Conductive paste, RFID inlay and manufacturing method of RFID inlay

Abstract

Provided is a conductive paste that can be placed on wiring with high precision, can prevent the misalignment of chips and uneven distribution of conductive fillers even when objects are transported vertically during the manufacturing process, and can improve the conductivity reliability of the resulting electronic components.　This conductive paste contains a curable compound, a curing agent, and a plurality of conductive fillers, wherein the conductive fillers have a specific gravity of 1.5-4.0, the content of the conductive fillers in 100 wt% of the conductive paste is 1.0-15 wt%, the ratio of the viscosity at 25°C and 0.5 rpm to the viscosity at 25°C and 5 rpm of the conductive paste is 1.5-4.5, and the conductive paste has a viscosity of 5-50 Pa·s at 25°C and 5 rpm.

Description

[Technical Field]

[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. [Background technology]

[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, UHF (Ultra High Frequency) band (860 MHz to 960 MHz) RFID inlays 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 is sometimes used to bond and connect a chip having electrodes on its surface to a substrate having wiring (antenna pattern) on its surface.

[0004] 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.

[0005] 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. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-144018 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-124330 Summary of the Invention [Problem to be solved by the invention]

[0007] In manufacturing methods for electronic components such as RFID inlays, a roll-to-roll method is sometimes adopted to enable mass production. In the roll-to-roll method, a laminate in which conductive paste and chips are arranged on the surface of a substrate may be transported not only horizontally but also vertically. For example, when a laminate being transported horizontally reaches a roll section, the transport direction may change to vertical at the roll section.

[0008] If the laminate is transported vertically while the conductive paste is not sufficiently hardened, the conductive material (conductive filler) in the conductive paste may not be dispersed but may be unevenly distributed depending on its specific gravity, resulting in reduced electrical reliability of the resulting electronic component. Furthermore, if the laminate is transported vertically, the position of the chips arranged on the surface of the substrate may shift, resulting in reduced electrical reliability of the resulting electronic component.

[0009] In addition, 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 can be placed on wiring with high precision.

[0010] The present invention aims to provide a conductive paste that can be positioned on wiring with high precision, that can prevent chip misalignment and uneven distribution of conductive filler even when transported vertically during the manufacturing process, and that can improve the electrical conductivity reliability of the resulting electronic component. Another object of the present invention is to provide an RFID inlay using the conductive paste and a method for manufacturing an RFID inlay. [Means for solving the problem]

[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 curable compound, a curing agent, and a plurality of conductive fillers, wherein the specific gravity of the conductive fillers is 1.5 or more and 4.0 or less, the content of the conductive fillers in 100% by weight of the conductive paste is 1.0% by weight or more and 15% by weight or less, the ratio of the viscosity of the conductive paste at 25°C and 0.5 rpm to the viscosity at 25°C and 5 rpm is 1.5 or more and 4.5 or less, and the viscosity of the conductive paste at 25°C and 5 rpm is 5 Pa s or more and 50 Pa s or less.

[0013] Item 2. The conductive paste according to Item 1, wherein the curable compound includes a (meth)acrylic compound.

[0014] Item 3. The conductive paste according to Item 1 or 2, wherein the conductive filler is conductive particles, and the particle diameter of the conductive particles is 10 μm or less.

[0015] Item 4. The conductive paste according to Item 3, wherein the conductive particles include a base particle and a conductive portion disposed on a surface of the base particle.

[0016] Item 5. The conductive paste according to any one of Items 1 to 4, which is applied to a substrate having a surface tension of 30 mN / m or more and 50 mN / m or less.

[0017] Item 6. The conductive paste according to any one of Items 1 to 5, which is used to obtain an RFID inlay.

[0018] Item 7. 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 6, and the wiring and the electrodes are electrically connected by the conductive filler in the adhesive portion.

[0019] Item 8. 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 6 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 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.

[0020] Item 9. A method for manufacturing an RFID inlay according to Item 8, 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. [Effects of the Invention]

[0021] The conductive paste according to the present invention includes a curable compound, a curing agent, and a plurality of conductive fillers. In the conductive paste according to the present invention, the specific gravity of the conductive filler is 1.5 or more and 4.0 or less. In the conductive paste according to the present invention, the content of the conductive filler is 1.0% by weight or more and 15% by weight or less, based on 100% by weight of the conductive paste. In the conductive paste according to the present invention, the ratio of the viscosity of the conductive paste at 25°C and 0.5 rpm to the viscosity at 25°C and 5 rpm is 1.5 or more and 4.5 or less, and the viscosity of the conductive paste at 25°C and 5 rpm is 5 Pa·s or more and 50 Pa·s or less. Because the conductive paste according to the present invention has the above-described configuration, it can be positioned on wiring with high precision, and even when transported items are transported vertically during the manufacturing process, it is possible to prevent chip misalignment and uneven distribution of the conductive fillers, thereby improving the conductivity reliability of the resulting electronic component. [Brief explanation of the drawings]

[0022] [Figure 1] 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. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described in detail below.

[0024] (Conductive paste) The conductive paste according to the present invention is a conductive paste containing a curable compound, a curing agent, and a plurality of conductive fillers. In the conductive paste according to the present invention, the specific gravity of the conductive filler is 1.5 or more and 4.0 or less. In the conductive paste according to the present invention, the content of the conductive filler in 100% by weight of the conductive paste is 1.0% by weight or more and 15% by weight or less. In the conductive paste according to the present invention, the ratio of the viscosity of the conductive paste at 25°C and 0.5 rpm to the viscosity at 25°C and 5 rpm is 1.5 or more and 4.5 or less, and the viscosity of the conductive paste at 25°C and 5 rpm is 5 Pa s or more and 50 Pa s or less.

