conductive adhesive

Abstract

To provide a conductive adhesive that is suitably usable for a jet dispenser and has low viscosity, and can maintain a fixed discharge shape and discharge amount, prevents clogging of a nozzle and can be continuously discharged, provides a quickly cured coated film and is excellent in bond strength and electric characteristics of the cured coated film.SOLUTION: A conductive adhesive contains silver powder in which flaky silver powder and spherical silver powder are mixed in a mass ratio of 40:60 to 60:40, an epoxy resin which is composed of an alicyclic epoxy resin and a bisphenol A type liquid epoxy resin, and a curing agent, wherein the content of the silver powder in the conductive adhesive is 75 pts.mass to 85 pts.mass, and the thixotropy value is 2.0-3.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive adhesive for joining electronic components. More specifically, it relates to a low-viscosity conductive adhesive that can be suitably used in a jet dispenser, which can maintain a constant discharge shape and discharge volume, is less prone to nozzle clogging and can be dispensed continuously, and moreover, the adhesive hardens quickly and the bond strength and conductivity of the hardened adhesive film are excellent. [Background technology]

[0002] As electronic devices become smaller, the miniaturization of the electronic components they contain is also accelerating.

[0003] When joining capacitor elements and other components to a lead frame, it is common practice to apply a conductive adhesive containing conductive filler using a dispenser. However, recently, there has been an increase in the use of jet dispensers, which allow for more precise and minute application.

[0004] While jet dispensers allow for control of the dispensing volume, similar to conventional dispensers, if the viscosity of the conductive adhesive is too high, it becomes difficult to maintain a consistent dispensing shape and volume, resulting in inconsistencies.

[0005] Variations in the discharge shape and volume can lead not only to cosmetic defects but also to paint peeling and short circuits in electrical circuits.

[0006] Generally, the viscosity of conductive adhesives can be reduced by adjusting the solvent content.

[0007] Solvent-free conductive adhesives can have their viscosity reduced by increasing the particle size of the conductive filler and decreasing its specific surface area. However, larger particle sizes make it easier for the nozzle of a jet dispenser to clog, which makes it difficult to maintain a consistent discharge shape and volume.

[0008] In particular, in microcoating, there is a problem that continuous coating cannot be performed when the nozzle becomes clogged.

[0009] Although a highly viscous conductive adhesive can also be applied with a jet dispenser, in order to discharge the highly viscous conductive adhesive from the nozzle, it is necessary to increase the pressure during discharge. However, if the pressure is high, there is a problem that it becomes difficult to maintain a constant discharge shape and discharge amount.

[0010] Therefore, there is a need to develop a low-viscosity conductive adhesive that can be suitably used for jet dispenser coating, which can maintain a constant discharge shape and discharge amount, is less likely to become clogged and can be continuously discharged, and moreover, has a fast curing speed of the coating film and excellent bonding strength and conductivity of the cured coating film.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] Patent Document 1 describes a conductive adhesive containing conductive particles, a solvent, a thermosetting resin, and silica particles having an average particle size of 1 to 50 nm and having high fluidity.

[0013] However, since the conductive adhesive described in Patent Document 1 contains a solvent, bubbles may occur in the coating film during thermosetting. If bubbles occur, there is a risk that the bonding strength or electrical characteristics may decrease, so it cannot be used in the process of thermosetting at high temperature for a short time.

[0014] The inventors have made solving the aforementioned problems a technical challenge, and as a result of numerous trial-and-error prototypes and experiments, they have found a remarkable finding that a conductive adhesive containing silver powder mixed in a mass ratio of 40:60 to 60:40, an epoxy resin consisting of an alicyclic epoxy resin and a bisphenol A type liquid epoxy resin, and a curing agent, wherein the silver powder content in the conductive adhesive is 75 parts by mass or more and 85 parts by mass or less, and the thixotropy of the conductive adhesive is 2.0 or more and 3.0 or less, is suitable for use in a jet dispenser, is a low-viscosity conductive adhesive that can maintain a constant discharge shape and discharge volume, is less prone to clogging and can be dispensed continuously, and moreover, the coating film hardens quickly, and the bond strength and conductivity of the hardened coating film are excellent, thus achieving the aforementioned technical challenge. [Means for solving the problem]

[0015] The aforementioned technical problems can be solved by the present invention as follows.

