| The light emitting diode(LED) was widely used due to a series of advantages, such as the small size, long life and low energy consumption. The main factors which affect the efficiency and reliability of LED luminous are current crowding and high junction temperature with the increasing demand of high power LED. Numbers of experimental results show that the optimizing electrode structure and chip on board technology(COB) can relieve the current crowding, improve the current injection rate, enhance the luminous efficiency, enhance the luminescence efficiency, prolong the LED life and improve the device reliability. It is a question that how to optimize the structure of the electrode and COB package. Firstly, it is necessary to simulate in the view of theory, so as to improve the pertinence of the experimental work.The optimizing GaN-LED chip electrode was used by the COMSOL multi- physics field finite element simulation software which based on current expansion theory. The optimizing contents include the electrode structure designing, graphene oxide and nickel composite transparent electrical layers(TCLs) which aim to ease the current crowding effect. The optimization of the reflector cup structure COB packaging metal substrate was used by the ray tracing software Tracepro. The temperature field of LED chip of two kinds of packaging methods(COB packaging and Surface Mount Technology(SMT)) were simulated and the advantages of heat dissipation of COB package was analyzed. Thermal stress and strain of the packaging materials, such as lens, silica gel were number calculated. Finally, the temperature field and the distribution of the multi-chip LED package were simulated.The main results are as follows:1) It is found that p-pad insertion type is better than n-pad insertion type electrode to expanse the current of the LED chip uniformly. It is benefit to expand the lateral current evenly with the increase of the length of the electrode and the number of teeth. However, the enhancement effect of the transverse current expansion is not so obvious after the number of teeth over 3.2) The graphene and nickel oxide thin films with different thickness which combine with transparent electrode were simulated for the chip(175?m×225?m) thermal and electrical properties. It indicates that the LED with the compound TCLs of 3 layers Gr and 1 nm NiOx hold the best thermal-electrical performance, and the TCLs light transmittance is 90%. The thermal-electrical performance of the chip is compared with chip only using 4 layers graphene(optimal number of layers), the junction temperature is reduced by 4.8 K. The current density distribution uniformity is increased by 11%. It is found that the p-pad buried depth is 40 nm, the n-pad electrode and the active layer etching distance is 4 ?m. The electrode structure p/n-pad size is 0.8 times than that of the chip, the temperature of the GaN-LEDs with the NiOx/Gr hybrid TCLs could drop about 7 K,and the current density uniformity could increase by 23.8% 0.4 times than that of chip size.3)The reflection cup structure optimization results show that the reflector cup mouth diameter is 3.0 mm, the diameter of the cup bottom is 1.6 mm, the depth of cup is 0.6 mm. the LED light output efficiency is increased by 20%, the angle of the light irradiation reduced to 85 degrees, and the Irradiation intensity is double times than COB structure without reflector cup. These results were validated by experimental test. When the COB chip LED package with a metal reflector cup which removal of low thermal conductivity insulation, the thermal resistance of LED is 5?/W lower than the general COB package.4) The coupling of COMSOL Joule heating module and structural mechanics module is used to simulate the calculation of the cob packaging, LED chip, silica gel, die attach adhesive, substrate thermal stress and strain with the reflection cup structure parameters, die attach adhesive thickness, die attach adhesive, substrate thickness, power changes of substrate chip, the results show that: maximum stress exhibited in the connection between lens and the substrate; the effect of the structure of reflection cup on silica gel heat stress and strain is very small; the die attach adhesive thickness is 40 ?m, die attach adhesive heat stress is 500 MPa. When the thermal conductivity of the die attach adhesive is more than 13 W/m×K, the chip junction temperature decreased slowly. From the effect of the sapphire, silicon and silicon carbide three kinds of substrate thickness on thermal stress and chip junction temperature, it is know that the thickness of the silicon material substrate below 100 ?m is the best.5) Studying the effect of the arrangement of 9, 16 LEDs array on chips junction temperature and light performance: the junction temperature of 9 chips package arrangement in a single ring distribution and 16 chips packaging arrangement of double ring(6+10) are lowest; The optical properties of the 3×3 array, 3+6 double ring and 9 chips single ring of 9 LEDs are almost the same; As to 16 LEDs: the light intensity of the 4 small rectangular arrangements is small while the irradiation range is wide, full width at half maximum is 101 degrees. The full width at half maximum of irradiation angle of 4×4 array antenna\ a single ring of 16 chips\ 6+10 bicyclo-arrangements are 84 degrees. Among them the irradiation strength of 6+10 bicyclo-arrangements are biggest, and the light distribution effect is the best. |
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