[0025] The conductive paste according to the present invention has the above-described configuration, allowing the conductive paste to be positioned on the wiring with high precision. Furthermore, the conductive paste according to the present invention has the above-described configuration, and therefore, even when the transported object is transported vertically during the manufacturing process, it is possible to prevent chip misalignment and uneven distribution of the conductive filler, thereby enabling the conductive filler to be well dispersed. As a result, electrical conductivity reliability can be improved. For example, when a transported object being transported horizontally reaches a roll portion, the transport direction may change to vertical at the roll portion. In this case, the orientation of the transported object changes, making chip misalignment and uneven distribution of the conductive filler more likely to occur. However, the configuration of the present invention makes it possible to prevent chip misalignment and uneven distribution of the conductive filler.

[0026] 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.

[0027] The viscosity (ηA) of the conductive paste at 25°C and 5 rpm is 5 Pa·s or more and 50 Pa·s or less. The viscosity (ηA) is preferably 7 Pa·s or more, more preferably 8 Pa·s or more, even more preferably 10 Pa·s or more, and preferably 45 Pa·s or less, more preferably 43 Pa·s or less, and even more preferably 40 Pa·s or less. When the viscosity (ηA) is equal to or greater than the lower limit, chip positional deviation can be more effectively prevented even when the transported object is transported vertically in the manufacturing process. When the viscosity (ηA) is equal to or less than the upper limit, the conductive paste can be arranged on the fine wiring with even greater precision.

[0028] The ratio (η / η) of the viscosity (η) of the conductive paste at 25°C and 0.5 rpm to the viscosity (η) at 25°C and 5 rpm is defined as the thixotropic index. The ratio (thixotropic index) of the viscosity (η) of the conductive paste at 25°C and 0.5 rpm to the viscosity (η) at 25°C and 5 rpm is 1.5 or more and 4.5 or less. The thixotropic index is preferably 2.0 or more, more preferably 2.2 or more, even more preferably 2.5 or more, and preferably 4.2 or less, more preferably 4.0 or less, and even more preferably 3.8 or less. When the thixotropic index is equal to or greater than the lower limit, chip positional deviation can be more effectively prevented even when the transported object is transported vertically during the manufacturing process. When the thixotropic index is equal to or less than the upper limit, the conductive paste can be arranged on the fine wiring with even greater precision.

[0029] The viscosity (ηA) of the conductive paste at 25°C and 5 rpm and the viscosity (ηB) of the conductive paste at 25°C and 0.5 rpm can be measured using, for example, an E-type viscometer. Examples of the E-type viscometer include the "TV22 Viscometer" manufactured by Toki Sangyo Co., Ltd.

[0030] The viscosity (ηC) of the composition of the conductive paste excluding the conductive filler at 25°C and 5 rpm is preferably 5 Pa·s or more and 50 Pa·s or less. The viscosity (ηC) is preferably 7 Pa·s or more, more preferably 8 Pa·s or more, even more preferably 10 Pa·s or more, and preferably 45 Pa·s or less, more preferably 43 Pa·s or less, and even more preferably 40 Pa·s or less. When the viscosity (ηC) is equal to or greater than the lower limit, chip positional deviation can be more effectively prevented even when the transported object is transported vertically during the manufacturing process. When the viscosity (ηC) is equal to or less than the upper limit, the conductive paste can be arranged on fine wiring with even greater precision.

[0031] The viscosity (ηC) of the composition of the conductive paste excluding the conductive filler at 25°C and 5 rpm can be measured, for example, by the following methods: A method of measuring a composition obtained by removing the conductive filler from the conductive paste using an E-type viscometer. A method of measuring a composition containing conductive paste materials other than the conductive filler using an E-type viscometer. Examples of the E-type viscometer include the TV22 viscometer manufactured by Toki Sangyo Co., Ltd.

[0032] The above conductive paste was placed at 25°C and a shear rate of 0.1 sec. -1 The viscosity (ηD) at this temperature is preferably 5 Pa·s or more, and preferably 50 Pa·s or less. If the viscosity (ηD) is equal to or greater than the lower limit, displacement of the chip can be more effectively prevented even when the transported object is transported vertically in the manufacturing process. If the viscosity (ηD) is equal to or less than the upper limit, the conductive paste can be arranged on the fine wiring with even greater precision.

[0033] The above conductive paste was stored at 25°C and a shear rate of 0.01 sec. -1 The viscosity (ηE) at this temperature is preferably 15 Pa·s or more, and preferably 200 Pa·s or less. If the viscosity (ηE) is equal to or greater than the lower limit, displacement of the chip can be more effectively prevented even when the transported object is transported vertically in the manufacturing process. If the viscosity (ηE) is equal to or less than the upper limit, the conductive paste can be arranged on the fine wiring with even greater precision.

[0034] The above conductive paste was stored at 25°C and a shear rate of 0.001 sec. -1 The viscosity (ηF) at this temperature is preferably 20 Pa·s or more, and preferably 10,000 Pa·s or less. If the viscosity (ηF) is equal to or greater than the lower limit, displacement of the chip can be more effectively prevented even when the transported object is transported vertically in the manufacturing process. If the viscosity (ηF) is equal to or less than the upper limit, the conductive paste can be arranged on the fine wiring with even greater precision.

[0035] The above viscosities (ηD), (ηE), and (ηF) can be measured using a rheometer (for example, manufactured by Thermo Scientific, Type: HAAKE) or the like.

[0036] The conductive paste has good adhesive properties, is suitable for use as an adhesive, and is particularly suitable for use in bonding a substrate and a chip.

[0037] From the viewpoint of further improving the conduction reliability, 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 electrodes 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 electrodes on its surface to a substrate having wiring (antenna pattern) on its surface).

[0038] The conductive paste is preferably applied to a substrate having a surface tension of 30 mN / m or more and 50 mN / m or less (use of the conductive paste on a substrate having a surface tension of 30 mN / m or more and 50 mN / m or less). 2 It is preferable to use it for bonding chips with a planar area of ​​0.50 mm or less. 2 (Use of the above conductive paste to bond the chip, which is below).

