Light-emitting or receiving device, encapsulant for light-emitting or receiving element and the method for encapsulating thereof

Abstract: There is provided a light-emitting or receiving device having improved weatherability , chemical resistance, hardness, and optical properties, which comprises a light-emitting or receiving element encapsulated with a polymer of a polymerizable liquid composition comprising at least one diallyl monomer or oligomer thereof. There is also provided a method for encapsulating a light-emitting or receiving element.

Description: BACKGROUND OF THE INVENTION This invention relates to an encapsulating method useful in the manufacture of light-emitting or receiving devices. In the prior art manufacture of light-emitting or receiving devices such as LED, laser diodes, and photosensors, light-emitting diodes and similar elements are encapsulated by casting epoxy resin followed by polymerization. The encapsulating method using epoxy resin, however, has the following drawbacks. (1) Since the epoxy resin has poor weatherability, its outdoor use is substantially limited. This is because light-emitting elements experience a drastic drop in luminous power with a lapse of time and light-receiving elements experience a drop in light-receiving sensitivity with a lapse of time when used outdoors. (2) Since it takes a long time of 5 to 20 hours to cure the epoxy resin, the productivity of light-emitting or receiving devices is low. (3) Since the epoxy resin has poor mold release characteristics, the productivity of light-emitting or receiving devices is low. If a mold release agent is used to improve mold release, it is necessary to remove the mold release agent adhered to the surface of the epoxy resin encapsulant, creating a serious problem in the production process. EP-A-0 114 080 and US-A-4 623 705 disclose methods for synthesizing carbonic allyl esters for optical applications. SUMMARY OF THE INVENTION An object of the present invention is to provide an encapsulating method suitable for the manufacture of a light-emitting or receiving device (or part) having improved weatherability, chemical resistance, hardness, and optical properties. According to the present invention, there is provided a method for encapsulating a light-emitting or receiving element, as outlined in the claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical cross section of a light-emitting or receiving device. FIG. 2 is a vertical cross section illustrating an encapsulating method. DETAILED DESCRIPTION OF THE INVENTION The invention will be described in detail by referring to the preferred embodiments shown in the drawings. FIG. 1 illustrates a light-emitting or receiving device. The light-emitting or receiving device 1 may be any such device and is not particularly limited in shape or the like insofar as a light-emitting or receiving element 4, for example, a diode 4 (such as light-emitting diode or ultraviolet light-emitting diode) is encapsulated with a specific polymer 3. In general, lead frames 6 which project beyond the polymer 3 are provided on the upper surface of the polymer 3. One lead frame 6 is connected to a die bonding electrode 7 to which the light-emitting or receiving element 4 is secured. The other lead frame 6 is connected to a bonding wire 5 such as a gold wire. The bonding wire 5 is connected to the light-emitting or receiving element 4. A lower portion of the lead frames 6, die bonding electrode 7, and bonding wire 5 are sealed in the polymer 3. The light-emitting or receiving device is characterized by encapsulation with a specific polymer, more particularly by encapsulation with a polymer of a polymerizable liquid composition (to be referred to as encapsulant A, hereinafter) comprising (a) a monomer or an oligomer or a mixture thereof containing a diallyl compound as an essential ingredient. The encapsulant [A] prior to polymerization into the polymer with which the light-emitting or receiving device of the present invention is encapsulated is a polymerizable liquid composition comprising (a) a monomer or an oligomer or a mixture thereof containing a diallyl compound as an essential ingredient, preferably comprising (a) a monomer or an oligomer or a mixture thereof of a bis(allyl carbonate) of an aliphatic, cycloaliphatic or aromatic dihydric alcohol as an essential ingredient. Examples of the diallyl compounds include a composition comprising (a′) a monomer or an oligomer or a mixture thereof of a bis(allyl carbonate) of an aliphatic, cycloaliphatic or aromatic dihydric alcohol having the general formula: