What is an LED chip? (part two)

The essence of flip chip is based on the traditional process, the light-emitting area of ​​the chip and the electrode area are not designed on the same plane. At this time, the electrode area faces the bottom of the lamp cup for mounting, which can save the process of bonding wires. However, the precision requirements for this process of die bonding are relatively high, and it is generally difficult to achieve a high yield.

Requirements for flip chip:

①The base material is silicon; ②The electrical surface and solder bumps are on the lower surface of the component; ③Underfill is required after assembly on the substrate.

The improvement of the luminous efficiency of LED chips determines the energy-saving ability of future 7 seg LED display street lamps. With the development of epitaxial growth technology and multiple quantum well structures, the internal quantum efficiency of epitaxial wafers has been greatly improved. How to meet the standards for street lamps depends to a large extent on how to extract the most light from the chip with the least power. Simply put, it is to reduce the driving voltage and increase the light intensity. The traditional LED chip with a positive mounting structure generally requires a semi-transparent conductive layer to be plated on p-GaN to make the current distribution more uniform, and this conductive layer will partially absorb the light emitted by the LED, and the p-electrode will cover part of it Light, which limits the light-emitting efficiency of the LED chip.　

Advantages of flip chip compared with traditional process:

The GaN-based LED structure layer is grown on the sapphire substrate by the MOCVD technology, and the light emitted from the P/N junction light-emitting area is emitted through the upper P-type area. Due to the poor conductivity of P-type GaN, in order to obtain good current expansion, it is necessary to form a metal electrode layer composed of Ni-Au on the surface of the P area by vapor deposition technology. The P area leads are led out through this layer of metal film. In order to obtain good current expansion, the Ni-Au metal electrode layer should not be too thin. For this reason, the luminous efficiency of the device will be greatly affected, and it is usually necessary to take into account the two factors of current expansion and luminous efficiency at the same time. However, under any circumstances, the existence of metal thin films will always make the light transmission performance worse. In addition, the presence of wire solder joints also affects the light extraction efficiency of the device. Using GaN LED flip chip structure can fundamentally eliminate the above problems.