Analysis of fatal problems affecting the life of high-brightness LEDs

Generally speaking, the stability and quality of LED lamps are closely related to the heat dissipation of the lamp body. The heat dissipation of high-brightness LED lamps on the market often adopts natural heat dissipation, which is not ideal. LED lamps made of LED light sources are composed of LED , heat dissipation structure, driver , and lens . Therefore, heat dissipation is also an important part. If the LED cannot dissipate heat well, its life will be affected.

1. Heat management is the main problem in high-brightness LED applications

Since the p-type doping of III-nitrides is limited by the solubility of Mg acceptors and the high activation energy of holes, heat is particularly likely to be generated in the p-type region. This heat must pass through the entire structure to dissipate on the heat sink; the heat dissipation pathways of LED devices are mainly heat conduction and heat convection; the extremely low thermal conductivity of the Sapphire substrate material leads to an increase in the thermal resistance of the device, resulting in a serious self-heating effect, which has a devastating impact on the performance and reliability of the device.

2. Impact of heat on high brightness LEDs

Heat is concentrated in a very small chip. The chip temperature rises, causing non-uniform distribution of thermal stress, reduced chip luminous efficiency and phosphor lasing efficiency; when the temperature exceeds a certain value, the device failure rate increases exponentially. Statistics show that for every 2°C increase in component temperature, reliability decreases by 10%. When multiple LEDs are densely arranged to form a white light lighting system, the heat dissipation problem becomes more serious. Solving the heat management problem has become a prerequisite for high-brightness LED applications.

3. Relationship between chip size and heat dissipation

The most direct way to improve the brightness of power LEDs is to increase the input power. In order to prevent the saturation of the active layer, the size of the pn junction must be increased accordingly. Increasing the input power will inevitably increase the junction temperature, thereby reducing the quantum efficiency. The increase in the power of a single tube depends on the device's ability to extract heat from the pn junction. Under the same conditions as the existing chip materials, structure, packaging process, current density on the chip, and heat dissipation, if the chip size is increased alone, the junction temperature will continue to rise.