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

Abstract

Provided is a conductive paste which 1) can enhance storage stability and, even when mounted in a relatively short time, 2) can enhance the curability, 3) can enhance the adhesiveness, 4) can achieve favorable tackiness of a cured product, and 5) can enhance the conduction 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. The thermosetting agent contains a microcapsule type thermosetting agent or a thermosetting agent that is solid at 25°C.

Description

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

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

[0002] RFID (Radio Frequency Identification) inlays, which enable contactless data transmission and reception, are widely used in contactless RFID tags, contactless RFID cards, etc. In particular, RFID inlays in the UHF (Ultra High Frequency) band (860 MHz to 960 MHz) have attracted attention due to their long communication distances, and UHF band RFID inlays are used for a variety of items and purposes, such as commuter passes, inventory management, distribution management, and history management.

[0003] In RFID inlays, a conductive paste containing a conductive filler and a binder resin may be used to bond and connect a chip having electrodes on its surface to a substrate having wiring (antenna pattern) on its surface.

[0004] In recent years, as electronic components using RFID inlays have become smaller, the chips used in RFID inlays have also become smaller, creating a demand for conductive pastes that have high adhesive properties and can be placed on wiring with even greater precision.

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

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

[0007] JP 2006-144018 A JP 2013-124330 A

[0008] Conventional adhesives (conductive pastes) such as those described in Patent Documents 1 and 2 can enhance adhesiveness to a certain extent. However, when electronic components are fabricated (mounted) using such conventional conductive pastes in an air atmosphere, the polymerization reaction of the conductive paste may not proceed sufficiently due to the influence of oxygen, resulting in uncured portions in the cured product of the conductive paste. As a result, there are problems in that the adhesiveness cannot be sufficiently enhanced, the tackiness of the cured product cannot be improved, and the electrical conductivity reliability of the resulting electronic components cannot be sufficiently improved. This problem is particularly pronounced when mounting is performed within a relatively short period of time (e.g., within 15 seconds).

[0009] In general, increasing the curability of an adhesive (conductive paste) tends to shorten its pot life (usable time). With conventional adhesives (conductive pastes), it is difficult to increase the curability of the adhesive (conductive paste) and also increase its storage stability.

[0010] The object of the present invention is to provide a conductive paste that 1) has improved storage stability, and that can improve curing properties even when mounted in a relatively short time, 3) can improve adhesiveness, 4) can improve tackiness of the cured product, and 5) can improve electrical conductivity reliability. Another object of the present invention is to provide an RFID inlay using the conductive paste, and a method for manufacturing an RFID inlay.

[0011] The present specification discloses the following conductive paste, RFID inlay, and method for manufacturing the RFID inlay.

[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 comprises a microencapsulated 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 size of the thixotropic agent to the particle size 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 together, wherein the adhesive portion is made of 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 arrangement step of arranging the conductive paste according to any one of Items 1 to 5 on a surface of a substrate having wiring on its surface; a second arrangement step of arranging a chip having electrodes on its surface on the surface of the conductive paste opposite the substrate side; and an adhesion step of forming an adhesive joint using the conductive paste to bond the substrate and the chip by heating and pressurizing the conductive paste, and electrically connecting the wiring and the electrodes via the conductive filler in the adhesive joint.

[0019] Item 8. The method for manufacturing an RFID inlay according to Item 7, wherein the substrate is long, and the RFID inlay is manufactured by transporting the long substrate by a roll-to-roll method in the first arrangement step, the second arrangement step, and the bonding step.

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

[0021] 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.

[0022] The present invention will be described in detail below.

[0023] (Conductive Paste) The conductive paste according to the present invention contains 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 contains a microcapsule-type thermosetting agent or a thermosetting agent that is solid at 25°C.

[0024] When conventional conductive pastes are used to fabricate (mount) electronic components in an air atmosphere, the polymerization reaction of the conductive paste may not proceed sufficiently due to the influence of oxygen, resulting in uncured portions of the cured conductive paste. As a result, the tackiness of the cured product may not be improved, the adhesiveness may not be sufficiently enhanced, and the electrical conductivity reliability of the resulting electronic component may not be sufficiently improved. This problem is particularly pronounced when only a (meth)acrylate compound is radically polymerized as the curable compound or when mounting is performed within a relatively short period of time (e.g., within 15 seconds). Furthermore, with conventional conductive pastes, it is difficult to improve the curability and storage stability of the conductive paste.

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

[0026] That is, since the conductive paste according to the present invention has the above-mentioned configuration, it is possible to extend the pot life (usable time) (enhance storage stability). Furthermore, since the conductive paste according to the present invention has the above-mentioned configuration, it is possible to enhance the curability and sufficiently cure even when mounted (heated) in a relatively short time (for example, within 15 seconds). Furthermore, since the conductive paste according to the present invention has the above-mentioned configuration, it is possible to enhance the adhesiveness and improve the tackiness of the cured product, thereby enhancing the reliability of electrical conduction, even when mounted in a relatively short time.

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

[0028] The viscosity (η25) of the conductive paste at 25°C is preferably 15 Pa·s or more, more preferably 25 Pa·s or more, even more preferably 40 Pa·s or more, and preferably 200 Pa·s or less, more preferably 150 Pa·s or less, and even more preferably 100 Pa·s or less. When the viscosity (η25) is equal to or greater than the lower limit, the conductive paste can be prevented from flowing out from the wiring. When the viscosity (η25) is equal to or less than the upper limit, the conductive paste can be arranged on the fine wiring with high precision.

