WO2006013066A2 - Resin-encapsulated light emitting diode and method for encapsulating light emitting diode - Google Patents

Resin-encapsulated light emitting diode and method for encapsulating light emitting diode Download PDF

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Publication number
WO2006013066A2
WO2006013066A2 PCT/EP2005/008247 EP2005008247W WO2006013066A2 WO 2006013066 A2 WO2006013066 A2 WO 2006013066A2 EP 2005008247 W EP2005008247 W EP 2005008247W WO 2006013066 A2 WO2006013066 A2 WO 2006013066A2
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Prior art keywords
light emitting
emitting diode
composition
silicone
resin
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PCT/EP2005/008247
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French (fr)
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WO2006013066A3 (en
Inventor
Tetsuya Murakami
Gerhard Staiger
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Wacker Chemie Ag
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Priority to CN2005800266201A priority Critical patent/CN101432894B/en
Publication of WO2006013066A2 publication Critical patent/WO2006013066A2/en
Publication of WO2006013066A3 publication Critical patent/WO2006013066A3/en

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
    • C08L83/04—Polysiloxanes
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
    • C08G77/04—Polysiloxanes
    • C08G77/12—Polysiloxanes containing silicon bound to hydrogen
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
    • C08G77/04—Polysiloxanes
    • C08G77/14—Polysiloxanes containing silicon bound to oxygen-containing groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
    • C08G77/04—Polysiloxanes
    • C08G77/14—Polysiloxanes containing silicon bound to oxygen-containing groups
    • C08G77/16—Polysiloxanes containing silicon bound to oxygen-containing groups to hydroxyl groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
    • C08G77/04—Polysiloxanes
    • C08G77/20—Polysiloxanes containing silicon bound to unsaturated aliphatic groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
    • C08G77/80—Siloxanes having aromatic substituents, e.g. phenyl side groups
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/52—Encapsulations
    • H01L33/56—Materials, e.g. epoxy or silicone resin

Definitions

  • the present invention relates to a light emitting diode device comprising a light emitting diode element (referred to as an LED element, hereinafter) encapsulated in silicone, which is composed of a light emitting diode chip, a lead frame and a bonding wire connecting the chip and the frame.
  • the present invention also relates to a method for encapsulating the LED element in silicone. More specifically, the present invention relates to a LED device comprising a blue to ultraviolet- emitting LED element encapsulated in silicone, as well as a method for encapsulating such an LED element in silicone.
  • LED elements are encapsulated in a transparent resin to make light emitting devices.
  • epoxy resins have been widely used as the transparent encapsulation resin for their high transparency, sufficient strength and rigidity
  • silicone resins have recently attracted significant attention as a material for encapsulating blue to ultraviolet-emitting LED elements for which demand is growing, or white-light emitting devices by encapsulating blue to ultraviolet-emitting LED elements with an addition of a phosphor.
  • Epoxy resins are less suitable for encapsulation of blue to ultraviolet-emitting LED elements with high brightness and shorter wave length, because they lack heat resistance and light resistance reguired for the use with such LED.
  • silicone resins are highly transparent and less susceptible to deterioration caused by ultraviolet rays and are thus considered as a suitable material for encapsulating blue to ultraviolet-emitting LED elements.
  • JP06-314816 A describes the use of a siloxane compound as a resin for encapsulating LED elements.
  • This siloxane compound contains alkoxyl groups that can react with hydroxyl groups on the compound semiconductor, so that it can generate a silicone resin through the addition reaction.
  • the compound used in this case is a polymer compound having organosiloxane unit.
  • the hard silicone resin can improve the light resistance, the large expansion coefficient of the silicone resin, or the large difference between expansion of the silicone resin and the metal parts of the LED elements, can cause a large distortion in the LED elements when the LED elements are exposed to a rapid temperature change. Since the LED elements with high energy can heat to a high temperature upon application of electric current, they are subjected to rapid temperature changes during on/off operations of the devices and are thus susceptible to cracking or other damages caused by distortion resulting from the repeated temperature changes .
  • Elastomers or gel-like silicones are also used to encapsulate LED elements.
  • JP2002-314142 A describes the use of a phosphor-dispersed liquid silicone in encapsulation of LED elements.
  • a silicone that forms a gel upon heat-curing is compared to a silicone rubber, and it is concluded that the silicone rubber is preferred to the silicone gel from the viewpoint of protection of LED elements.
  • the resilient silicone elastomer which is easily deformed by the exertion of outside mechanical force, may lead to breakage of bonding wires of LED elements depending on the degree of deformation.
  • the mechanical strength of the elastomer itself is not high enough.
  • JP54-019660 A proposes the use of an elastic silicone in the inner layer and an epoxy resin in the outer layer.
  • the inner silicone has a rubber elasticity comparable to elastomers.
  • JP2004-140220 A proposes a technique in which an LED element is first coated with a gel-like or elastomeric silicone and is then encapsulated in a hard silicone resin.
  • the problem of the large difference in the thermal expansion between the inner soft silicone and the metal parts of the LED elements still remains.
  • the large linear expansion coefficient of the soft silicone used in the inner layer leads to a significant difference in the thermal expansion between the lead frame and the resin, which brings about a distortion in the metal parts of the LED elements and adjacent silicone when the LED elements are exposed to a rapid temperature change. Such a distortion can eventually cause peeling at the interface of the materials as the LED elements are repeatedly subjected to rapid temperature changes .
  • the two-layered encapsulation structure with the soft silicone inner layer and the hard silicone outer layer still does not offer the complete solution and there has been a need for an optimum silicone composition of the inner layer. And there has also been a need for the composition of the hard silicone outer layer that makes an optimum combination with the soft silicone inner layer.
  • a combination of an addition- curable soft silicone of a particular composition with a particular addition-curable silicone resin can provide a suitable encapsulation for the LEDs.
  • the LED devices manufactured by using such an encapsulation are significantly less susceptible to cracking caused by rapid temperature changes and retain characteristics inherent to silicone materials, including high light transmittance, high refractive index, high light resistance and high heat resistance.
  • Such a silicone encapsulation is also hard, less susceptible to breakage and does not significantly shrink upon molding.
  • a first aspect of the present invention is a light emitting diode device in which a light emitting diode element is coated with an addition-curable soft silicone and is further encapsulated in a resin-like, addition-curable silicone resin, wherein the addition-curable soft silicone is characterized in having a cured hardness of 5 to 75 as measured by a Type E
  • Durometer and being a cured product of a composition comprising of components (A) to (C) below:
  • (C) a hydrosilylation catalyst in a catalytic amount that accelerates the curing of the composition.
  • a second aspect of the present invention is the light emitting diode device according to the first aspect, wherein the component (A) is an organopolysiloxane having an average of about 2 alkenyl groups per molecule bonded to the silicon atom and the alkenyl groups are positioned at the ends of the organopolysiloxane molecule.
  • the component (A) is an organopolysiloxane having an average of about 2 alkenyl groups per molecule bonded to the silicon atom and the alkenyl groups are positioned at the ends of the organopolysiloxane molecule.
  • a third aspect of the present invention is the light emitting diode device according to the first or the second aspect, wherein the addition-curable silicone resin is a cured product of a composition comprising:
  • R is identical or different and selected from the group consisting of substituted or unsubstituted hydrocarbon group, substituted or unsubstituted hydrocarbon group comprising a C- C multiple bond, hydroxyl group, and hydrogen atorn;
  • a fourth aspect of the present invention is a method for encapsulating the light emitting diode element according to anyone of the first to the third aspect, comprising: immersing the light emitting diode element in the liquid composition of the silicone that comprises the components (A) to (C) and cures to form the soft silicone, thereby applying the composition to the light emitting diode element; and subsequently cast molding the silicone resin composition to encapsulate the light emitting diode element under a cured or uncured state of the liquid composition which forms the soft silicone after curing.
  • the component (A) of the present invention is the major component of the silicone composition that forms the soft inner layer after curing.
