Conductive adhesive, electronic circuit using same, and manufacturing method thereof

Abstract

The purpose of the present invention is to provide: a conductive adhesive that can suppress an increase in the electrical resistance value at a joining part between a substrate and an electronic component at a high temperature and a high humidity while keeping the specific resistance value low; an electronic circuit using the conductive adhesive; and a method for producing same. According to the present invention, provided is a conductive adhesive that contains a conductive filler. A coating layer containing silver is provided to the surface of the conductive filler. The amount of the conductive filler blended with respect to the conductive adhesive is 29.0-63.0 vol%. The amount of the silver blended with respect to the conductive adhesive is 3.5-7.0 vol%. Also provided are an electronic circuit using the conductive adhesive according to the present invention, and a method for producing same.

Description

[Technical Field]

[0001] The present invention relates to a conductive adhesive used to electrically bond an electrical component such as a semiconductor element to a substrate having a conductive portion, an electronic circuit using the same, and a method for manufacturing the same. [Background technology]

[0002] Conductive adhesives, which are made by mixing conductive fillers such as silver powder with thermosetting resins such as epoxy resins, are used to bond electronic components such as semiconductor elements to substrates. Such conductive adhesives are used as an alternative to solder when bonding electronic components such as semiconductor elements to substrates. Because conductive adhesives can be bonded at lower temperatures than solder, they are effective for use on electronic components that may be damaged by heat.

[0003] However, conductive adhesives generally have the problem of increasing the electrical resistance of the joint in high-temperature, high-humidity environments. For this reason, Japanese Patent Application Laid-Open No. 2016-222795 (Patent Document 1) discloses a technology for suppressing the increase in the electrical resistance of the joint in high-temperature, high-humidity environments by adding zinc to the conductive adhesive.

[0004] However, there is a problem in that the addition of a metal such as zinc, which has a higher resistance than silver, increases the specific resistance of the conductive adhesive itself. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-222795 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, the present invention aims to provide a resin composition that can suppress an increase in the electrical resistance of the joint between an electronic component and a substrate under high temperature and high humidity conditions while maintaining a low specific resistance value, a conductive adhesive containing the resin composition, an electronic circuit using the resin composition, and a method for manufacturing the electronic circuit. [Means for solving the problem]

[0007] The present inventors have conducted extensive research into the amount of silver added that is effective in suppressing an increase in the electrical resistance of the joint between an electronic component and a substrate, and have found that by using a conductive filler whose surface is coated with silver, it is possible to suppress an increase in the electrical resistance of the joint between an electronic component and a substrate under high temperature and high humidity conditions while keeping the specific resistance low. That is, by using a conductive filler whose surface is coated with silver, even if the amount of silver is small, the conductive filler occupies a predetermined volume ratio, so that a flow path for electricity is secured throughout the conductive adhesive, and because the amount of silver is limited to a predetermined amount, an increase in the electrical resistance of the joint under high temperature and high humidity conditions is suppressed. This discovery led to the completion of the present invention.

[0008] According to the present invention, there is provided a conductive adhesive containing a conductive filler, the surface of which is a coating layer containing silver, the conductive filler content being 29.0 to 63.0 volume % relative to the conductive adhesive, and the silver content being 3.5 to 7.0 volume % relative to the conductive adhesive.

[0009] The conductive adhesive of the present invention can suppress an increase in the electrical resistance of the joint between an electronic component and a substrate under high temperature and high humidity conditions while maintaining a low specific resistance.

[0010] In addition, in this specification, numerical (ratio) ranges indicated using "from" or "to" indicate ranges that include the numerical (ratio) values ​​written before and after "from" or "to" as the minimum value (ratio) and maximum value (ratio), respectively.