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

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

[0031] The viscosity (ηα) after storage can be measured, for example, using an E-type viscometer at 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 E-type viscometer include the TV35 viscometer manufactured by Toki Sangyo Co., Ltd.

[0032] The conductive paste has good adhesive properties and is suitable for use as an adhesive. The conductive paste is particularly suitable for use in bonding a substrate and a chip.

[0033] From the viewpoint of further improving the reliability of conduction, the conductive paste is preferably an anisotropic conductive paste. The conductive paste is preferably used for electrically connecting electrodes. The conductive paste is preferably used for obtaining a connection structure. The conductive paste is preferably used for obtaining electronic components. The conductive paste is particularly preferably used for obtaining an RFID inlay (use of the conductive paste for obtaining an RFID inlay). The conductive paste is preferably used for bonding and connecting a chip having an electrode on its surface to a substrate having wiring (antenna pattern) on its surface (use of the conductive paste for bonding and connecting a chip having an electrode on its surface to a substrate having wiring (antenna pattern) on its surface).

[0034] The conductive paste contains a thermosetting compound and therefore has thermosetting properties. The conductive paste is a thermosetting conductive paste. More preferably, the conductive paste is a thermosetting anisotropic conductive paste.

[0035] When the conductive paste is heated from 30°C to 200°C at a temperature increase rate of 10°C / min and subjected to differential scanning calorimetry (DSC), the exotherm onset temperature is preferably 50°C or higher, the exotherm peak top temperature is preferably 80°C or higher and 125°C or lower, and the exotherm end temperature is preferably 200°C or lower. In this specification, the exotherm onset temperature refers to the temperature at which the amount of heat generated begins to increase from the baseline. In addition, in this specification, the exotherm end temperature refers to the temperature at which, after reaching the exotherm peak top, the amount of heat generated has decreased to 1% of the amount of heat generated at the exotherm peak top.

[0036] The differential scanning calorimetry (DSC) can be performed as follows. A differential scanning calorimeter is prepared. 5 mg of the conductive paste is placed in a dedicated aluminum pan and the lid is closed using a dedicated jig. This dedicated aluminum pan and an empty aluminum pan (reference) are placed in a heating unit, and heating is performed in an air atmosphere from 30°C to 200°C at a temperature increase rate of 10°C / min, and reverse heat flow and non-reverse heat flow are observed. The exothermic peak observed in the non-reverse heat flow is taken as the exothermic peak of the conductive paste. An example of the differential scanning calorimeter is the "TA7000" manufactured by Hitachi High-Tech Science Corporation.

[0037] The heat generation initiation temperature can be measured in the differential scanning calorimetry. From the viewpoint of improving the storage stability and discharge stability of the conductive paste and further improving the conductivity reliability even when mounted in a relatively short time, the heat generation initiation temperature is preferably 50°C or higher, more preferably 60°C or higher. The upper limit of the heat generation initiation temperature is not particularly limited. The heat generation initiation 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 heat generation initiation temperature can be set by appropriately selecting the lower limit and the upper limit.

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

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

[0040] In the differential scanning calorimetry, the absolute value of the difference between the heat generation start temperature and the heat generation end temperature is preferably 5° C. or more, more preferably 10° C. or more, even more preferably 15° C. or more, particularly preferably 20° C. or more, and is preferably 100° C. or less, more preferably 95° C. or less, even more preferably 90° C. or less, particularly preferably 85° C. or less, and most preferably 80° C. or less. When the absolute value of the difference between the heat generation start temperature and the heat generation end temperature is equal to or greater than the above lower limit and equal to or less than the above upper limit, the storage stability of the conductive paste can be further improved, and the conductivity reliability can be further improved even when the paste is mounted in a relatively short time.

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

[0042] Each component contained in the conductive paste will be described below.

[0043] In this specification, "(meth)acrylic" refers to acrylic and methacrylic, and "(meth)acrylate" refers to acrylate and methacrylate.

[0044] <Thermosetting Compound> The thermosetting compound is a compound that can be cured by heating. Examples of the 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. The thermosetting compound may be used alone or in combination of two or more.

[0045] From the viewpoint of further improving the conduction reliability even when mounting is performed in a relatively short time, the thermosetting compound preferably contains an epoxy compound.

[0046] Examples of the 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, biphenol 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 epoxy compound may be a glycidyl ether compound, which is a compound having at least one glycidyl ether group.

[0048] From the viewpoint of further improving the conduction reliability even when mounting is performed in a relatively short time, the thermosetting compound more preferably contains an epoxy compound having an aromatic skeleton, and further preferably contains a bisphenol A type epoxy compound or a bisphenol F type epoxy compound. Only one type of the epoxy compound may be used, or two or more types may be used in combination.

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

[0050] When the structural formula of the thermosetting compound can be identified, the molecular weight of the thermosetting compound refers to a molecular weight that can be calculated from the structural formula. When the structural formula of the thermosetting compound cannot be identified, the molecular weight refers to a weight average molecular weight. The weight average molecular weight refers to a weight average molecular weight calculated in terms of polystyrene measured by gel permeation chromatography (GPC). Since the molecular weight of the thermosetting compound is relatively small, the structural formula can generally be identified. The weight average molecular weight can be measured using the following measuring device and under the following measuring conditions.