  • the component (A) is an alkenyl-containing organopolysiloxane that has an average of at least 1.8 alkenyl groups per molecule bonded to a silicon atom.
  • the other organic groups bonded to the silicon atoms are each a substituted or unsubstituted Cl to C20 monovalent hydrocarbon group that does not contain carbon-carbon double bonds or carbon-carbon triple bonds.
  • the organopolysiloxane has a viscosity of 10 mPa-s to 10,000 mPa • s as determined at 25°C and at a shearing rate of 0.9 s "1 .
  • alkenyl group contained in the component (A) examples include C2 to C8 alkenyl groups, such as vinyl, allyl, 1- butenyl, and 1-hexenyl groups. Of these, vinyl and allyl groups are preferred with a vinyl group particularly preferred.
  • These alkenyl groups must react with the component (B) (which will be described later) to form a network structure and at least 1.8 of alkenyl group as an average of component (A) and preferably 1.6 to 10 of the alkenyl groups in each molecule of the component (A) may be present.
  • the alkenyl groups may be bonded to the silicon atom positioned within or at the end of the molecular chain.
  • the alkenyl-containing organopolysiloxane contains an average of two alkenyl groups per molecule, and the alkenyl groups which are bonded exclusively to the silicon atom positioned at the end of the molecular chain.
  • the organic groups other than the alkenyl groups that are bonded to the silicon atom in the component (A) are each a substituted or unsubstituted Cl to C12 monovalent hydrocarbon group that does not contain carbon-carbon double bonds or carbon-carbon triple bonds.
  • alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, neopentyl, hexyl, 2- ethylhexyl, heptyl, octyl, nonyl, and dodecyl groups; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl groups; aryl groups such as phenyl, tolyl, xylyl, biphenyl, and naphthyl groups; aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl groups; and substituted hydrocarbons in which some or all of the hydrogen atoms of the above hydrocarbon groups have been substituted by a halogen atom, a cyano group, or other substituents
  • methyl and phenyl groups are particularly preferred.
  • refractive indices of silicones vary depending on the type of organic groups bonded to their siloxane units: Silicones with aromatic groups such as phenyl groups bonded to their siloxane units tend to have a higher refractive index than those with methyl groups. For this reason, in the case that the outer resin-like silicone layer for encapsulating the LED device of the present invention contains a significant amount of aromatic groups, the proportion of phenyl groups in the soft inner silicone layer is preferably increased correspondingly to make the refractive index of the soft inner silicone layer same level with the refractive index of the outer layer.
  • the alkenyl-containing organopolysiloxane of the component (A) may be either a straight-chained or branched molecule and may be provided as a mixture of these molecules.
  • the branched chains of the polysiloxane unit serve as crosslinkages by themselves and may be trifunctional siloxane (T-structure) or tetrafunctional siloxane (Q-structure) , given that the cured inner silicone layer has a hardness in the range specified according to the present invention.
  • T-structure trifunctional siloxane
  • Q-structure tetrafunctional siloxane
  • the composition of the present invention that cures to form a soft silicone must have a proper fluidity to ensure operability in the coating step of LED elements.
  • the component (A) has a viscosity preferably in the range of 10 mPa • s to 10,000 mPa-s, more preferably in the range of 100 mPa-s to 5,000 mPa-s, and still more preferably in the range of 200 mPa*s to 3,000 mPa-s, as determined at 25°C and at a shearing rate of 0.9 s "1 .
  • a viscosity preferably in the range of 10 mPa • s to 10,000 mPa-s, more preferably in the range of 100 mPa-s to 5,000 mPa-s, and still more preferably in the range of 200 mPa*s to 3,000 mPa-s, as determined at 25°C and at a shearing rate of 0.9 s "1 .
  • Such an alkenyl-containing organopolysiloxane can be manufactured by techniques known to those skilled in the art.
  • the component (B) of the present invention serves as a crosslinker of the component (A) and comprises an organohydrogenpolysiloxane that has an average of at least 4 hydrogen atoms bonded to silicon atoms in the molecule, and 3 to 30 hydrogen atoms bonded to silicon atoms in each molecule.
  • the other organic groups other than hydrogen that are bonded to silicon atoms are substituted or unsubstituted Cl to C20 monovalent hydrocarbon groups that do not contain carbon-carbon double bonds or carbon-carbon triple bonds .
  • the organopolysiloxane (B) has a viscosity of 10 mPa• s to 10,000 mPa-s as determined at 25 C C and at a shearing rate of 0.9 s "1 .
  • the organic groups in the component (B) other than hydrogen are the same as those described above for the component (A) except alkenyl groups and are preferably methyl and phenyl groups. From the viewpoint of refractive index, the component (B) preferably contains phenyl groups for the same reason that methyl and phenyl groups are selected in the component (A) .
  • the component (B) to serve as the crosslinker may be either a straight-chained or branched molecule and may be provided as a mixture of these molecules.
  • Such organohydrogenpolysiloxanes can be manufactured by techniques known to those skilled in the art.
  • the component B must provide a proper fluidity as in the case of the component (A) of which viscosity is limited as above.
  • the component (B) has a viscosity preferably in the range of 10 mPa • s to 10,000 mPa-s, more preferably in the range of 50 mPa • s to 5,000 mPa-s, and still more preferably in the range of 100 mPa-s to 2,000 mPa-s, as determined at 25°C and at a shearing rate of 0.9 s "1 .
  • the component (B) according to the present invention is added in an amount such that 0.9 to 2 hydrogen atoms bonded to silicone atom are present for each alkenyl group in the component (A) .
  • the component (B) is added in an amount of 5 parts to 80 parts by weight with respect to 100 parts by weight of the component (A) .
  • the component (C) of the present invention is a catalyst, commonly used for hydrosilylation, that comprises a metal and/or metal compound to accelerate the addition reaction between Si-H group of the organopolysiloxane and the carbon- carbon multiple bond. Examples of such metals include platinum, rhodium, palladium, ruthenium, and iridium.
  • Preferred hydrosilylation catalysts are platinum and platinum compounds.
  • the platinum compounds include halogenated platinum compounds (such as PtCl 4 , H 2 PtCl 4 • 6H 2 O, and Na 2 PtCl 4 • 4H 2 O) , platinum-olefin complexes, platinum-alcohol complexes, platinum-alcoholate complexes, platinum-ether complexes, platinum-aldehyde complexes, platinum-ketone complexes, platinum-vinyl siloxane complexes (such as platinum-1, 3- divinyl-1, 1, 3, 3-tetramethyldisiloxane complex, bis- ( ⁇ picoline) -platinum dichloride, trimethylenedipyridine-platinum dichloride, dicyclopentadiene-platinum dichloride, cyclooctadiene-platinum dichloride, and cycl
  • the hydrosilylation catalysts may be used in the form of microcapsules.
  • the microcapsule one example of the solid fine particles that can contain the catalyst and are insoluble in organopolysiloxane is a resin (such as polyester resin and silicone resin) .
  • the hydrosilylation catalyst may be provided in the form of clathrate compounds, for example, in cyclodextrin.
  • the hydrosilylation catalyst is added in catalytic amounts.
  • a platinum catalyst is added in an amount preferably in the range of 0.1 to 500 ppm, and in particular in the range of 1 to 200 ppm as measured by the amount of platinum metal in the composition comprised of the components (A) and (B) .
  • the composition of the present invention comprised of the components (A) to (C) must exhibit a cured hardness in the range of 5 to 75, and preferably in the range of 5 to 60 by a hardness test of type E Durometer for a lOmm-thick sample piece according to JIS K6253.
  • the composition with a cured hardness of less than 5 becomes susceptible to large deformation during the encapsulation step using the silicone resin, whereas the composition with a cured hardness of more than 75 does not have a sufficient ability to absorb stress required for the soft layer.
  • the desired hardness can be achieved by adjusting the degree of polymerization, the alkenyl groups and branch structures of the component (A) to contribute crosslinkages, as well as the amount of Si-H bond and the degree of polymerization of the component (B) .
