WO2011129373A1 - 光反射性異方性導電接着剤及び発光装置 - Google Patents

光反射性異方性導電接着剤及び発光装置 Download PDF

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Publication number
WO2011129373A1
WO2011129373A1 PCT/JP2011/059194 JP2011059194W WO2011129373A1 WO 2011129373 A1 WO2011129373 A1 WO 2011129373A1 JP 2011059194 W JP2011059194 W JP 2011059194W WO 2011129373 A1 WO2011129373 A1 WO 2011129373A1
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Prior art keywords
light
reflective
anisotropic conductive
conductive adhesive
particles
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PCT/JP2011/059194
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English (en)
French (fr)
Inventor
秀次 波木
士行 蟹澤
英明 馬越
明 石神
Original Assignee
ソニーケミカル＆インフォメーションデバイス株式会社
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Application filed by ソニーケミカル＆インフォメーションデバイス株式会社 filed Critical ソニーケミカル＆インフォメーションデバイス株式会社
Priority to US13/640,784 priority Critical patent/US8916894B2/en
Priority to EP11768894.5A priority patent/EP2560198A4/en
Priority to CN201180018769.0A priority patent/CN102859673B/zh
Priority to KR1020117015024A priority patent/KR20130049689A/ko
Publication of WO2011129373A1 publication Critical patent/WO2011129373A1/ja
Priority to HK13105913.8A priority patent/HK1178320A1/zh
Priority to US14/543,550 priority patent/US9260634B2/en

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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/64—Manufacture or treatment of solid state devices other than semiconductor devices, or of parts thereof, not peculiar to a single device provided for in groups H01L31/00 - H10K99/00
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    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J9/00—Adhesives characterised by their physical nature or the effects produced, e.g. glue sticks
    • C09J9/02—Electrically-conducting adhesives
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
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Definitions

  • the present invention relates to a light-reflective anisotropic conductive adhesive used for anisotropically conductive connection of a light-emitting element to a wiring board, and a light-emitting element using the light-reflective anisotropic conductive adhesive.
  • the present invention relates to a light emitting device that is mounted on.
  • LED elements such as light emitting diode (LED) elements
  • 3 to 5 show structural examples of old-type light emitting devices.
  • the LED element 33 is bonded to the substrate 31 with a die bond adhesive 32, and the p electrode 34 and the n electrode 35 on the upper surface of the LED element 33 are bonded with a gold (Au) wire 37. Wire bonding is performed by silver plating 36. Thereby, the LED element 33 and the board
  • the light emitting device seals the entire LED element 33 with a resin such as a transparent mold resin (not shown), but the connection of the gold wire 37 depends on the difference in linear expansion coefficient between the resin and the LED element 33 and the gold wire 37. Separation may occur in the portion, or an electrical connection failure may occur due to the disconnection of the gold wire 37.
  • a resin such as a transparent mold resin
  • such a light emitting device is required to maintain the light emission efficiency (light extraction efficiency) by suppressing the reduction in the reflectance of the light emitted from the LED element.
  • gold electrodes are usually used as the p electrode 34 and the n electrode 35 of the LED element 33.
  • the gold electrode or the gold wire absorbs light having a wavelength of 400 to 500 nm emitted to the upper surface side, and the die bond adhesive 32 absorbs the light emitted downward.
  • Such light absorption reduces the light emission efficiency (light extraction efficiency) of the LED element 33.
  • the bonding process using the die-bonding adhesive 32 is based on oven curing, there is a problem that it takes time to manufacture.
  • a conductive paste 37 typified by a silver paste is used.
  • a p-electrode 34 and an n-electrode 35 on the lower surface of the LED element 33 and a silver-plated portion 36 on the substrate 31. are electrically connected.
  • the conductive paste 37 has a weak adhesive force, reinforcement with the sealing resin 38 is required.
  • light may be diffused or absorbed inside the conductive paste 37, thereby reducing the light emission efficiency of the LED element 33.
  • an anisotropic conductive adhesive (ACP) or an anisotropic conductive adhesive film (ACP) is cured, and the LED element and the substrate are connected and fixed and electrically joined.
  • Patent Document 1 describes a method of flip-chip mounting an LED element. Further, for example, in the light emitting device shown in FIG. 5, the p-electrode 34 and the n-electrode 35 on the lower surface of the LED element 33 and the substrate 31 are electrically bonded by flip chip mounting using a commercially available anisotropic conductive adhesive 39. It is a thing. In this flip chip mounting technique, bumps 40 are formed on the p electrode 34 and the n electrode 35, respectively.
  • a light reflection layer is provided on the LED element by a metal vapor deposition layer or the like so as to be insulated from the p electrode and the n electrode.
  • emitted from the LED element is suppressed, and luminous efficiency is maintained.
  • the technique of Patent Document 1 has a problem that the number of manufacturing steps of the light emitting device is increased and an increase in cost is inevitable.
  • Au or Ni used as conductive particles dispersed in the binder of ACP exhibits brown or dark brown, and the imidazole that the binder usually contains
  • the ACP binder exhibits an overall brown color due to the system latent curing agent exhibiting a brown color, thereby absorbing light. As a result, the light emission efficiency of the LED element 33 decreases.
  • the ACP uses an epoxy resin as a binder resin, but the ACP using the epoxy resin increases the conduction resistance and peels off the joint surface due to an internal stress based on a difference in thermal expansion coefficient with the connection substrate accompanying a temperature change. , Cracks and the like were generated. For this reason, reliability such as resistance to reflow of lead-free solder, resistance to thermal shock, and resistance to corrosion phenomenon of vapor deposition wiring when used and stored in a high temperature and high humidity atmosphere may be lowered.
  • the present invention has been proposed in view of such a conventional situation, and a light emitting element such as an LED element is flip-chip mounted on a wiring board using an anisotropic conductive adhesive, resulting in a manufacturing cost.
  • a light-emitting device that maintains the light-emitting efficiency of a light-emitting element without providing such a light reflection layer on the LED element, the object is to prevent the occurrence of cracks in the anisotropic conductive adhesive and to obtain high conduction reliability It is.
  • the inventors of the present invention have found that the occurrence of cracks can be prevented by making the light-reflective insulating particles added to the anisotropic conductive adhesive into a needle-like shape.
  • the present invention relates to a light-reflective anisotropic conductive adhesive used for anisotropically conductively connecting a light-emitting element to a wiring board, comprising a thermosetting resin, conductive particles, and light-reflective needle-like insulation. It is characterized by containing particles.
  • the present invention is characterized in that the light emitting element is mounted on the wiring board by the flip chip method through such a light reflective anisotropic conductive adhesive.
  • the light-reflective anisotropic conductive adhesive in the light-reflective anisotropic conductive adhesive can be obtained by adding light-reflective needle-like insulating particles to the anisotropic conductive adhesive. Generation of cracks can be prevented and high conduction reliability can be obtained.
  • FIG. 1A is a cross-sectional view of light-reflective conductive particles
  • FIG. 1B is a cross-sectional view of light-reflective conductive particles
  • FIG. 2 is a cross-sectional view of the light-emitting device in this embodiment.
  • FIG. 3 is a cross-sectional view of a conventional light emitting device.
  • FIG. 4 is a cross-sectional view of a conventional light emitting device.
  • FIG. 5 is a cross-sectional view of a conventional light emitting device.
  • the light-reflective anisotropic conductive adhesive in the present embodiment is an adhesive used for anisotropically connecting an LED element, which is a light-emitting element, to a wiring board, and includes a thermosetting resin composition, It contains conductive particles and light reflective acicular insulating particles.
  • the light-reflective acicular insulating particles are characterized by having an acicular shape having an aspect ratio within a predetermined range as will be described later.
  • the thermosetting resin composition contains spherical particles, cracks are generated from the interface between the spherical particles and the thermosetting resin composition due to internal stress of the thermosetting resin composition when the stretchability decreases with temperature change. There is a case.
  • electrical_connection reliability will be impaired. For this reason, the light-reflective anisotropic conductive adhesive needs to have excellent toughness.
  • the light-reflective anisotropic conductive adhesive in the present embodiment needle-shaped light-reflective insulating particles having an aspect ratio in a predetermined range are added to the thermosetting resin composition.
  • the acicular light-reflective insulating particles arranged in random directions propagate and absorb the internal stress of the thermosetting resin composition accompanying the temperature change in the acicular crystal.
  • the toughness of the thermosetting resin composition can be increased.
  • the light-reflective anisotropic conductive adhesive exhibits excellent toughness, and can suppress generation of cracks and peeling of the adhesive surface even when the thermosetting resin composition expands and contracts due to temperature change. .
  • the light-reflective needle-like insulating particles are made of a white needle-like inorganic compound and reflect light incident on the light-reflective anisotropic conductive adhesive to the outside.
  • the light-reflective needle-like insulating particles themselves exhibit white color, the wavelength dependence of the reflection characteristics with respect to visible light can be reduced, and visible light can be efficiently reflected.
  • the light-reflective anisotropic conductive adhesive in the present embodiment is a particle composed of an inorganic compound that exhibits white color and has an acicular shape with an aspect ratio in a predetermined range (hereinafter referred to as “white acicular inorganic material”).
  • white acicular inorganic material an inorganic compound that exhibits white color and has an acicular shape with an aspect ratio in a predetermined range.
  • Examples of the white acicular inorganic particles include acicular shapes such as titanate whiskers such as zinc oxide whisker, titanium oxide whisker, and potassium titanate whisker, aluminum borate whisker, and wollastonite (kaolin silicate acicular crystals). Mention may be made of inorganic compounds. Whisker is a crystal grown in a needle shape by a special manufacturing method, and since there is no disorder in the crystal structure, it has an advantage that it is rich in elasticity and hardly deforms. Since these inorganic compounds exhibit white color in a light emitting device that emits visible light, the wavelength dependency of the reflection characteristics with respect to visible light is small and the visible light is easily reflected.
  • acicular shapes such as titanate whiskers such as zinc oxide whisker, titanium oxide whisker, and potassium titanate whisker, aluminum borate whisker, and wollastonite (kaolin silicate acicular crystals).
  • inorganic compounds is a crystal grown in a needle shape by a special manufacturing method, and since there is no disorder in the crystal
  • the zinc oxide whisker has a high whiteness and is a catalyst for photodegradation even when photocuring of the cured product of the thermosetting resin composition in the cured anisotropic conductive adhesive is concerned. It is particularly preferable because it has no property.
  • the fiber diameter is preferably 5 ⁇ m or less.
  • the aspect ratio of the white needle-like inorganic particles made of single needle crystals is preferably greater than 10 and less than 35, and particularly preferably greater than 10 and less than 20.
  • the aspect ratio of the white needle-like inorganic particles is larger than 10, the internal stress of the thermosetting resin can be sufficiently propagated and absorbed.
  • the aspect ratio of the white needle-like inorganic particles is less than 35, the needle-like crystals are less likely to be broken and can be uniformly dispersed in the thermosetting resin. Connection is not hindered. When this aspect ratio is less than 20, the dispersibility in the thermosetting resin can be further improved.