[0051] Measurement apparatus: "Waters GPC System (Waters 2690 + Waters 2414 (RI))" manufactured by Japan Waters Column: Shodex GPC LF-G x 1, Shodex GPC LF-804 x 2 Mobile phase: THF 1.0 mL / min Sample concentration: 5 mg / mL Detector: Refractive index detector (RID) Standard substance: Polystyrene (manufactured by TOSOH Corporation, weight average molecular weight: 620 to 590,000)

[0052] The content of the thermosetting compound in 100% by weight of the conductive paste is preferably 15% by weight or more, more preferably 20% by weight or more, and preferably 90% by weight or less, more preferably 80% by weight or less, and even more preferably 70% by weight or less. When the content of the thermosetting compound is above the above lower limit and below the above upper limit, even when mounted in a relatively short time, the curing property can be further improved, the adhesiveness can be further improved, the tackiness of the cured product can be further improved, and the conductivity reliability can be further improved. Note that when the thermosetting compound contains two or more types of thermosetting compounds, the content of the thermosetting compound refers to the total content of the two or more types of thermosetting compounds.

[0053] The content of the epoxy compound in 100% by weight of the conductive paste is preferably 15% by weight or more, more preferably 20% by weight or more, and preferably 90% by weight or less, more preferably 80% by weight or less, and even more preferably 70% by weight or less. When the content of the epoxy compound is equal to or more than the lower limit and equal to or less than the upper limit, even when mounting is performed in a relatively short time, the curability can be further improved, the adhesiveness can be further improved, the tackiness of the cured product can be further improved, and the conductivity reliability can be further improved.

[0054] <Thermosetting Agent> In the conductive paste, the thermosetting agent includes a microencapsulated thermosetting agent or a thermosetting agent that is solid at 25°C. In the conductive paste, the thermosetting agent may include a thermosetting agent that is solid at 25°C or may include a microencapsulated thermosetting agent. From the viewpoint of further improving the curability and improving the tackiness of the cured product even when mounted in a relatively short time, the thermosetting agent preferably includes a thermosetting agent that is solid at 25°C, and is preferably a thermosetting agent that is solid at 25°C. From the viewpoint of further improving storage stability, and further improving the curability, adhesiveness, tackiness of the cured product, and conductivity reliability even when mounted in a relatively short time, the thermosetting agent preferably includes a microencapsulated thermosetting agent, and is preferably a microencapsulated thermosetting agent. The thermosetting agent may be used alone or in combination of two or more types.

[0055] In the microcapsule-type thermosetting agent, the thermosetting agent component is encapsulated in a microcapsule. In the microcapsule-type thermosetting agent, the encapsulation of the microcapsule is the thermosetting agent component. The microcapsule-type thermosetting agent is capable of releasing the thermosetting agent component. In the microcapsule-type thermosetting agent, the material of the microcapsule is not particularly limited. Examples of the material of the microcapsule include ethyl cellulose, polyvinyl alcohol, gelatin, and alginic acid.

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

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

[0058] The heat curing agent may be an anionic curing agent or a cationic curing agent. The heat curing agent preferably includes an anionic curing agent. Examples of the anionic curing agent include an amine curing agent (amine compound), an imidazole curing agent, a phenolic curing agent (phenolic compound), and an acid anhydride curing agent (acid anhydride).

[0059] In the conductive paste, it is particularly preferred that the thermosetting compound contains an epoxy compound and the thermosetting agent contains an anionic curing agent, which can further enhance the curability, adhesiveness, and tackiness of the cured product, even when mounted in a relatively short time, thereby further improving the electrical conductivity reliability.

[0060] The heat curing agent (anionic curing agent) preferably includes an amine curing agent (amine compound), an imidazole curing agent, a phenolic curing agent (phenolic compound), or an acid anhydride curing agent (acid anhydride), and more preferably includes an amine curing agent. In these cases, even when mounted in a relatively short time, the curability can be further improved, the adhesiveness can be further improved, the tackiness of the cured product can be further improved, and the conductivity reliability can be further improved.

[0061] Examples of the amine curing agent include dicyandiamide, an imidazole compound, diaminodiphenylmethane, and diaminodiphenylsulfone. From the viewpoint of further improving the conductivity reliability even when mounting is performed in a relatively short time, the amine curing agent preferably contains dicyandiamide or an imidazole compound. The amine curing agent may be a heat curing agent that is solid at 25°C or may be a microcapsule-type heat curing agent. The amine curing agent may be encapsulated in microcapsules.

[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-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole trimellitate, and 1-cyanoethyl-2-phenylimidazolium trimethylimidazole. Examples of suitable methylimidazole compounds include melitate, 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.

[0063] Examples of the phenol curing agent include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, polyparavinylphenol, bisphenol A 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 improving the flexibility and flame retardancy of the cured product, a phenolic resin having a melamine skeleton, a phenolic resin having a triazine skeleton, or a phenolic resin having an allyl group is preferred.

[0064] Commercially available 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 Gun-ei Chemical Industry Co., Ltd.).

[0065] The content of the thermosetting agent in 100% by weight of the conductive paste is preferably 1% by weight or more, more preferably 3% by weight or more, and even more preferably 5% by weight or more, and is preferably 20% by weight or less, more preferably 18% by weight or less, and even more preferably 15% by weight or less. When the content of the thermosetting agent is equal to or more than the lower limit and equal to or less than the upper limit, storage stability can be further improved, and curing properties can be further improved even when the paste is mounted in a relatively short time.