[0016] The present invention relates to a conductive adhesive containing silver powder, epoxy resin, and a curing agent, wherein the silver powder is a mixture of flake-shaped silver powder and spherical silver powder in a mass ratio of 40:60 to 60:40, the epoxy resin is an epoxy resin consisting of an alicyclic epoxy resin and a bisphenol A type liquid epoxy resin, the content of the silver powder in the conductive adhesive is 75 parts by mass or more and 85 parts by mass or less, and the thixotropy of the conductive adhesive is 2.0 or more and 3.0 or less.

[0017] Furthermore, the present invention relates to the conductive adhesive described above, wherein the epoxy resin is 50 parts by mass or less (but not including 0 parts by mass) of bisphenol A type liquid epoxy resin per 100 parts by mass of alicyclic epoxy resin.

[0018] Furthermore, the present invention relates to the conductive adhesive in which the curing agent is a sulfonium cation-based curing agent.

[0019] Furthermore, the present invention provides that the flake-shaped silver powder has an apparent density of 3.1 g / cm³. 3 In summary, the tap density is 5.5 g / cm³. 3 The above-mentioned conductive adhesive has a laser 50% particle size of 5.0 μm or larger.

[0020] Furthermore, the present invention provides that the flake-shaped silver powder has a BET specific surface area of ​​0.4 m². 2 The conductive adhesive has a particle size of 50% of the laser particles of 5.0 μm or more and a particle size of 50% of the laser particles of 1 / g or less.

[0021] Furthermore, the present invention provides that the spherical silver powder has an apparent density of 3.0 g / cm³. 3 In summary, the BET specific surface area is 0.4m². 2 The conductive adhesive has a particle size of 3.0 μm or more and a laser 50% particle size of 3.0 μm or more. [Effects of the Invention]

[0022] The present invention provides a conductive adhesive that contains silver powder, which is a mixture of flake-shaped silver powder and spherical silver powder in a mass ratio of 40:60 to 60:40, and an epoxy resin consisting of an alicyclic epoxy resin and a bisphenol A type liquid epoxy resin, and has low viscosity even when containing 75 to 85 parts by mass of silver powder.

[0023] Furthermore, because it contains a hardening agent, the coating hardens quickly, and because it does not contain solvents, it is less likely to generate bubbles even in high-temperature heat curing processes, resulting in a coating with excellent bonding strength. As a conductive adhesive, it can be suitably used in processes that require high-temperature, short-time heat curing.

[0024] Furthermore, because it contains 75 to 85 parts by mass of silver powder, it is a conductive adhesive with excellent conductivity.

[0025] Furthermore, because its thixotropic value is low (2.0-3.0), this conductive adhesive can maintain a consistent discharge shape and volume when applied with a jet dispenser.

[0026] Furthermore, the apparent density of the flake-shaped silver powder is 3.1 g / cm³. 3 In summary, the tap density is 5.5 g / cm³. 3If the laser 50% particle diameter is 5.0 μm or more as described above, it becomes a low-viscosity conductive adhesive that can be suitably used for jet dispenser coating.

[0027] Also, when the BET specific surface area of the flaky silver powder is 0.4 m 2 / g or less and the laser 50% particle diameter is 5.0 μm or more, the thixotropy value does not increase, so when used in a jet dispenser, it becomes a conductive adhesive that can better maintain a certain discharge shape.

