Conductive composition

Abstract

To provide a conductive composition capable of forming a cured matter in which a change in conductivity due to heat cycle is suppressed.SOLUTION: A conductive composition includes (A) an epoxy resin, (B) polyol, (C) a cationic polymerization initiator, and (D) conductive particles. The conductive composition includes (A-1) an alicyclic epoxy resin as the (A) epoxy resin, and (B-1) polyalkylene glycol whose molecular weight is 200 or more 1,000 or less as the (B) polyol.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a conductive composition.

Background Art

[0002] Conventionally, a printed wiring board has been manufactured by etching a copper-clad laminate in which a copper foil is laminated on a base material having electrical insulation properties, and an electronic element such as an LSI or a capacitor has been soldered to the printed wiring board to manufacture a printed circuit board. As a printed wiring board used for this type of printed circuit board, in addition to a rigid board having a base material impregnated with an epoxy resin in a glass cloth, a flexible board or a film board having a polyimide film or a polyethylene terephthalate resin film as a base material is known. Further, as this type of printed wiring board, a single-sided board in which wiring is provided only on one side of the base material, a double-sided board in which wiring is provided on both sides of the base material, a multilayer board in which a plurality of base materials are laminated alternately with wiring, etc. are known. Among these, in a double-sided board or a multilayer board, through holes penetrating the base material in the thickness direction are provided, and electrical connection between layers is made through the through holes.

[0003] By the way, in recent years, there have been an increasing number of cases where wiring is formed on a base material by a printing method using a conductive composition instead of a copper foil, or an electrical connection between an electronic element and wiring is made with a conductive composition instead of soldering. As this type of conductive composition, those containing conductive particles such as silver particles and a curable resin are known. When such a conductive composition is used as a wiring agent, it does not require a complicated process such as etching a copper foil, and when used as a conductive adhesive, it does not require a high-temperature process such as soldering, so it is excellent in convenience.

[0004] And, it is desirable that the conductive composition can exhibit excellent conductivity even when cured at a low temperature. From this perspective, Patent Document 1 and Patent Document 2 propose a conductive composition containing an alicyclic epoxy resin, conductive particles, and further a cationic polymerization initiator. Patent Document 1 shows that the above performance can be exhibited even when cured at a low temperature by a combination of an alicyclic epoxy resin and a cationic polymerization initiator.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, in a printed wiring board on which an electronic element is mounted, the electronic element becomes a heat source. Also, the wiring itself may generate heat due to Joule heat, and the degree of heat generation depends on the magnitude of the current flowing through the wiring. Therefore, in a printed circuit board, a heat cycle, which is a phenomenon in which a low-temperature state and a high-temperature state are repeated, can occur. And, due to the influence of this heat cycle, the cured product of the conductive composition may change in conductivity, which may reduce the reliability of the printed circuit board. Note that the heat cycle occurs not only when the conductive composition is used for a printed circuit board, that is, the requirement for conductivity stability is not limited to a specific application.

[0007] In view of the above circumstances, an object of the present invention is to provide a conductive composition capable of forming a cured product in which a change in conductivity due to a heat cycle is suppressed.

Means for Solving the Problems

[0008] The conductive composition according to the present invention is (A) An epoxy resin, (B) a polyol, (C) a cationic polymerization initiator, and (D) conductive particles, As the (A) epoxy resin, it contains (A-1) an alicyclic epoxy resin. As the (B) polyol, it contains (B-1) a polyalkylene glycol having a molecular weight of 200 or more and 1000 or less.

[0009] Since the conductive composition of the present invention contains (B-1) a polyalkylene glycol having a molecular weight of 200 or more and 1000 or less, the cured product formed by the conductive composition of the present invention has suppressed changes in conductivity due to heat cycles.

[0010] The conductive composition according to one aspect of the present invention is The (A-1) alicyclic epoxy resin has an epoxycycloalkyl group.

[0011] The cured product formed by the conductive composition of such an aspect is excellent in the above performance.

[0012] The conductive composition according to one aspect of the present invention is The (B-1) polyalkylene glycol is polyethylene glycol.

[0013] The cured product formed by the conductive composition of such an aspect is further excellent in the above performance.

[0014] The conductive composition according to one aspect of the present invention is The content of the polyethylene glycol is 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the (A) epoxy resin.

[0015] The cured product formed by the conductive composition of such an aspect is even more excellent in the above performance. [Effect of the Invention]

[0016] As described above, according to the present invention, it is possible to provide a conductive composition capable of forming a cured product in which changes in conductivity due to heat cycles are suppressed.

