Conductive paste, RFID inlay, and method for manufacturing RFID inlay

Abstract

Provided is a conductive paste that can: 1) enhance storage stability and can be implemented in a relatively short time; 2) enhance curability; 3) enhance adhesiveness; 4) improve the tackiness of the cured product; and 5) enhance conductive reliability. The conductive paste according to the present invention contains a thermosetting compound, a thermosetting agent, a conductive filler, a thixotropic agent, and an antioxidant, and the thermosetting agent includes a microcapsule-type thermosetting agent or a thermosetting agent that is solid at 25°C.

Description

Technical Field

[0001] The present invention relates to a conductive paste containing a conductive filler. The present invention also relates to an RFID inlay using the above conductive paste and a method for manufacturing the RFID inlay.

Background Art

[0002] An RFID (Radio Frequency Identification) inlay capable of performing non-contact data transmission and reception is widely used in non-contact RFID tags, non-contact RFID cards, and the like. In particular, an RFID inlay in the UHF (Ultra High Frequency) band (860 MHz to 960 MHz) has attracted attention because of its long communication distance, and the UHF band RFID inlay is used for various articles and purposes such as commuter passes, inventory management, distribution management, and history management.

[0003] In an RFID inlay, a conductive paste containing a conductive filler and a binder resin may be used for the adhesion and connection between a chip having an electrode on its surface and a substrate having a wiring (antenna pattern) on its surface.

[0004] In recent years, with the miniaturization of electronic components using RFID inlays, the chips used in RFID inlays have also been miniaturized, and there is a demand for a conductive paste having high adhesiveness and capable of being arranged more precisely on the wiring.

[0005] Patent Document 1 below discloses an adhesive applicable to electronic components. The above adhesive is an acrylic adhesive composition containing a radical initiator having a 10-hour half-life temperature of 80° C. or lower, a vinylene-containing oligomer, and at least one diluent. The above adhesive can be snap-cured at a low temperature, and the pot life of the above adhesive at room temperature is 24 hours or more.

[0006] Patent Document 2 below discloses a conductive adhesive containing a polymerizable acrylic compound, an organic peroxide, and solder particles, wherein the one-minute half-life temperature of the organic peroxide is lower than the solidus temperature of the solder particles.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] With conventional adhesives (conductive pastes) such as those described in Patent Documents 1 and 2, the adhesiveness can be increased to a certain extent. However, in conventional conductive pastes, when electronic components are fabricated (mounted) in an air atmosphere using the conductive paste, due to the influence of oxygen, the polymerization reaction of the conductive paste does not proceed sufficiently, and there may be uncured portions in the cured product of the conductive paste. As a result, there is a problem that the adhesiveness cannot be sufficiently increased, the tackiness of the cured product cannot be made good, and the conduction reliability of the obtained electronic components cannot be sufficiently increased. This problem is particularly prominent when mounting is performed in a relatively short time (for example, within 15 seconds).

[0009] Also, generally, when the curability of an adhesive (conductive paste) is increased, the pot life (usable time) tends to become shorter. With conventional adhesives (conductive pastes), it is difficult to increase the curability of the adhesive (conductive paste) and also increase the storage stability.

[0010] An object of the present invention is to provide a conductive paste that can 1) enhance storage stability and, even when implemented in a relatively short time, 2) enhance curability, 3) enhance adhesiveness, 4) improve the tackiness of the cured product, and 5) enhance conductive reliability. Another object of the present invention is to provide an RFID inlay using the above conductive paste and a method for manufacturing the RFID inlay.

Means for Solving the Problems

[0011] In this specification, the following conductive paste, RFID inlay, and method for manufacturing the RFID inlay are disclosed.

[0012] Item 1. A conductive paste comprising a thermosetting compound, a thermosetting agent, a conductive filler, a thixotropic agent, and an antioxidant, wherein the thermosetting agent includes a microcapsule type thermosetting agent or a thermosetting agent that is solid at 25°C.

[0013] Item 2. The conductive paste according to Item 1, wherein the thixotropic agent is solid at 25°C, and the ratio of the particle diameter of the thixotropic agent to the particle diameter of the conductive filler is 0.5 or less.

[0014] Item 3. The conductive paste according to Item 1 or 2, wherein the thermosetting compound includes an epoxy compound, and the thermosetting agent includes an anionic curing agent.

[0015] Item 4. The conductive paste according to any one of Items 1 to 3, wherein the conductive filler is conductive particles, and the particle diameter of the conductive particles is 10 μm or less.

[0016] Item 5. The conductive paste according to any one of Items 1 to 4, which is used to obtain an RFID inlay.

[0017] Item 6. An RFID inlay comprising a substrate having wiring on its surface, a chip having electrodes on its surface, and an adhesive portion bonding the substrate and the chip, wherein the material of the adhesive portion is the conductive paste according to any one of Items 1 to 5, and the wiring and the electrodes are electrically connected by the conductive filler in the adhesive portion.

[0018] Item 7. A method for manufacturing an RFID inlay, comprising: a first placement step of placing the conductive paste according to any one of Items 1 to 5 on the surface of a substrate having wiring on its surface; a second placement step of placing a chip having electrodes on its surface on the surface opposite to the substrate side of the conductive paste; and an adhesion step of forming an adhesive portion bonding the substrate and the chip with the conductive paste by heating and pressurizing the conductive paste, and electrically connecting the wiring and the electrodes by the conductive filler in the adhesive portion.

[0019] Item 8. The method for manufacturing an RFID inlay according to Item 7, wherein the substrate is in a long shape, and in the first placement step, the second placement step, and the adhesion step, the long substrate is conveyed by a roll-to-roll method to manufacture the RFID inlay.

Advantages of the Invention

[0020] The conductive paste according to the present invention includes a thermosetting compound, a thermosetting agent, a conductive filler, a thixotropic agent, and an antioxidant, and the thermosetting agent includes a microcapsule type thermosetting agent or a thermosetting agent that is solid at 25°C. In the conductive paste according to the present invention, since the above configuration is provided, 1) the storage stability can be enhanced, and even when mounted in a relatively short time, 2) the curability can be enhanced, 3) the adhesiveness can be enhanced, 4) the tackiness of the cured product can be improved, and 5) the electrical communication reliability can be enhanced.

Brief Description of the Drawings

[0021]

Figure 1

[0022] Hereinafter, the details of the present invention will be described.

[0023] (Conductive Paste) The conductive paste according to the present invention includes a thermosetting compound, a thermosetting agent, a conductive filler, a thixotropic agent, and an antioxidant. In the conductive paste according to the present invention, the thermosetting agent includes a microcapsule type thermosetting agent or a thermosetting agent that is solid at 25°C.

[0024] In a conventional conductive paste, when an electronic component is manufactured (mounted) in an air atmosphere using the conductive paste, the polymerization reaction of the conductive paste may not proceed sufficiently due to the influence of oxygen, and there may be an uncured portion in the cured product of the conductive paste. As a result, there is a problem that the tackiness of the cured product cannot be improved well, the adhesiveness cannot be sufficiently increased, and the conduction reliability of the obtained electronic component cannot be sufficiently increased. This problem is particularly remarkable when only a (meth)acrylate compound is radically polymerized as the curable compound or when mounting is performed in a relatively short time (for example, within 15 seconds). In addition, in a conventional conductive paste, it is difficult to increase the curability of the conductive paste and to increase the storage stability.

[0025] The inventors of the present invention have found that the above problems can be solved by using a combination of specific materials.

[0026] That is, in the conductive paste according to the present invention, since the above configuration is provided, the pot life (usable time) can be extended (the storage stability can be enhanced). Further, in the conductive paste according to the present invention, since the above configuration is provided, even when mounting (heating) is performed in a relatively short time (for example, within 15 seconds), the curability can be enhanced and sufficient curing can be achieved. Further, in the conductive paste according to the present invention, since the above configuration is provided, even when mounting is performed in a relatively short time, the adhesiveness can be enhanced, the tackiness of the cured product can be improved, and the conduction reliability can be enhanced.

[0027] The conductive paste according to the present invention is in a paste state at 25°C. The above conductive paste is, for example, discharged and used at 20°C to 50°C. The conductive paste according to the present invention is preferably discharged and used by a jet dispenser.

[0028] The viscosity (η25) of the above conductive paste at 25°C is preferably 15 Pa·s or more, more preferably 25 Pa·s or more, still more preferably 40 Pa·s or more, and preferably 200 Pa·s or less, more preferably 150 Pa·s or less, still more preferably 100 Pa·s or less. When the above viscosity (η25) is at least the above lower limit, outflow of the conductive paste from the wiring can be suppressed. When the above viscosity (η25) is at most the above upper limit, the conductive paste can be disposed on a fine wiring with high precision.