  • thermosetting resin composition Since the toughness of the thermosetting resin composition can be increased by adding white needle-like inorganic particles having an aspect ratio of more than 10 and less than 35 to the thermosetting resin composition, the light reflecting anisotropy Even if the conductive adhesive expands and contracts, it is possible to suppress the peeling or cracking of the adhesive surface.
  • the white needle-like inorganic particles instead of such a single needle-like crystal, for example, a shape formed by combining the center and apex of the tetrahedron, such as Tetrapod (registered trademark), etc.
  • a crystal having a plurality of needle-like shapes may be used.
  • the white needle-like inorganic particles of double needle crystals are superior in that they have a higher thermal conductivity than the white needle-like inorganic particles of single needle crystals, but they have a bulkier crystal structure than single needle crystals. It is necessary to be careful not to damage the substrate or the joined part of the element by the needle-like part during thermocompression bonding.
  • the acicular white inorganic particles may be treated with a silane coupling agent, for example. Dispersibility in the thermosetting resin composition can be improved by treating the acicular white inorganic particles with the silane coupling agent. For this reason, the acicular white inorganic particle processed with the silane coupling agent can be mixed in the thermosetting resin composition uniformly in a short time.
  • the white needle-like inorganic particles have a refractive index (JIS K7142) that is preferably larger than the refractive index of the cured product of the thermosetting resin composition (JIS K7142), more preferably at least about 0.02. preferable. This is because if the difference in refractive index is small, the reflection efficiency at the interface between them decreases. That is, as the white needle-like inorganic particles, those that are light-reflective and insulating inorganic particles whose refractive index is less than or equal to the refractive index of the thermosetting resin composition to be used, such as SiO2. Not applicable.
  • the content is preferably 1 to 50% by volume (Vol%), more preferably 5 to 25% by volume, based on the thermosetting resin composition.
  • the light-reflective anisotropic conductive adhesive in the present embodiment contains such white needle-like inorganic particles and covers most of the conductive particles, the conductive particles exhibit a color such as brown. Even in this case, the whiteness of the thermosetting resin composition is realized. Because of the whiteness of such a thermosetting resin composition, the wavelength dependence of the reflection characteristics with respect to visible light is reduced, and the visible light is easily reflected. While suppressing the fall of the reflectance of the emitted light, the light which a LED element light-emits toward the lower surface side can also be utilized efficiently. As a result, the light emission efficiency (light extraction efficiency) of the LED element can be improved.
  • the light-reflective anisotropic conductive adhesive in this Embodiment of the thermosetting resin composition accompanying a temperature change is because the shape of the white inorganic particle as a light-reflective insulating particle is needle shape. It is possible to prevent the internal stress from being transmitted to the thermosetting resin by propagating and absorbing the internal stress in the needle crystal. In addition, when the particle shape is spherical, the internal stress of the thermosetting resin composition is less likely to be propagated and absorbed in the particles than the needle-shaped particles.
  • the toughness of the thermosetting resin composition can be increased.
  • the light-reflective anisotropic conductive adhesive exhibits excellent toughness, and can suppress generation of cracks and peeling of the adhesive surface even when the thermosetting resin composition expands and contracts due to temperature change. .
  • the light-reflective anisotropic conductive adhesive in the present embodiment is a particle made of a spherical inorganic compound exhibiting white as light-reflective insulating particles (hereinafter referred to as “white spherical inorganic particles”).
  • White needle-like inorganic particles may be added to the thermosetting resin composition containing the.
  • the white spherical inorganic particles are preferably made of the same material as the above white needle-like inorganic particles, and those having a refractive index equal to or lower than the refractive index of the thermosetting resin composition used, such as SiO2, are not applicable. .
  • the thermosetting resin composition can be further whitened to further improve the light extraction efficiency of the LED element. Also in this case, the toughness of the thermosetting resin can be increased.
  • the addition amount (Vol%) of the white needle-like inorganic particles be equal to or more than the addition amount (Vol%) of the white spherical inorganic particles.
  • the size is preferably 0.02 to 20 ⁇ m, and 0 2 to 1 ⁇ m is more preferable.
  • the white spherical inorganic particles like the white needle-like inorganic particles, preferably have a refractive index (JIS K7142) greater than the refractive index of the cured product of the thermosetting resin composition (JIS K7142). More preferably, it is about 02 larger.
  • resin-coated metal particles obtained by coating the surface of the spherical metal particles with a transparent insulating resin may be used instead of such white spherical inorganic particles.
  • the metal particles include nickel, silver, and aluminum.
  • the size of the resin-coated metal particles is preferably from 0.1 to 30 ⁇ m, more preferably from 0.2 to 10 ⁇ m.
  • size of the resin coating metal particle has shown the magnitude
  • a cured product of an acrylic resin can be preferably used.
  • a preferable example is a resin obtained by radical copolymerization of methyl methacrylate and 2-hydroxyethyl methacrylate in the presence of a radical initiator such as an organic peroxide such as benzoyl peroxide.
  • a radical initiator such as an organic peroxide such as benzoyl peroxide.
  • it is more preferably crosslinked with an isocyanate-based crosslinking agent such as 2,4-tolylene diisocyanate.
  • metal particles it is preferable to introduce a ⁇ -glycidoxy group, a vinyl group or the like into the metal surface in advance with a silane coupling agent.
  • Such resin-coated metal particles for example, are charged with metal particles and a silane coupling agent in a solvent such as toluene and stirred at room temperature for about 1 hour, and then, a radical monomer, a radical polymerization initiator, and as necessary. It can be produced by adding a crosslinking agent and stirring the mixture while heating to the radical polymerization initiation temperature.
  • the light-reflective anisotropic conductive adhesive can exhibit excellent toughness even when white spherical inorganic particles are added together with white needle-like inorganic particles. By being able to do, even if it expands and contracts by a temperature change, it can suppress that peeling of an adhesive surface and a crack generate
  • the conductive particles contained in the light-reflective anisotropic conductive adhesive in the present embodiment particles of a metal material used in conventional conductive particles for anisotropic conductive connection can be used.
  • the metal material for the conductive particles include gold, nickel, copper, silver, solder, palladium, aluminum, alloys thereof, multilayered products thereof (for example, nickel plating / gold flash plating products), and the like. it can.
  • thermosetting resin composition since the white needle-like inorganic particles cover most of the conductive particles, the thermosetting resin composition exhibits a brown color due to the conductive particles. And the entire thermosetting resin composition exhibits high whiteness.
  • metal-coated resin particles obtained by coating resin particles with a metal material may be used.
  • resin particles include styrene resin particles, benzoguanamine resin particles, and nylon resin particles.
  • a method of coating the resin particles with a metal material a conventionally known method can be employed, and for example, an electroless plating method, an electrolytic plating method, or the like can be used.
  • the layer thickness of the metal material to be coated may be any thickness that can ensure good connection reliability, and is usually 0.1 to 3 ⁇ m, although it depends on the particle size of the resin particles and the type of metal.
  • the particle size of the resin particles is preferably 1 to 20 ⁇ m, more preferably 3 to 10 ⁇ m, and even more preferably 3 to 5 ⁇ m. preferable.
  • the shape of the resin particles is preferably a spherical shape, but may be a flake shape or a rugby ball shape.
  • the metal-coated resin particles have a spherical shape, and if the particle size is too large, the connection reliability is lowered, so 1 to 20 ⁇ m is preferable, and 3 to 10 ⁇ m is more preferable.
  • the conductive particles contained in the light-reflective anisotropic conductive adhesive in the present embodiment are light-reflective conductive with light reflectivity as shown in the cross-sectional views of FIGS. 1A and 1B, for example. It is also possible to use particles.
  • the light-reflective conductive particles 10 shown in FIG. 1A are selected from core particles 1 coated with a metal material, and titanium oxide (TiO2) particles, zinc oxide (ZnO) particles, or aluminum oxide (Al2O3) particles on the surface thereof. And a light reflecting layer 3 formed from at least one kind of inorganic particles 2 formed.
  • the light reflecting layer 3 formed from such inorganic particles exhibits a color in a range from white to gray. For this reason, as described above, the wavelength dependency of the reflection characteristic with respect to visible light is small and the visible light is easily reflected, so that the luminous efficiency of the LED element can be further improved.
  • Zinc oxide which is not catalytic to photodegradation and has a high refractive index can be preferably used.
  • the core particle 1 is used for anisotropic conductive connection, and its surface is made of a metal different material.
  • Examples of the core particle 1 include an embodiment in which the core particle 1 itself is a metal material, or an embodiment in which the surface of the resin particle is coated with a metal material.
  • the layer thickness of the light reflecting layer 3 formed from the inorganic particles 2 is preferably 0.5 to 50%, more preferably 1 to 25%.
  • the particle size of the inorganic particles 2 is preferably 0.02 to 4 ⁇ m, particularly preferably 0.1 to 1 ⁇ m, and 0.2 to 0.5 ⁇ m.
  • the particle size of the inorganic particles 2 is set so that the light to be reflected (that is, the light emitted from the light emitting element) is not transmitted. It is preferable that it is 50% or more.
  • examples of the shape of the inorganic particles 2 include an amorphous shape, a spherical shape, a scaly shape, and a needle shape.
  • a spherical shape is preferable from the viewpoint of the light diffusion effect
  • a scaly shape is preferable from the viewpoint of the total reflection effect.
  • the light-reflective conductive particles 10 are produced by a known film formation technique (so-called mechanofusion method) in which a film composed of small particles is formed on the surface of large particle diameter particles by physically colliding large and small powders. be able to.
  • the inorganic particles 2 are fixed so as to bite into the metal material on the surface of the core particle 1, and on the other hand, the inorganic particles monolayers constitute the light reflecting layer 3 because the inorganic particles are hardly fused and fixed together. Therefore, in the case of FIG. 1A, the layer thickness of the light reflecting layer 3 is considered to be equal to or slightly thinner than the particle size of the inorganic particles 2.
  • the light-reflective conductive particle 20 shown in FIG. 1B contains a thermoplastic resin 4 in which the light-reflective layer 3 functions as an adhesive, and the inorganic particles 2 are also fixed to each other by the thermoplastic resin 4. It differs from the light-reflective conductive particle 10 of FIG. 1A in that it is formed (for example, two layers or three layers). By containing such a thermoplastic resin 4, the mechanical strength of the light reflecting layer 3 is improved, and the inorganic particles are hardly peeled off.
  • thermoplastic resin 4 a halogen-free thermoplastic resin can be preferably used for the purpose of low environmental load.
  • polyolefins such as polyethylene and polypropylene, polystyrene, acrylic resins, and the like can be preferably used.
  • Such light-reflective conductive particles 20 can also be manufactured by a mechanical fusion method. If the particle size of the thermoplastic resin 4 applied to the mechanical fusion method is too small, the adhesion function is lowered, and if it is too large, it is difficult to adhere to the core particles. More preferred. Further, if the blending amount of the thermoplastic resin 4 is too small, the adhesion function is deteriorated, and if it is too large, aggregates of particles are formed. 500 parts by mass is preferable, and 4 to 25 parts by mass is more preferable.
