Electroconductive composition

Abstract

An electroconductive composition comprising metal particles, an epoxy resin, a curing agent, and a curing accelerator, the metal particles comprising first metal particles containing a high-melting metal having a melting point of 800°C or higher, and second metal particles containing a low-melting metal having a melting point of 240°C or lower, and the curing accelerator being at least one among a urea-based compound and a phosphorus-based compound.

Description

Conductive Composition Cross - reference to Related Applications

[0001] This application claims the priority of Japanese Patent Application No. 2024 - 167478, and is incorporated herein by reference in its entirety.

[0002] The present invention relates to a conductive composition.

[0003] Conventionally, conductive compositions have been used for electrically connecting various components. For example, conductive compositions are used as bonding materials in component mounting on printed wiring boards. As conductive compositions, those containing metal particles and a thermosetting resin composition containing an epoxy resin are known. When such a conductive composition is heated to the temperature at which the epoxy resin cures, the cured product of the epoxy resin reinforces the conductive paths formed by the metal particles.

[0004] Also, in order to reduce the thermal load on the substrate and enable the mounting of components with low heat resistance, it has been proposed to use a conductive composition containing low - melting - point metal particles. For example, in Patent Document 1, a conductive adhesive containing low - melting - point metal particles such as Sn - Bi - based alloy particles, high - melting - point metal particles such as silver particles, an epoxy resin, and a curing agent has been proposed. Such a conductive adhesive is applied between the circuit of the substrate and the electrodes of electronic components such as capacitors and resistors, and is heated to a temperature higher than the melting point of the low - melting - point metal particles and lower than the melting point of the high - melting - point metal particles. At this time, the melted low - melting - point metal forms an alloy with the metal of the circuit and the electrodes, and forms an alloy with the high - melting - point metal particles so as to coat the high - melting - point metal particles. Then, through these alloys, the high - melting - point metal particles are electrically connected to the circuit and the electrodes.

[0005] Japanese Patent Application Laid - Open No. 2008 - 108625

[0006] To form an alloy that exhibits conductivity, it is necessary to diffuse molten low-melting-point metal between high-melting-point metal particles. In other words, to achieve good conductivity, it is desirable to melt the low-melting-point metal particles before the epoxy resin has fully cured. For this reason, the conductive adhesive described in Patent Document 1 is thought to have a formulation that allows for relatively lenient curing conditions of the epoxy resin, such as by not including a curing accelerator. However, with such a formulation, sufficient bonding strength may not be obtained.

[0007] In view of the above circumstances, the object of the present invention is to provide a conductive composition that is excellent in conductivity and bonding properties.

[0008] The conductive compositions according to the present invention are as follows: [1] A conductive composition comprising metal particles, an epoxy resin, a curing agent, and a curing accelerator, wherein the metal particles comprise first metal particles containing a high-melting-point metal with a melting point of 800°C or higher and second metal particles containing a low-melting-point metal with a melting point of 240°C or lower, and the curing accelerator is at least one of a urea-based compound and a phosphorus-based compound. [2] The conductive composition according to [1] above, wherein the curing agent is at least one of a phenol-based curing agent.

[0009] [3] The conductive composition according to [2] above, wherein the phenolic curing agent is a novolac-type phenolic resin.

[0010] [4] The conductive composition according to any one of [1] to [3] above, wherein the content of the curing accelerator is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the epoxy resin.

[0011] [5] The conductive composition according to any one of [1] to [4] above, wherein the content of the first metal particles is 100 parts by mass or more and 1000 parts by mass or less per 100 parts by mass of the epoxy resin, and the content of the second metal particles is equal to or greater than the content of the first metal particles.

[0012] This is a schematic cross-sectional view of a printed circuit board according to one embodiment.

[0013] According to the present invention, a conductive composition with excellent conductivity and bonding properties can be provided.

[0014] A conductive composition according to an embodiment of the present invention will be described.

[0015] The conductive composition according to this embodiment comprises metal particles and a thermosetting resin composition. The metal particles include first metal particles (hereinafter referred to as high-melting-point metal particles) containing a high-melting-point metal with a melting point of 800°C or higher, and second metal particles (hereinafter referred to as low-melting-point metal particles) containing a low-melting-point metal with a melting point of 240°C or lower.

[0016] The thermosetting resin composition comprises an epoxy resin, a curing agent, and a curing accelerator. The conductive composition is liquid when the thermosetting resin composition is uncured. In this specification, "liquid" includes not only low-viscosity substances that exhibit fluidity solely due to gravity at room temperature, but also semi-solid substances such as pastes.

