2.Necessity of heat dissipation
Relevant data shows that when the temperature exceeds a certain value, the failure rate of the device will rise exponentially, and every 2 ° C increase in component temperature will reduce the reliability by 10%. In order to ensure the life of the device, the pn junction temperature is generally required to be below 110 ° C. As the temperature of the pn junction rises, the light-emitting wavelength of the white LED device will shift red. At 100 ° C. The wavelength can be shifted from 4 to 9 nm red, which causes the absorption rate of the phosphor to decrease, the total luminous intensity will decrease, and the white light chromaticity will be worse. Around room temperature, the luminous intensity of LED will decrease by about 1% per liter of temperature. When multiple LEDs are arranged in a density to form a white light lighting system, the problem of heat dissipation is more serious, so solving the problem of heat dissipation has become a prerequisite for power LED applications. If the heat generated by the current cannot be dissipated in time and the junction temperature of the pn junction is kept within the allowable range, it will not be able to obtain a stable light output and maintain a normal lamp string life.
LED packaging requirements: In order to solve the heat dissipation problem of high-power LED packaging, designers and manufacturers of domestic and foreign devices have optimized the thermal system of the device in terms of structure and materials.
(1) Package structure. In order to solve the heat dissipation problem of high-power LED packaging, various structures have been developed internationally, mainly including silicon-based flip-chip (FCLED) structure, metal circuit board-based structure, and micro-pump structure; After the package structure is determined, the thermal resistance of the system is further reduced by selecting different materials to improve the thermal conductivity of the system.