  • thermosetting resin contained in the light-reflective anisotropic conductive adhesive in the present embodiment it is preferable to use a colorless and transparent resin as much as possible. This is because the light reflecting efficiency of the light-reflective conductive particles in the anisotropic conductive adhesive is reflected without lowering the incident light without changing the light color of the incident light.
  • colorless and transparent means that the cured product of the anisotropic conductive adhesive 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 780 nm.
  • the blending amount of the conductive particles such as the light-reflective conductive particles with respect to 100 parts by mass of the thermosetting resin composition is too small, conduction failure occurs. Since short-circuit tends to occur, 1 to 100 parts by mass is preferable, and 10 to 50 parts by mass is more preferable.
  • the light-reflective anisotropic conductive adhesive in the present embodiment has a reflectance (JIS K7105) with respect to light having a wavelength of 450 nm of more than 9% by adding white needle-like inorganic particles to the thermosetting resin composition. High value.
  • the reflection characteristics of the light-reflective anisotropic conductive adhesive in the present embodiment include various other factors such as the reflection characteristics and blending amount of the light-reflective conductive particles, the blending composition of the thermosetting resin composition, and the like.
  • the reflectance (JIS K7105) with respect to light having a wavelength of 450 nm is realized to be 30% or more. Usually, if the amount of light-reflective conductive particles having good reflection characteristics is increased, the reflectance tends to increase.
  • the reflection characteristics of the light-reflective anisotropic conductive adhesive can be evaluated from the viewpoint of refractive index. That is, when the reflectance of the cured product is larger than the refractive index of the cured product of the thermosetting resin composition excluding the conductive particles and the light-reflective insulating particles, the light-reflective insulating particles and the heat surrounding them are heated. This is because the amount of light reflection at the interface between the curable resin composition and the cured product increases.
  • the difference obtained by subtracting the refractive index of the cured product of the thermosetting resin composition (JIS K7142) from the refractive index of the light-reflective insulating particles (JIS K7142) is preferably 0.02 or more, more preferably Is desirably 0.2 or more.
  • the refractive index of the thermosetting resin composition mainly composed of epoxy resin is about 1.5.
  • thermosetting resin composition those used in conventional anisotropic conductive adhesives and anisotropic conductive films can be used.
  • a thermosetting resin composition is obtained by blending an insulating binder resin with a curing agent.
  • the insulating binder resin is preferably an epoxy resin mainly composed of an alicyclic epoxy compound, a heterocyclic epoxy compound, a hydrogenated epoxy compound, or the like.
  • Preferred examples of the alicyclic epoxy compound include those having two or more epoxy groups in the molecule. These may be liquid or solid. Specific examples include glycidyl hexahydrobisphenol A, 3,4-epoxycyclohexenylmethyl-3 ', 4'-epoxycyclohexene carboxylate, and the like. Among them, glycidyl hexavidrobisphenol A, 3,4-epoxycyclohexenylmethyl-3 ′, 4 is preferable because it can ensure light transmission suitable for mounting LED elements on the cured product and is excellent in rapid curing. '-Epoxycyclohexenecarboxylate can be preferably used.
  • heterocyclic epoxy compound examples include an epoxy compound having a triazine ring, and particularly preferably 1,3,5-tris (2,3-epoxypropyl) -1,3,5-triazine-2,4, Mention may be made of 6- (1H, 3H, 5H) -trione.
  • water-added epoxy compound hydrogenated products of the above-described alicyclic epoxy compounds and 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, but two or more kinds may be used in combination.
  • other epoxy compounds may be used in combination as long as the effects of the present invention are not impaired.
  • the curing agent examples include acid anhydrides, imidazole compounds, and dicyan.
  • acid anhydrides that are difficult to discolor the cured product particularly alicyclic acid anhydride-based curing agents, can be preferably used.
  • methylhexahydrophthalic anhydride etc. can be mentioned preferably.
  • thermosetting resin composition when using an alicyclic epoxy compound and an alicyclic acid anhydride-based curing agent, the respective amounts used are uncured if there is too little alicyclic acid anhydride-based curing agent.
  • the epoxy compound increases, and if it is too much, the corrosion of the adherend material tends to be accelerated due to the influence of the excess curing agent. Therefore, the alicyclic acid anhydride-based curing is performed on 100 parts by mass of the alicyclic epoxy compound.
  • the agent is preferably used in a proportion of 80 to 120 parts by mass, more preferably 95 to 105 parts by mass.
  • the light-reflective anisotropic conductive adhesive in the present embodiment is manufactured by uniformly mixing a thermosetting resin composition, conductive particles, and white needle-like inorganic particles that are light-reflective insulating particles. can do.
  • a thermosetting resin composition, conductive particles, and white needle-like inorganic particles that are light-reflective insulating particles are dispersed and mixed together with a solvent such as toluene. Then, it may be applied to the peeled PET film so as to have a desired thickness and dried at a temperature of about 80 ° C.
  • a light-emitting device 200 shown in FIG. 2 includes a connection terminal 22 on a substrate 21 and a connection bump 26 formed on each of an n-electrode 24 and a p-electrode 25 of an LED element 23 as a light-emitting element.
  • This is a light emitting device in which the above-described light-reflective anisotropic conductive adhesive is applied and the substrate 21 and the LED element 23 are flip-chip mounted.
  • the light-reflective anisotropic conductive adhesive cured product 100 is formed by dispersing the light-reflective insulating particles 10 in the cured product 11 of the thermosetting resin composition.
  • the LED element 23 reflects light in the cured product 100 of the light-reflective anisotropic conductive adhesive from light emitted toward the substrate 21 side. Reflected by the conductive insulating particles 10 and emitted from the upper surface of the LED element 23. Accordingly, it is possible to prevent a decrease in luminous efficiency.
  • LED element 23, bump 26, substrate 21, connection terminal 22, etc. can be the same as the configuration of the conventional light-emitting device.
  • the light emitting device 200 can be manufactured using a conventional anisotropic conductive connection technique except that the light-reflective anisotropic conductive adhesive in the present embodiment is used.
  • the well-known light emitting element other than the LED element 23 can be applied in the range which does not impair the effect of this invention.
  • Thermosetting resin composition comprising white needle-like inorganic particles and conductive particles (particle size 5 ⁇ m) whose surface of a spherical resin is gold-plated, and epoxy curing adhesive (adhesive binder mainly composed of CEL2021P-MeHHPA) It mixed with the thing and produced the anisotropic conductive adhesive.
  • the amount of white needle-like inorganic particles added was 12.0% by volume with respect to the thermosetting resin composition.
  • titanium dioxide (TiO 2) whiskers having a long direction particle size of 1.7 ⁇ m and a short direction particle size of 0.13 ⁇ m (aspect ratio of 13.1) were used.
  • the addition amount of electroconductive particle was 10 mass% with respect to the thermosetting resin composition.
  • the produced anisotropic conductive adhesive was applied onto a white plate so as to have a thickness of 100 ⁇ m, and was cured by heating at 200 ° C. for 1 minute.
  • the total reflectance (specular reflection and diffuse reflection) with respect to the light of wavelength 450nm which used barium sulfate as a standard was measured using the spectrophotometer (Shimadzu Corporation UV3100).
  • the conduction reliability and the presence or absence of cracks were evaluated by a thermal cycle test (TCT). Place the test LED module in the TCT, (a) 30 minutes at -40 ° C ⁇ ⁇ 30 minutes at 100 ° C, 1000 cycles, (b) -55 ° C, 30 minutes ⁇ ⁇ 125 ° C, 30 minutes, 1000 cycles It was. That is, (a) exposure to an atmosphere of ⁇ 40 ° C. and 100 ° C. for 30 minutes each, and 1000 cycles of a cooling / heating cycle with this as one cycle, and (b) exposure to an atmosphere of ⁇ 55 ° C. and 125 ° C. for 30 minutes, 1000 cycles of the cooling / heating cycle with this as one cycle were performed.
  • TCT thermal cycle test
  • Evaluation of the presence or absence of cracks was made by performing 1000 cycles of TCT and then observing the test LED module taken out from the TCT from the upper surface of the blue LED element with a metal microscope to observe whether or not cracks occurred.
  • the case where no occurrence of cracks was observed in the light-reflective anisotropic conductive adhesive was evaluated as “ ⁇ ”, and the case where generation of cracks was observed in the light-reflective anisotropic conductive adhesive was determined as “x”.
  • Example 2 Example 1 except that zinc oxide (ZnO) whiskers (Panatetra WZ-05F1, Amtec) having a long particle size of 50 ⁇ m and a short particle size of 3 ⁇ m (aspect ratio of 16.7) were used as white needle-shaped inorganic particles. The same process was performed.
  • ZnO zinc oxide
  • Example 3 Example 1 except that potassium titanate whiskers (Tismo series, manufactured by Otsuka Chemical Co., Ltd.) having a long particle size of 20 ⁇ m and a short particle size of 0.6 ⁇ m (aspect ratio 33.3) were used as the white needle-like inorganic particles. The same process was performed.
  • Example 4 The surface of zinc oxide (ZnO) whisker (Panatetra WZ-05F1, Amtec) having a long particle size of 50 ⁇ m and a short particle size of 3 ⁇ m (aspect ratio of 16.7) is treated with a silane coupling agent as white needle-like inorganic particles. The same treatment as in Example 1 was performed, except that what was used was used.
  • ZnO zinc oxide
  • Example 5 As white needle-like inorganic particles, zinc oxide (ZnO) whiskers (Panatetra WZ-05F1, manufactured by Amtec) having a long direction particle size of 50 ⁇ m, a short direction particle size of 3 ⁇ m, and an aspect ratio of 16.7 were used as a thermosetting resin composition. In addition to the addition of 9.0% by volume, zinc oxide (ZnO) white spherical inorganic particles (type I, manufactured by Sakai Chemical Co., Ltd.) having a particle size of 0.6 ⁇ m (aspect ratio of 1.0) are thermosetting. The same treatment as in Example 1 was performed, except that the resin composition was added at a ratio of 3.0% by volume.
  • ZnO zinc oxide
  • Example 1 The same treatment as in Example 1 was performed except that the anisotropic conductive adhesive did not contain white needle-like inorganic particles.
  • Example 3 In place of the white needle-like inorganic particles of Example 1, 0.6 ⁇ m (aspect ratio: 1.0) zinc oxide white spherical inorganic particles were added at a ratio of 12.0 vol% with respect to the thermosetting resin composition. Except that, the same processing as in Example 1 was performed.
  • Example 1 TiO2 (titanium dioxide) having an aspect ratio of 13.1 as white needle-like inorganic particles was 12.0% by volume with respect to the thermosetting resin composition.
  • the reflectance at a wavelength of 450 nm of the cured product of the added light-reflective anisotropic conductive adhesive was 55%.
  • the total luminous flux of the LED mounting sample using this light-reflective anisotropic conductive adhesive was 350 (mlm). Both the reflectance and the light extraction efficiency from the LED were slightly lower than those of Comparative Example 2 using spherical TiO2 (white spherical inorganic particles).
