HK1191450B - Light-reflective anisotropic conductive adhesive and light-emitting device - Google Patents

Description

Light-reflective anisotropic conductive adhesive and light-emitting device

Technical Field

The present invention relates to a light-reflective anisotropic conductive adhesive for anisotropically and electrically connecting a light-emitting element to a wiring board, and a light-emitting device in which the light-emitting element is mounted on the wiring board using the adhesive.

Background

A light emitting device using a Light Emitting Diode (LED) element is widely used, and the structure of an old-fashioned light emitting device is configured as follows as shown in fig. 3: the LED element 33 is bonded to the substrate 31 with a die bonding adhesive (ダイボンド following) 32, the p-electrode 34 and the n-electrode 35 thereon are wire-bonded to the connection terminal 36 of the substrate 31 with a gold wire 37, and the entire LED element 33 is sealed with a transparent molding resin 38. However, in the case of the light emitting device of fig. 3, there are the following problems: of the light emitted from the LED element 33, the light having a wavelength of 400 to 500nm emitted to the upper surface side is absorbed by the gold wire, and a part of the light emitted to the lower surface side is absorbed by the die bonding adhesive 32, which lowers the light emission efficiency of the LED element 33.

Therefore, as shown in fig. 4, flip-chip mounting of the LED element 33 has been proposed (patent document 1). In this flip chip mounting technique, the p-electrode 34 and the n-electrode 35 are formed with bumps 39, respectively, and further, the bump formation surface of the LED element 33 is provided with a light reflection layer 40 for insulating the p-electrode 34 and the n-electrode 35. The LED element 33 and the substrate 31 are connected and fixed by curing them using an Anisotropic Conductive Paste (ACP) 41 or an Anisotropic Conductive Film (ACF) (not shown) using an epoxy resin as a binder resin. Therefore, in the light emitting device of fig. 4, the light emitted upward from the LED element 33 is not absorbed by the gold wire, and most of the light emitted downward is reflected by the light reflecting layer 40 and emitted upward, so that the light emission efficiency (light extraction efficiency) is not lowered.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 11-168235.

Disclosure of Invention

Problems to be solved by the invention

However, the technique of patent document 1 has the following problems: in order to insulate the p-electrode 34 and the n-electrode 35, the light reflection layer 40 must be provided on the LED element 33 by a metal deposition method or the like, and thus, a cost increase cannot be avoided in manufacturing.

On the other hand, when the light reflection layer 40 is not provided, there are also problems as follows: the surfaces of conductive particles coated with gold, nickel or copper in the cured ACP or ACF are brown or dark brown, and the epoxy resin adhesive in which the conductive particles are dispersed is brown due to the imidazole latent curing agent which is generally used for the curing, and it is difficult to improve the light emission efficiency (light extraction efficiency) of light emitted from the light emitting element.

In addition to the problems described above (the problem of increase in cost and the problem of light extraction efficiency), there is a further problem that cracks are generated in the anisotropic conductive connection portion and conduction reliability is lowered. That is, in the case of a light-emitting device obtained by anisotropically and electrically connecting the LED element 33 and the substrate 31 with such ACP or ACF, since an epoxy resin exhibiting a thermal expansion coefficient higher than that of the substrate 31 is used as a binder resin of the ACP or ACF, there are the following problems: as the ambient temperature of the light emitting device changes (for example, temperature changes in a reflow process, a thermal shock test, use/storage in a high temperature atmosphere, and the like due to a Pb-free solder), internal stress occurs in a cured ACP or ACF fixed to the substrate, and the anisotropic conductive connection portion cracks or the conduction reliability is lowered.

The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to improve light emission efficiency without providing a light-reflecting layer on a light-emitting diode (LED) element, which causes an increase in manufacturing cost, when a light-emitting device is manufactured by flip-chip mounting a light-emitting element such as an LED element on a wiring board using an anisotropic conductive adhesive, and to suppress or prevent a decrease in conduction reliability and the occurrence of cracks in an anisotropic conductive connection portion of the light-emitting device due to a change in ambient temperature.

Means for solving the problems

The present inventors have found that, when it is assumed that the light emission efficiency can be prevented from being lowered when the anisotropic conductive adhesive itself has a light reflection function: the light-emitting efficiency of the light-emitting element can be prevented from being lowered by blending the light-reflective insulating particles into the anisotropic conductive adhesive; in this case, the ability of the spherical light-reflective insulating particles to prevent a decrease in light emission efficiency is higher than that of the needle-shaped light-reflective insulating particles; on the other hand, the acicular light-reflective insulating particles are more effective for suppressing the decrease in conduction reliability of the anisotropic conductive connection part and the generation of cracks than the spherical light-reflective insulating particles; therefore, in order to achieve both improvement in light emission efficiency of the light-emitting element, suppression or prevention of reduction in conduction reliability, and suppression or prevention of occurrence of cracks, the present invention has been completed by setting a specific mixing ratio of the light-reflective needle-shaped insulating particles and the light-reflective spherical insulating particles.

That is, the present invention provides a light-reflective anisotropic conductive adhesive for anisotropically and electrically connecting a light-emitting element to a wiring board, comprising a thermosetting resin composition, conductive particles, light-reflective needle-like insulating particles, and light-reflective spherical insulating particles,

the amount of the light-reflective needle-shaped insulating particles and the amount of the light-reflective spherical insulating particles in the thermosetting resin composition are 1 to 50 vol% based on the thermosetting resin composition, and the ratio (V/V) of the light-reflective spherical insulating particles to the light-reflective needle-shaped insulating particles is 1:1 to 10.

