Light-emitting elements, such as light-emitting diodes, have recently come to be used widely as, for example, a source of light for electroluminescent display panels, or a source of backlight for cellular phones or personal computers, owing to the improved brightness of light thereby emitted. These light-emitting elements are used in packages in which they are stored.
Conventionally, as for a light-emitting element storing package, a light-emitting element storing package disclosed in Patent Document 1 (Japanese Patent Provisional Publication No. 2002-232017) is proposed.
The light-emitting element storing package 100 disclosed in the Patent Document 1, as shown in FIG. 6, has an insulating substrate 111, a reflector frame 112 disposed along the outer periphery of the substrate 111. Furthermore, in the package 100, a light-emitting element storing concave portion 119 is defined between the substrate 111 and the reflector frame 112.
At the position of the concave portion 119 of the insulating substrate 111, i.e. at the just under the position of the concave portion 119, a wiring through-hole (so called “via-hole”) 116, which is penetrated vertically through the substrate 111, is provided.
The wiring through-hole 116 is filled with a conductive member 117 and wiring pattern layers 114 and 115, which are respectively formed on the upper and lower surfaces of the substrate 111, are electrically connected to each other through the conductive member 117. As a result, the light-emitting element 118 mounted on the upper wiring pattern layer 114 may be electrically connected with an external electrical circuit.
After the light-emitting element 118 is mounted on the bottom of the light-emitting element storing concave portion 119, the concave portion 119 is filled with a transparent resin, such as an epoxy resin so that the light-emitting element is sealed gas-tightly. As a result, a light-emitting device as a final product is produced.
In the light-emitting element storing package 100, a light-reflecting layer 113 is formed on the inner wall surface of the concave portion 119, i.e. on the inner wall surface of the reflector frame 112. The light emitted by the light-emitting element 118 is reflected by the light-reflecting layer 113 so that brightness of the light-emitting element 118 is substantially increased.
As a result, the light emitted by the light-emitting element 118 shines brightly by the action of this light-reflecting layer 113, so that an electroluminescent display panel may display bright and very clear characters and images.
As for the light-reflecting layer 113, for example, gold, silver or nickel, etc. is utilized. In addition, for example, a metallized metal layer is previously formed on the inner concave wall surface of the insulating substrate 111 and gold, silver or nickel, etc. is formed on the metallized metal layer by plating, so that the light-reflecting layer 113 is formed on the inner wall surface of the reflector frame 112.
However, in such light-emitting element storing package 100 disclosed in the Patent Document 1, the light-reflecting layer 113 is formed on the whole inner wall surface of the reflector frame 112. Therefore, lower portion of the light-reflecting layer 113 and the wiring pattern layer 114 at the bottom of the light-emitting element storing concave portion 119 is short-circuited, so that there is a possibility of impairing the function of the light-emitting element 118.
For this reason, in a light-emitting element storing package 200 of Patent Document 2 (Japanese Patent Provisional Publication No. 2003-273405), as shown in FIG. 7, a light-reflecting layer 213 is formed on the inner wall surface of the light-emitting element storing concave portion 219 not to cover whole inner wall surface of the reflector frame 212. Moreover, in the package 200, the light-reflecting layer 213 is formed as it is spaced apart from the bottom of the light-emitting element storing concave portion 219.
As a result, the electrical short-circuit between the light-reflecting layer 213 and a wiring pattern layer 214 at the bottom of the light-emitting element storing concave portion 219 is prevented effectively.
Furthermore, in the package 200, an insulating layer 220 is disposed between the light-emitting layer 213 and the wiring pattern layer 214 to ensure the prevention of their electrical short-circuiting.
In addition, in the light-emitting element storing package 200 disclosed in Patent Document 2, as shown in FIG. 7, there is no wiring through-hole in an insulating substrate 211, and a wiring pattern layer 201, which is provided between the reflector frame 212 and the substrate 211, is extended along the outer surface of the substrate 211. As a result, the wiring pattern layers 214 and 215, which are respectively formed on the upper and lower surfaces of the substrate 211, are electrically connected to each other.