[0028] Also, when the apparent density of the spherical silver powder is 3.0 g / cm 3 or more, the BET specific surface area is 0.4 m 2 / g or less, and the laser 50% particle diameter is 3.0 μm or more, the thixotropy value does not increase, so when used in a jet dispenser, it becomes a conductive adhesive that can better maintain a certain discharge shape.

Mode for Carrying Out the Invention

[0029] The present invention is a solvent-free conductive adhesive containing silver powder, an epoxy resin, and a curing agent and not containing a solvent.

[0030] The silver powder in the present invention is a silver powder obtained by mixing flaky silver powder and spherical silver powder.

[0031] The flaky silver powder preferably has an apparent density of 3.1 g / cm 3 or more, a tap density of 5.5 g / cm 3 or more, and a laser 50% particle diameter of 5.0 μm or more. More preferably, the apparent density is 3.6 g / cm 3 or more, the tap density is 5.8 g / cm 3 or more, and the laser 50% particle diameter is 6.4 μm or more.

[0032] If the apparent density is less than 3.1 g / cm 3 or the tap density is less than 5.5 g / cm 3 or the laser 50% particle diameter is less than 5.0 μm, there is a risk that the viscosity of the conductive adhesive will become too high.

[0033] Furthermore, the BET specific surface area of ​​the flake-shaped silver powder is 0.4 m². 2 Preferably, the particle size is less than or equal to / g, and the laser 50% particle diameter is 5.0 μm or larger, and more preferably, the BET specific surface area is 0.23 m². 2 The particle size is less than / g, and the laser 50% particle size is 6.4 μm or larger.

[0034] BET specific surface area is 0.4m 2 If the value is greater than / g, or if the laser 50% particle size is less than 5.0 μm, the thixotropic value (viscosity at 1 rpm / viscosity at 10 rpm) increases, which worsens the ejection shape, causing it to become teardrop-shaped instead of circular, or causing droplets to split into multiple droplets and adhere to positions away from the center.

[0035] To achieve a desirable viscosity and thixotropy of the conductive adhesive, the flake-shaped silver powder should have an apparent density of 3.1 g / cm³. 3 ~4.9g / cm 3 The tap density is 5.5 g / cm³. 3 ~6.5g / cm 3 BET specific surface area is 0.1m 2 / g~0.4m 2 The laser 50% particle size is preferably 5.0 μm to 9.0 μm, and more preferably the apparent density is 3.6 g / cm³. 3 ~4.2g / cm 3 The tap density is 5.8 g / cm³. 3 ~6.2g / cm 3 The BET specific surface area is 0.16 m². 2 / g~0.23m 2 The particle size at 50% of the laser output per g is 6.4 μm to 8.5 μm.

[0036] The spherical silver powder in this invention has an apparent density of 3.0 g / cm³. 3 In addition, the BET specific surface area is 0.4m². 2 Preferably, the density is less than or equal to / g, the laser 50% particle size is 3.0 μm or larger, and more preferably, the apparent density is 3.3 g / cm³. 3 In addition, the BET specific surface area is 0.25 m². 2 The particle size is less than / g, and the laser 50% particle diameter is 3.2 μm or larger.

[0037] The apparent density is 3.0 g / cm³. 3 Less than, or BET specific surface area 0.4m² 2 This is because if the value is greater than / g, or if the laser 50% particle diameter is less than 3.0 μm, the thixotropic value will increase and the ejection shape will deteriorate.

[0038] To achieve a desirable viscosity and thixotropy of the conductive adhesive, the spherical silver powder should have an apparent density of 3.0 g / cm³. 3 ~6.0g / cm 3 The tap density is 5.0 g / cm³. 3 ~7.0g / cm 3 BET specific surface area is 0.1m 2 / g~0.4m 2 The laser 50% particle size is preferably in the range of 3.0 μm to 6.0 μm, and more preferably the apparent density is 3.3 g / cm³. 3 ~4.9g / cm 3 The tap density is 5.8 g / cm³. 3 ~6.7g / cm 3 The BET specific surface area is 0.18 m². 2 / g~0.25m 2 The laser particle size at 50% of the particle size ranges from 3.2 μm to 5.0 μm.