[0039] The conductive paste is preferably thermosetting, and is preferably a thermosetting conductive paste, more preferably a thermosetting anisotropic conductive paste.

[0040] Each component contained in the conductive paste will be described below.

[0041] In this specification, "(meth)acrylate" refers to acrylate and methacrylate, "(meth)acrylic" refers to acrylic and methacrylic, and "(meth)acryloyl" refers to acryloyl and methacryloyl.

[0042] <Curable compound> Examples of the curable compound include a thermosetting compound and a photocurable compound. The curable compound is preferably a thermosetting compound. The thermosetting compound is a compound that can be cured by heating. Examples of the thermosetting compound include (meth)acrylic compounds, oxetane compounds, epoxy compounds, episulfide compounds, phenol compounds, amino compounds, unsaturated polyester compounds, polyurethane compounds, silicone compounds, and polyimide compounds. Only one type of the curable compound may be used, or two or more types may be used in combination.

[0043] From the viewpoint of increasing the curing reactivity of the conductive paste and improving the conduction reliability of the resulting connection structure, the curable compound preferably contains an epoxy compound or a (meth)acrylic compound, more preferably a (meth)acrylic compound. From the viewpoint of increasing adhesiveness, the curable compound more preferably contains a compound having a (meth)acryloyl group ((meth)acrylate).

[0044] The (meth)acrylic compound may be a monofunctional (meth)acrylate or a polyfunctional (meth)acrylate. The polyfunctional (meth)acrylate may be a difunctional (meth)acrylate, a trifunctional (meth)acrylate, or a tetrafunctional or higher functional (meth)acrylate. The (meth)acrylic compound may have 100 or less (meth)acryloyl groups, 50 or less, or 10 or less. The (meth)acrylic compound may be used alone or in combination of two or more.

[0045] Examples of the monofunctional (meth)acrylate include 2-(2-ethoxyethoxy)ethyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, lauryl (meth)acrylate, isobutyl (meth)acrylate, isodecyl (meth)acrylate, isooctyl (meth)acrylate, octyl / decyl (meth)acrylate, tridecyl (meth)acrylate, nonyl (meth)acrylate, caprolactone (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, (3-ethyloxene methyl (meth)acrylate, methoxyethyl (meth)acrylate, methoxypolyethylene glycol (350) mono(meth)acrylate, methoxytriethylene glycol (meth)acrylate, alkoxylated tetrahydrofurfuryl (meth)acrylate, alkoxylated lauryl (meth)acrylate, dimethylacrylamide, diethylacrylamide, hydroxyethylacrylamide, dimethylaminopropylacrylamide, isopropylacrylamide, N-acryloyloxyethylhexahydrophthalimide, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0046] Examples of the polyfunctional (meth)acrylate include 1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol (meth)acrylate, 1,9-nonanediol di(meth)acrylate, polyethylene glycol (200) di(meth)acrylate, tetraethylene glycol di(meth)acrylate, triethylene glycol (meth)acrylate, tripropylene glycol di(meth)acrylate, polyethylene glycol (400) di(meth)acrylate, dipropylene glycol di(meth)acrylate, alkoxylated hexanediol di(meth)acrylate, dodecanediol di(meth)acrylate, and the like. acrylate, polyethylene glycol (600) di(meth)acrylate, polypropylene glycol (700) (meth)acrylate, propoxylated (2) neopentyl glycol di(meth)acrylate, alkoxylated neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tris-(2-hydroxyethyl) isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, ethoxylated (3) trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0047] From the viewpoints of adjusting the viscosity of the conductive paste within an appropriate range, improving the dischargeability, and disposing the conductive paste on the wiring with higher precision, it is preferable that the (meth)acrylic compound contains a polymerizable monomer having one (meth)acryloyl group (hereinafter, sometimes referred to as "polymerizable monomer (A)"). From the viewpoints of improving the dischargeability and disposing the conductive paste on the wiring with higher precision, it is preferable that the curable compound contains a polymerizable monomer having one (meth)acryloyl group (polymerizable monomer (A)). The polymerizable monomer (A) is a monofunctional (meth)acrylate. The polymerizable monomer (A) is a polymerizable component that can be homopolymerized or copolymerized.

[0048] From the viewpoint of improving the electrical conductivity reliability of the resulting connection structure, the (A) polymerizable monomer preferably has an aromatic skeleton or an alicyclic skeleton. The (A) polymerizable monomer may have an aromatic skeleton, an alicyclic skeleton, or both an aromatic skeleton and an alicyclic skeleton. The (A) polymerizable monomer may include a polymerizable monomer having an aromatic skeleton and a polymerizable monomer having an alicyclic skeleton.

[0049] Examples of the (A) polymerizable monomer having an aromatic skeleton include 2-phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, nonylphenoxy polyethylene glycol (meth)acrylate, ethoxylated (4) nonylphenol (meth)acrylate, and alkoxylated phenol (meth)acrylate.

[0050] Examples of the polymerizable monomer (A) having an alicyclic skeleton include cyclohexyl (meth)acrylate, dimethylol tricyclodecane di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, isobornyl (meth)acrylate, 4-tert-butylcyclohexanol, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, pentamethylpiperidyl (meth)acrylate, tetramethylpiperidyl (meth)acrylate, acrylomorpholine, and 3,3,5-trimethylcyclohexyl (meth)acrylate.

[0051] From the viewpoint of improving the electrical conductivity reliability of the resulting connection structure, the polymerizable monomer (A) is preferably isobornyl (meth)acrylate.

[0052] The molecular weight of the (A) polymerizable monomer is preferably 50 or more, more preferably 100 or more, even more preferably 150 or more, and particularly preferably 200 or more, and is preferably 1000 or less, more preferably less than 1000, even more preferably 900 or less, particularly preferably 800 or less, and most preferably 700 or less. When the molecular weight of the (A) polymerizable monomer is within the above range, the viscosity of the conductive paste can be adjusted to a suitable range, and the electrical conductivity reliability of the resulting connection structure can be further improved.