[0029] The above viscosity (η25) can be measured, for example, for the conductive paste immediately after production at 25°C and 5 rpm using an E-type viscometer. Examples of the above E-type viscometer include the "TV35 type viscometer" manufactured by Toki Sangyo Co., Ltd.

[0030] The ratio of the viscosity (ηα) of the above conductive paste at 25°C after storage at 25°C and 50% RH for 24 hours to the viscosity (η25) of the conductive paste at 25°C immediately after preparation is defined as the ratio (viscosity after storage (ηα) / viscosity immediately after preparation (η25)). The above ratio (viscosity after storage (ηα) / viscosity immediately after preparation (η25)) is preferably 0.7 or more, more preferably 0.8 or more, still more preferably 0.9 or more, preferably 1.25 or less, more preferably less than 1.25, still more preferably 1.2 or less, and particularly preferably 1.1 or less. When the above ratio (viscosity after storage (ηα) / viscosity immediately after preparation (η25)) is equal to or higher than the above lower limit, the storage stability can be further enhanced, and the outflow of the conductive paste from the wiring can be suppressed. When the above ratio (viscosity after storage (ηα) / viscosity immediately after preparation (η25)) is equal to or lower than the above upper limit or less than the above upper limit, the conductive paste can be accurately arranged on the fine wiring with high precision.

[0031] The viscosity (ηα) after the above storage can be measured, for example, using an E-type viscometer under the conditions of 25°C and 5 rpm after storing the conductive paste in a thermo-hygrostat at 25°C and 50% RH for 24 hours. Examples of the above E-type viscometer include the "TV35 viscometer" manufactured by Toki Sangyo Co., Ltd.

[0032] The above conductive paste has good adhesiveness. The above conductive paste is suitably used as an adhesive. The above conductive paste is particularly suitably used for adhering a substrate and a chip.

[0033] From the perspective of further enhancing the communication reliability, it is preferable that the above conductive paste is an anisotropic conductive paste. The above conductive paste is suitably used for the electrical connection of electrodes. The above conductive paste is suitably used to obtain a connection structure. The above conductive paste is suitably used to obtain an electronic component. The above conductive paste is particularly suitably used to obtain an RFID inlay (use of the above conductive paste for obtaining an RFID inlay). The above conductive paste is suitably used for the adhesion and connection between a chip having an electrode on its surface and a substrate having a wiring (antenna pattern) on its surface (use of the above conductive paste for adhering and connecting a chip having an electrode on its surface and a substrate having a wiring (antenna pattern) on its surface).

[0034] Since the above conductive paste contains a thermosetting compound, it has thermosetting properties. The above conductive paste is a thermosetting conductive paste. It is more preferable that the above conductive paste is a thermosetting anisotropic conductive paste.

[0035] In the above conductive paste, when differential scanning calorimetry (DSC) is performed by heating the conductive paste from 30°C to 200°C at a heating rate of 10°C / min, it is preferable that the heat generation start temperature is 50°C or higher, the heat generation peak top temperature is 80°C or higher and 125°C or lower, and the heat generation end temperature is 200°C or lower. In this specification, the heat generation start temperature refers to the temperature of the part where the heat generation amount starts to increase from the baseline. Also, in this specification, the heat generation end temperature refers to the temperature of the part where the heat generation amount has decreased to 1% of the heat generation amount at the heat generation peak top after reaching the heat generation peak top.

[0036] The above differential scanning calorimetry (DSC) can be carried out by the following method. Prepare a differential scanning calorimeter. Take 5 mg of the above conductive paste in a dedicated aluminum pan and cover it with a dedicated jig. Place this dedicated aluminum pan and an empty aluminum pan (reference) in the heating unit, heat them in an air atmosphere from 30°C to 200°C at a heating rate of 10°C / min, and observe the reverse heat flow and non-reverse heat flow. The exothermic peak observed in the non-reverse heat flow is taken as the exothermic peak of the conductive paste. Examples of the above differential scanning calorimeter include "TA7000" manufactured by Hitachi High-Tech Science Corporation.

[0037] In the above differential scanning calorimetry, the exothermic start temperature can be measured. From the viewpoint of enhancing the storage stability and discharge stability of the conductive paste and further enhancing the conduction reliability even when mounted in a relatively short time, the above exothermic start temperature is preferably 50°C or higher, more preferably 60°C or higher. The upper limit of the above exothermic start temperature is not particularly limited. The above exothermic start temperature may be 110°C or lower, 108°C or lower, 105°C or lower, 100°C or lower, or 90°C or lower. The range of the above exothermic start temperature can be set by appropriately selecting the above lower limit value and the above upper limit value.

[0038] In the above differential scanning calorimetry, the exothermic peak top temperature can be measured. From the viewpoint of further enhancing the conduction reliability even when mounted in a relatively short time, the above exothermic peak top temperature is preferably 80°C or higher, more preferably 85°C or higher, still more preferably 90°C or higher, and preferably 125°C or lower, more preferably 120°C or lower.

[0039] In the above differential scanning calorimetry, the heat release end temperature can be measured. From the perspective of further enhancing the conduction reliability even when implemented in a relatively short time, the heat release end temperature is preferably 200 °C or lower, more preferably 180 °C or lower. The lower limit of the heat release end temperature is not particularly limited. The heat release end temperature may be 90 °C or higher, or may be 95 °C or higher. The range of the heat release end temperature can be set by appropriately selecting the lower limit value and the upper limit value.

[0040] In the above differential scanning calorimetry, the absolute value of the difference between the heat release start temperature and the heat release end temperature is preferably 5 °C or higher, more preferably 10 °C or higher, still more preferably 15 °C or higher, particularly preferably 20 °C or higher, and preferably 100 °C or lower, more preferably 95 °C or lower, still more preferably 90 °C or lower, particularly preferably 85 °C or lower, and most preferably 80 °C or lower. When the absolute value of the difference between the heat release start temperature and the heat release end temperature is within the above lower limit and the above upper limit, the storage stability of the conductive paste can be further enhanced, and the conduction reliability can be further enhanced even when implemented in a relatively short time.

[0041] In the above differential scanning calorimetry, the heat release peak preferably has one peak. In the above differential scanning calorimetry, it is preferable that only one heat release peak is observed. In the above differential scanning calorimetry, it is preferable that two or more heat release peaks are not observed.

[0042] Hereinafter, each component contained in the conductive paste will be described.

[0043] In this specification, “(meth)acryl” represents acryl and methacryl, and “(meth)acrylate” represents acrylate and methacrylate.

[0044] <Thermosetting compound> The above-mentioned thermosetting compound is a compound that can be cured by heating. Examples of the above-mentioned thermosetting compound include epoxy compounds, (meth)acrylic compounds, oxetane compounds, episulfide compounds, phenol compounds, amino compounds, unsaturated polyester compounds, polyurethane compounds, silicone compounds, and polyimide compounds. Only one kind of the above-mentioned thermosetting compound may be used, or two or more kinds may be used in combination.

[0045] From the viewpoint of further enhancing the communication reliability even when implemented in a relatively short time, it is preferable that the above-mentioned thermosetting compound contains an epoxy compound.

[0046] Examples of the above-mentioned epoxy compound include glycidylamine type epoxy compounds, bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, bisphenol S type epoxy compounds, phenol novolac type epoxy compounds, biphenyl type epoxy compounds, biphenyl novolac type epoxy compounds, bisphenol type epoxy compounds, naphthalene type epoxy compounds, fluorene type epoxy compounds, phenol aralkyl type epoxy compounds, naphthol aralkyl type epoxy compounds, dicyclopentadiene type epoxy compounds, anthracene type epoxy compounds, epoxy compounds having an adamantane skeleton, epoxy compounds having a tricyclodecane skeleton, naphthylene ether type epoxy compounds, and epoxy compounds having a triazine nucleus in the skeleton.

[0047] The above-mentioned epoxy compound may be a glycidyl ether compound. The above-mentioned glycidyl ether compound is a compound having at least one glycidyl ether group.

[0048] From the viewpoint of further enhancing the communication reliability even when implemented in a relatively short time, it is more preferable that the above-mentioned thermosetting compound contains an epoxy compound having an aromatic skeleton, and it is even more preferable to contain a bisphenol A type epoxy compound or a bisphenol F type epoxy compound. Only one kind of the above-mentioned epoxy compound may be used, or two or more kinds may be used in combination.

[0049] The molecular weight of the above thermosetting compound is preferably 350 or more, more preferably 400 or more, still more preferably 450 or more, particularly preferably 500 or more, and preferably 4500 or less, more preferably 4000 or less, still more preferably 3500 or less, particularly preferably 3000 or less. When the molecular weight of the above thermosetting compound is within the above range, the viscosity of the conductive paste can be adjusted to a suitable range, and the conduction reliability can be further enhanced.

