JP2023076211A - conductive adhesive - Google Patents

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 The present invention relates to a conductive adhesive for bonding electronic components. More specifically, it is a low-viscosity conductive adhesive that can be suitably used in a jet dispenser, can maintain a constant discharge shape and discharge rate, and can be discharged continuously because clogging of the nozzle is unlikely to occur. The present invention relates to a conductive adhesive that cures quickly and has excellent bonding strength and conductivity of a cured coating film.

As electronic devices become smaller, the size of electronic components mounted on them is also becoming smaller.

When connecting a capacitor element to a lead frame, it is common to apply a conductive adhesive containing conductive filler with a dispenser. is increasing.

Jet dispensers can control the discharge amount in the same way as ordinary dispensers. However, if the viscosity of the conductive adhesive is too high, a constant discharge shape and discharge amount cannot be maintained, resulting in variations.

Variation in ejection shape and ejection amount may cause not only poor appearance, but also peeling of the coating film and short-circuiting of electric circuits.

In general, the viscosity of the conductive adhesive can be lowered by adjusting the content of the solvent.

Solvent-free conductive adhesives can reduce the viscosity by increasing the particle size of the conductive filler to reduce the specific surface area. Therefore, there is a problem that it becomes difficult to maintain a constant ejection shape and ejection amount.

In particular, there is a problem in microcoating that continuous coating cannot be performed if the nozzle is clogged.

A jet dispenser can be used to apply a high-viscosity conductive adhesive, but in order to eject a high-viscosity conductive adhesive from a nozzle, it is necessary to increase the pressure during ejection.
However, when the pressure is high, there is a problem that it becomes difficult to maintain a constant ejection shape and ejection amount.

Therefore, it is a low-viscosity conductive adhesive that can be suitably used for jet dispenser application, can maintain a constant discharge shape and discharge amount, is difficult to cause clogging, and can be discharged continuously. There is a demand for the development of a conductive adhesive that cures quickly, and has excellent bonding strength and electrical conductivity of the cured coating film.

JP 2020-139020

Patent Document 1 describes a highly fluid conductive adhesive containing conductive particles, a solvent, a thermosetting resin, and silica particles having an average particle size of 1 to 50 nm.

However, since the conductive adhesive described in Patent Document 1 contains a solvent, air bubbles may be generated in the coating film during heat curing. There is a problem that it cannot be used in a process in which heat curing is performed at a high temperature in a short period of time.

The inventors of the present invention have made it a technical task to solve the above-mentioned problems, and as a result of numerous trial and error trials and experiments, flaky silver powder and spherical silver powder are mixed at a mass ratio of 40:60 to 60:40. A conductive adhesive containing mixed silver powder, an epoxy resin composed of an alicyclic epoxy resin and a bisphenol A liquid epoxy resin, and a curing agent, wherein the content of the silver powder in the conductive adhesive is A conductive adhesive that is 75 parts by mass or more and 85 parts by mass or less and has a thixotropic value of 2.0 or more and 3.0 or less is preferably used for a jet dispenser. It is a low-viscosity conductive adhesive that can maintain a constant discharge shape and discharge volume, and can be discharged continuously because clogging is unlikely to occur. The present inventors have achieved the above-mentioned technical problems by obtaining remarkable knowledge that the conductive adhesive can be excellent in film bonding strength and conductivity.

The above technical problems can be solved by the present invention as follows.

The present invention provides a conductive adhesive containing silver powder, an epoxy resin, and a curing agent, wherein the silver powder is silver powder obtained by mixing flaky silver powder and spherical silver powder at a mass ratio of 40:60 to 60:40, and The epoxy resin is an epoxy resin composed of an alicyclic epoxy resin and a bisphenol A 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 The conductive adhesive has a thixotropic value of 2.0 or more and 3.0 or less.

Further, in the present invention, the above conductive adhesive is an epoxy resin containing 50 parts by mass or less (but not including 0 parts by mass) of bisphenol A liquid epoxy resin per 100 parts by mass of alicyclic epoxy resin. is an agent.

The present invention also provides the conductive adhesive, wherein the curing agent is a sulfonium cationic curing agent.

In the present invention, the flaky silver powder 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. Glue.

Further, the present invention is the conductive adhesive, wherein the flaky silver powder has a BET specific surface area of 0.4 m ² /g or less and a laser 50% particle size of 5.0 μm or more.

Further, in the present invention, the spherical silver powder has an apparent density of 3.0 g/cm ³ or more, a BET specific surface area of 0.4 m ² /g or less, and a laser 50% particle diameter of 3.0 μm or more. Glue.