[0053] The molecular weight of the (A) polymerizable monomer refers to a molecular weight that can be calculated from the structural formula when the structural formula of the (A) polymerizable monomer can be identified. Furthermore, when the structural formula of the (A) polymerizable monomer 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 measured by gel permeation chromatography (GPC) in terms of polystyrene. Since the (A) polymerizable monomer has a relatively small molecular weight, its 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.

[0054] Measurement equipment: Waters GPC System (Waters 2690 + Waters 2414 (RI)) manufactured by Japan Waters Columns: Shodex GPC LF-G x 1, Shodex GPC LF-804 x 2 Mobile phase: THF 1.0mL / min Sample concentration: 5mg / mL Detector: Refractive index detector (RID) Standard material: Polystyrene (TOSOH Corporation, weight average molecular weight: 620-590,000)

[0055] The viscosity of the polymerizable monomer (A) at 25°C is preferably 1 mPa·s or more, more preferably 2 mPa·s or more, and preferably 50 mPa·s or less, more preferably 45 mPa·s or less. When the viscosity of the polymerizable monomer (A) at 25°C is equal to or more than the above lower limit and equal to or less than the above upper limit, the conductive paste can be arranged on fine wiring with higher precision, and the wettability to the substrate can be improved.

[0056] The viscosity of the polymerizable monomer (A) at 25°C can be measured, for example, using an E-type viscometer at 25°C and 5 rpm. Examples of the E-type viscometer include the TV22 viscometer manufactured by Toki Sangyo Co., Ltd.

[0057] The (meth)acrylic compound may contain a (meth)acrylic compound other than the (A) polymerizable monomer. The (meth)acrylic compound other than the (A) polymerizable monomer may be used alone or in combination of two or more.

[0058] From the viewpoint of improving the electrical conductivity reliability of the resulting connection structure, the (meth)acrylic compound other than the (A) polymerizable monomer preferably has two or more (meth)acryloyl groups. The (meth)acrylic compound other than the (A) polymerizable monomer is preferably a polyfunctional (meth)acrylate. The (meth)acrylic compound other than the (A) polymerizable monomer may have two (meth)acryloyl groups, two or more, three or more, four or more, or ten or less.

[0059] From the viewpoint of improving the conduction reliability of the resulting connection structure, the (meth)acrylic compound other than the (A) polymerizable monomer preferably contains urethane (meth)acrylate.

[0060] The molecular weight of the urethane (meth)acrylate is preferably 1000 or more, more preferably 1500 or more, even more preferably 2000 or more, even more preferably 3000 or more, and particularly preferably 5000 or more, and is preferably 30000 or less, more preferably 25000 or less, even more preferably 20000 or less, and particularly preferably 18000 or less. When the molecular weight of the urethane (meth)acrylate is equal to or more than the above lower limit and equal to or less than the above upper limit, the adhesiveness can be further improved and the conduction reliability can be further improved.

[0061] When the structural formula of the urethane (meth)acrylate can be identified, the molecular weight of the urethane (meth)acrylate refers to a molecular weight that can be calculated from the structural formula. When the structural formula of the urethane (meth)acrylate 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 measured by gel permeation chromatography (GPC) in terms of polystyrene. The molecular weight of the urethane (meth)acrylate is preferably a weight average molecular weight measured by gel permeation chromatography (GPC) in terms of polystyrene. The weight average molecular weight can be measured using the following measuring device and under the following measuring conditions.

[0062] Measurement equipment: Waters GPC System (Waters 2690 + Waters 2414 (RI)) manufactured by Japan Waters Columns: Shodex GPC LF-G x 1, Shodex GPC LF-804 x 2 Mobile phase: THF 1.0mL / min Sample concentration: 5mg / mL Detector: Refractive index detector (RID) Standard material: Polystyrene (TOSOH Corporation, weight average molecular weight: 620-590,000)

[0063] The viscosity of the urethane (meth)acrylate at 25°C can be measured, for example, using an E-type viscometer at 25°C and 5 rpm. Examples of the E-type viscometer include the TV22 viscometer manufactured by Toki Sangyo Co., Ltd.

[0064] The content of the curable 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 60% by weight or less, more preferably 55% by weight or less, and even more preferably 50% by weight or less. When the content of the curable compound is equal to or more than the lower limit and equal to or less than the upper limit, adhesiveness can be further improved and conduction reliability can be further improved.

[0065] In 100% by weight of the conductive paste, the content of the (A) polymerizable monomer is preferably 10% by weight or more, more preferably 15% by weight or more, and preferably 50% by weight or less, more preferably 45% by weight or less, even more preferably 40% by weight or less, and particularly preferably 35% by weight or less. When the content of the (A) polymerizable monomer is equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the electrical conductivity reliability of the resulting connection structure can be further improved. Note that when the (A) polymerizable monomer contains a polymerizable monomer having an aromatic skeleton and a polymerizable monomer having an alicyclic skeleton, the content of the (A) polymerizable monomer refers to the total content of the polymerizable monomer having an aromatic skeleton and the polymerizable monomer having an alicyclic skeleton.

[0066] In 100% by weight of the curable compound, the content of the (A) polymerizable monomer is preferably 10% by weight or more, more preferably 15% by weight or more, and preferably 50% by weight or less, more preferably 45% by weight or less. When the content of the (A) polymerizable monomer is equal to or more than the above lower limit and equal to or less than the above upper limit, the electrical conductivity reliability can be further improved. When the polymerizable monomer contains a polymerizable monomer having an aromatic skeleton and a polymerizable monomer having an alicyclic skeleton, the content of the polymerizable monomer refers to the total content of the polymerizable monomer having an aromatic skeleton and the polymerizable monomer having an alicyclic skeleton.

