Improvement of Thermal Management in GaN-based Light Emitting Diode Device and Package with Diamond-like Carbon Heat Spreading Layer

  • 蔡 百揚

Student thesis: Doctoral Thesis


In this dissertation the high thermal conductivity and thermal diffusivity of diamond-like carbon (DLC) could reduce the heat crowding phenomenon in the epitaxy layer of light-emitting diodes (LEDs) The performance and reliability of LED devices were damaged or decreased owing to the heat crowding phenomenon leading to high junction temperature and self-heating effect in the LEDs At two or three times injection current the junction temperature of LEDs with DLC heat-spreading layer was decreased more than 5 °C The relative light intensity was increased by approximately 5% to 10% The surface temperature distribution of LED with DLC heat-spreading layer was more uniform than that of LED without DLC heat-spreading layer The thermal diffusivity of Al metal-core printed circuit board (PCB) was increased by using DLC as heat-spreading and insulating layer Metal core PCB substrate limits thermal dissipation because of the low thermal conductivity of the insulating layer between the Cu circuit and Al substrate Therefore heat was crowded under the LED device area and not spread all over the Al substrate area The DLC heat-spreading layer improved the low thermal conductivity with regular metal core PCB For the measurement of light intensity droop at the thermal equilibrium the light intensity of metal core PCB with DLC heat-spreading layer was improved by approximately 7% The junction temperature was decreased by more than 10 °C The relative light intensity was improved by 3% after turn-on of 1 000 h In addition to the heat dissipation capability of LED device and package material the thermal effect of phosphor material is important in the LED package The remote phosphor was directly attached to the metal-core printed circuit board (MCPCB) and then the phosphor layer and blue LED chip were separated by air Therefore the heat of the blue LED chip was indirectly conducted to the phosphor layer At high injection current the light intensity of remote phosphor type was not saturated and droop phenomenon was observed For the correlated color temperature shift the remote phosphor type was lower than the conventional phosphor coating technology The former type can be designed with different shapes for different light pattern applications This dissertation demonstrated the high efficiency and reliability of white LED light source for the solid-state lighting This light source is composed of remote phosphor LEDs and Al MCPCB with DLC heat-spreading layer
Date of Award2015 Oct 30
Original languageEnglish
SupervisorYeong-Her Wang (Supervisor)

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