  • no crack was generated after 1000 cycles of TCT ( ⁇ 40 to 100 ° C.) and 1000 cycles of TCT ( ⁇ 55 to 125 ° C.), and the crack resistance was improved.
  • Example 2 As can be seen from the results of Example 2, light in which ZnO (zinc oxide) having an aspect ratio of 16.7 was added as acicular white inorganic particles at a ratio of 12.0% by volume with respect to the thermosetting resin composition.
  • the reflectance at a wavelength of 450 nm of the cured product of the reflective anisotropic conductive adhesive was 35%.
  • the total luminous flux of the LED mounting sample using this light-reflective anisotropic conductive adhesive was 300 (mlm). Both the reflectance and the light extraction efficiency from the LED were slightly lower than those of Comparative Example 3 using spherical ZnO (white spherical inorganic particles). However, no crack was generated after 1000 cycles of TCT ( ⁇ 40 to 100 ° C.) and 1000 cycles of TCT ( ⁇ 55 to 125 ° C.), and the crack resistance was improved.
  • Example 3 light reflectivity obtained by adding potassium titanate having an aspect ratio of 33.3 as white needle-like inorganic particles in a proportion of 12.0% by volume with respect to the thermosetting resin composition.
  • the reflectance of the cured anisotropic conductive adhesive at a wavelength of 450 nm was 30%.
  • the total luminous flux of the LED mounting sample using this light-reflective anisotropic conductive adhesive was 250 (mlm).
  • Both the reflectance and the light extraction efficiency from the blue LED were slightly lower than those of Comparative Example 3 using granular ZnO (white spherical inorganic particles).
  • no crack was generated after 1000 cycles of TCT ( ⁇ 40 to 100 ° C.) and 1000 cycles of TCT ( ⁇ 55 to 125 ° C.), and the crack resistance was improved.
  • zinc oxide (ZnO) having an aspect ratio of 16.7 as white needle-like inorganic particles was added at a rate of 9.0% by volume with respect to the thermosetting resin composition.
  • the reflectance at a wavelength of 450 nm of a cured product of a light-reflective anisotropic conductive adhesive obtained by adding spherical ZnO (white spherical inorganic particles) at a ratio of 3.0% by volume to the thermosetting resin composition is 40%.
  • the total luminous flux of the LED mounting sample using this light-reflective anisotropic conductive adhesive was 250 (mlm).
  • the wavelength of the cured product of the anisotropic conductive adhesive in which 10% by mass of the conductive particles were added to the thermosetting resin composition without adding the needle-shaped white inorganic particles was 450 nm.
  • the reflectance at 8 was 8%.
  • the total luminous flux of the LED mounting sample using this anisotropic conductive adhesive was 200 (mlm). Since the light with a wavelength of 450 nm emitted from the blue LED is absorbed by gold (Au), the reflectance with respect to this light is lowered, and thereby the emission efficiency (light extraction efficiency) of the blue LED is lowered. No cracks occurred after 1000 cycles of TCT ( ⁇ 40 to 100 ° C.) and 1000 cycles of TCT ( ⁇ 55 to 125 ° C.).
  • a light-reflective anisotropic conductive adhesive having a white spherical inorganic particle of titanium dioxide (TiO2) added at 12.0% by volume with respect to the thermosetting resin composition at a wavelength of 450 nm.
  • the reflectance of was 62%.
  • the total luminous flux of the LED mounting sample using this light-reflective anisotropic conductive adhesive was 390 (mlm).
  • cracks did not occur after 1000 cycles of TCT ( ⁇ 40 to 100 ° C.), but cracks occurred after 1000 cycles of TCT ( ⁇ 55 to 125 ° C.).
  • the light-reflective anisotropic conductive adhesive obtained by adding 12.0% by volume of white spherical inorganic particles of zinc oxide (ZnO) to the thermosetting resin composition at a wavelength of 450 nm.
  • the reflectance of was 40%.
  • the total luminous flux of the LED mounting sample using this light-reflective anisotropic conductive adhesive was 350 (mlm).
  • Examples 1 to 5 using the light-reflective anisotropic conductive adhesive in which the white needle-like inorganic particles are added to the thermosetting resin composition the light emitted from the LED element is not affected. It was possible to suppress the decrease in reflectivity and improve the light emission efficiency (light extraction efficiency) of the LED element. Further, the light-reflective anisotropic conductive adhesives in Examples 1 to 5 were confirmed to have high crack resistance even after TCT. This is presumably because the toughness of the thermosetting resin composition could be increased by the white needle-like inorganic particles having a needle-like shape. Further, it was found that the light-reflective anisotropic conductive adhesives of Examples 1 to 5 have high resistance to temperature changes and exhibit excellent conduction reliability.

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Abstract

