Improve the heat dissipation structure and improve the service life of white LED

Past LED industry in order to white LED beam to profit fully, have developed large size LED chip way trying to reach the expected goal, but actually white LED applying power lasts more than 1W above the beam decreases, the luminous efficiency is relatively reduced by 2030%, in other words the brightness white LED if than traditional LED several times, power consumption characteristics of hope beyond the fluorescent lamp, we must first overcome the four major issues, including the following, suppress the temperature rise, to ensure that the service life and improve the luminous efficiency and light emitting properties of equalization.

The temperature rise of the specific method is to reduce the package thermal impedance; maintain the specific method of service life of LED, is to improve the chip shape, using a small chip; improve the luminous efficiency of LED specific methods is to improve the chip structure, using a small chip; as for the homogenization solution is to improve the encapsulation method of LED luminescence, and these methods have been developed.

Can solve the problem of heat dissipation is the fundamental method of packaging

Due to the increase in thermal resistance of power will cause a package of anti sharply below 10K/W, therefore the overseas industry had developed high temperature resistant white LED tried to solve these problems, but the heat actually high power LED is greater than the number of small power LED more than ten times, and the temperature rise of the luminous efficiency will fall sharply, even if the packaging technology allows high the heat, the temperature of LED chip bonding but is likely to exceed the allowable value, the industry finally realized to solve the problem of heat dissipation is the fundamental method of packaging.

The service life of the LED, such as the use of siliceous packaging materials and ceramic packaging materials, LED can improve the service life of a digit, especially white LED light emitting spectrum with wavelengths below 450nm short wavelength light, the traditional epoxy resin packaging material can easily be broken line of short wavelength, high power white LED light more big to accelerate the deterioration of the packaging material industry, according to the test results show that the continuous light less than ten thousand hours, has high brightness power LED reduced by more than half, simply can not meet the basic requirements of long-life lighting.

The luminous efficiency of LED, improve the chip structure and package structure, can reach the same level and low power LED, the main reason is the current density increased more than 2 times, not only easy from large chip out light, the result will cause the luminous efficiency as low power white LED dilemma, if the electrode chip structure improvement the theory can solve the problem of light.

- try to reduce the thermal resistance and improve heat dissipation

It is generally believed that as long as the improvement of the concentration uniformity of the fluorescent material of white LED and the fabrication technology of the fluorescent material, the above problems can be overcome. As mentioned above, to improve the applied power at the same time, must try to reduce the thermal resistance, improve the heat problem, specific content is: reduce the chip to the package thermal impedance, inhibiting the package to a printed circuit board, improve chip thermal impedance heat flow.

In order to reduce the thermal resistance of LED, many foreign manufacturers will LED chip fins made of copper and ceramics (heat sink) surface, then welding mode on the printed circuit board and radiating wire connected to the cooling fan forced air cooling fins, according to the German OSRAM Opto Semiconductors Gmb experimental results confirmed that the structure of the LED chip to the welding point can reduce the thermal resistance is about 9K/W, the traditional LED 1/6, packaged LED applied 2W electric power, LED chip junction temperature than the welding point of high 18K, even if the printed circuit board temperature rises to 500C junction temperature is only about 700C compared with at most; the thermal impedance once reduced, LED chip junction temperature will be affected by the temperature of the printed circuit board, so must try to reduce the temperature of the LED chip, change In other words, to reduce the heat resistance of the LED chip to the welding point, can effectively reduce the burden of LED chip cooling operations. Conversely if white LED has the structure to suppress the thermal impedance, if the heat can not be transmitted to the package from the printed circuit board, LED temperature rising of the luminous efficiency will tobogganed, therefore the development of Matsushita Electric printed circuit board and packaging integration technology, the company will 1mm Affirmative Blu ray LED package to flip chip on a ceramic substrate then, the ceramic substrate is pasted on the copper surface of a printed circuit board, which comprises a printed circuit board according to Matsushita said, the overall thermal impedance module is about 15K/W.

- everybody show thermal design skill

Between the radiating fins and the printed circuit board adhesion directly around the heat conduction effect, so the design of the printed circuit board becomes very complex, in the United States and Japan Lumileds CITIZEN lighting, LED packaging manufacturers have developed high power LED with simple cooling technology, CITIZEN white LED package for sample delivery in 2004, no need of special bonding technology will also be about 23mm thick fin heat directly discharged to the outside, according to the CITIZEN said that although the joint LED chip to 30K/W thermal impedance of fin than OSRAM 9K/W, but also in the general environment of room temperature will make the heat resistance increased about 1W, but even the traditional printed circuit board without cooling fan forced air cooling condition, the white LED module can be used for lighting.

Lumileds high power LED chip sample shipments in 2005, joining the permissible temperature is as high as +1850C, the products of high 600C than other companies, the use of traditional RF4 printed circuit board package, the ambient temperature in the range of 400C can be equivalent to the input current of 1.5W power (about 4