Further, the present invention provides a light-emitting device in which a light-emitting element is flip-chip mounted on a wiring board via the light-reflective anisotropic conductive adhesive.

ADVANTAGEOUS EFFECTS OF INVENTION

In the light-reflective anisotropic conductive adhesive, the light-reflective needle-shaped insulating particles and the spherical insulating particles are respectively blended in an amount of 1 to 50 vol% based on the thermosetting resin composition, and the blending ratio (V/V) of the light-reflective spherical insulating particles to the light-reflective needle-shaped insulating particles is set to 1:1 to 10. Therefore, the light emitting efficiency can be improved without providing a light reflecting layer on the LED element, which increases the manufacturing cost, and the reduction of the conduction reliability and the occurrence of cracks in the anisotropic conductive connection portion of the light emitting device due to the change in the ambient temperature can be suppressed or prevented.

Drawings

Fig. 1A is a cross-sectional view of light-reflective conductive particles used in the light-reflective anisotropic conductive adhesive of the present invention.

Fig. 1B is a cross-sectional view of the light-reflective conductive particles used in the light-reflective anisotropic conductive adhesive of the present invention.

Fig. 2 is a sectional view of a light emitting device of the present invention.

Fig. 3 is a sectional view of a conventional light-emitting device.

Fig. 4 is a sectional view of a conventional light-emitting device.

Detailed Description

The light-reflective anisotropic conductive adhesive of the present invention is used for anisotropic conductive connection of a light-emitting element on a wiring board, and contains a thermosetting resin composition, conductive particles, light-reflective needle-shaped insulating particles, and light-reflective spherical insulating particles.

In the present invention, the reason why the light-reflective needle-shaped insulating particles and the light-reflective spherical insulating particles are used in combination as the light-reflective insulating particles is as follows.

As a general theory, when the light-reflective insulating particles are contained in the thermosetting resin composition, if the stretchability of the resin composition decreases (hardens) with a change in temperature, cracks are likely to occur at the interface between the light-reflective insulating particles and the thermosetting resin composition due to internal stress of the thermosetting resin composition (or a cured product thereof). If cracks occur in the light-reflective anisotropic conductive adhesive, the conduction reliability is impaired. Therefore, the light-reflective anisotropic conductive adhesive is required to have excellent toughness, and high toughness can be imparted to the light-reflective anisotropic conductive adhesive by adding the light-reflective needle-shaped insulating particles as the light-reflective insulating particles to the thermosetting resin composition. This is because, in the thermosetting resin composition, the needle-shaped light-reflective insulating particles each arranged in a random direction are easily bent and bent by themselves, and therefore, the internal stress of the thermosetting resin composition generated by a change in temperature can be transmitted to and absorbed by the needle-shaped crystals, and the propagation of the internal stress in the thermosetting resin composition can be suppressed. Thus, the light-reflective anisotropic conductive adhesive containing the light-reflective needle-shaped insulating particles can exhibit excellent toughness, and even if the thermosetting resin composition expands or contracts due to a temperature change, the occurrence of cracks can be suppressed or prevented, and the decrease in conduction reliability can be suppressed or prevented.

On the other hand, when only the light-reflective needle-shaped insulating particles are used as the light-reflective insulating particles, the light reflectance tends to decrease. Therefore, in the present invention, spherical light-reflective insulating particles having good light reflection characteristics are used in combination with the light-reflective needle-shaped insulating particles.

The amount of the light-reflective needle-like insulating particles to be mixed in the thermosetting resin composition is 1 to 50 vol%, preferably 5 to 25 vol%, based on the thermosetting resin composition. This is because, when the amount of the light-reflective needle-like insulating particles is less than 1 vol%, it is difficult to sufficiently suppress or prevent the occurrence of cracks in the bonded portion bonded with the light-reflective anisotropic conductive adhesive and the decrease in conduction reliability; on the other hand, when the amount of the light-reflective needle-like insulating particles is too large, the following tendency is exhibited: the amount of the thermosetting resin composition blended is relatively reduced, the adhesiveness of the light-reflective anisotropic conductive adhesive is reduced, and the amount of the light-reflective spherical insulating particles blended is also reduced, so that the improvement of the light reflectance of the joint portion bonded with the light-reflective anisotropic conductive adhesive becomes insufficient; when the amount of the component is within this range, the effects of the present invention can be obtained.

The amount of the light-reflective spherical insulating particles to be incorporated into the thermosetting resin composition is 1 to 50 vol%, preferably 2 to 25 vol%, based on the thermosetting resin composition. This is because, when the amount of the light-reflective spherical insulating particles is less than 1% by volume, the improvement of the light reflectance of the joint portion joined with the light-reflective anisotropic conductive adhesive tends to be insufficient; on the other hand, when the amount of the light-reflective spherical insulating particles is too large, the following tendency is exhibited: the amount of the thermosetting resin composition added is relatively reduced, the adhesiveness of the light-reflective anisotropic conductive adhesive is reduced, and the amount of the light-reflective needle-like insulating particles added is also reduced, so that it is difficult to suppress the occurrence of cracks in the joint portion bonded with the light-reflective anisotropic conductive adhesive, and to improve the reduction in conduction reliability; when the amount of the component is within this range, the effects of the present invention can be obtained.

The ratio (V/V) of the light-reflective spherical insulating particles to the light-reflective needle-like insulating particles is 1:1 to 10, preferably 1:2 to 8. When the amount of the light-reflective spherical insulating particles is relatively smaller than that of the light-reflective needle-shaped insulating particles, the light reflection characteristics tend to be lowered, whereas when the amount is relatively large, the crack resistance tends to be lowered.