[0039] The apparent density can be measured by the method specified in JIS Z 2504.

[0040] The BET specific surface area can be measured using the BET method with a fluid-type automatic specific surface area measuring device or the like.

[0041] The 50% particle diameter obtained by laser analysis can be obtained by measuring the 50% average particle diameter using a laser diffraction particle size distribution analyzer or similar device.

[0042] Tap density can be measured by placing a predetermined amount (g) of silver powder into a graduated cylinder and tapping it for 20 minutes using a tap density measuring instrument in accordance with ISO 3953.

[0043] The silver powder used in this invention is a mixture of flake-shaped silver powder and spherical silver powder in a mass ratio of 40:60 to 60:40.

[0044] This is because deviating from the aforementioned mixing ratio may result in inconsistent discharge shape and volume when applied with a jet dispenser, potentially leading to variations.

[0045] The silver powder content in the conductive adhesive of the present invention is preferably 75 to 85 parts by mass, and more preferably 76 to 80 parts by mass.

[0046] This is because if the amount is less than 75 parts by mass, the conductivity will be poor, and if it exceeds 85 parts by mass, the viscosity will be high.

[0047] The epoxy resin in this invention is an epoxy resin obtained by mixing an alicyclic epoxy resin and a bisphenol A type liquid epoxy resin.

[0048] The alicyclic epoxy resin is not particularly limited, but examples include Celoxide 2081 (manufactured by Daicel Corporation) and TTA-26E (manufactured by Sun Chemical Co., Ltd.).

[0049] The bisphenol A type liquid epoxy resin is not particularly limited, but jER828 (manufactured by Mitsubishi Chemical Corporation) can be used as an example.

[0050] The preferred mixing ratio of alicyclic epoxy resin to bisphenol A type liquid epoxy resin is 50 parts by mass or less of bisphenol A type liquid epoxy resin per 100 parts by mass of alicyclic epoxy resin.

[0051] This is because the viscosity increases as the content of bisphenol A type liquid epoxy resin increases.

[0052] In the present invention, a sulfonium cation-based curing agent is preferred.

[0053] While the sulfonium cation-based curing agent is not particularly limited, San-Aid SI-60L (manufactured by Sanshin Chemical Industry Co., Ltd.) is given as an example.

[0054] The content of the curing agent in the conductive adhesive of the present invention is preferably 0.2 to 5.0 parts by mass, and more preferably 1.0 to 3.0 parts by mass.

[0055] The thixotropy of the conductive adhesive in this invention is in the range of 2.0 to 3.0.

[0056] If the thixotropy value is lower than 2.0, the conductive adhesive may drip and not be applied properly, and if it is higher than 3.0, the shape after application will be unstable.

[0057] In this invention, the thixotropic value (TI value) is obtained by measuring the viscosity of the conductive adhesive at 1 rpm and 10 rpm at 25°C using a rotational viscometer HBDV-III spindle CPE-42 (manufactured by Brookfield Corporation) and calculating the values ​​in the following equation (Equation 1).

[0058] (Equation 1) TI value = viscosity at 1 rpm (dPa·s) / viscosity at 10 rpm (dPa·s) [Examples]

[0059] Examples of the present invention are shown below, but the present invention is not limited thereto.

[0060] (Flake-shaped silver powder) Flake-shaped silver particles can be produced by placing granular silver powder with an average particle size of 0.5 μm to 10.0 μm into a ball mill equipped with stirring blades and rotating the stirring blades to create flakes.

[0061] The magnitude of the centrifugal force applied to the contents of the container in a ball mill is not particularly limited, but the stirring blades should be rotated so that a centrifugal force of 5G to 300G is applied to the contents of the container.