[0017] As shown in Figure 1, the conductive composition C is used as a bonding material to electrically connect a circuit 11 formed on a substrate 10 in a printed wiring board to the electrodes of electronic components 12 such as capacitors and resistors. In bonding the circuit and electrodes, for example, a printed pattern of the conductive composition is formed on the substrate by a printing method using a metal mask, electronic components are mounted in predetermined positions, and a reflow process is performed. At this time, the conductive composition is heated to a predetermined temperature in the reflow process, causing the low-melting-point metal particles to melt and diffuse between the high-melting-point metal particles, forming an alloy of the low-melting-point metal and the high-melting-point metal so as to cover the high-melting-point metal particles, and also forming an alloy with the metals of the circuit and the electrodes, thereby electrically connecting the circuit and the electrodes through these alloys.

[0018] The conductive composition of this embodiment is used under heating conditions that do not inhibit the formation of the alloy. For example, when differential scanning calorimetry is performed on the conductive composition under a heating condition of 10°C / min, it may show an endothermic peak temperature associated with the melting of the low-melting-point metal particles, followed by an exothermic peak temperature associated with the curing reaction of the thermosetting resin composition. The endothermic peak temperature is preferably 140 to 150°C. The exothermic peak temperature is preferably 140 to 160°C.

[0019] The high-melting-point metal particles have a surface layer made of a metal that can form an alloy with the molten low-melting-point metal. Examples of the metal forming the surface layer include copper, silver, nickel, and gold. Examples of the high-melting-point metal particles include copper particles, nickel particles, silver particles, silver-coated copper particles, gold-coated copper particles, silver-coated nickel particles, and gold-coated nickel particles. The high-melting-point metal particles may contain unavoidable impurities. The metal particles may consist of only one type or two or more types of the high-melting-point metal particles.

[0020] The median diameter (D50) in the particle size distribution of the high-melting-point metal particles is, for example, 0.5 μm or more and 30 μm or less, and preferably 0.5 μm or more and 20 μm or less. In this specification, the particle size distribution refers to the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution measurement method.

[0021] The low-melting-point metal particles of this embodiment preferably contain a lead-free alloy (which may contain unavoidable impurities) with Sn as the main component. Examples of the alloy include Sn-based alloys containing Sn as the main component and one or more selected from Bi, Ag, In, Ni, Cu, Zn, Ga, Sb, Au, Pa, Ge, Cr, Al, P, Cd, Tl, Si, Mg, and Pb. Examples of the Sn-based alloys include Sn-Bi, Sn-Zn, Sn-Zn-Bi, Sn-In, Sn-Sb, Sn-Cu, Sn-Cu-Ni, Sn-Cu-Bi, Sn-Ag, and Sn-Ag-Cu. The content of the Sn-based alloy in the low-melting-point metal particles is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more.

[0022] The melting point of the alloy is preferably 200°C or less, and more preferably 150°C or less. If the phase diagram of the alloy shows both a solidus and a liquidus, the melting point of the liquidus is preferably 200°C or less, more preferably 150°C or less, even more preferably 200°C or less, and even more preferably 150°C or less.

[0023] As the alloy, a Sn-Bi alloy with a relatively low melting point is preferred. Among the Sn-Bi alloys, those with a mass ratio of Sn to Bi of 40:60 to 50:50 (Sn:Bi) are more preferred. Such Sn-Bi alloys are preferred because the melting point of the liquidus line in the phase diagram is near the eutectic point, meaning they melt easily when heated in the reflow process.

[0024] In the particle size distribution of the low-melting-point metal particles, D50 is preferably 1 μm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less.

[0025] The shapes of the high-melting-point metal particles and the low-melting-point metal particles are not particularly limited, but may be spherical, dendritic, or flaky. Dendritic or flaky low-melting-point metal particles have the advantage of increasing the number of contact points with each other, making it easier to ensure conductivity. On the other hand, spherical low-melting-point metal particles have the advantage of reducing the influence of oxide films that can reduce conductivity because their specific surface area is relatively small.

[0026] The epoxy resin is preferably a liquid epoxy resin at room temperature (25°C). The epoxy equivalent of the epoxy resin is preferably 500 g / eq or less. For example, the epoxy equivalent of the epoxy resin is 90 g / eq or more.

[0027] Examples of the epoxy resin include bisphenol-type epoxy resins such as bisphenol A-type epoxy resin and bisphenol F-type epoxy resin; glycidyl ether-type epoxy resins such as 4-hydroxybutyl acrylate glycidyl ether; glycidylamine-type epoxy resins such as N,N-diglycidyl-4-glycidyloxyaniline and 4,4'-methylenebis(N,N-diglycidylaniline); and aliphatic epoxy resins. The thermosetting resin composition may also contain epoxy resins as reactive diluents that are liquid at room temperature (25°C), such as butyl glycidyl ether, 2-ethylhexyl glycidyl ether, and 1,6-hexanediol diglycidyl ether.