When the light-reflective acicular insulating particles are applied to a light-emitting device that emits visible light, an acicular inorganic compound that appears white is preferably used. Such light-reflective needle-like insulating particles can reflect light incident on the light-reflective anisotropic conductive adhesive to the outside, and since the light-reflective needle-like insulating particles themselves exhibit white color, the wavelength dependence of the light reflection characteristics with respect to visible light can be reduced, and visible light can be efficiently reflected.

The diameter of the light-reflective needle-like insulating particles is preferably 5 μm or less. In addition, the aspect ratio is preferably more than 10 in order to sufficiently conduct and absorb the internal stress of the thermosetting resin composition, and is preferably less than 35 in order to make the light-reflective needle-shaped insulating particles hard to break and uniformly dispersed in the thermosetting resin composition. In order to further improve dispersibility in the thermosetting resin composition, it is more preferably less than 20.

Preferred specific examples of such light-reflective needle-shaped insulating particles include white needle-shaped inorganic particles such as zinc oxide whiskers, titanium oxide whiskers, titanate whiskers such as potassium titanate whiskers or sodium titanate whiskers, aluminum borate whiskers, and wollastonite (needle-shaped crystals of kaolin silicate). One or more of them may be used. Here, the whisker is a crystal grown in a needle shape by a special production method, and has an advantage that it is rich in elasticity and hard to deform because the crystal structure is not disordered. These inorganic compounds exhibit white color in a light-emitting device that emits visible light, and therefore have little wavelength dependence on the light reflection characteristics of visible light, and are easy to reflect visible light. Among these, zinc oxide whiskers are particularly preferable because they have high whiteness and are not catalytic to light deterioration even when there is a concern that a cured product of a thermosetting resin composition in a cured anisotropic conductive adhesive will undergo light deterioration.

Instead of such a single needle crystal, a crystal having a plurality of needle shapes (multi-needle crystal) such as a tetrahedron (registered trademark) in which the center and the apex of the tetrahedron are bonded to each other may be used as the light-reflective needle-shaped insulating particles. White acicular inorganic particles of a multi-needle crystal are superior to white acicular inorganic particles of a single needle crystal in terms of high thermal conductivity, but have a bulky crystal structure as compared with a single needle crystal, and therefore care must be taken not to damage the needle-like portions of the bonding members of the substrate and the device during thermocompression bonding.

These light-reflective needle-shaped insulating particles may be particles treated with, for example, a silane coupling agent. When the inorganic particles are treated with the silane coupling agent, the dispersibility of the particles in the thermosetting resin composition can be improved. Therefore, the needle-shaped inorganic particles, preferably the light-reflective needle-shaped insulating particles obtained by treating the zinc oxide whiskers with the silane coupling agent, can be uniformly mixed in the thermosetting resin composition in a short time.

The light-reflective needle-like insulating particles preferably have a refractive index (JIS K7142) higher than that of a cured product of the thermosetting resin composition (JIS K7142), and more preferably, at least about 0.02 higher. This is because the light reflection efficiency of these interfaces decreases if the difference in refractive index is small.

In the light-reflective anisotropic conductive adhesive, when the light-reflective spherical insulating particles used in combination with the light-reflective needle-shaped insulating particles are applied to a light-emitting device that emits visible light, it is preferable to use a spherical inorganic compound that exhibits white color. Such light-reflective spherical insulating particles can reflect light incident on the light-reflective anisotropic conductive adhesive to the outside, and since the light-reflective spherical insulating particles themselves exhibit white color, the wavelength dependence of the light reflection characteristics with respect to visible light can be reduced, and visible light can be efficiently reflected.

When the average particle diameter of the light-reflective spherical insulating particles is too small, the light reflectance of the cured product of the light-reflective anisotropic conductive adhesive is low, while when too large, anisotropic conductive connection by the conductive particles tends to be inhibited, and therefore, the average particle diameter is preferably 0.02 to 20 μm, and more preferably 0.2 to 1 μm.

Preferred specific examples of the light-reflective spherical insulating particles include particles selected from titanium oxide (TiO)₂) Boron Nitride (BN), zinc oxide (ZnO) and aluminum oxide (Al)₂O₃) At least one inorganic particle of (1). Among them, TiO is preferably used from the viewpoint of high refractive index₂. Further, if necessary, a Si coating layer and an Al coating layer may be formed on the surfaces thereof by a conventional method.

The light-reflective spherical insulating particles preferably have a refractive index (JIS K7142) higher than that of a cured product of the thermosetting resin composition (JIS K7142), and more preferably, at least about 0.02 higher. This is because the light reflection efficiency of these interfaces decreases if the difference in refractive index is small.

As the light-reflective spherical insulating particles, resin-coated metal particles in which the surfaces of spherical metal particles are coated with a transparent insulating resin can be used. Examples of the metal material of the spherical metal particles include nickel, silver, aluminum, and the like, and among them, silver is preferably used.

The average particle diameter of the resin-coated metal particles as the light-reflective spherical insulating particles varies depending on the shape, and in general, when the average particle diameter is too large, anisotropic conductive connection by the conductive particles may be inhibited, and when the average particle diameter is too small, light is hardly reflected, and therefore, it is preferably 0.1 to 30 μm, and more preferably 0.2 to 10 μm. Here, the average particle diameter of the resin-coated metal particles is a size including the insulating coating.