　発光素子の発光効率を維持するとともに、クラックの発生を防止して高い導通信頼性を得ることが可能な光反射性異方性導電接着剤及び発光装置を提供する。光反射性異方性導電接着剤は、熱硬化性樹脂組成物と、導電性粒子と、光反射性針状絶縁粒子とを含有する。この光反射性針状絶縁粒子は、酸化チタン、酸化亜鉛及びチタン酸塩からなる群より選択される少なくとも１種の無機粒子である。

Description

光反射性異方性導電接着剤及び発光装置
　本発明は、発光素子を配線板に異方性導電接続するために使用する光反射性異方性導電接着剤、及び、この光反射性異方性導電接着剤を用いて発光素子を配線板に実装してなる発光装置に関する。
　本出願は、日本国において２０１０年４月１３日に出願された日本特許出願番号特願２０１０－０９２６７２を基礎として優先権を主張するものであり、この出願を参照することにより、本出願に援用される。
　従来、発光ダイオード（ＬＥＤ）素子等の発光素子を使用した発光装置が広く使用されている。図３～図５に、旧タイプの発光装置の構造例を示す。図３に示す発光装置の製造においては、基板３１上にダイボンド接着剤３２でＬＥＤ素子３３を接合し、ＬＥＤ素子３３の上面のｐ電極３４，ｎ電極３５を金（Ａｕ）ワイヤ３７で基板３１に銀メッキ３６によりワイヤボンディングする。これにより、ＬＥＤ素子３３と基板３１とを電気的に接合している。通常、発光装置は、ＬＥＤ素子３３全体を透明モールド樹脂等の樹脂で封止するが（図示せず）、樹脂とＬＥＤ素子３３及び金ワイヤ３７との線膨張係数の違いによって金ワイヤ３７の接続部分に剥離が生じたり、金ワイヤ３７の断線による電気接続不良が発生することがある。
　一般に、このような発光装置に対しては、ＬＥＤ素子から出射された光の反射率の低減を抑制して発光効率（光取り出し効率）を維持させることが要請されている。図３に示す発光装置において、ＬＥＤ素子３３のｐ電極３４、ｎ電極３５としては、通常、金電極を使用する。しかしながら、ＬＥＤ素子３３が出射する光の内、上面側に出射する波長４００～５００ｎｍの光を金電極や金ワイヤが吸収し、また、下側に出射した光をダイボンド接着剤３２が吸収する。このような光吸収は、ＬＥＤ素子３３の発光効率（光取り出し効率）を低下させてしまう。さらに、ダイボンド接着剤３２による接着プロセスは、オーブン硬化によるため、製造に時間がかかるといった問題もある。
　図４に示す発光装置は、銀ペーストに代表される導電性ペースト３７が使用され、この導電性ペースト３７によってＬＥＤ素子３３の下面のｐ電極３４、ｎ電極３５と基板３１上の銀メッキ部分３６とが電気的に接合されている。しかしながら、導電性ペースト３７は、接着力が弱いため、封止樹脂３８による補強が必要となる。その上、導電性ペースト３７の内部に光が拡散又は吸収することがあり、ＬＥＤ素子３３の発光効率を低下させてしまう。
　そこで、例えば異方性導電接着剤（ＡＣＰ）又は異方性導電接着フィルム（ＡＣＰ）を硬化させることでＬＥＤ素子と基板とを接続固定して電気的に接合したものが提案されている。例えば特許文献１には、ＬＥＤ素子をフリップチップ実装する方法が記載されている。また、例えば図５に示す発光装置は、市販の異方性導電接着剤３９を使用してフリップチップ実装によりＬＥＤ素子３３の下面のｐ電極３４、ｎ電極３５と基板３１とを電気的に接合したものである。このフリップチップ実装技術においては、ｐ電極３４とｎ電極３５とにバンプ４０がそれぞれ形成されている。
　特許文献１の技術では、ＬＥＤ素子に光反射層をｐ電極及びｎ電極と絶縁するように金属蒸着層等により設けている。これにより、ＬＥＤ素子から出射された光の反射率の低減を抑制して発光効率を維持させている。しかしながら、この特許文献１の技術では、発光装置の製造工程数が増加する上、コストアップが避けられないという問題がある。他方、図５に示す発光装置は、光反射層を設けないものの、ＡＣＰのバインダに分散される導電性粒子として使用されるＡｕ又はＮｉが茶色又は暗茶色を呈すること、バインダが通常含有するイミダゾール系潜在性硬化剤が茶色を呈すること等の原因により、ＡＣＰのバインダが全体的に茶色を呈し、これによって光を吸収してしまう。その結果、ＬＥＤ素子３３の発光効率が低下する。
特開平１１－１６８２３５号公報
　ところで、ＡＣＰは、エポキシ樹脂をバインダ樹脂として使用するが、エポキシ樹脂を使用するＡＣＰは、温度変化に伴う接続基板との熱膨張率差に基づく内部応力によって、導通抵抗の増大、接合面の剥離、クラック等を生じていた。このため、鉛フリーハンダの対応リフロー、熱衝撃の耐性、高温高湿度雰囲気中で使用及び貯蔵した場合の、蒸着配線の腐食現象に対する耐性等の信頼性が低下することがあった。
　本発明は、このような従来の実情に鑑みて提案されたものであり、ＬＥＤ素子等の発光素子を配線板に異方性導電接着剤を用いてフリップチップ実装してなり、製造コストを招くような光反射層をＬＥＤ素子に設けることなく発光素子の発光効率を維持させる発光装置において、異方性導電接着剤のクラックの発生を防止して高い導通信頼性を得ることを目的とするものである。
　本件発明者は、異方性導電接着剤中に添加する光反射性絶縁粒子を針状形状とすることによって、クラックの発生を防止できることを見出した。
　すなわち、本発明は、発光素子を配線板に異方性導電接続するために使用する光反射性異方性導電接着剤であって、熱硬化性樹脂、導電性粒子及び光反射性針状絶縁粒子を含有することを特徴とする。
　また、本発明は、このような光反射性異方性導電接着剤を介して、発光素子がフリップチップ方式で配線板に実装されていることを特徴とする。
　本発明の光反射性異方性導電接着剤及び発光装置によれば、異方性導電接着剤中に光反射性針状絶縁粒子を添加することにより、光反射性異方性導電接着剤におけるクラックの発生を防止して高い導通信頼性を得ることができる。
図１Ａは、光反射性導電性粒子の断面図であり、図１Ｂは、光反射性導電性粒子の断面図である。 図２は、本実施の形態における発光装置の断面図である。 図３は、従来の発光装置の断面図である。 図４は、従来の発光装置の断面図である。 図５は、従来の発光装置の断面図である。
　以下、本発明を適用した光反射性異方性導電接着剤の具体的な実施の形態（以下、これを「本実施の形態」という。）の一例について、図面を参照しながら説明する。本実施の形態における光反射性異方性導電接着剤は、発光素子であるＬＥＤ素子を配線板に異方性導電接続するために使用する接着剤であって、熱硬化性樹脂組成物と、導電性粒子と、光反射性針状絶縁粒子とを含有する。
　光反射性針状絶縁粒子は、後述するように、アスペクト比が所定範囲の値である針状形状からなることを特徴としている。熱硬化性樹脂組成物が球状粒子を含有する場合、温度変化に伴い伸縮性が低下すると、熱硬化性樹脂組成物の内部応力によって球状粒子と熱硬化性樹脂組成物との界面からクラックが発生する場合がある。このように光反射性異方性導電接着剤にクラックが生じると、導通信頼性を損なうことになる。そのため、光反射性異方導電接着剤は、優れた強靭性を有することが必要となる。
　本実施の形態における光反射性異方性導電接着剤は、アスペクト比が所定範囲の針状の光反射性絶縁粒子を熱硬化性樹脂組成物に添加する。熱硬化性樹脂組成物中において、それぞれランダムな方向に配置される針状の光反射性絶縁粒子は、温度変化に伴う熱硬化性樹脂組成物の内部応力を針状結晶中に伝搬及び吸収させて熱硬化性樹脂にこの内部応力が伝わるのを抑制することができるため、熱硬化性樹脂組成物の強靭性を高めることができる。これにより、光反射性異方導電接着剤は、優れた強靭性を発揮して、温度変化によって熱硬化性樹脂組成物が伸縮してもクラックの発生や接着面の剥離を抑制することができる。
　光反射性針状絶縁粒子は、可視光を発光する発光装置においては、白色を呈する針状無機化合物からなり、光反射性異方性導電接着剤に入射した光を外部に反射する。光反射性針状絶縁粒子自体が白色を呈することにより、可視光に対する反射特性の波長依存性を小さくすることができ、可視光を効率的に反射することができる。
　このように、本実施の形態における光反射性異方性導電接着剤は、白色を呈するとともにアスペクト比が所定範囲の針状形状を有する無機化合物からなる粒子（以下、これを「白色針状無機粒子」という。）を含有することにより、発光素子から出射された光に対する反射率の低減を抑制して発光素子の発光効率を維持するとともに、クラック等を防止して高い導通信頼性を得ることができる。
　白色針状無機粒子としては、例えば酸化亜鉛ウィスカ、酸化チタンウィスカ、チタン酸カリウムウィスカ等のチタン酸塩ウィスカ、ホウ酸アルミニウムウィスカ、ウォラストナイト（カオリンシリケートの針状結晶）等の針状形状の無機化合物を挙げることができる。ウィスカは、特殊な製法によって針状に成長した結晶であり、結晶構造に乱れがないため弾力性に富み、変形しにくいという利点を有する。これらの無機化合物は、可視光を発光する発光装置においては白色を呈するため、可視光に対する反射特性の波長依存性が小さく、且つ可視光を反射しやすい。中でも、酸化亜鉛ウィスカは、白色度が高く、且つ、硬化した異方性導電接着剤における熱硬化性樹脂組成物の硬化物の光劣化が懸念される場合であっても光劣化に対して触媒性がないことから、特に好ましい。
　白色針状無機粒子は、一本の針状形状を有する結晶（単針状結晶）からなる場合には、その繊維径（短方向粒径）は、５μｍ以下が好ましい。また、単針状結晶からなる白色針状無機粒子のアスペクト比は、１０よりも大きく３５未満が好ましく、１０よりも大きく２０未満が特に好ましい。白色針状無機粒子のアスペクト比が１０よりも大きい場合には、熱硬化性樹脂の内部応力を十分に伝搬及び吸収させることができる。また、白色針状無機粒子のアスペクト比が３５未満である場合には、針状の結晶が折れにくくなるとともに、熱硬化性樹脂中へ均一に分散することができ、導電性粒子による異方性接続を阻害することがない。このアスペクト比が２０未満である場合には、熱硬化性樹脂中への分散性をさらに向上させることができる。
　アスペクト比が１０よりも大きく３５未満の白色針状無機粒子を熱硬化性樹脂組成物に添加することにより、熱硬化性樹脂組成物の強靭性を高めることができるため、光反射性異方性導電接着剤が伸縮しても接着面の剥離やクラックが発生することを抑制することができる。
　なお、白色針状無機粒子としては、このような単針状結晶であるものに代えて、例えばテトラポッド（登録商標）のように四面体の中心部と頂点とをそれぞれ結合してなる形状等の、複数本の針状形状を有する結晶（複針状結晶）を使用するようにしてもよい。複針状結晶の白色針状無機粒子は、単針状結晶の白色針状無機粒子に比べて熱伝導性が大きい点で優れているが、単針状結晶よりもかさ高い結晶構造であるため、熱圧着時に針状部分によって基板や素子の接合部品を傷付けないように注意する必要がある。
　また、針状白色無機粒子は、例えばシランカップリング剤で処理したものであってもよい。針状白色無機粒子がシランカップリング剤で処理されていることにより、熱硬化性樹組成物中での分散性を向上させることができる。このため、シランカップリング剤で処理した針状白色無機粒子を短時間に均一に熱硬化性樹脂組成物中に混合させることができる。
　白色針状無機粒子は、その屈折率（ＪＩＳ　Ｋ７１４２）が、好ましくは熱硬化性樹脂組成物の硬化物の屈折率（ＪＩＳ　Ｋ７１４２）よりも大きいこと、より好ましくは少なくとも０．０２程度大きいことが好ましい。屈折率の差が小さいと、それらの界面での反射効率が低下するからである。すなわち、白色針状無機粒子としては、光反射性且つ絶縁性を有する無機粒子であっても、ＳｉＯ２のように、その屈折率が使用する熱硬化性樹脂組成物の屈折率以下であるものは適用できない。