[0067] The content of the urethane (meth)acrylate in 100% by weight of the curable compound is preferably 15% by weight or more, more preferably 20% by weight or more, and preferably 50% by weight or less, more preferably 45% by weight or less. When the content of the urethane (meth)acrylate is equal to or more than the lower limit and equal to or less than the upper limit, the adhesiveness can be improved and the conduction reliability can be further improved.

[0068] The total content of the (A) polymerizable monomer and the urethane (meth)acrylate in 100% by weight of the curable compound is preferably 20% by weight or more, more preferably 40% by weight or more, and preferably 90% by weight or less, more preferably 80% by weight or less. When the total content of the (A) polymerizable monomer and the urethane (meth)acrylate is equal to or more than the lower limit and equal to or less than the upper limit, the viscosity of the conductive paste can be adjusted within a suitable range, and the adhesiveness and the conduction reliability can be further improved.

[0069] The content of the (A) polymerizable monomer is preferably 15% by weight or more, more preferably 20% by weight or more, and preferably 55% by weight or less, more preferably 50% by weight or less, based on a total of 100% by weight of the (A) polymerizable monomer and the urethane (meth)acrylate. When the content of the (A) polymerizable monomer is equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the viscosity of the conductive paste can be adjusted within a suitable range, thereby improving adhesion and further improving conductivity reliability. When the (A) polymerizable monomer includes a polymerizable monomer having an aromatic skeleton and a polymerizable monomer having an alicyclic skeleton, the content of the (A) polymerizable monomer refers to the total content of the polymerizable monomer having an aromatic skeleton and the polymerizable monomer having an alicyclic skeleton.

[0070] <Conductive filler> The conductive paste contains a plurality of conductive fillers. The conductive fillers are not particularly limited. The conductive fillers may be conductive particles or carbon fibers. In this specification, "containing a plurality of conductive fillers" means that the conductive paste contains two or more conductive fillers. Only one type of the conductive fillers may be used, or two or more types may be used in combination.

[0071] The specific gravity of the conductive filler is 1.5 or more and 4.0 or less. The specific gravity of the conductive filler is preferably 1.8 or more, more preferably 2.0 or more, and preferably 3.8 or less, more preferably 3.5 or less. When the specific gravity of the conductive filler is equal to or more than the above lower limit and equal to or less than the above upper limit, uneven distribution of the conductive filler in the conductive paste can be prevented even when the transported object is transported vertically in the manufacturing process, and the electrical conductivity reliability of the obtained connection structure can be further improved.

[0072] The specific gravity of the conductive filler can be measured using, for example, "AccuPyc II 1340" manufactured by Micrometrics.

[0073] 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.

[0074] 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.

[0075] The particle diameter of the conductive particles 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 particles is equal to or greater than the above lower limit and equal to or less than the above upper limit, the electrical conductivity reliability can be further improved.

[0076] The particle size of the conductive particles is preferably an average particle size, more preferably a number average particle size, 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 size of each conductive particle, or by performing laser diffraction particle size distribution measurement.

[0077] The particle diameter of the conductive particles can be measured by observing 50 random conductive particles under an electron microscope or optical microscope, for example, as follows. The conductive particles are added to Kulzer's Technovit 4000 so that the content is 30% by weight, and dispersed to prepare a resin embedding body for conductive particle inspection. An ion milling machine (Hitachi High-Technologies Corporation's IM4000) is used to cut out a cross section of the conductive particles so that it passes through the center of the conductive particles dispersed in the resin embedding body for conductive particle inspection. Then, a field emission scanning electron microscope (FE-SEM) is used, with the image magnification set to 25,000x, to randomly select 50 conductive particles and observe each conductive particle. The equivalent circle diameter of each conductive particle is measured, and the arithmetic average is used to determine the particle diameter of the conductive particles.

[0078] 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. There is no particular limitation on the lower limit of the coefficient of variation (CV value) of the particle diameter of the conductive particles. 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.

[0079] The coefficient of variation (CV value) can be measured as follows.

[0080] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of the particle size of the conductive particles Dn: average particle diameter of conductive particles

[0081] The content of the conductive filler in 100% by weight of the conductive paste is 1.0% by weight or more and 15% by weight or less. The content of the conductive filler in 100% by weight of the conductive paste is preferably 2.0% by weight or more, more preferably 5.0% by weight or more, and preferably 13% by weight or less, more preferably 10% 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 conduction reliability can be further improved.

[0082] The content of the conductive filler relative to 100 parts by weight of the curable compound in the conductive paste is preferably 2.0 parts by weight or more, more preferably 3.0 parts by weight or more, even more preferably 5.0 parts by weight or more, and particularly preferably 7.0 parts by weight or more. The content of the conductive filler relative to 100 parts by weight of the curable compound in the conductive paste 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, and particularly preferably 20 parts by weight or less. When the content of the conductive filler in the conductive paste is equal to or greater than the lower limit and equal to or less than the upper limit, the conduction reliability can be further improved.

[0083] 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. The metal may be used alone or in combination of two or more.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] (base material 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.

[0088] 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.

[0089] Various resins are suitable for use as the material for the resin particles. Examples of materials 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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)propane ... Examples of suitable (meth)acrylates 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.

[0094] 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.

[0095] 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. It is preferable that 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, followed by calcination as necessary. Examples of the organic-inorganic hybrid particles include organic-inorganic hybrid particles formed from a crosslinked alkoxysilyl polymer and an acrylic resin.

[0096] 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.

[0097] Examples of the material for the organic core include the materials for the resin particles described above.

[0098] 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.

[0099] 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.

[0100] 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 equal to or greater than the lower limit, the electrical 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 equal to or less than 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.

