Detailed introduction of white LED part two

In order to reduce thermal resistance, many foreign LED manufacturers install LED chips on the surface of heat dissipation fins made of copper and ceramic materials, and use soldering to connect the heat dissipation wires on the printed circuit board to the heat dissipation fins that use cooling fans to force air cooling. The experimental results of OSRAM Opto Semiconductors Gmb in Germany have confirmed that the thermal resistance from the LED chip with the above structure to the solder joint can be reduced by 9K/W, which is about 1/6 of that of the traditional LED. When 2W electric power is applied to the packaged LED display module, the temperature of the LED chip is 18°C ​​higher than the solder joint. Even if the temperature of the printed circuit board rises to 500°C, the temperature of the LED chip is only about 700°C. Once the thermal resistance is reduced, the temperature of the LED chip will be affected by the temperature of the printed circuit board. For this reason, the thermal resistance from the LED chip to the soldering point must be reduced. Conversely, even if the white LED has a structure that suppresses thermal resistance, if heat cannot be conducted from the LED package to the printed circuit board, the rise in the temperature of the LED will reduce the luminous efficiency. Therefore, Panasonic has developed a printed circuit board and Packaging integration technology. The company encapsulates a square blue LED with a side length of 1mm on a ceramic substrate in a chip-on-chip manner, and then pastes the ceramic substrate on the surface of the copper printed circuit board, including the printed circuit board and the module The overall thermal impedance is about 15K/W.

In response to the longevity of white LEDs, the current countermeasures taken by LED manufacturers are to change the sealing material and disperse the fluorescent material in the sealing material, which can more effectively suppress the deterioration of the material and the reduction of light transmittance.

Since epoxy resin absorbs 45% of light with a wavelength of 400~450nm, and silicon sealing material is less than 1%, the time for epoxy resin to halve the brightness is less than 10,000 hours, and silicon sealing material can be extended to 4 About 10,000 hours, it is almost the same as the design life of the lighting equipment, which means that the lighting equipment does not need to replace the white light LED during use. However, the silicon sealing material is a highly elastic and soft material, and the silicon sealing material must not be scratched during processing. Surface production technology, in addition, the silicon sealing material is very easy to adhere to dust in the process, so in the future, it is necessary to develop technology that can improve the surface characteristics.