[0050] When the structural formula of the above thermosetting compound can be specified, the molecular weight of the above thermosetting compound means the molecular weight calculated from the structural formula. When the structural formula of the above thermosetting compound cannot be specified, the above molecular weight means the weight average molecular weight. The above weight average molecular weight indicates the weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC). Since the molecular weight of the above thermosetting compound is relatively small, the structural formula can generally be specified. The above weight average molecular weight can be measured under the following measuring apparatus and measuring conditions.

[0051] Measuring apparatus: "Waters GPC System (Waters 2690 + Waters 2414 (RI))" manufactured by Waters Corporation, Japan Column: 1 piece of Shodex GPC LF-G, 2 pieces of Shodex GPC LF-804 Mobile phase: THF 1.0 mL / min Sample concentration: 5 mg / mL Detector: Differential refractive index detector (RID) Standard substance: Polystyrene (manufactured by TOSOH Corporation, weight average molecular weight: 620 - 590000)

[0052] In 100% by weight of the above conductive paste, the content of the above thermosetting compound is preferably 15% by weight or more, more preferably 20% by weight or more, preferably 90% by weight or less, more preferably 80% by weight or less, and still more preferably 70% by weight or less. When the content of the above thermosetting compound is not less than the above lower limit and not more than the above upper limit, even when mounted in a relatively short time, the curability can be further enhanced, the adhesiveness can be further enhanced, the tackiness of the cured product can be made even better, and the conduction reliability can be further enhanced. When the above thermosetting compound contains two or more thermosetting compounds, the content of the above thermosetting compound indicates the total content of the two or more thermosetting compounds.

[0053] In 100% by weight of the above conductive paste, the content of the above epoxy compound is preferably 15% by weight or more, more preferably 20% by weight or more, preferably 90% by weight or less, more preferably 80% by weight or less, and still more preferably 70% by weight or less. When the content of the above epoxy compound is not less than the above lower limit and not more than the above upper limit, even when mounted in a relatively short time, the curability can be further enhanced, the adhesiveness can be further enhanced, the tackiness of the cured product can be made even better, and the conduction reliability can be further enhanced.

[0054] <Thermosetting agent> In the above conductive paste, the above thermosetting agent includes a microcapsule-type thermosetting agent or a thermosetting agent that is solid at 25°C. In the above conductive paste, the above thermosetting agent may include a thermosetting agent that is solid at 25°C or may include a microcapsule-type thermosetting agent. From the viewpoint of further enhancing the curability and making the tackiness of the cured product even better even when mounted in a relatively short time, it is preferable that the above thermosetting agent includes a thermosetting agent that is solid at 25°C, and it is preferable that it is a thermosetting agent that is solid at 25°C. From the viewpoint of further enhancing the storage stability, further enhancing the curability, further enhancing the adhesiveness, making the tackiness of the cured product even better, and further enhancing the conduction reliability even when mounted in a relatively short time, it is preferable that the above thermosetting agent includes a microcapsule-type thermosetting agent, and it is preferable that it is a microcapsule-type thermosetting agent. Only one type of the above thermosetting agent may be used, or two or more types may be used in combination.

[0055] In the above microcapsule-type thermosetting agent, the thermosetting agent component is included in the microcapsule. In the above microcapsule-type thermosetting agent, the inclusion of the microcapsule is the thermosetting agent component. The above microcapsule-type thermosetting agent can release the thermosetting agent component. In the above microcapsule-type thermosetting agent, the material of the above microcapsule is not particularly limited. Examples of the material of the above microcapsule include ethyl cellulose, polyvinyl alcohol, gelatin, and alginic acid.

[0056] From the viewpoint of further enhancing the curability and making the tackiness of the cured product even better even when mounted in a relatively short time, the melting point of the above thermosetting agent that is solid at 25°C is preferably 50°C or higher, more preferably 60°C or higher, still more preferably 70°C or higher, and preferably 150°C or lower, more preferably 140°C or lower, still more preferably 130°C or lower.

[0057] The melting point of the above thermosetting agent that is solid at 25°C can be calculated, for example, by performing differential scanning calorimetry (DSC) and calculating from the endothermic peak.

[0058] The above-mentioned thermosetting agent may be an anionic curing agent or a cationic curing agent. It is preferable that the above-mentioned thermosetting agent contains an anionic curing agent. Examples of the above-mentioned anionic curing agent include amine curing agents (amine compounds), imidazole curing agents, phenol curing agents (phenol compounds), and acid anhydride curing agents (acid anhydrides).

[0059] In the above-mentioned conductive paste, it is particularly preferable that the above-mentioned thermosetting compound contains an epoxy compound and the above-mentioned thermosetting agent contains an anionic curing agent. In this case, even when mounted in a relatively short time, the curability can be further enhanced, the adhesiveness can be further enhanced, the tackiness of the cured product can be made even better, and the conduction reliability can be further enhanced.

[0060] The above-mentioned thermosetting agent (anionic curing agent) preferably contains an amine curing agent (amine compound), an imidazole curing agent, a phenol curing agent (phenol compound), or an acid anhydride curing agent (acid anhydride), and more preferably contains an amine curing agent. In these cases, even when mounted in a relatively short time, the curability can be further enhanced, the adhesiveness can be further enhanced, the tackiness of the cured product can be made even better, and the conduction reliability can be further enhanced.

[0061] Examples of the above-mentioned amine curing agent include dicyandiamide, imidazole compounds, diaminodiphenylmethane, and diaminodiphenylsulfone. From the viewpoint of further enhancing the conduction reliability even when mounted in a relatively short time, it is preferable that the above-mentioned amine curing agent contains dicyandiamide or an imidazole compound. The above-mentioned amine curing agent may be a thermosetting agent that is solid at 25°C or a microcapsule-type thermosetting agent. The above-mentioned amine curing agent may be included in the microcapsule.

[0062] Examples of the imidazole curing agent include 2-undecylimidazole, 2-heptadecylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1,2-dimethylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-methylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-dihydroxymethylimidazole, etc.

[0063] Examples of the phenol curing agent include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, polypolyvinylphenol, bisphenol A type novolac, xylylene-modified novolac, decalin-modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, and poly(di-p-hydroxyphenyl)methane, etc. From the viewpoint of further enhancing the flexibility of the cured product and the flame retardancy of the cured product, a phenol resin having a melamine skeleton, a phenol resin having a triazine skeleton, or a phenol resin having an allyl group is preferred.

[0064] Examples of commercially available products of the above-mentioned phenolic curing agents include MEH-8005, MEH-8010, MEH-8015, and MEH-8000H (all manufactured by Meiwa Kasei Co., Ltd.), YLH903 (manufactured by Mitsubishi Chemical Corporation), LA-7052, LA-7054, LA-7751, LA-1356, and LA-3018-50P (all manufactured by DIC Corporation), and PS6313 and PS6492 (all manufactured by Gunei Chemical Industry Co., Ltd.), etc.

[0065] In 100% by weight of the above conductive paste, the content of the above thermosetting agent is preferably 1% by weight or more, more preferably 3% by weight or more, still more preferably 5% by weight or more, and preferably 20% by weight or less, more preferably 18% by weight or less, still more preferably 15% by weight or less. When the content of the above thermosetting agent is within the above lower limit and the above upper limit, the storage stability can be further enhanced, and the curability can also be further enhanced even when mounted in a relatively short time.

[0066] Based on 100 parts by weight of the content of the above thermosetting compound, the content of the above thermosetting agent is preferably 3 parts by weight or more, more preferably 5 parts by weight or more, still more preferably 10 parts by weight or more, and preferably 40 parts by weight or less, more preferably 30 parts by weight or less, still more preferably 20 parts by weight or less. When the content of the above thermosetting agent is within the above lower limit and the above upper limit, the storage stability can be further enhanced, and the curability can also be further enhanced even when mounted in a relatively short time.

[0067] <Conductive filler> The above conductive filler is not particularly limited. The above conductive filler may be conductive particles or carbon fiber.

[0068] From the perspective of further enhancing the communication reliability, in the above conductive paste, the conductive filler is preferably conductive particles including resin particles and a conductive layer disposed on the surface of the resin particles, or metal particles having a melting point exceeding 450°C. From the perspective of further enhancing the communication reliability, in the above conductive paste, the conductive filler is preferably metal particles having a melting point exceeding 450°C. The conductive filler described herein is different from solder particles. When the conductive particles described herein are used, the discharge stability of the above conductive paste can be enhanced. When only metal particles (for example, solder particles) having a melting point of 450°C or lower are used as the above conductive filler, it is difficult to sufficiently enhance the discharge stability of the conductive paste as compared with the case of using metal particles having a melting point exceeding 450°C.

[0069] The shape of the above conductive filler is not particularly limited. The shape of the above conductive filler may be spherical, may be a shape other than spherical, or may be a flat shape or the like.