Mode for Carrying Out the Invention

[0017] Hereinafter, the conductive composition according to an embodiment of the present invention will be described.

[0018] The conductive composition according to the embodiment includes a curable resin composition containing (A) an epoxy resin, (B) a polyol, and (C) a cationic polymerization initiator, and (D) conductive particles. Further, the curable resin composition may optionally contain (E) a solvent and (F) an additive.

[0019] The curable resin composition has reaction curability and may have thermosetting properties. The conductive composition is liquid in a state where the curable resin composition is uncured. In the present specification, the term "liquid" does not mean only a low-viscosity material that exhibits fluidity only by the action of gravity at normal temperature, but also includes a semi-solid state such as a paste state.

[0020] The curable resin composition contains (A-1) an alicyclic epoxy resin as the (A) epoxy resin. As the (A-1) alicyclic epoxy resin, those having an epoxy cycloalkyl group such as an epoxy cyclopentyl group or an epoxy cyclohexyl group are preferable. Further, the (A-1) alicyclic epoxy resin preferably has 2 to 4 epoxy cycloalkyl groups.

[0021] The (A-1) alicyclic epoxy resin may be an ester-type alicyclic epoxy resin in which two epoxy cycloalkyl groups are connected via an ester bond. Examples of the ester-type alicyclic epoxy resin include 3,4-epoxycyclohexylmethyl (3,4-epoxy) cyclohexanecarboxylate.

[0022] As the (A-1) alicyclic epoxy resin, a condensed-ring type alicyclic epoxy resin composed of two or more condensed rings having epoxy groups may be used. The condensed-ring type alicyclic epoxy resin may be one in which the condensed rings having epoxy groups share one carbon-carbon bond. Examples of such a condensed-ring type alicyclic epoxy resin include tetrahydroindene diepoxide obtained by epoxidizing the diene of tetrahydroindene (more specifically, 3,4:7,8-diepoxybicyclo[4,3,0]nonane). Further, the condensed-ring type alicyclic epoxy resin may be one in which the condensed rings having epoxy groups are connected via one or more condensed rings having no epoxy group. Examples of such a condensed-ring type alicyclic epoxy resin include tetracyclotetradecadiene diepoxide obtained by epoxidizing the diene of tetracyclotetradecadiene, 5,12-dioxahexacyclo[7.6.1.0(2,8).0(4,6).0(10,15).0(11,13)]hexadecane, and 5,12-dioxaheptacyclo[7.6.1.1(3,7).0(2,8).0(4,6).0(10,15).0(11,13)]heptadecane.

[0023] As the (A-1) alicyclic epoxy resin, a bicyclic type alicyclic epoxy resin in which two epoxycycloalkyl groups are connected via a carbon-carbon shared bond (single bond) may be used. Examples of the bicyclic type alicyclic epoxy resin include (3,3´,4,4´-diepoxy)bicyclohexyl.

[0024] As the (A-1) alicyclic epoxy resin, a cyclic siloxane type alicyclic epoxy resin in which 3 to 4 epoxycycloalkyl groups are connected via a 3 to 4-mer cyclic siloxane may be used. Examples of the cyclic siloxane type alicyclic epoxy resin include 2,4,6,8-tetrakis(2-(3,4-epoxycyclohexyl)ethyl)-2,4,6,8-tetramethylcyclotetrasiloxane).

[0025] The curable resin composition may contain any one of the above (A-1) alicyclic epoxy resins, or may contain two or more of them.

[0026] The content of the (A-1) alicyclic epoxy resin is preferably 80% by mass or more and 95% by mass or less, more preferably 90% by mass or more and 95% by mass or less, based on the total mass of the (A) epoxy resin that can be contained in the curable resin composition. Further, the mass ratio of the ester-based alicyclic epoxy resin in the (A-1) alicyclic epoxy resin is preferably 40% by mass or more. The curable resin composition may contain a rubber-modified epoxy resin such as an NBR-modified epoxy resin as the (A-1) alicyclic epoxy resin, but the mass ratio of the rubber-modified epoxy resin in the (A-1) alicyclic epoxy resin is preferably less than 5% by mass, more preferably less than 2% by mass, and even more preferably less than 1% by mass. It is even more preferable that the curable resin composition substantially does not contain the rubber-modified epoxy resin. The curable resin composition may contain a resin other than the (A) epoxy resin, but the content of the (A) epoxy resin is preferably 90% by mass or more, more preferably 95% by mass or more, based on the total mass of the resins that can be contained in the curable resin composition.