[0062] Alternatively, well-known metallic balls may be added to the stirring ball mill.

[0063] (spherical silver powder) The spherical silver powder is not particularly limited, and spherical silver powder obtained by conventionally known methods such as atomization, electrolysis, or chemical reduction can be used.

[0064] Various solvents and treatment agents can be added to a stirring ball mill during stirring to adjust particle size and other parameters.

[0065] The solvents to be added are not limited, but examples include water, methanol, ethanol, propanol, butanol, pentanol, dimethyl ketone, diethyl ketone, diethyl ether, dimethyl ether, diphenyl ether, toluene, and xylene. These solvents may be used individually or in appropriate combinations of two or more.

[0066] The treatment agents to be added are not particularly limited, but examples include nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and sorbitan fatty acid esters. These treatment agents may be used individually or in appropriate combinations of two or more types.

[0067] Furthermore, fatty acids such as oleic acid, stearic acid, and myristic acid can be used as processing agents. These fatty acids may be used individually or in appropriate combinations of two or more types.

[0068] The manufactured flake-shaped silver powder and spherical silver powder were measured using the following method.

[0069] (apparent density) Measurements were taken in accordance with JIS Z 2504:2000. That is, using a funnel with a 5mm orifice, the inner diameter is 28±0.5mm and the volume is 25±0.03cm³. 3 Flake-shaped or spherical silver powder was poured into a cylindrical cup, and the mass of each type of silver powder in the cup was calculated using the following formula (Equation 2).

[0070] (Formula 2) Apparent density (g / cm 3 ) = Mass of silver powder in the cup (g) / Volume of the cup (25cm³) 3 )

[0071] The apparent density of the flake-shaped silver powder is 4.19 g / cm³. 3 The apparent density of the spherical silver powder is 4.76 g / cm³. 3 That was the case.

[0072] (Tap density) The tap density was calculated using the following formula (Equation 3) after placing a predetermined amount (g) of powder into a graduated cylinder and tapping it for 20 minutes using a tap density measuring instrument in accordance with ISO 3953:1993.

[0073] (Equation 3) Tap density (g / cm³) 3 ) = specified amount (g) / volume of powder after tapping (cm³) 3 )

[0074] The tap density of the flake-shaped silver powder is 6.15 g / cm³. 3 The tap density of the spherical silver powder is 6.56 g / cm³. 3 That was the case.

[0075] (Laser 50% particle size) The 50% average particle size of each silver powder was measured using a laser diffraction particle size distribution analyzer SALD-3100 (manufactured by Shimadzu Corporation) and defined as the laser 50% particle size.

[0076] The 50% laser particle size for flake-shaped silver powder was 7.0 μm, and the 50% laser particle size for spherical silver powder was 4.8 μm.

[0077] (BET specific surface area) Each silver powder was measured for its specific surface area using the BET method with a flow-type automatic specific surface area measuring device, Flowsaw II2100 (manufactured by Shimadzu Corporation).

[0078] The BET specific surface area of ​​flake-shaped silver powder is 0.23 m². 2The BET specific surface area of ​​spherical silver powder is 0.19 m² / g. 2 It was / g.

[0079] (Thixotropic value) The viscosity of conductive adhesives at 1 rpm and 10 rpm was measured using a rotational viscometer HBDV-III with spindle CPE-42 (Brookfield Corporation) at 25°C, and the thixotropic value was calculated by dividing the 1 rpm / 10 rpm values.

[0080] (Epoxy resin) For the alicyclic epoxy resin, we used Celoxide 2081 (manufactured by Daicel Corporation).

[0081] The bisphenol A type liquid epoxy resin used was jER828 (manufactured by Mitsubishi Chemical Corporation).

[0082] (Hardening agent) The hardening agent used was San-Aid SI-60L (manufactured by Sanshin Chemical Industry Co., Ltd.).