As the resin in the resin-coated metal particles belonging to such light-reflective spherical insulating particles, various insulating resins can be used. From the viewpoint of mechanical strength, transparency, and the like, a cured product of an acrylic resin is preferably used. Preferably, the resin is obtained by radical copolymerization of methyl methacrylate and 2-hydroxyethyl methacrylate in the presence of a radical polymerization initiator such as an organic peroxide such as benzoyl peroxide. In this case, it is more preferable to crosslink the polyester with an isocyanate-based crosslinking agent such as 2, 4-tolylene diisocyanate. In addition, it is preferable that the metal particles are prepared by introducing γ -glycidoxy group, vinyl group, or the like to the metal surface with a silane coupling agent.

Such resin-coated metal particles can be produced, for example, as follows: metal particles and a silane coupling agent are put into a solvent such as toluene, stirred at room temperature for about 1 hour, and then a radical monomer, a radical polymerization initiator, and if necessary, a crosslinking agent are put into the mixture, and stirred while heated to a radical polymerization initiation temperature.

As the conductive particles constituting the light-reflective anisotropic conductive adhesive of the present invention, particles of metals used in conventional conductive particles for anisotropic conductive connection can be used. Examples thereof include gold, nickel, copper, silver, solder, palladium, aluminum, alloys thereof, and multilayered products thereof (e.g., nickel-plated object/gold-plated object). Among them, gold, nickel, and copper make the conductive particles brown, and thus the effects of the present invention can be enjoyed more than other metal materials.

As the conductive particles, metal-coated resin particles in which resin particles are coated with a metal material can be used. Examples of such resin particles include styrene resin particles, benzoguanamine resin particles, and nylon resin particles. As a method for coating the resin particles with the metal material, a conventionally known method may be used, and an electroless plating method, an electrolytic plating method, or the like may be used. The thickness of the metal material to be coated is a thickness sufficient to ensure good conduction reliability, and is usually 0.1 to 3 μm depending on the particle diameter of the resin particles and the type of metal.

Further, when the average particle diameter of the resin particles is too small, conduction failure occurs, while when too large, short circuit between patterns tends to occur, and therefore, it is preferably 1 to 20 μm, more preferably 3 to 10 μm, and particularly preferably 3 to 5 μm. In this case, the shape of the core particle 1 is preferably spherical, and may be a flake shape or a rugby shape.

The metal-coated resin particles are preferably spherical, and when the particle diameter is too large, conduction reliability is lowered, and therefore, the particle diameter is preferably 1 to 20 μm, and more preferably 3 to 10 μm.

In particular, in the present invention, it is preferable to provide the above-described conductive particles with light reflectivity to produce light-reflective conductive particles. Fig. 1A and 1B are cross-sectional views of such light-reflective conductive particles 10 and 20. First, the light-reflective conductive particles of fig. 1A will be described.

The light-reflective conductive particles 10 are composed of core particles 1 coated with a metal material and a light-reflective layer 3, wherein the light-reflective layer 3 is formed of a material selected from titanium oxide (TiO) on the surface of the core particles 1₂) Particles, zinc oxide (ZnO) particles or alumina (Al)₂O₃) At least one inorganic particle 2 in the particles. The titanium oxide particles, zinc oxide particles, or alumina particles are inorganic particles that appear white in sunlight. Thus, from themThe formed light-reflecting layer 3 appears white to gray. The appearance of white to gray means that the wavelength dependence of the light reflection characteristics with respect to visible light is small, and visible light is easily reflected.

Among the titanium oxide particles, zinc oxide particles, or aluminum oxide particles, zinc oxide particles having a high refractive index and no catalytic activity against photodegradation can be preferably used when there is a concern that a cured product of the thermosetting resin composition in the cured anisotropic conductive adhesive may be photodegraded.

The core particle 1 is used for making anisotropic conductive connection, and therefore its surface is composed of a metal material. Here, as a form in which the surface is coated with the metal material, there can be mentioned: the core particle 1 itself is in the form of a metal material or in the form of a resin particle having a surface coated with a metal material.

From the viewpoint of the relative size to the particle diameter of the core particle 1, the thickness of the light reflection layer 3 formed of the inorganic particles 2 is preferably 0.5 to 50%, more preferably 1 to 25%, because when the thickness is too small relative to the particle diameter of the core particle 1, the reflectance is remarkably reduced, and when the thickness is too large, conduction failure occurs.

In the light-reflective conductive particles 10, the particle size of the inorganic particles 2 constituting the light-reflective layer 3 is preferably 0.02 to 4 μm, more preferably 0.1 to 1 μm, and particularly preferably 0.2 to 0.5 μm, because the light-reflective phenomenon is less likely to occur when the particle size is too small, and the formation of the light-reflective layer 3 tends to be less likely to occur when the particle size is too large. In this case, the particle size of the inorganic particles 2 is preferably 50% or more of the wavelength of light to be reflected so that the light to be reflected (i.e., light emitted from the light-emitting element) does not pass therethrough, from the viewpoint of the wavelength of the light to be reflected. In this case, the shape of the inorganic particles 2 may be amorphous, spherical, scaly, needle-like, or the like, and among them, spherical is preferable from the viewpoint of the light diffusion effect, and scaly is preferable from the viewpoint of the total reflection effect.

The light-reflective conductive particles 10 in fig. 1A can be produced by a known film forming technique (so-called mechanofusion method) in which large and small powders are physically impacted with each other to form a film of small particles on the surface of large particles. At this time, the inorganic particles 2 are fixed so as to erode the metal material on the surface of the core particle 1, but the inorganic particles 2 are hard to be welded and fixed to each other, and therefore a single layer of the inorganic particles constitutes the light reflecting layer 3. Therefore, in the case of fig. 1A, the layer thickness of the light reflecting layer 3 is considered to be equal to or slightly smaller than the particle diameter of the inorganic particles 2.