wherein R is a residue of a dihydric alcohol, and n has a value or an average value in the range of from 1 to 10, preferably from 2 to 10. Component (a′) is preferably the reaction product of diallyl carbonate and a dihydric alcohol in a molar ratio of 4:1 or lower, more preferably in a molar ratio of 2:1. Preferred examples of the dihydric alcohol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyethylene glycol, dipropylene glycol, propylene glycol, neopentyl glycol, trimethylpentane diol, cyclohexane dimethanol, bis(hydroxymethyl)tricyclodecane, 2,7-norbornane diol, α,α′-xylene diol, 1,4-bis(hydroxyethoxybenzene), and 2,2-bis[4-(hydroxyethoxy)phenyl]propane alone and mixtures thereof. The encapsulant [A] of the present invention is preferably a liquid composition comprising components (a″), (b), and (c) shown below. Japanese Patent Application Kokai No. 59-140214 (corresponding to EP-A-0 114 080) is incorporated herein by reference. The preferred composition comprises (a″) 10 to 90% by weight of an oligomer or a mixture of oligomers of a bis(allyl carbonate) of an aliphatic, cycloaliphatic or aromatic dihydric alcohol having the general formula: wherein R is a residue of a dihydric alcohol, and n has a value or an average value in the range of from 1 to 10, preferably from 2 to 10, with the proviso that the content of a dihydric alcohol bis(allyl carbonate) monomer optionally present in the oligomer is up to 50% by weight; (b) 0 to 90% by weight of a compound selected from the group consisting of (b-1) a monomeric di- or tri(allyl carbonate) of an aliphatic, cycloaliphatic or aromatic di- or trihydric alcohol having the general formula: wherein R′ is a residue of a di- or trihydric alcohol, and n′ is equal to 2 or 3, or a mixture thereof, with the proviso that the content of an oligomeric di(allyl carbonate) of a di- or trihydric alcohol or a poly(allyl carbonate) of a di- or trihydric alcohol optionally present in the monomer or the mixture is up to 30% by weight, (b-2) an allyl ester of an aliphatic or aromatic di- or tricarboxylic acid having the general formula: wherein R″ is a residue of a di- or tricarboxylic acid, and n″ is equal to 2 or 3, and (b-3) triallyl cyanurate and triallyl isocyanurate; and (c) 0 to 30% by weight of an acrylic or vinyl monomer; with the proviso that the total of components (b) and (c) is more than 0. The preferred component (a″) is the reaction product of diallyl carbonate and a dihydric alcohol in a molar ratio of 4:1 or lower, more preferably in a molar ratio of 2:1. The dihydric alcohol is preferably selected from the group consisting of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyethylene glycol, dipropylene glycol, propylene glycol, neopentyl glycol, trimethylpentane diol, cyclohexane dimethanol, bis(hydroxymethyl)tricyclodecane, 2,7-norbornane diol, α,α′-xylene diol, 1,4-bis(hydroxyethoxybenzene), and 2,2-bis[4-(hydroxyethoxy)phenyl]propane. The preferred component (b) is the reaction product of diallyl carbonate and a di- or trihydric alcohol in a molar ratio of 6:1 or higher, more preferably in a molar ratio of 12:1. The di- or trihydric alcohol is preferably selected from the group consisting of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyethylene glycol, dipropylene glycol, propylene glycol, neopentyl glycol, trimethylpentane diol, cyclohexane dimethanol, bis(hydroxymethyl)tricyclodecane, 2,7-norbornane diol, α,α′-xylene diol, 1,4-bis(hydroxyethoxybenzene), 2,2-bis[4-(hydroxyethoxy)phenyl]propane, trimethylol propane, and tri(hydroxyethyl) isocyanurate alone and mixtures thereof. Also included in component (b) are diallyl phthalate, diallyl succinate, diallyl adipate, diallyl chlorendate, diallyl glycolate, diallyl naphthalene dicarboxylate, and triallyl mellitate. Component (c) is preferably selected from vinyl acetate, vinyl benzoate, methyl methacrylate, phenyl methacrylate, methyl acrylate, methyl maleate, maleic anhydride, and vinylidene chloride alone and mixtures thereof. Another example of the diallyl compounds include (I) a copolymerizable composition comprising a diallyl ester of a nuclearly halo-substituted benzene dicarboxylic acid and diethylene glycol diallyl carbonate as disclosed in Japanese Patent Application Kokai No. 59-45312; (II) a copolymerizable composition comprising at least one ester of a nuclearly halo-substituted benzene dicarboxylic acid (for example, bisallyl 2,4-dichloroterephthalate) and at least one radical-polymerizable monofunctional monomer bearing an aromatic ring and capable of forming a homopolymer having a refractive