  • the light emitting diode device is fabricated by coating an LED element with the above-described composition comprised of the components (A) to (C) , and further encapsulating the coated LED element in an addition-curable silicone resin composition that cures to form a resin-like material.
  • the addition-curable silicone resin is a composition comprising (a) an organopolysiloxane that is represented by the average composition formula;
  • the component (a) is a polymer that, in its average composition in the mixture, contains the branch structures of T-units (RSiO 3/ 2) and/or Q-units (SiO 4/2 ) , and can undergo crosslinking or other reactions to form three dimensional networks of even higher degrees. Thus, it should hold that Q + T > 0 in each average composition formula.
  • Such an organopolysiloxane also referred to as silicone resin, may be either a solid or a liquid prior to curing. Liquid compositions, however, are easily molded and are thus better suited for encapsulation of LEDs, which is the purpose of the present invention.
  • the organopolysiloxane to serve as the component (a) may be any organopolysiloxane produced by techniques known to those skilled in the art: It may be obtained by hydrolysis of organosilanes or organosiloxanes.
  • Rs in the component (a) may be each individually selected and may or may not be identical to one another.
  • the component (a) is defined by an average composition formula, so that Rs in the same structural units (R2SiO 2/ 2)D may differ from one another and may at the same time include methyl, phenyl, and hydrogen atom. These structural units may be linked by different unit structures .
  • R examples include straight-chained or branched Cl to C20 alkyl or alkenyl groups and halogenated forms thereof; acetylene group or hydrocarbons containing acetylene group; C5 to C25 cycloalkyl or cycloalkenyl groups and halogenated forms thereof; and C6 to C25 aralkyl or aryl groups and halogenated forms thereof.
  • these hydrocarbons may be those given above as examples of the alkenyl group or the other organic groups in the component (A) .
  • the phrase "R with a multiple bond" means a hydrocarbon group containing a carbon- carbon double bond or a carbon-carbon triple bond, including alkenyl or acetylene groups.
  • a vinyl group is the most preferred of the hydrocarbon groups with multiple bonds.
  • R may be selected from the group consisting of hydrogen, hydroxyl, alkoxyl, acyloxy, ketiminoxy, alkenyloxy, acid anhydride, carbonyl, sugar, cyano, oxazoline, and isocyanate groups and hydrocarbon-substituted forms thereof.
  • the component (a) includes several possible combinations.
  • the component (a) may be an organopolysiloxane or a mixture of organopolysiloxanes that containing in one molecule a multiple bond containing hydrocarbon group bonded to silicon atom and a hydrogen atom bonded to silicon atom, or a mixture of organopolysiloxanes that contain in one molecule a multiple bond containing hydrocarbon group bonded to silicon atom, but not any hydrogen atoms bonded to silicon atom, with organopolysiloxanes that contain in one molecule a hydrogen atom bonded to silicon atom, but not any hydrocarbon groups having a multiple bond, or a mixture of the organopolysiloxanes of (i) (which contain in one molecule a multiple bond containing hydrocarbon group bonded to silicon atom and a hydrogen atom bonded to silicon atom) with organopolysiloxanes that contain in one molecule a multiple bond containing hydrocarbon group bonded to silicon atom,
  • such a mixture should contain a multiple bond containing hydrocarbon group bonded to silicon atom and Si-H group, and contain T- units and/or Q-units in amounts that allow the mixture to form the resin-like material after curing.
  • the multiple bond containing hydrocarbon group bonded to silicon atom and the hydrogen atom bonded to silicon atom, the essential elements of the polysiloxane to serve as the component (a) are preferably present in either one or both of the selected units in the general formula of the component (a) .
  • the silicon-bonded multiple bond containing hydrocarbon group and the silicon-bonded hydrogen atom are most preferably present in the (R.2SiC>2 / 2) structural units .
  • the organopolysiloxane to serve as the component (a) of the present invention preferably contains, as R in the average composition formula, an aromatic group for the purpose of ensuring heat resistance, light resistance and refractive index required for the encapsulation material of LED elements. While this aromatic group may be aralkyl or aryl, phenyl is most preferred.
  • the aromatic groups preferably account for 5 to 90 mol% and, more preferably, 10 to 60 mol% of the total R groups in the entire units. If the amount of aromatic groups is too little, then the desired improvement in the heat resistance, light resistance, and refractive index cannot be achieved, whereas if the amount is too much, the product becomes economically unfavorable.
  • aromatic groups may be introduced into any of the units except the (Si ⁇ 4/2 ) units, introduction into the (R2SiO 2/ 2) and (RSiO 3/2 ) units is preferred, and the introduction into the (RSiO 3Z2 ) units is most preferred.
  • the silicon atoms directly bonded to hydrogen atoms preferably account for 1 to 40 mol%, more preferably 3 to 30 mol%, and most preferably 5 to 20 mol% of the entire silicon atoms. If this amount is too much, then the product tends to become more brittle although the hardness increases, whereas if the amount is too little, then the hardness does not increase adequately. Furthermore, in those cases where the component (a) contains both of the silicon-bonded hydrocarbon group with a multiple bond and the silicon-bonded hydrogen atom, then the silicon atoms directly bonded to hydrogen atoms preferably account for 1 to 40 mol%, more preferably 3 to 30 mol%. In amounts exceeding 40 mol%, although the hardness of the cured product increases, it tends to become more brittle, whereas in amounts less than 1 mol%, a cured product of satisfactory hardness cannot be obtained.
  • M, D, T, and Q are numbers representing relative proportion of each of the units, and each falls within a range from 0 (inclusive) to 1 (exclusive) .
  • Preferred ranges are from 0 to 0.6 for M, from 0.1 to 0.8 for D, from 0.1 to 0.7 for T, and from 0 to 0.3 for Q, and ideally M is from 0.1 to 0.4, D is from 0.1 to 0.6, T is from 0.3 to 0.6, and Q is 0.
  • the value of T + Q is preferably in the range of 0.3 to 0.9.
  • the hydrosilylation catalyst to serve as the component (b) of the resin-like addition-curable silicone of the present invention may be those given as examples of the component (C) .
  • the catalyst may be one that is commonly used to accelerate the addition reaction between Si-H group of the organopolysiloxane and the multiple bond of Si-bonded hydrocarbon.
  • the catalyst for the addition reaction is used in an effective amount (or catalytic amount) , which typically is in the range of 1 to 1000 ppm, preferably in the range of 2 to 500 ppm with respect to the component (a) .
  • the encapsulation composition of the present invention comprised of the components (a) and (b) must turn to a resin- like state after undergoing crosslinking by the addition reaction.
  • resin-like state means that the composition has a hardness in the range of 30 to 90, preferably in the range of 40 to 90, by the test of the Durometer D hardness using a ⁇ mm-thick sample piece according to JIS K6253.
  • the cured product with its hardness in the specified range can be obtained by adjusting the value (2D + 3T + 4Q) / (D + T + Q) to a predetermined range.
  • LED elements examples include conventional GaP, GaAs, and GaN based red, green, and yellow LED elements, as well as the more recently developed high brightness, short wavelength LED elements.
  • the composition of the present invention can be used for encapsulating conventional LED elements, it is most effective when used for encapsulating the more recently developed high brightness, short wavelength LED elements, including high brightness blue LED elements, white LED elements, and LED elements in the blue to near ultraviolet spectrum.
  • the peak wavelength of the emitted light falls within a range from 490 to 350 nm.
  • the encapsulating material used with these types of LED elements not only requires good light resistance relative to light of blue through ultraviolet wavelengths, but also requires superior light resistance and heat resistance, as it is exposed to a higher brightness, higher energy light emitted from the LED elements.
  • An encapsulating composition of the present invention provides superior light resistance and heat resistance to that offered by conventional epoxy based encapsulants, meaning the lifespan of the light emitting diode device can be improved significantly.
  • Specific examples of these high brightness blue LED elements, white LED elements, and LED elements in the blue to near ultraviolet spectrum include AlGaInN yellow LED elements, InGaN blue and green LED elements, and white light emitting diode elements that employ a combination of InGaN and a fluorescent material.
