The Surface Design And Key Techniques Of Novel Flat Flip-chip High Power Light-emitting Diodes

Light emitting diode (LED) has the advantages of energy-saving,environmental protection and long-life, it has the most potential to become themainstream device of new age solid-state lighting components. At present，most ofthe LED research around the world are focus on the high power LED with large areawhich more than1×1mm2. Increase chip power means that the heat generated bythe LED increase at the same time, and when LED used as a mainstream lighting, itusually requires using multiple high-power LED to achieve the demands of highbrightness, hence the heat increase dramatically. So the research on heat dissipationis very important.Based on the traditional flip-chip LED, this paper designed the flat surfaceflip-chip LED, and studied its optoelectronic properties and the heat dissipatingperformance. Compared with conventional LED, the heat generate by the flip-chipLED can conduct through the Au bumps to the Si submount, improving the thermalperformance. Only when flip-chip LED use more than4Au bumps, the flip-chipLED can have a better heat dissipation than conventional LED. With an increasingnumber of Au bumps, the thermal performance getting better and better, but theprocess difficulty and reverse leakage current level are also increased. Subject to thelimitation of the contact area between the chip and the subsmount, the chip junctiontemperature is difficult to reduce further. In this work, we present a flat surfaceflip-chip structure where the LED chip and Si submount are contacted by a flatsurface, it can greatly increase the contact area between the chip and the substrate,and then improve the performance of heat dissipation. The main research contents ofthis paper are as follows:(1) Designed the flat surface flip-chip LED, solving the limited contact areaproblem between the substrate and Au bumps of the conventional flip-chip LED.The new structure introduce the positive and negative electrode into a same plane,and then use the plane to connect the LED chip and Si submount. In theory, the newstructure can greatly improve the heat dissipation and temperature uniformity.(2) Modeling and simulation for the flat surface flip-chip LED andconventional flip-chip LED by the computer. Through the three-dimensional finiteelement model simulation, we have got the temperature field and current distribution results under the condition of the steady state. Simulation results showed that the flatsurface structure can greatly improve the heat dissipation performance. As thethermal conductivity of the SiO2is very small, it was hard to avoid that theintroduction of the SiO2layer may affect the thermal transfer. Through thesimulation, we found a3000insulating layer with different thermal conductivityhad a little impact on heat transfer.(3) According to the laboratory conditions, we had designed the process of flatsurface flip-chip LED. Through consulted relevant documents and constantly tested,the key processes of chip and submount were studied, verifying the feasibility ofeach single process, and then determined the process steps and the processparameters.(4) According to the process, designed the reticle of flat surface flip-chip LED.Through the integration of each individual process, we fabricated the conventional,flip-chip and flat surface flip-chip LED at the same epitaxial wafer. Finally, thephotovoltaic performance and thermal properties of these types were tested andanalysis.