[0011] <Conductive adhesive> The conductive adhesive of the present invention is an adhesive containing a conductive filler, a thermosetting resin, and a curing agent. Furthermore, the conductive adhesive of the present invention may contain other additives, such as reactive diluents, curing accelerators, fillers (e.g., silica, alumina, boron nitride, aluminum nitride, etc.), colorants (e.g., carbon black, dyes, etc.), flame retardants, ion trapping agents, leveling agents, antifoaming agents, dispersants, and anticorrosive agents, as needed, provided that the effects of the present invention are not impaired.

[0012] <Conductive filler> In the present invention, the conductive filler refers to a powder having electrical conductivity. The conductive filler used in the present invention has a core made of a metal or ceramic that is less noble than silver, and the surface of the core is coated with silver. Furthermore, the core of the conductive filler is preferably made of at least one material selected from the group consisting of alumina, silica, copper, and aluminum.

[0013] Examples of metal-coated ceramic particles include silver-plated ceramic particles in which the surface of alumina or silica is plated with silver or a silver-containing alloy. Cores of metals less noble than silver include aluminum and copper.

[0014] The shape of the conductive filler is not particularly limited, and in the case of particles, those having a spherical, flake (flat), fibrous, rod-like shape, etc. can be used. 50 The average particle diameter (D) is preferably 1 to 50 μm, and more preferably 2 to 20 μm. 50 If the average particle diameter (D) is 1 μm or less, the specific surface area of ​​the filler becomes large, making it impossible to reduce the amount of silver used while maintaining the volume ratio of the conductive filler, and it may become impossible to simultaneously suppress the specific resistance value and the increase in the electrical resistance of the joint. 50 If the thickness is 50 μm or more, it becomes difficult to draw fine lines, and the composition may not be able to be discharged from a nozzle when applied using a dispenser.

[0015] Average particle diameter (D 50) can be measured using a particle size distribution measuring device using a laser diffraction scattering method (for example, the device name: "Microtrac MT3300II" manufactured by Nikkiso Co., Ltd.). 50 ) indicates a value measured by a laser diffraction scattering method, and means a volume-based median diameter.

[0016] Furthermore, the amount of conductive filler added to the adhesive is preferably 29.0 to 63.0% by volume, assuming the total volume of the conductive adhesive to be 100% by volume. If the amount of conductive filler added is less than 29.0% by volume, the resistance value will increase, and if it is more than 63.0% by volume, the viscosity of the conductive adhesive will increase, making it difficult to discharge during kneading or dispensing.

[0017] Furthermore, the silver content in the conductive filler is preferably 3.5 to 7.0% by volume, assuming the total volume of the conductive adhesive to be 100% by volume. If the silver content is less than 3.5% by volume, the resistance value will increase, and if it is more than 7.0% by volume, it will not be possible to suppress the increase in electrical resistance value of the joint between the electronic component and the board over time.

[0018] <Thermosetting resin> In the present invention, the term "thermosetting resin" refers to a resin that hardens when heated. The thermosetting resin used in the present invention is not particularly limited. By using epoxy resins such as bisphenol A epoxy resin, bisphenol F epoxy resin, chelate-modified epoxy resin, amine epoxy resin, and alicyclic epoxy resin as the thermosetting resin, excellent printability and mechanical strength can be obtained. In addition to the above epoxy resins, unsaturated polyester resin, polyimide resin, thermosetting acrylic resin, and the like can also be used.

[0019] <Reactive diluent> In the present invention, the reactive diluent refers to a diluent for the conductive adhesive and has a polymerizable functional group. By using a reactive diluent as needed, the conductive adhesive of the present invention can be adjusted to an appropriate viscosity depending on the printing method or coating method for elements, substrates, etc.

[0020] Such reactive diluents include coconut fatty acid glycidyl esters, butyl glycidyl ether, and 2-ethylhexyl glycidyl ether. 、 Examples include allyl glycidyl ether, p-sec-butylphenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, glycidol, polyethylene glycol diglycidyl ether, glycidyl methacrylate, glycerin monomethacrylate, and styrene oxide.