　白色針状無機粒子の光反射性異方性導電接着剤中の配合量は、少なすぎると十分な光反射を実現することができず、その一方、多すぎると、熱硬化性樹脂の接着性が低下するため、熱硬化性樹脂組成物に対し、１～５０体積％（Ｖｏｌ％）であることが好ましく、５～２５体積％であることが特に好ましい。
　本実施の形態における光反射性異方性導電接着剤は、このような白色針状無機粒子を含有することで、導電性粒子の大部分を覆うため、導電性粒子が茶色等の色を呈する場合であっても、熱硬化性樹脂組成物の白色性を実現する。このような熱硬化性樹脂組成物の白色性により、可視光に対する反射特性の波長依存性を小さくし、且つ可視光を反射しやすくなるため、基板電極の色の種類に関係なく、ＬＥＤ素子から出射される光の反射率の低下を抑制するとともに、ＬＥＤ素子がその下面側に向けて発光する光も効率的に利用することができる。その結果、ＬＥＤ素子の発光効率（光取り出し効率）を向上させることができる。
　そして、本実施の形態における光反射性異方性導電接着剤は、光反射性絶縁粒子としての白色の無機粒子の形状が針状であることにより、温度変化に伴う熱硬化性樹脂組成物の内部応力を針状結晶中に伝搬及び吸収させて熱硬化性樹脂にこの内部応力が伝わるのを抑制することができる。なお、粒子形状が球状である場合には、熱硬化性樹脂組成物の内部応力を、針状形状の粒子に比べて粒子内に伝搬及び吸収させにくい。
　光反射性異方導電接着剤は、このようにして熱硬化性樹脂にこの内部応力が伝わるのを抑制するため、熱硬化性樹脂組成物の強靭性を高めることができる。これにより、光反射性異方導電接着剤は、優れた強靭性を発揮して、温度変化によって熱硬化性樹脂組成物が伸縮してもクラックの発生や接着面の剥離を抑制することができる。
　なお、本実施の形態における光反射性異方性導電接着剤は、光反射性絶縁粒子としての白色を呈する球状形状の無機化合物からなる粒子（以下、これを「白色球状無機粒子」という。）を含有する熱硬化性樹脂組成物に、白色針状無機粒子を添加するようにしてもよい。白色球状無機粒子は、上述の白色針状無機粒子と同様の材料からなることが好ましく、ＳｉＯ２のように、その屈折率が使用する熱硬化性樹脂組成物の屈折率以下であるものは適用できない。
　この白色針状無機粒子とともに白色球状無機粒子を添加することで、熱硬化性樹脂組成物をさらに白色化してＬＥＤ素子の光取り出し効率をより向上させることができる。また、この場合においても、熱硬化性樹脂の強靭性を高めることができる。ここで、白色針状無機粒子の添加量（Ｖｏｌ％）は、白色球状無機粒子の添加量（Ｖｏｌ％）と同量以上とすることが好ましい。
　白色球状無機粒子は、小さすぎると反射率が低くなり、大きすぎると異方性導電性粒子による接続を阻害する等の傾向があるので、その大きさは、０．０２～２０μｍが好ましく、０．２～１μｍがより好ましい。
　白色球状無機粒子は、白色針状無機粒子と同様に、その屈折率（ＪＩＳ　Ｋ７１４２）が、熱硬化性樹脂組成物の硬化物の屈折率（ＪＩＳ　Ｋ７１４２）よりも大きいことが好ましく、少なくとも０．０２程度大きいことがより好ましい。
　球状の光反射性絶縁粒子としては、このような白色球状無機粒子に代えて、球状の金属粒子の表面を透明な絶縁性樹脂で被覆した樹脂被覆金属粒子を使用してもよい。金属粒子としては、ニッケル、銀、アルミニウム等を挙げることができる。
　樹脂被覆金属粒子の大きさは、粒径０．１～３０μｍが好ましく、０．２～１０μｍであることがより好ましい。なお、樹脂被覆金属粒子の大きさは、絶縁被覆も含めての大きさを示している。
　このような樹脂被覆金属粒子における当該樹脂としては、種々の絶縁性樹脂を使用することができる。機能的強度や透明性の点から、アクリル系樹脂の硬化物を好ましく利用することができる。好ましくは、ベンゾイルパーオキサイド等の有機過酸化物等のラジカル開始剤の存在下で、メタクリル酸メチルとメタクリル酸２－ヒドロキシエチルとをラジカル共重合させた樹脂を挙げることができる。この場合、２，４－トリレンジイソシアネート等のイソシアネート系架橋剤で架橋されていることがより好ましい。
　また、金属粒子としては、予めシランカップリング剤でγ－グリシドキシ基やビニル基等を金属表面に導入しておくことが好ましい。
　このような樹脂被覆金属粒子は、例えばトルエン等の溶媒中に金属粒子とシランカップリング剤とを投入し、室温で約１時間攪拌した後、ラジカルモノマーとラジカル重合開始剤と、必要に応じて架橋剤とを投入し、ラジカル重合開始温度に加温しながら攪拌することにより製造することができる。
　光反射性異方性導電接着剤において、白色針状無機粒子とともに白色球状無機粒子が添加されている場合においても、光反射性異方性導電接着剤は、優れた強靭性を発揮することができることにより、温度変化によって伸縮しても接着面の剥離やクラックが発生することを抑制することができる。
　本実施の形態における光反射性異方性導電接着剤が含有する導電性粒子としては、異方性導電接続用の従来の導電性粒子において使用されている金属材料の粒子を使用することができる。すなわち、導電性粒子の金属材料としては、例えば金、ニッケル、銅、銀、半田、パラジウム、アルミニウム、それらの合金、それらの多層化物（例えば、ニッケルメッキ／金フラッシュメッキ物）等を挙げることができる。
　なお、金、ニッケル或いは銅を金属材料とする導電性粒子は、茶色を呈することから、本発明の効果を他の金属材料よりも享受することができる。すなわち、上述したように、熱硬化性樹脂組成物中において、白色針状無機粒子が導電性粒子の大部分を覆うため、導電性粒子に起因して熱硬化性樹脂組成物が茶色を呈するのを抑制し、熱硬化性樹脂組成物全体が高い白色性を呈するようになる。
　また、導電性粒子としては、樹脂粒子を金属材料で被覆した金属被覆樹脂粒子を使用するようにしてもよい。このような樹脂粒子としては、スチレン系樹脂粒子、ベンゾグアナミン樹脂粒子、ナイロン樹脂粒子等を挙げることができる。樹脂粒子を金属材料で被覆する方法としては、従来公知の方法を採用することができ、例えば無電解メッキ法、電解メッキ法等を利用することができる。また、被覆する金属材料の層厚は、良好な接続信頼性を確保できる厚さであればよく、樹脂粒子の粒径や金属の種類にもよるが、通常、０．１～３μｍである。
　また、樹脂粒子の粒径は、小さすぎると導通不良が生じ、大きすぎるとパターン間ショートが生じる傾向にあるので、１～２０μｍが好ましく、３～１０μｍがより好ましく、さらには３～５μｍが特に好ましい。この場合、樹脂粒子の形状としては球形が好ましいが、フレーク状、ラクビーボール状であってもよい。
　金属被覆樹脂粒子は、球状形状であり、その粒径は、大きすぎると接続信頼性の低下となるため、１～２０μｍが好ましく、３～１０μｍがより好ましい。
　なお、本実施の形態における光反射性異方性導電接着剤が含有する導電性粒子は、例えば図１Ａ、図１Ｂの断面図に示されるような、光反射性を付与した光反射性導電性粒子とすることも可能である。
　図１Ａに示す光反射性導電性粒子１０は、金属材料で被覆されているコア粒子１と、その表面に酸化チタン（ＴｉＯ２）粒子、酸化亜鉛（ＺｎＯ）粒子又は酸化アルミニウム（Ａｌ２Ｏ３）粒子から選択された少なくとも一種の無機粒子２から形成される光反射層３とから構成される。このような無機粒子から形成された光反射層３は、白色から灰色の範囲にある色を呈する。このため、上述したように、可視光に対する反射特性の波長依存性が小さく、且つ可視光を反射しやすくなり、ＬＥＤ素子の発光効率をより向上させることができる。
　なお、酸化チタン粒子、酸化亜鉛粒子又は酸化アルミニウム粒子の内、硬化した異方性導電接着剤の熱硬化性樹脂組成物の硬化物の光劣化が懸念される場合には、上述したように、光劣化に対して触媒性がなく、屈折率も高い酸化亜鉛を好ましく使用することができる。
　コア粒子１は、異方性導電接続に供するものであり、表面が金属異材料で構成されている。コア粒子１の態様としては、例えばコア粒子１そのものが金属材料である態様、又は樹脂粒子の表面が金属材料で被覆された態様を挙げることができる。
　無機粒子２から形成された光反射層３の層厚は、コア粒子１の粒径との相対的大きさの観点からみると、コア粒子１の粒径に対して小さすぎると反射率の低下が著しくなり、大きすぎると導通不良が生じる。このため、光反射層３の層厚は、０．５～５０％が好ましく、１～２５％がより好ましい。
　また、光反射性導電性粒子１０において、光反射層３を構成する無機粒子２の粒径は、小さすぎると光反射現象が生じ難くなり、大きすぎると光反射層の形成が困難となる傾向がある。このため、無機粒子２の粒径は、０．０２～４μｍが好ましく、０．１～１μｍ、０．２～０．５μｍが特に好ましい。この場合、光反射させる光の波長の観点からみると、無機粒子２の粒径は、反射させるべき光（すなわち、発光素子が発する光）が透過してしまわないように、その光の波長の５０％以上であることが好ましい。この場合、無機粒子２の形状としては無定型、球状、鱗片状、針状等を挙げることができるが、中でも、光拡散効果の点から球状、全反射効果の点から鱗片状の形状が好ましい。
　光反射性導電性粒子１０は、大小の粉末同士を物理的に衝突させることにより大粒径粒子の表面に小粒子からなる膜を形成させる公知の成膜技術（いわゆるメカノフュージョン法）により製造することができる。この場合、無機粒子２は、コア粒子１の表面の金属材料に食い込むように固定され、他方、無機粒子同士が融着固定されにくいから、無機粒子のモノレイヤが光反射層３を構成する。したがって、図１Ａの場合、光反射層３の層厚は、無機粒子２の粒径と同等乃至わずかに薄くなると考えられる。
　図１Ｂに示す光反射性導電性粒子２０は、光反射層３が接着剤として機能する熱可塑性樹脂４を含有し、この熱可塑性樹脂４により無機粒子２同士も固定され、無機粒子２が多層化（例えば２層又は３層）している点で、図１Ａの光反射性導電性粒子１０と相違する。このような熱可塑性樹脂４を含有することにより、光反射層３の機械的強度が向上し、無機粒子の剥落等が生じにくくなる。
　熱可塑性樹脂４としては、環境低負荷を意図してハロゲンフリーの熱可塑性樹脂を好ましく使用することができ、例えば、ポリエチレン、ポリプロピレン等のポリオレフィンやポリスチレン、アクリル樹脂等を好ましく使用することができる。
　このような光反射性導電性粒子２０も、メカフュージョン法により製造することができる。メカフュージョン法に適用する熱可塑性樹脂４の粒子径は、小さすぎると接着機能が低下し、大きすぎるとコア粒子に付着しにくくなるので、０．０２～４μｍが好ましく、０．１～１μｍがより好ましい。また、このような熱可塑性樹脂４の配合量は、少なすぎると接着機能が低下し、多すぎると粒子の凝集体が形成されるので、無機粒子２の１００質量部に対し、０．２～５００質量部が好ましく、４～２５質量部がより好ましい。
　本実施の形態における光反射性異方性導電接着剤に含まれる熱硬化性樹脂としては、なるべく無色透明なものを使用することが好ましい。異方性導電接着剤中の光反射性導電性粒子の光反射効率を低下させず、更には入射光の光色を変えずに反射させるためである。ここで、無色透明とは、異方性導電接着剤の硬化物が、波長３８０～７８０ｎｍの可視光に対して光路長１ｃｍの光透過率（ＪＩＳ　Ｋ７１０５）が８０％以上、好ましくは９０％以上となることを意味する。
　光反射性異方性導電接着剤において、熱硬化性樹脂組成物１００質量部に対する光反射性導電性粒子等の導電性粒子の配合量は、少なすぎると導通不良が生じ、多すぎるとパターン間ショートが生じる傾向があるので、１～１００質量部が好ましく、１０～５０質量部がより好ましい。