[0083] Flake-shaped silver powder, spherical silver powder, epoxy resin, and hardener were mixed and stirred in a rotary mixer as shown in Table 1 to obtain conductive adhesives for the examples and comparative examples.

[0084] The following evaluations were performed on each of the obtained conductive adhesives.

[0085] (Discharge shape) The product was evaluated by dispensing it from a jet dispenser designed for micro-dispensing.

[0086] We evaluated the discharge shape as follows: circular dispensers were marked with a circle (○), while teardrop-shaped dispensers, those with two separated droplets, and those with an irregular shape were marked with a cross (×).

[0087] (Continuous dispensing) We performed 1200 consecutive discharges to check for clogging and discharge pattern.

[0088] We evaluated products that clogged midway or failed to maintain a consistent discharge shape as "X" (indicating failure), and all others as "O" (indicating success).

[0089] (Electrical characteristics) Each conductive adhesive was used with a solid electrolytic capacitor, and the equivalent series resistance (ESR) at 100 kHz was measured using an LCR meter. This value was defined as the initial ESR.

[0090] Furthermore, a high-temperature storage test at 125°C for 500 hours was conducted as a reliability test for these solid electrolytic capacitor elements, and the ESR at 100kHz was measured after the test and recorded as the post-test ESR.

[0091] Products that met the specified standards for both initial and post-test ESR were marked with a circle (○), while all others were marked with a cross (×).

[0092] The results are shown in Table 1.

[0093] [Table 1]

[0094] Table 1 shows that the conductive adhesive of the present invention can be suitably used in a jet dispenser, maintains a constant discharge shape and discharge volume, exhibits excellent bonding strength and conductivity of the coating film, and is a low-viscosity conductive adhesive that is less prone to clogging even when dispensed continuously. [Industrial applicability]

[0095] The conductive adhesive in the present invention is a low-viscosity conductive adhesive that can be suitably used for jet dispenser application, and can maintain a constant discharge shape and discharge volume, and is less prone to nozzle clogging, allowing for continuous discharge. Furthermore, it is a conductive adhesive that hardens quickly and exhibits excellent bonding strength and conductivity of the hardened coating film. Therefore, the present invention is highly applicable to industry.

Claims

1. A conductive adhesive comprising silver powder, epoxy resin, and a curing agent, wherein the silver powder is a mixture of flake-shaped silver powder and spherical silver powder in a mass ratio of 40:60 to 60:40, the epoxy resin is an epoxy resin comprising an alicyclic epoxy resin and a bisphenol A type liquid epoxy resin, the content of the silver powder in 100 parts by mass of the conductive adhesive is 75 parts by mass or more and 85 parts by mass or less, and the thixotropy of the conductive adhesive is 2.0 or more and 3.0 or less.

2. The conductive adhesive according to claim 1, wherein the epoxy resin is an epoxy resin in which 50 parts by mass or less (but not including 0 parts by mass) of bisphenol A type liquid epoxy resin is present per 100 parts by mass of alicyclic epoxy resin.

3. The conductive adhesive according to claim 1 or 2, wherein the curing agent is a sulfonium cation-based curing agent.

4. The aforementioned flake-like silver powder has an apparent density of 3.1 g / cm³. ３ In summary, the tap density is 5.5 g / cm³. ３ The conductive adhesive according to any one of claims 1 to 3, wherein the laser 50% particle size is 5.0 μm or larger.

5. The aforementioned flake-shaped silver powder has a BET specific surface area of ​​0.4 m². ２ A conductive adhesive according to any one of claims 1 to 4, wherein the amount is less than or equal to / g and the laser 50% particle size is 5.0 μm or larger.

6. The aforementioned spherical silver powder has an apparent density of 3.0 g / cm³. ３ The above BET specific surface area is 0.4 m². ２ A conductive adhesive according to any one of claims 1 to 5, wherein the amount is less than or equal to / g and the laser 50% particle size is 3.0 μm or larger.

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