[0101] The particle diameter of the base particles is preferably an average particle diameter, and more preferably a number-average particle diameter. The number-average particle diameter of the base particles can be measured, for example, as follows: The conductive particles are added to Kulzer's Technovit 4000 so that the content is 30% by weight, and dispersed to prepare a resin embedding body for base particle inspection. An ion milling machine (Hitachi High-Technologies Corporation's IM4000) is used to cut out a cross section of the conductive particles dispersed in the resin embedding body for base particle inspection, passing through the vicinity of the center of the base particle. 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 the base particle of each conductive particle is observed. The particle diameter of the base particle in each conductive particle is measured, and the arithmetic average is calculated to determine the average particle diameter of the base particles.

[0102] (Conductive part) 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.

[0103] 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.

[0104] 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 99% by weight or less, 90% by weight or less, or 70% by weight or less.

[0105] 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.

[0106] 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.).

[0107] The thickness of the conductive portion is preferably 0.005 μm or more, more preferably 0.01 μm or more, and 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 lower limit and equal to or less than the 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.

[0108] 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.

[0109] 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).

[0110] Core material: The conductive particles preferably have a plurality of 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 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] The particle size (average particle size) 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 size 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.

[0117] 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.

[0118] <Curing agent> From the viewpoint of curing the curable compound containing the polymerizable monomer (A), the curing agent is preferably a polymerization initiator. Examples of the polymerization initiator include a photopolymerization initiator and a thermal polymerization initiator. The polymerization initiator may be used alone or in combination of two or more.

[0119] From the viewpoint of curing the curable compound by heating, the polymerization initiator preferably includes a thermal polymerization initiator. The thermal polymerization initiator preferably includes a thermal radical polymerization initiator, and is preferably a thermal radical polymerization initiator. Examples of the thermal radical polymerization initiator include a peroxide radical polymerization initiator, an azo radical polymerization initiator, and a redox radical polymerization initiator.

[0120] Examples of the azo radical polymerization initiator include azobisisobutyronitrile, azobiscyclohexanecarbonitrile, and azobisdimethylvaleronitrile.

[0121] Examples of the peroxide radical polymerization initiator include diacyl radical polymerization initiators, peroxyester radical polymerization initiators, dialkyl radical polymerization initiators, percarbonate radical polymerization initiators, and ketone peroxide radical polymerization initiators. Examples of the diacyl radical polymerization initiator include lauroyl peroxide and benzoyl peroxide. Examples of the peroxyester radical polymerization initiator include t-butyl peroxybenzoate, t-butyl peroxyacetate, t-butyl peroxypivalate, and t-butyl peroxy-2-ethylhexanoate. Examples of the dialkyl radical polymerization initiator include dicumyl peroxide and di-t-butyl peroxide. Examples of the percarbonate radical polymerization initiator include diisopropyl peroxydicarbonate. Examples of the ketone peroxide radical polymerization initiator include methyl ethyl ketone peroxide.

[0122] The redox radical polymerization initiator contains, for example, a peroxide and a reducing agent or a metal-containing compound. Specific examples of the redox radical polymerization initiator include a mixture of benzoyl peroxide and an organic amine, a mixture of the peroxyester radical polymerization initiator and a reducing agent such as a mercaptan, and a mixture of methyl ethyl ketone peroxide and an organic cobalt salt.

[0123] From the viewpoint of enhancing reactivity and storage stability, the polymerization initiator preferably contains a peroxide-based radical polymerization initiator.

[0124] From the viewpoint of improving reactivity and storage stability, the content of the curing agent (polymerization initiator) in 100% by weight of the conductive paste is preferably 0.1% by weight or more, more preferably 0.3% by weight or more, even more preferably 0.5% by weight or more, and is preferably 5% by weight or less, more preferably 4% by weight or less, even more preferably 3% by weight or less.

[0125] The content of the curing agent (polymerization initiator) relative to 100 parts by weight of the curable compound in the conductive paste is preferably 0.3 parts by weight or more, more preferably 0.5 parts by weight or more, even more preferably 0.7 parts by weight or more, and preferably 6 parts by weight or less, more preferably 5 parts by weight or less, and even more preferably 4 parts by weight or less. When the content of the curing agent (polymerization initiator) is equal to or more than the above lower limit and equal to or less than the above upper limit, reactivity and storage stability can be improved.

[0126] <Other ingredients> The conductive paste may contain components other than the curable compound, the curing agent, and the plurality of conductive fillers, such as a solvent, an inorganic filler, an organic filler, a colorant, a polymerization inhibitor, a chain transfer agent, an antioxidant, 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, and an adhesion promoter.

[0127] (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.

[0128] 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.

[0129] 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 a conductive filler 1. The adhesive portion 84 is formed from the conductive paste containing the conductive filler 1. The adhesive portion 84 is preferably formed by hardening the conductive paste containing the conductive filler 1.

[0130] Substrate 82 has wiring 82a on its surface (upper surface). Chip 83 has electrodes 83a on its surface (lower surface). Wiring 82a and electrodes 83a are electrically connected by conductive filler 1 in adhesive portion 84.

[0131] 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 a 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; 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.

[0132] In the RFID inlay and manufacturing method of the present invention, a specific conductive paste is used, thereby improving adhesion between the substrate and the chip. Furthermore, in the RFID inlay and manufacturing method of the present invention, a specific conductive paste is used, thereby enabling the conductive paste to be positioned on the wiring with high precision. Furthermore, in the RFID inlay and manufacturing method of the present invention, a specific conductive paste is used, thereby preventing chip misalignment and uneven distribution of conductive filler even when an object is transported vertically during the manufacturing process. As a result, conductivity reliability can be improved. In the manufacturing method of the RFID inlay, the conductive paste may be disposed on the surface of the substrate, or the chip and the conductive paste may be disposed on the surface of the substrate.

[0133] 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 arrangement step, the second arrangement step, and the bonding step. In this case, multiple RFID inlays can be manufactured continuously, further improving the manufacturing efficiency of RFID inlays.

