Light emitting diodes (LEDs) are environmentally friendly and possessing a long lifetime, energy efficiency, which have developed a huge, rapidly increasing application. High-power LEDs, which have an electrical power consumption exceeding 10 Watts, are of great interest owing to their applicability...
Light emitting diodes (LEDs) are environmentally friendly and possessing a long lifetime, energy efficiency, which have developed a huge, rapidly increasing application. High-power LEDs, which have an electrical power consumption exceeding 10 Watts, are of great interest owing to their applicability as surface light sources. However, their heat dissipation is a critical problem that must be solved in order to ensure the reliability of the LED performance as LED chip temperatures increase with the increased electrical power consumption. It has been reported that the optical output power degrades according to the junction temperature due to the activation of non-radiative recombination of electron-hole pairs. As a result, an increase in the chip junction temperature leads to the degradation of the conversion efficiency and color shifts. Currently, multi-chip LED packages which are made up of dozens of single LEDs make up the main part of the high power LED market. By adopting the multi-chip array for high power LED packages, the electrical power consumption for each LED chip is divided into each chip reducing the junction temperature of the individual chip. However, in this case, thermal superposition needs to be considered, especially in the case of small gaps between the adjacent chips. Therefore, in the case of multi-chip LED packages, the junction temperature is determined by both the heat dissipation characteristics of each chip and the thermal superposition of the chips. Direct measurement of the LED junction temperature is difficult, in this study, predicted through simulation. To enhance the thermal dissipation characteristics of the LED package, which consist of three research;
1. LED package with 4mm-height mold was manufactured and the surface temperature was measured directly using both thermocouple and thermal infrared (IR) camera. FVM(Finite Volume Method) simulation was conducted to estimate the surface temperature of the same LED package under the same condition, by which the accuracy of the simulation was secured. The results showed that the junction temperature decreased by 10℃ when the mold height was 3-5 mm.
2. Junction temperature estimation is important for multi-chip LED packages as heat superposition and temperature gradients are involved for each chip. 4-chip, 12-chip, and 16-chip LED packages were prepared in order to investigate the junction temperatures of these high power multi-chip LED packages. The surface temperatures of the epoxy mold, ceramic substrate, and the MPCB were measured using a thermocouple and a FLIR T-250 IR microscopy camera. The emissivity values of each surface were then determined by comparing the two measured data sets.
3. The heat dissipation through interchip structures was investigated by introducing 4-partition and 16-partition ceramic interchip structures for a 16-chip LED package. Using FVM simulation with ICEPAK V13.0, the temperature distribution inside the LED package and the junction temperature were estimated, from which the effect of the interchip structures on the heat dissipation characteristics of the LED package was investigated. The results showed that the ceramic interchip structures provided a more effective upward heat dissipation path for the LED package and contributed to a 23ºC decrease in the junction temperature for the 4-partition interchip structure and a 51ºC decrease for the 16-partition interchip structure at the 16W operation.
Light emitting diodes (LEDs) are environmentally friendly and possessing a long lifetime, energy efficiency, which have developed a huge, rapidly increasing application. High-power LEDs, which have an electrical power consumption exceeding 10 Watts, are of great interest owing to their applicability as surface light sources. However, their heat dissipation is a critical problem that must be solved in order to ensure the reliability of the LED performance as LED chip temperatures increase with the increased electrical power consumption. It has been reported that the optical output power degrades according to the junction temperature due to the activation of non-radiative recombination of electron-hole pairs. As a result, an increase in the chip junction temperature leads to the degradation of the conversion efficiency and color shifts. Currently, multi-chip LED packages which are made up of dozens of single LEDs make up the main part of the high power LED market. By adopting the multi-chip array for high power LED packages, the electrical power consumption for each LED chip is divided into each chip reducing the junction temperature of the individual chip. However, in this case, thermal superposition needs to be considered, especially in the case of small gaps between the adjacent chips. Therefore, in the case of multi-chip LED packages, the junction temperature is determined by both the heat dissipation characteristics of each chip and the thermal superposition of the chips. Direct measurement of the LED junction temperature is difficult, in this study, predicted through simulation. To enhance the thermal dissipation characteristics of the LED package, which consist of three research;
1. LED package with 4mm-height mold was manufactured and the surface temperature was measured directly using both thermocouple and thermal infrared (IR) camera. FVM(Finite Volume Method) simulation was conducted to estimate the surface temperature of the same LED package under the same condition, by which the accuracy of the simulation was secured. The results showed that the junction temperature decreased by 10℃ when the mold height was 3-5 mm.
2. Junction temperature estimation is important for multi-chip LED packages as heat superposition and temperature gradients are involved for each chip. 4-chip, 12-chip, and 16-chip LED packages were prepared in order to investigate the junction temperatures of these high power multi-chip LED packages. The surface temperatures of the epoxy mold, ceramic substrate, and the MPCB were measured using a thermocouple and a FLIR T-250 IR microscopy camera. The emissivity values of each surface were then determined by comparing the two measured data sets.
3. The heat dissipation through interchip structures was investigated by introducing 4-partition and 16-partition ceramic interchip structures for a 16-chip LED package. Using FVM simulation with ICEPAK V13.0, the temperature distribution inside the LED package and the junction temperature were estimated, from which the effect of the interchip structures on the heat dissipation characteristics of the LED package was investigated. The results showed that the ceramic interchip structures provided a more effective upward heat dissipation path for the LED package and contributed to a 23ºC decrease in the junction temperature for the 4-partition interchip structure and a 51ºC decrease for the 16-partition interchip structure at the 16W operation.
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#LED
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