[0028] The epoxy resin content is preferably 0.05 to 0.2 with respect to the mass of the metal particles.

[0029] The curing agent is preferably one that forms a cured product with the epoxy resin under heating conditions of 150°C to 200°C, more preferably 150°C to 160°C. Examples of such curing agents include phenolic curing agents and acid anhydride curing agents.

[0030] Examples of the phenolic curing agents include bisphenol A, bisphenol F, dihydroxynaphthalene, bisphenol sulfide, phenol novolac resin, and phenol aralkyl resin.

[0031] Examples of the acid anhydride-based curing agents include methyltetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and dodecenyl succinic anhydride.

[0032] The content of the curing agent is preferably 0.5 parts by mass or more and 20 parts by mass or less, and more preferably 1 part by mass or more and 10 parts by mass or less, per 100 parts by mass of the epoxy resin.

[0033] The curing accelerator is at least one of a urea-based compound and a phosphorus-based compound.

[0034] Examples of the urea-based compounds include 1,1-dimethylurea, 1,1,3-trimethylurea, 1,1-dimethyl-3-ethylurea, 1,1-dimethyl-3-phenylurea, 1,1-diethyl-3-methylurea, 1,1-diethyl-3-phenylurea, 1,1-dimethyl-3-(3,4-dimethylphenyl)urea, 1,1-dimethyl3-(p-chlorophenyl)urea, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU).

[0035] Examples of the phosphorus compounds include phosphines such as triphenylphosphine, diphenylphosphine, tributylphosphine, tri(p-methylphenyl)phosphine, and tri(nonylphenyl)phosphine; borane complexes such as triphenylphosphine and triphenylborane; and borate salts such as tetraphenylphosphonium tetraphenylborate, tetraphenylphosphonium tetra-p-tolylborate, p-tolyltriphenylphosphonium tetra-p-tolylborate, and tri-tert-butylphosphonium tetraphenylborate.

[0036] The content of the curing accelerator is preferably 1 part by mass or more and 10 parts by mass or less, and more preferably 1 part by mass or more and 5 parts by mass or less, per 100 parts by mass of the epoxy resin.

[0037] The thermosetting resin composition preferably contains flux.

[0038] Examples of the activators in the flux include carboxylic acids such as sebacic acid, adipic acid, glutaric acid, succinic acid, malonic acid, 8-ethyloctadecanediic acid, dicarboxylic acids such as pimelic acid, tricarboxylic acids such as citric acid, and aromatic carboxylic acids such as benzoic acid; alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine, and salts of the carboxylic acids and alkanolamines.

[0039] The content of the activator is preferably 10 parts by mass or more and 200 parts by mass or less, more preferably 20 parts by mass or more and 180 parts by mass or less, and even more preferably 30 parts by mass or more and 150 parts by mass or less, per 100 parts by mass of the epoxy resin.

[0040] The thermosetting resin composition may contain other additives. Examples of such additives include plasticizers, flame retardants, antioxidants, defoamers, leveling agents, rheology control agents, and fillers. The content of the additives is, for example, 0.5 to 20 parts by mass per 100 parts by mass of the epoxy resin.

[0041] It is preferable that the conductive composition does not contain a solvent. That is, the conductive composition is preferably a solvent-free system. Thereby, generation of voids due to volatilization of the solvent in thermosetting can be suppressed.

[0042] The viscosity of the conductive composition is preferably 30 to 70 Pa·s. The viscosity can be measured using a cone plate type viscometer under the conditions of 25°C and a shear rate of 10 (1 / sec).

[0043] Although embodiments have been shown as examples, the conductive composition according to the present invention is not limited to the configuration of the above embodiments. Also, the conductive composition according to the present invention is not limited by the above-described effects. The conductive composition according to the present invention can be variously modified without departing from the gist of the present invention.

[0044] Hereinafter, the present invention will be further described by way of examples, but the present invention is not limited thereto.