[0027] The curable resin composition may contain (A-2) other epoxy resins as epoxy resins other than the above (A-1) alicyclic epoxy resin. Examples of such (A-2) other epoxy resins include bisphenol type epoxy resins such as bisphenol A type epoxy resin, tetrabromobisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin; glycidyl ether type epoxy resins such as tris(glycidyloxyphenyl)methane and tetrakis(glycidyloxyphenyl)ethane; glycidyl amine type epoxy resins such as N,N-diglycidyl-4-glycidyloxyaniline and 4,4'-methylenebis(N,N-diglycidylaniline); novolak type epoxy resins such as cresol novolak type epoxy resin, phenol novolak type epoxy resin, α-naphthol novolak type epoxy resin, and brominated phenol novolak type epoxy resin. Further, reactive diluents that are liquid at normal temperature (25°C) such as butyl glycidyl ether, 2-ethylhexyl glycidyl ether, and 1,6-hexanediol diglycidyl ether are also included in (A-2) other epoxy resins. The content of these (A-2) other epoxy resins is preferably 1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 5% by mass or less, based on the total mass of the (A) epoxy resin that can be contained in the curable resin composition.

[0028] The curable resin composition contains (B-1) a polyalkylene glycol having a molecular weight of 200 or more and 1000 or less. In the present specification, the molecular weight of the (B) polyol means the weight average molecular weight, which can be determined by comparison with a polystyrene standard by gel permeation chromatography (GPC method).

[0029] The (B-1) polyalkylene glycol preferably has a repeating unit represented by the following chemical formula (1). R1 is preferably a (linear) alkylene structure having 2 to 5 carbon atoms. Examples of such (B-1) polyalkylene glycol include polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, a copolymer of oxyethylene and oxypropylene, polybutylene glycol, polypentylene glycol, and the like.

Chemical formula

[0030] The molecular weight of the (B-1) polyalkylene glycol is more preferably 200 or more and 500 or less, further preferably 200 or more and 400 or less, and even more preferably 200 or more and 300 or less.

[0031] The hydroxyl equivalent of the (B-1) polyalkylene glycol is preferably 100 to 500 g / eq.

[0032] The content of the (B-1) polyalkylene glycol is preferably 1 part by mass or more and 13 parts by mass or less, more preferably 1 part by mass or more and 10 parts by mass or less, and further preferably 2 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the (A) epoxy resin contained in the curable resin composition.

[0033] The above-mentioned (C) cationic polymerization initiator generates a strong acid by heat, and this strong acid initiates the polymerization reaction of the (A) epoxy resin. As the above-mentioned (C) cationic polymerization initiator, a salt of an aromatic sulfonium and an anion is preferable. Examples of the above-mentioned aromatic sulfonium include benzyl(4-hydroxyphenyl)methylsulfonium, (4-acetoxyphenyl)dimethylsulfonium, (4-hydroxyphenyl)dimethylsulfonium, (2-methylbenzyl)(4-hydroxyphenyl)methylsulfonium, (4-acetoxyphenyl)(2-methylbenzyl)methylsulfonium, (1-naphthylmethyl)(4-hydroxyphenyl)methylsulfonium, benzyl(4-acetoxyphenyl)methylsulfonium, and the like. Examples of the above-mentioned anion include tris(pentafluoroethyl)trifluorophosphate, hexafluorophosphate, tetrafluoroborate, tetrakis(pentafluorophenyl)borate, hexafluoroantimonate, p-toluenesulfonate, dodecylbenzenesulfonate, trifluoromethanesulfonate, perfluorobutanesulfonate.

[0034] The content of the above-mentioned (C) cationic polymerization initiator is preferably 0.1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the (A) epoxy resin contained in the curable resin composition.

[0035] The content of the above-mentioned (C) cationic polymerization initiator is preferably 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the (A) epoxy resin contained in the curable resin composition, more preferably 1 part by mass or more and 6 parts by mass or less, and still more preferably 1 part by mass or more and 4 parts by mass or less.