[0021] The amount of reactive diluent added is preferably 1.0 to 10.0% by weight, and more preferably 3.0 to 8.0% by weight, when the total weight of the conductive adhesive is 100% by weight. By adding the reactive diluent in an amount of 1.0 to 10.0% by weight, the viscosity of the conductive adhesive falls within an appropriate range, and good printability is achieved.

[0022] <Curing accelerator> A curing accelerator can be blended into the conductive adhesive of the present invention to achieve appropriate curing properties. This curing accelerator is not particularly limited as long as it can be used as a curing accelerator for epoxy resins, and any known accelerator can be used. It is preferable to use a curing accelerator that can be stored in a state where it is premixed with the epoxy resin and can be used as a one-component epoxy resin conductive adhesive.

[0023] For example, when the curing accelerator is a cationic polymerization initiator, examples include benzylmethyl p-methoxycarbonylphenylsulfonium hexafluoroantimonate, 1-naphthylmethylmethyl p-hydroxyphenylsulfonium hexafluoroantimonate, 2-methylbenzylmethyl p-hydroxyphenylsulfonium hexafluoroantimonate, benzylmethyl p-hydroxyphenylsulfonium hexafluoroantimonate, benzyl(4-hydroxyphenyl)(methyl)sulfonium hexafluorophosphate, and dimethyl-p-acetoxyphenylsulfonium hexafluoroantimonate.

[0024] Furthermore, if the curing accelerator is a solid dispersion-heat curing type, examples thereof include dicyandiamide types, dihydrazide compounds, amine adduct-based latent curing agents, polyamine types, 2-phenyl-4-methylimidazole, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and the like, as well as reactive group block types such as onium salts, boron halides, vinyl ether-blocked carboxylic acids, activated esters of polycarboxylic acids, ketimine compounds, and silanol group-containing polymers.

[0025] Examples of imidazole curing accelerators include imidazole compounds and derivatives thereof, such as 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and epoxy-imidazole adducts.

[0026] The amount of the curing accelerator used varies depending on the type of curing accelerator and epoxy resin used, but it is preferable to add it in a ratio of 5.0 to 40.0 parts by weight per 100 parts by weight of the epoxy resin.

[0027] The method for preparing the conductive adhesive of the present invention is not particularly limited, and it can be prepared by uniformly mixing the components at a predetermined mixing ratio using a mixing means such as a mortar and pestle mixer, a propeller mixer, a kneader, a pot mill, a three-roll mill, a rotary mixer, a twin-screw mixer, etc. A resin composition can be prepared by blending the epoxy resin, curing accelerator, and reactive diluent in advance, or by mixing the conductive filler and any fillers added as needed all together.

[0028] The conductive adhesive of the present invention may be in the form of an ink, and can be printed or applied to a substrate by any method, such as screen printing, gravure printing, or dispensing.

[0029] When an organic solvent is used as a diluent, after printing or coating, the circuit elements to be bonded are mounted, and the organic solvent is evaporated at room temperature or under heat.Then, depending on the type of resin and curing accelerator, the conductive adhesive is cured by heating for 20 to 60 minutes at a temperature of 120 to 180°C, and the circuit elements are bonded.

[0030] In this way, the conductive adhesive can be used to form circuit board electronic devices in which semiconductor elements, solar cells, thermoelectric elements, chip components, discrete components, or electrical components combining these are mounted on a substrate. The conductive adhesive can also be used to form wiring for film antennas, keyboard membranes, touch panels, and RFID antennas and connect them to a substrate to form electronic devices. [Effects of the Invention]

[0031] The conductive adhesive of the present invention, the electronic circuit using the same, and the method for manufacturing the same can achieve the excellent effect of suppressing an increase in the electrical resistance of the joint between the electronic component and the substrate under high temperature and high humidity conditions while maintaining a low specific resistance value. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 2 is a schematic diagram illustrating a circuit board for measuring a resistance value. DETAILED DESCRIPTION OF THE INVENTION