[0134] In the method for manufacturing an RFID inlay, in the first arrangement step, the second arrangement step, and the bonding step, the substrate may be transported horizontally, vertically, or both horizontally and vertically using a roll-to-roll system. In the method for manufacturing an RFID inlay, in the first arrangement step, the second arrangement step, and the bonding step, the substrate may be transported obliquely using a roll-to-roll system. In the method for manufacturing an RFID inlay, the conductive paste described above is used, so that even when an object is transported vertically using a roll-to-roll system, misalignment of the chip and uneven distribution of the conductive filler can be prevented. Note that the substrate may be transported with the conductive paste disposed on its surface, or with both the chip and the conductive paste disposed thereon.

[0135] When the roll-to-roll method is used, the transport speed of the substrate is not particularly limited.

[0136] Examples of methods for disposing the conductive paste include application using a dispenser, screen printing, and ejection using an inkjet device.

[0137] 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 can be achieved between the chip and the wiring (antenna pattern).

[0138] The pressure applied 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 pressure applied 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 connection reliability can be improved.

[0139] The heating and pressurizing time in the bonding step is not particularly limited, and may be 2 seconds or more, 15 seconds or less, or 10 seconds or less.

[0140] 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 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.

[0141] 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.

[0142] The substrate has wiring (antenna pattern) on its surface. The substrate has wiring (antenna pattern) formed on its surface. The substrate preferably has a base material and wiring (antenna pattern) disposed on the surface of the base material.

[0143] 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.

[0144] 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 920 MHz), the wiring is preferably aluminum wiring.

[0145] From the viewpoint of preventing 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.

[0146] 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.

[0147] The surface tension of the substrate (base material) is preferably 30 mN / m or more, more preferably 32 mN / m or more, even more preferably 34 mN / m or more, and preferably 50 mN / m or less, more preferably 48 mN / m or less, even more preferably 45 mN / m or less. When the surface tension of the substrate (base material) is above the above lower limit and below the above upper limit, adhesion can be further improved. The conductive paste according to the present invention can be suitably used for application to a substrate (base material) having a surface tension above the above lower limit and below the above upper limit.

[0148] The surface tension of the substrate (base material) can be measured in accordance with JIS K6768 using the following method: A cotton swab is dipped in a JIS-specified liquid and applied to the substrate (base material). The surface tension is determined from the shape of the coating film 2 seconds after application.

[0149] The chip may be a semiconductor chip (IC chip) or the like.

[0150] The chip has an electrode on its surface. Examples of the electrode 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 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.

[0151] 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.

[0152] The shape of the tip is not particularly limited, and may be rectangular, triangular, or circular.

[0153] The planar area of ​​the chip is preferably 0.04 mm 2 More than 0.09mm, preferably 0.09mm 2 More preferably, 0.16 mm 2or more, preferably 0.50 mm 2 Less than or equal to 0.40 mm, preferably 2 Less than 0.30 mm, more preferably 2 When 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 of the present invention can be suitably used for bonding relatively small chips.

[0154] 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.

[0155] The following materials were prepared:

[0156] Curable compound: Isobornyl acrylate ((A) polymerizable monomer, molecular weight: 208) Polyester urethane acrylate (Negami Chemical Industrial Co., Ltd. "UN-353", molecular weight (weight average molecular weight): 5000) Tricyclodecane dimethanol diacrylate (Daicel Allnex "IRR214", molecular weight: 304) Bisphenol A epoxy resin (DIC "EXA850CRP", molecular weight (weight average molecular weight): 340)

[0157] Conductive filler: Conductive particle A (conductive particle having a base particle and a conductive portion on the surface of the base particle (base particle: resin particle, conductive portion: nickel), average particle diameter: 5 μm, specific gravity: 2.0) Conductive particle B (conductive particle having a base particle and a conductive portion on the surface of the base particle (base particle: resin particle, conductive portion: nickel), average particle diameter: 5 μm, specific gravity: 1.5) Conductive particle C (conductive particle having a base particle and a conductive portion on the surface of the base particle (base particle: resin particle, conductive portion: nickel), average particle diameter: 5 μm, specific gravity: 4.0) Conductive particle D (conductive particle having a base particle and a conductive portion on the surface of the base particle (base particle: resin particle, conductive portion: silver 75% by weight, nickel 25% by weight), average particle diameter: 5 μm, specific gravity: 2.3) Conductive particle E (conductive particle having a base particle and a conductive portion on the surface of the base particle (base particle: resin particle, conductive portion: nickel), average particle diameter: 5 μm, specific gravity: 1.3) Conductive particle F (conductive particle having a base particle and a conductive portion on the surface of the base particle (base particle: resin particle, conductive portion: nickel), average particle diameter: 5 μm, specific gravity: 6.0) Conductive particles G (metal particles (copper), average particle size: 5μm, specific gravity: 8.9) Conductive particles H (metal particles (nickel), average particle size: 5 μm, specific gravity: 8.9)

[0158] Hardener: NOF Corporation's "Perloyl L" (diacyl radical polymerization initiator (lauroyl peroxide)) Asahi Kasei's Novacure HXA3922HP (latent curing agent for epoxy resins)

[0159] Inorganic fillers: Silica (Tokuyama "PM-20L")

[0160] Tips: IC chip (gold electrode, NXP "UCODE8", surface area: 0.22 mm 2 )

[0161] substrate: PET film (long, resin film with aluminum wiring, operating frequency in the UHF band (860MHz to 920MHz), surface tension: 43mN / m)

[0162] Example 1 (1) Preparation of conductive paste The materials shown in Table 1 below were mixed in the amounts shown in Table 1 below and stirred using a planetary mixer (Thinky Corporation's "Awatori Rentaro") to obtain a conductive paste (anisotropic conductive paste).

