured film measuring 0.11 cm in length, 0.11 cm in width, and 100 μm in thickness, and after holding the paste in an environment of 175°C or 200°C for a predetermined time, the shear strength is 30 N / mm 2 More than 35N / mm is preferable. 2 More preferably, 40N / mm 2 The above is particularly preferred.

[0045] <Evaluation> 1. Test example Test examples relating to the technology disclosed herein will be described below, but it is not intended that the technology disclosed herein be limited to such test examples.

[0046] (1) Example 1 A conductive paste was prepared by kneading flaky silver particles, spherical silver particles, an epoxy resin, and an antioxidant with a triple roller. The flake silver particles have an average particle diameter of 3.0 μm and a specific surface area of ​​0.63 m 2 / g, TAP density 5.4g / cm 3 The material was used at 80.75 mass %. The spherical silver particles have an average particle diameter of 0.7 μm and a specific surface area of ​​2.05 m 2 / g, TAP density 2.8g / cm 3 The amount used was 4.25 mass %. As the epoxy resin, EP-4901E (manufactured by ADEKA) was used in an amount of 13.78 mass %. As a curing agent, 0.68 mass % of 2PHZ-PW (manufactured by Shikoku Kasei) was used. As the antioxidant, 0.54 mass % of AO-330 (manufactured by ADEKA) was used.

[0047] (2) Example 2 It was prepared in the same manner as in Example 1, except that the content ratio of flaky silver particles to spherical silver particles was different.

[0048] (3) Comparative Examples 1 to 3 It was prepared in the same manner as in Example 1, except that the type of spherical silver particles was different.

[0049] 2.Evaluation Test (1) Volume resistivity of cured film A conductive paste coating measuring 2 cm long x 2 cm wide x 20 μm thick was prepared on a glass plate, and then heated at 200°C for 60 minutes to obtain a cured conductive paste film. The volume resistivity was then measured using the four-point probe method.

[0050] (2) Heat-resistant adhesiveness of the cured film A copper substrate measuring 3 cm long x 1 cm wide x 0.15 cm thick was bonded to a silicon carbide substrate measuring 0.1 cm long x 0.1 cm wide x 300 μm thick via a cured film measuring 0.11 cm long x 0.11 cm wide x 100 μm thick. The test specimens were held at 175°C or 200°C for a specified time, after which the shear strength (die shear strength) was measured using a bond tester (Stellar 4000, manufactured by Nordson Advanced Technologies). The shear strength was 30 N / mm 2 If the above was true, the evaluation was marked as "good."

[0051] 3. Evaluation Results Table 1 summarizes the test results for volume resistivity and heat resistance bondability for each sample. [Table 1]

[0052] The volume resistivity test results for each sample are summarized in Figure 2.

[0053] As shown in Table 1 and Figure 2, Examples 1 and 2 are examples in which spherical silver particles with a relatively large specific surface area were used. In these cases, it was confirmed that the volume resistivity of the cured film was suitably reduced. On the other hand, in Comparative Examples 1 to 3 in which spherical silver particles with a relatively small specific surface area were used, it was confirmed that the volume resistivity of the cured film was not suitably reduced. From the above, it was confirmed that the volume resistivity of the cured film of the conductive paste can be reduced by using a combination of specified flaky silver particles and spherical particles with a large specific surface area. Regarding heat-resistant bonding properties, since the same amount of the same epoxy resin was added in all of Examples 1 and 2 and Comparative Examples 1 to 3, no significant differences were observed.

[0054] Although the present invention has been described in detail above using specific embodiments, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the above-described embodiments.

[0055] This specification includes the following items 1 to 7. The following items 1 to 7 are not limited to the above-described embodiments.