[0045] [Raw materials used] (A) Epoxy resin: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, JER871, liquid, epoxy equivalent 390 - 470 g / eq) (B1) High melting point metal particles 1: Silver-coated copper powder, spherical, D50: 5 μm High melting point metal particles 2: Silver powder, spherical, D50: 5 μm High melting point metal particles 3: Silver-coated copper nickel zinc alloy powder (copper 89% by mass, nickel 1% by mass, zinc 10% by mass), spherical, D50: 5 μm (B2) Low melting point metal particles: Sn - Bi system alloy (Sn / Bi = 42:58 = 0.72), D50: 5 μm (C) Curing agent: Phenol novolak resin (manufactured by Arakawa Chemical Industries, Ltd., Tamanol 758) (D) Curing accelerator 1: 1,1 - Dimethylurea (manufactured by Tokyo Chemical Industry Co., Ltd.) Curing accelerator 2: Triphenylphosphine (manufactured by Kitakyo Chemical Industry Co., Ltd.) (E) Flux (activator): 8 - Ethyloctadecanedioic acid (manufactured by Okamura Oil Co., Ltd.)

[0046] [Production example] Each component was blended at the blending ratios shown in Tables 1 - 2 to prepare a conductive composition.

[0047] [Evaluation 1: Conductivity] A conductive composition was line-printed onto a glass epoxy substrate using a metal mask (length 60 mm, width 1 mm, thickness approximately 100 μm), and then cured by heating at 180°C for 60 minutes to create a test substrate with a conductive pattern. Next, the resistance value (R, Ω) between both ends of the conductive pattern was measured using a tester, and the cross-sectional area (S, cm²) was measured. ２ The resistivity was calculated from the length (L, cm) using the following formula (1). Furthermore, 15 conductive patterns were formed by printing 5 lines on each of three glass epoxy substrates, and the average resistivity of these patterns was calculated. The resistivity was 3 × 10⁻⁶. －４ If the resistivity is less than Ω·cm, it is evaluated as having excellent conductivity and is indicated with "○" in Tables 1 and 2. If the resistivity is 3 × 10⁻⁴ Ω·cm or more, it is evaluated as having poor conductivity and is indicated with "×" in Tables 1 and 2. Resistivity = (S / L) × R (1) (Evaluation criteria) Resistivity is 3 × 10 －４ If the conductivity is less than Ω·cm, it can be considered to have excellent conductivity.

[0048] [Evaluation 2: Heat Cycle Resistance] The test substrate was subjected to 1000 heat cycles, consisting of 30 minutes at -65°C and 30 minutes at 125°C. The conductivity of the test substrate after the heat cycle test was determined in the same manner as in Evaluation 1. (Evaluation Criteria) Let a be the resistance value before the heat cycle test and b be the resistance value after the heat cycle test. The rate of change in resistance was calculated using the following formula. If the rate of change in resistance is within ±10%, it can be evaluated as having excellent heat cycle resistance. Rate of change in resistance (%) = (b - a) × 100 / a

[0049] [Evaluation 3: Bonding (Adhesive Strength)] The conductive composition was printed on a portion of two copper plates (100 mm long x 25 mm wide x 1 mm thick) (12 mm long, 25 mm wide, approximately 100 μm thick). The coated surfaces were placed together and heated at 150°C for 60 minutes to fully cure, and samples were prepared. Next, the tensile shear strength was measured using a precision universal testing machine, Auto Bluff (Shimadzu Corporation, AGX-V series). (Evaluation Criteria) If the shear strength is 10 MPa or higher, the bonding can be evaluated as having excellent bonding properties.

[0050] [Evaluation 4: Storage Stability (Pot Life)] The initial viscosity (V0) of each conductive composition immediately after manufacturing was measured using a cone-plate viscometer rotor CP52 (5 rpm). The viscosity (V1) of each conductive composition after being left at room temperature for one day was also measured. The percentage change in viscosity (%) was then calculated using the following formula: Percentage change = [(V1 - V0) / V0] × 100 (Evaluation criteria) If the percentage change is 20% or less, it can be evaluated as having excellent storage stability.

[0051]

[0052]

Claims

1. A conductive composition comprising metal particles, epoxy resin, a curing agent, and a curing accelerator, wherein the metal particles comprise first metal particles containing a high-melting-point metal with a melting point of 800°C or higher, and second metal particles containing a low-melting-point metal with a melting point of 240°C or lower, and the curing accelerator is at least one of a urea-based compound and a phosphorus-based compound.

2. The conductive composition according to claim 1, wherein the curing agent is at least one phenolic curing agent.

3. The conductive composition according to claim 2, wherein the phenolic curing agent is a novolac-type phenolic resin.

4. The conductive composition according to any one of claims 1 to 3, wherein the content of the curing accelerator is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the epoxy resin.

5. The conductive composition according to any one of claims 1 to 3, wherein the content of the first metal particles is 100 parts by mass or more and 1000 parts by mass or less per 100 parts by mass of the epoxy resin, and the content of the second metal particles is equal to or greater than the content of the first metal particles.

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