[0036] Examples of the (D) conductive particles include copper particles, silver particles, nickel particles, silver-coated copper particles, nickel-coated copper particles, gold-coated copper particles, silver-coated nickel particles, gold-coated nickel particles, solder particles (including not only those made of an alloy mainly composed of lead and tin but also those made of so-called lead-free solder that does not contain lead), and the like. The shape of the (D) conductive particles is not particularly limited, and examples include spherical, flaky, dendritic, and the like. The average particle size of the (D) conductive particles is preferably 0.5 to 30 μm. The average particle size of the (D) conductive particles can be determined from the volume-based particle size distribution measured by the laser diffraction scattering method for particle size distribution measurement.

[0037] The content of the (D) conductive particles is preferably 250 parts by mass or more and 1500 parts by mass or less, more preferably 300 parts by mass or more and 800 parts by mass or less, and even more preferably 300 parts by mass or more and 600 parts by mass or less with respect to 100 parts by mass of the (A) epoxy resin contained in the curable resin composition.

[0038] As the (E) solvent, those having a boiling point of about 150 to 250 °C are preferred, and examples include esters such as γ-butyrolactone and propylene carbonate, and ether alcohols such as butyl carbitol. The curable resin composition may contain only one type of solvent or may contain a plurality of types of solvents.

[0039] The content of the (E) solvent is preferably 10 parts by mass or less with respect to 100 parts by mass of the (A) epoxy resin contained in the curable resin composition. Further, the conductive composition may be a solvent-free system that does not contain a solvent. For example, the content of the (E) solvent may be 1 part by mass or less, or may be 0.5 mass% or less.

[0040] Examples of the (F) additive include colorants such as pigments, plasticizers, flame retardants, antioxidants, defoamers, adhesion promoters, leveling agents, rheology control agents, fillers, and the like. The content of the (F) additive is, for example, 0.5 to 20 parts by mass with respect to 100 parts by mass of the (A) epoxy resin contained in the curable resin composition.

[0041] The viscosity of the conductive composition is preferably 80 Pa·s or less, more preferably 50 Pa·s or less, and even more preferably 40 Pa·s or less. The viscosity is a value measured using a cone plate viscometer under the conditions of 25°C and a shear rate of 10 (1 / sec).

[0042] The curable resin composition is cured after being adhered to an adherend in an uncured state to obtain a cured product having excellent conductivity. The curable resin composition can be applied to the adherend by a printing method, a transfer method, a spraying method, or the like, or can be spot-supplied by a dispenser or the like. The curable resin composition can be used to form wiring of an electric and electronic circuit with a cured product. In that case, examples of the adherend to which the curable resin composition is adhered include metal materials such as copper foil; insulating materials (electric insulating sheets) such as epoxy resin-impregnated glass sheets, polyimide resin sheets, polyethylene terephthalate resin sheets, and ceramic sheets. When used as a constituent material of a circuit board, the curable resin composition can be used as a wiring material, a bonding material for electrically connecting wiring and electronic elements instead of soldering, a filling material for filling through holes, and the like.

[0043] The curable resin composition can be cured at a low temperature (for example, 180 °C or lower) compared to the melting point of solder. The curable resin composition can be particularly useful in a scenario where a polyethylene terephthalate resin sheet having a lower softening temperature than a polyimide resin sheet or the like is used as an adherend. The polyethylene terephthalate resin has a high affinity with an epoxy resin and exhibits good wettability with respect to the curable resin composition. Therefore, the adherend to which the curable composition is adhered may be composed of a resin composition containing polyethylene terephthalate resin at least on the adherend surface to which the curable composition is adhered.

[0044] The adherend surface of the adherend may be subjected to surface treatment such as mechanical surface treatment for enhancing the anchor effect such as hairline processing or mat processing, electrical surface treatment for increasing functional groups such as hydroxyl groups on the surface such as plasma treatment or corona treatment, and coating with a primer or coupling agent.

[0045] The curable resin composition can be used as a conductive adhesive other than for circuit formation, and can also be used as a thermal conductive adhesive or the like mainly for heat dissipation purposes.

[0046] The conductive composition can form a cured product excellent in conductivity by heating at a low temperature of 150 °C or lower, more preferably 120 °C or lower, and even more preferably 100 °C or lower, by a combination of (A-1) an alicyclic epoxy resin and (B-1) a polyalkylene glycol having a molecular weight of 200 or more and 1000 or less. And such a cured product is suitable for forming a circuit in a printed wiring board, filling a via, adhering a substrate and an electronic element, and the like.

[0047] In the above, one embodiment was shown as an example, but the conductive composition according to the present invention is not limited to the configuration of the above embodiment. 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.