　本実施の形態における光反射性異方性導電接着剤は、熱硬化性樹脂組成物に白色針状無機粒子を加えることで、波長４５０ｎｍの光に対する反射率（ＪＩＳ　Ｋ７１０５）が、９％よりも高い値となる。本実施の形態における光反射性異方性導電接着剤の反射特性は、その他の様々な因子、例えば光反射性導電性粒子の反射特性や配合量、熱硬化性樹脂組成物の配合組成等を適宜調整することで、波長４５０ｎｍの光に対する反射率（ＪＩＳ　Ｋ７１０５）で、３０％以上を実現する。通常、反射特性の良好な光反射性導電性粒子の配合量を増量すれば、反射率も増大する傾向がある。
　また、光反射性異方性導電接着剤の反射特性は屈折率という観点から評価することもできる。すなわち、その硬化物の反射率が、導電性粒子と光反射性絶縁粒子とを除いた熱硬化性樹脂組成物の硬化物の屈折率よりも大きいと、光反射性絶縁粒子とそれを取り巻く熱硬化性樹脂組成物の硬化物との界面での光反射量が増大するからである。具体的には、光反射性絶縁粒子の屈折率（ＪＩＳ　Ｋ７１４２）から、熱硬化性樹脂組成物の硬化物の屈折率（ＪＩＳ　Ｋ７１４２）を差し引いた差が、好ましくは０．０２以上、より好ましくは０．２以上であることが望まれる。なお、通常、エポキシ樹脂を主体とする熱硬化性樹脂組成物の屈折率は、約１．５である。
　熱硬化性樹脂組成物としては、従来の異方性導電接着剤や異方性導電フィルムにおいて使用されているものを利用することができる。一般に、このような熱硬化性樹脂組成物は、絶縁性バインダ樹脂に硬化剤を配合したものである。絶縁性バインダ樹脂としては、脂環式エポキシ化合物や複素環系エポキシ化合物や水素添加エポキシ化合物等を主成分としたエポキシ系樹脂が好ましく挙げられる。
　脂環式エポキシ化合物としては、分子内に２つ以上のエポキシ基を有するものが好ましく挙げられる。これらは、液状であっても固体状であってもよい。具体的には、グリシジルヘキサヒドロビスフェノールＡ、３，４－エポキシシクロヘキセニルメチル－３’，４’－エポキシシクロヘキセンカルボキシレート等を挙げることができる。中でも、硬化物にＬＥＤ素子の実装等に適した光透過性を確保でき、速硬化性にも優れている点から、グリシジルヘキサビドロビスフェノールＡ、３，４－エポキシシクロヘキセニルメチル－３’，４’－エポキシシクロヘキセンカルボキシレートを好ましく使用することができる。
　複素環状エポキシ化合物としては、トリアジン環を有するエポキシ化合物を挙げることができ、特に好ましくは１，３，５－トリス（２，３－エポキシプロピル）－１，３，５－トリアジン－２，４，６－（１Ｈ，３Ｈ，５Ｈ）－トリオンを挙げることができる。
　水添加エポキシ化合物としては、先述の脂環式エポキシ化合物や複素環系エポキシ化合物の水素添加物や、その他公知の水素添加エポキシ樹脂を使用することができる。
　脂環式エポキシ化合物や複素環系エポキシ化合物や水素添加エポキシ化合物は、単独で使用してもよいが、２種以上を併用することができる。また、これらのエポキシ化合物に加えて本発明の効果を損なわない限り、他のエポキシ化合物を併用してもよい。例えば、ビスフェノールＡ、ビスフェノールＦ、ビスフェノールＳ、テトラメチルビスフェノールＡ、ジアリールビスフェノールＡ、ハイドロキノン、カテコール、レゾルシン、クレゾール、テトラブロモビスフェノールＡ、トリヒドロキシビフェニル、ベンゾフェノン、ビスレゾルシノール、ビスフェノールヘキサフルオロアセトン、テトラメチルビスフェノールＡ、テトラメチルビスフェノールＦ、トリス（ヒドロキシフェニル）メタン、ビキシレノール、フェノールノボラック、クレゾールノボラック等の多価フェノールとエピクロルヒドリンとを反応させて得られるグリシジルエーテル；グリセリン、ネオペンチルグリコール、エチレングリコール、プロピレングリコール、ヘキシレングリコール、ポリエチレングリコール、ポリプロピレングリコール等の脂肪族多価アルコールとエピクロルヒドリンとを反応させて得られるポリグリシジルエーテル；ｐ－オキシ安息香酸、β－オキシナフトエ酸のようなヒドロキシカルボン酸とエピクロルヒドリンとを反応させて得られるグリシジルエーテルエステル；フタル酸、メチルフタル酸、イソフタル酸、テレフタル酸、テトラハイドロフタル酸、エンドメチレンテトラハイドロフタル酸、エンドメチレンヘキサハイドロフタル酸、トリメット酸、重合脂肪酸のようなポリカルボン酸から得られるポリグリシジルエステル；アミノフェノール、アミノアルキルフェノールから得られるグリシジルアミノグリシジルエーテル；アミノ安息香酸から得られるグリシジルアミノグリシジルエステル；アニリン、トルイジン、トリブロムアニリン、キシリレンジアミン、ジアミノシクロヘキサン、ビスアミノメチルシクロヘキサン、４，４’－ジアミノジフェニルメタン、４，４’－ジアミノジフェニルスルホン等から得られるグリシジルアミン；エポキシ化ポリオレフィン等の公知のエポキシ樹脂類が挙げられる。
　硬化剤としては、酸無水物、イミダゾール化合物、ジシアン等を挙げることができる。中でも、硬化物を変色させ難い酸無水物、特に脂環式酸無水物系硬化剤を好ましく使用できる。具体的には、メチルヘキサヒドロフタル酸無水物等を好ましく挙げることができる。
　熱硬化性樹脂組成物において、脂環式エポキシ化合物と脂環式酸無水物系硬化剤とを使用する場合、それぞれの使用量は、脂環式酸無水物系硬化剤が少なすぎると未硬化エポキシ化合物が多くなり、多すぎると余剰の硬化剤の影響で被着体材料の腐食が促進される傾向があるので、脂環式エポキシ化合物１００質量部に対し、脂環式酸無水物系硬化剤を、好ましくは８０～１２０質量部、より好ましくは９５～１０５質量部の割合で使用する。
　本実施の形態における光反射性異方性導電接着剤は、熱硬化性樹脂組成物と、導電性粒子と、光反射性絶縁粒子である白色針状無機粒子とを均一に混合することにより製造することができる。また、光反射性異方性導電フィルムとする場合には、熱硬化性樹脂組成物と、導電性粒子と、光反射性絶縁粒子である白色針状無機粒子とをトルエン等の溶媒とともに分散混合し、剥離処理したＰＥＴフィルムに所期の厚さとなるように塗布し、約８０℃程度の温度で乾燥すればよい。
　次に、本実施の形態における光反射性異方性導電接着剤を用いて発光素子を配線板に実装してなる発光装置について、図２を参照しながら説明する。図２に示す発光装置２００は、基板２１上の接続端子２２と、発光素子としてのＬＥＤ素子２３のｎ電極２４とｐ電極２５とのそれぞれに形成された接続用のバンプ２６との間に、上述の光反射性異方性導電接着剤を塗布し、基板２１とＬＥＤ素子２３とがフリップチップ実装されている発光装置である。ここで、光反射性異方性導電接着剤の硬化物１００は、光反射性絶縁粒子１０が熱硬化性樹脂組成物の硬化物１１中に分散してなるものである。なお、必要に応じて、ＬＥＤ素子２３の全体を覆うように透明モールド樹脂で封止してもよい。
　このように構成されている発光装置２００において、ＬＥＤ素子２３は、発した光の内、基板２１側に向かって発した光が光反射性異方性導電接着剤の硬化物１００中の光反射性絶縁粒子１０で反射し、ＬＥＤ素子２３の上面から出射する。したがって、発光効率の低下を防止することができる。
　発光装置２００における光反射性異方性導電接着剤以外の構成（ＬＥＤ素子２３、バンプ２６、基板２１、接続端子２２等）は、従来の発光装置の構成と同様とすることができる。また、発光装置２００は、本実施の形態における光反射性異方性導電接着剤を使用すること以外は、従来の異方性導電接続技術を利用して製造することができる。なお、発光素子としては、ＬＥＤ素子２３の他、本発明の効果を損なわない範囲で公知の発光素子を適用することができる。
　以下、本発明の具体的な実施例について説明する。なお、本発明の範囲は、下記のいずれかの実施例に限定されるものではない。
＜実施例１＞
（異方性導電接着剤の作製）
　白色針状無機粒子と、球状樹脂の表面を金メッキ処理した導電性粒子（粒径５μｍ）とをエポキシ硬化系接着剤（ＣＥＬ２０２１Ｐ－ＭｅＨＨＰＡを主成分とした接着性バインダ）からなる熱硬化性樹脂組成物に混合し、異方性導電接着剤を作製した。白色針状無機粒子の添加量は、熱硬化性樹脂組成物に対して１２．０体積％とした。白色針状無機粒子としては、長方向粒径１．７μｍ、短方向粒径０．１３μｍ（アスペクト比１３．１）の二酸化チタン（ＴｉＯ２）ウィスカを使用した。また、導電性粒子の添加量は、熱硬化性樹脂組成物に対して１０質量％とした。
（光反射率の評価）
　作製した異方性導電接着剤を白色板上に厚さ１００μｍとなるように塗布し、２００℃で１分間加熱して硬化させた。得られた硬化物について、分光光度計（島津製作所社製　ＵＶ３１００）を用いて硫酸バリウムを標準とした波長４５０ｎｍの光に対する全反射率（鏡面反射及び拡散反射）を測定した。
（ＬＥＤ実装サンプルの作製）
　１００μｍピッチの銅配線にＮｉ／Ａｕ（５．０μｍ厚／０．３μｍ厚）メッキ処理した配線を有するガラスエポキシ基板に、バンプホルダ（ＦＢ７００、カイジョー（株））を用いて１５μｍ高の金（Ａｕ）バンプを形成した。この金バンプ付きエポキシ基板に、光反射性異方性導電接着剤を用いて、青色ＬＥＤ（Ｖｆ＝３．２Ｖ（Ｉｆ＝２０ｍＡ））素子を２００℃、２０秒、１ｋｇ／チップの条件でフリップチップ実装し、テスト用ＬＥＤモジュールを得た。
（全光束量の評価）
　得られたテスト用ＬＥＤモジュールについて、全光束量測定システム（積分全球）（ＬＥ－２１００、大塚電子株式会社製）を用いて全光束量を測定した（測定条件　Ｉｆ＝２０ｍＡ（定電流制御））。
（導通信頼性及びクラック発生の有無の評価）
　導通信頼性及びクラック発生の有無を、冷熱サイクル試験（ＴＣＴ）により評価した。テスト用ＬＥＤモジュールをＴＣＴに入れ、（ａ）－４０℃で３０分間←→１００℃で３０分間、１０００サイクル、（ｂ）－５５℃、３０分←→１２５℃、３０分、１０００サイクルを行った。すなわち、（ａ）－４０℃及び１００℃の雰囲気に各３０分間曝し、これを１サイクルとする冷熱サイクルを１０００サイクル行い、また（ｂ）－５５℃及び１２５℃の雰囲気に各３０分間曝し、これを１サイクルとする冷熱サイクルを１０００サイクル行った。
　導通信頼性の評価は、ＴＣＴを１０００サイクル行った後に、ＴＣＴから取り出したテスト用ＬＥＤモジュールについて、Ｉｆ＝２０ｍＡ時のＶｆ値を測定した。初期Ｖｆ値からのＶｆ値の上昇分が５％以内である場合には導通信頼性が良好であると判断して「○」とし、初期Ｖｆ値からのＶｆ値の上昇分が５％以上である場合には導通信頼性が良好ではないと判断して「×」とした。
　クラック発生の有無の評価は、ＴＣＴを１０００サイクル行った後に、ＴＣＴから取り出したテスト用ＬＥＤモジュールについて、金属顕微鏡にて青色ＬＥＤ素子の上面より観察を行い、クラックの発生の有無を観察した。光反射性異方性導電接着剤にクラックの発生が観察されない場合を「○」とし、光反射性異方性導電接着剤にクラックの発生が観察された場合を「×」とした。
　＜実施例２＞
　白色針状無機粒子として、長方向粒径５０μｍ、短方向粒径３μｍ（アスペクト比１６．７）の酸化亜鉛（ＺｎＯ）ウィスカ（パナテトラＷＺ－０５Ｆ１、アムテック製）を使用した以外は、実施例１と同様の処理を行った。
　＜実施例３＞
　白色針状無機粒子として、長方向粒径２０μｍ、短方向粒径０．６μｍ（アスペクト比３３．３）のチタン酸カリウムウィスカ（ティスモシリーズ、大塚化学製）を使用した以外は、実施例１と同様の処理を行った。
　＜実施例４＞
　白色針状無機粒子として、長方向粒径５０μｍ、短方向粒径３μｍ（アスペクト比１６．７）の酸化亜鉛（ＺｎＯ）ウィスカ（パナテトラＷＺ－０５Ｆ１、アムテック製）の表面をシランカップリング剤で処理したものを使用した以外は、実施例１と同様の処理を行った。