The present invention contains an epoxy resin composed of silver powder obtained by mixing flaky silver powder and spherical silver powder at a mass ratio of 40:60 to 60:40, an alicyclic epoxy resin, and a bisphenol A type liquid epoxy resin, and contains the silver powder. Even if it contains 75 to 85 parts by mass, it is a conductive adhesive with low viscosity.

In addition, since it contains a curing agent, the coating film cures quickly, and since it does not contain a solvent, air bubbles are less likely to occur even in the high-temperature thermosetting process, and it is a conductive adhesive that forms a coating film with excellent bonding strength. It can also be suitably used in a step of thermosetting in a short time.

Moreover, since it contains 75 to 85 parts by mass of silver powder, it is a conductive adhesive with excellent electrical conductivity.

In addition, since the thixotropic value is as low as 2.0 to 3.0, it is a conductive adhesive that can maintain a constant ejection shape and ejection amount by jet dispenser application.

In addition, if the flaky silver powder 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 size of 5.0 μm or more, it is preferably used by jet dispenser application. It becomes a low-viscosity conductive adhesive that can be

In addition, 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 thixotropic value does not increase, so when used in a jet dispenser, a certain ejection shape can be obtained. It becomes a conductive adhesive that can maintain the

In addition, when the spherical silver powder has an apparent density of 3.0 g/cm ³ or more, a BET specific surface area of 0.4 m ² /g or less, and a laser 50% particle diameter of 3.0 μm or more, the thixotropic value does not increase, so the jet dispenser It becomes a conductive adhesive that can maintain a constant discharge shape more when used in .

The present invention is a solventless conductive adhesive containing silver powder, an epoxy resin and a curing agent and containing no solvent.

The silver powder in the present invention is silver powder obtained by mixing flaky silver powder and spherical silver powder.

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. 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 size is 6.4 μm or more.

If the apparent density is less than 3.1 g/cm ³ , the tap density is less than 5.5 g/cm ³ , or the laser 50% particle size is less than 5.0 μm, the viscosity of the conductive adhesive may become too high. because there is

In addition, the BET specific surface area of the flaky silver powder is preferably 0.4 m ² /g or less, and the laser 50% particle diameter is preferably 5.0 μm or more, more preferably 0.23 m ² /g or less, the laser A 50% particle size is 6.4 μm or more.

When the BET specific surface area is greater than 0.4 m ² /g or the laser 50% particle diameter is less than 5.0 μm, the thixotropic value (1 rpm viscosity/10 rpm viscosity) increases, and the ejection shape does not become circular. This is because the droplet becomes tear-shaped, or the droplet is divided into a plurality of droplets and adheres to a position away from the center, which deteriorates the droplet.

In order to make the viscosity and thixotropic value of the conductive adhesive within the preferable ranges, the flaky silver powder has an apparent density of 3.1 g/cm ³ to 4.9 g/cm ³ and a tap density of 5.5 g/cm ^{3 .} up to 6.5 g/cm ³ , a BET specific surface area of 0.1 m ² /g to 0.4 m ² /g, a laser 50% particle size of 5.0 μm to 9.0 μm, more preferably an apparent density of 3.6 g/cm ³ to 4.2 g/cm ³ , tap density of 5.8 g/cm ³ to 6.2 g/cm ³ , BET specific surface area of 0.16 m ^{2 /g} to 0.23 m ² /g, laser The 50% particle size is 6.4 μm to 8.5 μm.

The spherical silver powder in the present invention preferably has an apparent density of 3.0 g/cm ³ or more, a BET specific surface area of 0.4 m ² /g or less, and a laser 50% particle diameter of 3.0 μm or more. It has a density of 3.3 g/cm ³ or more, a BET specific surface area of 0.25 m ² /g or less, and a laser 50% particle diameter of 3.2 μm or more.

If the apparent density is less than 3.0 g/cm ³ , or the BET specific surface area is greater than 0.4 m ² /g, or the laser 50% particle size is less than 3.0 μm, the thixotropic value increases and the ejection shape This is because the

In order to keep the viscosity and thixotropic value of the conductive adhesive within the preferable range, the spherical silver powder has an apparent density of 3.0 g/cm ³ to 6.0 g/cm ³ and a tap density of 5.0 g/cm 3 to 6.0 g/cm ³ . 7.0 g/cm ³ , a BET specific surface area of 0.1 m ² /g to 0.4 m ² /g, a laser 50% particle size of 3.0 μm to 6.0 μm, more preferably an apparent density is 3.3 g/cm ³ to 4.9 g/cm ³ , tap density is 5.8 g/cm ³ to 6.7 g/cm ³ , BET specific surface area is 0.18 m ^{2 /g} to 0.25 m ² /g, The laser 50% particle size ranges from 3.2 μm to 5.0 μm.