[0066] The content of the thermosetting agent relative to 100 parts by weight of the thermosetting compound is preferably 3 parts by weight or more, more preferably 5 parts by weight or more, even more preferably 10 parts by weight or more, and is preferably 40 parts by weight or less, more preferably 30 parts by weight or less, and even more preferably 20 parts by weight or less. When the content of the thermosetting agent is equal to or more than the above lower limit and equal to or less than the above upper limit, storage stability can be further improved, and curing properties can be further improved even when the composition is mounted in a relatively short time.

[0067] <Conductive Filler> The conductive filler is not particularly limited, and may be conductive particles or carbon fibers.

[0068] From the viewpoint of further improving the conductivity reliability, the conductive filler in the conductive paste 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 viewpoint of further improving the conductivity reliability, the conductive filler in the conductive paste is preferably metal particles having a melting point exceeding 450°C. The conductive filler described here is different from solder particles. When the conductive particles described here are used, the discharge stability of the conductive paste can be improved. When only metal particles (e.g., solder particles) having a melting point of 450°C or less are used as the conductive filler, it is difficult to sufficiently improve the discharge stability of the conductive paste compared to when metal particles having a melting point exceeding 450°C are used.

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

[0070] The conductive filler is preferably a conductive particle. The conductive particle may be a solder particle or a metal particle. The metal particle may be a metal powder. The conductive particle may include a base particle and a conductive portion disposed on the surface of the base particle. From the viewpoint of further improving the conduction reliability, the conductive particle preferably includes a base particle and a conductive portion disposed on the surface of the base particle.

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

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

[0073] When measuring the particle diameter of the conductive particles by observing 50 random conductive particles using an electron microscope or optical microscope, the measurement can be performed, for example, as follows. The conductive particles are added to Kulzer's "Technovit 4000" so that the content is 30 wt % and dispersed to prepare a conductive particle inspection embedding resin body. A cross section of the conductive particles is cut out using an ion milling device (Hitachi High-Technologies Corporation's "IM4000") so as to pass through the vicinity of the center of the conductive particles dispersed in the conductive particle inspection embedding resin body. Then, using a field emission scanning electron microscope (FE-SEM) with an image magnification set to 25,000x, 50 conductive particles are randomly selected and observed. The circle-equivalent diameter of each conductive particle is measured, and the arithmetic average is taken as the particle diameter of the conductive particles.

[0074] The coefficient of variation (CV value) of the particle diameter of the conductive particles is preferably 10% or less, more preferably 5% or less. When the coefficient of variation of the particle diameter of the conductive particles is equal to or less than the upper limit, the electrical conductivity reliability can be further improved. The lower limit of the coefficient of variation (CV value) of the particle diameter of the conductive particles is not particularly limited. The coefficient of variation (CV value) of the particle diameter of the conductive particles may be 0% or more, or may be 1% or more.

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

[0076] CV value (%) = (ρ / Dn) × 100, where ρ: standard deviation of particle diameter of conductive particles, and Dn: average particle diameter of conductive particles.

[0077] The content of the conductive filler in 100% by weight of the conductive paste is preferably 0.1% by weight or more, more preferably 1% by weight or more, and even more preferably 5% by weight or more, and is preferably 80% by weight or less, more preferably 60% by weight or less, and even more preferably 40% by weight or less. When the content of the conductive filler is equal to or more than the lower limit and equal to or less than the upper limit, the conductivity reliability can be further improved even when mounting is performed in a relatively short time.

[0078] The content of the conductive filler relative to 100 parts by weight of the thermosetting compound is preferably 2 parts by weight or more, more preferably 3 parts by weight or more, even more preferably 5 parts by weight or more, particularly preferably 7 parts by weight or more, and is preferably 35 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 25 parts by weight or less, particularly preferably 20 parts by weight or less. When the content of the conductive filler is equal to or more than the above lower limit and equal to or less than the above upper limit, the conductivity reliability can be further improved even when mounting is performed in a relatively short time.

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

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

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

[0082] Hereinafter, the conductive particle including a base particle and a conductive portion disposed on the surface of the base particle will be described in detail.

[0083] (Base Particles) Examples of the base particles include resin particles, inorganic particles excluding metal particles, organic-inorganic hybrid particles, and metal particles. The base particles are preferably base particles excluding metal particles, and more preferably resin particles, inorganic particles excluding metal particles, or organic-inorganic hybrid particles. The base particles may be core-shell particles having 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 particles are more preferably resin particles or organic-inorganic hybrid particles, and may be either resin particles or organic-inorganic hybrid particles. By using these preferred base particles, the effects of the present invention are more effectively exhibited.

[0085] Various resins are suitable for use as the material for the resin particles. Examples of the material for 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, polyamide-imide, polyether ether ketone, polyether sulfone, divinylbenzene polymer, and polymers obtained by polymerizing one or more of various polymerizable monomers having an ethylenically unsaturated group. The divinylbenzene polymer may be a divinylbenzene copolymer. Examples of the divinylbenzene copolymer include a divinylbenzene-styrene copolymer and a divinylbenzene-(meth)acrylic acid ester copolymer.