index of at least 1.55 (for example, phenyl methacrylate) as disclosed in Japanese Patent Application Kokai No. 59-8709 (corresponding to EP-A-0 112 927); (III) a copolymerizable composition comprising at least one bisallyl carbonate or bis-β-methylallyl carbonate (for example, 1,4-bis(hydroxyethoxy)benzene bisallyl carbonate) and at least one radical-polymerizable monofunctional monomer bearing an aromatic ring and capable of forming a homopolymer having a refractive index of at least 1.55 (for example, phenyl methacrylate) as disclosed in Japanese Patent Application Kokai No. 59-8710; (IV) a copolymerizable composition comprising a monomer obtained by reacting a monool (for example, 4-benzyl-phenol) with an unsaturated carboxylic acid or chloride thereof (for example, acrylic acid or chloride thereof) and a radical-polymerizable monomer capable of forming a homopolymer having a refractive index of at least 1.55 (for example, styrene) as disclosed in Japanese Patent Application Kokai No. 59-96109; (V) a copolymerizable composition comprising a chlorobenzoic acid allyl ester (for example, 2,3-dichlorobenzoic acid diallyl ester) and a difunctional monomer (for example, tetrabromophthalic acid diallyl ester) as disclosed in Japanese Patent Application Kokai No. 59-96113 (corresponding to EP-A-0 112 927); (VI) a copolymerizable composition as disclosed in Japanese Patent Application Kokai No. 59-184210; (VII) diethylene glycol bisallyl carbonate; and (VIII) copolymereizable compositions of a bisallyl compound such as diethylene glycol bisallyl carbonate, 1-4-bis(hydroxyethoxy)benzene bisallyl carbonate, and 2,4-dichloroterephthalic acid bisallyl ester and a vinyl monomer having an aromatic ring such as phenyl methacrylate and benzyl methacrylate. The polymerizable liquid composition may contain another monomer and a filler in such amounts that they do not detract from the physical properties of the resulting polymer. For example, a mono (meth)acrylic compound, di(meth)acrylic compound, or unsaturated carboxylic acid such as maleic anhydride may be added in an amount of up to 30% by weight, or a silane coupling agent such as vinyl triethoxysilane may be added in an amount of up to 10% by weight, based on the weight of the polymer. The encapsulant [A] may further contain a polymerization initiator [B]. The polymerization initiator [B] used in polymerizing encapsulant [A] may be any of photo polymerization initiators, thermal polymerization initiators, and photo and thermal polymerization initiators, and mixtures thereof. The photo polymerization initiators include electron beam and radiation polymerization initiators as well as photo polymerization initiators. A typical example of the photo polymerization initiator is 2-hydroxy-2-methyl-1-phenyl-propan-1-one. Examples of the thermal polymerization initiators include peroxydicarbonates such as diisopropyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, and tert-butyl perbenzoate; organic peroxides such as benzoyl peroxide, acetyl peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, di-tert-butyl peroxide, tert-butyl peroxybenzoate, lauroyl peroxide, diisopropyl peroxydicarbonate, dimethyl ethyl ketone peroxide, and diacyl peroxide; and radical initiators such as azobisisobutyronitrile and azobismethylisovaleronitrile. A typical example of the photo and thermal polymerization initiators is the compound of the following formula: Polymerization initiator [B] may be used to polymerize encapsulant [A] in an amount of 0.1 to 10% by weight, preferably 1 to 6% by weight based on encapsulant [A]. Encapsulant [A] may be used in semi-cured state or B stage if desired. The method for encapsulating the element 4 with encapsulant [A] is not particularly limited insofar as the method can form the polymer 3 (see FIG. 1) by placing the element 4 in a mold 2, filling the mold with encapsulant [A] 13, polymerizing encapsulant [A] as shown in FIG. 2. The following encapsulating method according to the invention is hereafter described. Encapsulant [A] is polymerized in the mold while the surface of encapsulant [A] 13 in the mold is covered with a liquid [C] 8 having low solubility in encapsulant [A] 13 and a lower density than encapsulant [A] 13. Liquid [C] is not particularly limited as long as it is less soluble in encapsulant [A] and has a lower density than encapsulant [A]. The density of liquid [C] is preferably from 0.7 to 1 g/cm³, more preferably from 0.8 to 0.95 g/cm³. If encapsulant [A] to be polymerized in the presence of a radical polymerization initiator is in contact with