[0070] The above conductive filler is preferably conductive particles. The above conductive particles may be solder particles or metal particles. The above metal particles may be metal powder. The above conductive particles may include base material particles and a conductive portion disposed on the surface of the base material particles. From the perspective of further enhancing the communication reliability, the above conductive particles preferably include base material particles and a conductive portion disposed on the surface of the base material particles.

[0071] When the above conductive filler is conductive particles, the particle diameter of the above conductive particles is preferably 0.1 μm or more, more preferably 1 μm or more, still more preferably 2 μm or more, preferably 100 μm or less, more preferably 30 μm or less, and still more preferably 10 μm or less. When the particle diameter of the above conductive particles is equal to or greater than the above lower limit and equal to or less than the above upper limit, the communication reliability can be further enhanced even when mounted in a relatively short time.

[0072] The particle size of the above conductive particles is preferably the average particle size, and more preferably the number average particle size. The average particle size of the above conductive particles can be determined, for example, by observing 50 arbitrary conductive particles with an electron microscope or an optical microscope and calculating the average value of the particle sizes of each conductive particle, or by performing laser diffraction particle size distribution measurement.

[0073] In the above conductive particles, when measuring the particle size of the above conductive particles by observing 50 arbitrary conductive particles with an electron microscope or an optical microscope, it can be measured, for example, as follows. Add to "Technovit 4000" manufactured by Kulzer so that the content of the conductive particles is 30% by weight, disperse it, and produce an embedding resin body for conductive particle inspection. Cut out the cross section of the conductive particles using an ion milling device ("IM4000" manufactured by Hitachi High-Technologies Corporation) so as to pass through the vicinity of the center of the conductive particles dispersed in the above embedding resin body for conductive particle inspection. Then, using a field emission scanning electron microscope (FE-SEM), set the image magnification to 25,000 times, randomly select 50 conductive particles, and observe each conductive particle. Measure the equivalent circle diameter of each conductive particle, and calculate their arithmetic mean as the particle size of the conductive particles.

[0074] The coefficient of variation (CV value) of the particle size of the above conductive particles is preferably 10% or less, and more preferably 5% or less. When the coefficient of variation of the particle size of the above conductive particles is below the above upper limit, the communication reliability can be further enhanced. The lower limit of the coefficient of variation (CV value) of the particle size of the above conductive particles is not particularly limited. The coefficient of variation (CV value) of the particle size of the above conductive particles may be 0% or more, or may be 1% or more.

[0075] The above coefficient of variation (CV value) can be measured as follows.

[0076] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of the particle size of the conductive particles Dn: Average value of the particle size of the conductive particles

[0077] In 100% by weight of the above conductive paste, the content of the above conductive filler is preferably 0.1% by weight or more, more preferably 1% by weight or more, still more preferably 5% by weight or more, and preferably 80% by weight or less, more preferably 60% by weight or less, still more preferably 40% by weight or less. When the content of the above conductive filler is equal to or higher than the above lower limit and equal to or lower than the above upper limit, the conduction reliability can be further enhanced even when mounted in a relatively short time.

[0078] With respect to 100 parts by weight of the content of the above thermosetting compound, the content of the above conductive filler is preferably 2 parts by weight or more, more preferably 3 parts by weight or more, still more preferably 5 parts by weight or more, particularly preferably 7 parts by weight or more, and preferably 35 parts by weight or less, more preferably 30 parts by weight or less, still more preferably 25 parts by weight or less, particularly preferably 20 parts by weight or less. When the content of the above conductive filler is equal to or higher than the above lower limit and equal to or lower than the above upper limit, the conduction reliability can be further enhanced even when mounted in a relatively short time.

[0079] The above conductive filler preferably contains a metal. Examples of the above metal include gold, silver, copper, platinum, palladium, zinc, lead, aluminum, cobalt, indium, ruthenium, nickel, chromium, titanium, antimony, bismuth, germanium, cadmium, and alloys thereof. Further, tin-doped indium oxide (ITO) may be used as the above metal. Only one kind of the above metal may be used, or two or more kinds may be used in combination.

[0080] From the viewpoint of further reducing the connection resistance between electrodes, the above conductive filler preferably contains an alloy containing tin, nickel, palladium, ruthenium, silver, copper, or gold, and more preferably contains nickel or palladium. From the viewpoint of enhancing the corrosion resistance of the above conductive filler and maintaining high conduction reliability, the above conductive filler preferably contains nickel or gold, and more preferably contains nickel. From the viewpoint of enhancing the corrosion resistance of the above conductive filler and maintaining high conduction reliability, it is particularly preferable that the outer surface of the above conductive filler contains nickel.

[0081] When the conductive particles are metal particles, examples of the metal that is the material of the metal particles include silver, copper, nickel, silicon, gold, titanium, and alloys such as solder. From the viewpoint of more effectively enhancing the conduction reliability, the material of the metal particles preferably contains nickel or a nickel alloy, and more preferably, the material of the metal particles is nickel or a nickel alloy. From the viewpoint of more effectively enhancing the conduction reliability, the outer surface portion of the metal particles preferably contains nickel or a nickel alloy.

[0082] Hereinafter, details of the conductive particles including the base material particles and the conductive portion disposed on the surface of the base material particles will be described.

[0083] (Base material particles) Examples of the base material particles include resin particles, inorganic particles excluding metal particles, organic-inorganic hybrid particles, and metal particles. The base material particles are preferably base material particles excluding metal particles, and more preferably resin particles, inorganic particles excluding metal particles, or organic-inorganic hybrid particles. The base material particles may be core-shell particles including a core and a shell disposed on the surface of the core. The core may be an organic core, and the shell may be an inorganic shell.

[0084] The base material particles are more preferably resin particles or organic-inorganic hybrid particles, and may be resin particles or organic-inorganic hybrid particles. By using these preferred base material particles, the effects of the present invention can be more effectively exerted.

[0085] As the material of the resin particles, various resins are preferably used. Examples of the material of the resin particles include polyolefin resins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyisobutylene, and polybutadiene; acrylic resins such as polymethyl methacrylate and polymethyl acrylate; polyalkylene terephthalate, polycarbonate, polyamide, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, phenol resin, melamine resin, benzoguanamine resin, urea resin, epoxy resin, unsaturated polyester resin, saturated polyester resin, polysulfone, polyphenylene oxide, polyacetal, polyimide, polyamideimide, polyetheretherketone, polyethersulfone, divinylbenzene polymer, and polymers obtained by polymerizing one or more polymerizable monomers having an ethylenically unsaturated group. The divinylbenzene polymer may be a divinylbenzene copolymer. Examples of the divinylbenzene copolymer include divinylbenzene-styrene copolymer and divinylbenzene-(meth)acrylate copolymer.

[0086] Resin particles having any compression characteristics suitable for the conductive paste can be designed and synthesized, and the hardness of the resin particles can be easily controlled within a suitable range. Therefore, the material of the resin particles is preferably a polymer obtained by polymerizing one or two or more polymerizable monomers having a plurality of ethylenically unsaturated groups.

[0087] When the resin particles are obtained by polymerizing a polymerizable monomer having an ethylenically unsaturated group, examples of the polymerizable monomer having an ethylenically unsaturated group include non-crosslinkable monomers and crosslinkable monomers.

[0088] Examples of the non-crosslinkable monomer include styrene monomers such as styrene and α-methylstyrene; carboxyl group-containing monomers such as (meth)acrylic acid, maleic acid, and maleic anhydride; alkyl (meth)acrylate compounds such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate; oxygen atom-containing (meth)acrylate compounds such as 2-hydroxyethyl (meth)acrylate, glycerol (meth)acrylate, polyoxyethylene (meth)acrylate, and glycidyl (meth)acrylate; nitrile-containing monomers such as (meth)acrylonitrile; vinyl ester compounds such as vinyl acetate, vinyl butyrate, vinyl laurate, and vinyl stearate; unsaturated hydrocarbons such as ethylene, propylene, isoprene, and butadiene; and halogen-containing monomers such as trifluoromethyl (meth)acrylate, pentafluoroethyl (meth)acrylate, vinyl chloride, vinyl fluoride, and chlorostyrene.

[0089] Examples of the crosslinkable monomer include polyfunctional (meth)acrylate compounds such as tetramethylolmethane tetra(meth)acrylate, tetramethylolmethane tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, glycerol tri(meth)acrylate, glycerol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, (poly)tetramethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate; silane-containing monomers such as triallyl (iso)cyanurate, triallyl trimellitate, divinylbenzene, diallyl phthalate, diallyl acrylamide, diallyl ether, γ-(meth)acryloxypropyltrimethoxysilane, trimethoxysilylstyrene, vinyltrimethoxysilane, etc.

[0090] The resin particles can be obtained by polymerizing the polymerizable monomer having an ethylenically unsaturated group by a known method. Examples of this method include a method of suspension polymerization in the presence of a radical polymerization initiator, and a method of swelling and polymerizing a monomer together with a radical polymerization initiator using non-crosslinked seed particles.