Next, the light-reflective conductive particles 20 in fig. 1B will be described. The light-reflective conductive particles 20 are different from the light-reflective conductive particles 10 in fig. 1A in that the light-reflective layer 3 contains the thermoplastic resin 4 functioning as a binder, and the inorganic particles 2 are also fixed to each other by the thermoplastic resin 4, and the inorganic particles 2 are multilayered (for example, multilayered to 2 layers or 3 layers). By containing such a thermoplastic resin 4, the mechanical strength of the light reflecting layer 3 is improved, and peeling of the inorganic particles 2 and the like are less likely to occur.

As the thermoplastic resin 4, a halogen-free thermoplastic resin can be preferably used in order to realize low environmental load, and for example, polyolefin such as polyethylene and polypropylene, polystyrene, acrylic resin, or the like can be used.

Such light-reflective conductive particles 20 can also be produced by mechanofusion. The particle size of the thermoplastic resin 4 applied to the mechanofusion method is preferably 0.02 to 4 μm, more preferably 0.1 to 1 μm, because the adhesive function is lowered when it is too small, and the adhesion to the core particle 1 becomes difficult when it is too large. When the amount of the thermoplastic resin 4 is too small, the adhesive function is lowered, while when too large, aggregates of the light-reflective conductive particles and the core particles are formed, and therefore, the amount is preferably 0.2 to 500 parts by mass, and more preferably 4 to 25 parts by mass, based on 100 parts by mass of the inorganic particles 2.

As the thermosetting resin composition used in the light-reflective anisotropic conductive adhesive of the present invention, it is preferable to use a composition which is as colorless and transparent as possible. This is to reflect light without reducing the light reflection efficiency of the light-reflective conductive particles in the light-reflective anisotropic conductive adhesive and without changing the color of incident light. The colorless and transparent state means that the cured product of the thermosetting resin composition has a light transmittance (JIS K7105) of 80% or more, preferably 90% or more, with respect to visible light having a wavelength of 380 to 780nm and an optical path length of 1 cm.

In the light-reflective anisotropic conductive adhesive of the present invention, when the amount of the conductive particles such as the light-reflective conductive particles is too small relative to 100 parts by mass of the thermosetting resin composition, conduction failure occurs, and when the amount is too large, short circuit between patterns tends to occur, and therefore, it is preferably 1 to 100 parts by mass, and more preferably 10 to 50 parts by mass.

Regarding the light reflection characteristics of the light-reflective anisotropic conductive adhesive of the present invention, in order to improve the light emission efficiency of the light-emitting element, it is preferable that the reflectance of the cured product of the light-reflective anisotropic conductive adhesive against light having a wavelength of 450nm (JIS K7105) is at least 30%. In order to obtain such light reflectance, the light reflectance characteristics and the amount of the light-reflective conductive particles to be used, the compounding composition of the thermosetting resin composition, and the like can be appropriately adjusted. In general, when the amount of the light-reflective conductive particles having good light reflection characteristics is increased, the reflectance tends to be increased.

The light reflection characteristics of the light-reflective anisotropic conductive adhesive can also be evaluated from the viewpoint of the refractive index. That is, this is because, when the refractive index of the cured product of the thermosetting resin composition is higher than the refractive index of the cured product of the thermosetting resin composition excluding the conductive particles, the light-reflective needle-shaped insulating particles, and the light-reflective spherical insulating particles, the amount of light reflection at the interface between the light-reflective needle-shaped insulating particles, the light-reflective spherical insulating particles, and the cured product of the thermosetting resin composition surrounding them increases. Specifically, the difference obtained by subtracting the refractive index (JIS K7142) of the cured product of the thermosetting resin composition from the refractive index (JIS K7142) of each of the light-reflective needle-shaped insulating particles and the light-reflective spherical insulating particles is preferably 0.02 or more, and more preferably 0.2 or more. In general, the refractive index of a thermosetting resin composition mainly composed of an epoxy resin is about 1.5.

As the thermosetting resin composition constituting the light-reflective anisotropic conductive adhesive of the present invention, a composition used in conventional anisotropic conductive adhesives and anisotropic conductive films can be used. Generally, such a thermosetting resin composition is obtained by blending a curing agent with an insulating binder resin. The insulating binder resin is preferably an epoxy resin containing an alicyclic epoxy compound, a heterocyclic epoxy compound, a hydrogenated epoxy compound, or the like as a main component.

The alicyclic epoxy compound is preferably an epoxy compound having 2 or more epoxy groups in the molecule. These may be in the form of a liquid or a solid. Specific examples thereof include glycidyl hexahydrobisphenol A and 3, 4-epoxycyclohexenylmethyl-3, 4' -epoxycyclohexene carboxylate. Among them, glycidyl hexahydrobisphenol a and 3, 4-epoxycyclohexenylmethyl-3 ', 4' -epoxycyclohexene carboxylate are preferably used from the viewpoint that the cured product can be excellent in light transmittance and rapid curability suitable for mounting LED elements and the like.

Examples of the heterocyclic epoxy compound include epoxy compounds having a triazine ring, and 1,3, 5-tris (2, 3-epoxypropyl) -1,3, 5-triazine-2, 4,6- (1H, 3H, 5H) -trione is particularly preferable.

As the hydrogenated epoxy compound, the above alicyclic epoxy compound, hydrogenated products of heterocyclic epoxy compounds, and other known hydrogenated epoxy resins can be used.