air, oxygen will consume active radicals so that the surface of the polymerizing encapsulant in contact with air may sometimes remain liquid or gel without reaching a sufficient molecular weight. Liquid [C] may be water, for example, which seals any opening to block oxygen. Water is suitable for polymerization at relatively low temperatures because of its high vapor pressure. Liquid [C] may also be a liquid synthetic hydrocarbon polymer having a low molecular weight or a liquid hydrocarbon mixture such as mineral oil. Examples of the synthetic hydrocarbon polymers include poly(α-olefin) oils such as polydecene-1, alkyl aromatic oils such as alkylbenzenes, polybutene oil or liquid polybutene, polyhexene, alkylnaphthene oils such as 2,4-dicyclohexyl-2-methylpentane oil, and ethylene-α-olefin random copolymer oils such as ethylene-propylene random copolymer oil. Preferred among them are those having a molecular weight of at least 500, more preferably from 1,000 to 10,000. Also preferred are ethylene-α-olefin random copolymer oils having a number average molecular weight ( Mn ) of from 500 to 5,000, especially from 1,500 to 3,000. Particularly preferred are liquid, low-molecular weight ethylene-α-olefin copolymers consisting of 30 to 70 mol% of ethylene units and 30 to 70 mol% of α-olefin units and having a number average molecular weight ( Mn ) of from 1,000 to 5,000 and a Q value (weight average molecular weight/number average molecular weight) of up to 3. When liquid [C] is a liquid polyolefin or the like, the liquid itself exhibits mold release effect, considerably facilitating mold release operation. At the end of polymerization, the liquid polyolefin may be readily removed with an organic solvent such as hexane, kerosene, and trichloroethylene. Polymerization may be carried out under various conditions depending on the identity of polymerization initiator. In the case of thermal polymerization, the composition may be heated in a heating tank to a temperature of about 30 to 150°C, preferably about 40 to 120°C for about 1/2 to 72 hours, preferably about 1 to 4 hours, although the exact value will vary with the shape and size. In the case of photo polymerization, polymerization may be carried out under a high-pressure mercury lamp with a power of 60 to 150 W/cm for about 1 minute to 2 hours, preferably 3 to 30 minutes at a temperature of about 40 to 120°C, preferably about 60 to 100°C. EXAMPLES Example 1 An assembly of a GaAlAs light-emitting diode with lead frames was set in a mold of polypropylene having an inner diameter of 5 mm and a depth of 10 mm. The mold was changed. with a homogeneously mixed liquid composition given below as encapsulant [A]-I. The mold was placed in a vacuum oven, which was purged with argon gas and then heated stepwise from 40°C to 90°C, completing polymerization in 3 hours. [A]-I The reaction product obtained by reacting diallyl carbonate with diethylene glycol in a molar ratio of 2:1 in the presence of sodium ethoxide under the conditions described in Japanese Patent Application Kokai No. 56-133246 (consisting of 30% by weight of diethylene glycol bisallyl carbonate and 70% by weight of oligo-carbonate, n = 3 to 10) 55% by weight Tris(allyl carbonate) of tris(hydroxyethyl) isocyanurate obtained by reacting diallyl carbonate with tris(hydroxyethyl) isocyanurate in a molar ratio of 12:1 12.4% by weight Diethylene glycol bisallyl carbonate 27.5% by weight Vinyl acetate 5% by weight Polymerization initiator (per 100 parts of the foregoing ingredients) Diisopropyl peroxydicarbonate 2.5 pbw Example 2 An assembly of a light-emitting diode with lead frames was set in a mold TPX® having an inner diameter of 5 mm and a depth of 10 mm as shown in FIG. 2. A composition given below as encapsulant [A]-II was cast into the mold and then covered with a layer of a liquid ethylene-propylene copolymer (Mn 2500, Q 2.0, specific gravity 0.846) having a thickness of about 2 mm. The mold was placed in an air oven, which was heated stepwise from 40°C from 90°C, completing polymerization in 3 hours. [A]-II The reaction product obtained by reacting diallyl carbonate with diethylene glycol in a molar ratio of 2:1 in the presence of sodium ethoxide under the conditions described in Japanese Patent Application Kokai No. 56-133246 (consisting of 30% by weight of diethylene glycol bisallyl carbonate and 70% by weight of oligo-carbonate, n = 3 to 10) 58% by weight Tris(allyl carbonate) of tris(hydroxyethyl) isocyanurate obtained by reacting diallyl carbonate with tris(hydroxyethyl) isocyanurate in a molar ratio of 12:1 13% by