Apparent density can be measured by the method specified in JISZ2504.

The BET specific surface area can be measured by the BET method using a flow-type automatic specific surface area measuring device or the like.

The laser 50% particle size can be obtained by measuring the 50% average particle size using a laser diffraction particle size distribution analyzer or the like.

The tap density can be measured by putting a predetermined amount (g) of silver powder in a graduated cylinder and tapping for 20 minutes using a tap density measuring machine conforming to ISO3953.

The silver powder in the present invention is silver powder in which flaky silver powder and spherical silver powder are mixed at a mass ratio of 40:60 to 60:40.

This is because if the mixing ratio is out of the above range, there is a risk that a constant ejection shape and ejection amount cannot be maintained when the liquid is applied by a jet dispenser, resulting in variations.

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

This is because if the amount is less than 75 parts by mass, the electrical conductivity is deteriorated, and if the amount exceeds 85 parts by mass, the viscosity increases.

The epoxy resin in the present invention is an epoxy resin obtained by mixing an alicyclic epoxy resin and a bisphenol A liquid epoxy resin.

Although the alicyclic epoxy resin is not particularly limited, Celoxide 2081 (manufactured by Daicel Corporation) and TTA-26E (manufactured by Sun Chemical Co., Ltd.) are exemplified.

Although the bisphenol A type liquid epoxy resin is not particularly limited, jER828 (manufactured by Mitsubishi Chemical Corporation) can be exemplified.

The mixing ratio of the alicyclic epoxy resin and the bisphenol A liquid epoxy resin is preferably 50 parts by mass or less of the bisphenol A liquid epoxy resin per 100 parts by mass of the alicyclic epoxy resin.

This is because the higher the content of the bisphenol A liquid epoxy resin, the higher the viscosity.

The curing agent in the present invention is preferably a sulfonium cationic curing agent.

The sulfonium cationic curing agent is not particularly limited, but San-Aid SI-60L (manufactured by Sanshin Chemical Industry Co., Ltd.) is exemplified.

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

The thixotropic value of the conductive adhesive in the present invention ranges from 2.0 to 3.0.

This is because if the thixotropic value is lower than 2.0, the conductive adhesive may sag and may not be applied normally, and if the thixotropic value is higher than 3.0, the shape after application will be unstable.

The thixotropic value (TI value) in the present invention is obtained by measuring the viscosity of the conductive adhesive at 1 rpm and 10 rpm at 25 ° C. with a rotary viscometer HBDV-III spindle CPE-42 (manufactured by Brookfield). It is a value obtained by including in Equation 1).

(Formula 1) TI value = 1 rpm viscosity (dPa s) / 10 rpm viscosity (dPa s)

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

(flaky silver powder)
The flaky silver particles can be produced by putting granular silver powder having an average particle size of 0.5 μm to 10.0 μm into a ball mill equipped with a stirring blade and rotating the stirring blade to form flakes.

The magnitude of the centrifugal force applied to the contents of the vessel of the stirring ball mill is not particularly limited, but the stirring blades may be rotated so as to apply a centrifugal force of 5G to 300G to the contents of the vessel.

Moreover, well-known metallic balls may be put into the stirring ball mill.

(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.

Various solvents and various processing agents can be added to the agitation ball mill during agitation in order to adjust the particle size and the like.

The solvent to be introduced is not limited, but examples thereof 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 alone or in combination of two or more.

The treatment agent to be introduced is not particularly limited, but nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and sorbitan fatty acid esters are used. can be mentioned. These treating agents may be used alone or in combination of two or more.

Fatty acids such as oleic acid, stearic acid and myristic acid can also be used as the treating agent. These fatty acids may be used alone or in combination of two or more.

The produced flaky silver powder and spherical silver powder were measured by the following methods.

(apparent density)
Measured according to JISZ2504:2000.
That is, using a funnel with an orifice of 5 mm, flaky silver powder or spherical silver powder was poured into a cylindrical cup with an inner diameter of 28 ± 0.5 mm and a volume of 25 ± 0.03 cm ³ , and the mass of each silver powder in the cup was calculated as follows ( It was calculated by the formula 2).

(Formula 2) Apparent density (g/cm ³ ) = mass of silver powder in cup (g)/cup volume (25 cm ³ )

The apparent density of the flaky silver powder was 4.19 g/cm ³ and the apparent density of the spherical silver powder was 4.76 g/cm ³ .

(tap density)
A predetermined amount (g) of powder was placed in a graduated cylinder, tapped for 20 minutes using a tap density measuring machine conforming to ISO3953:1993, and the tap density was calculated by the following (Equation 3).

