The nodal and heat dissipation of the LED chip
Heat dissipation is a technical problem that the power type white light LED needs to focus on. The heat dissipation effect is directly related to the life of the street lamp and the energy saving effect. LED generates light by the transition between electrons in the interband, and there is no infrared part in the spectrum, so the heat of the LED can not be emitted by radiation. If the heat in the LED chip can't be sent out in time, the accelerator parts will be aging. Once the temperature of the LED exceeds the maximum critical temperature (according to the different epitaxy and process, the chip temperature is about 150 degrees C), the permanent failure of the LED is often caused. It is important to effectively solve the heat dissipation of LED chip and to improve the reliability and life of the LED street lamp. To do this, the most direct way is to provide a good thermal channel heat dissipated from node to. Compared with the traditional positive structure, the vertical and flip chip structure has better heat dissipation ability on the chip level compared with the traditional positive structure. The copper alloy is used directly as the substrate for the vertical structure chip, which effectively improves the cooling capacity of the chip. The flip chip (Flip-Chip) technology through the LED eutectic solder flip chip to a silicon substrate with a higher thermal conductivity (on thermal conductivity of about 120W/mK, traditional dress chip sapphire thermal conductivity is about 20W/mK), gold bump and the silicon substrate and the substrate between the chip and improve the heat dissipation capability of LED chip, LED heat protection can quickly export from the chip.
ESD protection of LED chips
In addition, the ability of antistatic release (ESD) is another factor that affects the reliability of LED chips. The blue and negative chips of sapphire substrate are all located on the chip. The spacing between them is very small. For InGaN/AlGaN/GaN double heterojunction, the thickness of InGaN activation layer is only tens of nanometer, and the static capacity is limited, so it is easy to be damaged by electrostatic breakdown. In order to prevent the damage of LED chip caused by static electricity, on the one hand, we can use the production management method such as grounding the production equipment and isolating human body static electricity. On the other hand, we can add Zener protection circuit in LED chip. In the field of street lighting, the ESDHBM of the traditional chip structure is about 2000V, which usually needs parallel Zener chip in the packaging process to enhance the ESD protection ability. It not only increases the cost and difficulty of the packaging, but also has greater risk for reliability. By integrating Zener protection circuit inside silicon substrate, we can greatly improve the antistatic release capacity (ESDHBM=4000~8000V) of LED chip, save the cost of encapsulation, simplify the packaging process and improve product reliability.