The alicyclic epoxy compound, heterocyclic epoxy compound and hydrogenated epoxy compound may be used alone or in combination of 2 or more. In addition, other epoxy compounds may be used in combination within a range not impairing the effects of the present invention. Examples thereof include glycidyl ethers obtained by reacting epichlorohydrin with polyhydric phenols such as bisphenol a, bisphenol F, bisphenol S, tetramethylbisphenol a, diarylbisphenol a, hydroquinone, catechol, resorcinol, cresol, tetrabromobisphenol a, trihydroxybiphenyl, benzophenone, bisresorcinol, bisphenol hexafluoroacetone, tetramethylbisphenol a, tetramethylbisphenol F, tris (hydroxyphenyl) methane, xylenol, phenol novolac (フェノールノボラック), cresol novolac (クレゾールノボラック), and the like; polyglycidyl ethers obtained by reacting epichlorohydrin with an aliphatic polyhydric alcohol such as glycerin, neopentyl glycol, ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, polyethylene glycol, or polypropylene glycol; glycidyl ether esters obtained by reacting a hydroxycarboxylic acid such as p-oxybenzoic acid or β -oxynaphthoic acid with epichlorohydrin; polyglycidyl esters derived from polycarboxylic acids such as phthalic acid, methylphthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, endomethylenehexahydrophthalic acid, trimellitic acid, and polymerized fatty acids; glycidyl amino glycidyl ethers derived from aminophenols, aminoalkylphenols; glycidyl amino glycidyl esters derived from aminobenzoic acid; glycidylamines obtained from aniline, toluidine, tribromoaniline, xylylenediamine, diaminocyclohexane, bisaminomethylcyclohexane, 4 '-diaminodiphenylmethane, 4' -diaminodiphenylsulfone, or the like; known epoxy resins such as epoxidized polyolefins, and the like.

Examples of the curing agent include acid anhydrides, imidazole compounds, and dicyan compounds. Among these, an acid anhydride-based curing agent which hardly discolors a cured product, and particularly an alicyclic acid anhydride-based curing agent, can be preferably used. Specifically, methylhexahydrophthalic anhydride and the like are preferably mentioned.

In the thermosetting resin composition of the light-reflective anisotropic conductive adhesive of the present invention, when the alicyclic epoxy compound and the alicyclic acid anhydride-based curing agent are used, if the amount of the alicyclic acid anhydride-based curing agent used is too small, the amount of the uncured epoxy compound increases, and if the amount of the alicyclic acid anhydride-based curing agent is too large, the corrosion of the adherend material tends to be promoted by the influence of the excessive curing agent, and therefore the alicyclic acid anhydride-based curing agent is used in a proportion of preferably 80 to 120 parts by mass, more preferably 95 to 105 parts by mass, based on 100 parts by mass of the alicyclic epoxy compound.

The light-reflective anisotropic conductive adhesive of the present invention can be produced by uniformly mixing the light-reflective needle-shaped insulating particles, the light-reflective spherical insulating particles, the conductive particles, and the thermosetting resin composition. When the light-reflective anisotropic conductive adhesive of the present invention is used as a light-reflective anisotropic conductive film, the light-reflective needle-shaped insulating particles, the light-reflective spherical insulating particles, the conductive particles, and the thermosetting resin composition are dispersed and mixed together with a solvent such as toluene, and the resultant mixture is applied so that the PET film after the peeling treatment has a desired thickness, and then dried at a temperature of about 80 ℃.

Next, a light-emitting device of the present invention will be described with reference to fig. 2. The light-emitting device 200 is a light-emitting device as follows: the light-reflective anisotropic conductive adhesive of the present invention is applied between the connection terminals 22 on the substrate 21 and the connection bumps 26 formed on the n-electrode 24 and the p-electrode 25 of the LED element 23 as a light-emitting element, respectively, and the substrate 21 and the LED element 23 are flip-chip mounted. Here, the cured product 100 of the light-reflective anisotropic conductive adhesive is obtained by dispersing the light-reflective conductive particles 10, and further the light-reflective needle-shaped insulating particles and the light-reflective spherical insulating particles in the cured product 11 of the thermosetting resin composition. If necessary, the entire LED element 23 may be sealed with a transparent molding resin so as to be covered. Further, the LED element 23 may be provided with a light reflecting layer in the same manner as in the conventional case.

In the light emitting device 200 configured as described above, among the light emitted from the LED element 23, the light emitted toward the substrate 21 side is reflected by the light-reflective conductive particles 10 in the cured product 100 of the light-reflective anisotropic conductive adhesive, and is emitted from the upper surface of the LED element 23. Therefore, the reduction of the light emission efficiency can be prevented. Further, since the light-reflective needle-shaped insulating particles are contained, the conduction reliability of a cured product of the light-reflective anisotropic conductive adhesive can be improved, and the occurrence of cracks can be suppressed or prevented.

The configuration (the LED element 23, the bump 26, the substrate 21, the connection terminal 22, and the like) other than the light-reflective anisotropic conductive adhesive in the light-emitting device 200 of the present invention may be the same as that of the conventional light-emitting device. The light-emitting device 200 of the present invention can be manufactured by a conventional anisotropic conductive connection technique, except that the light-reflective anisotropic conductive adhesive of the present invention is used. As the light emitting element, a known light emitting element can be applied to the range not impairing the effect of the present invention, in addition to the LED element.

Examples

Hereinafter, specific examples of the present invention will be described. The scope of the present invention is not limited to any of the following examples.