However, in the light-emitting element storing package 200 disclosed in this Patent Document 2, the light-reflecting layer 213 is formed as it is spaced apart from the bottom of the light-emitting element storing concave portion 219 and the insulating layer 220 is disposed therebetween. Therefore, the light emitted from the light-emitting element 218 is not reflected by the surface of the insulating layer 220 so that brightness is substantially lowered.
Furthermore, according to both of Patent Documents 1 and 2, the light-reflecting layer is of, for example, gold, silver or nickel. However, gold and nickel have a light reflectance of as low as 50% or less for a wavelength of 400 nm or less. In addition, silver generally has a reflectance of as low as 50% or less for a wavelength of 350 nm or less, since it has absorption at a wavelength of 300 to 350 nm.
However, a light-emitting element for a white LED usually emits blue or near-ultraviolet light and it is converted to various wavelengths by various fluorescent materials. Therefore, it is important for improving its brightness that a light emitted from a light-emitting element having a wavelength of 350 to 430 nm is efficiently reflected.
Therefore, in Patent Document 3 (Japanese Patent Provisional Publication No. 8 (1996)-274378), as shown in FIG. 8, a light-reflecting layer is not formed and an insulating substrate 312 itself formed from a white sintered compact of aluminum oxide having relatively high light-reflecting property. As a result, a light emitted from a light-emitting element 318 is reflected by a light-reflecting surface 320.
In addition, in the light-emitting element storing package 300 disclosed in Patent Document 3, as shown in FIG. 8, a wiring through-hole 316 is formed. The wiring through-hole 316 is extending from the lower portion of a light-emitting element storing concave portion 319 of the insulating substrate 312 to the bottom surface of the insulating substrate 312 through an intermediate wiring portion 313 formed in the middle position of the insulating substrate 312.
The wiring through-hole 316 is filled with a conductive member 317 and wiring pattern layers 314 and 315, which are respectively formed on the upper and lower surfaces of the insulating substrate 312, are electrically connected to each other. Consequently, the light-emitting element 318, which is mounted on the upper wiring pattern layer 314, may be electrically connected with an external electrical circuit.
However, the white sintered compact of aluminum oxide constituting the substrate 312 according to Patent Document 3 has a relatively low thermal conductivity in the order of about 20 W/m·K despite its reflectance of 50% or more for light having a wavelength of 350 to 400 nm. Therefore, the heat from the light-emitting element 318 is thermally accumulated in the light-emitting element storing package 300 and the accumulated heat can not radiate therefrom so that there is possibility of damaging the light-emitting element 318.
Moreover, Patent Document 4 (Japanese Patent Provisional Publication No. 2004-152952) discloses a light-emitting element storing package in which a reflector frame is composed of white ceramics.
However, in this Patent Document, the ceramics actually used for the reflector frame are SiO2—Al2O3—MgO—ZrO2—CaO ceramics having a specific composition, which is mainly consisting of alumina. As apparent from this Patent Document, the ceramic has 96.25% by weight of alumina content so that it has a low thermal conductivity.
Patent Document 4 also states that, as a reflectance of 80% or higher for light having a wavelength of 400 to 700 nm with respect to aluminum nitride (AlN), the amount of Er2O3 in a sintered compact of aluminum nitride is preferably from 1 to 10% by weight based on the weight of the sintered compact.
However, in Patent Document 4, there is no specific embodiment corresponding to this statement. In addition, in fact, it has been confirmed that no white sintered compact of aluminum nitride can be obtained by sintering a material having an Er2O3 content of 1 to 10% by weight (see Comparative Example 4 below).
Patent Document 1 (Japanese Patent Provisional Publication No. 2002-232017)
Patent Document 2 (Japanese Patent Provisional Publication No. 2003-273405)
Patent Document 3 (Japanese Patent Provisional Publication No. 8 (1996)-274378)
Patent Document 4 (Japanese Patent Provisional Publication No. 2004-152952)