[0086] Since it is possible to design and synthesize resin particles having any compression characteristics suitable for a conductive paste, and the hardness of the resin particles can be easily controlled within a suitable range, it is preferable that the material of the resin particles is a polymer obtained by polymerizing one or more polymerizable monomers having multiple ethylenically unsaturated groups.

[0087] When the resin particles are obtained by polymerizing a polymerizable monomer having an ethylenically unsaturated group, the polymerizable monomer having an ethylenically unsaturated group may be a non-crosslinkable monomer or a crosslinkable monomer.

[0088] Examples of the non-crosslinkable monomer include styrene-based 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; and 2-hydroxyethyl Examples of the monomer include oxygen atom-containing (meth)acrylate compounds such as (meth)acrylate, glycerol (meth)acrylate, polyoxyethylene (meth)acrylate, and glycidyl (meth)acrylate; nitrile-containing monomers such as (meth)acrylonitrile; acid 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 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, and (poly)propylene glycol di(meth)acrylate. Examples of suitable monomers include polyfunctional (meth)acrylate compounds such as pyrene glycol di(meth)acrylate, (poly)tetramethylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate; and silane-containing monomers such as triallyl (iso)cyanurate, triallyl trimellitate, divinylbenzene, diallyl phthalate, diallyl acrylamide, diallyl ether, γ-(meth)acryloxypropyltrimethoxysilane, trimethoxysilylstyrene, and vinyltrimethoxysilane.

[0090] The resin particles can be obtained by polymerizing the polymerizable monomer having an ethylenically unsaturated group by a known method, such as a suspension polymerization method in the presence of a radical polymerization initiator, or a method in which non-crosslinked seed particles are used to swell and polymerize the monomer together with the radical polymerization initiator.

[0091] When the base particles are inorganic particles other than metal particles or organic-inorganic hybrid particles, examples of the inorganic material of the base particles include silica, alumina, barium titanate, zirconia, and carbon black. Preferably, the inorganic material is not metal. The particles formed from silica are not particularly limited, but examples include particles obtained by hydrolyzing a silicon compound having two or more hydrolyzable alkoxysilyl groups to form crosslinked polymer particles, and then optionally baking the particles. Examples of the organic-inorganic hybrid particles include organic-inorganic hybrid particles formed from a crosslinked alkoxysilyl polymer and an acrylic resin.

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

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

[0094] Examples of materials for the inorganic shell include the inorganic substances listed as materials for the base particle described above. The material for the inorganic shell is preferably silica. The inorganic shell is preferably formed by forming a shell-like substance from a metal alkoxide on the surface of the core by a sol-gel method and then firing the shell-like substance. The metal alkoxide is preferably a silane alkoxide. The inorganic shell is preferably formed from a silane alkoxide.

[0095] When the base 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.

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

[0097] The particle diameter of the base particle is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.5 μm or more, even more preferably 1 μm or more, particularly preferably 3 μm or more, and preferably 50 μm or less, more preferably 30 μm or less, even more preferably 20 μm or less, particularly preferably 10 μm or less. When the particle diameter of the base particle is above the lower limit, the conductivity reliability is further improved. Furthermore, when forming a conductive portion on the surface of the base particle, aggregation is less likely to occur, and aggregated conductive particles are less likely to be formed. When the particle diameter of the base particle is below the upper limit, the conductive particles are easily compressed sufficiently, and the connection resistance between electrodes connected via the conductive particles can be further effectively reduced.

[0098] The particle diameter of the substrate particles is preferably an average particle diameter, and more preferably a number-average particle diameter. The number-average particle diameter of the substrate particles can be measured, for example, as follows. The conductive particles are added to Kulzer's "Technovit 4000" so that the content is 30 wt %, and dispersed to prepare an embedding resin for substrate particle inspection. A cross section of the conductive particles dispersed in the embedding resin for substrate particle inspection is cut out using an ion milling device (Hitachi High-Technologies Corporation's "IM4000") so as to pass through the vicinity of the center of the substrate particle. Then, using a field emission scanning electron microscope (FE-SEM) set at an image magnification of 25,000x, 50 conductive particles are randomly selected, and the substrate particle of each conductive particle is observed. The particle diameter of the substrate particle in each conductive particle is measured, and the arithmetic average is taken to determine the average particle diameter of the substrate particles.

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

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

[0101] The nickel content in 100% by weight of the nickel-containing conductive portion is preferably 10% by weight or more, more preferably 50% by weight or more, even more preferably 60% by weight or more, even more preferably 70% by weight or more, and particularly preferably 90% by weight or more. The nickel content in 100% by weight of the nickel-containing conductive portion 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 nickel content in 100% by weight of the nickel-containing conductive portion can be set by appropriately selecting the lower limit and the upper limit.

[0102] The conductive portion may be formed of one layer. The conductive portion may be formed of multiple layers. That is, the conductive portion may have a laminated structure of two or more layers. When the conductive portion is formed of multiple 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 one of these preferred metals, the connection resistance between the electrodes is further reduced.

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

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

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

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

[0107] Core material: The conductive particles preferably have multiple protrusions on the outer surface of the conductive portion. An oxide film is often formed on the surface of the electrodes connected by the conductive particles. When conductive particles having protrusions on the outer surface of the conductive portion are used, the oxide film can be effectively removed by placing the conductive particles between the electrodes and pressing them together. This ensures more reliable contact between the electrodes and the conductive portion, further reducing the connection resistance between the electrodes. Furthermore, when connecting the electrodes, the protrusions of the conductive particles can effectively remove the filler between the conductive particles and the electrodes. This further increases the reliability of conduction between the electrodes.