Examples 1 to 7 and comparative examples 1 to 4

(preparation of Anisotropic conductive adhesive)

An anisotropic conductive adhesive was prepared by mixing 10 parts by mass of light-reflective white needle-shaped insulating particles (metal oxide whiskers) and/or light-reflective white spherical insulating particles (metal oxide particles) and, as conductive particles, gold-coated resin particles (average particle diameter of 5 μm) in which a gold plating layer was formed on the surface of spherical acrylic resin particles or light-reflective conductive particles (average particle diameter of 5 μm) coated with titanium oxide microparticles, with the addition amounts shown in table 1, into a transparent epoxy thermosetting resin composition (refractive index of 1.45) containing 50 parts by mass of an alicyclic epoxy compound (CEL 2021P, Daicel Corporation) and 50 parts by mass of methylhexahydrophthalic anhydride.

The light-reflective conductive particles used in example 6 were produced as follows: a mechanical fusion device (AMS-GMP, Hosokawa Micron Ltd.) was charged with 4 parts by mass of titanium oxide powder having a particle size of 0.5 μm, 3 parts by mass of polystyrene powder having a particle size of 0.2 μm, and 20 parts by mass of conductive particles having a particle size of 5 μm (particles (20 GNR4.6EH, Nippon chemical industries, Ltd.) obtained by applying electroless gold plating having a thickness of 0.2 μm to spherical acrylic resin particles having an average particle size of 4.6 μm), and a light-reflecting layer having a thickness of about 1 μm and comprising titanium oxide particles was formed on the surface of the gold-coated resin particles. The appearance color of the light-reflective conductive particles was gray.

The light-reflective white spherical insulating particles used in examples 1 and 2 were prepared by mixing TiO particles having a particle size of 0.5. mu.m₂Particles having a surface coated with a Si film and an Al film. The light-reflective white needle-like insulating particles used in example 6 were particles in which the surfaces of ZnO whiskers were surface-treated with a silicon coupling agent (silicon dioxide treatment) (Pana-Tetra, AMTEC co., ltd.).

(evaluation of light reflectance)

The anisotropic conductive adhesive thus prepared was applied to a white plate to a thickness of 100 μm, and cured by heating at 200 ℃ for 1 minute. The total reflectance (specular reflectance and diffuse reflectance) of the resulting cured product with respect to light having a wavelength of 450nm was measured using a spectrophotometer (UV 3100, Shimadzu corporation). The results are shown in Table 1. Practically, the light reflectance is preferably more than 30%.

(preparation of LED mounting Module sample)

Gold (Au) bumps 15 μm high were formed on a glass epoxy substrate having a wiring in which Ni/Au (5.0 μm thick/0.3 μm thick) plating treatment was applied to copper wirings of a pitch of 100 μm using a bump support (FB 700, KAIJOcorporation). A blue LED (Vf =3.2V (If =20 mA)) device was flip-chip mounted on the gold-bumped epoxy substrate using a light-reflective anisotropic conductive adhesive at 200 ℃, 20 seconds, and 1 kg/chip, thereby obtaining a test LED module.

(evaluation of total Beam quantity)

The total light flux amount was measured for the obtained test LED module using a total light flux amount measurement system (global integration) (LE-2100, tsukamur electronics corporation) (measurement condition If =20mA (constant current control)). The results are shown in Table 1. Ideally, in practice, the total beam size exceeds 300 mlm.

(evaluation of conduction reliability and crack resistance)

The conduction reliability and crack resistance were evaluated by performing the following 2 kinds of cold-hot cycle tests (TCT).

＜TCT-A＞

The test LED modules were exposed to an atmosphere of-40 ℃ and 100 ℃ for 30 minutes each, as 1 cycle, and the cold-hot cycle was performed 1000 times.

＜TCT-B＞

The test LED modules were exposed to an atmosphere of-55 ℃ and 125 ℃ for 30 minutes each, as 1 cycle, and the cold-hot cycle was performed 1000 times.

The evaluation of the conduction reliability was performed as follows: after the TCT was performed for 1000 cycles, Vf values at If =20mA were measured for the test LED modules taken out of the TCT, and evaluated according to the following criteria.

Grade (rank): datum

A: when the rising portion of the Vf value from the initial Vf value is less than 3%

B: the increase of Vf value from the initial Vf value is 3% or more and less than 5%

C: the increase in Vf value from the initial Vf value is 5% or more.

The presence or absence of crack generation was evaluated as follows: after TCT was performed for 1000 cycles, the LED module for test taken out of TCT was observed from the upper surface of the blue LED element with a metal microscope to observe whether or not cracks were generated in the cured product of the light reflective anisotropic conductive adhesive, and evaluated according to the following criteria.

Grade: datum

A: when generation of cracks is not observed at all

B: the occurrence of cracks was slightly observed, but at a level where there was no practical problem

C: when the occurrence of cracks was observed.

[ Table 1]

As can be seen from table 1, in the case of the anisotropic conductive adhesives of examples 1 to 7, the total reflectance was 37% or more and the total beam amount was 340mlm or more. The crack resistance and the conduction reliability were evaluated as "a".

On the other hand, in the case of the anisotropic conductive adhesive of comparative example 1, since the appearance color was brown without blending the light-reflective insulating particles, the total reflectance was 8%, which was very low, and the total light flux amount was also 200mlm, which was very low.

In the case of the anisotropic conductive adhesive of comparative example 2, although the total amount of light-reflective insulating particles was the same as that of the anisotropic conductive adhesive of example 3, the total reflectance was reduced from 42% (example 3) to 35% and the total light flux was also reduced from 360mlm (example 3) to 300mlm because only the light-reflective white needle-like insulating particles were used without the light-reflective white spherical insulating particles.

