1. Field of the Invention
The present invention relates to a light-emitting device using a light-emitting diode as a light source, and particularly, to a light-emitting device which is excellent in productivity as well as light resistance, moisture resistance, heat resistance, and heat dissipation.
2. Description of the Related Art
As conventional representative light-emitting devices using a light-emitting diode (LED) element as a light source, there are light-emitting devices in which an LED element and specified portion of leads (power-feeding members) are integrally sealed with a sealing material having light transmissivity. As such sealing materials, there are generally used sealing materials of resin, such as epoxy resin, silicon resin, or the like, from the points of view of molding property, mass productivity, and cost.
In recent years, blue LEDs with as high brightness as that of red and green LEDs have been developed, and thereby used in applications of LED traffic lights, white LEDs, and the like. Also, in order to obtain higher brightness, the development of high-power LEDs has proceeded, and high-power LEDs of a few watts have already been manufactured. In high-power LED elements, large current flows therethrough so that, from the points of view of light-emitting property and durability, an unnegligible level of heat is produced.
In such LEDs, resin sealing materials have large thermal expansion coefficient, so that increasing heat with increasing power and light of LED elements causes an increase in internal stress due to thermal expansion, and therefore cracking in the package, and peeling resulting from thermal expansion differences between the members. There is also the disadvantage of fast optical deterioration in resin sealing materials, such as yellowing. Because particularly in high-power LEDs, the above-mentioned tendencies are developed notably, LEDs with excellent durability are desired.
To improve such optical deterioration, heat resistance, and durability of LEDs, Japanese patent application laid-open No. 11-204838, for example, discloses using glass material as the sealing material.
According to the conventional light-emitting device, because sealing LED elements, etc. with glass generally requires softening and thermocompression-bonding glass material, or fusing and molding glass for being integral with the LED elements, etc., the portions to be sealed expand thermally due to exposure to heat during the processing, and are formed integrally and with no stress in this state, which is returned to normal temperature. In this case, however, if the thermal expansion coefficient differences between the LED elements and mounting substrate, etc. are large, there are the problems that peeling thereof is caused in the mounting interface by thermal stress due to the thermal contraction differences, and that cracking is caused in the sealing glass material, which reduce reliability.