Detailed introduction of white LED part one

In order to obtain a sufficient white light LED beam, large-size LED chips have been developed in an attempt to achieve the desired goal in this way. In fact, when the electric power applied to the white LED continues to exceed 1W, the beam will decrease, and the luminous efficiency will be relatively reduced by 20%~30%. The problems that must be overcome to improve the input power and luminous efficiency of the white LED are: restrain temperature rise; ensure Service life; improve luminous efficiency; equalize luminous characteristics.

Increasing power will reduce the thermal resistance of the white LED package to below 10K/W. Therefore, high-temperature resistant white LEDs have been developed abroad in an attempt to improve the temperature rise problem. Because the heat of high-power white LED is dozens of times higher than that of low-power white LED, even if the white SMD LED 3014 package allows high heat, the allowable temperature of the white LED chip is certain. The specific method to suppress the temperature rise is to reduce the thermal resistance of the package.

The specific method to improve the service life of white LEDs is to improve the chip shape and adopt small chips. Since the emission spectrum of white light LEDs contains short-wavelength light with a wavelength below 450nm, traditional epoxy resin sealing materials are easily damaged by short-wavelength light, and the large amount of light of high-power white light LEDs accelerates the deterioration of the sealing material. Switching to silicon sealing materials and ceramic packaging materials can increase the service life of white LEDs by one digit.

The specific method to improve the luminous efficiency of white light LEDs is to improve the chip structure and packaging structure to achieve the same level as low-power white light LEDs. The main reason is that when the current density is increased by more than 2 times, it is not easy to extract light from the large chip, but the result is The luminous efficiency is not as good as that of low-power white LEDs. If the electrode structure of the chip is improved, the above light extraction problem can be solved theoretically.

The specific method to achieve uniform light-emitting characteristics is to improve the packaging method of white light LEDs. It is generally believed that the above-mentioned problems can be overcome by improving the uniformity of the phosphor material concentration of the white light LED and the production technology of the phosphor.

The specific contents of reducing thermal impedance and improving heat dissipation are:

① Reduce the thermal resistance from chip to package.

② Suppress the thermal resistance of the package to the printed circuit board.

③ Improve the heat dissipation of the chip.