　＜実施例５＞
　白色針状無機粒子として、長方向粒径５０μｍ、短方向粒径３μｍ、アスペクト比１６．７である酸化亜鉛（ＺｎＯ）ウィスカ（パナテトラＷＺ－０５Ｆ１、アムテック製）を、熱硬化性樹脂組成物に対して９．０体積％の割合で添加するとともに、粒径０．６μｍ（アスペクト比１．０）の酸化亜鉛（ＺｎＯ）の白色球状無機粒子（Ｉ種、堺化学製）を、熱硬化性樹脂組成物に対して３．０体積％の割合で添加した以外は、実施例１と同様の処理を行った。
　＜比較例１＞
　異方性導電接着剤に白色針状無機粒子を含有させない以外は、実施例１と同様の処理を行った。
　＜比較例２＞
　実施例１の白色針状無機粒子に代え、粒径０．９μｍ（アスペクト比１．０）の酸化チタンの白色球状無機粒子を、熱硬化性樹脂組成物に対して１２．０体積％の割合で添加した以外は、実施例１と同様の処理を行った。
　＜比較例３＞
　実施例１の白色針状無機粒子に代え、０．６μｍ（アスペクト比１．０）の酸化亜鉛の白色球状無機粒子を、熱硬化性樹脂組成物に対して１２．０体積％の割合で添加した以外は、実施例１と同様の処理を行った。
　［表１］に、実施例１～５、比較例１～３の結果を示す。
Figure JPOXMLDOC01-appb-T000001
　［表１］に示す実施例１の結果からわかるように、白色針状無機粒子としてアスペクト比が１３．１であるＴｉＯ２（二酸化チタン）を熱硬化性樹脂組成物に対して１２．０体積％添加した光反射性異方性導電接着剤の硬化物の波長４５０ｎｍでの反射率は、５５％であった。また、この光反射性異方性導電接着剤を用いたＬＥＤ実装サンプルの全光束量は、３５０（ｍｌｍ）であった。球状のＴｉＯ２（白色球状無機粒子）を使用した比較例２よりも、反射率及びＬＥＤからの光の取り出し効率は、ともにやや低下した。しかしながら、ＴＣＴ（－４０～１００℃）１０００サイクル、ＴＣＴ（－５５～１２５℃）１０００サイクル何れの後においてもクラックの発生はなく、耐クラック性が向上した。
　実施例２の結果からわかるように、針状白色無機粒子としてアスペクト比が１６．７であるＺｎＯ（酸化亜鉛）を熱硬化性樹脂組成物に対して１２．０体積％の割合で添加した光反射性異方性導電接着剤の硬化物の波長４５０ｎｍでの反射率は、３５％であった。また、この光反射性異方性導電接着剤を用いたＬＥＤ実装サンプルの全光束量は、３００（ｍｌｍ）であった。球状のＺｎＯ（白色球状無機粒子）を使用した比較例３よりも、反射率及びＬＥＤからの光の取り出し効率は、ともにやや低下した。しかしながら、ＴＣＴ（－４０～１００℃）１０００サイクル、ＴＣＴ（－５５～１２５℃）１０００サイクル何れの後においてもクラックの発生はなく、耐クラック性が向上した。
　実施例３の結果からわかるように、白色針状無機粒子としてアスペクト比が３３．３であるチタン酸カリウムを熱硬化性樹脂組成物に対して１２．０体積％の割合で添加した光反射性異方性導電接着剤の硬化物の波長４５０ｎｍでの反射率は、３０％であった。また、この光反射性異方性導電接着剤を用いたＬＥＤ実装サンプルの全光束量は、２５０（ｍｌｍ）であった。粒状のＺｎＯ（白色球状無機粒子）を使用した比較例３よりも、反射率及び青色ＬＥＤからの光の取り出し効率は、ともにやや低下した。しかしながら、ＴＣＴ（－４０～１００℃）１０００サイクル、ＴＣＴ（－５５～１２５℃）１０００サイクル何れの後においてもクラックの発生はなく、耐クラック性が向上した。
　実施例４の結果からわかるように、白色針状無機粒子としてアスペクト比が１６．７であるＺｎＯを熱硬化性樹脂組成物に対して１２．０体積％の割合で添加した光反射性異方性導電接着剤の硬化物の波長４５０ｎｍでの反射率は、３５％であった。また、この光反射性異方性導電接着剤を用いたＬＥＤ実装サンプルの全光束量は、３００（ｍｌｍ）であった。粒状のＺｎＯ（白色球状無機粒子）を使用した比較例３よりも、反射率及びＬＥＤからの光の取り出し効率は、ともにやや低下した。しかしながら、ＴＣＴ（－４０～１００℃）１０００サイクル、ＴＣＴ（－５５～１２５℃）１０００サイクル何れの後においてもクラックの発生はなく、耐クラック性が向上した。
　実施例５の結果からわかるように、白色針状無機粒子としてアスペクト比が１６．７である酸化亜鉛（ＺｎＯ）を熱硬化性樹脂組成物に対して９．０体積％の割合で添加するとともに、球状のＺｎＯ（白色球状無機粒子）を熱硬化性樹脂組成物に対して３．０体積％の割合で添加した光反射性異方性導電接着剤の硬化物の波長４５０ｎｍでの反射率は、４０％であった。また、この光反射性異方性導電接着剤を用いたＬＥＤ実装サンプルの全光束量は、２５０（ｍｌｍ）であった。白色球状無機粒子として球状の酸化亜鉛（ＺｎＯ）を使用した比較例３よりも、反射率及びＬＥＤからの光の取り出し効率は、ともにやや低下した。しかしながら、ＴＣＴ（－４０～１００℃）１０００サイクル、ＴＣＴ（－５５～１２５℃）１０００サイクル何れの後においてもクラックの発生はなく、耐クラック性が向上した。
　比較例１の結果からわかるように、針状白色無機粒子を添加せず、導電性粒子を熱硬化性樹脂組成物に対して１０質量％添加した異方性導電接着剤の硬化物の波長４５０ｎｍでの反射率は、８％であった。この異方性導電接着剤を用いたＬＥＤ実装サンプルの全光束量は、２００（ｍｌｍ）であった。青色ＬＥＤから出射された波長４５０ｎｍの光は、金（Ａｕ）に吸収されるため、この光に対する反射率が低下し、これにより、青色ＬＥＤの発光効率（光取り出し効率）が低くなった。ＴＣＴ（－４０～１００℃）１０００サイクル、ＴＣＴ（－５５～１２５℃）１０００サイクル何れの後においてもクラックの発生はなかった。
　比較例２の結果からわかるように、二酸化チタン（ＴｉＯ２）の白色球状無機粒子を熱硬化性樹脂組成物に対して１２．０体積％添加した光反射性異方性導電接着剤の波長４５０ｎｍでの反射率は、６２％であった。この光反射性異方性導電接着剤を用いたＬＥＤ実装サンプルの全光束量は、３９０（ｍｌｍ）であった。しかしながら、ＴＣＴ（－４０～１００℃）１０００サイクル後においてはクラックの発生はなかったものの、ＴＣＴ（－５５～１２５℃）１０００サイクル後においてクラックが発生した。
　比較例３の結果からわかるように、酸化亜鉛（ＺｎＯ）の白色球状無機粒子を熱硬化性樹脂組成物に対して１２．０体積％添加した光反射性異方性導電接着剤の波長４５０ｎｍでの反射率は、４０％であった。この光反射性異方性導電接着剤を用いたＬＥＤ実装サンプルの全光束量は、３５０（ｍｌｍ）であった。ＴＣＴ（－４０～１００℃）１０００サイクル後においてはクラックの発生はなかったものの、ＴＣＴ（－５５～１２５℃）１０００サイクル後においてクラックが発生した。
　なお、実施例１～５、比較例１～３の異方導電接着剤では、初期、ＴＣＴ（－４０～１００℃）１０００サイクル後、ＴＣＴ（－５５～１２５℃）１０００サイクル後の何れにおいても、このような温度変化に対して高い耐性を有し、優れた導通信頼性を発揮することがわかった。
　以上の結果からわかるように、白色針状無機粒子を熱硬化性樹脂組成物に添加した光反射性異方性導電接着剤を用いた実施例１～５では、ＬＥＤ素子から出射された光に対する反射率の低下を抑制し、ＬＥＤ素子の発光効率（光取り出し効率）を向上させることができた。また、実施例１～５における光反射性異方性導電接着剤は、ＴＣＴ後においても高い耐クラック性を確認できた。これは、針状形状からなる白色針状無機粒子によって熱硬化性樹脂組成物の強靭性を高めることができたためと考えられる。また、実施例１～５の光反射性異方性導電接着剤は、温度変化に対して高い耐性を有し、優れた導通信頼性を発揮することがわかった。
　２１　基板、２２　接続端子、２３　ＬＥＤ素子、２４　ｎ電極、２５　ｐ電極、２６ バンプ、２００　発光装置

Claims (10)

  1. 発光素子を配線板に異方性導電接続するために使用する光反射性異方性導電接着剤であって、熱硬化性樹脂、導電性粒子及び光反射性針状絶縁粒子を含有することを特徴とする光反射性異方性導電接着剤。
  2. 上記光反射性針状絶縁粒子が、酸化チタン、酸化亜鉛及びチタン酸塩からなる群より選択される少なくとも１種の無機粒子であることを特徴とする請求項１記載の光反射性異方性導電接着剤。
  3. 上記光反射性針状絶縁粒子が、酸化亜鉛の表面をシラン剤で処理してなることを特徴とする請求項１記載の光反射性異方性導電接着剤。
  4. 上記光反射性針状絶縁粒子のアスペクト比が、１０よりも大きく３５未満であることを特徴とする請求項１乃至３の何れか１項記載の光反射性異方性導電接着剤。
  5. 上記光反射性針状粒子のアスペクト比が、１０よりも大きく２０未満であることを特徴とする請求項１乃至３の何れか１項記載の光反射性異方性導電接着剤。
  6. 上記熱硬化性樹脂組成物における上記光反射性針状粒子の配合量が、該熱硬化性樹脂組成物に対して１～５０体積％であることを特徴とする請求項１乃至５の何れか１項記載の光反射性異方性導電接着剤。
  7. 光反射性球状絶縁粒子を更に含むことを特徴とする請求項１乃至６の何れか１項記載の光反射性異方性導電接着剤。
  8. 上記光反射性針状絶縁粒子は、上記光反射性球状絶縁粒子の体積量と同量以上の体積量で含有されていることを特徴とする請求項７記載の光反射性異方性導電接着剤。
  9. 請求項１乃至８の何れか１項記載の光反射性異方性導電接着剤を介して、発光素子がフリップチップ方式で配線板に実装されていることを特徴とする発光装置。
  10. 上記発光素子は、発光ダイオードであることを特徴とする請求項９記載の発光装置。
PCT/JP2011/059194 2010-04-13 2011-04-13 光反射性異方性導電接着剤及び発光装置 WO2011129373A1 (ja)

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US13/640,784 US8916894B2 (en) 2010-04-13 2011-04-13 Light-reflective anisotropic conductive adhesive agent, and light emitting device
EP11768894.5A EP2560198A4 (en) 2010-04-13 2011-04-13 LIGHT REFLECTIVE AND ELECTRICALLY CONDUCTIVE ANISOTROPIC ADHESIVE AND LIGHT-EMITTING DEVICE THEREFOR
CN201180018769.0A CN102859673B (zh) 2010-04-13 2011-04-13 光反射性各向异性导电粘接剂及发光装置
KR1020117015024A KR20130049689A (ko) 2010-04-13 2011-04-13 광반사성 이방성 도전 접착제 및 발광 장치
HK13105913.8A HK1178320A1 (zh) 2010-04-13 2013-05-20 光反射性各向異性導電粘接劑及發光裝置
US14/543,550 US9260634B2 (en) 2010-04-13 2014-11-17 Light-reflective anisotropic conductive adhesive agent, and light emitting device

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US9260634B2 (en) 2016-02-16
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