In the case of the anisotropic conductive adhesive of comparative example 3, although the total amount of the light-reflective insulating particles was the same as that of the anisotropic conductive adhesive of example 3, the total reflectance was improved from 42% (example 3) to 50% because only the light-reflective white spherical insulating particles were used without the light-reflective white acicular insulating particles, but the crack resistance was evaluated as "C" and the conduction reliability was evaluated as "B" in TCT-B.

In the case of the anisotropic conductive adhesive of comparative example 4, the total reflectance and the total beam quantity were improved by increasing the light-reflective white spherical insulating particles from 4 vol% to 16 vol% as compared with the case of the anisotropic conductive adhesive of example 3, but the crack resistance was evaluated as "B" or "C", and the conduction reliability was evaluated as "B" in the case of TCT-B.

Industrial applicability

In the light-reflective anisotropic conductive adhesive of the present invention, the light-reflective needle-shaped insulating particles and the spherical insulating particles are each blended in an amount of 1 to 50% by volume with respect to the thermosetting resin composition, and the blending ratio of the light-reflective spherical insulating particles to the light-reflective needle-shaped insulating particles is set to 1:1 to 10. Therefore, the light emitting efficiency can be improved without providing a light reflecting layer on the LED element, which increases the manufacturing cost, and the reduction of the conduction reliability and the occurrence of cracks in the anisotropic conductive connection portion of the light emitting device due to the change in the ambient temperature can be suppressed or prevented. Therefore, the light-reflective anisotropic conductive adhesive of the present invention is useful for flip-chip mounting of an LED element.

Description of the reference numerals

1 core particle

2 inorganic particles

3. 40 light reflecting layer

4 thermoplastic resin

10. 20 light-reflective conductive particles

11 cured product of thermosetting resin composition

21. 31 base plate

22. 36 connecting terminal

23. 33 LED element

24. 35 n electrode

25. 34 p electrode

26. 39 convex point

32 die bonding adhesive

37 gold wire

38 transparent molding resin

41 Anisotropic Conductive Paste (ACP)

Cured product of 100-light-reflective anisotropic conductive adhesive

200 light emitting device

Claims (16)

1. A light-reflective anisotropic conductive adhesive for anisotropic conductive connection of a light-emitting element to a wiring board, which contains a thermosetting resin composition, conductive particles, light-reflective needle-like insulating particles, and light-reflective spherical insulating particles,

the amount of the light-reflective needle-shaped insulating particles and the amount of the light-reflective spherical insulating particles in the thermosetting resin composition are 1 to 50 vol% based on the thermosetting resin composition, and the ratio (V/V) of the light-reflective spherical insulating particles to the light-reflective needle-shaped insulating particles is 1:1 to 10.

2. The light-reflective anisotropic conductive adhesive according to claim 1, wherein the light-reflective needle-shaped insulating particles are at least one needle-shaped inorganic particle selected from titanium oxide whiskers, zinc oxide whiskers, titanate whiskers, aluminum borate whiskers, and wollastonite.

3. The light-reflective anisotropic conductive adhesive according to claim 2, wherein the light-reflective needle-shaped insulating particles are zinc oxide whiskers.

4. The light-reflective anisotropic conductive adhesive according to any one of claims 1 to 3, wherein the light-reflective acicular insulating particles are obtained by treating acicular inorganic particles with a silane coupling agent.

5. The light-reflective anisotropic conductive adhesive according to any one of claims 1 to 3, wherein the light-reflective acicular insulating particles have an aspect ratio of more than 10 and less than 35.

6. The light-reflective anisotropic conductive adhesive according to any one of claims 1 to 3, wherein the light-reflective needle-like insulating particles have a refractive index higher than that of a cured product of the thermosetting resin composition, the refractive index being obtained in accordance with JIS K7142.

7. The light-reflective anisotropic conductive adhesive according to any one of claims 1 to 3, wherein the light-reflective spherical insulating particles are at least one spherical inorganic particle selected from titanium oxide, boron nitride, zinc oxide, and aluminum oxide.

8. The light-reflective anisotropic conductive adhesive according to claim 7, wherein the light-reflective spherical insulating particles have an average particle diameter of 0.02 to 20 μm.

9. The light-reflective anisotropic conductive adhesive according to any one of claims 1 to 3, wherein the refractive index of the light-reflective spherical insulating particles is larger than the refractive index of a cured product of the thermosetting resin composition, the refractive index being obtained in accordance with JIS K7142.

10. The light-reflective anisotropic conductive adhesive according to any one of claims 1 to 3, wherein the light-reflective spherical insulating particles are resin-coated metal particles in which surfaces of the spherical metal particles are coated with an insulating resin.

11. The light-reflective anisotropic conductive adhesive according to claim 10, wherein the light-reflective spherical insulating particles are resin-coated silver particles in which surfaces of the spherical silver particles are coated with an insulating resin.

12. The light-reflective anisotropic conductive adhesive according to any one of claims 1 to 3, wherein the thermosetting resin composition contains an epoxy resin and an acid anhydride curing agent.

13. The light-reflective anisotropic conductive adhesive according to any one of claims 1 to 3, wherein the conductive particles are light-reflective conductive particles including core particles coated with a metal material and a light-reflective layer formed on the surface of the core particles and comprising at least one inorganic particle selected from titanium oxide particles, zinc oxide particles, and aluminum oxide particles.

14. The light-reflective anisotropic conductive adhesive according to claim 13, wherein the amount of the light-reflective conductive particles is 1 to 100 parts by mass per 100 parts by mass of the thermosetting resin composition.

15. A light-emitting device, wherein the light-emitting element is flip-chip mounted on the wiring board via the light-reflective anisotropic conductive adhesive according to any one of claims 1 to 14.

16. The light emitting device of claim 15, wherein the light emitting element is a light emitting diode.