  • encapsulated light emitting diode devices include lamp-type devices, large scale package devices, and surface mounted devices. These different types of LED device are described, for example, in “Flat Panel Display Dictionary, " published by Kogyo Chosakai Publishing Co., Ltd., publication date 25 December 2001, pp. 897 to 906.
  • the composition of the present invention may be applied to LED elements using any suitable technique.
  • an entire LED element may be immersed in a liquid composition, or droplets of a liquid composition may be dropped onto an LED element.
  • the immersion technique is particularly suitable since the LED element can be coated relatively uniformly by this technique.
  • the composition may be applied to any suitable thickness, it is applied typically to a thickness of about 0.01 to 2 mm.
  • the composition may or may not be cured prior to the encapsulation step. It is preferred to cure the composition prior to the encapsulation step, however.
  • the composition can be easily cured by passing the coated LED element through a furnace adjusted to a temperature suitable for curing. The curing step is typically carried at a temperature in the range of 50 to 180 0 C and over a time period of 1 to 120 min.
  • the LED element is further encapsulated in the composition comprised of the components (a) and (b) that cures to a resin-like state.
  • the encapsulation may be carried out using any suitable technique.
  • the encapsulation may be carried out by pouring the silicone composition of the present invention in a resin mold, immersing an LED element in the composition, and then heating the composition to cure.
  • the encapsulation may also be carried out by transfer molding.
  • One advantage of the encapsulation using the silicone resin of the present invention is that the resin can be used not only with resin molds, but also with metal molds, which have not previously been used with the conventional epoxy-based encapsulating materials.
  • Additives may be added to the composition of the present invention, provided that the advantages of the invention are not affected.
  • additives include addition reaction control agents for imparting improved curability and pot life, reactive or non-reactive straight chain or cyclic low molecular weight organopolysiloxanes or the like for regulating the hardness and viscosity of the composition, fluorescent agents such as YAG to enable the emission of white light, inorganic fillers or pigments such as fine particulate silica and titanium dioxide and the like, organic fillers, fire retardant agents, heat resistant agents, and anti-oxidants.
  • the light emitting diode devices of the present invention in particular, the light emitting diode devices of the present invention comprising blue to ultraviolet-emitting LED elements are less susceptible to cracking of encapsulation when exposed to rapid temperature changes.
  • the encapsulation of the LED device advantageously exhibits strength and hardness in a well- balanced manner while retaining the transparency, light resistance, and heat resistance of the silicone-based material.
  • a 10mm- or 6mm-thick sheet of the cured product was used to measure its hardness by the Durometer.
  • a heat-shock test was performed to evaluate the crack-resistance of the sheet.
  • TSE-Il-A small heat-shock tester manufactured by ESPEC Corp.
  • the temperature of the tester was changed from -40 0 C to 110 0 C and from HO 0 C to -4O 0 C within three minutes .
  • the resulting light emitting diode device with two-layered encapsulation was tested on a heat-shock tester. After 300 cycles, no cracks were observed in the LED device.
  • Example 1 100 parts by weight of organopolysiloxane of (a) and 0.02 parts by weight of hydrosilylation catalyst of (b) were weighed and mixed until uniform. After deaeration under reduced pressure, the mixture had a viscosity of 800 mPa • s.
  • the resulting silicone resin mixture was poured in a resin casting case (5mm lamp-type) and a silver-plated metal lead frame without soft silicone coating was inserted into the casting case. The resin casting case was then heated at 150 0 C for 3 hours for curing. The resulting light emitting diode device with single-layered encapsulation was tested on a heat-shock tester. After 10 cycles, cracks were formed in every sample.

Abstract

A LED device is provided, in which a LED element is encapsulated in a material less susceptible to damages caused by rapid temperature changes. The LED element is coated with an addition-curable soft silicone and is further encapsulated in a resin-like, addition-curable silicone. The soft silicone is characterized in having a cured hardness of 5 to 75 by a Type E Durometer and being a cured product of a composition comprising of (A) an organopolysiloxane that has an average of at least 1.8 alkenyl groups per molecule bonded to a silicon atom, (B) an organohydrogenpolysiloxane that has an average of at least 4 hydrogen atoms per molecule bonded to a silicon atom, and (C) a hydrosilylation catalyst.

Description

RESIN-ENCAPSULATED LIGHT EMITTING DIODE AND METHOD FOR ENCAPSULATING LIGHT EMITTING DIODE
The present invention relates to a light emitting diode device comprising a light emitting diode element (referred to as an LED element, hereinafter) encapsulated in silicone, which is composed of a light emitting diode chip, a lead frame and a bonding wire connecting the chip and the frame. The present invention also relates to a method for encapsulating the LED element in silicone. More specifically, the present invention relates to a LED device comprising a blue to ultraviolet- emitting LED element encapsulated in silicone, as well as a method for encapsulating such an LED element in silicone.
In general, LED elements are encapsulated in a transparent resin to make light emitting devices. Although epoxy resins have been widely used as the transparent encapsulation resin for their high transparency, sufficient strength and rigidity, silicone resins have recently attracted significant attention as a material for encapsulating blue to ultraviolet-emitting LED elements for which demand is growing, or white-light emitting devices by encapsulating blue to ultraviolet-emitting LED elements with an addition of a phosphor. Epoxy resins are less suitable for encapsulation of blue to ultraviolet-emitting LED elements with high brightness and shorter wave length, because they lack heat resistance and light resistance reguired for the use with such LED. Specifically, as the epoxy resin encapsulating LED chips is exposed to ultraviolet rays emitted from the chips, linkages within the organic polymer break, resulting in deterioration of optical or chemical characteristics of the resin. As a result, the epoxy resin gradually turns yellow from the adjacent region of the LED chip. This causes coloring of light and, consequently, limits the life of LED devices. On the other hand, silicone resins are highly transparent and less susceptible to deterioration caused by ultraviolet rays and are thus considered as a suitable material for encapsulating blue to ultraviolet-emitting LED elements.
For example, JP06-314816 A describes the use of a siloxane compound as a resin for encapsulating LED elements. This siloxane compound contains alkoxyl groups that can react with hydroxyl groups on the compound semiconductor, so that it can generate a silicone resin through the addition reaction. The compound used in this case is a polymer compound having organosiloxane unit. While the hard silicone resin can improve the light resistance, the large expansion coefficient of the silicone resin, or the large difference between expansion of the silicone resin and the metal parts of the LED elements, can cause a large distortion in the LED elements when the LED elements are exposed to a rapid temperature change. Since the LED elements with high energy can heat to a high temperature upon application of electric current, they are subjected to rapid temperature changes during on/off operations of the devices and are thus susceptible to cracking or other damages caused by distortion resulting from the repeated temperature changes .
Elastomers or gel-like silicones are also used to encapsulate LED elements. For example, JP2002-314142 A describes the use of a phosphor-dispersed liquid silicone in encapsulation of LED elements. According to JP2002-314142 A, a silicone that forms a gel upon heat-curing is compared to a silicone rubber, and it is concluded that the silicone rubber is preferred to the silicone gel from the viewpoint of protection of LED elements. Nonetheless, when used to encapsulate LED elements, the resilient silicone elastomer, which is easily deformed by the exertion of outside mechanical force, may lead to breakage of bonding wires of LED elements depending on the degree of deformation. Furthermore, the mechanical strength of the elastomer itself is not high enough.
Rather than encapsulating LED elements in a single hard resin or single soft material such as an elastomer, it is proposed that a LED element is first covered with a soft material, and is then encapsulated in a hard resin to form a two-layered structure. For example, JP54-019660 A proposes the use of an elastic silicone in the inner layer and an epoxy resin in the outer layer. The inner silicone has a rubber elasticity comparable to elastomers. JP2004-140220 A proposes a technique in which an LED element is first coated with a gel-like or elastomeric silicone and is then encapsulated in a hard silicone resin.
