A light-emitting device in which an LED chip and a fluorescent material are used, the fluorescent material emitting fluorescence by being excited by light emission by the LED chip, is classified into the following known types according to how to provide the fluorescent material in a vicinity of the LED chip.
The known types include a two-stage sealing type (Patent Literature 1) in which an LED chip 151 is sealed by carrying out compression molding with respect to a sealing resin 153 containing a fluorescent material 152, and the sealing resin 153 is sealed by further carrying out compression molding with respect to a sealing resin 154 that is transparent (see (a) of FIG. 33).
A light-emitting device of this type deteriorates in productivity since compression molding needs to be carried out two times. Further, compression molding carried out two times requires two molds, and respective shapes of the sealing resin 153 containing the fluorescent material 152 and the sealing resin 154 are determined while the sealing resins 153 and 154 are being subjected to compression molding. Therefore, a change in size of the LED chip 151 changes an amount of the sealing resin 153 containing the fluorescent material 152 (a relative thickness of the sealing resin 153) (see (b) of FIG. 33). This may cause a change in color of emitted light. Therefore, in order to obtain an unchanged color of the emitted light, it is necessary to adjust a concentration (contained amount) of the fluorescent material 152 or to change the shape of the sealing resin 153 by replacing the mold with another mold.
The known types also include a precipitation type (Patent Literature 2) in which an LED chip is sealed by carrying out compression molding with respect to a sealing resin containing a fluorescent material, and precipitating the fluorescent material contained in the sealing resin so as to spread the fluorescent material in a vicinity of the LED chip.
This type makes it difficult to cause the fluorescent material to be precipitated and spread in a stable amount. This is (i) because it is difficult for resins for compression molding (most of which contain silicone), which are higher in viscosity than resins for transfer potting, to precipitate the fluorescent material and (ii) because a resin is cured in a short time during compression molding, so that the resin is cured before the fluorescent material is precipitated.
The known types also include a sheet covering type in which an LED chip 161 is sealed by carrying out compression molding with respect to a transparent sealing resin 162 and covering a vicinity of the transparent sealing resin 162 with a resin sheet 164 containing a fluorescent material 163 (see (c) of FIG. 33).
According to this type, light emitted by the LED chip 161 is partially reflected in an inner surface of the resin sheet 64 containing the fluorescent material 163 and returns inward, so that a loss occurs in the light. This reduces a light extraction efficiency.
Patent Literature 3 proposes a technique, which is irrelevant to a fluorescent material, for covering an LED chip connected to a substrate with a heat-curable film (an epoxy resin composition), and sealing the LED chip by heat-curing the heat-curable film. Patent Literature 4 proposes a technique in which a sealing sheet having (i) an outermost resin layer (e.g., a polycarbodiimide layer), (ii) an optical diffusion layer containing light diffusion particles (e.g., a polycarbodiimide layer), and (iii) a resin layer having a low refractive index (e.g., an epoxy resin layer) is stacked by use of a vacuum laminator on a wiring circuit board mounted with an optical semiconductor element, so as to be pressure-molded by use of a stamper.
Note here that in order to seal an LED chip by use of silicone containing a fluorescent material, normally, a substrate 172 is filled with silicone 171 that is in a liquid state and contains a fluorescent material (see (a) of FIG. 34) and then an LED chip 173 is sealed by heating the silicone 171 by use of an oven or the like (see (b) of FIG. 34). This causes a problem (i) such that a concentration of the fluorescent material contained in the silicone 171 sensitively changes in accordance with an environment in which each process is carried out and (ii) such that a viscosity of the silicone 171 changes in accordance with an ambient environment.
In order to solve this problem, Patent Literature 5, for example discloses a technique for molding, into sheet semi-cured silicone, liquid silicone in which a fluorescent material is mixed. According to the technique disclosed in Patent Literature 5, molding, into sheet semi-cured silicone, of liquid silicone in which a fluorescent material is mixed allows an improvement in treatment of silicone, and prevents a change in viscosity in accordance with an ambient environment.    Patent Literature 1
Japanese Patent Application Publication, Tokukai, No. 2008-211205A (Publication Date: Sep. 11, 2008)    Patent Literature 2
Japanese Patent Application Publication, Tokukai, No. 2006-229054A (Publication Date: Aug. 31, 2006)    Patent Literature 3
Japanese Patent Application Publication, Tokukai, No. 2009-010109A (Publication Date: Jan. 15, 2009)    Patent Literature 4
Japanese Patent Application Publication, Tokukai, No. 2006-140362A (Publication Date: Jun. 1, 2006)    Patent Literature 5
Japanese Patent Application Publication, Tokukai, No. 2010-159411A (Publication Date: Jul. 22, 2010)