Thermal Simulation And Optimization Design For High-power LED

Light-emitting diode(LED) is a new type of green lighting light source in the 21 st century, with the advantages of environmental protection and energy saving, small volume, long life, etc. But the electro-optic conversion efficiency is not high, heat is generated from 80 ~ 90% power and transfer to the air, and causing the LED junction temperature become high, which in turn affect the LED luminous efficiency, so it has vital significance that researching heat dissipation efficient of LED. Let high-power LED as the research object, related numerical simulation research on high-power LED is conducted with ANSYS Workbench software in this paper, the main contents and results are as follows:(1) Steady-state heat transfer model for the solid structure of high-power LED is established, it is concluded that junction temperature of simulation is 65.073 ℃, total thermal resistance is 47.145 ℃/W; And according to the theory of thermal resistance network model, total thermal resistance of high power LED is 49.9 ℃/W, junction temperature is 67.415 ℃; The junction temperature of steady-state simulation is lower than the junction temperature of theoretical calculation, which is 2.342 ℃, about 3.47%, the thermal resistance of steady-state simulation is lower than the thermal resistance of theoretical calculation, which is 2.755 ℃/W, about 5.52%.(2) Coupling model of high-power LED based on the air forced cooling and heat transfer and thermal stress of the structure is established; It is concluded that junction temperature of coupling simulation is 65.114 ℃, and total thermal resistance is 47.19 ℃/W; The junction temperature of coupling simulation is lower than the junction temperature of theoretical calculation,which is 2.301 ℃, about 3.41%, the total thermal resistance of coupling simulation is lower than the total thermal resistance of theoretical calculation,which is 2.71 ℃/W, about 5.43%; Maximum temperature of coupling simulation is at the GaN chip, the minimum temperature location is at the top of the lens; Maximum total deformation of LED structure is 5.2529 ? 10-3 mm, maximum thermal strain is 8.8363 ? 10-4 mm/mm, maximum equivalent(von-mises) stress of GaN chip is 266.67 MPa, maximum equivalent(von-mises) stress of aluminum alloy material structure is approximately 40 MPa.(3) The influencing factors of high-power LED are analyzed based on coupling simulation, including air inlet velocity and inlet radius, and substrate thickness, and fin height, and bonding material, and plate material, and fin slotted, which have effect on the heat dissipation performance of LED, respectively, it is concluded that: 1) With the increase of air inlet velocity(1~8 m/s) and inlet radius(1~7 mm) and fin height(4~22 mm) and slotted fin number(4 ? 1, 4 ? 2, 4 ? 3), it shows a gradually reduced trend of junction temperature and total deformation and equivalent elastic strain and thermal strain and equivalent(von-mises) stress and strain energy; 2) With the increase of substrate thickness from 0.5mm to 3.0mm, junction temperature is gradually decreased, and the change curve keep even; Total deformation first decreases and then increases with the increase of substrate thickness; Equivalent elastic strain and equivalent(von-mises) stress first increases quickly with the increase of substrate thickness, and then tiny changes, finally gradually decreases; Thermal strain and strain energy decreases with the increase of substrate thickness. 3) The influence of bonding material on junction temperature and equivalent elastic strain and thermal strain and equivalent(von-mises) stress: Au80Sn20 < Pb40Sn60; The influence of bonding material on total deformation and strain energy: Au80Sn20 > Pb40Sn60; 4) The influence of board surface material on junction temperature and thermal strain: aluminum alloy > silicon carbide > copper; The influence of board surface material on total deformation and strain energy: silicon carbide > aluminum alloy > copper; The influence of board surface material on equivalent elastic strain and equivalent(von-mises) stress: aluminum alloy > copper > silicon carbide.(4) Based on coupling simulation, multi-objective optimization for four independent variables of high-power LED was studied based on genetic algorithm research, which are air inlet velocity and inlet radius and substrate thickness and fin height. Before optimization, air inlet velocity is 4 m/s, inlet radius is 1 mm, base board thickness is 5 mm, and fin height is 5 mm, but after optimization design, air inlet velocity is 4.7067 m/s, inlet radius is 5.8511 mm, base board thickness is 1.1412 mm, and fin height is 22.498 mm; Before optimization, junction temperature is 65.114 ℃, total thermal resistance is 47.19 ℃/W, equivalent(von-mises) stress of GaN chip is 266.67 MPa; After optimization, junction temperature is 37.913 ℃, total thermal resistance is 15.19 ℃/W, equivalent(von-mises) stress is 76.79 MPa. The optimized junction temperature is decreased by 27.201 ℃ than before optimization, about 41.77%, the optimized total thermal resistance is decreased by 32 ℃/W than before optimization, about 67.81%, the optimized equivalent(von-mises) stress of GaN chip is decreased by 189.88 MPa than before optimization, about 71.20%; After optimization, heat dissipation perfomance of high-power LED is significantly enhanced and thermal stress is smaller, and its reliability is raised.