Sumita Optical Glass Inc and Toyoda Gosei Co Ltd developed a glass-packaged white LED and showcased it at CEATEC JAPAN 2008.
Compared with plastic-packaged LEDs, the new LED has the following three advantages.
(1) It has a longer product cycle because the glass package deteriorates more slowly than the plastic package.
(2) Because of its high heat resistance, light-emitting elements can be arranged more densely.
(3) A high electric current can be applied to realize a higher luminance.
The glass-packaged white LED was made by the following method. First, a white LED element manufactured by Toyoda Gosei, a blue LED topped with a fluorescent material, is mounted on a ceramic substrate, and it is then placed in a mold. Second, low-melting glass is placed on it and heated to be softened. Third, pressure is applied on it.
It is important to heat and soften the low-melting glass at a temperature that does not destroy the element, Sumita Optical Glass and Toyoda Gosei said. Though the companies did not disclose the composition of the glass, their proprietary technologies of manufacturing optical glass were applied. By changing the shape of the mold, it is possible to make the glass-packaged white LED in various shapes depending on application.
LEDs packaged with epoxide resin and silicone resin have to be used at a temperature of +80°C or below. In contrast, the new LED can be used at a temperature of up to +200°C, the companies said. As a result, for a certain usage, the amount of current that can be applied increased from 20mA to 150mA.
At present, Sumita Optical Glass and Toyoda Gosei plan to use the new LED as a light source of a line camera used to inspect surfaces of glass substrates for flat-panel displays. At the exhibition, the companies displayed a sample of the product for this application.
Because of its enhanced heat resistance, it is possible to densely array elements, apply an electric current of as high as 100mA and realize a luminance of about 200,000lx, the companies said.
Existing while LEDs have not been used as light sources of line cameras because their luminance is not high enough, and, therefore, light is guided through optical cables from external light sources.
Sumita Optical Glass and Toyoda Gosei aim to expand the application of the glass-packaged white LED. Also, Toyoda Gosei plan to announce the details of the new technology at an early date.