Examples

[0048] Hereinafter, the present invention will be further described by way of examples, but the present invention is not limited thereto.

[0049] [Raw materials used] (A-1) Alicyclic epoxy resin 1 (ester-type alicyclic epoxy resin): 3,4-epoxycyclohexylmethyl (3,4-epoxy) cyclohexanecarboxylate (manufactured by Daicel Corporation, Celoxide (registered trademark) 2021P) (A-1) Alicyclic epoxy resin 2 (condensed-ring type alicyclic epoxy resin): tetrahydroindene diepoxide NBR-modified epoxy resin (manufactured by ADEKA Corporation, Adeka Resin (registered trademark) EPR-4030, 40% by mass of NBR-modified epoxy resin, 60% by mass of bisphenol A type epoxy resin) (B-1) Polyalkylene glycol 1: polyethylene glycol (molecular weight 200, hydroxyl equivalent 100 g / eq): Potethylene glycol 200, manufactured by Wako Pure Chemical Industries, Ltd. (C) Cationic polymerization initiator 1: salt of aromatic sulfonium and hexafluoroantimonate, manufactured by Sanshin Chemical Industry Co., Ltd., Sun-Aid (registered trademark) SI-100 (C) Cationic polymerization initiator 2: 1-naphthylmethylmethyl p-hydroxyphenylsulfonium = hexafluorophosphate, manufactured by Sanshin Chemical Industry Co., Ltd., Sun-Aid (registered trademark) SI-360 (D) Conductive particles: silver powder, flake-shaped, average particle diameter 6 μm

[0050] [Measurement of the molecular weight of (B) polyol] Apparatus: Alliance GPC System Column: KF-802 + KF-803 connected column Exclusion limit molecular weight: 2,000,000 Column packing agent: styrene divinylbenzene copolymer (particle size: 6 μm) Column size: 8 mm I.D. × 300 mL Apparatus settings: detector wavelength (2D) 254 nm, detector temperature 40 °C, oven temperature 40 °C, flow rate 1 mL / min, solvent THF, injection volume 0.01 mL Sample preparation: The sample is dissolved in THF to a concentration of 1% by mass and filtered through a syringe filter (PTFE, diameter 25 mm, pore size 0.45 μm).

[0051] [Production Example] Each component was blended at the blending ratios shown in Table 1 to prepare a conductive composition.

[0052] [Method for Measuring Conductivity] The conductivity was evaluated by measuring the resistance value of the cured product formed using the prepared conductive composition. Specifically, the conductive composition was line-printed (length 60 mm, width 1 mm, thickness approximately 100 μm, 5 lines per substrate) on a 100 mm × 65 mm glass epoxy substrate using a metal plate. Next, heat treatment was performed at 120°C for 30 minutes using a hot air drying oven to cure the conductive composition and prepare a measurement sample. For this measurement sample, the resistance value (Ω) at both ends was measured using a four-terminal method electrical resistance measuring instrument.

[0053] [Evaluation: Conductivity after Heat Cycle (HC) Test] Apparatus: Chamber-type temperature cycle tester (manufactured by Kusumoto Chemical Co., Ltd., ETAC WINTECH NEO NT1050A) Evaluation method: The initial measurement sample for conductivity evaluation used in Evaluation 1 was subjected to 300 heat cycles of 30 minutes at -40°C and 30 minutes at 85°C. The resistance value of the sample after the heat cycle test was measured and the average value was calculated, and the change rate with respect to the initial resistance value before the heat cycle was determined and evaluated according to the following evaluation criteria. The results are as shown in Table 1. (Evaluation Criteria) ○: The change rate of the resistance value is within -30% to 10% ×: The change rate of the resistance value exceeds -30% to 10%

[0054]

Table 1

Claims

1. comprising (A) an epoxy resin, (B) a polyol, (C) a cationic polymerization initiator, and (D) conductive particles, wherein the (A) epoxy resin includes an alicyclic epoxy resin (A-1), and the (B) polyol includes a polyalkylene glycol (B-1) having a molecular weight of 200 or more and 1000 or less, a conductive composition.

2. The conductive composition according to claim 1, wherein the (A-1) alicyclic epoxy resin has an epoxy cycloalkyl group.

3. The conductive composition according to claim 1 or 2, wherein the (B-1) polyalkylene glycol is polyethylene glycol.

4. The conductive composition according to claim 3, wherein the content of the polyethylene glycol is 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the (A) epoxy resin.

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