Light Source Fabrication And Thermal Analysis Based On High Voltage Flip Chip LED Chips

In recent years,the application of light emitting diode has been gradually popularized in general lighting.People make higher demand on the volume,brightness and power of LED.The development of this high power,high integration trends to the chip and packaging industry business opportunities.At the same time,the chip and packaging industry are also facing increasing challenges.The heat dissipation technology of LED is becoming more and more important.Poor heat dissipation leads to the accumulation of heat,which rises the junction temperature of LED chip.The increase of junction temperature may lead to decrease of quantum efficiency and excitation efficiency of phosphors,red shift of LED peak wavelength and deteriorate of light uniformity for white LEDs.Elevate junction temperature may generate reliability issues or even catastrophic failure.Therefore,research on how to solve the heat problem of LED lighting is of practical significance.The solutions to heat dissipation should be based on advanced packaging technology and materials,such as using the ceramic substrate with better thermal conductivity,reducing the void ratio of welding layer,matching the package substrate surface material and solid crystal material,which can in a certain extent improve the LED heat dissipation capacity.The article uses the normal chip 2835 to make TV back light and the high voltage(HV)flip-LED chip to make integrated lighting engine.The thermal problem of them was studied and analyzed.Two aspects were investigated in this paper.Firstly,TV back lights were made using 2835 chip and chip on board(COB)integrated lighting engine were made using HV-flip-LED chips.The high voltages of PFC-LED devices were made by PFC technology.Then we used them to make corresponding source components.Secondly,the sample sources were tested by using integrating sphere,T3 Ster and ANSYS simulation software.The main results for this study are as follows:Firstly,the effects of the void ratio of welding layer on the thermal performance of LED back light are studied.The results show that both the junction temperature and thermal resistance increase with the void ratio,which is linearly growing.When the void ratio is 17%,the thermal resistance increases by 6.03% and the junction temperature increases by 1.74%.When the void ratio is 73%,the thermal resistance increases by 24.7% and the junction temperature increases by 9%.Secondly,two kinds of COB downlight source are made and has been tested.Compared to the ordinary sources on the market,the results show that the junction temperature of flip-chip COB downlight source(38.83?)is 20% lower than the ordinary's(48.6?).the junction temperature of 9V flip-chip COB downlight source is 29.18?,reduced by 25% compared by ordinary flip-chip COB downlight sources.This shows that the use of HV flip-chip can effectively reduce the junction temperature of LED lighting components and the light source integration which will cut down the cost.Thirdly,the thermal performances of a new kind of HV flip package free chip LED(PFC-LED)lighting components are studied.The results show that the thermal resistance of 9V flip-chip PFC-LED device is about 0.342 K/W,which is far below than the ordinary LED device with 9V(3.5 K/W).The paper made two kinds of downlight source by using HV flip-LED chip.The flip light sources have many advantages,such as using less chip,small size and light weight,easy to integrate,no gold wire bonding and so on.It can not only increase the difficulty of integration and reduce the costs and the size of the COB light source but also short the cooling channels for packaging process.The cool path down is conducive to cooling design and being directly welded on printed circuit substrate,which avoid second encapsulation improving the heat dissipation and the reliability of chip.Flip-LED chip cannot use the gold wire for electrical connection avoiding the reliability problem of spot weld failure.It can simplify the encapsulation process too.The built light source had been relevant tested and analyst about optics and thermotics.The experimental results provide a thermal design basis for the packaging and application of high voltage flip-chip LED...