LED industry in the past in order to profit fully white LED beam, once the development of large-size LED chips trying to take this way to achieve the desired goals, but actually exert power white LED lights continuous beam but will decline more than 1W above, the luminous efficiency is relatively lower 2030 %, in other words white LED brightness several times larger than traditional LED power consumption characteristics beyond the fluorescent lights, you must first overcome the following four topics, including inhibition of the temperature rise to ensure that the service life, improve light-emitting efficiency, as well as luminescent properties equalization.
Is to reduce the package thermal impedance on temperature rise problems; maintain LED life is to improve the chip shape, a small chip; specific methods to improve the chip architecture, small chip to improve the LED luminous efficiency; As for the light-emitting characteristics of uniform of specific methods of improvement of the LED package, and these methods have gradually been developed.
The package thermal problem is the fundamental method
It will cause the package thermal impedance is drastically reduced to below 10K / W due to the increased power, foreign companies have developed high-temperature white LED an attempt to improve the problem, However, in practice the high-power LED heat than low-power LED high number of more than ten times the luminous efficiency and temperature rise will be declined substantially, even if the packaging technology allows high-calorie, but the LED chip junction temperature there is likely to exceed the allowable value
And finally the industry has finally realized that the heat dissipation problem is the fundamental method to solve the package.
LED life, for example, to switch to the silicon packaging materials and ceramic packaging materials, make the life of the LED’s to improve a number of white LED light spectrum contains wavelengths below 450nm short wave length light, traditional epoxy encapsulated materials can easily be short-wavelength light damage, high-power white LED light to accelerate the degradation of packaging materials, continuous lighting of less than one million hours, according to the test results of the industry, high-power white LED brightness has been reduced by more than half simply can not meet the basic requirements for lighting long life.
Remove, not easy from the large chip, can achieve the same level with the low-power white LED chip package structure for LED luminous efficiency improvement, mainly due to the current density increased by more than 2 times, not only light, a result, it will cause the luminous efficiency the dilemma of not as good as low-power white LED, improving the electrode structure of the chip, in theory, the light extraction issues can be resolved.
try to reduce the thermal resistance to improve the heat dissipation problem
For light-emitting characteristics of uniformity, is generally believed that as long as the production technology to improve the uniformity and phosphor white LED phosphor materials concentration should be able to overcome this trouble. As described above to improve exert power at the same time, it is necessary to reduce the thermal impedance to improve the heat dissipation problem, the specific contents are: to reduce the chip to the package thermal impedance, inhibiting the thermal impedance of the package to the printed circuit board, improve the smoothness of chip cooling.
In order to reduce the thermal resistance, many foreign LED manufacturers LED chip set heat sink made of copper and ceramic materials (heat sink) surface, and then using the welding heat to the printed circuit board with a wire connected to the use of the cooling fan forced air cooling fins, according to German OSRAM Opto Semiconductors Gmb experimental results confirmed the above-mentioned structure of the LED chip to the thermal impedance of the welding point can reduce the 9K / W is about 1/6 of the traditional LED, the LED package to impose 2W of power, the LED chip junction temperature than welding point high 18K, even if the printed circuit board temperature rises to 500C junction temperature at most only about 700C; previous thermal impedance contrast lower, then the LED chip junction temperature will The temperature of printed circuit board, this way necessary to try to reduce the temperature of the LED chip, in other words reduce the thermal impedance of the LED chip to the welding point, can effectively reduce the burden of the LED chip cooling operation. On the other hand the white LED is able to inhibit the thermal impedance of the structure, if the heat conduction from the package to the printed circuit board, LED temperature rise results luminous efficiency will be dramatically decreased by Matsushita Electric Works to develop printed circuit board and package integration technologies, the 1mm square blue LED flip chip packaged in a ceramic substrate, and then paste then the ceramic substrate in the surface of copper printed circuit board, according to Matsushita said contains a printed circuit board module as a whole, including the thermal impedance is about 15K / W or so.