[0033] Hereinafter, a conductive adhesive according to one embodiment of the present invention, an electronic circuit using the same, and a method for manufacturing the same will be described in detail with reference to the drawings. Note that the present invention is not limited to the examples shown below, and various modifications are possible within the scope of the technical concept of the present invention. [Example]

[0034] 1. Fabrication of Conductive Adhesive The conductive adhesive according to one embodiment of the present invention and the conductive adhesive of the comparative example were produced using the following materials and conditions (see "Table 1"). [Example 1] A 200 ml disposable cup was charged with 2 g of epoxy resin (product name: "EP49-10N", manufactured by ADEKA Corporation) (9.6 vol% of the produced conductive adhesive; hereafter, the blending amount of each raw material is also shown in "vol%" using the same standard), 6 g of epoxy resin (product name: "EP-4088S", manufactured by ADEKA Corporation) (30.0 vol%), 1.38 g of reactive diluent (product name: "Epiol B", manufactured by NOF Corporation) (8.5 vol%), 1.41 g of curing accelerator (product name: "Sanaid SI-100L", manufactured by Sanshin Chemical Industry Co., Ltd.) (5.8 vol%), and block-shaped silver-plated alumina powder (product name: "TFM-L05B", average particle size (D 50 ): 5 μm, silver content (coating amount): 13.9 vol% (6.4 vol% of the produced conductive adhesive, manufactured by Toyo Aluminum K.K.) was added and mixed uniformly with a spatula, and then further mixed using a three-roll mill (product name: "EXAKT 80S PLUS", manufactured by Nagase Screen Printing Laboratory Co., Ltd.) with roll spacings of 0.05 mm and 0.03 mm to produce the conductive adhesive of Example 1.

[0035] [Example 2] As a conductive filler, spherical silver-plated silica powder (product name: "TFM-S02P"), average particle diameter (D50 The conductive adhesive of Example 2 was prepared under the same conditions as Example 1, except that the amount (g) of each component was changed to 43.8 g (61.1 vol% of the prepared conductive adhesive), the amount (g) of each component was changed to 2 μm, the silver content (coating amount): 8.3 vol% (5.1 vol% of the prepared conductive adhesive), and the amount (g) of each component was changed to 43.8 g (61.1 vol% of the prepared conductive adhesive).

[0036] That is, into a 200 ml disposable cup, 2 g (6.9 vol%) of epoxy resin A (product name: "EP49-10N", manufactured by ADEKA Corporation), 6 g (21.7 vol%) of epoxy resin B (product name: "EP-4088S", manufactured by ADEKA Corporation), 1.38 g (6.1 vol%) of reactive diluent (product name: "Epiol B", manufactured by NOF Corporation), 1.41 g (4.2 vol%) of curing accelerator (product name: "Sanaid SI-100L", manufactured by Sanshin Chemical Industry Co., Ltd.), and spherical silver-plated silica powder (product name: "TFM-S02P", average particle diameter (D 50 ): 2 μm, silver content (coating amount): 8.3 vol% (5.1 vol% of the produced conductive adhesive, manufactured by Toyo Aluminum K.K.) was added and mixed uniformly with a spatula, and then further mixed using a three-roll mill (product name: "EXAKT 80S PLUS", manufactured by Nagase Screen Printing Laboratory Co., Ltd.) with roll spacings of 0.05 mm and 0.03 mm to produce the conductive adhesive of Example 2.

[0037] [Example 3] The conductive adhesive of Example 3 was prepared under the same conditions as Example 1, except that the curing accelerator was changed to 1.41 g (5.7 volume % of the prepared conductive adhesive) of product name: "Sanaid SI-150L" (manufactured by Sanshin Chemical Industry Co., Ltd.), with the amount of each component (g) being the same as Example 1.

