Share: Solutions for LED temperature rise problems

In the past, in order to obtain a sufficient white LED beam, the LED industry has developed large-size LED chips in an attempt to achieve the desired goal. However, in fact, when the applied power of the white LED continues to exceed 1W, the beam will decrease, and the luminous efficiency will be relatively reduced by 20~30%. In other words, if the brightness of the white LED is several times larger than that of the conventional LED, the power consumption characteristic exceeds the fluorescent lamp. In this case, it is necessary to overcome the following four major problems: suppressing temperature rise, ensuring service life, improving luminous efficiency, and equalizing luminescence characteristics.

The solution to the temperature rise problem is to reduce the thermal impedance of the package; the method of maintaining the service life of the LED is to improve the chip shape and use a small chip; the method for improving the luminous efficiency of the LED is to improve the chip structure and use a small chip; The method is to improve the packaging method of LEDs, and these methods have been developed one after another.

Solving the heat dissipation problem of the package is the fundamental method

As the increase in power will cause the thermal impedance of the package to drop sharply below 10K/W, foreign companies have developed high-temperature resistant white LEDs to try to improve the above problems. However, in fact, the heat output of high-power LEDs is several times higher than that of low-power LEDs, and the temperature rise also causes the luminous efficiency to drop drastically. Even though the packaging technology allows high heat, the junction temperature of the LED chip may exceed the allowable value. Finally, the operator finally realized that solving the heat dissipation problem of the package is the fundamental method.

The service life of LEDs, such as the use of silicon packaging materials and ceramic packaging materials, can increase the lifetime of LEDs by a single digit, especially the white LED's emission spectrum contains short wavelengths of light below 450nm, traditional epoxy packaging The material is easily destroyed by short-wavelength light, and the large amount of high-power white LED accelerates the deterioration of the packaging material. According to the test results of the industry, the continuous lighting is less than 10,000 hours, and the brightness of the high-power white LED has been reduced by more than half. The basic requirements for long life of lighting sources.

The LED's luminous efficiency, improved chip structure and package structure can reach the same level as low-power white LEDs. The main reason is that when the current density is increased by more than 2 times, it is not easy to take out light from a large chip, but the result is that the luminous efficiency is not as good as that of a low-power white LED. If the electrode structure of the chip is improved, the above-mentioned light extraction problem can be solved theoretically.

Try to reduce thermal impedance and improve heat dissipation

Regarding the uniformity of the luminescent characteristics, it is generally considered that the above-mentioned problems should be overcome as long as the uniformity of the phosphor material concentration of the white LED and the fabrication technique of the phosphor are improved. While increasing the applied power as described above, it is necessary to try to reduce the thermal impedance and improve the heat dissipation problem. The specific contents are: reducing the thermal impedance of the chip to the package, suppressing the thermal impedance of the package to the printed circuit board, and improving the heat dissipation of the chip.