While the light emitting diode devices with the two-layered structure have eliminated some of the problems associated with the light emitting diode devices encapsulated in either one of the two materials alone, the problem of the large difference in the thermal expansion between the inner soft silicone and the metal parts of the LED elements still remains. Specifically, the large linear expansion coefficient of the soft silicone used in the inner layer leads to a significant difference in the thermal expansion between the lead frame and the resin, which brings about a distortion in the metal parts of the LED elements and adjacent silicone when the LED elements are exposed to a rapid temperature change. Such a distortion can eventually cause peeling at the interface of the materials as the LED elements are repeatedly subjected to rapid temperature changes . As described above, although intended to provide a solution to the problems associated with the LED elements encapsulated in a single silicone composition, the two-layered encapsulation structure with the soft silicone inner layer and the hard silicone outer layer still does not offer the complete solution and there has been a need for an optimum silicone composition of the inner layer. And there has also been a need for the composition of the hard silicone outer layer that makes an optimum combination with the soft silicone inner layer.
In view of the above-described problems associated with conventional two-layered structures, it is an object of the invention to provide a composition for encapsulating LED elements, which exhibits a strength and hardness in a well- balanced manner, while retaining transparency, light resistance and heat resistance of silicone materials, and is significantly less susceptible to cracking caused by distortion that results when the LED elements are exposed to rapid temperature changes. It is another objective of the present invention to provide a light emitting diode device encapsulated in the above composition.
During the course of the study to solve the above-described problems, it has been found that a combination of an addition- curable soft silicone of a particular composition with a particular addition-curable silicone resin can provide a suitable encapsulation for the LEDs. The LED devices manufactured by using such an encapsulation are significantly less susceptible to cracking caused by rapid temperature changes and retain characteristics inherent to silicone materials, including high light transmittance, high refractive index, high light resistance and high heat resistance. Such a silicone encapsulation is also hard, less susceptible to breakage and does not significantly shrink upon molding.
Accordingly, the present invention comprises the following: A first aspect of the present invention is a light emitting diode device in which a light emitting diode element is coated with an addition-curable soft silicone and is further encapsulated in a resin-like, addition-curable silicone resin, wherein the addition-curable soft silicone is characterized in having a cured hardness of 5 to 75 as measured by a Type E
Durometer and being a cured product of a composition comprising of components (A) to (C) below:
(A) an organopolysiloxane that has an average of at least 1.8 alkenyl groups per molecule bonded to a silicon atom and has a viscosity of 10 mPa• s to 10,000 mPa• s as determined at 25°C and at a shearing rate of 0.9 s"1;
(B) an organohydrogenpolysiloxane that has an average of at least 4 hydrogen atoms per molecule bonded to a silicon atom and has a viscosity of 10 mPa• s to 10,000 mPa• s as determined at 25°C and at a shearing rate of 0.9 s'1 (the organohydrogenpolysiloxane is provided in an amount such that 0.9 to 2 silicon atoms bonded to a hydrogen atom are present for each of the alkenyl group in the component (A) ) ; and
(C) a hydrosilylation catalyst in a catalytic amount that accelerates the curing of the composition.
A second aspect of the present invention is the light emitting diode device according to the first aspect, wherein the component (A) is an organopolysiloxane having an average of about 2 alkenyl groups per molecule bonded to the silicon atom and the alkenyl groups are positioned at the ends of the organopolysiloxane molecule.
A third aspect of the present invention is the light emitting diode device according to the first or the second aspect, wherein the addition-curable silicone resin is a cured product of a composition comprising:
(a) one or more organopolysiloxanes that are represented by the average composition formula (I)
(R3Si0i/2)M- (R2SiO2Z2)D- (RSiO3/2)τ- (SiO4/2)Q (D ,
wherein
R is identical or different and selected from the group consisting of substituted or unsubstituted hydrocarbon group, substituted or unsubstituted hydrocarbon group comprising a C- C multiple bond, hydroxyl group, and hydrogen atorn;
M, D, T, Q are each a number greater than or equal to 0 and less than 1, with the provision that M + D + T + Q = 1; and Q + T > 0) ;
comprising at least one organopolysiloxane containing at least a hydrocarbon group with a C-C multiple bond and a hydrogen atom, or a mixture of at least one organopolysiloxane containing at least a hydrocarbon group with a C-C multiple bond with of at least one organopolysiloxane containing a hydrogen atom; and (b) an effective amount of a hydrosilylation catalyst.
A fourth aspect of the present invention is a method for encapsulating the light emitting diode element according to anyone of the first to the third aspect, comprising: immersing the light emitting diode element in the liquid composition of the silicone that comprises the components (A) to (C) and cures to form the soft silicone, thereby applying the composition to the light emitting diode element; and subsequently cast molding the silicone resin composition to encapsulate the light emitting diode element under a cured or uncured state of the liquid composition which forms the soft silicone after curing.
The component (A) of the present invention is the major component of the silicone composition that forms the soft inner layer after curing. The component (A) is an alkenyl-containing organopolysiloxane that has an average of at least 1.8 alkenyl groups per molecule bonded to a silicon atom. The other organic groups bonded to the silicon atoms are each a substituted or unsubstituted Cl to C20 monovalent hydrocarbon group that does not contain carbon-carbon double bonds or carbon-carbon triple bonds. The organopolysiloxane has a viscosity of 10 mPa-s to 10,000 mPa•s as determined at 25°C and at a shearing rate of 0.9 s"1.
Examples of the alkenyl group contained in the component (A) include C2 to C8 alkenyl groups, such as vinyl, allyl, 1- butenyl, and 1-hexenyl groups. Of these, vinyl and allyl groups are preferred with a vinyl group particularly preferred. These alkenyl groups must react with the component (B) (which will be described later) to form a network structure and at least 1.8 of alkenyl group as an average of component (A) and preferably 1.6 to 10 of the alkenyl groups in each molecule of the component (A) may be present. The alkenyl groups may be bonded to the silicon atom positioned within or at the end of the molecular chain. Considering the curing rate and properties, it is preferred that the alkenyl-containing organopolysiloxane contains an average of two alkenyl groups per molecule, and the alkenyl groups which are bonded exclusively to the silicon atom positioned at the end of the molecular chain.
Preferably, the organic groups other than the alkenyl groups that are bonded to the silicon atom in the component (A) are each a substituted or unsubstituted Cl to C12 monovalent hydrocarbon group that does not contain carbon-carbon double bonds or carbon-carbon triple bonds. Specific examples thereof include alkyl groups, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, neopentyl, hexyl, 2- ethylhexyl, heptyl, octyl, nonyl, and dodecyl groups; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl groups; aryl groups such as phenyl, tolyl, xylyl, biphenyl, and naphthyl groups; aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl groups; and substituted hydrocarbons in which some or all of the hydrogen atoms of the above hydrocarbon groups have been substituted by a halogen atom, a cyano group, or other substituents, including chloromethyl, 2-bromoethyl, 3, 3, 3-trifluoropropyl, 3- chloropropyl, chlorophenyl, dibromophenyl, tetrachlorophenyl, difluorophenyl, β-cyanoethyl, γ-cyanopropyl, and β-cyanopropyl groups. Of these, methyl and phenyl groups are particularly preferred. In general, refractive indices of silicones vary depending on the type of organic groups bonded to their siloxane units: Silicones with aromatic groups such as phenyl groups bonded to their siloxane units tend to have a higher refractive index than those with methyl groups. For this reason, in the case that the outer resin-like silicone layer for encapsulating the LED device of the present invention contains a significant amount of aromatic groups, the proportion of phenyl groups in the soft inner silicone layer is preferably increased correspondingly to make the refractive index of the soft inner silicone layer same level with the refractive index of the outer layer.