weight Diethylene glycol bisallyl carbonate 29% by weight Polymerization initiator (per 100 parts of the foregoing ingredients) Diisopropyl peroxydicarbonate 2.7 pbw Example 3 The procedure of Example 2. was repeated except that encapsulant [A]-II was replaced by [A]-I, completing polymerization in 3 hours as in Example 2. Comparative Example 1 An assembly of a light-emitting diode with lead frames was set in a mold of TPX® having an inner diameter of 5 mm and a depth of 10 mm as shown in FIG. 2. An epoxy resin of the light-emitting diode encapsulating grade was cast into the mold, the epoxy resin consisting of 100 parts of a major agent, Pelnox XN-1886-3 and 110 parts of a curing agent, Pelcure XV-2263 (manufactured by NIPPON PELNOX K.K.). The epoxy resin was cured at 120°C for 8 hours. The light-emitting or receiving devices obtained in the foregoing Examples and Comparative Example were evaluated as follows, with the results shown in Table 1. (1) Mold Release Mold release was evaluated by removing the cured resin from the mold without using a mold release agent. O ○: very easily releasable O: manually releasable X: manually unreleasable (2) Transparency Visual observation O: good O ○: excellent In the case of Comparative Example only, evaluation was made by removing the cured resin using a silicone mold release agent for light-emitting diodes. No mold release agent was used in Examples. Separately, encapsulants [A]-I and [A]-II were polymerized into plates of 3.0 mm thick by the same method as described for Examples 1-3 and Comparative Example 1 and measured for light transmittance using a spectrophotometer. Light transmittance measurement: auto-recording spectrophotometer, model U-3400 of Hitachi, Ltd. (3) Weathering test (a) Using an accelerated weathering tester (model SUV-W11 of Iwasaki Electric K.K.), a sample was exposed to light under the following conditions. Ultraviolet intensity: 100 mW/cm² Black panel temperature: 63°C Relative humidity: 50-70% A cycle consisting of an exposure time of 8 hours and a dewing time of 4 hours was repeated to a total exposure of 48 hours. Weathering test (b) Accelerated weathering tester (model WEL-6X-HC-BEC of Suga Tester K.K.). Light source: 6.0 kW xenon lamp Black panel temperature: 63°C Relative humidity: 50% A cycle consisting of an exposure time of 200 minutes (including a raining time of 18 minutes) was repeated to a total exposure of 100 hours. The light transmittance and luminous power were measured before and after the above-mentioned weathering tests. (4) Surface hardness A barrel portion of the encapsulant was measured for surface hardness by a similar method according to JIS K5401. Example Comparative Example 1 1 2 3 Mold release O O ○ O ○ X Transparency O ○ O ○ O ○ O Polymerizing time 3 hrs. 3 hrs. 3 hrs. 8 hrs. Weathering test (a) (1) Light transmittance, % Before test 760 nm 92 92 92 84 620 nm 92 92 92 81 400 nm 90 90 90 69 After test 760 nm 92 92 92 83 620 nm 92 92 92 78 400 nm 83 83 83 33 Weathering test (b) (2) Luminous power, mW Before test - 2.3 - 2.3 After test - 2.2 - 2.0 Surface hardness 4H 4H 4H 3H The encapsulating method of the present invention using a cover liquid can produce a light-emitting or receiving device with a high surface hardness. The device can be readily removed from the mold because the cover liquid has mold release property.

Claims: A method for encapsulating a light-emitting or receiving element, comprising placing a light-emitting or receiving element in a mold, casting an encapsulant [A] comprising at least one diallyl monomer or oligomer thereof into the mold, and polymerizing said encapsulant [A] while a liquid [C] which is insoluble in said encapsulant [A] and has a lower density than said encapsulant [A] covers the surface of encapsulant [A] to block oxygen. A method according to claim 1 wherein said diallyl monomer is a bis(allyl carbonate) of an aliphatic, cycloaliphatic or aromatic dihydric alcohol. A method according to claim 1 or 2 wherein said liquid [C] is a liquid synthetic hydrocarbon polymer having a low molecular weight or a liquid hydrocarbon mixture or a mixture thereof.

Inventors: KAUCHI KAKUTARO, KITAYAMA HIDEYUKI, TOMOSHIGE TORU, USUDA SHOJI, KAUCHI, KAKUTARO C/O MITSUI PETROCHEMICAL IND.,LTD, KITAYAMA, HIDEYUKI C/O IDEX IZUMI CORPORATION, TOMOSHIGE, TORU C/O MITSUI PETROCHEMICAL IND.,LTD, USUDA, SHOJI C/O IDEX IZUMI CORPORATION
Applicants: IDEC IZUMI CORP, MITSUI PETROCHEMICAL IND, IDEC IZUMI CORPORATION, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1989
Main classification: H01L33
IPC codes: H01L31, H01L33