[0038] [Example 4] As a conductive filler, spherical silver-plated silica powder (product name: "TFM-S02P"), average particle diameter (D 50The conductive adhesive of Example 4 was prepared under the same conditions as Example 2, except that the amount of each component (g) was changed to 23.5 g (45.7 volume % of the prepared conductive adhesive), and the amount of aluminum nitride (manufactured by Toyo Aluminum K.K.) was changed to 2 μm, silver content (coating amount): 8.3 volume % (3.8 volume % of the prepared conductive adhesive), and the amount of aluminum nitride (manufactured by Toyo Aluminum K.K.) was changed to 23.5 g (45.7 volume % of the prepared conductive adhesive).

[0039] [Example 5] As a conductive filler, block-shaped silver-plated alumina powder (product name: "TFM-L05B"), average particle diameter (D 50 The conductive adhesive of Example 5 was prepared under the same conditions as Example 1, except that the amount of each component (g) was changed to 45.0 g (49.3 volume % of the conductive adhesive prepared), and the amount of aluminum nitride (manufactured by Toyo Aluminum K.K.) was changed to 5 μm, silver content (coating amount): 13.9 volume % (6.8 volume % of the conductive adhesive prepared), and the amount of aluminum nitride (manufactured by Toyo Aluminum K.K.) was changed to 45.0 g (49.3 volume % of the conductive adhesive prepared).

[0040] [Example 6] As a conductive filler, block-shaped silver-plated alumina powder (product name: "TFM-L05B"), average particle diameter (D 50 The conductive adhesive of Example 6 was prepared under the same conditions as Example 1, except that the amount of each component (g) was changed to 35.0 g (43.0 volume % of the prepared conductive adhesive), and the amount of aluminum nitride (manufactured by Toyo Aluminum K.K.) was changed to 5 μm, silver content (coating amount): 13.9 volume % (5.9 volume % of the prepared conductive adhesive), and the amount of aluminum nitride (manufactured by Toyo Aluminum K.K.) was changed to 35.0 g (43.0 volume % of the prepared conductive adhesive).

[0041] [Example 7] The conductive adhesive of Example 7 was prepared under the same conditions as Example 2, except that the resin was changed to product name: AER8000 (manufactured by Asahi Kasei Corporation) 8g (27.4% by volume of the prepared conductive adhesive), including the amount (g) of each component.

[0042] [Example 8] As a conductive filler, flake-shaped silver-plated copper flakes (product name: "TFM-C05F") (average particle diameter (D 50The conductive adhesive of Example 8 was prepared under the same conditions as Example 1, except that the amount (g) of each component was changed to 39.5 g (30.8 volume % of the conductive adhesive prepared), the amount (g) of each component was changed to 5 μm, the silver content (coating amount): 16.8 volume % (5.3 volume % of the conductive adhesive prepared), and the amount (g) of each component was changed to 39.5 g (30.8 volume % of the conductive adhesive prepared).

[0043] [Example 9] As a conductive filler, spherical silver-plated aluminum powder (product name: "TFM-A05P") with an average particle diameter (D 50 The conductive adhesive of Example 9 was prepared under the same conditions as Example 1, except that the amount of each component (g) was changed to 1.65 g (5.8 volume%), the amount of silver (coating amount): 5 μm, the amount of silver (coating amount): 10.0 volume% (5.3 volume% of the conductive adhesive prepared), the amount of curing accelerator (product name: "Sanaid SI-100L", manufactured by Sanshin Chemical Industry Co., Ltd.) was changed to 39.5 g (53.5 volume% of the conductive adhesive prepared), and the amount of curing accelerator (product name: "Sanaid SI-100L", manufactured by Sanshin Chemical Industry Co., Ltd.) was changed to 1.65 g (5.8 volume%).

[0044] [Comparative Example 1] The conductive adhesive of Comparative Example 1 was prepared under the same conditions as Example 1, except that the conductive filler was changed to 20 g (16.5 volume % of the prepared conductive adhesive) of silver particles (product name: "AgC104WR", manufactured by Fukuda Metal Foil and Powder Co., Ltd.), with the amount (g) of each component being the same.