[0108] Methods for forming the protrusions include a method of adhering a core material to the surface of a base particle and then forming a conductive portion by electroless plating, and a method of forming a conductive portion on the surface of a base particle by electroless plating, then adhering a core material, and then further forming a conductive portion by electroless plating, etc. Alternatively, to form the protrusions, a method may be used in which, without using the core material, a conductive portion is formed on the base particle by electroless plating, and then a protruding plating is deposited on the surface of the conductive portion, and then a conductive portion is formed by electroless plating, etc.

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

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

[0111] The metal is not particularly limited. Examples of the metal include gold, silver, copper, platinum, zinc, iron, lead, tin, aluminum, cobalt, indium, nickel, chromium, titanium, antimony, bismuth, germanium, and cadmium, as well as alloys composed of two or more metals, such as tin-lead alloys, tin-copper alloys, tin-silver alloys, tin-lead-silver alloys, and tungsten carbide. From the viewpoint of further improving the reliability of conduction 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 core material is preferably in the form of a mass. Examples of the core material include particulate masses, aggregates formed by aggregating multiple microparticles, 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, and preferably 0.9 μm or less, more preferably 0.2 μm or less. When the particle diameter of the core material is equal to or more than the lower limit and equal to or less than the upper limit, the connection resistance between electrodes can be effectively reduced.

[0114] The particle size of the core substance is preferably an average particle size, more preferably a number average particle size, which can be determined, for example, by observing 50 random core substances with an electron microscope or an optical microscope and calculating the average particle size of each core substance, or by performing laser diffraction particle size distribution measurement.

[0115] <Thixotropic Agent> Examples of the thixotropic agent include silica, titania, alumina, sorbitol, zinc oxide, etc. The thixotropic agent may be used alone or in combination of two or more.

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

[0117] The thixotropic agent is preferably a solid at 25° C. From the viewpoint of further improving 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 size of the thixotropic agent is preferably 0.001 μm or more, more preferably 0.01 μm or more, even more preferably 0.1 μm or more, and is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less. When the particle size of the thixotropic agent is equal to or more than the above lower limit and equal to or less than the above upper limit, storage stability can be further improved, and conductivity reliability can be further improved even when mounting is performed in a relatively short time.

[0119] The particle size of the thixotropic agent is preferably an average particle size, more preferably a number average particle size, which can be determined, for example, by observing 50 arbitrary thixotropic agents with an electron microscope or an optical microscope and calculating the average particle size 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, even more preferably 0.02 or more, and is preferably 1.0 or less, more preferably 0.8 or less, even more preferably 0.5 or less, particularly preferably 0.1 or less, and most preferably 0.05 or less. When the 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, storage stability can be further improved, and conductivity reliability can be further improved even when mounting is performed 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 upper limit, the storage stability can be further improved, and the conductivity reliability can be further improved even when the device is mounted 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 particle size of thixotropic agent Dn: average particle size of thixotropic agent

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

[0125] The content of the thixotropic agent relative to 100 parts by weight of the thermosetting compound is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, and 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 thixotropic agent is equal to or more than the above lower limit and equal to or less than the above upper limit, storage stability can be further improved, and conductivity reliability can be further improved even when mounting is performed in a relatively short time.

[0126] <Antioxidant> The conductive paste contains an antioxidant, which can improve the reliability of conduction even when mounting is performed in a relatively short time.

[0127] Examples of the antioxidant include hindered phenol-based antioxidants and thioether-based antioxidants. The antioxidants may be used alone or in combination of two or more.

[0128] From the viewpoint of further improving the reliability of conduction even when mounting is performed in a relatively short time, the antioxidant preferably contains a hindered phenol-based antioxidant.

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

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

[0131] The content of the antioxidant in 100% by weight of the conductive paste is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and is 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 more than the lower limit and equal to or less than the upper limit, storage stability can be further improved, and conductivity reliability can be further improved even when mounting is performed in a relatively short time.

[0132] The content of the antioxidant is preferably 0.1 part by weight or more, more preferably 0.5 part by weight or more, and 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, relative to 100 parts by weight of the thermosetting compound. When the content of the antioxidant is equal to or more than the lower limit and equal to or less than the upper limit, storage stability can be further improved, and conductivity reliability can be further improved even when the capacitor is mounted in a relatively short time.

[0133] <Other Components> The conductive paste may contain components other than the thermosetting compound, the thermosetting agent, the conductive filler, the thixotropic agent, and the antioxidant. The conductive paste may contain, as other components, 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 deodorizer, a fragrance, a preservative, an antibacterial agent, an antistatic agent, an adhesion imparting agent, etc.

[0134] (RFID inlay and manufacturing method of RFID inlay) The RFID inlay of the present invention comprises a substrate having wiring on its surface, a chip having electrodes on its surface, and an adhesive portion bonding the substrate and the chip. In the RFID inlay of the present invention, the material of the adhesive portion is the conductive paste described above. In the RFID inlay of the present invention, the wiring and the electrodes are electrically connected by the conductive filler in the 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] 1 includes a substrate 82 having wiring on its surface, a chip 83 having electrodes on its surface, and an adhesive portion 84 that bonds the substrate 82 and the chip 83. The material of the adhesive portion 84 is a conductive paste containing conductive filler 1. The adhesive portion 84 is formed from the conductive paste containing conductive filler 1. The adhesive portion 84 is preferably formed by hardening the conductive paste containing 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 conductive filler 1 in the adhesive portion 84.