[0091] When the base material particles are inorganic particles excluding metal particles or organic-inorganic hybrid particles, examples of the inorganic substance that is the material of the base material particles include silica, alumina, barium titanate, zirconia, and carbon black. It is preferable that the inorganic substance is not a metal. The particles formed by the silica are not particularly limited, and examples include particles obtained by hydrolyzing a silicon compound having two or more hydrolyzable alkoxysilyl groups to form crosslinked polymer particles and then performing firing as necessary. Examples of the organic-inorganic hybrid particles include organic-inorganic hybrid particles formed by a crosslinked alkoxysilyl polymer and an acrylic resin.

[0092] The above-mentioned organic-inorganic hybrid particles are preferably core-shell type organic-inorganic hybrid particles having a core and a shell disposed on the surface of the core. It is preferable that the above core is an organic core. It is preferable that the above shell is an inorganic shell. From the viewpoint of more effectively reducing the connection resistance between electrodes, the above base material particles are preferably organic-inorganic hybrid particles having an organic core and an inorganic shell disposed on the surface of the above organic core.

[0093] Examples of the material of the above organic core include the materials of the resin particles described above.

[0094] Examples of the material of the above inorganic shell include the inorganic substances mentioned as the material of the above base material particles. The material of the above inorganic shell is preferably silica. The above inorganic shell is preferably formed by sol-gel method of metal alkoxide into a shell-like substance on the surface of the above core and then firing the shell-like substance. The above metal alkoxide is preferably silane alkoxide. The above inorganic shell is preferably formed by silane alkoxide.

[0095] When the above base material particles are metal particles, examples of the metal which is the material of the metal particles include silver, copper, nickel, silicon, gold, titanium, and alloys such as solder.

[0096] The melting point of the above metal particles is preferably above 450 °C, more preferably 500 °C or higher, even more preferably 600 °C or higher, still more preferably 700 °C or higher, even still more preferably 800 °C or higher, and particularly preferably 900 °C or higher. When the melting point of the above metal particles is above the above lower limit, the discharge stability of the above conductive paste can be further enhanced. The melting point of the above metal particles may be 3000 °C or lower, or may be 2500 °C or lower. The range of the melting point of the above metal particles can be set by appropriately selecting the above lower limit value and the above upper limit value.

[0097] The particle diameter of the above-mentioned base material particles is preferably 0.01 μm or more, more preferably 0.05 μm or more, still more preferably 0.5 μm or more, further preferably 1 μm or more, and particularly preferably 3 μm or more, and is preferably 50 μm or less, more preferably 30 μm or less, still more preferably 20 μm or less, and particularly preferably 10 μm or less. When the particle diameter of the above-mentioned base material particles is at least the above lower limit, the communication reliability becomes even higher. Furthermore, when forming a conductive portion on the surface of the base material particles, it becomes difficult to aggregate, and it becomes difficult to form aggregated conductive particles. When the particle diameter of the above-mentioned base material particles is at most the above upper limit, the conductive particles are easily compressed sufficiently, and the connection resistance between the electrodes connected via the conductive particles can be made even lower more effectively.

[0098] The particle diameter of the above-mentioned base material particles is preferably the average particle diameter, and more preferably the number average particle diameter. The number average particle diameter of the above-mentioned base material particles can be measured, for example, as follows. Add and disperse in "Technovit 4000" manufactured by Kulzer so that the content of the conductive particles becomes 30% by weight to produce an embedded resin body for inspecting the base material particles. Using an ion milling device ("IM4000" manufactured by Hitachi High-Technologies Corporation), cut out the cross-section of the conductive particles so as to pass near the center of the base material particles in the conductive particles dispersed in the above-mentioned embedded resin body for inspecting the base material particles. Then, using a field emission scanning electron microscope (FE-SEM), set the image magnification to 25,000 times, randomly select 50 conductive particles, and observe the base material particles of each conductive particle. Measure the particle diameter of the base material particles in each conductive particle, and calculate their arithmetic mean to obtain the average particle diameter of the base material particles.

[0099] (Conductive portion) The above conductive part preferably contains a metal. The metal constituting the above conductive part is not particularly limited. Examples of the above metal include gold, silver, copper, platinum, palladium, zinc, lead, aluminum, cobalt, indium, ruthenium, nickel, chromium, titanium, antimony, bismuth, germanium, cadmium, and alloys thereof. Further, tin-doped indium oxide (ITO) may be used as the above metal. Only one kind of the above metal may be used, or two or more kinds may be used in combination. From the viewpoint of further reducing the connection resistance between electrodes, an alloy containing tin, nickel, palladium, ruthenium, silver, copper, or gold is preferable, and nickel or palladium is more preferable.

[0100] From the viewpoint of more effectively enhancing the conduction reliability, it is preferable that the above conductive part contains nickel, and it is more preferable that the outer surface portion of the above conductive part contains nickel.

[0101] The content of nickel in the conductive part containing nickel is preferably 10% by weight or more, more preferably 50% by weight or more, still more preferably 60% by weight or more, further preferably 70% by weight or more, and particularly preferably 90% by weight or more. The content of nickel in the conductive part containing nickel may be 100% by weight or less, 99% by weight or less, 90% by weight or less, or 70% by weight or less. The range of the content of nickel in the conductive part containing nickel can be set by appropriately selecting the above lower limit value and the above upper limit value.

[0102] The above conductive part may be formed by one layer. The above conductive part may be formed by a plurality of layers. That is, the above conductive part may have a laminated structure of two or more layers. When the above conductive part is formed by a plurality of layers, the metal constituting the outermost layer is preferably an alloy containing gold, silver, nickel, palladium, ruthenium, copper, or tin, and more preferably nickel. When the metal constituting the outermost layer is these preferable metals, the connection resistance between electrodes becomes even lower.

[0103] The method for forming the conductive portion on the surface of the base material particles is not particularly limited. Examples of the method for forming the conductive portion include a method by electroless plating, a method by electroplating, a method by physical collision, a method by mechanochemical reaction, a method by physical vapor deposition or physical adsorption, and a method of coating the surface of the base material particles with a paste containing metal powder or a metal powder and a binder. The method for forming the conductive portion is preferably a method by electroless plating, electroplating or physical collision. Examples of the method by physical vapor deposition include methods such as vacuum evaporation, ion plating and ion sputtering. In the method by physical collision, for example, a sheeter composer (manufactured by Tokuju Kousakusho Co., Ltd.) is used.

[0104] The thickness of the conductive portion is preferably 0.005 μm or more, more preferably 0.01 μm or more, preferably 10 μm or less, more preferably 1 μm or less, and still more preferably 0.3 μm or less. When the thickness of the conductive portion is equal to or more than the lower limit and equal to or less than the upper limit, sufficient conductivity can be obtained, and the conductive particles do not become too hard, so that the conductive particles can be sufficiently deformed during connection.

[0105] When the conductive portion is formed of a plurality of layers, the thickness of the outermost layer of the conductive portion is preferably 0.001 μm or more, more preferably 0.01 μm or more, preferably 0.5 μm or less, and more preferably 0.1 μm or less. When the thickness of the outermost layer of the conductive portion is equal to or more than the lower limit and equal to or less than the upper limit, the outermost layer of the conductive portion becomes uniform, the corrosion resistance becomes sufficiently high, and the connection resistance between the electrodes can be made sufficiently low.

[0106] The thickness of the conductive portion can be measured, for example, by observing the cross section of the conductive particles using a transmission electron microscope (TEM).

[0107] Core material: Preferably, the conductive particles have a plurality of protrusions on the outer surface of the conductive portion. An oxide film is often formed on the surface of the electrode connected by the conductive particles. When using conductive particles having protrusions on the outer surface of the conductive portion, by arranging and crimping the conductive particles between the electrodes, the oxide film can be effectively removed by the protrusions. Therefore, the electrode and the conductive portion are more reliably in contact with each other, and the connection resistance between the electrodes becomes even lower. Further, when connecting the electrodes, the filler between the conductive particles and the electrodes can be effectively removed by the protrusions of the conductive particles. Therefore, the conduction reliability between the electrodes becomes even higher.

[0108] Examples of the method for forming the protrusions include a method of forming a conductive portion by electroless plating after attaching a core material to the surface of the base material particles, and a method of forming a conductive portion by electroless plating on the surface of the base material particles, then attaching a core material, and further forming a conductive portion by electroless plating. In addition, in order to form protrusions, after forming a conductive portion on the base material particles by electroless plating without using the core material, a method of depositing a plating in a protrusion shape on the surface of the conductive portion and further forming a conductive portion by electroless plating may be used.