The alkenyl-containing organopolysiloxane of the component (A) may be either a straight-chained or branched molecule and may be provided as a mixture of these molecules. The branched chains of the polysiloxane unit serve as crosslinkages by themselves and may be trifunctional siloxane (T-structure) or tetrafunctional siloxane (Q-structure) , given that the cured inner silicone layer has a hardness in the range specified according to the present invention. The composition of the present invention that cures to form a soft silicone must have a proper fluidity to ensure operability in the coating step of LED elements. In this respect, the component (A) has a viscosity preferably in the range of 10 mPa•s to 10,000 mPa-s, more preferably in the range of 100 mPa-s to 5,000 mPa-s, and still more preferably in the range of 200 mPa*s to 3,000 mPa-s, as determined at 25°C and at a shearing rate of 0.9 s"1. Such an alkenyl-containing organopolysiloxane can be manufactured by techniques known to those skilled in the art.
The component (B) of the present invention serves as a crosslinker of the component (A) and comprises an organohydrogenpolysiloxane that has an average of at least 4 hydrogen atoms bonded to silicon atoms in the molecule, and 3 to 30 hydrogen atoms bonded to silicon atoms in each molecule. The other organic groups other than hydrogen that are bonded to silicon atoms are substituted or unsubstituted Cl to C20 monovalent hydrocarbon groups that do not contain carbon-carbon double bonds or carbon-carbon triple bonds . The organopolysiloxane (B) has a viscosity of 10 mPa• s to 10,000 mPa-s as determined at 25CC and at a shearing rate of 0.9 s"1.
The organic groups in the component (B) other than hydrogen are the same as those described above for the component (A) except alkenyl groups and are preferably methyl and phenyl groups. From the viewpoint of refractive index, the component (B) preferably contains phenyl groups for the same reason that methyl and phenyl groups are selected in the component (A) .
The component (B) to serve as the crosslinker may be either a straight-chained or branched molecule and may be provided as a mixture of these molecules. Such organohydrogenpolysiloxanes can be manufactured by techniques known to those skilled in the art. The component B must provide a proper fluidity as in the case of the component (A) of which viscosity is limited as above. In this respect, the component (B) has a viscosity preferably in the range of 10 mPa• s to 10,000 mPa-s, more preferably in the range of 50 mPa• s to 5,000 mPa-s, and still more preferably in the range of 100 mPa-s to 2,000 mPa-s, as determined at 25°C and at a shearing rate of 0.9 s"1.
To ensure that the component (A) is crosslinked to achieve required hardness, the component (B) according to the present invention is added in an amount such that 0.9 to 2 hydrogen atoms bonded to silicone atom are present for each alkenyl group in the component (A) . Typically, the component (B) is added in an amount of 5 parts to 80 parts by weight with respect to 100 parts by weight of the component (A) . The component (C) of the present invention is a catalyst, commonly used for hydrosilylation, that comprises a metal and/or metal compound to accelerate the addition reaction between Si-H group of the organopolysiloxane and the carbon- carbon multiple bond. Examples of such metals include platinum, rhodium, palladium, ruthenium, and iridium. If necessary, the metal is fixed to a fine particle carrier material (such as activated carbon, aluminum oxide, and silicon oxide) . Preferred hydrosilylation catalysts are platinum and platinum compounds. Examples of the platinum compounds include halogenated platinum compounds (such as PtCl4, H2PtCl4 • 6H2O, and Na2PtCl4 • 4H2O) , platinum-olefin complexes, platinum-alcohol complexes, platinum-alcoholate complexes, platinum-ether complexes, platinum-aldehyde complexes, platinum-ketone complexes, platinum-vinyl siloxane complexes (such as platinum-1, 3- divinyl-1, 1, 3, 3-tetramethyldisiloxane complex, bis- (γ~ picoline) -platinum dichloride, trimethylenedipyridine-platinum dichloride, dicyclopentadiene-platinum dichloride, cyclooctadiene-platinum dichloride, and cyclopentadiene- platinum dichloride) , bis (alkynyl)bis (triphenylphosphine)platinum complexes, and bis (alkynyl) (cyclooctadiene)platinum complexes. The hydrosilylation catalysts may be used in the form of microcapsules. For the microcapsule, one example of the solid fine particles that can contain the catalyst and are insoluble in organopolysiloxane is a resin (such as polyester resin and silicone resin) . The hydrosilylation catalyst may be provided in the form of clathrate compounds, for example, in cyclodextrin. The hydrosilylation catalyst is added in catalytic amounts. For example, a platinum catalyst is added in an amount preferably in the range of 0.1 to 500 ppm, and in particular in the range of 1 to 200 ppm as measured by the amount of platinum metal in the composition comprised of the components (A) and (B) .
The composition of the present invention comprised of the components (A) to (C) must exhibit a cured hardness in the range of 5 to 75, and preferably in the range of 5 to 60 by a hardness test of type E Durometer for a lOmm-thick sample piece according to JIS K6253. The composition with a cured hardness of less than 5 becomes susceptible to large deformation during the encapsulation step using the silicone resin, whereas the composition with a cured hardness of more than 75 does not have a sufficient ability to absorb stress required for the soft layer. The desired hardness can be achieved by adjusting the degree of polymerization, the alkenyl groups and branch structures of the component (A) to contribute crosslinkages, as well as the amount of Si-H bond and the degree of polymerization of the component (B) .
The light emitting diode device according to the present invention is fabricated by coating an LED element with the above-described composition comprised of the components (A) to (C) , and further encapsulating the coated LED element in an addition-curable silicone resin composition that cures to form a resin-like material. The addition-curable silicone resin is a composition comprising (a) an organopolysiloxane that is represented by the average composition formula;
(R3Si0i/2)M- (R2SiO2/2)D* (RSiO3/2)τ- (SiO4/2)Q (where R is individually selected from the group consisting of organic group, hydroxyl group and hydrogen atom; M, D, T and Q are each a number greater than or equal to 0 and less than 1; M + D + T + Q = 1; and Q + T > 0) and contains as R a hydrocarbon group with a multiple bond and/or a hydrogen atom or a mixture thereof; and (b) an effective amount of a catalyst for the addition reaction. The component (a) is a polymer that, in its average composition in the mixture, contains the branch structures of T-units (RSiO3/2) and/or Q-units (SiO4/2) , and can undergo crosslinking or other reactions to form three dimensional networks of even higher degrees. Thus, it should hold that Q + T > 0 in each average composition formula.
Such an organopolysiloxane, also referred to as silicone resin, may be either a solid or a liquid prior to curing. Liquid compositions, however, are easily molded and are thus better suited for encapsulation of LEDs, which is the purpose of the present invention. The organopolysiloxane to serve as the component (a) may be any organopolysiloxane produced by techniques known to those skilled in the art: It may be obtained by hydrolysis of organosilanes or organosiloxanes.
Rs in the component (a) may be each individually selected and may or may not be identical to one another. The component (a) is defined by an average composition formula, so that Rs in the same structural units (R2SiO2/2)D may differ from one another and may at the same time include methyl, phenyl, and hydrogen atom. These structural units may be linked by different unit structures .
Examples of R include straight-chained or branched Cl to C20 alkyl or alkenyl groups and halogenated forms thereof; acetylene group or hydrocarbons containing acetylene group; C5 to C25 cycloalkyl or cycloalkenyl groups and halogenated forms thereof; and C6 to C25 aralkyl or aryl groups and halogenated forms thereof. Specifically, these hydrocarbons may be those given above as examples of the alkenyl group or the other organic groups in the component (A) . The phrase "R with a multiple bond" means a hydrocarbon group containing a carbon- carbon double bond or a carbon-carbon triple bond, including alkenyl or acetylene groups. A vinyl group is the most preferred of the hydrocarbon groups with multiple bonds.
Alternatively, R may be selected from the group consisting of hydrogen, hydroxyl, alkoxyl, acyloxy, ketiminoxy, alkenyloxy, acid anhydride, carbonyl, sugar, cyano, oxazoline, and isocyanate groups and hydrocarbon-substituted forms thereof. Specific examples are methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, hexyloxy, isohexyloxy, 2- hexyloxy, octyloxy, isooctyloxy, 2-octyloxy, acetoxy, dimethylketoxime, methylethylketoxime, glycidyl, ethylene glycoxy, diethylene glycoxy, polyethylene glycoxy, propylene glycoxy, dipropylene glycoxy, polypropylene glycoxy, methoxyethylene glycoxy, ethoxyethylene glycoxy, methoxydiethylene glycoxy, ethoxydiethylene glycoxy, methoxypropylene glycoxy, methoxydipropylene glycoxy, and ethoxydipropylene glycoxy groups. Of the above groups, methyl, ethyl, propyl, phenyl, and vinyl groups, and a hydrogen atom are particularly preferred.
