【 Weak current College 】 improve thermal structure enhance white led service life 】

In the past LED manufacturers to profit fully white LED light beam, has developed a large LED chip is trying to take this method achieves its intended purpose, but actually exert power white led's last more than 1W above beams but will decline, light-emitting efficiency is relatively lower 2030 per cent, in other words white led brightness to traditional LED number times the consumer power of hope beyond the fluorescent lamps, they must first overcome the following four topics, including the Suppression of temperature rise, ensuring that the service life and improve the efficiency and luminescent properties of equalization.

The temperature rise of specific methods to reduce the package thermal resistance; maintenance of LED service life of the specific method is to improve the chip shape, a small chip; improve the efficiency of LED by improving chip architecture, a small chip; luminescent properties of homogenization is LED by the improvement in packaging methods, these methods are being developed.

■ Solution package thermal problem is method

Due to the increase in power would result in package thermal resistance sharply reduced to 10K/W, so foreign firms have developed high temperature white light LED attempts to improve these problems, but in fact high-power led calorific value than low power LED to more than double the high scores, and temperature rise may also make the luminous efficiency dropped considerably, even packaging technology allows high-calorie, however LED chip junction temperature is likely to exceed the allowed values, and operators finally realize the solution package thermal issue is fundamental.

The life of the LED, for example, use silica-packaging materials and ceramic packaging materials, can cause the service life of LED to improve a bit, especially with white led's light spectrum than with wavelength 450nm short wavelength light, conventional epoxy materials can easily be short wavelength light damage, high power white led's large amount of light is more accelerated deterioration of the packaging material, according to industry test results show continuous lighting to ten thousand hours, high power white led brightness is reduced by more than half simply cannot meet the lighting requirements for long life.

The LED light-emitting efficiency, improve the chip structure and the package structure, you can reach and low-power white led the same level, mainly because of the current density increase more than two times, but not easy to remove the chip from the large, light will cause the result instead of emitting less efficient than low-power white led's predicament, structure to improve chip electrodes, theoretically, can solve the above problem by light.

■ Try to reduce the thermal resistance, improve the heat problem

The luminescent properties of uniformity, General believes that improving the white led's fluorescent material density uniformity and fluorescence of production technology, should be able to overcome these difficulties. As mentioned above exert power increase, the need to reduce thermal resistance, improve the heat problems, specific contents are: reduced chip to package thermal resistance, and inhibitory package to printed circuit board of thermal resistance, improve the chip thermal smoothly.

In order to reduce the thermal impedance, many overseas LED manufacturers will led chip in bronze and ceramic material fin (heatsink) surface, then reuse welding heat on the printed circuit board, with a wire connected to the use of forced air cooling cooling fan cooling fins on the experimental results confirmed Germany OSRAMOptoSemiconductorsGmb, the structure of the LED chip to the welding point of thermal impedance reduces 9K/W, about traditional LED by about 1/6, package of imposing power LED 2W, LED chip junction temperature higher than the welding point 18K, even if temperature rises to the printed circuit board, junction temperature 500C at only around 700C; comparatively lower thermal resistance once in the past, the LED chip junction temperature is the temperature of the printed circuit board, necessary to reduce the temperature of LED chip, in other words reduce LED chip to the welding point of thermal impedance, can effectively reduce the LED chip cooling operation. On the contrary even white led has the structure of suppressing heat resistance, if heat conduction from the package to the printed circuit board, the results of the temperature rise LED luminous efficiency will sharply decline, so Panasonic Denko developing printed circuit board and packaging integration technology, the company will 1mm square blue LED the way with flipchip encapsulated in a ceramic substrate, and then paste the ceramic substrate in copper printed circuit board surface, according to Matsushita said contains printed circuit board, module as a whole is about thermal impedance 15K/W.