[0109] Examples of the method for attaching a core material to the surface of the base material particles include a method of adding a core material to a dispersion of the base material particles and accumulating and attaching the core material to the surface of the base material particles by van der Waals forces, and a method of adding a core material to a container containing the base material particles and attaching the core material to the surface of the base material particles by a mechanical action such as rotation of the container. From the viewpoint of controlling the amount of the core material to be attached, the method of attaching the core material to the surface of the base material particles is preferably a method of accumulating and attaching the core material to the surface of the base material particles in the dispersion.

[0110] Examples of the material constituting the core material include a conductive material and a non-conductive material. Examples of the conductive material include metals, metal oxides, conductive non-metals such as graphite, and conductive polymers. Examples of the conductive polymer include polyacetylene. Examples of the non-conductive material include silica, alumina, titanium oxide, tungsten carbide, and zirconia. From the viewpoint of further enhancing the conduction reliability between electrodes, it is preferable that the core material is a metal.

[0111] The metal is not particularly limited. Examples of the metal include metals such as gold, silver, copper, platinum, zinc, iron, lead, tin, aluminum, cobalt, indium, nickel, chromium, titanium, antimony, bismuth, germanium, and cadmium, and alloys composed of two or more metals such as tin-lead alloy, tin-copper alloy, tin-silver alloy, tin-lead-silver alloy, and tungsten carbide. From the viewpoint of further enhancing the conduction reliability between electrodes, the metal is preferably nickel, copper, silver, or gold. The metal may be the same as or different from the metal constituting the conductive portion.

[0112] The shape of the core material is not particularly limited. The shape of the core material is preferably a massive shape. Examples of the core material include particulate masses, agglomerates formed by aggregation of a plurality of fine particles, and amorphous masses.

[0113] The particle diameter of the core material is preferably 0.001 μm or more, more preferably 0.05 μm or more, preferably 0.9 μm or less, and more preferably 0.2 μm or less. When the particle diameter of the core material is within the above lower limit and the above upper limit, the connection resistance between electrodes can be effectively reduced.

[0114] The particle diameter of the core material is preferably an average particle diameter, and more preferably a number average particle diameter. The particle diameter of the core material can be obtained, for example, by observing 50 arbitrary core materials with an electron microscope or an optical microscope and calculating the average value of the particle diameters of each core material, or by performing laser diffraction particle size distribution measurement.

[0115] <Thixotropic agent> Examples of the thixotropic agent include silica, titania, alumina, sorbitol, and zinc oxide. Only one type of the thixotropic agent may be used, or two or more types may be used in combination.

[0116] From the viewpoint of further enhancing the storage stability, the thixotropic agent preferably contains silica, sorbitol, titania, or alumina, and more preferably contains sorbitol.

[0117] The thixotropic agent is preferably solid at 25°C. From the viewpoint of further enhancing the storage stability, the thixotropic agent is preferably present in a dispersed state in the conductive paste.

[0118] When the thixotropic agent is solid at 25°C, the particle diameter of the thixotropic agent is preferably 0.001 μm or more, more preferably 0.01 μm or more, still more preferably 0.1 μm or more, preferably 10 μm or less, more preferably 5 μm or less, and still more preferably 1 μm or less. When the particle diameter of the thixotropic agent is within the above lower limit and the above upper limit, the storage stability can be further enhanced, and the conduction reliability can be further enhanced even when mounted in a relatively short time.

[0119] The particle diameter of the thixotropic agent is preferably the average particle diameter, and more preferably the number average particle diameter. The average particle diameter of the thixotropic agent can be obtained, for example, by observing 50 arbitrary thixotropic agents with an electron microscope or an optical microscope and calculating the average value of the particle diameters of each thixotropic agent, or by performing laser diffraction particle size distribution measurement.

[0120] The ratio of the particle size of the thixotropic agent to the particle size of the conductive filler (particle size of thixotropic agent / particle size of conductive filler) is preferably 0.0002 or more, more preferably 0.002 or more, still more preferably 0.02 or more, preferably 1.0 or less, more preferably 0.8 or less, still more preferably 0.5 or less, particularly preferably 0.1 or less, and most preferably 0.05 or less. When the above ratio (particle size of thixotropic agent / particle size of conductive filler) is equal to or greater than the above lower limit and equal to or less than the above upper limit, the storage stability can be further enhanced, and the communication reliability can be further enhanced even when implemented in a relatively short time.

[0121] The coefficient of variation (CV value) of the particle size of the thixotropic agent is preferably 10% or less, more preferably 5% or less. When the coefficient of variation of the particle size of the thixotropic agent is equal to or less than the above upper limit, the storage stability can be further enhanced, and the communication reliability can be further enhanced even when implemented in a relatively short time. The lower limit of the coefficient of variation (CV value) of the particle size of the thixotropic agent is not particularly limited. The coefficient of variation (CV value) of the particle size of the thixotropic agent may be 0% or more, or may be 1% or more.

[0122] The coefficient of variation (CV value) can be measured as follows.

[0123] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of the particle size of the thixotropic agent Dn: Average value of the particle size of the thixotropic agent

[0124] In 100% by weight of the conductive paste, the content of the thixotropic agent is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, still more preferably 1% by weight or more, preferably 20% by weight or less, more preferably 10% by weight or less, still more preferably 7% by weight or less. When the content of the thixotropic agent is equal to or greater than the above lower limit and equal to or less than the above upper limit, the storage stability can be further enhanced, and the communication reliability can be further enhanced even when implemented in a relatively short time.

[0125] With respect to 100 parts by weight of the content of the above thermosetting compound, the content of the above thixotropic agent is preferably 0.1 part by weight or more, more preferably 0.5 part by weight or more, preferably 30 parts by weight or less, more preferably 20 parts by weight or less, and still more preferably 10 parts by weight or less. When the content of the above thixotropic agent is within the above lower limit and the above upper limit, the storage stability can be further enhanced, and the conduction reliability can be further enhanced even when mounted in a relatively short time.

[0126] <Antioxidant> Since the above conductive paste contains an antioxidant, the conduction reliability can be enhanced even when mounted in a relatively short time.

[0127] Examples of the above antioxidant include hindered phenol-based antioxidants and thioether-based antioxidants. Only one kind of the above antioxidant may be used, or two or more kinds may be used in combination.

[0128] From the viewpoint of further enhancing the conduction reliability even when mounted in a relatively short time, the above antioxidant preferably contains a hindered phenol-based antioxidant.

[0129] The above antioxidant may be solid at 25°C or may be liquid at 25°C. From the viewpoint of improving the storage stability, the above antioxidant is preferably solid at 25°C.

[0130] When the above antioxidant is solid at 25°C, the particle size of the above antioxidant is preferably 0.01 μm or more, more preferably 0.05 μm or more, still more preferably 0.1 μm or more, preferably 10 μm or less, more preferably 5 μm or less, and still more preferably 1 μm or less. When the particle size of the above antioxidant is within the above lower limit and the above upper limit, the storage stability can be further enhanced, and the conduction reliability can be further enhanced even when mounted in a relatively short time.

[0131] In 100% by weight of the above conductive paste, the content of the above antioxidant is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, preferably 10% by weight or less, more preferably 7% by weight or less, and even more preferably 5% by weight or less. When the content of the antioxidant is equal to or higher than the above lower limit and equal to or lower than the above upper limit, the storage stability can be further enhanced, and the conduction reliability can be further enhanced even when mounted in a relatively short time.

[0132] Based on 100 parts by weight of the content of the above thermosetting compound, the content of the above antioxidant is preferably 0.1 part by weight or more, more preferably 0.5 part by weight or more, preferably 30 parts by weight or less, more preferably 20 parts by weight or less, and even more preferably 10 parts by weight or less. When the content of the antioxidant is equal to or higher than the above lower limit and equal to or lower than the above upper limit, the storage stability can be further enhanced, and the conduction reliability can be further enhanced even when mounted in a relatively short time.

[0133] <Other components> The above conductive paste may contain components other than the above thermosetting compound, the above thermosetting agent, the above conductive filler, the above thixotropic agent, and the above antioxidant. As other components of the above conductive paste, a solvent, an inorganic filler, an organic filler, a colorant, a polymerization inhibitor, a chain transfer agent, an ultraviolet absorber, an antifoaming agent, a leveling agent, a surfactant, a slip agent, an antiblocking agent, a wax, a masking agent, a deodorant, a fragrance, a preservative, an antibacterial agent, an antistatic agent, an adhesion promoter, etc. may be included.

[0134] (RFID inlay and method for manufacturing RFID inlay) The RFID inlay according to the present invention includes a substrate having wiring on its surface, a chip having electrodes on its surface, and an adhesive portion bonding the above substrate and the above chip. In the RFID inlay according to the present invention, the material of the above adhesive portion is the above conductive paste described above. In the RFID inlay according to the present invention, the above wiring and the above electrodes are electrically connected by the above conductive filler in the above adhesive portion.

[0135] FIG. 1 is a cross-sectional view schematically showing an RFID inlay using a conductive paste according to a first embodiment of the present invention.