[0138] The method for manufacturing an RFID inlay according to the present invention comprises the following steps (1) to (3): (1) a first placement step of placing the above-mentioned 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 the substrate side; and (3) a bonding step of forming an adhesive joint that bonds 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 joint.

[0139] In the RFID inlay and the manufacturing method of the RFID inlay according to the present invention, a specific conductive paste is used, which can improve the adhesion between the substrate and the chip and also improve the reliability of the electrical connection.

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

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

[0142] Examples of methods for disposing the conductive paste include application using a dispenser, screen printing, and ejection using an inkjet device.

[0143] The heating temperature in the bonding step is preferably 100° C. or higher, more preferably 150° C. or higher, and 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, good electrical connection between the chip and the substrate can be achieved.

[0144] The applied pressure in the bonding step is preferably 0.5 N or more, more preferably 1 N or more, and is preferably 3.5 N or less, more preferably 3 N or less, and even more preferably 2.5 N or less. When the applied pressure in the bonding step is equal to or greater than the lower limit and equal to or less than the upper limit, the adhesion between the substrate and the chip can be improved, and the electrical conductivity reliability can be improved.

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

[0146] The RFID inlay may be cut to a predetermined size as needed, or may be used after being cut. Preferably, a plurality of the chips are adhered to a long substrate by a plurality of the adhesive parts. A plurality of stacks of the chips and the adhesive parts may be arranged on the long substrate. In the first arranging step, it is preferable to arrange the conductive paste at a plurality of locations on the surface of the long substrate. In the second arranging step, it is preferable to use a plurality of chips and arrange the chips on the surface opposite to the substrate side of each of the conductive pastes arranged at a plurality of locations. After the chips are adhered to the long substrate by the adhesive parts, the long substrate may be cut.

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

[0148] The substrate has wiring (antenna pattern) on its surface. The substrate has wiring (antenna pattern) formed on its surface. The substrate preferably has a substrate and wiring (antenna pattern) disposed on the surface of the substrate.

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

[0150] Examples of the 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 viewpoint of improving the operating sensitivity in the UHF band (860 MHz to 960 MHz), the wiring is preferably aluminum wiring.

[0151] From the viewpoint of suppressing deformation of the substrate due to heat when mounting a chip (e.g., an IC chip) and increasing flexibility, the thickness of the substrate is preferably 20 μm or more, more preferably 30 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less.

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

[0153] The chip may be a semiconductor chip (IC chip) or the like.

[0154] The chip has an electrode on its surface. Examples of the electrode include a metal electrode such as a gold electrode, a nickel electrode, a tin electrode, an aluminum electrode, a silver electrode, a SUS electrode, a copper electrode, a molybdenum electrode, and a tungsten electrode. From the viewpoint of further improving the electrical conductivity reliability, the electrode is preferably a copper electrode or a gold electrode, and more preferably a copper electrode.

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

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

[0157] The planar area of ​​the chip is preferably 0.04 mm ２ More preferably, 0.09 mm ２ More preferably, 0.16 mm ２ or more, preferably 0.50 mm ２ Less than or equal to 0.40 mm, more preferably ２ Less than 0.30 mm, more preferably ２When the planar area of ​​the chip is equal to or greater than the lower limit, the conductive paste can be placed on fine wiring with high precision. When the planar area of ​​the chip is equal to or less than the upper limit, the RFID inlay can maintain its electrical conductivity reliability even when left in a high-temperature, high-humidity environment for a long period of time. The conductive paste according to the present invention can be suitably used for bonding relatively small chips.

[0158] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0159] The following materials were prepared:

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

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

[0162] Conductive filler: "CN050" manufactured by Nikko Rica Corporation (nickel particles, average particle size: 5 μm)

[0163] Thixotropic agents: "PM-20L" manufactured by Tokuyama Corporation (silica, solid at 25°C, average particle size: 0.012 μm); "Gelall D" manufactured by New Japan Chemical Co., Ltd. (sorbitol, solid at 25°C, average particle size: 0.10 μm); "43-00-502" manufactured by Micromod Corporation (silica, solid at 25°C, average particle size: 0.5 μm); "43-00-303" manufactured by Micromod Corporation (silica, solid at 25°C, average particle size: 3 μm); "43-00-503" manufactured by Micromod Corporation (silica, solid at 25°C, average particle size: 5 μm).

[0164] Antioxidant: "Irganox 1010" manufactured by BASF Japan (hindered phenol-based antioxidant, solid at 25°C, average particle size: 0.1 µm)

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

[0166] Substrate: PET film (long, resin film with aluminum wiring and 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 mixed in the amounts (parts by weight) shown in Table 1 below, and the mixture was stirred using a planetary mixer (Thinky Corporation's "Awatori Rentaro") to obtain a conductive paste (anisotropic conductive paste).