[0056] Section 1: Silver particles, A thermosetting epoxy resin that is liquid at room temperature (25°C), A conductive paste containing the silver particles consist of flaky silver particles and spherical silver particles, The flaky silver particles are Average particle size: 2.0 μm or more and 3.5 μm or less, Specific surface area 0.3m 2 / g or more 1.0m 2 / g or less, TAP density 4.5g / cm 3 That's all, and The spherical silver particles are Average particle size: 0.1 μm or more and 1.0 μm or less, Specific surface area 1.5m 2 / g or more, TAP density 2.0g / cm 3 below, wherein the mass mixing ratio of the flaky silver particles to the spherical silver particles (flaky silver particles / spherical silver particles) is in the range of 90 / 10 to 98 / 2; Conductive paste.

[0057] Section 2: Item 1. The conductive paste according to item 1, which does not contain a solvent.

[0058] Section 3: Item 3. The conductive paste according to item 1 or 2, wherein the content of the epoxy resin is 10% by mass or more and 20% by mass or less of the entire conductive paste.

[0059] Section 4: Item 4. The conductive paste according to any one of items 1 to 3, wherein the spherical silver particles have an average particle size of 0.2 μm or more and 0.8 μm or less.

[0060] Section 5: The specific surface area of ​​the spherical silver particles is 3.0 m 2 Item 5. The conductive paste according to any one of items 1 to 4, wherein the conductivity is 1 / g or more.

[0061] Item 6: When a cured film measuring 2 cm in length, 2 cm in width, and 20 μm in thickness was prepared on a glass plate, the volume resistivity of the cured film was 9.0 × 10 4 Item 6. The conductive paste according to any one of items 1 to 5, having a resistivity of Ω·cm or less.

[0062] Section 7: A copper substrate and a silicon carbide substrate are bonded via a hardened film measuring 0.11 cm long x 0.11 cm wide x 100 μm thick, and the shear strength after being held at 175°C or 200°C for a specified time is 30 N / mm 2 Item 7. The conductive paste according to any one of items 1 to 6, wherein [Explanation of symbols]

[0063] 1. Flake-shaped silver particles 2 Spherical silver particles 3. Matrix portion of the cured film made of epoxy resin 10 Cured film

Claims

1. Silver particles, a thermosetting epoxy resin that is liquid at room temperature (25°C); A conductive paste containing the silver particles consist of flaky silver particles and spherical silver particles, The flaky silver particles are Average particle size: 2.0 μm or more and 3.5 μm or less, Specific surface area 0.3 m ２ / g above 1.0m ２ / g or less, TAP density 4.5g / cm ３ above, and The spherical silver particles are Average particle size: 0.1 μm or more and 1.0 μm or less, Specific surface area 1.5m ２ / g or more, TAP density 2.0g / cm ３ above, wherein the mass mixing ratio of the flaky silver particles to the spherical silver particles (flaky silver particles / spherical silver particles) is in the range of 90 / 10 to 98 / 2; Conductive paste.

2. The conductive paste of claim 1 which is solvent-free.

3. The conductive paste according to claim 1 or 2, wherein a content of the epoxy resin is 10% by mass or more and 20% by mass or less of the entire conductive paste.

4. 3. The conductive paste according to claim 1, wherein the spherical silver particles have an average particle size of 0.2 μm or more and 0.8 μm or less.

5. The specific surface area of ​​the spherical silver particles is 3.0 m ２ The conductive paste according to claim 1 or 2, wherein the SiO 2 content is 1 / g or more.

6. When a cured film measuring 2 cm in length, 2 cm in width, and 30 μm in thickness was prepared on a glass plate, the volume resistivity of the cured film was 9.0×10 －４ The conductive paste according to claim 1 or 2, having a resistivity of Ω·cm or less.

7. A copper substrate and a silicon carbide substrate are bonded via a cured film measuring 0.11 cm long x 0.11 cm wide x 100 μm thick, and the shear strength after being held for a predetermined time in an environment of 175°C or 200°C is 30 N / mm ２ The conductive paste according to claim 1 or 2, wherein the conductive paste is a conductive paste having the above-mentioned properties.

Images