[0136] The RFID inlay 81 shown in FIG. 1 includes a substrate 82 having wiring on its surface, a chip 83 having electrodes on its surface, and an adhesive portion 84 that adheres the substrate 82 and the chip 83. The material of the adhesive portion 84 is a conductive paste containing a conductive filler 1. The adhesive portion 84 is formed of a conductive paste containing a conductive filler 1. Preferably, the adhesive portion 84 is formed by curing a conductive paste containing a conductive filler 1.

[0137] The substrate 82 has wiring 82a on its surface (upper surface). The chip 83 has electrodes 83a on its surface (lower surface). The wiring 82a and the electrodes 83a are electrically connected by the conductive filler 1 in the adhesive portion 84.

[0138] The method for manufacturing an RFID inlay according to the present invention includes the following steps (1) to (3). (1) A first placement step of placing the above-described conductive paste on the surface of a substrate having wiring on its surface. (2) A second placement step of placing a chip having electrodes on its surface on the surface of the conductive paste opposite to the substrate side. (3) An adhesion step of forming an adhesive portion that adheres the substrate and the chip with the conductive paste by heating and pressurizing the conductive paste, and electrically connecting the wiring and the electrodes with the conductive filler in the adhesive portion.

[0139] In the RFID inlay and the method for manufacturing an RFID inlay according to the present invention, since a specific conductive paste is used, the adhesiveness between the substrate and the chip can be enhanced, and the conduction reliability can be enhanced.

[0140] In the method for manufacturing the RFID inlay, the substrate is in a long shape, and in the first placement step, the second placement step, and the bonding step, it is preferable to manufacture the RFID inlay by conveying the long substrate in a roll-to-roll manner. In this case, a plurality of RFID inlays can be continuously manufactured, and the manufacturing efficiency of the RFID inlay can be further improved.

[0141] When the roll-to-roll method is used, the conveyance speed of the substrate is not particularly limited.

[0142] Examples of the method for disposing the conductive paste include coating by a dispenser, screen printing, and ejection by an inkjet device.

[0143] The heating temperature in the bonding step is preferably 100°C or higher, more preferably 150°C or higher, preferably 400°C or lower, more preferably 300°C or lower, and even more preferably 250°C or lower. When the heating temperature in the bonding step is equal to or higher than the lower limit and equal to or lower than the upper limit, the electrical connection between the chip and the substrate can be made good.

[0144] The pressing pressure in the bonding step is preferably 0.5 N or higher, more preferably 1 N or higher, preferably 3.5 N or lower, more preferably 3 N or lower, and even more preferably 2.5 N or lower. When the pressing pressure in the bonding step is equal to or higher than the lower limit and equal to or lower than the upper limit, the adhesiveness between the substrate and the chip can be enhanced, and the conduction reliability can be enhanced.

[0145] The heating and pressing time in the bonding step is not particularly limited. The heating and pressing time in the bonding step may be 2 seconds or more, may be 15 seconds or less, may be 10 seconds or less, may be 9 seconds or less, or may be 7 seconds or less.

[0146] The above RFID inlay may be cut to a predetermined size as required and may be used after being cut. It is preferable to adhere a plurality of the above chips to a plurality of the above adhesive portions on a long substrate. A plurality of laminates of the above chip and the above adhesive portion may be arranged on the long substrate. In the above first arranging step, it is preferable to arrange the above conductive paste at a plurality of locations on the surface of the long substrate. In the above second arranging step, it is preferable to arrange the above chips on the surfaces opposite to the respective substrate sides of the conductive paste arranged at a plurality of locations using a plurality of chips. After adhering the above chips to the long substrate with the above adhesive portion, the long substrate may be cut.

[0147] The above substrate is not particularly limited. The above substrate is preferably a circuit board. Examples of the above circuit board include a resin film, a flexible printed circuit board, a rigid-flexible circuit board, a glass substrate, and a paper substrate. The above substrate may be a resin substrate, a glass substrate, or a paper substrate.

[0148] The above substrate has wiring (antenna pattern) on its surface. Wiring (antenna pattern) is formed on the surface of the above base material. The above substrate preferably has a base material and wiring (antenna pattern) arranged on the surface of the above base material.

[0149] Examples of the material of the above base material include resin, glass, and paper. Examples of the above resin include PET (polyethylene terephthalate), PP (polypropylene), and PVC (polyvinyl chloride). The above paper may be impregnated with an epoxy resin or a phenolic resin. From the viewpoint of further enhancing adhesiveness and from the viewpoint of manufacturing an RFID inlay by a roll-to-roll method, the material of the above base material is preferably resin or paper, and more preferably PET (polyethylene terephthalate) or paper. The above base material may be resin, glass, or paper.

[0150] Examples of the above wiring (antenna pattern) include gold wiring, nickel wiring, tin wiring, aluminum wiring, silver wiring, SUS wiring, copper wiring, molybdenum wiring, and tungsten wiring. From the perspective of improving the operating sensitivity in the UHF band (860 MHz to 960 MHz), the above wiring is preferably aluminum wiring.

[0151] From the perspective of suppressing deformation of the substrate due to heat during chip (e.g., IC chip) mounting and enhancing flexibility, the thickness of the above substrate is preferably 20 μm or more, more preferably 30 μm or more, preferably 200 μm or less, and more preferably 100 μm or less.

[0152] The shapes of the above substrate and the above base material are not particularly limited. From the perspective of manufacturing the RFID inlay by the roll-to-roll method, the above substrate and the above base material are preferably in a long shape. The lengths of the above substrate and the above base material are not particularly limited. The lengths of the above substrate and the above base material may be 1 m or more, 10 m or more, 5000 m or less, or 1000 m or less.

[0153] Examples of the above chip include semiconductor chips (IC chips).

[0154] The above chip has electrodes on its surface. Examples of the above electrodes include metal electrodes such as gold electrodes, nickel electrodes, tin electrodes, aluminum electrodes, silver electrodes, SUS electrodes, copper electrodes, molybdenum electrodes, and tungsten electrodes. From the perspective of further enhancing the communication reliability, the above electrodes are preferably copper electrodes or gold electrodes, and more preferably copper electrodes.

[0155] The number of the above electrodes per above chip is not particularly limited. The number of the above electrodes per above chip may be 1 or more, 4 or more, 20 or less, or 10 or less.

[0156] The shape of the above chip is not particularly limited. The shape of the above chip may be rectangular, triangular, or circular.

[0157] The planar area of the above chip is preferably 0.04 mm 2 or more, more preferably 0.09 mm 2 or more, even more preferably 0.16 mm 2 or more, and preferably 0.50 mm 2 or less, more preferably 0.40 mm 2 or less, even more preferably 0.30 mm 2 or less. When the planar area of the above chip is equal to or greater than the above lower limit, the conductive paste can be accurately arranged on the fine wiring. When the planar area of the above chip is equal to or less than the above upper limit, the communication reliability can be maintained even when the RFID inlay is left in a high-temperature and high-humidity environment for a long time. The conductive paste according to the present invention can be suitably used for adhering relatively small chips.

[0158] Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited only to the following Examples.

[0159] The following materials were prepared.

[0160] Thermosetting compound: "EXA830CRP" manufactured by DIC Corporation (bisphenol F type epoxy compound) "EXA850CRP" manufactured by DIC Corporation (bisphenol A type epoxy compound)

[0161] Thermosetting agent: "Amicure PN23" manufactured by Ajinomoto Fine-Techno Co., Inc. (amine curing agent, solid at 25°C) "Novacure HX3932HP" manufactured by Asahi Kasei Corporation (amine curing agent, microcapsule type thermosetting agent) "TD-984" manufactured by DIC Corporation (polyamideamine curing agent, liquid at 25°C) "Diethylenetriamine" manufactured by TCI (amine curing agent, liquid at 25°C)

[0162] Conductive filler: "CN050" manufactured by Nikko Rica Co., Ltd. (nickel particles, average particle diameter: 5 μm)

[0163] Thixotropic agent: "PM-20L" manufactured by Tokuyama Corporation (silica, solid at 25°C, average particle diameter: 0.012 μm) "Gelol D" manufactured by Shin Nippon Rika Co., Ltd. (sorbitol, solid at 25°C, average particle diameter: 0.10 μm) "43-00-502" manufactured by micromod (silica, solid at 25°C, average particle diameter: 0.5 μm) "43-00-303" manufactured by micromod (silica, solid at 25°C, average particle diameter: 3 μm) "43-00-503" manufactured by micromod (silica, solid at 25°C, average particle diameter: 5 μm)

[0164] Antioxidant: "Irganox1010" manufactured by BASF Japan Ltd. (hindered phenol-based antioxidant, solid at 25°C, average particle diameter: 0.1 μm)

[0165] Chip: IC chip (copper electrode, "UCODE9" manufactured by NXP, planar area: 0.22 mm 2 )

[0166] Substrate: PET film (long strip-shaped, resin film having aluminum wiring with an operating frequency in the UHF band (860 MHz to 960 MHz))

[0167] (Example 1) (1) Preparation of conductive paste The materials shown in Table 1 below were blended in the blending amounts (parts by weight) shown in Table 1 below, and stirred using a planetary stirrer ("Avatori Rentaro" manufactured by Shinki Co., Ltd.) to obtain a conductive paste (anisotropic conductive paste).