The component (a) includes several possible combinations. For example, the component (a) may be an organopolysiloxane or a mixture of organopolysiloxanes that containing in one molecule a multiple bond containing hydrocarbon group bonded to silicon atom and a hydrogen atom bonded to silicon atom, or a mixture of organopolysiloxanes that contain in one molecule a multiple bond containing hydrocarbon group bonded to silicon atom, but not any hydrogen atoms bonded to silicon atom, with organopolysiloxanes that contain in one molecule a hydrogen atom bonded to silicon atom, but not any hydrocarbon groups having a multiple bond, or a mixture of the organopolysiloxanes of (i) (which contain in one molecule a multiple bond containing hydrocarbon group bonded to silicon atom and a hydrogen atom bonded to silicon atom) with organopolysiloxanes that contain in one molecule a multiple bond containing hydrocarbon group bonded to silicon atom, but not any hydrogen atoms bonded to silicon atom and/or organopolysiloxanes that contain a hydrogen atom bonded to silicon atom, but not any hydrocarbon groups having a multiple bond.
In brief, when the component (a) is provided as a mixture, such a mixture should contain a multiple bond containing hydrocarbon group bonded to silicon atom and Si-H group, and contain T- units and/or Q-units in amounts that allow the mixture to form the resin-like material after curing.
The multiple bond containing hydrocarbon group bonded to silicon atom and the hydrogen atom bonded to silicon atom, the essential elements of the polysiloxane to serve as the component (a) , are preferably present in either one or both of the selected units in the general formula of the component (a) . According to the present invention, the silicon-bonded multiple bond containing hydrocarbon group and the silicon-bonded hydrogen atom are most preferably present in the (R.2SiC>2/2) structural units .
The organopolysiloxane to serve as the component (a) of the present invention preferably contains, as R in the average composition formula, an aromatic group for the purpose of ensuring heat resistance, light resistance and refractive index required for the encapsulation material of LED elements. While this aromatic group may be aralkyl or aryl, phenyl is most preferred. The aromatic groups preferably account for 5 to 90 mol% and, more preferably, 10 to 60 mol% of the total R groups in the entire units. If the amount of aromatic groups is too little, then the desired improvement in the heat resistance, light resistance, and refractive index cannot be achieved, whereas if the amount is too much, the product becomes economically unfavorable. Although the aromatic groups may be introduced into any of the units except the (Siθ4/2) units, introduction into the (R2SiO2/2) and (RSiO3/2) units is preferred, and the introduction into the (RSiO3Z2) units is most preferred.
Furthermore, in the component (a) of the present invention, the silicon atoms directly bonded to hydrogen atoms preferably account for 1 to 40 mol%, more preferably 3 to 30 mol%, and most preferably 5 to 20 mol% of the entire silicon atoms. If this amount is too much, then the product tends to become more brittle although the hardness increases, whereas if the amount is too little, then the hardness does not increase adequately. Furthermore, in those cases where the component (a) contains both of the silicon-bonded hydrocarbon group with a multiple bond and the silicon-bonded hydrogen atom, then the silicon atoms directly bonded to hydrogen atoms preferably account for 1 to 40 mol%, more preferably 3 to 30 mol%. In amounts exceeding 40 mol%, although the hardness of the cured product increases, it tends to become more brittle, whereas in amounts less than 1 mol%, a cured product of satisfactory hardness cannot be obtained.
M, D, T, and Q are numbers representing relative proportion of each of the units, and each falls within a range from 0 (inclusive) to 1 (exclusive) . Preferred ranges are from 0 to 0.6 for M, from 0.1 to 0.8 for D, from 0.1 to 0.7 for T, and from 0 to 0.3 for Q, and ideally M is from 0.1 to 0.4, D is from 0.1 to 0.6, T is from 0.3 to 0.6, and Q is 0. The value of T + Q is preferably in the range of 0.3 to 0.9. The value of (2D + 3T + 4Q) / (D + T + Q) , wherein 2D is double D, 3T is triple T and 4Q is fourfold Q, which represents the degree of branching, preferably satisfies the requirement 3.0 > (2D + 3T + 4Q) / (D + T + Q) > 2.0, and even more preferably the requirement 2.8 > (2D + 3T + 4Q) / (D + T + Q) > 2.2.
The hydrosilylation catalyst to serve as the component (b) of the resin-like addition-curable silicone of the present invention may be those given as examples of the component (C) . The catalyst may be one that is commonly used to accelerate the addition reaction between Si-H group of the organopolysiloxane and the multiple bond of Si-bonded hydrocarbon. The catalyst for the addition reaction is used in an effective amount (or catalytic amount) , which typically is in the range of 1 to 1000 ppm, preferably in the range of 2 to 500 ppm with respect to the component (a) .
The encapsulation composition of the present invention comprised of the components (a) and (b) must turn to a resin- like state after undergoing crosslinking by the addition reaction. As used herein, the term "resin-like state" means that the composition has a hardness in the range of 30 to 90, preferably in the range of 40 to 90, by the test of the Durometer D hardness using a βmm-thick sample piece according to JIS K6253. The cured product with its hardness in the specified range can be obtained by adjusting the value (2D + 3T + 4Q) / (D + T + Q) to a predetermined range.
Examples of LED elements that can be used with the present invention include conventional GaP, GaAs, and GaN based red, green, and yellow LED elements, as well as the more recently developed high brightness, short wavelength LED elements. Although the composition of the present invention can be used for encapsulating conventional LED elements, it is most effective when used for encapsulating the more recently developed high brightness, short wavelength LED elements, including high brightness blue LED elements, white LED elements, and LED elements in the blue to near ultraviolet spectrum. For these LED elements, the peak wavelength of the emitted light falls within a range from 490 to 350 nm. The encapsulating material used with these types of LED elements not only requires good light resistance relative to light of blue through ultraviolet wavelengths, but also requires superior light resistance and heat resistance, as it is exposed to a higher brightness, higher energy light emitted from the LED elements. An encapsulating composition of the present invention provides superior light resistance and heat resistance to that offered by conventional epoxy based encapsulants, meaning the lifespan of the light emitting diode device can be improved significantly. Specific examples of these high brightness blue LED elements, white LED elements, and LED elements in the blue to near ultraviolet spectrum include AlGaInN yellow LED elements, InGaN blue and green LED elements, and white light emitting diode elements that employ a combination of InGaN and a fluorescent material.
Specific examples of encapsulated light emitting diode devices include lamp-type devices, large scale package devices, and surface mounted devices. These different types of LED device are described, for example, in "Flat Panel Display Dictionary, " published by Kogyo Chosakai Publishing Co., Ltd., publication date 25 December 2001, pp. 897 to 906.
The composition of the present invention, comprised of the components (A) to (C) and cured to form a soft silicone, may be applied to LED elements using any suitable technique. For example, an entire LED element may be immersed in a liquid composition, or droplets of a liquid composition may be dropped onto an LED element. The immersion technique is particularly suitable since the LED element can be coated relatively uniformly by this technique. While the composition may be applied to any suitable thickness, it is applied typically to a thickness of about 0.01 to 2 mm. After application of a liquid composition, the composition may or may not be cured prior to the encapsulation step. It is preferred to cure the composition prior to the encapsulation step, however. The composition can be easily cured by passing the coated LED element through a furnace adjusted to a temperature suitable for curing. The curing step is typically carried at a temperature in the range of 50 to 1800C and over a time period of 1 to 120 min.