(Formula 3) Tap density (g/cm ³ ) = predetermined amount (g)/powder volume after tapping (cm ³ )

The tap density of the flaky silver powder was 6.15 g/cm ³ and the tap density of the spherical silver powder was 6.56 g/cm ³ .

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

The laser 50% particle size of the flaky silver powder was 7.0 μm, and the laser 50% particle size of the spherical silver powder was 4.8 μm.

(BET specific surface area)
For each silver powder, the specific surface area value was measured by the BET method using a flow type automatic specific surface area measuring device FLOWSO II 2100 (manufactured by Shimadzu Corporation).

The BET specific surface area of the flaky silver powder was 0.23 m ² /g, and the BET specific surface area of the spherical silver powder was 0.19 m ² /g.

(thixotropic value)
Measure the viscosity of the conductive adhesive at 1 rpm and 10 rpm at 25° C. with a rotary viscometer HBDV-III spindle CPE-42 (manufactured by Brookfield), and calculate the thixotropic value by calculating 1 rpm/10 rpm. bottom.

(Epoxy resin)
Celoxide 2081 (manufactured by Daicel Corporation) was used as an alicyclic epoxy resin.

As the bisphenol A type liquid epoxy resin, jER828 (manufactured by Mitsubishi Chemical Corporation) was used.

(curing agent)
San-Aid SI-60L (manufactured by Sanshin Chemical Industry Co., Ltd.) was used as a curing agent.

As shown in Table 1, flaky silver powder, spherical silver powder, epoxy resin, and curing agent were stirred and mixed in a revolutionary mixer to obtain conductive adhesives of Examples and Comparative Examples.

Each conductive adhesive obtained was evaluated as follows.

(Discharge shape)
Evaluation was made by ejecting from a jet dispenser for micro-application.

Those with a circular ejection shape were evaluated as ◯, and those with a teardrop shape, two droplets, or irregular shapes were evaluated as x.

(Continuous ejection)
Continuous ejection was performed 1200 times, and clogging and ejection shape were confirmed.

Those that clogged on the way or those that could not maintain a constant discharge shape were evaluated as x, and the others were evaluated as ◯.

(Electrical characteristics)
Each conductive adhesive was used for a solid electrolytic capacitor, an LCR meter was used to measure the equivalent series resistance (ESR) at 100 kHz, and this value was taken as the initial ESR.

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

When both the initial ESR and the ESR after the test satisfy the predetermined standards, the samples were rated as ◯, and the others were rated as x.

Table 1 shows the results.

From Table 1, the conductive adhesive in the present invention can be suitably used for a jet dispenser, can maintain a constant discharge shape and discharge rate, is excellent in bonding strength and conductivity of the coating film, and is continuous. It was proved to be a low-viscosity conductive adhesive that can be ejected continuously without causing clogging even if it is ejected in a continuous manner.

The conductive adhesive in the present invention is a low-viscosity conductive adhesive that can be suitably used for jet dispenser coating, and can maintain a constant discharge shape and discharge rate, and is less likely to clog nozzles. Therefore, it is a conductive adhesive that can be discharged continuously, cures the coating film quickly, and has excellent bonding strength and electrical conductivity of the cured coating film.
Therefore, the present invention is an invention with high industrial applicability.

Claims (6)

A conductive adhesive containing silver powder, an epoxy resin, and a curing agent, wherein the silver powder is silver powder obtained by mixing flaky silver powder and spherical silver powder at a mass ratio of 40:60 to 60:40, and the epoxy resin is an oil. An epoxy resin composed of a cyclic 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 conductive adhesive A conductive adhesive having a thixotropic value of 2.0 or more and 3.0 or less. 2. The conductive adhesive according to claim 1, wherein said epoxy resin contains 50 parts by weight or less (but not including 0 parts by weight) of bisphenol A liquid epoxy resin per 100 parts by weight of alicyclic epoxy resin. 3. The conductive adhesive according to claim 1, wherein said curing agent is a sulfonium cationic curing agent. 4. The flaky silver powder according to any one of claims 1 to 3, wherein the apparent density is 3.1 g/cm ³ or more, the tap density is 5.5 g/cm ³ or more, and the laser 50% particle diameter is 5.0 µm or more. Conductive adhesive. The conductive adhesive according to any one of claims 1 to 4, wherein the flaky silver powder has a BET specific surface area of 0.4 ^m2 /g or less and a laser 50% particle diameter of 5.0 µm or more. The conductive powder according to any one of claims 1 to 5, wherein the spherical silver powder has an apparent density of 3.0 g/cm ³ or more, a BET specific surface area of 0.4 m ² /g or less, and a laser 50% particle diameter of 3.0 µm or more. adhesive.