[0168] (2) Preparation of RFID inlay On a PET film, the obtained conductive paste was applied by the jet dispensing method to form a conductive paste layer (adhesive layer) (first placement step). Next, an IC chip was laminated on the surface of the conductive paste layer (adhesive layer) opposite to the substrate side such that the wiring on the PET film surface and the electrodes on the chip surface faced each other (second placement step). Thereafter, thermal compression bonding was performed under the conditions of an upper heat tool at 180°C, a lower heat tool at 180°C, a pressure of 2 N, and a compression bonding time of 3 seconds to cure the conductive paste layer (adhesive layer) and form an adhesive portion. Also, the wiring on the surface of the PET film and the electrodes on the surface of the chip were electrically connected by the conductive filler (conductive particles) in the adhesive portion to obtain a connection structure (adhesive step). Note that the first placement step, the second placement step, and the adhesive step were performed using "DDA40000" (roll-to-roll method) manufactured by Muhlbauer. The obtained connection structure was cut into a size of 5 cm × 1.5 cm using "DCL30000" manufactured by Muhlbauer to obtain 50 RFID inlays.

[0169] (Examples 2 to 4, 6, Reference Example 5 7 and Comparative Examples 1 to 4) Conductive pastes and RFID inlays were obtained in the same manner as in Example 1, except that the compounding components and compounding amounts of the conductive paste were changed as shown in Tables 1 to 3.

[0170] (Evaluation) (1) Differential Scanning Calorimetry A differential scanning calorimeter ("TA7000" manufactured by Hitachi High-Technologies Corporation) was prepared, 5 mg of the obtained conductive paste was placed in a dedicated aluminum pan, and the lid was closed using a dedicated jig. This dedicated aluminum pan and an empty aluminum pan (reference) were placed in the heating unit, and heating was performed in an air atmosphere from 30°C to 200°C at a heating rate of 10°C / min, and the reverse heat flow and non-reverse heat flow were observed. The exothermic peak observed in the non-reverse heat flow was defined as the exothermic peak of the conductive paste, and the exotherm start temperature, exotherm peak top temperature, and exotherm end temperature were determined.

[0171] (2) Storage Stability (Pot Life) Regarding the as-prepared conductive paste, the viscosity at 25°C (η25) was measured by the method described above. Also, by the method described above, the viscosity at 25°C (ηα) after storing the conductive paste at 25°C and 50% RH for 24 hours was measured. The ratio of the viscosity after storage (ηα) to the viscosity as-prepared (η25) (viscosity after storage (ηα) / viscosity as-prepared (η25)) was determined, and the storage stability (pot life) was judged according to the following criteria.

[0172] [Criteria for judging storage stability (pot life)] ○○: The ratio of the viscosity after storage to the viscosity as-prepared is less than 1.1 ○: The ratio of the viscosity after storage to the viscosity as-prepared is 1.1 or more and less than 1.25 ×: The ratio of the viscosity after storage to the viscosity as-prepared is 1.25 or more

[0173] (3) Curing property (gel time) of the conductive paste The conductive paste was applied on a glass plate with a thickness of 30 μm. The glass plate was placed on the surface of a hot plate (set temperature: 180°C) from the surface opposite to the side where the paste was applied, and the elapsed time until the paste gelled was measured. The curing property (gel time) of the conductive paste was judged according to the following criteria. In addition, thread pulling was checked every 5 seconds using a handled needle, and when the thread could no longer be broken, it was judged that gelation had occurred.

[0174] [Criteria for judging the curing property (gel time) of the conductive paste] ○○: The elapsed time until the paste gels is less than 15 seconds ○: The elapsed time until the paste gels is 15 seconds or more and less than 30 seconds ×: The elapsed time until the paste gels is 30 seconds or more

[0175] (4) Adhesion (die shear strength) Regarding the obtained RFID inlay, using a die shear tester ("DAGE4000PLUS" manufactured by Nordson Corporation), the chip was peeled off from the substrate under the conditions of a tool height of 30 μm and a speed of 100 μm / second, and the die shear strength at 25°C was evaluated. The adhesiveness (die shear strength) was determined according to the following criteria.

[0176] [Criteria for Determining Adhesiveness (Die Shear Strength)] ○○: Die shear strength is 7.0 N or more ○: Die shear strength is 4.0 N or more and less than 7.0 N ×: Die shear strength is less than 4.0 N

[0177] (5) Tackiness of the cured product A prepared conductive paste filled in a PTFE mold was heated in an oven at 180°C for 300 seconds to obtain a strip-shaped cured product of 5 mm × 40 mm × 2 mm. The obtained cured product was left at room temperature for 12 hours or more and then cooled. At 25°C, when the tip of a handled needle touched one end of the cured product, it was observed whether the cured product was lifted. The tackiness of the cured product was determined according to the following criteria.

[0178] [Criteria for Determining Tackiness of the Cured Product] ○○: The cured product does not lift ○: While the other end where the handled needle is not touching remains grounded, one end side of the cured product lifts ×: The entire cured product lifts

[0179] (6) Communication reliability After leaving 50 obtained RFID inlays at 85°C and 85% RH (under high temperature and high humidity environment) for 168 hours, they were placed in a dark box that blocks external radio waves, and using a frequency reader ("Tagformance Pro" manufactured by Voyantic), the peak sensitivity at 25°C in the UHF band (860 MHz to 960 MHz) was measured. The communication reliability was determined according to the following criteria.

[0180] [Criteria for Determining Communication Reliability] ○○: The peak sensitivity of all RFID inlays is less than -18 dBm ○: Does not correspond to either ○○ or × ×: The peak sensitivity of at least one RFID inlay is -16.4 dBm or more

[0181] The composition of the conductive paste and the results are shown in Tables 1 to 3 below.

[0182] [Table 1]

[0183] [Table 2]

[0184] [Table 3]

[0185] Note that Reference In Example 5 Reference and Example 7, the determination results of storage stability were both "〇". However, the value of "the ratio of the viscosity after storage to the viscosity immediately after production", which is the criterion for judging storage stability, Reference was smaller for Example 7 Reference than for Example 5, Reference and Example 7 Reference was more excellent in storage stability than Example 5. [Description of Reference Signs]

[0186] 1... Conductive filler 81... RFID inlay 82... Substrate having wiring on the surface 82a... Wiring 83... Chip having electrodes on the surface 83a... Electrodes 84... Adhesive part

Claims

1. A heat-curable compound, a heat-curing agent, a conductive filler, a thixotropic agent, and an antioxidant, wherein the heat-curing agent includes a microcapsule-type heat-curing agent or a heat-curing agent that is solid at 25°C, the thixotropic agent is solid at 25°C, and a ratio of a particle diameter of the thixotropic agent to a particle diameter of the conductive filler is 0.002 or more and 0.1 or less. A conductive paste.

2. The conductive paste according to claim 1, wherein, in 100% by weight of the conductive paste, the thixotropic agent is included in a content of 20% by weight or less.

3. The heat-curable compound includes an epoxy compound, and the heat-curing agent includes an anionic curing agent. The conductive paste according to claim 1 or 2.

4. The conductive filler is conductive particles, and a particle diameter of the conductive particles is 10 μm or less. The conductive paste according to claim 1 or 2.

5. The conductive paste according to claim 1 or 2, which is an anisotropic conductive paste used for electrical connection of electrodes.

6. The conductive paste according to claim 1 or 2, which is used to obtain an RFID inlay.

7. An RFID inlay includes a substrate having wiring on a surface, a chip having an electrode on a surface, and an adhesive portion bonding the substrate and the chip, wherein a material of the adhesive portion is the conductive paste according to claim 1 or 2, and the wiring and the electrode are electrically connected by the conductive filler in the adhesive portion.

8. A first arranging step of arranging the conductive paste according to claim 1 or 2 on a surface of a substrate having wiring on the surface, a second arranging step of arranging a chip having an electrode on a surface on a surface opposite to the substrate side of the conductive paste, and an adhesion step of forming an adhesive portion bonding the substrate and the chip with the conductive paste by heating and pressurizing the conductive paste, and electrically connecting the wiring and the electrode by the conductive filler in the adhesive portion. A method for manufacturing an RFID inlay.

9. The substrate is in a long shape, and in the first arranging step, the second arranging step, and the adhesion step, the long substrate is conveyed by a roll-to-roll method to manufacture an RFID inlay. The method for manufacturing an RFID inlay according to claim 8.

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