After coated with the silicone that cures to form a soft silicone, the LED element is further encapsulated in the composition comprised of the components (a) and (b) that cures to a resin-like state. The encapsulation may be carried out using any suitable technique. For example, the encapsulation may be carried out by pouring the silicone composition of the present invention in a resin mold, immersing an LED element in the composition, and then heating the composition to cure. The encapsulation may also be carried out by transfer molding. One advantage of the encapsulation using the silicone resin of the present invention is that the resin can be used not only with resin molds, but also with metal molds, which have not previously been used with the conventional epoxy-based encapsulating materials.
Additives may be added to the composition of the present invention, provided that the advantages of the invention are not affected. Examples of possible additives include addition reaction control agents for imparting improved curability and pot life, reactive or non-reactive straight chain or cyclic low molecular weight organopolysiloxanes or the like for regulating the hardness and viscosity of the composition, fluorescent agents such as YAG to enable the emission of white light, inorganic fillers or pigments such as fine particulate silica and titanium dioxide and the like, organic fillers, fire retardant agents, heat resistant agents, and anti-oxidants.
The light emitting diode devices of the present invention, in particular, the light emitting diode devices of the present invention comprising blue to ultraviolet-emitting LED elements are less susceptible to cracking of encapsulation when exposed to rapid temperature changes. The encapsulation of the LED device advantageously exhibits strength and hardness in a well- balanced manner while retaining the transparency, light resistance, and heat resistance of the silicone-based material.
Examples
The present invention will now be described in detail with reference to examples, which are not intended to limit the scope of the invention in any way. The following silicone compositions were used in the examples of the present invention:
(A-I) Dimethylpolysiloxane that has each end blocked with a dimethylvinylsilyl group and has a viscosity of 900 mPa• s at 250C. (B-I) Methylhydrogenpolysiloxane that has each end blocked with a trimethylsilyl group, has a viscosity of 300 mPa• s at 25°C, and contains 14 methylhydrogensiloxane units in its main unit. (C, b) Vinyl-containing siloxane-platinum complex derived from chloroplatinic acid (hydrosilylation catalyst) . (a) Organopolysiloxane that has an average composition of (Me3SiOl/2) 0.17- (MeHSiO2/2) 0.20 • (MeViSiO2/2) 0.25• (PhSiO3/2) 0.38 (where Me, Vi, and Ph represent methyl, vinyl, and phenyl groups, respectively) and has a viscosity of 900 mPa■s at 25°C.
In each example, a 10mm- or 6mm-thick sheet of the cured product was used to measure its hardness by the Durometer. A heat-shock test was performed to evaluate the crack-resistance of the sheet. Using a small heat-shock tester (TSE-Il-A) manufactured by ESPEC Corp., the test was performed by cyclically changing temperatures of -400C and 1100C, and maintaining each temperature for 30 min. The temperature of the tester was changed from -400C to 1100C and from HO0C to -4O0C within three minutes .
Example 1
90 parts by weight of dimethylpolysiloxane of (A-I) , 10 parts by weight of methylhydrogenpolysiloxane of (B-I), and 0.05 parts by weight of platinum complex (C) were weighed and were mixed until uniform. Using an aspirator, the mixture was deaerated under reduced pressure. The resulting addition- curable silicone mixture was determined to have a viscosity of 700 mPa-s. A silver-plated metal lead frame (for 5mm-lamp type) was immersed in the mixture for 2 minutes, pulled out of the mixture and then held in the air for 3 minutes to remove the extra addition-curable silicone mixture. Subsequently, the lead frame was heated at 1000C for 15 minutes to cure the silicone mixture. The microscopy of the resulting lead frame, which was coated with the soft addition-curable silicone, revealed that the lead frame was coated to a thickness of approximately 50 to 200 microns. The lOmm-thick sheet, obtained by heating the addition-curable mixture at 100°C for 15 minutes, had a hardness of 50 as determined by a type-E Durometer.
Next, 100 parts by weight of organopolysiloxane of (a) and 0.02 parts by weight of platinum complex of (b) were mixed until uniform. Using an aspirator, the mixture was deaerated under reduced pressure to obtain an addition-curable silicone resin mixture with a viscosity of 800 mPa*s. The obtained addition- curable silicone resin mixture was poured in a resin casting case (5mm lamp-type) and the previously obtained lead frame coated with the soft addition-curable silicone was inserted into the casting case. The resin casting case was then heated at 1500C for 3 hours for curing. The 6mm-thick sheet, obtained by heating the addition-curable silicone resin at 1500C for 3 hours, was transparent and had a hardness of 60 as determined by a type-D Durometer.
The resulting light emitting diode device with two-layered encapsulation was tested on a heat-shock tester. After 300 cycles, no cracks were observed in the LED device.
[Comparative Example 1]
As in Example 1, 100 parts by weight of organopolysiloxane of (a) and 0.02 parts by weight of hydrosilylation catalyst of (b) were weighed and mixed until uniform. After deaeration under reduced pressure, the mixture had a viscosity of 800 mPa• s. The resulting silicone resin mixture was poured in a resin casting case (5mm lamp-type) and a silver-plated metal lead frame without soft silicone coating was inserted into the casting case. The resin casting case was then heated at 1500C for 3 hours for curing. The resulting light emitting diode device with single-layered encapsulation was tested on a heat-shock tester. After 10 cycles, cracks were formed in every sample.

Claims

1. A light emitting diode device in which a light emitting diode element is coated with an addition-curable soft silicone and is further encapsulated in a resin-like, addition-curable silicone resin, wherein the addition- curable soft silicone is characterized in having a cured hardness of 5 to 75 as measured by a Type E Durometer and being a cured product of a composition comprising
(A) an organopolysiloxane that has an average of at least 1.8 alkenyl groups per molecule bonded to a silicon atom and has a viscosity of 10 mPa• s to 10,000 mPa-s as determined at 250C and at a shearing rate of 0.9 s"1;
(B) an organohydrogenpolysiloxane that has an average of at least 4 hydrogen atoms per molecule bonded to a silicon atom and has a viscosity of 10 mPa• s to 10,000 mPa• s as determined at 25°C and at a shearing rate of 0.9 s~x, wherein the organohydrogenpolysiloxane is provided in such an amount that 0.9 to 2 silicon atoms bonded to a hydrogen atom are present for each of the alkenyl group in the component (A) ; and
(C) a hydrosilylation catalyst in a catalytic amount that accelerates the curing of the composition.
2. The light emitting diode device according to claim 1, wherein the component (A) is an organopolysiloxane having an average of about two alkenyl groups per molecule bonded to the silicon atom and the alkenyl groups are positioned at the ends of the organopolysiloxane molecule.
3. The light emitting diode device according to claim 1 or 2, wherein the addition-curable silicone resin is a cured product of a composition comprising:
(a) one or more organopolysiloxanes that are represented by the average composition formula (I)
(R3SiOiZ2)M- (R2SiO2Z2)D- (RSiO3/2)T- (SiO4/2)Q (I) ,
wherein
R is identical or different and selected from the group consisting of substituted or unsubstituted hydrocarbon group, substituted or unsubstituted hydrocarbon group comprising a C-C multiple bond, hydroxyl group, and hydrogen atom;
M, D, T, Q are each a number greater than or equal to 0 and less than 1, with the provision that
M + D + T + Q = l ; and Q + T > 0 ) ;
comprising at least one organopolysiloxane containing at least a hydrocarbon group with a C-C multiple bond and a hydrogen atom, or a mixture of at least one organopolysiloxane containing at least a hydrocarbon group with a C-C multiple bond with of at least one organopolysiloxane containing a hydrogen atom; and
(b) an effective amount of a hydrosilylation catalyst.
4. A method for encapsulating the light emitting diode element according to anyone of claims 1 to 3, comprising - immersing the light emitting diode element in a liquid composition of the soft silicone, which comprises the components (A) to (C) , thereby - applying the composition to the light emitting diode element; and
- subsequently cast molding the silicone resin composition to encapsulate the light emitting diode element under a cured or uncured state of the liquid composition which forms the soft silicone after curing.
PCT/EP2005/008247 2004-08-04 2005-07-28 Resin-encapsulated light emitting diode and method for encapsulating light emitting diode WO2006013066A2 (en)

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