[0163] (2) RFID inlay fabrication 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). Then, thermocompression bonding was performed under conditions of an upper heat tool temperature of 180°C, a lower heat tool temperature of 175°C, a pressure of 2N, and a compression time of 7 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 by the conductive filler 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 Muhlbauer "DDA40000" (roll-to-roll method, with a section in the conveying path where the conveyed object is conveyed vertically). The resulting connection structure was cut into a size of 5 cm x 1.5 cm using a "DCL30000" manufactured by Muhlbauer to obtain an RFID inlay.

[0164] (Examples 2 to 10 and Comparative Examples 1 to 9) 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, 3, 5, and 7.

[0165] (evaluation) (1) Viscosity The viscosity (η) of the obtained conductive paste at 25°C and 5 rpm and the viscosity (η) of the conductive paste at 25°C and 0.5 rpm were measured using an E-type viscometer (Toki Sangyo Co., Ltd., "TV22 Type Viscometer"). The thixotropic index (ratio (η / η)) was calculated from the obtained results. Furthermore, the components of the conductive paste other than the conductive filler in each example and comparative example were mixed in the amounts shown in Tables 1, 3, 5, and 7 and stirred using a planetary mixer (Thinky Corporation, "Awatori Rentaro") to obtain a composition containing the conductive paste materials other than the conductive filler. The viscosity (η) of the obtained composition, excluding the conductive filler, at 25°C and 5 rpm was measured using an E-type viscometer (Toki Sangyo Co., Ltd., "TV22 Type Viscometer").

[0166] (2) Dispensability using a jet dispenser (positioning of conductive paste) The adhesive joints of 50 RFID inlays were observed under a microscope to see if the conductive paste was applied to the wiring in the correct amount (with high precision). The jet dispenser's dischargeability was evaluated according to the following criteria.

[0167] [Jet dispenser discharge criteria] ○: In all RFID inlays, the conductive paste is placed on the wiring with high precision. ×: In at least one RFID inlay, the conductive paste is not placed on the wiring with high precision.

[0168] (3) Prevention of chip misalignment The adhesive joints of 50 RFID inlays were examined under a microscope to see if the chip was properly positioned in the center of the wiring (the center of the conductive paste) even when the inlays were transported vertically during the manufacturing process. The chip misalignment prevention was evaluated according to the following criteria.

[0169] [Criteria for determining tip misalignment prevention] ○: In all RFID inlays, the chip is properly positioned in the center of the wiring. ×: In at least one RFID inlay, the chip is not properly positioned in the center of the trace.

[0170] (4) Prevention of uneven distribution of conductive filler For 50 of the obtained RFID inlays, the chips were peeled off from the wiring, and the number of conductive fillers on the electrodes on the chip surface was counted using a microscope. The ability to prevent uneven distribution of the conductive fillers was evaluated according to the following criteria.

[0171] [Criteria for preventing uneven distribution of conductive filler] ○: The number of conductive fillers on all electrodes is 3 or more ×: The number of conductive fillers on at least one electrode is 2 or less

[0172] (5) Conduction reliability Fifty of the resulting RFID inlays were left at 60°C and 90% RH (high temperature and humidity environment) for 250 hours, then placed in a dark box that blocks external radio waves, and the peak sensitivity in the UHF band (860 MHz to 920 MHz) at 25°C was measured using a frequency reader (Voyantic's "Tagformance Pro"). The conductivity reliability (frequency characteristics) was evaluated according to the following criteria.

[0173] [Conductivity reliability criteria] ○: Peak sensitivity of all RFID inlays is less than -18dBm ×: Peak sensitivity of at least one RFID inlay is -18dBm or higher

[0174] The compositions of the conductive pastes and the results are shown in Tables 1 to 8 below.

[0175] [Table 1]

[0176] [Table 2]

[0177] [Table 3]

[0178] [Table 4]

[0179] [Table 5]

[0180] [Table 6]

[0181] [Table 7]

[0182] [Table 8] [Explanation of symbols]

[0183] 1...Conductive filler 81...RFID inlay 82...Substrate having wiring on its surface 82a...Wiring 83...Chip with electrode on its surface 83a...Electrode 84...Adhesive part

Claims

1. A conductive paste including a curable compound, a curing agent, and a plurality of conductive fillers, The specific gravity of the conductive filler is 1.5 or more and 4.0 or less, The content of the conductive filler in 100% by weight of the conductive paste is 1.0% by weight or more and 15% by weight or less, the ratio of the viscosity of the conductive paste at 25°C and 0.5 rpm to the viscosity at 25°C and 5 rpm is 1.5 or more and 4.5 or less; The conductive paste has a viscosity of 8 Pa·s or more and 50 Pa·s or less at 25°C and 5 rpm.

2. The conductive paste according to claim 1 , wherein the curable compound comprises a (meth)acrylic compound.

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

4. The conductive paste according to claim 3 , wherein the conductive particles comprise a base particle and a conductive portion disposed on a surface of the base particle.

5. 3. The conductive paste according to claim 1, which is applied to a substrate having a surface tension of 30 mN / m or more and 50 mN / m or less.

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

7. The device comprises a substrate having wiring on its surface, a chip having electrodes on its surface, and an adhesive portion that bonds the substrate and the chip together, The material of the adhesive portion is the conductive paste according to claim 1 or 2, An RFID inlay, wherein the wiring and the electrode are electrically connected by the conductive filler in the adhesive portion.

8. a first disposing step of disposing the conductive paste according to claim 1 or 2 on a surface of a substrate having wiring on the surface; a second placement step of placing a chip having an electrode on a surface of the conductive paste opposite to the substrate; A method for manufacturing an RFID inlay, comprising: a bonding process in which an adhesive joint that bonds the substrate and the chip is formed using the conductive paste by heating and pressurizing the conductive paste, and the wiring and the electrode are electrically connected by the conductive filler in the adhesive joint.

9. The substrate is long, The method for manufacturing an RFID inlay according to claim 8 , wherein the RFID inlay is manufactured by transporting the long substrate using a roll-to-roll method in the first placement step, the second placement step, and the bonding step.

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