[0045] Comparative Example 2 The conductive adhesive of Comparative Example 2 was prepared under the same conditions as Example 1, including the amount (g) of each component, except that the conductive filler was changed to 30 g (22.9 volume % of the prepared conductive adhesive) of silver particles (product name: "AgC104WR", manufactured by Fukuda Metal Foil and Powder Co., Ltd.).

[0046] Comparative Example 3 The conductive adhesive of Comparative Example 3 was prepared under the same conditions as Example 1, except that the conductive filler was changed to 88.0 g (46.5 volume % of the prepared conductive adhesive) of silver particles (product name: "AgC104WR", manufactured by Fukuda Metal Foil and Powder Co., Ltd.), with the amount (g) of each component being the same.

[0047] Comparative Example 4 As a conductive filler, spherical silver-plated silica powder (product name: "TFM-S02P"), average particle diameter (D 50 The conductive adhesive of Comparative Example 4 was prepared under the same conditions as Example 2, except that the amount of each component (g) was changed to 51.1 g (64.7 vol% of the prepared conductive adhesive), and the amount of aluminum nitride (manufactured by Toyo Aluminum K.K.) was changed to 2 μm, silver content (coating amount): 8.3 vol% (5.4 vol% of the prepared conductive adhesive), and the amount of aluminum nitride (manufactured by Toyo Aluminum K.K.) was changed to 51.1 g (64.7 vol% of the prepared conductive adhesive).

[0048] Comparative Example 5 As a conductive filler, flake-shaped silver-plated copper flakes (product name: "TFM-C05F") (average particle diameter (D 50 The conductive adhesive of Comparative Example 5 was prepared under the same conditions as Example 1, except that the amount (g) of each component was changed to 5 μm, silver content (coating amount): 16.8 vol% (4.4 vol% of the conductive adhesive prepared), and the amount (g) of each component (manufactured by Toyo Aluminum K.K.) was changed to 30.0 g (25.3 vol% of the conductive adhesive prepared).

[0049] Table 1 shows the amount (volume %) (g) of each component blended into the conductive adhesives of Examples 1 to 9 and Comparative Examples 1 to 5. [Table 1]

[0050] 2. Resistance measurement As shown in FIG. 1, an aluminum-etched circuit board (9 μm thick aluminum foil / 250 μm thick PET film) or a copper-etched circuit board (12 μm thick copper foil / 250 μm thick PET film) was prepared with a foil line width of 5 mm, a foil length of 10 mm, and a distance between each foil of 10 mm. Using a screen printer (DP-320 screen printer, manufactured by Newlong Precision Industry Co., Ltd.), the conductive adhesive of Examples 1 to 10 and Comparative Examples 1 to 5 was printed in a width of 2.5 mm and a thickness of 50 μm or less across the aluminum-etched circuit or the copper-etched circuit. After printing, the conductive adhesive was cured at 150°C for 30 minutes, and a resistance meter (device name: "3541 9771 Pin-type Lead", manufactured by Hioki E.E. Corporation) was used to measure the change in resistance between a and b (Figure 1) after 0, 100, 200, 300, 400, and 500 hours in a high-temperature, high-humidity environment of 85°C and 85% humidity. Specifically, the pin-type lead was brought into contact with the conductor (aluminum foil or copper foil) that was the circuit wiring, and the resistance was measured.

[0051] Resistance measurements using an aluminum-etched circuit board were performed for the conductive adhesives of Examples 1 to 9 and Comparative Examples 1 to 5. Resistance measurements using a copper-etched circuit board were performed only for the conductive adhesive of Example 3, and the measurement method and results of this resistance were designated as "Example 10."