[0168] (2) Fabrication of RFID Inlay The obtained conductive paste was applied to a PET film by jet dispensing to form a conductive paste layer (adhesive layer) (first placement step). Next, an IC chip was laminated on the surface opposite the substrate side of the conductive paste layer (adhesive layer) so that the wiring on the PET film surface and the electrodes on the chip surface faced each other (second placement step). Subsequently, thermocompression bonding was performed under conditions of an upper heat tool temperature of 180°C, a lower heat tool temperature of 180°C, a pressure of 2N, and a compression time of 3 seconds to harden the conductive paste layer (adhesive layer) and form an adhesive bond. Furthermore, the wiring on the surface of the PET film and the electrodes on the surface of the chip were electrically connected via conductive filler (conductive particles) in the adhesive bond to obtain a connection structure (adhesion step). The first placement step, the second placement step, and the adhesion step were performed using a "DDA40000" (roll-to-roll method) manufactured by Muhlbauer. The resulting connection structure was cut into pieces measuring 5 cm x 1.5 cm using a "DCL30000" manufactured by Muhlbauer, to obtain 50 RFID inlays.

[0169] Examples 2 to 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 ingredients and amounts of the conductive pastes were changed as shown in Tables 1 to 3.

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

[0171] (2) Storage Stability (Pot Life) The viscosity (η25) of the conductive paste immediately after preparation was measured at 25°C using the method described above. The viscosity (ηα) of the conductive paste after storage at 25°C and 50% RH for 24 hours was also measured using the method described above. The ratio of the viscosity (ηα) after storage to the viscosity (η25) immediately after preparation (viscosity after storage (ηα) / viscosity (η25) immediately after preparation) was determined, and the storage stability (pot life) was evaluated according to the following criteria.

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

[0173] (3) Curability (Gel Time) of Conductive Paste A conductive paste was applied to a glass plate to a thickness of 30 μm. The glass plate was placed on the surface of a hot plate (set temperature 180°C) from the side opposite to the side on which the paste was applied, and the elapsed time until the paste gelled was measured. The curability (gel time) of the conductive paste was evaluated according to the following criteria. Stringiness was checked every 5 seconds using a needle with a handle, and gelation was judged to have occurred when the string no longer broke.

[0174] [Evaluation criteria for hardening (gel time) of conductive paste] ○○: The time elapsed until the paste gelled was less than 15 seconds. ○: The time elapsed until the paste gelled was 15 seconds or more but less than 30 seconds. ×: The time elapsed until the paste gelled was 30 seconds or more.

[0175] (4) Adhesion (die shear strength) For the obtained RFID inlay, the die shear strength was evaluated at 25° C. by peeling the chip from the substrate using a die shear tester ("DAGE4000PLUS" manufactured by Nordson Corporation) at a tool height of 30 μm and a speed of 100 μm / sec. The adhesion (die shear strength) was evaluated 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 but less than 7.0 N; ×: Die shear strength is less than 4.0 N

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

[0178] [Criteria for assessing tackiness of cured product] ◯: The cured product does not lift up. ○: One end of the cured product lifts up while the other end that is not touching the needle with a handle remains in contact with the ground. ×: The entire cured product lifts up.

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

[0180] [Criteria for determining continuity reliability] ○○: The peak sensitivity of all RFID inlays is less than -18 dBm. ○: Does not fall under either ○○ or ×. ×: The peak sensitivity of at least one RFID inlay is -16.4 dBm or more.

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

[0182]

[0183]

[0184]

[0185] The storage stability evaluation results for both Example 5 and Example 7 were "Good." However, the value of "the ratio of the viscosity after storage to the viscosity immediately after preparation," which is the evaluation criterion for storage stability, was smaller for Example 7 than for Example 5, and Example 7 had better storage stability than Example 5.

[0186] REFERENCE SIGNS LIST 1... conductive filler 81... RFID inlay 82... substrate having wiring on its surface 82a... wiring 83... chip having electrode on its surface 83a... electrode 84... adhesive portion

Claims

1. A conductive paste comprising a thermosetting compound, a thermosetting agent, a conductive filler, a thixotropic agent, and an antioxidant, wherein the thermosetting agent comprises a microencapsulated thermosetting agent or a thermosetting agent that is solid at 25°C.

2. The conductive paste according to claim 1, wherein the thixotropic agent is solid at 25° C., and the ratio of the particle size of the thixotropic agent to the particle size of the conductive filler is 0.5 or less.

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

4. The conductive paste according to any one of claims 1 to 3, wherein the conductive filler is a conductive particle, and the conductive particle has a particle diameter of 10 μm or less.

5. The conductive paste according to any one of claims 1 to 4, used to obtain an RFID inlay.

6. An RFID inlay comprising a substrate having wiring on its surface, a chip having electrodes on its surface, and an adhesive bonding the substrate and the chip, the adhesive being made of a conductive paste according to any one of claims 1 to 5, and the wiring and the electrodes being electrically connected by the conductive filler in the adhesive.

7. A method for manufacturing an RFID inlay, comprising: a first arrangement step of arranging a conductive paste according to any one of claims 1 to 5 on a surface of a substrate having wiring on its surface; a second arrangement step of arranging a chip having an electrode on its surface on the surface of the conductive paste opposite the substrate; and a bonding step of forming an adhesive part using the conductive paste to bond the substrate and the chip by heating and pressurizing the conductive paste, and electrically connecting the wiring and the electrode by the conductive filler in the adhesive part.

8. A method for manufacturing an RFID inlay as described in claim 7, wherein the substrate is long, and the RFID inlay is manufactured by transporting the long substrate using a roll-to-roll method in the first placement process, the second placement process, and the bonding process.

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