[0052] 3.Measurement of resistivity To measure the resistivity, the conductive adhesives of Examples 1 to 9 and Comparative Examples 1 to 5 were applied to a PET film using an applicator to a dry thickness of 30 to 40 μm. The samples were cured at 150°C for 30 minutes. Measurements were taken at three random points at 0 and 500 hours using a four-probe surface resistivity meter (product name: "Loresta GP," manufactured by Mitsubishi Chemical Analytech Co., Ltd.), and the average value was used as the resistivity (Ω·cm). Specifically, the dimensions of the conductive coating, the average coating thickness, and the coordinates of the measurement points were entered into the four-probe surface resistivity meter, and the value obtained by automatic calculation was used as the resistivity of the conductive coating. Note that a lower resistivity value indicates better conductivity. The adhesive thickness was confirmed by measuring with a Digimatic Standard Outside Micrometer (product name: "IP65 Coolant Proof Micrometer," manufactured by Mitutoyo Corporation).

[0053] 4. Viscosity Measurement The viscosity of the conductive adhesives of Examples 1 to 9 and Comparative Examples 1 to 5 was measured at 25° C. and 2.5 rpm using a Brookfield type viscometer (model number: DV2THBCJ0).

[0054] Table 2 shows the conductive adhesives of Examples 1 to 10 and Comparative Examples 1 to 5, and the measurement results of their viscosity, resistivity, and resistance in a constant temperature and humidity environment of 85°C / 85%. [Table 2]

[0055] 5. Discussion As shown in Table 2, in the case of the conductive adhesives of Comparative Examples 1 and 2, which used silver particles themselves as the conductive filler, the resistance value increased to the point where it could not be measured after 400 hours for the conductive adhesive of Comparative Example 1, and the resistance value increased to the point where it could not be measured after 100 hours for the conductive adhesive of Comparative Example 2. Thus, it was confirmed that using silver particles themselves as the conductive filler is effective in keeping the specific resistance value low, but also leads to an increase in the electrical resistance value of the joint between the electronic component and the board under high temperature and high humidity conditions.

[0056] Furthermore, comparing the conductive adhesives of Examples 1 to 10 and Comparative Examples 1 to 5 in Table 2, it was found that when the amount of conductive filler added was less than 29.0% by volume, the resistance value increased, and when it was more than 63.0% by volume, the viscosity of the conductive adhesive increased, making it difficult to discharge during mixing or dispensing. For this reason, it was found that the amount of conductive filler added to the adhesive is preferably 29.0 to 63.0% by volume, assuming the total volume of the conductive adhesive to be 100% by volume.

[0057] Furthermore, if the silver content in the conductive filler is less than 3.5% by volume relative to the conductive adhesive, the resistance value increases, and if it is more than 7.0% by volume, it becomes impossible to suppress the increase in the electrical resistance value of the joint between the electronic component and the board over time. For this reason, it was found that the silver content in the conductive filler is preferably 3.5 to 7.0% by volume, assuming the total volume of the conductive adhesive to be 100% by volume. [Explanation of symbols]

[0058] 1. Circuit board 2. Conductive adhesive a~e...Circuit X...Circuit width Y Circuit spacing L...Circuit length

Claims

1. A conductive adhesive containing a conductive filler, wherein a surface of the conductive filler is a coating layer containing silver, the conductive filler is blended in an amount of 29.0 to 63.0% by volume with respect to the conductive adhesive, and the silver is blended in an amount of 3.5 to 7.0% by volume with respect to the conductive adhesive; The conductive filler has a core made of at least one material selected from the group consisting of alumina and silica, and The conductive adhesive is characterized in that the conductive filler does not include any other conductive filler attached to its surface (excluding those containing fluorine or nitrogen).

2. The conductive adhesive according to claim 1 , wherein the conductive adhesive is in ink form.

3. An electronic circuit characterized in that a semiconductor element, a thermoelectric element, a chip component, an LED component, or an electrical component that is a combination of these is electrically joined to a resin substrate having a conductive portion by the conductive adhesive described in claim 1 or 2.

4. 4. The electronic circuit according to claim 3, wherein the conductive portion of the resin substrate is made of aluminum or copper.

5. 3. A method for manufacturing an electronic circuit, wherein the conductive adhesive according to claim 1 or 2 is applied to a resin substrate having a conductive portion by any one of dispensing, screen printing, and gravure printing.

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